A Phase 1b/2 Open-Label Study of the Efficacy and Safety of Etigilimab (MPH313) Administered in Combination With Nivolumab to Subjects With Locally Advanced or Metastatic Solid Tumors (ACTIVATE)
Phase: PHASE1
Conditions: Solid Tumor, Adult, Advanced Solid Tumor, Metastatic Solid Tumor
Sponsor: Mereo BioPharma

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 1 of 110 
Protocol Title 
A Phase 1b/2 Open-Label Study of the Efficacy and Safety 
of Etigilimab (MPH313) Administered in Combination with 
Nivolumab to Subjects with Locally Advanced or Metastatic 
Solid Tumors (ACTIVATE) 
Protocol Number 
MPH313-1-02 
Product Number 
MPH313 (previously OMP-313M32) 
Sponsor Name and 
Registered Address 
Mereo BioPharma 5, Inc. 
800 Chesapeake Drive 
Redwood City, California 94063 
United States 
Regulatory Identifying 
Numbers 
IND Number: 152856 
EudraCT Number: 2020-004222-37 
Approval Date 
29 June 2022 
History of Protocol Versions 
Original Protocol Version 1.0 dated 11 September 2020 
Amendment 1 Version 2.0 dated 20 October 2020 
Amendment 2 Version 3.0 dated 26 March 2021 
Amendment 3 Version 4.0 dated 29 June 2022 
NCT #: NCT04761198

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 2 of 110 
TABLE OF CONTENTS 
1. 
INTRODUCTION AND BACKGROUND ..................................................................5 
1.1. 
Introduction .......................................................................................................................5 
1.2. 
Background .......................................................................................................................5 
1.3. 
Study Design .....................................................................................................................8 
1.4. 
Study Rationale ...............................................................................................................10 
1.4.1. 
Rationale for Study Design .............................................................................................10 
1.4.2. 
Scientific Rationale for Selected Endpoints ...................................................................14 
1.4.3. 
Justification for Dose and Schedule ................................................................................14 
1.5. 
Benefit/Risk Assessment ................................................................................................15 
2. 
OBJECTIVES AND ENDPOINTS .............................................................................16 
2.1. 
Number of Subjects ........................................................................................................17 
2.2. 
Study Start and End Definition .......................................................................................17 
2.2.1. 
Start of Study Definition .................................................................................................17 
2.2.2. 
End of Study Definition ..................................................................................................17 
2.2.3. 
Post Study Access to Therapy .........................................................................................17 
2.2.4. 
Trial Termination ............................................................................................................18 
3. 
STUDY POPULATION ...............................................................................................18 
3.1. 
Inclusion Criteria ............................................................................................................18 
3.2. 
Exclusion Criteria ...........................................................................................................25 
3.3. 
Prohibited Concomitant Medications and Treatments....................................................28 
3.4. 
Screen Failures ................................................................................................................28 
4. 
TREATMENTS ............................................................................................................29 
4.1. 
Treatments Administered ................................................................................................29 
4.2. 
Treatment Discontinuation .............................................................................................30 
4.3. 
Method of Treatment Assignment ..................................................................................30 
4.4. 
Preparation/Handling/Storage/Accountability ................................................................30 
4.5. 
Treatment Compliance ....................................................................................................31 
4.6. 
Permitted Concomitant Therapy or Standard of Care Treatment ...................................31 
5. 
DISCONTINUATION, DOSE HOLD, AND RESUMPTION .................................33 
5.1. 
Etigilimab Dose Holds and Discontinuation ..................................................................33 
5.2. 
Nivolumab Dose Hold, Resumption and Discontinuation ..............................................35 
5.3. 
Dosing Interruptions .......................................................................................................37 
5.4. 
Toxicity Management Guidelines for Specific Adverse Events .....................................37 
6. 
RESPONSE ASSESSMENTS ......................................................................................38 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 3 of 110 
6.1. 
Radiographic Evaluations and Confirmation of Disease 
Progression......................................................................................................................38 
6.2. 
Treatment Beyond Progression .......................................................................................39 
6.3. 
Response Evaluation Criteria in Solid Tumors ...............................................................40 
7. 
PERMANENT AND TEMPORARY DISCONTINUATION 
CRITERIA ....................................................................................................................42 
7.1. 
Lost to Follow Up ...........................................................................................................42 
8. 
STUDY ASSESSMENTS AND PROCEDURES .......................................................43 
8.1. 
Schedule of Assessments ................................................................................................44 
8.2. 
Efficacy Assessments .....................................................................................................50 
8.3. 
Safety ..............................................................................................................................50 
8.3.1. 
Adverse Events ...............................................................................................................50 
8.3.2. 
Pregnancy ........................................................................................................................52 
8.3.3. 
Physical Examinations ....................................................................................................52 
8.3.4. 
Vital Signs .......................................................................................................................52 
8.3.5. 
Electrocardiograms .........................................................................................................53 
8.3.6. 
Clinical Safety Laboratory Assessments ........................................................................53 
8.3.7. 
Immunogenicity Assessments .........................................................................................53 
8.4. 
Pharmacokinetics ............................................................................................................54 
8.5. 
Pharmacogenomics .........................................................................................................54 
8.6. 
Biomarkers and Biopsies ................................................................................................54 
8.7. 
Skin Biopsy .....................................................................................................................55 
8.8. 
Deviation Reporting ........................................................................................................55 
9. 
STATISTICAL CONSIDERATIONS ........................................................................56 
9.1. 
Sample Size Determination ............................................................................................56 
9.2. 
Populations for Analyses ................................................................................................57 
9.3. 
Statistical Analyses .........................................................................................................57 
9.3.1. 
Efficacy Analyses ...........................................................................................................58 
9.3.2. 
Safety Analyses ...............................................................................................................59 
9.3.3. 
Pharmacokinetic Analyses ..............................................................................................59 
9.3.4. 
Immunogenicity Analyses ..............................................................................................60 
9.3.5. 
Exploratory Analyses ......................................................................................................60 
10. 
REFERENCES .............................................................................................................61 
11. 
APPENDICES ...............................................................................................................63 
APPENDIX 1: 
ABBREVIATIONS AND TRADEMARKS .............................................63 
APPENDIX 2: 
CLINICAL LABORATORY TESTS .......................................................66 
APPENDIX 3: 
STUDY GOVERNANCE CONSIDERATIONS .....................................68 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 4 of 110 
APPENDIX 4: 
ADVERSE EVENTS: DEFINITIONS AND 
PROCEDURES FOR RECORDING, EVALUATING, 
FOLLOW-UP, AND REPORTING ............................................................................71 
APPENDIX 5: 
CONTRACEPTIVE GUIDANCE AND 
COLLECTION OF PREGNANCY INFORMATION .............................................76 
APPENDIX 6: 
ECOG PERFORMANCE STATUS CRITERIA ....................................79 
APPENDIX 7: 
RECIST CRITERIA VERSION 1.1 .........................................................80 
APPENDIX 8: 
ADVERSE EVENT MANAGEMENT .....................................................87 
APPENDIX 9: 
PROTOCOL SYNOPSIS ..........................................................................97 
APPENDIX 10: 
SUMMARY OF VERSIONS AND CHANGES ....................................109 
APPENDIX 11: 
SPONSOR’S ELECTRONIC PROTOCOL 
SIGNATURE PAGE...................................................................................................110 
 
TABLE OF TABLES 
Table 1 
Historical ORR with CPI monotherapy for Treatment Cohorts ............................13 
Table 2 
Evaluation of Best Overall Response When Confirmation of CR and PR 
Required .................................................................................................................41 
Table 3 
Phase 1b Subjects: PK and ADA Sample Collection Schedule .............................49 
Table 4 
Protocol-Required Safety Laboratory Assessments ...............................................66 
Table 5 
Highly Effective Contraceptive Methods That Are User Dependent ....................77 
Table 6 
Evaluation of Overall Response .............................................................................83 
 
TABLE OF FIGURES 
Figure 1 
Broad Expression of TIGIT’s Ligand PVR across TCGA Tumor 
Collection .................................................................................................................6 
Figure 2 
Study Schema...........................................................................................................9 
Figure 3 
Prevalence of TIGIT in TCGA Tumors .................................................................11 
Figure 4 
TIGIT and PD1 Co-expression on TCGA .............................................................12 
Figure 5 
Simon Two-stage Study Design ............................................................................56 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 5 of 110 
1. 
INTRODUCTION AND BACKGROUND 
1.1. 
Introduction 
Etigilimab, a humanized immunoglobulin G (IgG1) monoclonal antibody that specifically binds 
to human TIGIT (T-cell immunoreceptor with Ig and ITIM domains), blocks TIGIT interaction 
with its ligand PVR (poliovirus receptor), inhibits downstream signaling, and mediates target cell 
killing. Anti-TIGIT was shown preclinically to inhibit tumor growth in mouse models. 
Etigilimab is being developed for the treatment of solid cancer tumors in humans. 
1.2. 
Background 
TIGIT is an important co-inhibitory receptor; it contains 2 immunoreceptor tyrosine-based 
inhibition motifs (ITIMs) and its expression at the surface of immune cells is markedly increased 
upon activation. TIGIT is found on CD4 and CD8 T-cells, on natural killer (NK) cells, and on a 
subset of Tregs (regulatory T cells) (Chan et al 2012, Yu et al 2009, Joller et al 2014). Consistent 
with its structure and expression pattern, TIGIT was found to have an inhibitory function on both 
T-cells and NK cells and to increase Tregs’ suppressive capacity (Joller et al 2014, 
Joller et al 2011, Levin et al 2011, Stanietsky et al 2009). Known ligands for TIGIT are PVR, 
PVRL2, and with weaker binding, PVRL3 and PVRL4 (Yu et al 2009) (data on file at Mereo). 
The TIGIT signaling axis also contains a co-stimulatory receptor, CD226, which binds to PVR 
and PVRL2 with lower affinity than TIGIT (Bottino et al 2003, Martinet & Smyth 2015). 
Therefore, when TIGIT is expressed, the ligands preferentially engage TIGIT rather than CD226, 
leading to immune suppression. 
Given TIGIT’s immunomodulatory functions and the expression of PVR and PVRL2 in most 
cancers (Stanietsky et al 2009, Gromeier et al 2000), it has been postulated that blocking TIGIT 
binding to its ligands may reverse tumor-induced immune suppression and result in tumor 
regression in a broad range of cancer types (Figure 1). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 6 of 110 
Figure 1 
Broad Expression of TIGIT’s Ligand PVR across TCGA Tumor Collection 
 
Abbreviations: PVR = poliovirus receptor; TCGA = The Cancer Genome Atlas; RPKM = reads per kilobase per 
million; TIGIT = T-cell immunoreceptor with Ig and ITIM domains 
Legend: PVR gene expression levels are plotted for 32 different tumor types as available from The Cancer Genome 
Atlas (TCGA). Each symbol represents one patient. Levels are expressed in reads per kilobase per million (RPKM).   
 
The anti-tumor activity of TIGIT blockade was verified in different murine cancer models where 
it was shown to operate through multiple mechanisms to inhibit tumor growth 
(Johnston et al 2014, Kurtulus et al 2015). Further supporting TIGIT targeting for cancer 
treatment are reports of its overexpression on patient tumor-associated T-cells 
(Johnston et al 2014, Chauvin et al 2015). 
TIGIT targeting is likely to be most efficient when combined with other immunotherapies. 
In preclinical and clinical studies, targeting TIGIT together with the programmed death-
1/programmed death ligand-1 (PD-1/PD-L1) pathway demonstrated superior tumor suppression 
compared to either monotherapy.  
A Phase 1a/b open-label, dose-escalation study was conducted to evaluate the safety and 
pharmacokinetics (PK) of etigilimab administered as a single agent or in combination with 
nivolumab to subjects with locally advanced or metastatic solid tumors (study number 
313M32-001). A total of 23 subjects were enrolled on the Phase 1a portion of the study for 
treatment with etigilimab and 10 subjects were enrolled on the Phase 1b portion of the study for 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 7 of 110 
treatment with etigilimab in combination with nivolumab. Doses investigated in the Phase 1a 
portion of the study were 
 mg/kg (for dose-escalation) and 
 mg/kg (for dose-
expansion) , and doses evaluated in the Phase 1b dose-escalation portion of the study were 
 
 mg/kg. To characterize the PK properties of etigilimab and pharmacodynamic responses 
to treatment, blood samples were taken at various timepoints before and after dosing. Subjects 
underwent tumor assessments at screening and every 8 weeks during the study. Subjects 
remained on treatment at the discretion of the investigator until disease progression, 
unacceptable toxicity, initiation of a new anticancer therapy, withdrawal of subject consent, 
physician decision, or death. Efficacy endpoints included tumor response. Time-to-event 
endpoints included duration of response (DoR), progression-free survival (PFS), and overall 
survival. Safety endpoints included adverse events (AEs), vital signs, 12-lead electrocardiograms 
(ECGs), clinical laboratory testing, and immunogenicity testing. 
Treatment with etigilimab was well-tolerated in study 313M32-001; no dose-limiting toxicities 
(DLTs) were reported in either the Phase 1a or Phase 1b portions of the study. Thus, the 
maximum tolerated dose was not reached. All subjects in the study reported 1 or more treatment-
emergent AEs (TEAEs). The most commonly reported TEAEs in the Phase 1a portion of the 
study were nausea (8 subjects, 34.8%) and fatigue (7 subjects, 30.4%), and the most commonly 
reported TEAEs in the Phase 1b portion of the study were decreased appetite and nausea (each 
reported by 5 subjects, 50.0%). Immune-related TEAEs were reported by 10 subjects (43.5%) in 
the Phase 1a and 5 subjects (50.0%) in the Phase 1b portions of the study. The most commonly 
reported immune-related TEAEs in the Phase 1a portion of the study were pruritus, rash, and 
maculopapular rash (each reported by 3 subjects, 15.0%). In the Phase 1b portion of the study, 
the most commonly reported immune-related TEAEs were pruritus, rash, and pruritic rash (each 
reported by 2 subjects, 20.0%). The most commonly reported National Cancer Institute Common 
Terminology Criteria for Adverse Events (NCI CTCAE) Grade 3 or higher abnormal laboratory 
test results in the Phase 1a portion of the study were lymphocytes (8 subjects 34.8%), alkaline 
phosphatase (3 subjects 13.0%), and alanine aminotransferase (ALT) and sodium (each reported 
by 2 subjects, 8.7%). In the Phase 1b portion of the study, the most commonly reported CTCAE 
Grade 3 or higher laboratory results were alkaline phosphatase (3 subjects, 30.0%) and aspartate 
aminotransferase (AST) (2 subjects, 20.0%). Treatment-emergent AEs with a fatal outcome were 
reported for 3 subjects (13.0%) in the Phase 1a portion of the study and 2 subjects (20.0%) in the 
Phase 1b portion of the study. There were no related TEAEs with a fatal outcome in the Phase 1a 
and the Phase 1b portions of the study. 
In the single agent portion of the study no Response Evaluation Criteria in Solid Tumors 
(RECIST) responses were reported. However, a number of subjects demonstrated tumor 
reduction or stable disease (SD). The tumor types where clinical benefit was observed included 
endometrial, fallopian tube, parotid adenocarcinoma, salivary duct adenocarcinoma, and 
colorectal cancer. In the group who received both etigilimab and nivolumab, all subjects treated 
received a prior checkpoint point inhibitor. A partial response was observed in a patient with 
ovarian cancer, and other patients with microsatellite instability (MSI), colorectal (CRC), head 
and neck, gastric and renal cancer appeared to benefit with evidence of tumor reduction or 
stabilization. 
The median (95% confidence interval [CI]) PFS in the Phase 1a portion of the study was 
56.0 (51.0, 112.0) days, and the PFS estimates (95% CI) at 3, 6, and 12 months were 30.0% 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 8 of 110 
(12.3, 50.1), 10.0% (1.7, 27.2), and 0%, respectively. The median (95% CI) PFS in the Phase 1b 
portion of the study was 57.5 (14.0, 224.0) days, and the PFS estimates (95% CI) at 3, 6, and 
12 months were 37.5% (8.7, 67.4), 25.0% (3.7, 55.8), and 0%, respectively. The median (95% 
CI) overall survival in the Phase 1a portion of the study was 173.0 (88.0, 268.0) days, and the 
survival estimates (95% CI) at 3, 6, and 12 months were 30.0% (12.3, 50.1), 10.0% (1.7, 27.2), 
and 0%, respectively. The median (95% CI) overall survival in the Phase 1b portion of the study 
was 205.0 (19.0, N/A) days, and the survival estimates (95% CI) at 3 months were 57.9% 
(15.3, 85.2) and not applicable at 6 and 12 months. 
1.3. 
Study Design  
This is an open-label, multicenter, Phase 1b/2 basket study designed to evaluate the efficacy, 
safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of etigilimab in 
combination with nivolumab in subjects with recurrent, locally advanced and/or metastatic solid 
tumors who are not candidates for available, curative standard of care therapies. In cohorts 
enrolling tumor types for whom anti-PD-1 antibody therapy is approved treatment for recurrent, 
locally advanced or metastatic disease, subjects may be enrolled prior to treatment with anti-PD-
1 antibody therapy. 
Subjects will be assigned to receive etigilimab (
 mg every 2 weeks for subjects ≥50 kg, 
 mg/kg dose every 2 weeks for subjects <50 kg) in combination with nivolumab (240 mg 
every 2 weeks) and will continue until protocol-defined discontinuation criteria are met (refer to 
Section 7). Additional doses and schedules may also be evaluated. This study will evaluate both 
subjects who have not previously been treated with immune checkpoint inhibitors (CPI) as well 
as those who have received prior CPI therapy and will include tumor types chosen for higher 
prevalence of TIGIT, and in select cohorts, subjects with high PD-L1 expressing tumors as 
measured by immunohistochemistry (IHC). Tumor types selected for this study include 
recurrent, locally advanced and/or metastatic endometrial carcinoma (EC), cervical cancer (CC), 
gastric cancer and gastro-esophageal junction carcinoma (GC), squamous cell carcinoma of the 
head and neck (HNSCC), ovarian cancer (OC), rare cancers (metastatic testicular germ cell 
tumor, uveal melanoma and sarcoma) and any subject with concomitant tumor mutation burden 
high (TMB-high) and microsatellite stable (MSS) tumors. As TIGIT has been implicated in PD-
L1 resistance, subjects who have received or progressed following a CPI (post-CPI subjects) will 
also be enrolled in select tumors including EC, HNSCC and TMB-high/MSS tumors. Parallel 
cohorts of up to 20 subjects per cohort will be evaluated. 
Cohorts will be enrolled at the discretion of the sponsor. Selected cohorts will be open for the 
first 20 subjects enrolled without increasing the total number of subjects proposed for the trial. 
During the conduct of this open-label study an Independent Data Monitoring Committee (IDMC) 
will be established and will review study data on an ongoing basis. The IDMC will consist of at 
least 3 members with expertise in their field of practice as well as in the conduct of clinical 
studies. The committee members will be free of significant conflicts of interest. The IDMC will 
hold regularly scheduled data review meetings at pre-specified intervals as defined in the IDMC 
charter. The IDMC will also be available on an ad hoc basis e.g., to provide guidance related to 
any emerging safety signals or if requested by the sponsor. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 9 of 110 
The IDMC will have periodic safety reviews of the study that will start after the first 20 subjects 
are enrolled. A safety review of the study will be conducted by the IDMC approximately every 3 
months. The IDMC and sponsor may decide to meet less frequently, based upon rate of accrual 
and the amount of new data generated (refer to the IDMC charter). .  
Futility monitoring will be evaluated in each cohort of the study using a Simon’s two-stage 
design as described in Section 9.1 of the protocol. For each cohort, the second stage may be 
opened for enrollment only after discussion with the IDMC and the sponsor. The sponsor may 
have an independent assessment of responses to verify investigator-reported responses. The 
responses based on independent assessments, if available, will be used for sensitivity analysis 
with sponsor and will make recommendations regarding study conduct, including whether to 
continue, modify, or stop the study. 
An analysis will be conducted when the first 30 TIGIT IHC biopsy results have been complete. 
This is to confirm the expected TIGIT positive rate based on data on file and reported in the 
literature. The efficacy of the combination will be evaluated by cohort and efficacy of the 
combination will be evaluated based on TIGIT IHC positive subjects.  
Figure 2 
Study Schema 
 
Abbreviations: ECOG = Eastern Cooperative Oncology Group; GEJ = gastroesophageal junction adenocarcinoma; 
Tumor mutation burden – high (TMB-H) + microsatellite stable (MSS); OS = overall survival;  
PD = pharmacodynamic; PD-1 = programmed death-1; PD-L1 = programmed death ligand-1;  
PFS = progression-free survival; PK = pharmacokinetic; ADA=anti-drug antibody  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 10 of 110 
1.4. 
Study Rationale 
1.4.1. 
Rationale for Study Design 
A number of checkpoint inhibitors such as PD-L1 and PD-1 can act by blocking interactions 
between ligands and receptors on tumor cells and T cells and lead to enhanced anti-tumor 
immunity. A number of anti-PD-1 inhibitors, including nivolumab and anti-PD-L1 antibodies 
have been approved for numerous indications. However, a large proportion of patients who 
receive CPI do not derive a clinical benefit, progress or become resistant. Strategies improving 
the effectiveness or reversing resistance to these agents in high unmet need indications are being 
studied.  
One such strategy explored is inhibiting TIGIT. It has been postulated that blocking TIGIT 
binding to its ligands may reverse tumor-induced immune suppression and result in tumor 
regression in a broad range of cancer types. Etigilimab is a novel immunotherapy that binds to 
TIGIT, an immune checkpoint protein found on immune cells. Both TIGIT and PD-1 are 
involved in immune suppression and blocking both pathways have the potential for improving 
anti-tumor activity. 
A Phase 1 study of single agent etigilimab (n = 23) and in combination with nivolumab (n = 10) 
in heavily pretreated advanced cancer subjects was completed. Clinical benefit was noted in 
subjects with endometrial, ovarian, head and neck, and some MSI high and TMB-H tumors (data 
on file at Mereo). Finally, other anti-TIGIT anti-bodies in development have reported 
preliminary evidence of potential clinical benefit by stabilization of disease activity in both CPI 
naïve and post-CPI subjects in a number of tumor types including non-small cell lung cancer 
(NSCLC), small-cell lung cancer (SCLC), ovarian, cervical and gastroesophageal junction 
adenocarcinoma.  
The tumor types selected for evaluation in this study have been identified based on the likelihood 
of high TIGIT/PVR expression and co-expression of both TIGIT and PD-1 (Figure 3 and 
Figure 4). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 11 of 110 
Figure 3 
Prevalence of TIGIT in TCGA Tumors 
 
Abbreviations: RSEM = RNA-Seq by Expectation-Maximization; TCGA = The Cancer Genome Atlas; 
TIGIT = T-cell immunoreceptor with Ig and ITIM domains 
Legend: Prevalence of TIGIT gene expression in tumor types as available from TCGA. The quartile RSEM value of 
TIGIT gene expression is 100.   
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 12 of 110 
Figure 4 
TIGIT and PD1 Co-expression on TCGA 
 
Abbreviations: PD-1 = programmed death-1; TCGA = The Cancer Genome Atlas; TIGIT = T-cell immunoreceptor 
with Ig and ITIM domains 
Legend: TIGIT and PD1 expression in TCGA. Tumor ranked by R value; tumors with correlation greater than 
R=.7 are shaded. 
 
The purpose of the study is to determine preliminary clinical activity of this combination in 
several selected tumor groups and identify which subject characteristics, based on histology, 
biomarker or prior therapy are most like to benefit from this combination.  
This open-label basket study trial design is the most effective to evaluate pan tumor safety and 
clinical activity by histology, TIGIT, and PD-L1 status.  
Subject selected for evaluation in this study all have advanced or metastatic disease, who are not 
candidates for available, curative standard of care therapies, with cancer types considered as high 
unmet therapeutic need indications for which limited therapeutic options exist. Table 1 illustrates 
TCGA
Detail
TIGIT:PD1 (CD279) R (correlation)
UVM
Uveal Melanoma
0.95
SARC
Sarcoma
0.92
SKCM
Skin Cutaneous Melanoma
0.91
TGCT
Testicular Germ Cell Tumors
0.9
KIRP
Kidney renal papillary cell carcinoma
0.88
HNSC
Head and Neck squamous cell carcinoma
0.87
BLCA
Bladder Urothelial Carcinoma
0.86
COAD
Colon adenocarcinoma
0.86
ESCA
Esophageal carcinoma
0.84
LUSC
Lung squamous cell carcinoma
0.83
MESO
Mesothelioma
0.83
BRCA
Breast invasive carcinoma
0.82
PRAD
Prostate adenocarcinoma
0.82
PAAD
Pancreatic adenocarcinoma
0.81
THCA
Thyroid carcinoma
0.81
UCEC
Uterine Corpus Endometrial Carcinoma
0.8
KICH
Kidney Chromophobe
0.78
CESC
Cervical squamous cell carcinoma and endocervical adenocarcinoma
0.76
OV
Ovarian serous cystadenocarcinoma
0.76
READ
Rectum adenocarcinoma
0.74
KIRC
Kidney renal clear cell carcinoma
0.73
LUAD
Lung adenocarcinoma
0.73
ACC
Adrenocortical carcinoma
0.72
STAD
Stomach adenocarcinoma
0.72
UCS
Uterine Carcinosarcoma
0.72
PCPG
Pheochromocytoma and Paraganglioma
0.52
DLBC
Lymphoid Neoplasm Diffuse Large B-cell Lymphoma
0.49
GBM
Glioblastoma multiforme
0.46
LIHC
Liver hepatocellular carcinoma
0.46
CHOL
Cholangio carcinoma
0.34
LGG
Brain Lower Grade Glioma
0.3
LAML
Acute Myeloid Leukemia
0.076
THYM
Thymoma
0.047

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 13 of 110 
the historic objective response rate (ORR) for monotherapy with anti-PD-1/anti-PD-L1 
antibodies in the tumor types included in this study. 
Table 1 
Historical ORR with CPI monotherapy for Treatment Cohorts 
Tumor Type 
ORR for Single Agent CPI 
PD-L1 Positive tumors 
Advanced and/or recurrent or metastatic squamous cell 
carcinoma of the head and neck or for the first-line treatment 
of subjects with metastatic or with unresectable, recurrent head 
and neck squamous cell carcinoma (HNSCC)  
14%-18% 
Recurrent or metastatic cervical cancer with disease 
progression on or after chemotherapy whose tumors express 
PD-L1 
14% (Chung et al 2019) 
Recurrent locally advanced or metastatic gastric or 
gastroesophageal junction adenocarcinoma with disease 
progression on or after 2 or more prior lines of therapy 
including fluoropyrimidine- and platinum-containing 
chemotherapy and if appropriate, HER2/neu-targeted therapy. 
16%-22% 
TMB-H 
Advanced or metastatic TMB-H and MSS solid tumors, that 
have progressed following prior treatment and who have no 
satisfactory alternative treatment options. 
28% 
Independent of PD-L1 Status 
Advanced and/or metastatic endometrial carcinoma, who have 
disease progression following prior systemic therapy and are 
not candidates for curative surgery or radiation 
23% ~ 40% 
Histologically confirmed high grade serous and endometrioid 
recurrent ovarian cancer, fallopian tube cancer or primary 
peritoneal cancer following platinum-based front-line regimen 
per standard of care after primary or interval debulking surgery 
with documented radiological recurrence.    
~10% (Matulonis et al 2020) 
Rare disease with high prevalence of TIGIT expression  
• germ cell tumors 
0%-15% 
• sarcoma 
0%-15% 
• uveal melanoma 
0%-15% 
Schmidt et al 2020  
Abbreviations:  CPI = checkpoint inhibitor; MSS = microsatellite stable; ORR = overall response rate; 
PD-L1 = programmed death ligand-1; TIGIT = T-cell immunoreceptor with Ig and ITIM domains; 
TMB-H = tumor mutational burden‐high  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 14 of 110 
This ORR together with the DoR is expected to inform future studies of this combination 
depending on tumor type.   
1.4.2. 
Scientific Rationale for Selected Endpoints  
In oncology clinical trials, many different endpoints can be used as primary or secondary 
endpoints including OS, ORR, DoR, disease control rate (DCR), disease-free survival (DFS), 
and PFS. 
The ORR, as per RECIST v1.1, is an increasingly important endpoint for accelerated 
development of highly active anticancer therapies and will be the primary endpoint for this 
study. This surrogate marker, used in single arm studies, is able to evaluate early if there is a 
direct effect on tumor size seen on radiology. The ORR has correlated with endpoints such as 
PFS and OS.  
As per Food and Drug Administration (FDA) guidance document on oncology endpoints, ORR 
was chosen because: 
• ORR is generally assessed earlier and with smaller sample size compared with survival 
studies.  
• ORR measures the effect on tumor attributable to drug(s), not natural history.  
• ORR is generally based on objective and quantitative assessment.  
Additional secondary and exploratory endpoints that will also be evaluated include the 
following: 
The DoR is defined as the time from first documented objective response (RECIST v1.1) by 
Independent Central Review until the date of documented disease progression. Cancer drugs 
that demonstrate improved DoR can produce a durable, meaningful delay in disease 
progression, as opposed to a temporary response without any lasting benefit. The DCR, as 
per RECIST v1.1 is a modification of ORR that includes subjects with SD exceeding a minimum 
duration as responders. This may be a suitable preliminary or exploratory measure of antitumor 
activity for indications where complete response (CR) or partial responses (PR) may be more 
difficult to attain, stable disease does not reflect the natural history of the disease, and SD is a 
clinically meaningful outcome. Duration of stable disease is measured from the start of the 
treatment (the first treatment date for non-randomized studies, the randomization date for 
randomized studies) until the date when the criteria for overall disease progression are first met 
also provides supportive data for assessment of clinical activity of experimental anti-cancer 
regimens.  
1.4.3. 
Justification for Dose and Schedule 
The flat dose of etigilimab of 
 mg for subjects ≥50 kg was selected for MPH313-1-02 based 
on data from study 313M32-001. In this study, a trough exposure of approximately 
20 to 30 µg/mL was associated with maximum reduction in Treg and maximal increase in Ki67 
biomarkers. This exposure was also associated with subjects who appeared to achieve clinical 
benefit from etigilimab. The trough exposure is this range can be obtained with a dose of 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 15 of 110 
 mg every 2 weeks. See the Investigator Brochure Section 5.3.4 (data on file at Mereo) for 
more detailed information. For subjects <50 kg, a weight-based dose of 
 mg/kg will be utilized 
to not exceed the highest dose examined in the 313M32-001 study. 
Nivolumab is an FDA-approved human IgG4 kappa immunoglobulin that blocks the interaction 
between PD-1 and its ligands PD-L1 and PD-L2 indicated for the treatment of advanced 
melanoma, NSCLC, renal cell carcinoma, Hodgkin lymphoma, advanced HNSCC, MSI-high or 
mismatch repair-deficient CRC, and hepatocellular carcinoma (OPDIVO 2018). The mechanism 
of action of nivolumab involves blocking inhibiting signals mediated by the PD-L1/L2-PD-1 
interaction on effector T-cell function leading to enhanced T-cell activity/immunosurveillance 
within the tumor microenvironment.  
Nivolumab is given at either 3 mg/kg or flat 240 mg intravenous (IV) every 2 weeks (Q2W) with 
similar safety, PK and efficacy seen between the 2 dosing strategies in several FDA-approved 
tumor types (OPDIVO 2018). For this study, nivolumab will be dosed at the flat rate of 240 mg 
IV Q2W. Clinical trial data on over 1900 patients treated with nivolumab as a single agent and 
400 melanoma patients treated with nivolumab in combination with ipilimumab provide a 
substantial database of safety information. Immune-related toxicities are common and 
well-described and include pneumonitis, colitis, hepatitis endocrinopathies, nephritis, skin 
reactions, encephalitis, infusion reactions and others. Many of these adverse effects are managed 
with corticosteroid immunosuppression with interruption/stopping rules guided by the nivolumab 
package insert (OPDIVO 2018). 
1.5. 
Benefit/Risk Assessment 
More detailed information about the known and expected benefits and risks and reasonably 
expected adverse events (AEs) of etigilimab may be found in the Investigator’s Brochure (data 
on file at Mereo). There are risks from some of the study-specific procedures. If a fresh tumor 
biopsy is required, the risks include pain and discomfort, bleeding, tenderness, scaring, and 
rarely infection. Uncommonly, complications from biopsies can be life threatening. Potentially 
serious complications from bleeding or organ damage may occur. These might require additional 
surgical intervention. Collection of blood samples may cause fainting, redness, pain, bruising, 
bleeding, and infection. The ECG sticky pads may cause redness or itching and if the hair under 
the patches needs to be shaved, this may cause irritation of the skin.   

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 16 of 110 
2. 
OBJECTIVES AND ENDPOINTS 
Objectives 
Endpoints 
PRIMARY 
To make a preliminary assessment of the 
antitumor activity of etigilimab in 
combination with nivolumab in subjects 
with pre-specified recurrent solid tumors. 
Each cohort will be evaluated 
independently. 
• Objective response rate (ORR) 
SECONDARY 
Evaluate the safety and tolerability of 
etigilimab administered in combination 
with nivolumab. 
• Count and % of subjects who experience at 
least 1 adverse event (AE) and abnormal 
safety laboratory parameters 
• Adverse events of special interest [(AESIs) 
infusion reactions, immune-related adverse 
events)] 
• Relationship of PK and safety 
To evaluate preliminary anti-tumor activity 
of etigilimab in combination with 
nivolumab in subjects with pre-specified 
recurrent solid tumors. Each cohort will be 
evaluated independently. 
• Disease control rate (DCR; is the proportion 
of subjects whose BOR is CR, PR, or SD) 
• Duration of response (DoR)  
• Duration of stable disease 
To characterize the PK of etigilimab in a 
subset of subjects who have advanced, 
relapsed, or refractory solid tumors in 
combination with nivolumab. 
• PK levels of etigilimab in combination with 
nivolumab 
To characterize the immunogenicity of 
etigilimab in a subset of subjects who have 
advanced, relapsed, or refractory solid 
tumors in combination with nivolumab. 
• Anti-drug antibodies (ADA) to etigilimab; 
Impact of developed etigilimab ADAs on PK 
levels of etigilimab 
EXPLORATORY 
To assess exploratory pharmacodynamic 
biomarkers following etigilimab treatment 
in combination with nivolumab.  
Pharmacodynamic biomarkers will be assessed to 
determine their correlation with response to 
etigilimab treatment as follows: 
• Changes in peripheral blood mononuclear cell 
populations and activation 
• TIGIT and immune-related gene expression 
by messenger RNA (mRNA) detection 
(eg, CD226, TIGIT, T-cell genes) 
• Plasma proteins (eg, interleukin 17 [IL17], 
interleukin 2 [IL2], interferon gamma [IFNγ] 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 17 of 110 
Objectives 
Endpoints 
To assess potential predictive biomarkers 
for correlation with response to etigilimab 
treatment and exploratory biomarkers with 
treatment response. 
• To correlate levels of TIGIT, PVR, TMB, PD-
L1, and other immune markers with anti-
tumor activity endpoints 
• BAP1 (BRCA1 associated protein-1) tumor 
mutations with etigilimab treatment response 
To evaluate preliminary anti-tumor activity 
of etigilimab in combination with 
nivolumab according to iRECIST. 
Each cohort will be evaluated 
independently. 
• ORR (proportion of iCR plus iPR subjects) 
• DoR (iRECIST) 
• Progression-free survival (PFS) using 
RECIST v1.1 and iRECIST 
• OS 
Abbreviations:  BOR = best overall response; CR = complete response; DoR = duration of response; 
ORR = overall response rate; OS = overall survival; PD-L1 = programmed death ligand-1; PK = 
pharmacokinetic; PR = partial response; PVR = poliovirus receptor; SD = stable disease; TIGIT = T-cell 
immunoreceptor with Ig and ITIM domains; RECIST = Response Evaluation Criteria in Solid Tumors;  
TMB = tumor mutational burden  
 
2.1. 
Number of Subjects 
Approximately 135 subjects may be screened to achieve 125 enrolled such that 115 evaluable 
subjects complete the study. Cohorts will be enrolled at the discretion of the sponsor. Selected 
cohorts may be open for the first 10 subjects enrolled without increasing the total number of 
subjects proposed for the trial.  
2.2. 
Study Start and End Definition 
2.2.1. 
Start of Study Definition 
The start of the study is defined as the date of the first visit involving a trial procedure, excluding 
consent, of the first subject in the study. 
2.2.2. 
End of Study Definition 
The trial is considered completed when the last subject dies or withdraws from the trial. 
However, the maximum trial duration is 3 years after the last subject’s first treatment in the trial.  
2.2.3. 
Post Study Access to Therapy 
At the end of the protocol-specified maximum trial duration, the sponsor will not continue to 
supply study drug to subjects/investigators unless the sponsor chooses to extend the study. The 
investigator should ensure that the subject receives appropriate standard of care to treat the 
condition under study.  
In the event of approval of study drug by the responsible health authority, subjects who continue 
to demonstrate clinical benefit will be eligible to receive study drug up to 12 months after or 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 18 of 110 
until the study drug becomes commercially available within the country, whichever occurs 
sooner. Sponsor reserves the right to terminate access to study drug if any of the following occur: 
a) the marketing application is rejected by the responsible health authority; b) the study is 
terminated due to safety concerns; c) the subject can obtain medication from a government 
sponsored or private health program; or d) therapeutic alternatives become available in the local 
market. 
2.2.4. 
Trial Termination 
The sponsor reserves the right to close a given trial site or terminate the trial at any time for any 
reason at the sole discretion of the sponsor. Reasons for the early closure of a trial site by the 
sponsor may include but are not limited to: 
• Failure of the investigator to comply with the protocol, the requirements of the 
independent ethics committee (IEC) and institutional review board (IRB) or local health 
authorities, the sponsor’s procedures, or International Conference on Harmonization 
(ICH) Good Clinical Practice (GCP) guidelines. 
• Inadequate recruitment of subjects by the investigator. 
• Discontinuation of further trial drug development. 
3. 
STUDY POPULATION 
Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as 
protocol waivers or exemptions, is not permitted. 
3.1. 
Inclusion Criteria 
1) Type of Subject and Disease Characteristics by Cohort 
Cohort A  
• Histologically confirmed diagnosis of endometrial carcinoma (EC);  
Note: carcinosarcoma (malignant mixed Mullerian tumor), endometrial 
leiomysarcoma and endometrial stromal sarcomas are excluded. 
• Recurrent, advanced, and/or metastatic disease without potential for local 
curative surgery or radiation. 
• Radiographic evidence of progression after 1 prior systemic platinum-based 
chemotherapy regimen for EC with at least 1 measurable target lesion 
according to RECIST 1.1 that is suitable for repeat measurement including:  
o non-nodal lesion that measures ≥10 mm in the longest diameter 
o radiographic evidence of subsequent growth after locoregional therapy 
or external beam radiotherapy (EBRT). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 19 of 110 
• Up to 1 additional line of platinum-based chemotherapy if given in the 
neoadjuvant or adjuvant treatment setting. There is no restriction regarding 
prior hormonal therapy.  
• Treatment with prior anti-PD-1/anti-PD-L1/2 antibodies is not allowed.  
Cohort B 
• Histological or cytological evidence of advanced and/or recurrent or 
metastatic HNSCC or for the first-line treatment of subjects with metastatic or 
with unresectable, recurrent HNSCC whose tumors express PD-L1 (combined 
positive score [CPS] >1%). Diagnosis of squamous cell carcinoma of the oral 
cavity, nasal cavity, paranasal sinuses, nasopharynx, oropharynx, 
hypopharynx. or larynx are permitted. Primary or recurrent disease for which 
no curative or established palliative treatments are amenable.   
• Subjects without prior anti-PD-1/anti-PD-L1/2 antibody treatment are eligible.  
• Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies are 
eligible provided they have had (i) documented best observed response (BOR) 
of SD or better in response to an anti-PD1/PD-L1/2 therapy, AND (ii) 
≥6 weeks interval since their last dose of prior anti-PD-1/anti-PD-L1/2 
treatment 
Cohort C  
• Histologically confirmed cervical cancer  
• Recurrent, advanced and/or metastatic disease with disease progression on or 
after one or more lines of chemotherapy, without potential for local curative 
treatment options including systemic chemotherapy, surgery or radiation and 
PD-L1-expressing tumors (CPS >1%).  
Note: Chemotherapy administered in the adjuvant or neoadjuvant setting, or in 
combination with radiation therapy, should not be counted as a systemic 
therapy regimen.   
• Treatment with prior anti-PD-1/anti-PD-L1/2 antibodies is not allowed.  
Cohort D  
• Histological or cytological evidence of recurrent advanced and/or metastatic 
gastric or gastroesophageal junction adenocarcinoma whose tumors 
express PD-L1 (CPS >1%), with disease progression on or after 2 or more 
prior lines of therapy including fluoropyrimidine- and platinum-containing 
chemotherapy and if appropriate, HER2/neu-targeted therapy.  
• Subjects without prior anti-PD-1/anti-PD-L1/2 antibody treatment are eligible.  
• Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies are 
eligible provided (i) they have had documented best observed response (BOR) 
of SD or better in response to an anti-PD1/PD-L1/2 therapy, AND  
(ii) ≥6 weeks interval since their last dose of prior anti-PD-1/anti-PD-L1/2 
treatment 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 20 of 110 
Cohort E  
• Histological or cytological evidence of unresectable or metastatic TMB-H 
and MSS solid tumors (TMB as defined by an FDA-approved test, e.g., 
Foundation Medicine >10 mutations/megabase or a Laboratory Developed 
Test approved by the sponsor (e.g., Guardant Health), that have progressed 
following prior treatment and who have no satisfactory alternative treatment 
options. Subjects without prior treatment with anti-PD-1/anti-PD-L1/2 
antibody treatment are eligible. Subjects who have received prior anti-PD-
1/PD-L1/2 treatment are eligible with at least 6 weeks since their last dose of 
these prior treatments. Subjects must have had a previous SD or better in 
response to an anti-PD1/PDL-1/2 therapy. Subjects with the following TMB-
H and MSS solid tumors will enroll into the tumor specific cohorts noted 
below after discussion with the sponsor: 
Cohort A: Endometrial cancer PD-1/PD-L1/2 naïve 
Cohort C: Cervical carcinoma 
Cohort F: Rare tumors (sarcoma, uveal melanoma, germ cell carcinoma) 
Cohort H: Ovarian cancer 
Cohort F  
Rare Tumors 
1. Germ Cell Tumors 
• Histologically or cytologically confirmed seminoma or non-seminoma 
testicular germ cell tumors. 
• Recurrent, advanced and/or metastatic disease, including new lesions, 
persistently elevated β- human chorionic gonadotropin (HCG) or alpha 
1-fetoprotein (AFP) or increase in consecutive elevated serum tumor markers 
(β-HCG or AFP) done at least one week apart after prior high-dose 
chemotherapy (HDCT). 
Subjects deemed not to be candidates for benefit from potentially curative 
HDCT may also be eligible including those with: 
(i) 
inadequate renal function for HDCT 
(ii) 
relapse >2 years after last therapy 
(iii) 
inadequate stem cell collection to move forward with HDCT  
(iv) 
significant medical or psychosocial comorbidities that are felt to be a 
contraindication to HDCT by the treating investigator. 
• Subjects with serum tumor marker ≥S2 HCG and AFP (levels ≥1000 for AFP 
and ≥5000 for HCG are excluded). 
• Subjects who have received prior anti-PD1/anti-PD-L1/2 antibodies are 
excluded. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 21 of 110 
2. Sarcoma 
• Histological diagnosis (with archival or new biopsy sample available for 
pathology review) of locally advanced/unresectable and/or metastatic soft 
tissue sarcoma histopathological subtypes as noted below, who have 
radiological evidence of measurable disease and are not candidates for any 
curative surgery of multimodality therapy: 
o De-differentiated liposarcoma (n=10) 
o Undifferentiated pleomorphic sarcoma (UPS) (n=10) 
o Alveolar soft part sarcoma, malignant peripheral nerve sheath 
tumors, myxofibrosarcoma (grade 2 or higher), OR pleomorphic 
dermal sarcoma (total n=5) 
• Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies as 
standard of care are excluded. 
3. Uveal Melanoma 
• Histologically confirmed recurrent uveal melanoma with disease progression 
beyond prior approved standard of care therapy administered in the advanced 
setting (prior surgical resection of liver metastases, local radiation therapy and 
adjuvant systemic therapy are acceptable) are eligible. 
• Subjects who have received prior anti-PD1/anti-PD-L1/2 antibodies are 
excluded. 
Cohort G 
• Histologically confirmed diagnosis of EC;  
Note: carcinosarcoma (malignant mixed Mullerian tumor), endometrial 
leiomyosarcoma, and endometrial stromal sarcomas are excluded. 
• Subjects must have recurrent, advanced, and/or metastatic disease and must 
not be candidates for local curative surgery and radiation or intolerant to 
known standard of care systemic chemotherapy.  
• Radiographic evidence of progression after >1 and no more than 3 prior 
systemic anti-cancer therapy regimens for EC (neoadjuvant, adjuvant, and 
maintenance treatment are considered part of one treatment line).  
• At least 1 measurable target lesion according to RECIST 1.1 that is suitable 
for repeat measurement including (i) non-nodal lesion that measures ≥10 mm 
in the longest diameter, and (ii) radiographic evidence of subsequent growth 
after locoregional therapy or EBRT.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 22 of 110 
• Prior treatment with any treatment targeting vascular endothelial growth 
factor (VEGF)-directed angiogenesis, any anti-PD-1, anti-PD-L1/2 agent is 
allowed. 
o Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies 
are also eligible provided (i) they have had documented BOR of SD or 
better in response to an anti-PD1/PD-L1/2 therapy, AND  
(ii) ≥3 months interval prior to first study drug administration (C1D1) 
since their last dose of prior anti-PD-1/anti-PD-L1/2 treatment 
Cohort H  
• Histologically confirmed high grade serous and endometrioid ovarian 
cancer, fallopian tube cancer or primary peritoneal cancer    
• Must have received a front-line platinum-based regimen per standard of care 
after primary or interval debulking surgery and have documented radiological 
disease recurrence  
• Must have measurable disease by RECIST 1.1 as determined by the local 
investigator/radiology assessment including 2 sites of disease/biopsy 
accessible disease. Subjects with less than 2 sites will need approval of 
sponsor prior to enrollment. Note: Maintenance treatment following front-line 
treatment is permitted and counted together as part of the front-line treatment.  
• Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies as 
treatment are excluded. 
Subjects are eligible to be included in the study only if the following criteria apply: 
2) Prior Therapy 
• Radiation therapy must be completed >3 weeks prior to first study drug 
administration (C1D1). Participants must have recovered from all 
radiation-related toxicities and/or complications prior to enrollment. Palliative 
radiotherapy is allowed if completed at least 2 weeks prior to first study drug 
administration. Subjects must have recovered from all radiation-related 
toxicities and/or complications prior to enrollment. Subjects must have 
measurable disease outside the radiation field to be eligible; subjects with 
progression in a previously radiated field will also be eligible. 
• All toxicities attributed to prior anticancer therapy, with the exception of 
peripheral neuropathy, alopecia, vitiligo, active thyroiditis, and fatigue, must 
have resolved to Grade 1 (per NCI CTCAE version 5 or higher) or baseline of 
prior treatment prior to enrollment. Peripheral neuropathy must have resolved 
to Grade 2 (per NCI CTCAE version 5 or higher). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 23 of 110 
3) Tumor Specimen 
• Confirmed availability of representative tumor specimens in paraffin blocks is 
required for enrollment with an associated pathology report including PD-L1status for 
PD-L1 positive cohorts.  
• Latest available archival tumor sample eg, ideally within 6 months or up to 1 year 
prior to screening is strongly preferred. In instances where archival tissue is not 
available, a pre-dose biopsy will be required for submission with 3 core samples from 
an 18-gauge needle or larger. Only tissue from a surgical resection or a core needle, 
punch, or excisional/incisional biopsy sample collection will be accepted. Fine needle 
aspirate samples are not acceptable. Sponsor medical review is required if a fresh 
tumor biopsy cannot be provided during screening due to potential risk to subject 
from procedure. 
o For endometrial cancer (Cohorts A and G) archival or fresh biopsy specimen 
for determination of mismatched repair (MMR) status is required if historical 
MMR result is unavailable.  
o For study participants with sarcoma, archival tumor sample must be available 
for pathology review. If no archival material is available, a fresh biopsy 
should be performed to obtain tissue.   
4) Hematologic and End Organ Function 
• Adequate hematologic and end organ function, defined by the following laboratory 
results obtained within 14 days prior to the first study treatment (Cycle 1, Day 1):  
a. Absolute neutrophil count ≥1500 cells/μL.  
b. Platelet count ≥100,000/μL (without transfusion within 14 days prior to Cycle 1, 
Day 1). 
c. Hemoglobin ≥9.0 g/dL (without transfusion of packed red blood cells (RBCs) or 
erythropoietic treatment within 14 days prior to Cycle 1, Day 1). 
d. Total bilirubin ≤1.5 × upper limit of normal (ULN) unless elevated due to Gilbert’s 
syndrome.  
e. AST (SGOT) and ALT (SGPT) ≤3.0 × ULN with the following exception:  
– Subjects with documented liver metastases:  
AST and/or ALT ≤5.0 × ULN. 
– Total bilirubin <1.5 × ULN (subjects with Gilbert’s syndrome may be 
enrolled with sponsor approval). 
f. Prothrombin time (PT)/international normalized ratio (INR), activated partial 
thromboplastin time (aPTT) ≤1.5 × ULN and INR ≤1.5 × ULN in subjects not on 
anticoagulant therapy; subjects receiving therapeutic anticoagulation should be on 
a stable dose with PT, INR, and aPTT within the intended therapeutic range. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 24 of 110 
g. Creatinine ≤1.5 × ULN or measured or calculated creatinine clearance 
≥45 mL/min on the basis of the Cockcroft-Gault glomerular filtration rate 
estimation:  
(140-age) × (weight in kg) × (0.85 if female) 72 × (serum creatinine in mg/dL).  
5) Contraception 
NOTE: The reliability of sexual abstinence for male and/or female enrollment eligibility 
needs to be evaluated in relation to the duration of the clinical study and the preferred and 
usual lifestyle of the subject. Periodic abstinence (eg, calendar, ovulation, symptothermal, 
or post-ovulation methods) and withdrawal are not acceptable methods of contraception. 
• Male Subject: 
A male subject must agree to use a highly effective contraception as detailed in 
Appendix 5 of this protocol during the treatment period and for at least 6 months after 
the last dose of study treatment and refrain from donating sperm during this period. 
• Female Subject:  
A female subject is eligible to participate if she is not pregnant (see Appendix 5), not 
breastfeeding, and at least 1 of the following conditions applies: 
a. Not a woman of childbearing potential (WOCBP) as defined in Appendix 5 
OR 
b. A WOCBP who agrees to follow the contraceptive guidance in Appendix 5 
during the treatment period and for at least 6 months after the last dose of 
study treatment. 
6) Age 
• Age ≥18 years. 
7) ECOG Performance Status 
• ECOG performance status of 0 or 1. 
8) Life Expectancy 
• Life expectancy ≥12 weeks.  
9) Informed Consent 
• Capable of giving signed informed consent as described in Appendix 3 which 
includes compliance with the requirements and restrictions listed in the informed 
consent form (ICF) and in this protocol. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 25 of 110 
10) Compliance with Study Procedure and Visits 
• Ability to adhere to the study and follow-up procedures. 
11) Measurable Disease 
• Have measurable disease based on RECIST 1.1 as determined by the local 
investigator/radiology assessment. Target lesions situated in a previously irradiated 
area are considered measurable if progression has been demonstrated in such lesions. 
3.2. 
Exclusion Criteria  
Subjects are excluded from the study if any of the following criteria apply: 
1) Medical Conditions 
a) Severe allergic or anaphylactic reaction to any monoclonal antibody therapy, murine 
protein, or known hypersensitivity to any excipient in the study drugs. 
b) Major surgery within 4 weeks prior to screening. 
c) Subjects who have received radiotherapy within <1 week of starting study treatment, 
or who have unresolved associated AEs. 
d) Following known active viral infections: 
• Known HIV infection. 
• Active hepatitis B or hepatitis C infection at the time of screening for the 
study. Active hepatitis B is defined as a known positive hepatitis B surface 
antigen (HBsAg) result. Active hepatitis C is defined as a known positive 
hepatitis C antibody result and known quantitative HCV RNA results greater 
than the lower limit of detection of the assay.   
• Subjects with past hepatitis B virus (HBV) infection or resolved HBV 
infection (defined as the presence of hepatitis B core antibody and absence of 
HBsAg) are eligible. HBV DNA must be obtained in these subjects prior to 
randomization. Subjects with positive hepatitis B serology who are immune 
due to vaccination, resolved wild-type infection or passive immunization due 
to immunoglobulin therapy will be eligible.  
• Subjects with past hepatitis C (HCV) infection and positive for HCV antibody 
are eligible only if PCR is negative for HCV RNA.  
• History of active non-infectious pneumonitis or history of pneumonitis that 
required steroids or current pneumonitis. 
e) Ongoing systemic bacterial, fungal, or viral infections at screening. 
• NOTE: Subjects on antimicrobial, antifungal, or antiviral prophylaxis are not 
specifically excluded if all other inclusion/exclusion criteria are met. 
f) Female subjects who are pregnant or breastfeeding. Serum pregnancy test (for women 
of childbearing potential, including women who have had a tubal ligation) must be 
performed and documented as negative within 7 days prior to Cycle 1 Day 1. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 26 of 110 
g) Concurrent active malignancy other than non-melanoma skin cancer, carcinoma in situ 
of the cervix, or prostate intraepithelial neoplasia.  
h) Subjects with active, known, or suspected autoimmune disease. Subjects with vitiligo, 
type I diabetes mellitus, residual hypothyroidism due to autoimmune condition only 
requiring hormone replacement, psoriasis not requiring systemic treatment, or 
conditions not expected to recur in the absence of an external trigger are permitted to 
enroll. Subjects with minor autoimmune disease after discussion with the Medical 
Monitor. 
i) History of stroke, unstable angina, myocardial infarction, or ventricular arrhythmia 
requiring medication or mechanical control within the last 6 months prior to screening. 
j) Unstable or severe uncontrolled medical condition (eg, unstable cardiac function, 
unstable pulmonary condition including pneumonitis and/or interstitial lung disease, 
uncontrolled diabetes) or any important medical illness or abnormal laboratory finding 
that would, in the investigator’s judgment, increase the risk to the subject associated 
with his or her participation in the study. 
k) History of any Grade 3 or 4 immune-related AE toxicity from prior immunotherapy 
that resulted in treatment discontinuation. 
l) Has primary central nervous system (CNS) malignancy or known untreated/active 
CNS metastases and/or carcinomatous meningitis.  
• Subjects with previously treated, asymptomatic brain metastases may 
participate provided they meet the following criteria: clinically stable for at 
least 4 weeks and have no evidence of new or enlarging brain metastases and 
are off steroids 14 days prior to dosing with study medication. Stable brain 
metastases by this definition should be established prior to the first dose of 
study drug.  
• Subjects with asymptomatic brain metastases (ie, no neurological symptoms, 
no requirements for corticosteroids, and no lesion >1.5 cm) may participate 
but will require regular imaging of the brain as a site of disease. 
• Subjects with CNS symptoms should undergo a computed tomography (CT) 
scan or magnetic resonance imaging (MRI) of the brain to exclude new or 
progressive brain metastases. Spinal cord metastasis is acceptable. However, 
subjects with spinal cord compression must be excluded. 
m) Medical psychological or social conditions that may interfere with the subject's 
participation in the trial ore evaluation of trial results 
2) Prior Therapy 
a) Prior treatment with CD137 agonists, anti-CTLA-4 and anti-TIGIT antibodies for 
all cohorts. Any prior anti-PD-1 and anti-PD-L1/2 therapeutic antibodies is 
excluded for Cohorts A, C, F and H only. 
b) Immune-related AEs that lead to discontinuation of prior immune therapies 
including anti-PD-1 or anti-PDL-1/2 or anti-CTLA-4 therapies. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 27 of 110 
c) Treatment with systemic immunostimulatory agents (including but not limited to 
IFNα, IL2) within 6 weeks or 5 half-lives of the drug, whichever is shorter, prior to 
Cycle 1, Day 1. 
d) Systemic anti-cancer chemotherapy, biologic therapy, or other investigational 
agent within <5 times the half-life of the agent or <28 days (whichever is shorter) 
of starting study drug with the following exceptions: 
• Hormone-replacement therapy or oral contraceptives. 
• Herbal therapy intended as anti-cancer therapy must be discontinued at 
least 1 week before Cycle 1, Day 1.  
• Subjects with castrate resistant prostate cancer should be allowed to 
remain on luteinizing hormone-releasing hormone analogues for medical 
castration.   
• Previously initiated chronic bisphosphonate or denosumab therapy for 
bone metastases may be continued during study participation. 
e) Ongoing treatment with chronic immunosuppressants (eg, cyclosporine) or corticosteroids 
(>10 mg daily prednisone equivalents) or other immunosuppressive medications within 
14 days prior to first dose of study drug. Inhaled steroids and adrenal replacement steroid 
doses >10 mg daily prednisone equivalents are permitted in the absence of active 
autoimmune disease. 
f) Received oral or IV antibiotics within 2 weeks prior to Cycle 1, Day 1: 
Subjects receiving prophylactic antibiotics (eg, for prevention of a urinary tract infection 
or chronic obstructive pulmonary disease) are eligible. 
g) Administration of a live, attenuated vaccine within 4 weeks before Cycle 1, Day 1 or 
anticipation that such a live attenuated vaccine will be required during the study. 
Inactivated influenza vaccination is permitted during influenza season only. 
h) History of severe allergic, anaphylactic, or other hypersensitivity reactions to chimeric or 
humanized antibodies or fusion proteins. 
3) Prior Procedures 
a) Major surgical procedure within 28 days prior to Cycle 1, Day 1 or anticipation of 
need for a major surgical procedure during the course of the study. 
b) Subjects who received investigational (not authorized or approved by relevant 
Health Authorities) COVID-19 vaccine or therapies prior to screening are not 
eligible without discussion with sponsor.  
c) History of additional prior malignancy with the exception of cured skin, bladder, 
prostate, cervical, or other carcinoma in situ with no evidence of active disease for 
at least 1 year. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 28 of 110 
3.3. 
Prohibited Concomitant Medications and Treatments 
Use of the following therapies is prohibited during the study:  
• Any concomitant therapy intended for the treatment of subject’s current cancer, 
whether health authority-approved or experimental, including (but not limited to) the 
following: chemotherapy, hormonal therapy for cancer treatment, immunotherapy, 
radiotherapy, investigational agents, or herbal therapy.  
• Immunostimulatory agents or immunotherapy not specified in the protocol. 
• Immunosuppressive medications, including but not limited to cyclophosphamide, 
azathioprine, methotrexate, thalidomide, and immunosuppressive doses of 
corticosteroids (i.e. >10 mg daily prednisone equivalent). (These agents may be 
administered at the discretion of the treating physician in an emergency or after 
consultation with the Medical Monitor). 
• Surgical resection except for palliative surgical resection. 
3.4. 
Screen Failures 
Screen failures are defined as subjects who consent to participate in the clinical study but are not 
subsequently enrolled. A minimal set of screen failure information is required to ensure 
transparent reporting of screen failure subjects to meet the Consolidated Standards of Reporting 
Trials (CONSORT) publishing requirements and to respond to queries from regulatory 
authorities. Minimal information includes demography, screen failure details, eligibility criteria, 
and any serious adverse events (SAE) related to protocol required procedures. Retesting of 
individual laboratory parameters to determine eligibility is permitted if the values are: 
• Not consistent with life or the subject’s current medical status. 
• Aberrant due to a spoiled sample. e.g., hemolyzed hematology sample. 
Individuals who do not meet the criteria for participation in this study (screen failure) may be 
rescreened, if their medical status changes and they subsequently qualify for the study or there is 
an amendment to the protocol which allows participation. Rescreened subjects should not be 
assigned the same subject number as for the initial screening. 
Screen failures may be rescreened only once, after approval from the sponsor. If rescreening is 
less than 28 days prior to first study drug administration (Cycle 1, Day 1), the following 
assessments may be used for rescreening: 
• Previously submitted CT and MRI scans with acquisition date ≤28 days prior to Cycle 1 
Day 1. Scans that exceed the 28-day window may be used for enrollment with sponsor 
approval. 
• Previously submitted tumor biopsy sample 
• Screening laboratory assessments that meet protocol-defined timelines as indicated in 
Table 3 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 29 of 110 
If rescreening is more than 28 days after the initial screen failure, the subject must be re-
consented, and all eligibility criteria must be re-assessed with repeat screening assessments as 
per protocol specified guidelines with the following exceptions: 
• Scans that exceed the 28-day window may be used for enrollment with sponsor approval. 
• Previously submitted tumor biopsy sample 
4. 
TREATMENTS 
Study treatment is defined as any investigational treatment(s), marketed product(s), placebo, or 
medical device(s) intended to be administered to a study subject according to the study protocol. 
4.1. 
Treatments Administered 
Study Treatment Name: 
Etigilimab 
Nivolumab 
Dosage formulation: 
mg/mL in a 
-mL single-use glass 
vial filled to 
 mL to deliver a total of 
 mg per vial  
40 mg/4 mL (10 mg/mL), 100 mg/10 
mL (10 mg/mL), or 240 mg (24 mL) 
solution in a single-use vial 
Unit dose strength(s) 
/Dosage level(s): 
 mg if subject is ≥50 kg 
 mg/kg if subject is <50 kg 
240 mg 
Route of Administration: 
IV 
IV 
Dosing instructions: 
The initial dose of etigilimab will be 
delivered on Day 1 over 90 ± 10 minutes 
followed by a 90-minute observation 
period. If the 90-minute infusion is 
tolerated without infusion-associated 
adverse events, the second infusion may 
be delivered over 60 ± 10 minutes 
followed by a 60-minute observation 
period.  If the 60-minute infusion is well 
tolerated, all subsequent infusions may 
be delivered over 30 ± 10 minutes 
followed by a 30-minute observation 
period per investigator’s discretion. 
Etigilimab will be delivered prior to 
nivolumab. The etigilimab observation 
period will need to be completed before 
dosing nivolumab. If the subject is <50 
kg, the dose will be based on the 
subject’s weight at each treatment visit.  
Vials will be diluted with 0.9% 
sodium chloride injection, USP or 
5% dextrose injection, USP prior to 
use. It is administered over 30 + 
10 minutes (never <30 minutes) 
through an intravenous line 
containing as sterile, non-pyrogenic, 
low protein binding in-line filter 
(pore size of 0.2 micrometer to 1.2 
micrometer). The initial dose of 
nivolumab will be delivered on 
Day 3. 
Packaging and Labeling: 
Study Treatment will be provided as 10 
vials in a carton. Each vial and carton 
will be labeled as required per country 
requirement. 
Commercial stock will be utilized. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 30 of 110 
4.2. 
Treatment Discontinuation 
Treatment discontinuation occurs when a subject is no longer receiving study drug(s).  
Note that treatment discontinuation is not the same as study withdrawal. A subject should be 
discontinued from study treatment if, in the opinion of the investigator, it is medically necessary, 
or if it is the wish of the subject. All subjects who discontinue study treatment should enter safety 
follow-up followed by survival follow-up; if a subject discontinues study treatment prior to 
confirmed progression of disease, the subject will continue to be followed for disease 
progression as per the planned study visits and procedures.  
Subjects will be discontinued from study treatment for any the following reasons: 
• An AE that requires permanent discontinuation of study drug(s). 
• Confirmed progression of disease (Note: subjects may continue treatment beyond 
RECIST v1.1 determined PD). 
• Noncompliance with protocol. 
• Investigator decision. 
• Subject becomes pregnant. 
• Subject death. 
• Subject lost to follow-up. 
• Termination of the study by the sponsor. 
• Voluntary withdrawal from the study treatment by the subject. 
4.3. 
Method of Treatment Assignment  
Upon enrollment, subjects will be assigned a unique number in ascending numerical.  
4.4. 
Preparation/Handling/Storage/Accountability 
1. The investigator or designee must confirm appropriate temperature conditions have been 
maintained during transit for all study treatment received and any discrepancies are 
reported and resolved before use of the study treatment. 
2. Store etigilimab and nivolumab under refrigeration at 2°C to 8°C (36°F to 46°F). Protect 
nivolumab from light by storing in the original package until time of use. Do not freeze or 
shake.  
3. The diluted etigilimab solution may be stored for no more than 8 hours at room 
temperature or at 2°C- 8°C for up to 48 hours. 
4. Only subjects enrolled in the study may receive study treatment and only authorized site 
staff may supply or administer study treatment. All study treatments must be stored in a 
secure, environmentally controlled, and monitored (manual or automated) area in 
accordance with the labeled storage conditions with access limited to the investigator and 
authorized site staff. 
5. Any unused portion left in a vial may not be used for another subject, as the product 
contains no preservative (ie, they are single-use vials). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 31 of 110 
6. The investigator, institution, or the head of the medical institution (where applicable) is 
responsible for study treatment accountability, reconciliation, and record maintenance 
(ie, receipt, reconciliation, and final disposition records). 
7. Further guidance and information for the final disposition of unused study treatment are 
provided in the Pharmacy Manual.  
4.5. 
Treatment Compliance 
Etigilimab and nivolumab are administered IV by study site personnel. Thus, compliance with 
each infusion will be documented in the subject’s medical records and then recorded on the 
appropriate electronic case report form (eCRF) screen. In addition, drug accountability and PK 
monitoring will be done. 
4.6. 
Permitted Concomitant Therapy or Standard of Care Treatment 
Investigators may prescribe concomitant medications deemed necessary to provide adequate 
supportive care except those identified as prohibited (refer to Section 3.3). Standard supportive 
medications may be used in accordance with institutional guidelines and investigator discretion. 
These may include hematopoietic growth factors to treat neutropenia or thrombocytopenia in 
accordance with American Society for Clinical Oncology guidelines (but not for prophylaxis in 
Cycle 1), packed RBC and platelet transfusions, and anti-emetics and antidiarrheals. 
Palliative surgical resection and palliative radiotherapy to specific sites of disease is permitted if 
considered medically necessary by the treating physician provided that: 
• Subjects are otherwise deriving benefit (i.e., subject does not have progressive disease).  
• Target lesions being used to measure response are not irradiated without discussion with 
the Medical Monitor. Irradiated lesions will be considered not evaluable for response but 
still can be used to assess disease progression. The intensities, number, and dates of doses 
received for allowed palliative radiotherapy should be recorded on the appropriate eCRF. 
Because COVID-19 vaccine response and safety may have the potential to be affected by 
administration of a particular investigational product (IP), a decision to vaccinate individuals 
with approved COVID-19 vaccines while on treatment with study drug is up to the individual 
and the treating physician. When feasible, the full vaccination series should be completed prior 
to enrollment when a delay in enrollment would not put the study participant at risk. Because 
potential AEs related to vaccine administration may confound study treatment infusion reactions, 
overlap of administration should be avoided (with study drug and vaccine dosing at least 7 days 
apart)  
The administration of all other vaccines (with the exception of live, attenuated vaccines) is 
allowed on study as per institutional or standard of care guidelines.  Note: vaccines should be 
administered within 2 days before or after study drug administration.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 32 of 110 
Any medication or vaccine (including over-the-counter or prescription medicines, vitamins, 
and/or herbal supplements) that the subject is receiving at the time of enrollment through 90 days 
after treatment termination must be recorded on the Concomitant Medications eCRF along with: 
• Reason for use. 
• Dates of administration including start and end dates. 
• Dosage information including dose and frequency. 
• Appropriate information to assess any potential vaccine- related AEs. 
Subjects who experience infusion-associated symptoms may be treated symptomatically with 
acetaminophen, ibuprofen, diphenhydramine, and/or cimetidine or another H2 receptor 
antagonist, as per standard practice (for sites outside the U.S., equivalent medications may be 
substituted per local practice). Serious infusion-associated events manifested by dyspnea, 
hypotension, wheezing, bronchospasm, tachycardia, reduced oxygen saturation, or respiratory 
distress should be managed with supportive therapies as clinically indicated (e.g., supplemental 
oxygen and β2-adrenergic agonists). Premedication may be administered for Cycles ≥2 at the 
discretion of the treating physician after consultation with the Medical Monitor.  
Subjects are permitted the use of topical, ocular, intra-articular, intranasal, and inhalational 
corticosteroids (with minimal systemic absorption). Adrenal replacement steroid doses >10 mg 
daily prednisone are permitted. A brief (single dose up to less than 3 weeks) course of 
corticosteroids for prophylaxis (e.g., contrast dye allergy) or for treatment of non-autoimmune 
conditions (e.g., delayed-type hypersensitivity reaction caused by a contact allergen) is 
permitted. Systemic corticosteroids >10 mg daily, TNFα antagonists, and other 
immunosuppressive agents may attenuate potential beneficial immunologic effects of treatment 
with etigilimab and nivolumab but may be administered at the discretion of the treating physician 
in an emergency or after consultation with the Medical Monitor. If feasible, alternatives to 
corticosteroids should be considered. The use of inhaled corticosteroids and mineralocorticoids 
(eg, fludrocortisone for subjects with orthostatic hypotension or adrenocortical insufficiency) is 
allowed. Physiologic doses of corticosteroids for adrenal insufficiency are allowed. Megestrol 
administered as an appetite stimulant is also permitted.  
Subjects who use oral contraceptives, hormone-replacement therapy, prophylactic or therapeutic 
anticoagulation therapy (such as low molecular weight heparin or warfarin at a stable dose level), 
or other maintenance therapy for non-malignant indications should continue their use.  
The Medical Monitor should be contacted if there are any questions regarding concomitant or 
prior therapy. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 33 of 110 
5. 
DISCONTINUATION, DOSE HOLD, AND RESUMPTION 
Subjects will be monitored continuously for toxicity while on study treatment. Toxicity will be 
assessed using the NCI CTCAE version 5.0 or higher. 
If a subject has an AE related to etigilimab and/or nivolumab then dose interruptions/holds may 
occur as described below. 
5.1. 
Etigilimab Dose Holds and Discontinuation 
Permanent Discontinuation Criteria for Etigilimab 
Dosing with etigilimab should be permanently discontinued for the following toxicities: 
• ≥Grade 4 neutropenia persisting for ≥7 days and/or complicated by infection febrile 
neutropenia. 
• ≥Grade 4 thrombocytopenia. 
• Grade 3 drug-related thrombocytopenia >7 days or associated with clinically significant 
bleeding requires discontinuation. 
• Any ≥Grade 3 non-hematologic toxicity, except: 
o Grade 3 fatigue lasting <7 days. 
o Grade 3 nausea, emesis, or diarrhea responding to supportive treatment within 
5 days. 
• Grade 3 drug-related AE of the skin requires dose discontinuation. 
• ≥ Grade 3 non-hematological laboratory abnormalities do not require treatment 
discontinuation except: 
o Grade ≥3 AST, ALT, total bilirubin requires dose discontinuation  
o Concurrent AST or ALT >3 x ULN and total bilirubin >2 x ULN requires 
permanent dose discontinuation.  
Note: In most cases of Grade 3 AST or ALT elevation, study treatment will be 
permanently discontinued. If the investigator determines a possible favorable 
benefit/risk ratio that warrants continuation of study treatment, a discussion between 
the investigator and the Medical Monitor or designee must occur. 
o Isolated Grade 4 electrolyte imbalances/abnormalities that are not associated with 
clinical sequelae and are corrected with supplementation/appropriate management 
within 72 hours of their onset. 
Etigilimab may be held/delayed due to toxicity. The dose level of etigilimab will not be modified 
for individual subjects in this study.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 34 of 110 
Dose Delay Criteria for Etigilimab 
• Grade 2 non-skin, drug-related AE, except for fatigue. 
• Grade 2 drug-related creatinine, AST, ALT, and/or total bilirubin abnormalities.  
• Grade 3 skin drug-related AE. 
• Grade 3 drug-related laboratory abnormality with the following exceptions: 
o Grade 3 lymphopenia or asymptomatic amylase or lipase does not require a dose 
delay. 
• Any AE, laboratory abnormality or inter-current illness which, in the judgment of the 
investigator, warrants delaying the dose of study medication. 
The maximum duration of a dose hold is 28-days, unless a longer hold is approved by the 
Medical Monitor or designee; thereafter, the subject should be discontinued from etigilimab 
treatment. Etigilimab infusions may be delayed to allow subjects to recover from study treatment 
related AEs or intercurrent illness. Subjects who require delay of etigilimab should be re-
evaluated weekly or more frequently if clinically indicated and resume etigilimab dosing when 
re-treatment criteria are met (see below) following discussion with the Medical Monitor. 
Individual subject cases should be discussed with the Sponsor Medical Monitor or designee for 
individual treatment decisions. 
Dosing visits are not skipped, only delayed. Tumor assessments should continue as per protocol 
even if dosing is delayed.  
Criteria to Resume Etigilimab Dosing 
• Subjects will be permitted to resume etigilimab therapy following resolution of the AE to 
≤Grade 1 or to baseline value, with the following exceptions.  
• Subjects may resume treatment in the presence of Grade 2 fatigue. 
• Subjects who have not experienced a Grade 3 drug-related skin AE may resume 
treatment in the presence of Grade 2 skin toxicity. 
• For subjects with Grade 2 AST, ALT, and/or total bilirubin abnormalities, dosing may 
resume when laboratory values return to baseline and management with corticosteroids, if 
needed, is complete (See Appendix 8). 
• Drug-related pulmonary toxicity, diarrhea, or colitis must have resolved to baseline 
before treatment is resumed. Subjects with persistent Grade 1 pneumonitis after 
completion of a steroid taper over at least 1 month may be eligible for retreatment if 
discussed with and approved by the Medical Monitor or designee. 
• Subjects with drug-related endocrinopathies adequately controlled with only physiologic 
hormone replacement may resume treatment after consultation with the Medical Monitor 
or designee. Adrenal insufficiency requires discontinuation regardless of control with 
hormone replacement. 
Subjects who meet criteria for permanent discontinuation must not receive further study therapy. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 35 of 110 
5.2. 
Nivolumab Dose Hold, Resumption and Discontinuation 
Nivolumab may be held/interrupted due to toxicity. The dose level of nivolumab will not be 
modified in this study. Repeat nivolumab infusions may be delayed to allow subjects to recover 
from study treatment related AEs or intercurrent illness. Dosing visits are not skipped, only 
delayed. Tumor assessments should continue as per protocol even if dosing is delayed. 
A pattern of immune-related AEs has been defined for nivolumab treatment for which 
management algorithms have been developed (OPDIVO 2018). Most high- grade events were 
manageable with dose delays and the use of corticosteroids or hormone replacement therapy 
(endocrinopathies) as instructed in these algorithms. 
Details on dose delays, re-initiation of treatment and discontinuation of nivolumab are provided 
below. 
Dose Delay Criteria for Nivolumab 
Nivolumab administration should be delayed for the following:  
• Grade 2 non-skin, drug-related AE, except for fatigue. 
• Grade 2 drug-related creatinine, AST, ALT and/or total bilirubin abnormalities.  
• Grade 3 skin drug-related AE. 
• Grade 3 drug-related laboratory abnormality with the following exceptions: 
o Grade 3 lymphopenia or asymptomatic amylase or lipase does not require a dose 
delay. 
o Grade ≥3 AST, ALT, total bilirubin required dose discontinuation (see below). 
• Any AE, laboratory abnormality or inter-current illness which, in the judgment of the 
investigator, warrants delaying the dose of study medication. 
Subjects who require delay of nivolumab should be re-evaluated weekly or more frequently if 
clinically indicated and resume nivolumab dosing when re-treatment criteria are met (see below). 
If the decision is to resume nivolumab dosing, the subject should restart treatment on the next 
regularly scheduled dosing visit. Skipped doses are not to be replaced. If treatment is delayed 
>8 weeks, the subject may potentially be permanently discontinued from all study therapy, 
except as specified in the treatment discontinuation criteria below. Individual subject cases 
should be discussed with the Medical Monitor or designee for individual treatment decisions. 
Criteria to Resume Nivolumab Dosing 
Subjects will be permitted to resume nivolumab therapy following resolution of the AE to 
≤Grade 1 or to baseline value, with the following exceptions:  
• Subjects may resume treatment in the presence of Grade 2 fatigue. 
• Subjects who have not experienced a Grade 3 drug-related skin AE may resume 
treatment in the presence of Grade 2 skin toxicity. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 36 of 110 
• For subjects with Grade 2 AST, ALT, and/or total bilirubin abnormalities, dosing may 
resume when laboratory values return to baseline and management with corticosteroids, if 
needed, is complete. 
• Drug-related pulmonary toxicity, diarrhea or colitis must have resolved to baseline before 
treatment is resumed. Subjects with persistent Grade 1 pneumonitis after completion of a 
steroid taper over at least 1 month may be eligible for retreatment if discussed with and 
approved by the Medical Monitor or designee. 
• Subjects with drug-related endocrinopathies adequately controlled with only physiologic 
hormone replacement may resume treatment after consultation with the Medical Monitor 
or designee. Adrenal insufficiency requires discontinuation regardless of control with 
hormone replacement. 
• Subjects who meet criteria for permanent discontinuation must not receive further study 
therapy. 
Permanent Treatment Discontinuation Criteria for Nivolumab 
Subjects meeting any of the following criteria will be required to permanently discontinue 
nivolumab: 
• Any Grade 2 drug-related uveitis or eye pain or blurred vision that does not respond to 
topical therapy and does not improve to Grade 1 severity within 8 weeks OR requires 
systemic treatment. 
• Any Grade 3 non-skin, drug-related AE lasting >7 days or recurs, with the following 
exceptions for laboratory abnormalities, drug-related uveitis, pneumonitis, 
bronchospasm, neurologic toxicity, hypersensitivity reactions, infusion reactions, and 
endocrinopathies: 
o Grade 3 drug-related uveitis, pneumonitis, bronchospasm, neurologic toxicity, 
myocarditis, hypersensitivity reaction, or infusion reaction of any duration 
requires discontinuation. 
o Grade 3 drug-related endocrinopathies adequately controlled with only physiologic 
hormone replacement do not require discontinuation. Adrenal insufficiency requires 
discontinuation regardless of control with hormone replacement. 
• Grade 3 drug-related laboratory abnormalities do not require treatment discontinuation 
except: 
o Grade 3 drug-related thrombocytopenia >7 days or associated with clinically 
significant bleeding requires discontinuation. 
o Grade ≥3 drug-related AST, ALT, or total bilirubin requires discontinuation. 
o Concurrent AST or ALT >3 × ULN and total bilirubin >2 × ULN. 
o In most cases of Grade 3 AST or ALT elevation, study treatment will be 
permanently discontinued. If the investigator determines a possible favorable 
benefit/risk ratio that warrants continuation of study treatment, a discussion between 
the investigator and the Medical Monitor or designee must occur. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 37 of 110 
• Any Grade 4 drug-related AE or laboratory abnormality (including but not limited to 
creatinine, AST, ALT, or total bilirubin), except for the following events, which do not 
require discontinuation: 
o Grade 4 neutropenia ≤7 days. 
o Grade 4 lymphopenia or leukopenia or asymptomatic amylase or lipase. 
o Isolated Grade 4 electrolyte imbalances/abnormalities that are not associated with 
clinical sequelae and are corrected with supplementation/appropriate management 
within 72 hours of their onset. 
o Grade 4 drug-related endocrinopathy AEs such as hyper- or hypothyroidism, or 
glucose intolerance, which resolve or are adequately controlled with physiologic 
hormone replacement (corticosteroids, thyroid hormones) or glucose-controlling 
agents, respectively, may not require discontinuation after discussion with and 
approval from the Medical Monitor or designee. 
• Any AE, laboratory abnormality, or intercurrent illness, which, in the judgment of the 
investigator, presents a substantial clinical risk to the subject with continued treatment. 
Criteria for Further Discussion with Medical Monitor or Designee Before Deciding to Continue 
or Discontinue Nivolumab Treatment 
For subjects meeting any of the following criteria, discussion with the Medical Monitor or 
designee is to occur to determine whether treatment should continue. Any dosing interruption of 
nivolumab lasting >8 weeks after the last dose. Dosing interruptions to allow for prolonged 
steroid tapers to manage drug- related AEs are allowed. Prior to re-initiating treatment in a 
subject with a dosing interruption lasting >8 weeks after the last dose and with no more than 
2 missed doses, the Medical Monitor or designee must be consulted. Tumor assessments should 
continue as per protocol even if dosing is interrupted. 
5.3. 
Dosing Interruptions  
Dose interruptions >8 weeks after the last dose, which occur for non-drug related reasons, may 
be allowed if approved by the Medical Monitor or designee. Prior to re-initiating treatment in a 
subject with a dosing interruption lasting >8 weeks after the last dose and with no more than 
2 missed doses, the Medical Monitor or designee must be consulted. Tumor assessments should 
continue as per protocol even if dosing is interrupted, and subjects must otherwise meet the 
criteria for continued treatment at the time re-initiation of study therapy is considered. 
5.4. 
Toxicity Management Guidelines for Specific Adverse Events 
Because of the potential for clinically meaningful immune-related AEs requiring early 
recognition and prompt intervention, established management algorithms are recommended for 
suspected pulmonary toxicity, gastrointestinal (GI) toxicity, hepatotoxicity, endocrinopathy, skin 
toxicity, neurological toxicity, and renal toxicity. 
These AE management algorithms are included in Appendix 8. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 38 of 110 
6. 
RESPONSE ASSESSMENTS 
6.1. 
Radiographic Evaluations and Confirmation of Disease Progression 
Response and progression will be determined by investigator assessment of on-trial radiographic 
evaluations, that will be conducted every 8 (±1) weeks through Week 48 and then at least every 
12 (±1) weeks until confirmed progression of disease (as defined below), alternate anticancer 
therapy, withdrawal of consent, or death, whichever occurs first. The radiographic assessments 
are to be conducted as noted, independent of dose delays and/or dose interruptions. RECIST 1.1 
criteria will be used for primary endpoint evaluation (Eisenhauer et al., 2009), iRECIST will be 
used for exploratory endpoint response evaluation (Seymour et al., 2017). 
Radiographic evaluation may be done using either CT or MRI, but the modality chosen to 
evaluate each individual subject should be the same as the screening evaluation throughout the 
duration of the study. 
Under specific circumstances subjects who develop PD per RECIST v1.1 may continue 
treatment and be followed for improved response or confirmed progression of disease [treatment 
beyond progression (Section 6.2)]. Regardless of whether or not a subject continues treatment in 
the event of RECIST-determined PD, follow-up radiographic assessments to confirm progression 
or show improvement in response are to be conducted at least 4 weeks after the assessment of 
PD per RECIST v1.1 (unless there is prior clinical deterioration, initiation of other cancer 
therapy, or withdrawal of consent).  
For subjects who continue treatment beyond progression (Section 6.2), iRECIST PD should be 
confirmed at least 4 to 8 weeks after the first radiologic evidence of PD in clinically stable 
participants. 
Subjects who have unconfirmed PD (iUPD) may continue study treatment until progression is 
confirmed as long as the subject is clinically stable and has provided written informed consent 
prior to receiving additional treatment (Section 6.2). Clinically unstable subjects should be 
discontinued from study treatment at the first occurrence of radiographic PD (iUPD) and are not 
required to have repeat imaging to confirm PD by iRECIST (though a confirmation of 
progression scan may be obtained at the investigator’s discretion after consultation with the 
sponsor). 
If repeat imaging shows iRECIST confirmed disease progression (iCPD), subjects will 
discontinue treatment. However, if the subject is deriving benefit after iCPD is observed, an 
exception to continue study treatment must be approved by the sponsor’s Medical Monitor. 
Subjects who have repeat imaging to confirm progression are not required to undergo the next 
scheduled tumor imaging if it is less than 4 weeks later. 
If repeat imaging shows iRECIST stable disease (iSD), iRECIST partial response (iPR), or 
iRECIST complete response (iCR), imaging should be continued every 8 (±1) weeks and the 
subject should continue on trial treatment.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 39 of 110 
Note that the date of progression to be used for all relevant efficacy endpoints will be based on 
first documentation of PD (ie, RECIST v1.1 date of PD), regardless of date of confirmation of 
PD for subjects who continue on treatment. 
All radiographic evaluations performed on the study will be collected and held for a potential 
independent review. Details regarding initiating an independent review will be outlined in the 
statistical analysis plan (SAP). 
Confirmed progression of disease is defined as one of the following: 
Clinical deterioration with or without radiographic PD per RECIST v1.1 (See Appendix 7) will 
confirm progression of disease. Note, however, that radiographic evaluation should be conducted 
at the time of clinical signs and/or symptoms of PD whenever possible. 
• In subjects without clinical deterioration at the time of a radiographic scan showing PD 
per RECIST v1.1, a second scan conducted at least 4 weeks later showing progression of 
disease as outlined below will confirm progression: 
• An additional 10% increase in tumor burden with a minimum 5 mm absolute increase 
from time of initial PD. This includes an increase in the sum of diameters of all target 
lesions and/ or the diameters of new measurable lesions compared to the time of initial 
PD. 
• New lesions are considered measurable at the time of initial progression if the longest 
diameter is at least 10 mm (except for pathological lymph nodes which must have a short 
axis of at least 15 mm). Any new lesion considered non-measurable at the time of initial 
progression may become measurable and therefore included in the tumor burden if the 
longest diameter increases to at least 10 mm (except for pathological lymph nodes which 
must have a short axis of at least 15 mm). In situations where the relative increase in total 
tumor burden by 10% is solely due to inclusion of new lesions which become 
measurable, these new lesions must demonstrate an absolute increase of at least 5 mm. 
Subjects should discontinue study therapy upon evidence of confirmed progression. Subjects 
who discontinue study treatment prior to confirmed progression of disease will continue to 
undergo radiographic and response assessments per protocol. 
Note that all radiographic scans will be collected and archived for potential independent central 
review of response. 
6.2. 
Treatment Beyond Progression  
Accumulating evidence indicates that a minority of subjects with solid tumors treated with 
immunotherapy may derive clinical benefit despite initial evidence of radiographic PD. 
Following approval of the medical monitor or designee and consent of the subject for continued 
treatment beyond initial RECIST v1.1-defined PD, subjects who meet the following criteria will 
be permitted to continue on their treatment: 
• Investigator-assessed clinical benefit and without rapid disease progression; Subject 
continues to meet all other study protocol eligibility criteria. 
• Subject tolerates study drug. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 40 of 110 
• Subject has stable ECOG performance status. 
• Treatment beyond progression will not delay an imminent intervention to prevent serious 
complications of disease progression (eg, CNS metastases). 
The assessment of clinical benefit should take into account whether the subject is clinically 
deteriorating and unlikely to receive further benefit from continued treatment. All decisions to 
continue treatment beyond initial RECIST v1.1 PD must be discussed with the Medical Monitor 
or designee, and an assessment of the risk/benefit of continuing with study therapy must be 
documented in the study records. 
Subjects should continue to attend study visits and undergo monitoring according to the 
protocol-defined on-treatment assessments. Radiographic assessment is required when subjects 
continue treatment after RECIST v1.1 determined PD. 
6.3. 
Response Evaluation Criteria in Solid Tumors 
Assessment of response and progression status in all subjects will be evaluated using the 
definitions from RECIST v1.1 for clinical decision-making and assessment of endpoints. 
Evaluation for target, non-target, and new lesions based on RECIST v1.1 are to be considered. 
For a best overall response of CR or PR, confirmation of the response is required at a subsequent 
timepoint at least 4 weeks after the initial observation. Confirmed CR or PR will be claimed only 
if the criteria for each are met at that subsequent timepoint as outlined in Appendix 7. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 41 of 110 
Table 2 
Evaluation of Best Overall Response When Confirmation of CR and PR 
Required 
Overall Response 
Best Overall Response at that Time Point 
First Time Point 
Second Time Point 
CR 
CR 
CR 
CR 
PR 
SD, PD, or PRa 
CR 
SD 
SD provided minimum criteria for SD duration 
metb, otherwise, PD 
CR 
PD 
SD provided minimum criteria for SD duration 
metb, otherwise, PD 
CR 
NE 
SD provided minimum criteria for SD duration 
metb, otherwise, PD 
PR 
CR 
PR 
PR 
PR 
PR 
PR 
SD 
SD 
PR 
PD 
SD provided minimum criteria for SD duration 
metb, otherwise, PD 
PR 
NE 
SD provided minimum criteria for SD duration 
metb, otherwise, PD 
Abbreviations: CR = complete response; NE = not evaluable; PD = progressive disease; PR = partial 
response; SD = stable disease. 
a If a CR is truly met at the first timepoint, then any disease seen at a subsequent timepoint, even 
disease meeting PR criteria relative to baseline, makes the disease PD at that point (since disease 
must have reappeared after CR). Best response would depend on whether minimum duration for SD 
was met. However, CR may be claimed when subsequent scans suggest small lesions were likely still 
present and in fact the subject had PR, not CR at the first timepoint. Under these circumstances, the 
original CR should be changed to PR and the best response is PR. 
b Minimum required duration of SD is 6 weeks. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 42 of 110 
7. 
PERMANENT AND TEMPORARY DISCONTINUATION 
CRITERIA  
In the absence of unacceptable toxicities or disease progression, subjects will be offered 
continued study treatment up until disease progression. Regardless of discontinuation of study 
drug, subjects should continue on study with regular follow-up. All subjects who have 
discontinued etigilimab and nivolumab will return to the clinic for a treatment termination visit 
within 30 days after the last dose of etigilimab study treatment or nivolumab, whichever occurs 
last).  
Subjects may withdraw or be withdrawn from the study at any time. 
Subjects will be withdrawn from the study treatment for the following reasons: 
• Clinically significant disease progression, as assessed by the investigator. 
• Intercurrent illness that prevents further administration of treatment. 
• Unacceptable AEs. 
• Dose delay due to drug-related toxicity >28 days. 
• Non-protocol anti-cancer therapy. 
• Subject decides to withdraw from the study. 
• General or specific changes in the subject's condition render further treatment 
unacceptable for the subject in the judgment of the investigator. 
• Protocol non-compliance. 
In the absence of progressive disease and additional anti-cancer therapy, all attempts should be 
made to continue tumor assessments per RECIST criteria until disease progression or initiation 
of subsequent anti-cancer therapy for up to 2 years. 
All subjects will undergo the treatment termination evaluations. 
7.1. 
Lost to Follow Up 
A subject will be considered lost to follow-up if he or she repeatedly fails to return for scheduled 
visits and is unable to be contacted by the study site.  
The following actions must be taken if a subject fails to return to the clinic for a required study 
visit: 
• The site must attempt to contact the subject and reschedule the missed visit as soon as 
possible and counsel the subject on the importance of maintaining the assigned visit 
schedule and ascertain whether or not the subject wishes to and/or should continue in the 
study. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 43 of 110 
• In cases in which the subject is deemed lost to follow up, the investigator or designee 
must make every effort to regain contact with the subject (where possible, 3 telephone 
calls and, if necessary, a certified letter to the subject’s last known mailing address or 
local equivalent methods). These contact attempts should be documented in the subject’s 
medical record. 
• Should the subject continue to be unreachable, he/she will be considered to have 
withdrawn from the study with a primary reason of lost to follow-up.  
8. 
STUDY ASSESSMENTS AND PROCEDURES 
• Study procedures and their timing are summarized in the SoA.  
• As protocol waivers or exemptions are not allowed with the exception of immediate safety 
concerns, these should be discussed with the sponsor immediately upon occurrence or 
awareness to determine if the subject should continue or discontinue study treatment. 
• Adherence to the study design requirements, including those specified in the SoA, is essential 
and required for study conduct. 
• All screening evaluations must be completed and reviewed to confirm that potential subjects 
meet all eligibility criteria. The investigator will maintain a screening log to record details of 
all subjects screened and to confirm eligibility or record reasons for screening failure, as 
applicable.  
• Once the screening process has been completed, the investigator must submit a completed 
enrollment form to the sponsor for approval. Once the investigator has received the signed 
and dated form back from the sponsor, the subject is considered to be enrolled in the study. 
• Procedures conducted as part of the subject’s routine clinical management (eg, blood count) 
and obtained before signing of ICF may be utilized for screening or baseline purposes 
provided the procedure met the protocol-specified criteria and were performed within the 
time frame defined in the SoA 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 44 of 110 
8.1. 
Schedule of Assessments 
Cycle Day 
Screening 
Cycle 1 
D1        D3        D8 
Cycle 2 
D1          D8 
Cycle 3 
D1           D8 
Cycle 4 
D1           D8 
Cycle 5 
D1          D8 
Cycle 6w 
D1           D8 
Treatment  
Terminationx 
Follow up 
Study Day 
-28 to 1 
    1 
     3 
8 
15 
22 
29 
36 
43 
50 
57 
64 
71 
78 
Informed consenta 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Review of eligibility 
criteria 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Medical, surgical, and 
cancer histories, and 
demographic datab 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Tumor assessmentc 
X 
 
 
 
 
 
 
 
 
 
X 
 
 
 
X 
 
Concomitant medicationsd 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
Vital signse 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
Complete physical 
examinationf 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Symptom-directed 
physical examination 
 
X 
 
X 
X 
X 
X 
 
X 
 
X 
 
X 
 
X 
 
Height 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Weightg 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
 
ECOG performance status 
X 
X 
 
X 
X 
X 
X 
 
X 
 
X 
 
X 
 
X 
 
12-Lead ECGh 
X 
X 
 
 
 
 
 
 
X 
 
 
 
 
 
X 
 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 45 of 110 
Cycle Day 
Screening 
Cycle 1 
D1         D3         D8 
Cycle 2 
D1          D8 
Cycle 3 
D1            D8 
Cycle 4 
D1          D8 
Cycle 5 
D1           D8 
Cycle 6w 
D1          D8 
Treatment  
Terminationx 
Follow up 
Study Day 
-28 to -1 
1 
3 
8 
15 
22 
29 
36 
43 
50 
57 
64 
71 
78 
Hematologyi 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
Serum or plasma 
chemistryj 
X 
X 
 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
 
Etigilimab infusionk 
 
X 
 
 
X 
 
X 
 
X 
 
X 
 
X 
 
 
 
Nivolumab infusionl 
 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 
 
 
Adverse event 
evaluationm 
 
------------------------------------------------------------------------------------------------------------------------------------------------------------- 
TSH, free T3, free T4n 
X 
 
 
 
 
 
 
 
 
 
X 
 
 
 
X 
 
Coagulation 
(INR/PT/aPTT) 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
X 
 
Urinalysiso 
X 
 
 
 
 
X 
 
 
 
 
 
X 
 
 
X 
 
Serum pregnancy testp 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
X 
 
Tumor marker 
assessmentq  
(if applicable) 
X 
 
 
 
 
 
X 
 
 
 
X 
 
 
 
 
 
Pharmacokineticsr 
See Table 3 below for PK Schedule for Ph Ib Subjects 
Anti-drug antibodyr 
See Table 3 below for ADA Schedule for Ph Ib Subjects 
Blood for PD biomarkerss 
X 
X 
 
X 
 
X 
 
X 
 
 
 
 
 
X 
X 
 
Blood for 
pharmacogenomicst 
 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Blood for cell free DNAu 
X 
X 
 
 
 
 
 
X 
 
 
 
 
 
X 
X 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 46 of 110 
 
Cycle Day 
Screening 
Cycle 1 
   D1       D3        D8 
Cycle 2 
D1         D8 
Cycle 3 
D1           D8 
Cycle 4 
D1           D8 
Cycle 5 
D1          D8 
Cycle 6w 
D1           D8 
Treatment  
Terminationx 
Follow up 
Study Day 
-28 to -1 
1 
3 
8 
15 
22 
29 
36 
43 
50 
57 
64 
71 
78 
Tumor biopsyv 
X 
 
 
 
 
 
 
 
 
 
X 
 
 
 
 
 
Archival FFPE tumor 
tissuev 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Survival and anti-cancer 
therapy follow up 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
X 
Contrast Enhanced Head 
CT or MRI scan 
X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Abbreviations:  ALT = alanine aminotransferase; aPTT = activated partial thromboplastin time; AST = aspartate aminotransferase; BUN = blood urea nitrogen; 
CBC = complete blood count; CT = computed tomography; ECG = electrocardiogram; ECOG = Eastern Cooperative Oncology Group; FFPE = formalin-fixed, 
paraffin-embedded; INR = international normalized ratio; IV = intravenous; MRI = magnetic resonance imaging; mRNA = messenger RNA; 
MSS = microsatellite stable; PBMC = peripheral blood mononuclear cells; PT = prothrombin time; RBC = red blood cell; RECIST = Response Evaluation 
Criteria in Solid Tumors; TIGIT = T-cell immunoreceptor with Ig and ITIM domains; TMB-H = tumor mutational burden‐high; TSH = thyroid-stimulating 
hormone; WBC = white blood cell 
Notes to Schedule of Assessments 
a. 
Written informed consent is required before performing any study-specific tests or procedures and may be obtained at any time prior to such tests or 
procedures. Results of standard-of-care tests or examinations performed prior to obtaining informed consent and within 28 days prior to Cycle 1 Day 1 may 
be used for screening assessments rather than repeating such tests. Results for the following laboratory tests must be obtained within 14 days prior to Cycle 1 
Day 1: hematology, serum or plasma chemistry and coagulation panel. 
b. Medical and surgical histories are required. Cancer history includes stage, date of diagnosis, and prior anti-cancer therapy. Demographic information 
includes sex, age, and self-reported race/ethnicity. 
c. 
Screening and subsequent tumor assessments must include CT scans (with IV contrast unless contraindicated and oral contrast as appropriate per 
institutional standards) of the chest, abdomen, and pelvis. If a CT scan for tumor assessment is performed in a positron emission tomography (PET)/CT 
scanner, the CT acquisition must be consistent with the standards for a full-contrast CT scan. Brain imaging (either MRI or contrast-enhanced CT) is 
required at screening for all subjects. Further investigations such as bone scans and CT scans of the neck should also be performed if there is any clinical 
suspicion of disease at any site that may not be demonstrated by the minimum schedule of assessments listed above. At the investigator’s discretion, other 
methods of assessment of measurable disease as per RECIST v1.1 may be used. 
The same radiographic procedures used to assess disease sites at screening should be used throughout the study (eg, the same contrast protocol for CT 
scans). Response will be assessed by the investigator on the basis of physical examinations and the imaging modalities detailed above, using RECIST 
criteria. Assessments should be performed by the same evaluator if possible to ensure internal consistency across visits. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 47 of 110 
Tumor assessments will be performed every 8 weeks (±1) from Cycle 1 Day 1 or as clinically indicated through to week 48 and then at least every 12 (±1) 
weeks. Response assessment data (i.e., progressive disease or no progression of disease) will continue to be collected (based on standard-of-care 
radiographs) for subjects who have not progressed at the time of the termination visit. until the subject starts alternative anti-cancer treatment or develops 
progressive disease, whichever occurs first. Response assessment and assessment of tumor markers will be obtained at treatment termination, unless a prior 
radiographic assessment has been performed within the last 14 days or at a prior response assessment that documented progressive disease. At the 
investigator’s discretion, scans may be performed at any time if progressive disease is suspected. 
d. Concomitant medications include any prescription medications or over-the-counter medications. At subsequent visits, changes to current medications, or 
medications used since the last documentation of medications will be recorded. 
e. 
Vital signs include heart rate, respiratory rate, blood pressure and temperature. For the first etigilimab infusion, measure vital signs within 60 minutes before 
infusion, every 15 (±5 minutes) during the infusion and 30 (±10 minutes) and 90 (±15) minutes after the end of the infusion. For subsequent etigilimab 
infusions, measure vital signs within 60 minutes before infusion, during infusion if clinically indicated and 30 (±10) minutes after the end of the etigilimab 
infusion. Vital signs during and after nivolumab infusion are per institutional guidelines. 
f. 
A complete physical examination will be done at baseline. At all other study visits a symptom-directed physical examination must be performed focusing on 
the subject’s signs and symptoms. A more complete physical examination should be conducted when clinically indicated. 
g. The etigilimab dose should be based on the Cycle 1 Day 1 weight throughout the study, unless the weight changes by >10%. 
h. A 12-lead ECG will be obtained during screening, 30 (+30 minutes) after infusion of etigilimab on Cycle 1 Day 1, and 30 (+30 minutes) after infusion of 
etigilimab on Cycle 4 Day 1 and at treatment termination. Subjects should be resting and in a supine or semi-recumbent position for at least 10 minutes prior 
to each ECG collection.  
i. 
Hematology can be performed within a -2-day window of the visit and consists of CBC, including RBC count, hemoglobin, hematocrit, WBC count with 
automated differential (neutrophils, lymphocytes, eosinophils, monocytes, basophils,), and platelet count. A manual differential can be done if clinically 
indicated. During screening, hematology results must be obtained within 14 days prior to Cycle 1, Day 1. If screening laboratory results available within 
72 hours C1D1 laboratory tests do not need to be repeated.  
j. 
Serum or plasma chemistry can be performed within a -2 day window of the visit and includes BUN, creatinine, sodium, potassium, magnesium, chloride, 
bicarbonate, calcium, phosphorus, glucose, total bilirubin, direct bilirubin, ALT, AST, alkaline phosphatase, lactate dehydrogenase, total protein, and 
albumin.  During screening, serum or plasma chemistry results must be obtained within 14 days prior to Cycle 1, Day 1. If screening laboratory results 
available within 72 hours C1D1 laboratory tests do not need to be repeated. 
k. Etigilimab must be dosed as described in the Protocol. Dosing of etigilimab should be within ± 2 days of the Study Day listed in the schedule of assessments. 
If etigilimab cannot be administered in this 2-day window, then that dose is considered missed. If treatment with etigilimab is delayed for >4 weeks, 
etigilimab will be permanently discontinued. 
l. 
Nivolumab must be dosed as described in the Protocol within ± 2 days of the Study Day listed in the schedule of assessments. If the etigilimab dose is 
delayed ± 2 days then the nivolumab dose would be delayed and administered on the same day as the etigilimab (except for C1D1 where etigilimab is 
administered without nivolumab). 
m. After initiation of study drug, report all adverse events until 90 days after the treatment termination visit. 
n. Thyroid function tests (TSH, free T3, and free T4) must be performed every 8 weeks or as clinically indicated and at treatment termination. 
o. Urinalysis (specific gravity, pH, glucose, protein, ketones, and blood) will be obtained during screening, at Study Days 22, 64, and at the time of treatment 
termination. Microanalysis is required if protein or blood is detected. 
p. Serum pregnancy test (for women of childbearing potential, including women who have had a tubal ligation) must be performed and documented as negative 
within 7 days prior to Cycle 1, Day 1 and at treatment termination. 
q. Perform tests for pertinent tumor markers (e.g., CEA for subjects with colorectal cancer or others) every 4 weeks or as needed starting at Cycle1 Day1. 
r. 
PK and ADA samples will be drawn according to Table 3 listed below. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 48 of 110 
s. 
A pre-dose sample of 33 mL will be drawn during screening and on Study Days, 1, 8, 22, and 36 and every 6 weeks after day 36 for subjects continuing on 
study drug to evaluate changes in plasma proteins (8 mL) by immunochemistry, TIGIT and immune-related gene expression by mRNA (5 mL) and changes 
in peripheral blood mononuclear cell (PBMC, 20 mL) populations and activation. A sample will also be collected at the time of treatment termination, unless 
one has been obtained during the prior 14 days. Instructions for the collection, handling, storage, and shipment are provided in the Laboratory Manual.  
t. 
A 6 mL of blood will be collected for pharmacogenetic testing if the subject has consented to have this optional sample collected. 
u. For TMB-H/MSS cohort, a 20 mL blood collection will occur during screening using the Guardant provided IUO kit. If collected in screening for TMB-
H/MSS cohort, Study Day 1 collection does not need to occur. For all other cohorts, a 10 mL of plasma for cell-free tumor DNA assessment will be collected 
pre-dose on Study Days 1, 36, 78, and at treatment termination. As outlined in Section 3.1 TMB-H/MSS (Cohort E) subjects with the following solid tumors 
will enroll into respective tumor specific cohorts after discussion with the sponsor:  Cohorts A, C, F and H. For these subjects, a 20 mL blood collection will 
still be required using the Guardent Health provided IUO kit. 
v. Archival FFPE is required for enrolment and must have been collected preferably within 6 months but no longer than 1 year from screening. If archival 
tumor tissue is not available either fresh core or punch needle biopsy at study entry (3 fresh cores/punches preferred whenever possible) is required. Fine 
needle aspirate samples are not acceptable. Instructions for the collection, handling, storage, and shipment of these samples are provided in the Laboratory 
Manual. 
. Pre-treatment Biopsy: Baseline fresh tumor tissue samples consisting of 3 core needle biopsies of deep tumor tissue or lymph nodes or excisional, 
incisional, punch, or forceps biopsies of cutaneous, subcutaneous, or mucosal lesions will be obtained for all subjects. Subjects undergoing core needle 
biopsy should have accessible lesion(s) that permit a total of at least two biopsies (pretreatment and on-treatment) without unacceptable risk of major 
procedural complication (one pretreatment and at least one on-treatment biopsy will be performed; minimum diameter, 18 gauge). If possible, at least 3 cores 
should be collected from each lesion.   
Optional On-treatment Biopsy may be considered only in patients who provided fresh baseline biopsy. This subsequent fresh biopsy may be performed 
approximately 8 weeks (within ± 5 days of Day 57) following the first administration of etigilimab.  
An additional optional biopsy may be collected per investigator discretion, preferably at the time of radiographic progression or response. Requirements and 
procedures for pre-treatment and on-treatment biopsy collection are identical.   
For pre and on-treatment, 1-2 cores will be fixed and shipped to central lab in ethanol and an additional 1 core will be fresh frozen as specified in the 
Laboratory Manual. 
w. At Cycle 7 and beyond. safety laboratory testing is completed every two weeks at each treatment visit only.   
x. The termination visit should be done as soon as possible, but no later than 30 days, after one of the discontinuation criteria for the study are met (See 
Protocol). The termination visit may occur later after discussion with the Sponsor Medical Monitor for specific circumstances, such as prolonged 
hospitalization. The visit at which a tumor assessment shows progressive disease may be used as the treatment termination visit provided that all required 
assessments were performed as outlined in the Schedule of Assessments. Tumor assessments do not have to be repeated if they were performed within 
14 days of the termination visit or at a prior response evaluation that documented progressive disease. ECG does not have to be repeated if they were 
performed within 14 days of the termination visit.  
 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 49 of 110 
Table 3 
Phase 1b Subjects: PK and ADA Sample Collection Schedule 
 
Abbreviations: ADA = anti-drug antibody; AE = adverse event; PK = pharmacokinetics 
PK will be drawn pre-infusion every cycle of etigilimab until treatment termination. ADA will be drawn pre-infusion every other cycle of etigilimab through the 
first 6 months of treatment.  After 6 months, ADA will be collected pre-infusion every 3 months and then once every 6 months after the first year until 
treatment termination.  Should any immune-related AE continue beyond the 4-week post treatment termination visit, a blood sample for PK and ADA may 
be requested by the Medical Monitor. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 50 of 110 
8.2. 
Efficacy Assessments  
Planned timepoints for all efficacy assessments are provided in the SoA. 
Screening and subsequent tumor assessments must include CT scans (with IV contrast unless 
contraindicated and oral contrast as appropriate per institutional standards) of the head and 
neck, chest, abdomen, pelvis and other site of disease for sarcoma as needed. If a CT scan for 
tumor assessment is performed in a positron emission tomography (PET)/CT scanner, the CT 
acquisition must be consistent with the standards for a full-contrast CT scan. Brain imaging 
(either MRI or contrast-enhanced CT) is required at screening for all subjects. Further 
investigations such as bone scans and CT scans of the neck should also be performed if there 
is any clinical suspicion of disease at any site that may not be demonstrated by the minimum 
schedule of assessments listed above. At the investigator’s discretion, other methods of 
assessment of measurable disease as per RECIST v1.1 may be used. 
The same radiographic procedures used to assess disease sites at screening should be used 
throughout the study (eg, the same contrast protocol for CT scans). Response will be assessed 
by the investigator on the basis of physical examinations and the imaging modalities detailed 
above, using RECIST criteria. Assessments should be performed by the same evaluator, if 
possible, to ensure internal consistency across visits. 
Tumor assessments will be performed every 8 (±1) weeks from Cycle 1 Day 1 through Week 
48 and then at least every 12 (±1) weeks or as clinically indicated until confirmed progression 
of disease (as defined below), alternate anticancer therapy, withdrawal of consent, or death, 
whichever occurs first. The radiographic assessments are to be conducted as noted, 
independent of dose delays and/or dose interruptions. RECIST 1.1 criteria will be used for 
primary endpoint evaluation (Eisenhauer et al., 2009), iRECIST will be used for exploratory 
endpoint response evaluation (Seymour et al., 2017). 
Response assessment data (ie, progressive disease or no progression of disease) will continue 
to be collected (based on standard-of-care radiographs) for subjects who have not progressed 
at the time of the termination visit. until the subject starts alternative anti-cancer treatment or 
develops progressive disease, whichever occurs first. Response assessment and assessment of 
tumor markers will be obtained at treatment termination, unless a prior radiographic 
assessment has been performed within the last 14 days or at a prior response assessment that 
documented progressive disease. At the investigator’s discretion, scans may be performed at 
any time if progressive disease is suspected. 
8.3. 
Safety  
Planned timepoints for all safety assessments are provided in the SoA. 
8.3.1. 
Adverse Events 
Measures will be taken to ensure the safety of subjects participating in this trial, including the 
use of stringent inclusion and exclusion criteria (see Section 3.1 and Section 3.2) and close 
monitoring. All subjects will be monitored closely for toxicity. Administration of etigilimab 
and nivolumab will be performed in a setting with available emergency medical facilities 
with access to a critical care unit and staff who are trained to monitor for and respond to 
medical emergencies.   

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 51 of 110 
The definitions of an AE or SAE can be found in Appendix 4. Management guidelines for 
specific AEs can be found in Appendix 8. 
AE will be reported by the subject (or, when appropriate, by a caregiver, surrogate, or the 
subject’s legally authorized representative).  
The investigator and any designees are responsible for detecting, documenting, and reporting 
events that meet the definition of an AE or SAE and remain responsible for following up AE 
that are serious, considered related to the study treatment or the study, or that caused the 
subject to discontinue the study treatment.  
8.3.1.1 
Time Period and Frequency for Collecting AE and SAE Information 
All AEs will be collected from the start of treatment with etigilimab until 90 days after the 
treatment termination visit and at the timepoints specified in the SoA. SAEs will be collected 
starting after signature of the informed consent until 90 days after the treatment termination 
visit. 
Medical occurrences that begin before the start of study treatment but after obtaining 
informed consent will be recorded on the Medical History/Current Medical Conditions 
section of the case report form (CRF). 
All SAEs will be recorded and reported to the sponsor or designee within 24 hours, as 
indicated in Appendix 4. The investigator will submit any updated SAE data to the sponsor 
within 24 hours of it being available. 
Investigators are not obligated to actively seek AE or SAE information in former study 
subjects. However, if the investigator learns of any SAE, including a death, at any time after a 
subject has been discharged from the study, and he/she considers the event to be reasonably 
related to the study treatment or study participation, the investigator must promptly notify the 
sponsor. 
The method of recording, evaluating, and assessing causality of AE and SAE and the 
procedures for completing and transmitting SAE reports are provided in Appendix 4. 
8.3.1.2 
Method of Detecting AE and SAE 
Care will be taken not to introduce bias when detecting AE and/or SAE. Open-ended and 
non-leading verbal questioning of the subject is the preferred method to inquire about 
AE occurrence.  
8.3.1.3 
Follow-up of AE and SAE 
After the initial AE/SAE report, the investigator is required to proactively follow each subject 
at subsequent visits/contacts. All SAEs and immune-related AEs will be followed until 
resolution, stabilization, until the event is otherwise explained, or the subject is lost to follow-
up (as defined in Section 7.1). Further information on follow-up procedures is given in 
Appendix 4. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 52 of 110 
8.3.1.4 
Regulatory Reporting Requirements for SAE 
• Prompt notification by the investigator to the sponsor of an SAE is essential so that 
legal obligations and ethical responsibilities towards the safety of subjects and the 
safety of a study treatment under clinical investigation are met.  
• The sponsor has a legal responsibility to notify both the local regulatory authority and 
other regulatory agencies about the safety of a study treatment under clinical 
investigation. The sponsor will comply with country-specific regulatory requirements 
relating to safety reporting to the regulatory authority, IRB/IEC, and investigators. 
• Investigator safety reports must be prepared for suspected unexpected serious adverse 
reactions according to local regulatory requirements and sponsor policy and 
forwarded to investigators as necessary. 
• An investigator who receives an investigator safety report describing an SAE or other 
specific safety information (eg, summary or listing of SAE) from the sponsor will file 
it along with the Investigator’s Brochure and will notify the IRB/IEC, if appropriate 
according to local requirements. 
8.3.2. 
Pregnancy 
• Details of all pregnancies in female subjects and, if indicated, female partners of male 
subjects will be collected after the start of study treatment and until the pregnancy 
outcome is known. 
• If a pregnancy is reported, the investigator should inform sponsor within 24 hours of 
learning of the pregnancy. 
• Abnormal pregnancy outcomes (eg, spontaneous abortion, fetal death, stillbirth, 
congenital anomalies, ectopic pregnancy) are considered SAEs. 
8.3.3. 
Physical Examinations 
• A complete physical examination will include, at a minimum, assessments of the 
cardiovascular, respiratory, gastrointestinal and neurological systems. Height and 
weight will also be measured and recorded. 
• A symptom-driven physical examination will focus on the evaluation of the subject’s 
reported signs and symptoms.  
• Investigators should pay special attention to clinical signs related to previous serious 
illnesses. 
8.3.4. 
Vital Signs 
• Temperature, pulse rate, respiratory rate, and blood pressure will be assessed. 
• Blood pressure and pulse measurements will be assessed with a completely automated 
device. Manual techniques will be used only if an automated device is not available. 
• Blood pressure and pulse measurements should be preceded by at least 5 minutes of 
rest for the subject in a quiet setting without distractions (eg, television, cell phones). 
• Vital signs will be measured in a semi-supine position after 5 minutes rest and will 
include temperature, systolic and diastolic blood pressure, pulse, and respiratory rate.  
• For etigilimab infusions: 
o For first infusion measure vital signs within 60 minutes before infusion, every 
15 (±5 minutes) during the infusion and 30 (±10 min) and 90 (±15) minutes after 
the end of the infusion.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 53 of 110 
o For subsequent infusions, measure vital signs within 60 minutes before infusion, 
during infusion if clinically indicated and 30 (±10) minutes after the end of the 
etigilimab infusion.   
• For nivolumab infusions vital signs should be taken per institutional guidelines. 
8.3.5. 
Electrocardiograms 
• 12-lead ECG will be obtained as outlined in the SoA (see Section 8.1) using an ECG 
machine that automatically calculates the heart rate and measures pulse rate, QRS, 
QT, and corrected QT intervals.  
8.3.6. 
Clinical Safety Laboratory Assessments 
• Refer to Appendix 2 for the list of clinical laboratory tests to be performed and to the 
SoA for the timing and frequency.  
• The investigator must review the laboratory report, document this review, and record 
any clinically relevant changes occurring during the study in the AE section of the 
CRF. The laboratory reports must be filed with the source documents. Clinically 
significant abnormal laboratory findings are those which are not associated with the 
underlying disease, unless judged by the investigator to be more severe than expected 
for the subject’s condition. 
• All laboratory tests with values considered clinically significantly abnormal during 
participation in the study or within 30 days after the last dose of study treatment 
should be repeated until the values return to normal or baseline. If such values do not 
return to normal/baseline within a period of time judged reasonable by the 
investigator, the etiology should be identified, and the sponsor notified. 
• All protocol-required laboratory assessments, as defined in Appendix 2, must be 
conducted in accordance with the laboratory manual and the SoA.  
• If laboratory values from non-protocol specified laboratory assessments performed at 
the institution’s local laboratory require a change in subject management or are 
considered clinically significant by the investigator (eg, SAE or AE or dose hold), 
then the results must be recorded in the CRF. 
8.3.7. 
Immunogenicity Assessments  
Antibodies to etigilimab will be evaluated in serum samples collected from all subjects 
according to the SoA. Additionally, serum samples should also be collected at the final visit 
from subjects who discontinued study treatment or were withdrawn from the study. These 
samples will be tested by the sponsor or sponsor’s designee. 
Serum samples will be screened for antibodies binding to etigilimab and the titer of 
confirmed positive samples will be reported. Other analyses may be performed to verify the 
stability of antibodies to etigilimab and/or further characterize the immunogenicity of 
etigilimab. 
The detection and characterization of antibodies to etigilimab will be performed using a 
validated assay method by a lab vendor under the supervision of the sponsor. All samples 
collected for detection of antibodies to study treatment will also be evaluated for etigilimab 
serum concentration to enable interpretation of the antibody data. Antibodies may be further 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 54 of 110 
characterized and/or evaluated for their ability to neutralize the activity of the study 
treatment(s). 
Samples may be stored for a maximum of 1 year following the last subject’s last visit for the 
study at a facility selected by the sponsor to enable further analysis of immune responses to 
etigilimab.  
8.4. 
Pharmacokinetics 
• Blood samples will be collected for measurement of serum concentrations of 
etigilimab as specified in Table 3. Other samples may be collected at additional 
timepoints during the study if warranted and agreed upon between the investigator 
and the sponsor. Instructions for the collection and handling of biological samples 
will be provided by the sponsor in the laboratory manual. The actual date and time 
(24-hour clock time) of each sample will be recorded. 
• Genetic analyses will not be performed on these blood or serum samples. Subject 
confidentiality will be maintained. At visits during which samples for the 
determination of serum concentration of etigilimab will be taken, 1 blood draw of 
sufficient volume can be used. 
8.5. 
Pharmacogenomics  
A 6-mL blood sample for DNA isolation will be collected from subjects who have consented 
to participate in the pharmacogenomics component of the study. Participation is optional. 
Subjects who do not wish to participate in the genetic research may still participate in the 
study. 
DNA samples may be used for research related to etigilimab and nivolumab. 
Pharmacogenomic research may consist of the analysis of 1 or more candidate genes or the 
analysis of genetic markers throughout the genome (as appropriate) in relation to etigilimab 
and nivolumab or oncology clinical endpoints.  
The final disposition of samples will be conducted per local regulations. Details on processes 
for collection and shipment of these samples can be found in the Laboratory Manual.  
8.6. 
Biomarkers and Biopsies  
Blood and tumor samples will be obtained for biomarker evaluation from all eligible subjects 
prior to treatment and on treatment as detailed in the SoA. Samples will be processed for the 
determination of changes in signaling markers downstream of the TIGIT-PVR/PVRL2 axis, 
Tregs, and potential predictive biomarkers. 
Blood biomarkers: A predose sample of 33 mL will be drawn at screening, on Study Days 1, 
8, 22, and 36, every 6 weeks after Day 36 for subjects continuing on study drug, and at 
treatment termination to evaluate changes in plasma proteins eg, IL17, IL2, IFNγ, etc., TIGIT 
and immune-related gene expression and possible T-cell clonality by mRNA detection 
(eg, CD226, T-cell genes) and changes in peripheral blood mononuclear cell populations 
(PBMCs) and activation by flow cytometry. 
Tumor tissue: Tumor tissue is required for enrollment. If archival formalin-fixed, paraffin-
embedded (FFPE) tumor tissue has not been collected preferably within 6 months of 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 55 of 110 
screening, but no longer than 1 year, or is not available, either fresh core or punch needle 
biopsy is required at study entry (3 fresh cores/punches preferred whenever possible). 
Pre-treatment biopsy: Baseline tumor tissue samples consisting of core needle biopsies of 
deep tumor tissue or lymph nodes or excisional, incisional, punch, or forceps biopsies of 
cutaneous, subcutaneous, or mucosal lesions will be obtained for all subjects. Subjects 
undergoing core needle biopsy should have accessible lesion(s) that permit a total of at least 
2 biopsies (pretreatment and on-treatment) without unacceptable risk of major procedural 
complication (one pretreatment and an optional one on-treatment biopsy will be performed; 
minimum diameter, 18 gauge). If possible, at least 3 cores will be collected. One or 2 cores 
will be shipped to central laboratory formalin fixed in ethanol and an additional core will be 
fresh frozen.  
On-treatment biopsy: An optional subsequent biopsy will be performed if the subject 
consents to the procedure. The biopsy will be performed approximately 8 weeks (± 5 days) 
following the first administration of etigilimab if not medically contraindicated. In the event 
that the second biopsy cannot be performed approximately 8 weeks after the first 
administration of etigilimab, the Medical Monitor should be notified to discuss alternative 
timing for the second biopsy. An additional biopsy may be collected per investigator 
discretion, preferably at the time of radiographic progression or response. If possible, at least 
3 cores will be collected. One or 2 cores will be shipped to central lab formalin fixed in 
ethanol and an additional core will be fresh frozen. 
Requirements and procedures for pre-treatment and on-treatment biopsy collection are 
identical. The expression of TIGIT, PVR, PVRL2, FOXP3 and other immune markers 
(eg, protein and/or RNA) may be assessed in tumor specimens. The expression levels of 
additional proteins and genes (eg, immune gene signatures) may be evaluated and correlated 
with clinical benefit. Additionally, DNA testing (eg, TMB, mismatch repair genes, TIGIT 
pathway related genes etc.) of the tumor tissue may be performed on subjects using the tumor 
specimens collected. 
Cell-free DNA: A 10 mL blood sample for cell-free tumor DNA assessments will be 
collected pre-dose on Study Day 1, Day 36, Day 78 and treatment termination. Analysis of 
genes relevant to TIGIT, disease genes, mutation burden, and mismatch repair etc. may be 
performed. 
8.7. 
Skin Biopsy 
If a skin rash occurs during study treatment, an optional biopsy and pictures of the skin rash 
will be performed. The expression of immune infiltrate may be assessed by hematoxylin and 
eosin staining and/or IHC. 
8.8. 
Deviation Reporting 
The following protocol deviations will be recorded and summarized in the final report: 
1) enrollment violations, 2) dosing violations, 3) concomitant therapy violations, and 
4) continuation of therapy when treatment should have been discontinued. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 56 of 110 
9. 
STATISTICAL CONSIDERATIONS  
Data collected in this study will be presented descriptively using summary tables, figures, and 
data listings. Continuous variables will be summarized using mean, standard deviation, 
median, minimum, and maximum. Categorical variables will be summarized using counts 
and percentages. Missing values will not be imputed unless otherwise stated. 
9.1. 
Sample Size Determination  
This is a Phase 1b/2 open‐label basket study of etigilimab (MPH313) (
 mg dose for 
subjects ≥50 kg, 
 mg/kg dose for subjects <50 kg) IV administered Q2W with nivolumab 
240 mg Q2W to evaluate preliminary anti-tumor activity, safety and tolerability, PK 
parameters, immunogenicity, and biomarkers in up to 9 cohorts of subjects with endometrial 
carcinoma, HNSCC, cervical cancer, ovarian cancer, gastric cancer and gastroesophageal 
junction adenocarcinoma, TMB-H/MSS cancer, sarcoma, germ cell tumors, and uveal 
melanoma. Each cohort will be evaluated using a Simon Two-Stage design appropriate to the 
clinically meaningful response rate for the indication as depicted in Figure 5 below. Interim 
futility monitoring for each individual cohort using the clinically meaningful response rate 
criteria per cohort will be carried out in accordance with the optimal Simon Two-Stage 
design when up to 10 subjects have sufficient data (either discontinued study drug treatment 
or having at least one post-baseline imaging assessment) for ORR and DoR evaluation by 
RECIST v1.1. For each cohort, the second stage may be opened for enrollment only after 
discussion with the IDMC and the sponsor. The sponsor may have an independent assessment 
of responses to verify investigator-reported responses. The responses based on independent 
assessments, if available, will be used for sensitivity analysis with sponsor and will make 
recommendations regarding study conduct, including whether to continue, modify, or stop the 
study. 
Figure 5 
Simon Two-stage Study Design 
 
Abbreviations: CC = cervical cancer; EC = endometrial cancer; GC = gastric cancer and gastroesophageal 
junction adenocarcinoma; GCT = germ cell tumors; HNSCC = head and neck squamous cell carcinoma; 
OC = ovarian cancer; SR = sarcoma; TMB-H = tumor mutational burden-high; UM = uveal melanoma 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 57 of 110 
Type 1 Cohort 
The null hypothesis that the true response rate is 0.05 will be tested against a one-sided 
alternative that the true response rate is at least 0.2. In the first stage, 10 subjects will be 
enrolled and enrollment in this cohort will be halted until the response data are mature. 
If there are fewer than 1 responder in these 10 subjects, further enrollment in the cohort may 
be stopped after review of efficacy and safety data, and discussion by Sponsor with the 
IDMC. Otherwise, once 1 or more responders in stage 1 are observed, 19 additional subjects 
may be enrolled for a total of 29. The null hypothesis will be rejected and the treatment will 
be declared effective and worthy of further testing if 4 or more responders are observed in 
29 subjects. This design yields a type I error rate of 0.0468 and power of 80.11% when the 
true response rate is 0.2. 
Type 2 Cohort 
The null hypothesis that the true response rate is 0.1 will be tested against a one-sided 
alternative that the true response rate is at least 0.3. In the first stage, 10 subjects will be 
enrolled and enrollment in this cohort will be halted until the response data are mature. 
If there are fewer than 2 responders in these 10 subjects, enrollment in the cohort may be 
stopped after review of efficacy and safety data, and discussion by Sponsor with the IDMC. 
Otherwise, once 2 or more responders in stage 1 are observed, 19 additional subjects may be 
enrolled for a total of 29. The null hypothesis will be rejected and the treatment will be 
declared effective and worthy of further testing if 6 or more responders are observed in 
29 subjects. This design yields a type I error rate of 0.0471 and power of 80.51% when the 
true response rate is 0.3. 
9.2. 
Populations for Analyses 
The intent-to-treat (ITT) analysis set is defined as all subjects who signed an informed 
consent form and were enrolled into the study. 
The Safety analysis set is defined as all subjects who received any amount of study drug. 
All safety analyses will be performed using the Safety analysis set. 
The Response-Evaluable analysis set is a modified ITT analysis set defined as all subjects 
with measurable disease at baseline who received study treatment and had at least one post-
baseline response assessment or discontinued treatment due to disease progression (including 
death due to disease progression) within 16 weeks (+ a 2-week window) of the first dose of 
study treatment. All efficacy analyses will be performed using the Response-Evaluable 
analysis set. 
9.3. 
Statistical Analyses 
All statistical analyses for this study will be undertaken by a contract research organization 
under the supervision of sponsor personnel. Any data analysis carried out independently by 
the investigator should be submitted to the sponsor prior to publication or presentation. 
All data will be listed. All trial endpoints will be described using summary statistics. Data 
will be summarized using descriptive statistics for continuous data (safety laboratory data, 
pharmacodynamic and relevant biomarker data), and contingency tables for categorical data 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 58 of 110 
(demographics and other baseline characteristics, efficacy measurements, safety 
measurements and all relevant PK measurements. 
For statistical analyses and summaries, baseline is defined as the available data from the last 
recorded measurement prior to first administration of study drug.  
Details of statistical analysis and data reporting will be provided in a SAP document finalized 
prior to database lock. Additional analyses may be added in the SAP and tables, listings and 
figures shells will also be provided. 
The SAP will be developed and finalized before database lock and will describe the selection 
of subjects to be included in the analyses, and procedures for accounting for missing, unused, 
and spurious data. Below is a summary of planned statistical analyses of the study endpoints. 
9.3.1. 
Efficacy Analyses 
Efficacy analyses will be performed separately for each cohort. RECIST 1.1 criteria will be 
used for the primary endpoint evaluation (Eisenhauer et al., 2009), and iRECIST will be used 
for the exploratory endpoint response evaluation (Seymour et al., 2017). The iRECIST 
endpoints are analyzed using the same statistical methodology and the results will be 
presented in the same ways for the corresponding RECIST 1.1 endpoints.  
The primary efficacy endpoint is the ORR defined as the proportion of subjects who achieve 
confirmed CR or PR per RECIST v1.1. The best overall response is the best response 
recorded from the start of the treatment until PD. The smallest measurements recorded since 
the treatment started will be used as the reference for PD. Subjects with CR or PR are 
considered to have obtained objective response. Subjects with not-evaluable response (NE) 
are counted as non-responders. Exact 95% CI will be constructed for the ORR for each 
cohort. 
Subjects with CR, PR or SD are considered to have achieved disease control. Disease control 
rate is defined as the proportion of subjects who have achieved CR, PR, and SD. Duration of 
response only applies to subjects whose best overall response is CR or PR and is defined as 
the number of days from the first documentation of objective tumor response to the date of 
first PD or death due to underlying cancer. 
Duration of stable disease is measured from the start of the treatment (the first treatment date 
for non-randomized studies, the randomization date for randomized studies) until the date 
when the criteria for overall disease progression are first met.  
Duration of response is the time from first evaluation showing CR or PR (response 
confirmation required at subsequent tumor assessment no earlier than 4 weeks after first 
evaluation showing CR or PR) to the time of the first subsequent evaluation showing PD or 
death. Only subjects who experience a confirmed CR or PR will be analyzed for DoR. 
Subjects who do not experience PD or death will be censored per the censoring rules in the 
statistical analysis plan. 
Progression-free survival is defined as the number of days from Day 1 in Cycle 1 to the first 
documented progression or death due to any cause. Only deaths that occurred within 30 days 
of the last progression assessed. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 59 of 110 
Overall survival is defined as the time from the first dose of study drug to death due to any 
cause. 
Overall survival, PFS, and DoR will be summarized for each group using Kaplan-Meier 
methodology. Censoring rules will be detailed in the statistical analysis plan. 
• For analysis of OS, all subjects will be followed for survival for up to 2 years, until 
withdrawal of consent, loss to follow up, or death, whichever occurs first. At the time 
of analysis of OS, any subjects who remain alive will be censored at the last date they 
were known to be alive. 
• PFS is the time from the start of study treatment to the first evaluation showing PD or 
death, whichever occurs first. Subjects who do not experience PD or death will be 
censored per the censoring rules in the statistical analysis plan. 
9.3.2. 
Safety Analyses 
Adverse events will be coded using the Medical Dictionary for Regulatory Activities 
(MedDRA) version 18.0 or higher and will be graded according to the NCI‐CTCAE, v 4.03 
or higher. 
Summaries of AEs will be based on TEAEs. A TEAE is an AE that emerges or worsens in 
the period from the first dose of study treatment etigilimab or nivolumab, whichever is 
earlier, to 100 days after the last dose of etigilimab or nivolumab (whichever is dosed last) or 
until starting another treatment. 
TEAEs will be summarized by treatment group and by the frequency of subjects experiencing 
TEAEs corresponding to MedDRA system organ classes and preferred terms. 
Separate tabulations will also be produced for TEAEs assessed as related to study drug(s), 
TEAEs that led to treatment discontinuation, TEAEs that led to death, and TEAEs ≥Grade 3 
in severity. Treatment‐emergent serious AEs and SAEs related to study drug(s) will also be 
tabulated. 
Laboratory results (hematology, serum or plasma chemistry, and coagulation) and the 
corresponding change from baseline values will be summarized by group and scheduled 
timepoint. A shift table, tabulation for baseline to each scheduled assessment and the worst 
post treatment value according to the CTCAE grade, will be provided for selected clinical 
laboratory tests. Laboratory results together with the normal ranges and CTCAE grade will be 
listed. Laboratory values that are below or above the normal ranges will be flagged. 
Vital signs and ECGs and the corresponding changes from baseline will be summarized by 
group and scheduled timepoint.  
9.3.3. 
Pharmacokinetic Analyses 
The PK analysis set will include all Phase 1b subjects with sufficient plasma concentration 
data to allow the characterization of the PK parameters. Plasma etigilimab concentration data 
at each assessment timepoint will be summarized and listed and will be plotted across time. 
Pharmacokinetic parameters will be calculated using non-compartmental techniques from 
plasma concentrations and will include the following parameters: maximum concentration 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 60 of 110 
observed, clearance, elimination half-life, and area under the curve. Pharmacokinetic 
parameters will be summarized descriptively for each group.  
9.3.4. 
Immunogenicity Analyses  
The immunogenicity analysis set will include all subjects with at least one evaluable post-
treatment immunogenicity sample. Blood samples for evaluation of ADA will be collected to 
determine the relationship between ADA and etigilimab PK parameters. 
9.3.5. 
Exploratory Analyses  
Blood samples for evaluation of pharmacodynamics biomarkers, immune biomarkers, and 
exploratory predictive biomarkers will be collected from all subjects to determine their 
correlation with ORR and DCR. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 61 of 110 
10. 
REFERENCES 
1. Bottino C, et al., Identification of PVR (CD155) and Nectin-2 (CD112) as cell surface 
ligands for the human DNAM-1 (CD226) activating molecule. J Exp Med, 2003. 198(4): 
p. 557-67. 
2. Chan CJ, Andrews DM, and Smyth MJ. Receptors that interact with nectin and nectin-
like proteins in the immunosurveillance and immunotherapy of cancer. Curr Opin 
Immunol, 2012. 24(2): p. 246-51. 
3. Chauvin JM, et al., TIGIT and PD-1 impair tumor antigen-specific CD8(+) T cells in 
melanoma patients. J Clin Invest, 2015. 125(5): p. 2046-58. 
4. Chung HC, et al., Efficacy and Safety of Pembrolizumab in Previously Treated Advanced 
Cervical Cancer: Results From the Phase II KEYNOTE-158 Study. J Clin Oncol. 2019 
Jun 10; 37(17): 1470-1478.  
5. Eisenhauer EA, Therasse P, Bogaerts J, et al. New response evaluation criteria in solid 
tumors: Revised RECIST guideline (Version 1.1). Eur J Cancer 2009;45:228−47. 
6. Gromeier M, et al., Intergeneric poliovirus recombinants for the treatment of malignant 
glioma. Proc Natl Acad Sci U S A, 2000. 97(12): p. 6803-8. 
7. Johnston RJ, et al., The immunoreceptor TIGIT regulates antitumor and antiviral CD8(+) 
T cell effector function. Cancer Cell, 2014. 26(6): p. 923-37. 
8. Joller N, et al., Cutting edge: TIGIT has T cell-intrinsic inhibitory functions. J Immunol, 
2011. 186(3): p. 1338-42. 
9. Joller N, et al., Treg cells expressing the coinhibitory molecule TIGIT selectively inhibit 
proinflammatory Th1 and Th17 cell responses. Immunity, 2014. 40(4): p. 569-81. 
10. Kurtulus S, et al., TIGIT predominantly regulates the immune response via regulatory 
T cells. J Clin Invest, 2015. 125(11): p. 4053-62. 
11. Levin SD, et al., Vstm3 is a member of the CD28 family and an important modulator of 
T-cell function. Eur J Immunol, 2011. 41(4): p. 902-15. 
12. Martinet L and MJ Smyth. Balancing natural killer cell activation through paired 
receptors. Nat Rev Immunol, 2015. 15(4): p. 243-54. 
13. Matulonis UA, et al., Final results from the KEYNOTE-100 trial of pembrolizumab in 
patients with advanced recurrent ovarian cancer. J Clin Oncol. 2020. 38 (15_suppl), 6005.  
14. OPDIVO (nivolumab) [package insert].  Princeton, NJ: Bristol-Meyers Squibb, 2018. 
15. Puzanov I, Diab, A., Abdallah, K. et al. Managing toxicities associated with immune 
checkpoint inhibitors: consensus recommendations from the Society for Immunotherapy 
of Cancer (SITC) Toxicity Management Working Group. J Immunother Cancer. 2017 
Nov 21;5(1):95. doi: 10.1186/s40425-017-0300-z.  
16. Schmidt EV, Chisamore MJ, Chaney MF, et al. Assessment of clinical activity of PD-1 
checkpoint inhibitor combination therapies reported in clinical trials. JAMA Netw Open. 
2020;3(2):e1920833. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 62 of 110 
17. Seymour L, et al., iRECIST: guidelines for response criteria for use in trials testing 
immunotherapeutics. Lancet Oncol, 2017. Mar; 18(3): e143-e152.  
18. Stanietsky N, et al., The interaction of TIGIT with PVR and PVRL2 inhibits human NK 
cell cytotoxicity. Proc Natl Acad Sci U S A, 2009. 106(42): p. 17858-63. 
19. Yu X, et al., The surface protein TIGIT suppresses T cell activation by promoting the 
generation of mature immunoregulatory dendritic cells. Nat Immunol, 2009. 10(1): p. 48-
57. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 63 of 110 
11. 
APPENDICES 
APPENDIX 1: 
ABBREVIATIONS AND TRADEMARKS 
Abbreviation or Term 
Definition/Explanation 
ADA 
anti-drug antibody 
AE 
adverse event 
AFP 
alpha 1-fetoprotein 
ALT (SGPT) 
alanine aminotransferase  
(serum or plasma glutamic pyruvic transaminase) 
aPTT 
activated partial thromboplastin time 
AST (SGOT) 
aspartate aminotransferase  
(serum or plasma glutamic oxaloacetic transaminase) 
BAP1 
BRCA 1-associated protein-1 
BOR 
best observed response 
BUN 
blood urea nitrogen 
CBC 
complete blood count 
CC 
cervical cancer 
CD 
cluster differentiation 
CPI 
checkpoint inhibitor  
CR 
complete response 
CRC 
colorectal cancer 
CRF 
case report form 
CT 
computed tomography 
CTCAE 
Common Toxicity Criteria for Adverse Events 
DCR 
disease control rate 
DFR 
disease-free survival 
DLT 
dose-limiting toxicity 
DoR 
duration of response 
EBRT 
external beam radiotherapy 
EC 
endometrial carcinoma 
ECG 
electrocardiogram 
ECOG 
Eastern Cooperative Oncology Group 
eCRF 
electronic case report form 
eg 
exempli gratia (or ‘for example’) 
FDA 
Food and Drug Administration 
FDG PET 
fluorodeoxyglucose positron emission tomography 
FFPE 
formalin-fixed, paraffin-embedded 
GC 
gastric cancer 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 64 of 110 
Abbreviation or Term 
Definition/Explanation 
GCP 
Good Clinical Practice 
GEJ 
gastroesophageal junction adenocarcinoma 
GLP 
Good laboratory practice 
HIPAA 
Health Insurance Portability and Accountability Act 
HBV 
hepatitis B virus 
HBsAg 
hepatitis B surface antigen 
HDCT 
high-dose chemotherapy 
HCG 
human chorionic gonadotropin 
HCV 
hepatitis C virus 
HNSCC 
head and neck squamous cell carcinoma 
ICF 
informed consent form 
ICH 
International Conference on Harmonization 
IDMC 
Independent Data Monitoring Committee 
ie 
id est (or ‘that is’) 
IEC 
independent ethics committee 
IFN 
interferon 
IgG 
immunoglobulin G 
IHC 
immunohistochemistry 
IL 
interleukin 
INR 
international normalized ratio 
IRB 
institutional review board 
ITIM 
tyrosine-based inhibition motifs 
ITT 
intent-to-treat 
IV 
intravenous 
LD 
longest diameter 
MCV 
mean corpuscular volume 
MCH 
mean corpuscular hemoglobin 
MedDRA 
Medical Dictionary for Regulatory Activities 
MMR 
mismatched repair 
MRI 
magnetic resonance imaging 
mRNA 
messenger RNA 
MSI 
microsatellite instability 
MSS 
microsatellite stable 
NA 
not applicable 
NCI 
National Cancer Institute 
NE 
not evaluable 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 65 of 110 
Abbreviation or Term 
Definition/Explanation 
NK 
natural killer 
NSCLC 
non-small cell lung cancer 
ORR 
overall response rate 
PBMC 
peripheral blood mononuclear cell 
PD  
progressive disease 
PD-1 
programmed death-1 
PDL-1 
programmed death ligand-1 
PFS 
progression-free survival 
PK 
pharmacokinetics 
PR 
partial response 
PT 
prothrombin time 
PVR 
poliovirus receptor 
Q2W 
every 2 weeks 
RBC 
red blood cell 
RECIST 
Response Evaluation Criteria in Solid Tumors 
RPKM 
reads per kilobase per million 
RSEM 
RNA-Seq by Expectation-Maximization 
SAE 
serious adverse event 
SCLC 
small-cell lung cancer 
SD 
stable disease 
SoA 
Schedule of Activities 
TCR 
T-cell receptor 
TCGA 
The Cancer Genome Atlas 
TEAEs 
treatment‐emergent adverse events 
TIGIT 
T-cell immunoreceptor with Ig and ITIM domains 
TMB-H 
tumor mutational burden‐high cancer 
Tregs 
regulatory T-cells 
TSH 
thyroid-stimulating hormone 
TILs 
tumor infiltrating lymphocytes 
ULN 
upper limit of normal 
VEGF 
vascular endothelial growth factor 
WBC 
white blood cell 
WOCBP 
woman of childbearing potential 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 66 of 110 
APPENDIX 2: 
CLINICAL LABORATORY TESTS  
• The tests detailed in Table 4 will be performed by the local laboratory.  
• Protocol-specific requirements for inclusion or exclusion of subjects are detailed in 
Sections 3.1 and 3.2 of the protocol. 
• Additional tests may be performed at any time during the study as determined 
necessary by the investigator or required by local regulations. 
Table 4 
Protocol-Required Safety Laboratory Assessments 
Laboratory 
Assessments 
Parameters 
Hematology 
Platelet count 
Red blood cell (RBC) count 
Hemoglobin 
Hematocrit 
RBC indices mean corpuscular volume (MCV), mean corpuscular 
hemoglobin (MCH) 
White blood cell (WBC) count with differential: neutrophils, 
lymphocytes, monocytes, eosinophils, basophils 
Clinical Chemistry 
Blood urea nitrogen (BUN) 
Potassium 
Sodium 
Calcium 
Phosphorus 
Magnesium 
Chloride 
Bicarbonate 
Alkaline phosphatase 
Aspartate aminotransferase (AST) /serum glutamic-oxaloacetic 
transaminase (SGOT) 
Alanine aminotransferase (ALT)/ serum glutamic-pyruvic 
transaminase (SGPT) 
Total bilirubin 
Total protein 
Albumin 
Lactate dehydrogenase 
Creatinine 
Glucose 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 67 of 110 
Laboratory 
Assessments 
Parameters 
Urinalysis 
Specific gravity   
pH 
Glucose 
Protein 
Ketones 
Blood 
Microscopic examination (if blood or protein is abnormal) 
Thyroid Function 
Tests 
Thyroid stimulating hormone (TSH) 
Free T3 
Free T4 
Coagulation 
International normalized ratio (INR) 
Prothrombin time (PT) 
Activated partial prothrombin time (aPTT) 
Other 
Serum pregnancy test 
 
Investigators must document their review of each laboratory safety report. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 68 of 110 
APPENDIX 3: 
STUDY GOVERNANCE CONSIDERATIONS 
Regulatory and Ethical Considerations 
• This study will be conducted in accordance with the protocol and with: 
o Consensus ethical principles derived from international guidelines including the 
Declaration of Helsinki and Council for International Organizations of Medical 
Sciences (CIOMS) International Ethical Guidelines 
o Applicable ICH Good Clinical Practice (GCP) Guidelines 
o Applicable laws and regulations 
• The protocol, protocol amendments, ICF, Investigator Brochure, and other relevant 
documents (e.g., advertisements) must be submitted to an IRB/IEC by the investigator 
and reviewed and approved by the IRB/IEC before the study is initiated.  
• Any amendments to the protocol will require IEC/IRB approval before 
implementation of changes made to the study design, except for changes necessary to 
eliminate an immediate hazard to study subjects.  
• The investigator will be responsible for the following: 
o Providing written summaries of the status of the study to the IRB/IEC annually or 
more frequently in accordance with the requirements, policies, and procedures 
established by the IRB/EC 
o Notifying the IRB/IEC of SAE or other significant safety findings as required by 
IRB/IEC procedures 
o Overall conduct of the study at the site and adherence to requirements of 21 CFR, 
ICH guidelines, the IRB/IEC, European regulation 536/2014 for clinical studies 
(if applicable), and all other applicable local regulations 
Financial Disclosure 
Investigators and sub-investigators will provide the sponsor with sufficient, accurate financial 
information in accordance with local regulations to allow the sponsor to submit complete and 
accurate financial certification or disclosure statements to the appropriate regulatory 
authorities. Investigators are responsible for providing information on financial interests 
during the course of the study and for 1 year after completion of the study. 
Informed Consent Process 
• The investigator or his/her representative will explain the nature of the study to the 
subject or his/her legally authorized representative and answer all questions regarding 
the study.  
• Subjects must be informed that their participation is voluntary. Subjects or their 
legally authorized representative will be required to sign a statement of informed 
consent that meets the requirements of 21 CFR 50, local regulations, ICH guidelines, 
Health Insurance Portability and Accountability Act (HIPAA) requirements, where 
applicable, and the IRB/IEC or study center.  
• The medical record must include a statement that written informed consent was 
obtained before the subject was enrolled in the study and the date the written consent 
was obtained. The authorized person obtaining the informed consent must also sign 
the ICF. 
• Subjects must be re-consented to the most current version of the ICF(s) during their 
participation in the study.  
• A copy of the ICF(s) must be provided to the subject or the subject’s legally 
authorized representative.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 69 of 110 
A subject who is rescreened is not required to sign another ICF if the rescreening occurs 
within >28 days from the previous ICF signature date. 
Data Protection 
• Subjects will be assigned a unique identifier by the sponsor. Any subject records or 
datasets that are transferred to the sponsor will contain the identifier only; subject 
names or any information which would make the subject identifiable will not be 
transferred.  
• The subject must be informed that his/her personal study-related data will be used by 
the sponsor in accordance with local data protection law. The level of disclosure must 
also be explained to the subject.  
• The subject must be informed that his/her medical records may be examined by 
Clinical Quality Assurance auditors or other authorized personnel appointed by the 
sponsor, by appropriate IRB/IEC members, and by inspectors from regulatory 
authorities. 
Publication Policy 
• The results of this study may be published or presented at scientific meetings. If this is 
foreseen, the investigator agrees to submit all manuscripts or abstracts to the sponsor 
before submission. This allows the sponsor to protect proprietary information and to 
provide comments.  
• The sponsor will comply with the requirements for publication of study results. In 
accordance with standard editorial and ethical practice, the sponsor will generally 
support publication of multicenter studies only in their entirety and not as individual 
site data. In this case, a coordinating investigator will be designated by mutual 
agreement. 
• Authorship will be determined by mutual agreement and in line with International 
Committee of Medical Journal Editors authorship requirements. 
Dissemination of Clinical Study Data 
These study results will be generated once the study is complete and can be made available to 
the investigators.  Information will also be available upon request for IRB/IEC Annual 
Reports.  
Data Quality Assurance 
• All subject data relating to the study will be recorded on printed or electronic CRF 
unless transmitted to the sponsor or designee electronically (e.g., laboratory data). The 
investigator is responsible for verifying that data entries are accurate and correct by 
physically or electronically signing the CRF.  
• The investigator must maintain accurate documentation (source data) that supports the 
information entered in the CRF.  
• The investigator must permit study-related monitoring, audits, IRB/IEC review, and 
regulatory agency inspections and provide direct access to source data documents.  
• The sponsor or designee is responsible for the data management of this study 
including quality checking of the data.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 70 of 110 
• Study monitors will perform ongoing source data verification to confirm that data 
entered into the CRF by authorized site personnel are accurate, complete, and 
verifiable from source documents; that the safety and rights of subjects are being 
protected; and that the study is being conducted in accordance with the currently 
approved protocol and any other study agreements, ICH GCP, and all applicable 
regulatory requirements.  
• 
Records and documents pertaining to the conduct of this study and the 
distribution of investigational product, including signed ICF, laboratory test 
results, study medication inventory records, and regulatory documents, must 
be retained by the Principal Investigator for 2 years after marketing 
application approval. If no application is filed, these records must be kept for 
2 years after the study is discontinued and the FDA and other applicable 
regulatory authorities are notified. sponsor will notify the Principal 
Investigator of these events. No records may be transferred to another 
location or party without written notification to the sponsor. 
Source Documents 
• Source documents provide evidence for the existence of the subject and substantiate 
the integrity of the data collected. Source documents are filed at the investigator’s 
site. Data reported entered in the eCRF that are transcribed from source documents 
must be consistent with the source documents or the discrepancies must be explained. 
The investigator may need to request previous medical records or transfer records, 
depending on the study. Also, current medical records must be available. Source 
documents include primary documents such as medical records, CT scans, ECG 
scans, etc. 
Study and Site Closure 
The sponsor or its designee may stop the study or study site participation in the study for 
medical, safety, regulatory, administrative, or other reasons consistent with applicable laws, 
regulations, and GCP.  
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 71 of 110 
APPENDIX 4: 
ADVERSE EVENTS: DEFINITIONS AND PROCEDURES FOR 
RECORDING, EVALUATING, FOLLOW-UP, AND 
REPORTING 
Definition of AE 
AE Definition 
• 
An AE is any untoward medical occurrence in a subject or clinical study subject, temporally 
associated with the use of a medicinal product, whether or not considered related to the 
medicinal product. 
• 
NOTE: An AE can therefore be any unfavorable and unintended sign (including an abnormal 
laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the 
use of a medicinal product. 
 
Events Meeting the AE Definition  
• 
Any abnormal laboratory test results (hematology, clinical chemistry, or urinalysis) or other 
safety assessments (e.g., ECG, radiological scans, vital signs measurements), including those 
that worsen from baseline, considered clinically significant in the medical and scientific 
judgment of the investigator (ie, not related to progression of underlying disease). 
• 
Exacerbation of a chronic or intermittent pre-existing condition including either an increase in 
frequency and/or intensity of the condition. 
• 
New conditions detected or diagnosed after study treatment administration even though it may 
have been present before the start of the study. 
• 
Signs, symptoms, or the clinical sequelae of a suspected drug-drug interaction. 
• 
Signs, symptoms, or the clinical sequelae of a suspected overdose of either study treatment or 
a concomitant medication. Overdose per se will not be reported as an AE/SAE unless it is an 
intentional overdose taken with possible suicidal/self-harming intent. Such overdoses should 
be reported regardless of sequelae. 
• 
“Lack of efficacy” or “failure of expected pharmacological action” per se will not be reported 
as an AE or SAE. Such instances will be captured in the efficacy assessments. However, the 
signs, symptoms, and/or clinical sequelae resulting from lack of efficacy will be reported as 
AE or SAE if they fulfil the definition of an AE or SAE.  
• 
The signs, symptoms, and/or clinical sequelae resulting from lack of efficacy will be reported 
as AE or SAE if they fulfil the definition of an AE or SAE. Also, “lack of efficacy” or “failure 
of expected pharmacological action” also constitutes an AE or SAE. 
 
Events NOT Meeting the AE Definition  
• 
Any clinically significant abnormal laboratory findings or other abnormal safety assessments 
which are associated with the underlying disease, unless judged by the investigator to be more 
severe than expected for the subject’s condition. 
• 
The disease/disorder being studied or expected progression, signs, or symptoms of the 
disease/disorder being studied, unless more severe than expected for the subject’s condition. 
• 
Medical or surgical procedure (eg, endoscopy, appendectomy): the condition that leads to the 
procedure is the AE. 
• 
Situations in which an untoward medical occurrence did not occur (social and/or convenience 
admission to a hospital). 
• 
Anticipated day-to-day fluctuations of pre-existing disease(s) or condition(s) present or 
detected at the start of the study that do not worsen. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 72 of 110 
Definition of SAE 
If an event is not an AE per definition above, then it cannot be an SAE even if serious 
conditions are met (eg, hospitalization for signs/symptoms of the disease under study, death 
due to progression of disease). 
A SAE is defined as any untoward medical occurrence that, at any dose: 
a. Results in death 
b. Is life-threatening 
The term ‘life-threatening’ in the definition of ‘serious’ refers to an event in which the 
subject was at risk of death at the time of the event. It does not refer to an event, which 
hypothetically might have caused death, if it were more severe. 
c. 
Requires inpatient hospitalization or prolongation of existing hospitalization 
In general, hospitalization signifies that the subject has been detained (usually involving at 
least an overnight stay) at the hospital or emergency ward for observation and/or treatment 
that would not have been appropriate in the physician’s office or outpatient setting. 
Complications that occur during hospitalization are AE. If a complication prolongs 
hospitalization or fulfills any other serious criteria, the event is serious. When in doubt as 
to whether “hospitalization” occurred or was necessary, the AE should be considered 
serious. 
Hospitalization for elective treatment of a pre-existing condition that did not worsen from 
baseline is not considered an AE. 
d. Results in persistent disability/incapacity 
• 
The term disability means a substantial disruption of a person’s ability to conduct 
normal life functions. 
• 
This definition is not intended to include experiences of relatively minor medical 
significance such as uncomplicated headache, nausea, vomiting, diarrhea, influenza, 
and accidental trauma (eg, sprained ankle) which may interfere with or prevent 
everyday life functions but do not constitute a substantial disruption. 
e. 
Is a congenital anomaly/birth defect 
f. 
Other situations: 
• 
Medical or scientific judgment should be exercised in deciding whether SAE reporting 
is appropriate in other situations such as important medical events that may not be 
immediately life-threatening or result in death or hospitalization but may jeopardize 
the subject or may require medical or surgical intervention to prevent one of the other 
outcomes listed in the above definition. These events should usually be considered 
serious. 
Examples of such events include invasive or malignant cancers, intensive treatment in 
an emergency room or at home for allergic bronchospasm, blood dyscrasias or 
convulsions that do not result in hospitalization, or development of drug dependency 
or drug abuse. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 73 of 110 
Definition of AESI 
Adverse events of special interest (AESIs) are defined as events (serious or non-serious) 
which are of scientific and medical concern specific to the sponsor’s product or program, for 
which ongoing monitoring and rapid communication by the investigator to the sponsor may 
be appropriate. Such events may require further investigation in order to characterize and 
understand them. 
AESIs for etigilimab 
Some AEs, despite their severity or outcome, will be expedited due to the relevance for 
participant safety or study treatment safety profile. These events should be reported to the 
sponsor/designee within 24 hours. This is to enable follow-up to be performed on all these 
reported adverse events that have not been reported as serious adverse events (SAEs). The 
AESIs for etigilimab are: 
• Infusion reactions,  
• Immune‐related adverse events 
AESIs that are considered to be clinically significant by the PI and/ or medical team will 
also be submitted to the independent DMC for review. 
 
Recording AE / AESI and SAE 
AE, AESI and SAE Recording 
• 
When an AE/AESI /SAE occurs, it is the responsibility of the investigator to review all 
documentation (eg, hospital progress notes, laboratory, and diagnostics reports) related 
to the event. 
• 
The investigator will then record all relevant AE/AESI/SAE information in the CRF. 
• 
It is not acceptable for the investigator to send photocopies of the subject’s medical 
records to the sponsor or their representatives in lieu of completion of the 
AE/AESI/SAE CRF page. 
• 
There may be instances when copies of medical records for certain cases are requested 
by the sponsor or their representatives. In this case, all subject identifiers, with the 
exception of the subject number, will be blinded on the copies of the medical records 
before submission to the sponsor or their representatives. 
• 
The investigator will attempt to establish a diagnosis of the event based on signs, 
symptoms, and/or other clinical information. In such cases, the diagnosis (not the 
individual signs/symptoms) will be documented as the AE/AESI/SAE. 
 
Assessment of Intensity 
• 
The investigator will make an assessment of Grade for each AE, AESI and SAE 
reported during the study according to the NCI Common Terminology Criteria for 
Adverse Events version 5 (CTCAE v 5) or higher.  
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 74 of 110 
Assessment of Causality 
• 
The investigator is obligated to assess the relationship between study treatment and 
each occurrence of each AE/AESI/SAE. 
• 
A “reasonable possibility” of a relationship conveys that there are facts, evidence, 
and/or arguments to suggest a causal relationship, rather than a relationship cannot be 
ruled out. 
• 
The investigator will use clinical judgment to determine the relationship. 
• 
Alternative causes, such as underlying disease(s), concomitant therapy, and other risk 
factors, as well as the temporal relationship of the event to study treatment 
administration will be considered and investigated. 
• 
The investigator will also consult the Investigator’s Brochure (IB) and/or Product 
Information, for marketed products, in his/her assessment. 
• 
For each AE/AESI/SAE, the investigator must document in the medical notes that 
he/she has reviewed the AE/AESI/SAE and has provided an assessment of causality. 
• 
There may be situations in which an SAE /AESI has occurred and the investigator has 
minimal information to include in the initial report. However, it is very important 
that the investigator always make an assessment of causality for every event 
before the initial transmission of the SAE / AESI data. 
• 
The investigator may change his/her opinion of causality in light of follow-up 
information and send an SAE / AESI follow-up report with the updated causality 
assessment. 
• 
The causality assessment is one of the criteria used when determining regulatory 
reporting requirements. 
 
Follow-up of AE, AESI and SAE 
• 
The investigator is obligated to perform or arrange for the conduct of supplemental 
measurements and/or evaluations as medically indicated or as requested by the sponsor 
or their representatives to elucidate the nature and/or causality of the AE, AESI or 
SAE as fully as possible. This may include additional laboratory tests or 
investigations, histopathological examinations, or consultation with other health care 
professionals. 
• 
If a subject dies during participation in the study or during a recognized follow-up 
period, the investigator will provide the sponsor or their representatives with a copy of 
any post-mortem findings including the autopsy report and histopathology. 
• 
New or updated information will be recorded in the originally completed CRF. 
• 
The investigator will submit any updated SAE / AESI data to the sponsor within 
24 hours of receipt of the information. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 75 of 110 
Reporting of SAE to Sponsor 
SAE / AESI Reporting to Sponsor via email 
• 
The primary mechanism for reporting SAE / AESI to Sponsor or its representatives 
will be the report form via email:  
Email: Syneos Health Safety and Pharmacovigilance 
safetyreporting@syneoshealth.com and Mereo Biopharma 
mph313safetyalerts@mereobiopharma.com 
• 
If the email is unavailable please report via fax +1-877-464-7787  
• 
The site will report the SAE /AESI data via email report as soon as it becomes 
available. 
• 
If a site receives a report of a new SAE /AESI from a study subject or receives updated 
data on a previously reported SAE /AESI an updated SAE /AESI form should be 
submitted to the same email addresses above. 
• 
Further contacts for SAE /AESI reporting can be found in the Study Binder. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 76 of 110 
APPENDIX 5: 
CONTRACEPTIVE GUIDANCE AND COLLECTION OF 
PREGNANCY INFORMATION 
Definitions 
Woman of Childbearing Potential (WOCBP) 
A woman is considered fertile following menarche and until becoming post-menopausal 
unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral 
salpingectomy, and bilateral oophorectomy. 
Women in the following categories are not considered WOCBP 
1. Premenopausal female with 1 of the following: 
• Documented hysterectomy 
• Documented bilateral salpingectomy 
• Documented bilateral oophorectomy 
Note:  Documentation can come from the site personnel’s: review of subject’s 
medical records, medical examination, or medical history interview. 
2. Premenarchal  
3. Postmenopausal female 
• A postmenopausal state is defined as no menses for 12 months without an 
alternative medical cause. A high follicle stimulating hormone (FSH) level in 
the postmenopausal range may be used to confirm a postmenopausal state in 
women not using hormonal contraception or hormonal replacement therapy 
(HRT). However, in the absence of 12 months of amenorrhea, a single FSH 
measurement is insufficient.  
• Females on HRT and whose menopausal status is in doubt will be required to 
use one of the non-hormonal highly effective contraception methods if they 
wish to continue their HRT during the study. Otherwise, they must 
discontinue HRT to allow confirmation of postmenopausal status before study 
enrollment. 
Contraception Guidance 
Males Subjects 
1. Male subjects with female partners of child-bearing potential are eligible to 
participate if they agree to the following: 
• Are abstinent from penile-vaginal intercourse as their usual and preferred 
lifestyle (abstinent on a long term and persistent basis) and agree to remain 
abstinent for duration of study and for 6 months after study completion or 
from last dose 
• Female partner is using a highly effective contraceptive method  
2. For non-genotoxic IMPs with demonstrated or suspected human teratogenicity / 
fetotoxicity at subtherapeutic exposure levels {where it is theoretically possible 
that relevant systemic concentrations may be achieved in WOCBP from exposure 
to seminal fluid) to prevent exposure of an embryo/fetus   
3. Agree to use a male condom plus an additional method with a failure rate of <1% 
per year as described in the table below when having penile-vaginal intercourse 
with a woman of childbearing potential   

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 77 of 110 
4. Men with a pregnant or breastfeeding partner must agree to remain abstinent from 
penile-vaginal intercourse or use a male condom during each episode of penile 
penetration for duration of study and for 6 months after study completion or from 
last dose 
5. Refrain from donating sperm for duration of study and for 6 months after study 
completion or from last dose 
Table 5 
Highly Effective Contraceptive Methods That Are User Dependent  
Failure rate of <1% per year when used consistently and correctly.  
Combined (estrogen- and progestogen-containing) hormonal contraception associated with 
inhibition of ovulationb  
• 
oral  
• 
intravaginal 
• 
transdermal 
Progestogen-only hormonal contraception associated with inhibition of ovulationb  
• 
oral  
• 
injectable  
Highly Effective Methods That Are User Independent  
• 
Implantable progestogen-only hormonal contraception associated with inhibition of 
ovulationb 
• 
Intrauterine device (IUD) 
• 
Intrauterine hormone-releasing system (IUS) 
• 
bilateral tubal occlusion 
Vasectomized partner  
(A vasectomized partner is a highly effective contraception method provided that the partner is 
the sole male sexual partner of the WOCBP and the absence of sperm has been confirmed. If not, 
an additional highly effective method of contraception should be used)  
Sexual abstinence  
(Sexual abstinence is considered a highly effective method only if defined as refraining from 
heterosexual intercourse during the entire period of risk associated with the study drug. The 
reliability of sexual abstinence needs to be evaluated in relation to the duration of the study and 
the preferred and usual lifestyle of the subject.)  
NOTES:  
a) Typical use failure rates may differ from those when used consistently and correctly. Use 
should be consistent with local regulations regarding the use of contraceptive methods for 
subjects participating in clinical studies.  
b) Hormonal contraception may be susceptible to interaction with the study drug, which may 
reduce the efficacy of the contraceptive method. In this case two highly effective methods of 
contraception should be utilized during the treatment period and for at least 6 months after the 
last dose of study drug  
 
Female Subjects 
Female subjects of reproductive potential are eligible to participate if they agree to use a 
highly effective method of contraception consistently and correctly as described in Table 5 
above.  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 78 of 110 
Pregnancy Testing  
• WOCBP should only be included after a confirmed menstrual period and a highly 
sensitive negative serum pregnancy test  
• Additional pregnancy testing will be performed at Treatment Termination after the last 
dose of study drug and as required by local clinical guidance  
• Pregnancy testing will be performed whenever a menstrual cycle is missed or when 
pregnancy is otherwise suspected  
• Pregnancy testing will be performed and assayed in a certified laboratory  
Collection of Pregnancy Information of Male subjects with partners of reproductive 
potential who become pregnant  
• Investigator will attempt to collect pregnancy information on any female partner of a 
male study subject who becomes pregnant while participating in this study. This applies 
only to subjects who receive study drug. 
• After obtaining the necessary signed informed consent from the pregnant female partner 
directly, the investigator will record pregnancy information on the appropriate form and 
submit it to Sponsor within 24 hours of learning of the partner’s pregnancy  
• Partner will also be followed to determine the outcome of the pregnancy. Information on 
the status of the mother and child will be forwarded to Sponsor 
• Generally, follow-up will be no longer than 6 to 8 weeks following the estimated 
delivery date. Any termination of the pregnancy will be reported regardless of fetal 
status (presence or absence of anomalies) or indication for procedure  
Female Subjects who become pregnant  
Any female subject who becomes pregnant while participating will discontinue study drug or 
be withdrawn from the study.  
• Investigator will collect pregnancy information on any female subject, who becomes 
pregnant while participating in this study  
• Information will be recorded on the appropriate form and submitted to Sponsor within 
24 hours of learning of a subject’s pregnancy.  
• Subject will be followed to determine the outcome of the pregnancy. The investigator 
will collect follow up information on subject and neonate, which will be forwarded to 
Sponsor. Generally, follow-up will not be required for longer than 6 to 8 weeks beyond 
the estimated delivery date.   
• Any termination of pregnancy will be reported, regardless of fetal status (presence or 
absence of anomalies) or indication for procedure.  
• While pregnancy itself is not considered to be an AE or SAE, any pregnancy 
complication or elective termination of a pregnancy will be reported as an AE or SAE.  
• A spontaneous abortion is always considered to be an SAE and will be reported as such.   
• Any SAE occurring as a result of a post-study pregnancy which is considered reasonably 
related to the study drug by the investigator, will be reported to Sponsor. While the 
investigator is not obligated to actively seek this information in former study subjects, he 
or she may learn of an SAE through spontaneous reporting.  
 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 79 of 110 
APPENDIX 6: 
ECOG PERFORMANCE STATUS CRITERIA 
ECOG Performance Status Scale 
Grade 
Descriptions 
0 
Normal activity. Fully active, able to carry on all pre-disease 
performance without restriction. 
1 
Symptoms, but ambulatory. Restricted in physically strenuous activity, 
but ambulatory and able to carry out work of a light or sedentary nature  
(e.g., light housework, office work). 
2 
In bed <50% of the time. Ambulatory and capable of all self-care, but 
unable to carry out any work activities. Up and about more than 50% of 
waking hours. 
3 
In bed >50% of the time. Capable of only limited self-care, confined to 
bed or chair more than 50% of waking hours. 
4 
100% bedridden. Completely disabled. Cannot carry on any self-care.  
Totally confined to bed or chair. 
5 
Dead 
 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 80 of 110 
APPENDIX 7: 
RECIST CRITERIA VERSION 1.1  
Response Evaluation Criteria in Solid Tumors (RECIST) Quick Reference 
ELIGIBILITY 
Only subjects with measurable or evaluable disease at baseline should be included in 
protocols where objective tumor response is the primary endpoint. 
Measurable Disease – the presence of at least one measurable lesion. If the measurable 
disease is restricted to a solitary lesion, its neoplastic nature should be confirmed by 
cytology/histology. 
Measurable Lesions – lesions that can be accurately measured in at least one dimension with 
the minimum size of: 
o 10 mm by CT scan or MRI (no less than double the slice thickness and a minimum of 
10 mm). 
o 10 mm caliper measurement by clinical exam (lesions which cannot be accurately 
measured with calipers should be recorded as non-measurable). 
o 15 mm for nodal disease in short axis 
o 20 mm by chest X-ray (if clearly defined and surrounded by aerated lung) 
o Malignant lymph node: 15 mm in short axis when assessed by CT scan (CT scan slice 
thickness no greater than 5 mm). At baseline and in follow-up only the short axis is to 
be followed. 
Non-Measurable Lesions – all other lesions, including small lesions (longest diameter 
<10 mm or pathological lymph nodes with >10 to <15 mm short axis) as well as truly non-
measurable lesions. Lesions considered truly non-measurable include leptomeningeal disease, 
ascites, pleural/pericardial effusion, inflammatory breast disease, lymphangitic involvement 
of skin or lung, abdominal masses/abdominal organomegaly identified by physical 
examination that is not measurable by reproducible imaging techniques, and nodal disease 
that is 10 to <15 mm in short axis.  
Special Considerations Regarding Lesion Measurability:  Bone lesions, cystic lesions, and 
lesions previously treated with local therapy require particular comment: 
Bone lesions: 
• 
Bone scan, PET scan or plain films are not considered adequate imaging techniques to 
measure bone lesions. However, these techniques can be used to confirm the presence or 
disappearance of bone lesions. 
• 
Lytic bone lesions or mixed lytic-blastic lesions, with identifiable soft tissue components, 
that can be evaluated by cross sectional imaging techniques such as CT or MRI can be 
considered as measurable lesions if the soft tissue component meets the definition of 
measurability described above. 
• 
Blastic bone lesions are non-measurable. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 81 of 110 
Cystic lesions: 
• 
Lesions that meet the criteria for radiographically defined simple cysts should not be 
considered as malignant lesions (neither measurable nor non-measurable) since they are, 
by definition, simple cysts. 
• 
‘Cystic lesions’ thought to represent cystic metastases can be considered as measurable 
lesions, if they meet the definition of measurability described above. However, if 
noncystic lesions are present in the same subject, these are preferred for selection as 
target lesions. 
Lesions with prior local treatment: 
• 
Tumor lesions situated in a previously irradiated area, or in an area subjected to other 
loco-regional therapy, are usually not considered measurable unless there has been 
demonstrated progression in the lesion. Study protocols should detail the conditions under 
which such lesions would be considered measurable. 
Measurement of Lesions 
• 
All measurements should be taken and recorded in metric notation, using calipers if 
clinically assessed. All baseline evaluations should be performed as closely as possible to 
the beginning of treatment and never more than 28 days before the beginning of the 
treatment. 
Methods of Measurement 
• 
The same method of assessment and the same technique should be used to characterize 
each identified and reported lesion at baseline and at each subsequent response 
assessment. Imaging based evaluation should always be done rather than clinical 
examination unless the lesion(s) being followed cannot be imaged but are assessable by 
clinical examination. 
• 
For the case of skin lesions, documentation by color photography, including a ruler to 
estimate the size of the lesion, is recommended. 
• CT is currently the best currently available and reproducible method to measure target 
lesions selected for response assessment. The CT scan slice thickness should be 5 mm or 
less. When the CT scans have a slice thickness that is greater than 5 mm, the minimum 
size for a measurable lesion should be twice the slice thickness. MRI is also acceptable.   
• Lesions on chest X-ray are acceptable as measurable lesions when they are clearly 
defined and surrounded by aerated lung. However, CT is preferable. 
• Ultrasound (US) should not be used to measure tumor lesions. The utilization of 
endoscopy and laparoscopy for objective tumor evaluations not advised. 
• Fluorodeoxyglucose positron emission tomography (FDG-PET) can be used to determine 
a new lesion if the lesion was absent at baseline on FDG-PET 
• Tumor markers alone cannot be used to assess response. If markers are initially above the 
upper normal limit, they must normalize for a subject to be considered in complete 
response when all lesions have disappeared. 
• 
Cytology and histology can be used to differentiate between PR and CR in rare cases 
(eg, after treatment to differentiate between residual benign lesions and residual 
malignant lesions in tumor types such as germ cell tumors). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 82 of 110 
Baseline Documentation of “Target” and “Non-Target” Lesions 
• All measurable lesions up to a maximum of two lesions per organ and 5 lesions in total, 
representative of all involved organs should be identified as target lesions and recorded 
and measured at baseline. 
• Target lesions should be selected on the basis of their size (lesions with the longest 
diameter [LD]) and be representative of all involved organs, but in addition should lend 
themselves accurate repeated measurements. 
• A sum of the LD for all target lesions will be calculated and reported as the baseline sum 
diameters. The baseline sum diameters will be used as reference by which to characterize 
the objective tumor. If lymph nodes are to be included in the sum, then as noted above, 
only the short axis is added to the sum. 
• If a target lesion becomes too small to measure, a default value of 5 mm is assigned.  If 
the lesion disappears, the measurement is recorded at 0 mm. 
• If extranodal target lesions fragment, the LDs of the fragmented portions are added in the 
sum. If targets lesions coalesce and cannot be distinguished, the LD of the coalesced 
lesion is added to the sum. 
• For a subject with SD or PR, a lesion which disappears and then reappears will continue 
to be measured and added to the sum. Response will depend upon the status of the other 
lesions. For a subject with CR, reappearance of a lesion is considered PD. 
• New lesions should be unequivocal and not attributable to differences in scanning 
technique or findings which may not be tumor. If a new lesion is equivocal, repeat scans 
are needed to confirm. If confirmed, PD is assessed from the date of the first scan. 
• All other lesions (or sites of disease) should be identified as non-target lesions and 
should also be recorded at baseline. Measurements of these lesions are not required, but 
the presence or absence of each or in rare case unequivocal progression should be noted 
at each subsequent response assessment. 
RESPONSE CRITERIA 
Evaluation of Target Lesions 
Complete Response (CR): 
Disappearance of all target lesions. Any pathological lymph node 
(whether target or nontarget) must have reduction in short axis to 
<10 mm 
Partial Response (PR): 
At least a 30% decrease in the sum of the diameters of target 
lesions, taking as reference the baseline sum diameters 
Progressive Disease (PD): 
At least a 20% increase in the sum of the diameters of target 
lesions, taking as reference the smallest sum on study (this includes 
the baseline sum if that is the smallest on study). In addition to the 
relative increase of 20%, the sum must also demonstrate an 
absolute increase of at least 5 mm. The appearance of one or more 
new lesions is also considered progression. 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 83 of 110 
Evaluation of Non-Target Lesions 
Complete Response (CR): 
Disappearance of all non-target lesions and normalization of tumor 
marker level. All lymph nodes must be non-pathological in size 
(ie, <10 mm short axis). 
Non-CR/Non-PD 
Persistence of one or more non-target lesion(s) and/or maintenance 
of tumor marker level above the normal limits 
Progressive Disease (PD): 
Unequivocal progression of the existing non-target lesions. The 
appearance of one or more new lesions is also considered 
progressive disease. 
Although a clear progression of “non target” lesions only is exceptional, in such circumstances, the 
opinion of the investigator should prevail. 
 
Evaluation of Overall Response 
Table 6 
Evaluation of Overall Response 
Target lesions 
Non-Target lesions 
New Lesions 
Overall response 
CR 
CR 
No 
CR 
CR 
Non-CR/Non-PD 
No 
PR 
CR 
Not evaluated 
No 
PR 
PR 
Non-PD or not all evaluated 
No 
PR 
SD 
Non-PD or not all evaluated 
No 
SD 
Not all evaluated 
Non-PD 
No 
NE 
PD 
Any 
Yes or No 
PD 
Any 
PD 
Yes or No 
PD 
Any 
Any 
Yes 
PD 
 
• Subjects with a global deterioration of health status requiring discontinuation of treatment 
without objective evidence of disease progression at that time should be classified as 
having “symptomatic deterioration”.  Every effort should be made to document the 
objective progression even after discontinuation of treatment. 
• In some circumstances it may be difficult to distinguish residual disease from normal 
tissue. When the evaluation of complete response depends on this determination, it is 
recommended that the residual lesion be investigated (fine needle aspirate/biopsy) to 
confirm the complete response status.  If described in the clinical protocol, FDG-PET 
may be used to upgrade a response to a CR in a manner similar to a biopsy in cases where 
a residual radiographic abnormality is thought to represent fibrosis or scarring 
REPORTING OF RESULTS 
All subjects included in the study must be assessed for response to treatment, even if there are 
major protocol treatment deviations or if they are ineligible. Each subject will be assigned 
one of the following categories:  1) complete response, 2) partial response, 3) stable disease, 
4) progressive disease, 5) not evaluable for response:  specify reason such as early death from 
malignant disease, early death from toxicity, tumor assessments not repeated/incomplete, or 
other (specify). 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 84 of 110 
RECIST 1.1 and iRECIST 
 
RECIST 1.1 
iRECIST 
Definitions of measurable 
and non-measurable disease; 
numbers and site of target 
disease 
Measurable lesions are 10 mm or 
more in long diameter (15 mm for 
nodal lesions); maximum of 5 
lesions (2 per organ); all other 
disease considered not target (must 
be 10 mm or longer in short axis for 
nodal disease) 
No change; however, NEW lesions are 
evaluated as per RECIST 1.1 but are 
recorded separately on the CRF (but not 
included in the sum of lesions for target 
lesions identified at baseline) 
R, PR or SD 
Cannot have met criteria for PD 
prior to CR, PR or SD 
May have had iUPD (1 or more instances), 
but not iCPD, prior to iCR, iPR or iSD 
Confirmation of CR, PR 
Only required for non-randomised 
trials 
As per RECIST 1.1 
Confirmation of SD 
Not required 
As per RECIST 1.1 
New lesions 
Results in PD. Recorded but not 
measured 
Results in iUPD but iCPD is only assigned 
based on this category if at next assessment 
• 
Additional NL appear or 
• 
Increase in size of NLs (≥5 mm for sum 
of NLT or any increase in NLNT) 
NLs, where none have previously been 
recorded can also confirm iCPD 
Independent blinded review 
and central collection of 
scans 
Recommended in some 
circumstances 
Collection of scans (but not independent 
review) recommended for all trials 
Confirmation of PD 
Not required (unless equivocal) 
Required 
Consideration of clinical 
status 
Not included in assessment 
Clinical stability (see definition) is 
considered in whether treatment is continued 
after iUPD 
NT = non-target, T = target; NL = new lesions; NLT = new lesion target; NLNT = new lesion non target; iUPD = 
unconfirmed immune PD; iCPD = confirmed immune PD; SOM= sum of measures. iCR = immune complete 
response; iPR = immune partial response; iSD = immune stable disease 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 85 of 110 
Assigning time-point response for iRECIST 
Time-point response 
Target Lesions* 
Non-Target 
Lesions* 
New 
Lesions* 
Time Point Response 
No prior 
iUPD** 
Prior iUPD**; *** 
iCR 
iCR 
No 
iCR 
iCR 
iCR 
Non-iCR/Non-
iUPD 
No 
iPR 
iPR 
iPR 
Non-iCR/Non-
iUPD 
No 
iPR 
iPR 
iSD 
Non-iCR/Non-
iUPD 
No 
iSD 
iSD 
iUPD with no change 
OR decrease from last 
TP 
iUPD with no 
change OR 
decrease from 
last TP 
Yes 
NA 
NLs confirms iCPD if NLs were 
previously identified and increase in size 
(≥5 mm in SOM for NLT or any increase 
for NLNT) or number; If no change in 
NLs (size or number) from last TP, 
remains iUPD 
iSD, iPR, iCR 
iUPD 
No 
iUPD 
Remains iUPD unless iCPD confirmed 
based in further increase in size of NT 
disease (need not meet RECIST 1.1 
criteria for unequivocal PD) 
iUPD 
Non-iCR/Non-
iUPD; iCR 
No 
iUPD 
Remains iUPD unless iCPD confirmed 
based on: 
• further increase in SOM of at least 5 
mm, otherwise remains iUPD 
iUPD 
iUPD 
No 
iUPD 
Remains iUPD unless iCPD confirmed 
based on further increase 
in: 
• previously identified T lesion iUPD in 
SOM ≥5 mm and / or 
• NT lesion iUPD (prior assessment - 
need not be unequivocal PD) 
iUPD 
iUPD 
Yes 
iUPD 
Remains iUPD unless iCPD confirmed 
based on further increase in  
• previously identified T lesion iUPD 
SOM ≥5 mm and / or 
• previously identified NT lesion iUPD 
(need not be unequivocal) and /or 
• size or number of new lesions 
previously identified 
Non-iUPD/PD 
Non-iUPD/PD 
Yes 
iUPD 
Remains iUPD unless iCPD confirmed 
based on 
• increase in size or number of new 
lesions previously identified 
* Using RECIST 1.1 principles. If no PSPD occurs, RECIST 1.1 and iRECIST categories for CR, PR and SD would 
be the same. ** in any lesion category. *** previously identified in assessment immediately prior to this TP. 
iCR = immune complete response; iPR = immune partial response; iSD = immune stable disease; iUPD = immune 
unconfirmed progression; iCPD = immune confirmed progression; NL = new lesion; NLT = new lesion target; 
NLNT = new lesion non target; T = target; TP = timepoint; NA = not applicable; NE = not evaluable / evaluated 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 86 of 110 
Assigning best overall response for iRECIST 
Best overall response 
TPR1 
TPR2 
TPR3 
TPR4 
TPR5 
iBOR 
iCR 
iCR, iPR, iUPD, NE 
iCR, iPR, iUPD, NE 
iUPD 
iCPD 
iCR 
iUPD 
iPR, iSD, NE 
iCR 
iCR, iUPD, NE 
iCR, iPR, iSD, iUPD, 
iCPD, NE 
iCR 
iUPD 
iPR 
iPR, iSD, iUPD, NE 
PR, iSD, iUPD, 
NE, iCPD 
iPR, iSD, iUPD, NE, 
iCPD 
iPR 
iUPD 
iSD, NE 
iPR 
iPR, iSD, iUPD, 
NE 
PR, iSD, iUPD, iCPD, 
NE 
iPR 
iUPD 
iSD 
iSD, iUPD, NE 
iSD, iUPD, iCPD, 
NE 
iSD, iUPD, iCPD, NE 
 
iUPD 
iCPD 
Anything 
Anything 
Anything 
iCPD 
iUPD 
iUPD (no iCPD) 
iCPD 
Anything 
Anything 
iCPD 
iUPD 
NE 
NE 
NE 
NE 
iUPD 
Examples only – many more scenarios exist but follow the same principles 
Table assumes a randomised study where confirmation of CR or PR is not required 
For patients with non-target disease only at baseline, only iCR or non-CR/non-PD can be assigned at each TPR but 
is not shown in the table for ease of presentation 
iCR =immune complete response; iPR = immune partial response; iSD = immune stable disease; iUPD = immune 
unconfirmed progression; iCPD = immune confirmed progression; NL = new lesion; NLT = new lesion target; 
NLNT = new lesion non target; T = target; TP = timepoint; NA = not applicable; NE = not evaluable / evaluated 
Source: 
As part of paper presented at the EORTC-NCI-AACR 2016 Meeting (Munich)  
Later published as part of Seymour, L., et al., iRECIST: guidelines for response criteria for 
use in trials testing immunotherapeutics. Lancet Oncol, 2017. Mar; 18(3): e143-e152.  
 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 87 of 110 
APPENDIX 8: 
ADVERSE EVENT MANAGEMENT   
These general guidelines constitute guidance to the investigator and may be supplemented by 
discussions with the Medical Monitor or designee. The guidance applies to all immuno-
oncology agents and regimens. 
A general principle is that differential diagnoses should be diligently evaluated according to 
standard medical practice. Non-inflammatory etiologies should be considered and 
appropriately treated. 
Corticosteroids are a primary therapy for immuno-oncology drug-related adverse events. The 
oral equivalent of the recommended IV doses may be considered for ambulatory subjects 
with low-grade toxicity. The lower bioavailability of oral corticosteroids should be taken into 
account when switching to the equivalent dose of oral corticosteroids. 
Consultation with a medical or surgical specialist, especially prior to an invasive diagnostic 
or therapeutic procedure, is recommended. 
The frequency and severity of the related adverse events covered by these algorithms will 
depend on the immuno-oncology agent or regimen being used. 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 88 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 89 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 90 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 91 of 110 
 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 92 of 110 
 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 93 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 94 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 95 of 110 
 
 

Mereo Biopharma 5, Inc. 
 
Etigilimab 
CONFIDENTIAL 
 
Page 96 of 110 
 
Additional Guidelines for Management of CTCAE-based immune-related hepatic adverse events (Puzanov 2017) 
Hepatitis (AST, ALT and Total Bilirubin) 
Grade 
CTCAE Description* 
1 
AST, ALT >ULN -3xULN; total bilirubin >ULN-1.5xULN 
• 
Continue study drug 
• 
Continue Liver function panel once weekly 
2 
AST, ALT >3- < 5xULN; total bilirubin >1.5 - 3xULN 
• 
Hold study drug 
• 
Rule out viral hepatitis, autoimmune disease, biliary obstruction, 
new metastasis or thrombosis 
• 
Start prednisone 0.5-1 mg/kg/day (or equivalent dose of 
methylprednisolone) with 4 week taper 
• 
Monitor liver function panel twice a week 
• 
Liver biopsy is optional 
• 
Resume study drug as per Section 5 
3 and 4 
AST, ALT >5xULN; total bilirubin >3xULN 
• 
Permanently discontinue Study Drug 
• 
Monitor liver function panel every 1–2 days 
• 
Start prednisone 1–2 mg/kg/day 
• 
If refractory after 3 days, consider mycophenolate 
• 
If liver enzymes improve, taper corticosteroid over 4 weeks 
• 
Consider liver biopsy 
* https://ctep.cancer.gov/protocoldevelopment/electronic_applications/docs/ctcae_v5_quick_reference_5x7.pdf 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 97 of 110 
APPENDIX 9: 
PROTOCOL SYNOPSIS 
Name of Sponsor: 
Mereo BioPharma 5, INC 
Name of Product: 
Etigilimab (MPH313) ‐ A humanized immunoglobulin G1 
kappa monoclonal antibody 
Title of Study: 
A Phase 1b/2 Open‐Label Study of the Efficacy and Safety of 
Etigilimab (MPH313) Administered in Combination with Nivolumab 
to Subjects with Locally Advanced or Metastatic Solid Tumors 
(ACTIVATE) 
Development Phase: 
1b/2 
 
Overall Design 
Schematic: 
 
Written description 
This is an open-label, multicenter, Phase 1b/2 basket study designed to 
evaluate the efficacy, safety, tolerability, pharmacokinetics (PK), and 
pharmacodynamics (PD) of etigilimab in combination with nivolumab in 
subjects with recurrent, locally advanced and/or metastatic solid tumors 
who are not candidates for available, curative standard of care therapies. In 
cohorts enrolling tumor types for whom anti-PD-1 antibody therapy is 
approved treatment for recurrent, locally advanced or metastatic disease, 
subjects may be enrolled prior to treatment with anti-PD-1 antibody 
therapy. Subjects will be assigned to receive etigilimab (
 mg every 
2 weeks for subjects ≥50 kg, 
 mg/kg dose every 2 weeks for subjects 
<50 kg) in combination with nivolumab (240 mg every 2 weeks) and will 
continue until protocol-defined discontinuation criteria are met. Cohorts 
will be enrolled at the discretion of the sponsor. Selected cohorts will be 
open for the first 20 subjects enrolled without increasing the total number 
of subjects proposed for the trial. During the conduct of this open label 
study an Independent Data Monitoring Committee (IDMC) will be 
established and will review study data on an ongoing basis.     
Screening period 
All screening tests must be performed within 28 days preceding Day 1 
(defined as the first day of study drug administration), unless otherwise 
indicated. Results of standard‐of‐care tests or examinations performed prior 
to obtaining informed consent and within the screening window may be 
used and do not have to be repeated if they meet protocol specifications. 
The screening period will include medical history and demographic data 
collection, physical examination including vital signs, laboratory 
assessments including hematology, serum chemistry and urinalysis, 
electrocardiogram (ECG), collection of blood for immunogenicity, PK, and 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 98 of 110 
tumor marker assessments, and collection of blood and formalin‐fixed 
paraffin‐embedded (FFPE) or fresh tumor samples for biomarker 
assessments. 
Treatment period 
Subjects will be assigned to receive etigilimab (
 mg every 2 weeks for 
subjects ≥50 kg, 
 mg/kg dose every 2 weeks for subjects <50 kg) in 
combination with nivolumab (240 mg every 2 weeks) and will continue 
until protocol-defined discontinuation criteria are met. 
Follow‐up period 
All subjects who have discontinued study drug treatment will return to the 
clinic for a treatment termination visit within 30 days after the last dose of 
etigilimab or nivolumab, whichever occurs last. Following etigilimab and 
nivolumab study treatment discontinuation, all subjects will be followed for 
survival and subsequent anti‐cancer therapy via telephone calls, subject 
medical records, and/or clinic visits approximately every 3 months until 
death, loss to follow‐up, or study termination by the sponsor unless the 
subject requests to be withdrawn from follow‐up. 
Number of subjects: 
Screened: 135 
Enrolled: 125 
Completed: 115 
Planned number of sites: 
20 (10 in US, 5 in UK and 5 in Spain) 
Planned Subject Population for Study 
Inclusion Criteria 
Subjects who have 
Cohort A  
Histologically confirmed diagnosis of endometrial carcinoma (EC);  
Note: carcinosarcoma (malignant mixed Mullerian tumor), endometrial 
leiomysarcoma and endometrial stromal sarcomas are excluded. 
Recurrent, advanced, and/or metastatic disease without potential for local 
curative surgery or radiation. 
Radiographic evidence of progression after 1 prior systemic platinum-based 
chemotherapy regimen for EC with at least 1 measurable target lesion 
according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 
that is suitable for repeat measurement including:  
• 
non-nodal lesion that measures ≥10 mm in the longest diameter 
• 
radiographic evidence of subsequent growth after locoregional 
therapy or external beam radiotherapy (EBRT). 
Up to 1 additional line of platinum-based chemotherapy if given in the 
neoadjuvant or adjuvant treatment setting. There is no restriction regarding 
prior hormonal therapy.  
Treatment with prior anti-programmed death (PD)-1/anti-programmed death 
ligand (PD L)1/2 antibodies is not allowed Cohort B. 
Histological or cytological evidence of advanced and/or recurrent or 
metastatic head and neck squamous cell carcinoma (HNSCC) or for the 
first-line treatment of subjects with metastatic or with unresectable, 
recurrent HNSCC whose tumors express PD-L1 (combined positive score 
[CPS] >1%). Diagnosis of squamous cell carcinoma of the oral cavity, nasal 
cavity, paranasal sinuses, nasopharynx oropharynx, hypopharynx. or larynx 
are permitted. Primary or recurrent disease for which no curative or 
established palliative treatments are amenable: 
• 
Subjects without prior anti-PD-1/anti-PD-L1/2 antibody treatment 
are eligible.  
Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies are 
eligible provided they have had (i) documented best observed response 
(BOR) of stable disease (SD) or better in response to an anti-PD1/PD-L1/2 
therapy, AND (ii) ≥6 weeks interval since their last dose of prior anti-PD-
1/anti-PD-L1/2 treatment 
Cohort C  
Histologically confirmed cervical cancer  
Recurrent, advanced and/or metastatic disease with disease progression on 
or after one or more lines of chemotherapy, without potential for local 
curative treatment options including systemic chemotherapy, surgery or 
radiation and PD-L1-expressing tumors (CPS >1%).  

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 99 of 110 
Note: Chemotherapy administered in the adjuvant or neoadjuvant setting, or 
in combination with radiation therapy, should not be counted as a systemic 
therapy regimen.   
Treatment with prior anti-PD-1/anti-PD L1/2 antibodies is not allowed. 
Cohort D  
Histological or cytological evidence of recurrent advanced and/or metastatic 
gastric or gastroesophageal junction adenocarcinoma whose tumors express 
PD-L1 (CPS >1%), with disease progression on or after 2 or more prior 
lines of therapy including fluoropyrimidine- and platinum-containing 
chemotherapy and if appropriate, HER2/neu-targeted therapy.  
Subjects without prior anti-PD-1/anti-PD-L1/2 antibody treatment are 
eligible.  
Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies are 
eligible provided (i) they have had documented BOR of SD or better in 
response to an anti-PD1/PD-L1/2 therapy, AND (ii) ≥6 weeks interval since 
their last dose of prior anti-PD-1/anti-PD-L1/2 treatment 
Cohort E  
Histological or cytological evidence of unresectable or metastatic tumor 
mutational burden-high (TMB-H) and microsatellite stable (MSS) solid 
tumors (TMB as defined by an FDA-approved test, e.g. Foundation 
Medicine >10 mutations/megabase or an Laboratory Developed Test 
(approved by the sponsor (e.g. Guardant Health), that have progressed 
following prior treatment and who have no satisfactory alternative treatment 
options. Subjects without prior treatment with anti-PD1 antibody treatment 
are eligible. Subjects who have received prior anti-PD-1/PD-L1/2 treatment 
are eligible with at least 6 weeks since their last dose of these prior 
treatments. Subjects must have had a previous SD or better in response to an 
anti-PD1/PDL-1/2 therapy. Subjects with the following TMB-H and MSS 
solid tumors will enroll into the tumor specific cohorts noted below after 
discussion with the sponsor: 
• 
Cohort A: Endometrial cancer PD-1/PD-L1/2 naïve 
• 
Cohort C: Cervical carcinoma 
• 
Cohort F: Rare tumors (sarcoma, uveal melanoma, germ cell 
carcinoma) 
• 
Cohort H: Ovarian cancer 
Cohort F Rare Tumors 
• 
Germ cell tumors 
Histologically or cytologically confirmed seminoma or non-seminoma 
testicular germ cell tumors 
Recurrent, advanced and/or metastatic disease, including new lesions, 
persistently elevated β-human chorionic gonadotropin (HCG) or alfa 1-
fetoprotein (AFP) or increase in consecutive elevated serum tumor markers 
(β-HCG or AFP) done at least one week apart after prior high-dose 
chemotherapy (HDCT). 
Subjects deemed not to be candidates for benefit from potentially curative 
HDCT may also be eligible including those with: 
• 
Inadequate renal function for HDCT 
• 
relapse >2 years after last therapy 
• 
inadequate stem cell collection to move forward with HDCT  
• 
significant medical or psychosocial comorbidities that are felt to be 
a contraindication to HDCT by the treating investigator. 
Subjects with serum tumor marker ≥S2 HCG and AFP (levels ≥1000 for 
AFP and ≥5000 for HCG are excluded). 
Subjects who have received prior anti-PD1/anti-PD-L1/2 antibodies are 
excluded. 
• 
Sarcoma 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 100 of 110 
Histological diagnosis (with archival or new biopsy sample available for 
pathology review) of locally advanced/unresectable and/or metastatic soft 
tissue sarcoma histopathological subtypes as noted below, who have 
radiological evidence of measurable disease and are not candidates for any 
curative surgery of multimodality therapy: 
• 
De-differentiated liposarcoma (n=10) 
• 
Undifferentiated pleomorphic sarcoma (UPS) (n=10) 
• 
Alveolar soft part sarcoma, malignant peripheral nerve sheath 
tumors, myxofibrosarcoma (grade 2 or higher), OR pleomorphic 
dermal sarcoma (total n=5) 
Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies as 
standard of care are excluded. 
• 
Uveal Melanoma 
Histologically confirmed recurrent uveal melanoma with disease 
progression beyond prior approved standard of care therapy administered in 
the advanced setting (prior surgical resection of liver metastases, local 
radiation therapy and adjuvant systemic therapy are acceptable) are eligible. 
Subjects who have received prior anti-PD1/anti-PD-L1/2 antibodies are 
excluded. 
Cohort G 
Histologically confirmed diagnosis of endometrial carcinoma (EC);  
Note: carcinosarcoma (malignant mixed Mullerian tumor), endometrial 
leiomyosarcoma, and endometrial stromal sarcomas are excluded. 
Subjects must have recurrent, advanced, and/or metastatic disease and must 
not be candidates for local curative surgery and radiation or intolerant to 
known standard of care systemic chemotherapy.  
Radiographic evidence of progression after >1 and no more than 3 prior 
systemic anti-cancer therapy regimens for EC, (neoadjuvant, adjuvant, and 
maintenance treatment are considered part of one treatment line).  
At least 1 measurable target lesion according to RECIST 1.1 that is suitable 
for repeat measurement including (i) non-nodal lesion that measures 
≥10 mm in the longest diameter (ii) radiographic evidence of subsequent 
growth after locoregional therapy or external beam radiotherapy (EBRT).  
Prior treatment with any treatment targeting vascular endothelial growth 
factor (VEGF)-directed angiogenesis, any anti-PD-1, anti-PD-L1/2 agent is 
allowed. 
• 
Subjects who have received prior anti-PD-1/anti-PD-L1/2 
antibodies are also eligible provided (i) they have had documented 
Best Observed Response (BOR) of SD or better in response to an 
anti-PD1/PD-L1/2 therapy, AND (ii) ≥ 3 months interval prior to 
first study drug administration (C1D1) since their last dose of prior 
anti-PD-1/anti-PD-L1/2 treatment 
Cohort H  
Histologically confirmed high grade serous and endometrioid ovarian 
cancer, fallopian tube cancer or primary peritoneal cancer    
Must have received a front-line platinum-based regimen per standard of care 
after primary or interval debulking surgery and have documented 
radiological disease recurrence  
Must have measurable disease by RECIST 1.1 as determined by the local 
investigator/radiology assessment including 2 sites of disease/biopsy 
accessible disease. Subjects with less than 2 sites will need approval of the 
sponsor prior to enrollment. Note: Maintenance treatment following front-
line treatment is permitted and counted together as part of the front-line 
treatment.  
Subjects who have received prior anti-PD-1/anti-PD-L1/2 antibodies as 
treatment are excluded. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 101 of 110 
Prior Cancer Treatments 
Radiation therapy must be completed >3 weeks prior to first study drug 
administration (C1D1). Participants must have recovered from all 
radiation-related toxicities and/or complications prior to enrollment. 
Palliative radiotherapy is allowed if completed at least 2 weeks prior to first 
study drug administration. Subjects must have recovered from all radiation-
related toxicities and/or complications prior to enrollment. 
Subjects must have measurable disease outside the radiation field to be 
eligible; subjects with progression in a previously radiated field will also be 
eligible. 
All toxicities attributed to prior anticancer therapy, with the exception of 
peripheral neuropathy, alopecia, vitiligo, active thyroiditis, and fatigue, must 
have resolved to Grade 1 (per National Cancer Institute Common Toxicity 
Criteria for Adverse Events (NCI CTCAE) version 5 or higher) or baseline 
of prior treatment prior to enrollment. Peripheral neuropathy must have 
resolved to Grade 2 (per NCI CTCAE version 5 or higher). 
Aged 
≥18 years 
ECOG performance status 
Eastern Cooperative Oncology Group (ECOG) of 0 or 1 
Disease status 
Have measurable disease based on RECIST 1.1 as determined by the local 
investigator/radiology assessment. Target lesions situated in a previously 
irradiated area are considered measurable if progression has been 
demonstrated in such lesions. 
Tumor tissue availability 
Confirmed availability of representative tumor specimens in paraffin blocks 
is required for enrollment with an associated pathology report including 
PD-L1 status for PD-L1 positive cohorts.  
Latest available archival tumor sample eg, within 6 months to 1 year prior to 
screening is strongly preferred. In instances where archival tissue is not 
available, a pre-dose biopsy will be required for submission with 3 core 
samples from an 18-gauge needle or larger. Only tissue from a surgical 
resection or a core needle, punch, or excisional/incisional biopsy sample 
collection will be accepted. Fine needle aspirate samples are not acceptable. 
Sponsor medical review is required if a fresh tumor biopsy cannot be 
provided during screening due to potential risk to subject from procedure. 
For endometrial cancer (Cohorts A and G) archival or fresh biopsy specimen 
for determination of mismatched repair (MMR) status is required if 
historical MMR results are unavailable.  
For study participants with sarcoma, archival tumor sample must be 
available for pathology review. If no archival material is available, a fresh 
biopsy should be performed to obtain tissue.   
Hematologic and end organ 
function 
Adequate hematologic and end organ function, defined by the following 
laboratory results obtained within 14 days prior to the first study treatment 
(Cycle 1, Day 1):  
a. Absolute neutrophil count ≥1500 cells/μL.  
b. Platelet count ≥100,000/μL (without transfusion within 14 days 
prior to Cycle 1, Day 1). 
c. Hemoglobin ≥9.0 g/dL (without transfusion of packed red blood 
cells (RBCs) or erythropoietic treatment within 14 days prior to 
Cycle 1, Day 1). 
d. Total bilirubin ≤1.5 × upper limit of normal (ULN) unless elevated 
due to Gilbert’s syndrome.  
e. Aspartate aminotransferase (AST/SGOT) and alanine 
aminotransferase (ALT/SGPT) ≤3.0 × ULN with the following 
exception:  
– Subjects with documented liver metastases:  
AST and/or ALT ≤5.0 × ULN. 
– Total bilirubin <1.5 × ULN (subjects with Gilbert’s 
syndrome may be enrolled with sponsor approval). 
f. Prothrombin time (PT)/International normalized ratio (INR), 
activated partial thromboplastin time (aPTT) ≤1.5 × ULN and INR 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 102 of 110 
≤1.5 × ULN in subjects not on anticoagulant therapy; subjects 
receiving therapeutic anticoagulation should be on a stable dose 
with PT, INR, and aPTT within the intended therapeutic range. 
g. Creatinine ≤1.5 × ULN or measured or calculated creatinine 
clearance ≥45 mL/min on the basis of the Cockcroft-Gault 
glomerular filtration rate estimation:  
(140-age) × (weight in kg) × (0.85 if female) 72 × (serum 
creatinine in mg/dL).  
Contraception 
• Male Subject: 
A male subject must agree to use a highly effective contraception as 
detailed in Appendix 5 of this protocol during the treatment period and 
for at least 6 months after the last dose of study treatment and refrain 
from donating sperm during this period. 
• Female Subject:  
A female subject is eligible to participate if she is not pregnant (see 
Appendix 5), not breastfeeding, and at least 1 of the following conditions 
applies: 
o 
Not a woman of childbearing potential (WOCBP) as defined in 
Appendix 5 
OR 
o 
A WOCBP who agrees to follow the contraceptive guidance in 
Appendix 5 during the treatment period and for at least 6 months 
after the last dose of study treatment. 
Informed Consent 
Capable of giving signed informed consent which includes compliance with 
the requirements and restrictions listed in the informed consent form (ICF) 
and in this protocol. 
Exclusion criteria 
Medical conditions 
• 
Severe allergic or anaphylactic reaction to any monoclonal antibody 
therapy, murine protein, or known hypersensitivity to any excipient 
in the study drugs. 
• 
Major surgery within 4 weeks prior to screening. 
• 
Subjects who have received radiotherapy within <1 week of starting 
study treatment, or who have unresolved associated AEs. 
• 
Following known active viral infections: 
o Known HIV infection. 
o Active Hepatitis B or Hepatitis C infection at the time of 
screening for the study. Active Hepatitis B is defined as a known 
positive HbsAg result. Active Hepatitis C is defined as a known 
positive Hep C Ab result and known quantitative hepatitis C 
(HCV) RNA results greater than the lower limit of detection of 
the assay.   
o 
Subjects with past hepatitis B virus (HBV) infection or 
resolved HBV infection (defined as the presence of hepatitis 
B core antibody [HBcAb] and absence of HBsAg) are 
eligible. HBV DNA must be obtained in these subjects prior 
to randomization. Subjects with positive Hepatitis B serology 
who are immune due to vaccination, resolved wild-type 
infection or passive immunization due to immunoglobulin 
therapy will be eligible.  
o 
Subjects with past HCV infection and positive for HCV 
antibody are eligible only if PCR is negative for HCV RNA. 
o 
History of active non-infectious pneumonitis or history of 
pneumonitis that required steroids or current pneumonitis. 
• 
Ongoing systemic bacterial, fungal, or viral infections at screening. 
NOTE: Subjects on antimicrobial, antifungal, or antiviral 
prophylaxis are not specifically excluded if all other 
inclusion/exclusion criteria are met. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 103 of 110 
• 
Female subjects who are pregnant or breastfeeding. Serum pregnancy 
test (for women of childbearing potential, including women who have 
had a tubal ligation) must be performed and documented as negative 
within 7 days prior to Cycle 1 Day 1. 
• 
Concurrent active malignancy other than non-melanoma skin cancer, 
carcinoma in situ of the cervix, or prostate intraepithelial neoplasia.  
• 
Subjects with active, known, or suspected autoimmune disease. 
Subjects with vitiligo, type I diabetes mellitus, residual 
hypothyroidism due to autoimmune condition only requiring 
hormone replacement, psoriasis not requiring systemic treatment, or 
conditions not expected to recur in the absence of an external trigger 
are permitted to enroll. Subjects with minor autoimmune disease 
after discussion with the Medical Monitor. 
• 
History of stroke, unstable angina, myocardial infarction, or 
ventricular arrhythmia requiring medication or mechanical control 
within the last 6 months prior to screening. 
• 
Unstable or severe uncontrolled medical condition (eg, unstable 
cardiac function, unstable pulmonary condition including 
pneumonitis and/or interstitial lung disease, uncontrolled diabetes) 
or any important medical illness or abnormal laboratory finding that 
would, in the investigator’s judgment, increase the risk to the subject 
associated with his or her participation in the study. 
• 
History of any Grade 3 or 4 immune-related adverse event (AE) 
toxicity from prior immunotherapy that resulted in treatment 
discontinuation. 
• 
Has primary central nervous system (CNS) malignancy or known 
untreated/active CNS metastases and/or carcinomatous meningitis.  
o Subjects with previously treated, asymptomatic brain metastases 
may participate provided they meet the following criteria: 
clinically stable for at least 4 weeks and have no evidence of new 
or enlarging brain metastases and are off steroids 14 days prior to 
dosing with study medication. Stable brain metastases by this 
definition should be established prior to the first dose of study 
drug.  
o Subjects with asymptomatic brain metastases (ie, no neurological 
symptoms, no requirements for corticosteroids, and no lesion 
>1.5 cm) may participate but will require regular imaging of the 
brain as a site of disease. 
o Subjects with CNS symptoms should undergo a computed 
tomography (CT) scan or magnetic resonance imaging (MRI) of 
the brain to exclude new or progressive brain metastases. Spinal 
cord metastasis is acceptable. However, subjects with spinal cord 
compression must be excluded. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 104 of 110 
Prior medications 
• 
Prior treatment with CD137 agonist, -CTLA-4 and anti- TIGIT 
antibodies for all cohorts. Any prior anti-PD-1 and anti-PD-L1 
therapeutic antibodies is excluded for Cohorts A, C, F and H only. 
• 
Immune-related adverse events that lead to discontinuation of prior 
immune therapies including anti-PD-1 or PDL-1 therapy. 
• 
Treatment with systemic immunostimulatory agents (including but 
not limited to interferon (IFN)α, IL2) within 6 weeks or 5 half-lives 
of the drug, whichever is shorter, prior to Cycle 1, Day 1. 
• 
Systemic anti-cancer chemotherapy, biologic therapy, or other 
investigational agent within <5 times the half-life of the agent or 
<28 days (whichever is shorter) of starting study drug with the 
following exceptions: 
o 
Hormone-replacement therapy or oral contraceptives. 
o 
Herbal therapy intended as anti-cancer therapy must be 
discontinued at least 1 week before Cycle 1, Day 1.  
o 
Subjects with castrate resistant prostate cancer should be 
allowed to remain on luteinizing hormone-releasing 
hormone analogues for medical castration.   
o 
Previously initiated chronic bisphosphonate or denosumab 
therapy for bone metastases may be continued during 
study participation. 
• 
Ongoing treatment with chronic immunosuppressants 
(eg, cyclosporine) or corticosteroids (>10 mg daily prednisone 
equivalents) or other immunosuppressive medications within 14 days 
prior to first dose of study drug. Inhaled steroids and adrenal 
replacement steroid doses >10 mg daily prednisone equivalents are 
permitted in the absence of active autoimmune disease. 
• 
Received oral or IV antibiotics within 2 weeks prior to Cycle 1, 
Day 1: 
Subjects receiving prophylactic antibiotics (e.g., for prevention of a 
urinary tract infection or chronic obstructive pulmonary disease) are 
eligible. 
• 
Administration of a live, attenuated vaccine within 4 weeks before 
Cycle 1, Day 1 or anticipation that such a live attenuated vaccine will 
be required during the study. Inactivated influenza vaccination is 
permitted during influenza season only. 
• 
History of severe allergic, anaphylactic, or other hypersensitivity 
reactions to chimeric or humanized antibodies or fusion proteins. 
Prior Procedures 
• 
Major surgical procedure within 28 days prior to Cycle 1, Day 1 or 
anticipation of need for a major surgical procedure during the course 
of the study. 
• 
Subjects who received investigational (not authorized or approved by 
relevant Health Authorities) COVID-19 vaccine or therapies prior to 
screening are not eligible without discussion with sponsor.  
• 
History of additional prior malignancy with the exception of cured 
skin, bladder, prostate, cervical, or other carcinoma in situ with no 
evidence of active disease for at least 1 year. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 105 of 110 
Study Objectives and Endpoints 
To make a preliminary assessment of the antitumor 
activity of etigilimab in combination with nivolumab 
in subjects with pre-specified locally advanced or 
metastatic solid tumors based on RECIST v1.1 
criteria. Each cohort will be evaluated independently. 
• 
Objective response rate (ORR) 
Evaluate the safety and tolerability of etigilimab 
administered in combination with nivolumab. 
• 
Count and % of subjects who experience at 
least 1 adverse event (AE) and abnormal safety 
laboratory parameters 
• 
Adverse events of special interest (AESIs; 
infusion reactions, immune-related adverse 
events) 
• 
Relationship of PK and safety 
To evaluate preliminary anti-tumor activity of 
etigilimab in combination with nivolumab according 
to RECIST v1.1. Each cohort will be evaluated 
independently. 
• 
Disease control rate (DCR; is the proportion of 
subjects whose BOR is CR, PR, or SD) 
• 
Duration of Response (DoR)  
• 
Duration of stable disease 
To characterize the PK of etigilimab in a sub-set of 
subjects who have advanced, relapsed, or refractory 
solid tumors in combination with nivolumab. 
• 
PK levels of etigilimab in combination with 
nivolumab. 
To characterize the immunogenicity of etigilimab in 
a subset of subjects who have advanced, relapsed, 
or refractory solid tumors in combination with 
nivolumab. 
• 
Anti-drug antibodies (ADA) to etigilimab; 
Impact of developed etigilimab ADAs on PK 
levels of etigilimab. 
EXPLORATORY 
To assess exploratory pharmacodynamic biomarkers 
following etigilimab treatment in combination with 
nivolumab. 
Pharmacodynamic biomarkers will be assessed to 
determine their correlation with response to 
etigilimab treatment as follows: 
• 
Changes in peripheral blood mononuclear cell 
populations and activation. 
• 
TIGIT and immune-related gene expression by 
messenger RNA (mRNA) detection 
(eg, CD226, TIGIT, T-cell genes). 
• 
Plasma proteins (eg, interleukin 17 [IL17], 
interleukin 2 [IL2], interferon gamma [IFNγ]. 
To assess potential predictive biomarkers for 
correlation with response to etigilimab treatment and 
exploratory biomarkers with treatment response. 
• 
To correlate levels of TIGIT, PVR, TMB, 
PD-L1, and other immune markers with anti-
tumor activity endpoints. 
• 
BAP1 (BRCA1 associated protein-1) tumor 
mutations with etigilimab treatment response. 
To evaluate preliminary anti-tumor activity of 
etigilimab in combination with nivolumab according 
to iRECIST. 
Each cohort will be evaluated independently. 
• 
ORR (proportion of iCR [complete response] 
plus iPR [partial response] subjects) 
• 
DoR (iRECIST) 
• 
Progression-free survival (PFS) using RECIST 
v1.1 and iRECIST 
• 
Overall survival (OS) 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 106 of 110 
Study Treatments 
Treatment under evaluation 
Etigilimab IV on Day 1 of 14‐day cycles 
 mg if subject is ≥50 kg 
 mg/kg if subject is <50 kg  
Standard of care 
Nivolumab 240 mg IV every 2 weeks (Q2W) on Day 1 of the first 14‐day 
cycle except for Cycle 1 when it will be administered on Day 3 to 
separate potential confounding infusion reactions. 
Treatment Durations 
In the absence of unacceptable toxicities or investigator‐determined 
disease progression, subjects will be offered continued study until 
progression, death, unacceptable toxicities or other reasons. 
Statistical Methods 
This is a Phase 1b/2 Open‐Label Basket Study of etigilimab (MPH313) (
 mg dose for subjects ≥50 kg, 
 mg/kg dose for subjects <50 kg) IV administered Q2W with nivolumab 240 mg Q2W to evaluate 
preliminary anti-tumor activity, safety and tolerability, PK parameters, immunogenicity, and biomarkers in up 
to 9 cohorts of subjects with EC, HNSCC, cervical cancer, ovarian cancer, gastric cancer and 
gastroesophageal junction adenocarcinoma, TMB-H/MSS cancer, sarcoma, germ cell tumors, and uveal 
melanoma) Each cohort will be evaluated using a Simon Two-Stage design appropriate to the clinically 
meaningful response rate for the indication. Interim futility monitoring for each individual cohort using the 
clinically meaningful response rate criteria per cohort will be carried out in accordance with the optimal 
Simon Two-Stage design when up to 10 subjects have sufficient data (either discontinued study drug 
treatment or having at least one post-baseline imaging assessment) for ORR and DoR evaluation by 
RECIST v1.1. For each cohort, the second stage may be opened for enrollment only after discussion with the 
IDMC and the sponsor. 
Type 1 Cohort 
The null hypothesis that the true response rate is 0.05 will be tested against a one-sided alternative that the 
true response rate is at least 0.2. In the first stage, 10 subjects will be enrolled and enrollment in this cohort 
will be halted until the response data are mature. If there are fewer than 1 responder in these 10 subjects, 
further enrollment in the cohort may be stopped after review of efficacy and safety data, and discussion by 
Sponsor with the IDMC. Otherwise, once 1 or more responders in stage 1 are observed, 19 additional subjects 
may be enrolled for a total of 29. The null hypothesis will be rejected and the treatment will be declared 
effective and worthy of further testing if 4 or more responders are observed in 29 subjects. This design yields 
a type I error rate of 0.0468 and power of 80.11% when the true response rate is 0.2. 
Type 2 Cohort 
The null hypothesis that the true response rate is 0.1 will be tested against a one-sided alternative that the true 
response rate is at least 0.3. In the first stage, 10 subjects will be enrolled and enrollment in this cohort will be 
halted until the response data are mature. If there are fewer than 2 responders in these 10 subjects, enrollment 
in the cohort may be stopped after review of efficacy and safety data, and discussion by Sponsor with the 
IDMC. Otherwise, once 2 or more responders in stage 1 are observed, 19 additional subjects may be enrolled 
for a total of 29. The null hypothesis will be rejected and the treatment will be declared effective and worthy 
of further testing if 6 or more responders are observed in 29 subjects. This design yields a type I error rate of 
0.0471 and power of 80.51% when the true response rate is 0.3. 
The Intent-to-Treat (ITT) analysis set is defined as all subjects who signed an informed consent form and 
were enrolled into the study. 
The Safety analysis set is defined as all subjects who received any amount of study drug. All safety analyses 
will be performed using the Safety analysis set. 
The Response-Evaluable analysis set is a modified ITT analysis set defined as all subjects with measurable 
disease at baseline who received study treatment and had at least one post-baseline response assessment or 
discontinued treatment due to disease progression (including death due to disease progression) within 
16 weeks (+ a 2-week window) of the first dose of study treatment. All efficacy analyses will be performed 
using the Response-Evaluable analysis set. 
Efficacy analyses will be performed separately for each cohort. RECIST 1.1 criteria will be used for primary 
endpoint evaluation (Eisenhauer et al., 2009), iRECIST will be used for exploratory endpoint response 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 107 of 110 
evaluation (Seymour et al., 2017). The iRECIST endpoints are analyzed using the same statistical 
methodology and the results will be presented in the same ways for the corresponding RECIST 1.1 endpoints.  
The primary efficacy endpoint is the objective response rate (ORR) defined as the proportion of subjects who 
achieve confirmed CR or PR per RECIST v1.1. The best overall response is the best response recorded from 
the start of the treatment until PD. The smallest measurements recorded since the treatment started will be 
used as the reference for PD. Subjects with CR or PR are considered to have obtained objective response. 
Subjects with not-evaluable response (NE) are counted as non-responders. Exact 95% confidence intervals 
will be constructed for the ORR for each cohort. 
Disease control rate: Subjects with CR, PR or SD are considered to have achieved disease control. Disease 
control rate is defined as the proportion of subjects who have achieved CR, PR, and SD. Duration of 
Response only applies to subjects whose best overall response is CR or PR and is defined as the number of 
days from the first documentation of objective tumor response to the date of first PD or death due to 
underlying cancer. 
Duration of stable disease is measured from the start of the treatment (the first treatment date for non-
randomized studies, the randomization date for randomized studies) until the date when the criteria for overall 
disease progression are first met. Duration of stable disease is defined as follows for the following cohort will 
also be considered for Simon-2 Stage futility monitoring in the rare cancer cohort for subjects with germ cell 
tumors only. 
Progression-free Survival 
PFS is defined as the number of days from Day 1 in Cycle 1 to the first documented progression or death due 
to any cause. Only deaths that occurred within 30 days of the last progression assessed. 
OS, PFS, and DoR will be summarized for each group using Kaplan-Meier methodology. Censoring rules will 
be detailed in the statistical analysis plan. 
• 
For analysis of OS, all subjects will be followed for survival for up to 2 years, until withdrawal of 
consent, loss to follow-up, or death, whichever occurs first. At the time of analysis of OS, any 
subjects who remain alive will be censored at the last date they were known to be alive. 
• 
PFS is the time from the start of study treatment to the first evaluation showing PD or death, 
whichever occurs first. Subjects who do not experience PD or death will be censored per the 
censoring rules in the statistical analysis plan. 
DoR is the time from first evaluation showing CR or PR (response confirmation required at subsequent tumor 
assessment no earlier than 4 weeks after first evaluation showing CR or PR) to the time of the first subsequent 
evaluation showing PD or death. Only subjects who experience a confirmed CR or PR will be analyzed for 
DoR. Subjects who do not experience PD or death will be censored per the censoring rules in the statistical 
analysis plan. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 108 of 110 
The Safety analysis set is defined as all subjects who received any amount of study drug.  All safety analyses 
will be performed using the Safety analysis set. 
Adverse events will be coded using the Medical Dictionary for Regulatory Activities (MedDRA) version 18.0 
or higher and will be graded according to the NCI‐CTCAE, v 4.03 or higher. 
Summaries of AEs will be based on treatment‐emergent AEs (TEAEs). A TEAE is an AE that emerges or 
worsens in the period from the first dose of study treatment etigilimab or nivolumab, whichever is earlier) to 
100 days after the last dose of etigilimab or nivolumab (whichever is dosed last) or until starting another 
treatment. 
TEAEs will be summarized by treatment group and by the frequency of subjects experiencing TEAEs 
corresponding to MedDRA system organ classes and preferred terms. 
Separate tabulations will also be produced for TEAEs assessed as related to study drug(s), TEAEs that led to 
treatment discontinuation, TEAEs that led to death, and TEAEs ≥Grade 3 in severity. Treatment‐emergent 
serious adverse events (SAEs) and SAEs related to study drug(s) will also be tabulated. 
Laboratory results (hematology, serum or plasma chemistry and coagulation) and the corresponding change 
from baseline values will be summarized by group and scheduled timepoint. A shift table, tabulation for 
baseline to each scheduled assessment and the worst post treatment value according to the CTCAE grade, will 
be provided for selected clinical laboratory tests. Laboratory results together with the normal ranges and 
CTCAE grade will be listed. Lab values that are below or above the normal ranges will be flagged. 
Vital signs and ECGs and the corresponding changes from baseline will be summarized by group and 
scheduled timepoint. 
The PK analysis set will include all Phase 1b subjects with sufficient plasma concentration data to allow the 
characterization of the PK parameters. Plasma etigilimab concentration data at each assessment timepoint will 
be summarized and listed and will be plotted across time. Pharmacokinetic parameters will be calculated using 
non-compartmental techniques from plasma concentrations and will include the following parameters: 
maximum concentration observed, clearance, elimination half-life, and area under the curve. Pharmacokinetic 
parameters will be summarized descriptively for each group.  
The immunogenicity analysis set will include all subjects with at least one evaluable post-treatment 
immunogenicity sample. Blood samples for evaluation of anti-drug antibodies (ADA) will be collected to 
determine the relationship between ADA and etigilimab PK parameters. 
Blood samples for evaluation of pharmacodynamics biomarkers, immune biomarkers, and exploratory 
predictive biomarkers will be collected from all subjects to determine their correlation with ORR and DCR. 
Independent Data Monitoring Committee: 
An Independent Data Monitoring Committee (IDMC), consisting of at least 3 members with expertise in their 
field of practice as well as in the conduct of clinical studies, will hold regularly scheduled data review 
meetings. The IDMC will consist of at least 3 members with expertise in their field of practice as well as in 
the conduct of clinical studies. The committee members will be free of significant conflicts of interest. The 
IDMC will hold regularly scheduled data review meetings at pre-specified intervals as defined in the IDMC 
charter. The IDMC will also be available on an ad hoc basis e.g. to provide guidance related to any emerging 
safety signals or if requested by the sponsor. 
Independent Response Committee: 
The sponsor may have an independent assessment of responses to verify investigator‐reported responses. The 
responses based on independent assessments, if available, will be used for sensitivity analysis. 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
 
 
 
Page 109 of 110 
APPENDIX 10: 
SUMMARY OF VERSIONS AND CHANGES  
Summary of Versions 
Protocol 
Version 
Date 
Summary of Change 
Original 
1.0 
11 September 2020 Not Applicable 
Amendment 1 
2.0 
20 October 2020 
Added etigilimab weight-based dosing, dose adjusting guidelines for weight-based 
dosing, clarified the schedule for PK and ADA sample collection, limited the time 
that diluted etigilimab can remain in solution to 4 hours prior to administration, 
defined protocol deviations that will be reported in the Clinical Study Report, and 
made other administrative changes. 
Amendment 2 
3.0 
26 March 2021 
Refinement of basket study design and modification of cohort inclusion criteria for 
study population. Clarification around inclusion requirements. Adjustments to 
treatment hold and discontinuation criteria. Inclusion of iRECIST criteria as 
exploratory endpoint.  
General corrections and administrative changes. 
Amendment 3 
4.0 
29 June 2022 
Frequency of IDMC meetings clarified to be consistent with the language in 
the IDMC charter, supporting flexibility based on rate of accrual and amount 
of new data for review with the IDMC. 
 
Protocol Amendment 3 V4.0 Changes 
Sections Applied 
Rationale 
Removal of language that was inconsistent with IDMC 
Charter 
Section 1.3, Study Design; 
and Appendix 9; Protocol 
Synopsis 
Flexibility needed as captured in IDMC charter 
based on rate of accrual and amount of new data for 
review with the IDMC 
 

Mereo Biopharma 5, Inc. 
Etigilimab 
CONFIDENTIAL 
Page 110 of 110 
APPENDIX 11: 
SPONSOR’S ELECTRONIC PROTOCOL SIGNATURE PAGE 
 

Signature Page for MPH313-1-02_Protocol_V4.0_29Jun2022 v4.0
Signature Page for VV-TMF-65634 v4.0
Reason for signing: Approved
Name:
Function:
Date of signature: 29-Jun-2022 12:01:28 GMT+0000
Reason for signing: Approved
Name:
Function:
Date of signature: 29-Jun-2022 12:19:26 GMT+0000