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A Phase **1B Dose-escalation Trial of Human Anti-4-1BB Agonistic Antibody**  
  
Utomilumab (PF-05082566) **in Combination with**
Ado-trastuzumab Emtansine or Trastuzumab in **Patients with**
HER2-postive Advanced Breast Cancer
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confidential

21 September 2020 Protocol Director / Principal Investigator **/ IND-holder**
George W Sledge, Jr, MD, Professor of Medicine Chief, Division of Oncology Stanford University School of Medicine, CCSR 1115 69 Campus Drive West Stanford, CA 94305-5456 Telephone: XXX-XXX-XXXX; Fax: XXX-XXX-XXXX
e-mail: gsledge@stanford.edu Biostatistician George W Sledge, Jr, MD
(with support from the Stanford Cancer Institute biostatistics core service, and from Pfizer)
IRB-37299 BRS0070 NCT03364348
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participating investigators and center

The participating Clinical Center is Stanford University, Stanford (USA). Details of the Principal Investigators, Sub-investigators, and other key study personnel are recorded on the Participating Investigators and Centers list Trial Master File.  
| IND:                  | IND 131822      |
|-----------------------|-----------------|
| IRB number:           | IRB-37299       |
| Initial IRB approval: | 25 October 2016 |
| Initial SRC approval: | 25 May 2017     |  
| PROTOCOL VERSION AND AMENDMENT HISTORY: Protocol  Amendment No. Date of Issue Reason for Protocol Amendment Incorporation of comments from FDA and Stanford Cancer Institute  Amendment 1 1 Nov 2016 Scientific Peer Review Committee  (See Appendix 8 Change Summary Tables)  Objectives and Endpoints re-stated and re-organized to enable  revised expression of ClinicalTrials.gov outcomes consistent with  ClinicalTrials.gov requirements   Clarify duration of treatment Amendment 2 16 Nov 2017 1. The name used for study agent PF-05082566 is updated to  utomilumab. For ease of review, this is only tracked in  presentations of the protocol title.  2. Updates clinical experience and safety profile of utomilumab.  3. Eligibility criteria and Eligibility Checklist harmonized to a single  instance at Section 3.1. Note: the move of the checklist is not  tracked in track document, changes to the eligibility are tracked.  4. Eligibility criteria are simplified and edited for clarity, and revised  to improve eligibility of appropriate candidate subjects 5. Clarifies that cohort accrual, ie, to utomilumab in combination  with ado-trastuzumab emtansine (T-DM1) or trastuzumab, will be  in parallel.  6. The sample size has been decreased to not exceed the first step of  the Simon two-step study design.  7. References to the sponsor-investigator, other investigators, and the  utomilumab manufacturer have been aligned to those roles.  8. Information regarding oversight of possible additional clinical  sites has been added throughout.  9. Performance windows defined for procedures. 10. Collection of blood samples for pharmacokinetics harmonized to  other procedures 11. Treatment beyond 24 cycles (about 18 months) will be allowed by  investigator discretion.  12. Study identifiers, including NCT number, added to title page 13. CTCAE reference updated to version 5 14. Verbatim change summary table (Appendix 8 and 9) deleted. 15. Other changes as indicated.Amendment 3 11 Mar 2019   |
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| Clarifies/harmonizes the response evaluation criteria as the Response  Evaluation Criteria in Solid Tumors (RECIST) v1.1 rather than  immune-related RECIST. Removes reference to extended treatment after 24 cycles (te3xt for  Study Schema), and clarifies rationale for continued dosing  (Section 8.9). Clarifies Inclusion Criteria regarding prior treatment, for Cohort 1  and 2 (Section 3, Inclusion Criteria 1) Removes unnecessary details in Exclusion Criteria regarding venous  thromboembolism (Section 3, Exclusion Criteria 14) Harmonizes study schema at Figure 9 to correct version (see pg 12). Clarifies window for administration of ado-trastuzumab emtansine  and trastuzumab (Section 5.5) Clarifies timing and requirements for tumor assessments (Section 5.5)   |                                                                                                                                                      |    |                                        |
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| Amendment 4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 25 Jul 2019                                                                                                                                          |   | Makes the study a single-center study. |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | Close enrollment in Cohort 2 (utomilumab plus trastuzumab) with  a total of 5 subjects enrolled.                                                     |    |                                        |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | For Cohort 1 (utomilumab plus ado-trastuzumab-emtansine),  specify a maximum enrollment of 17 subjects to received 100 mg  ado-trastuzumab-emtansine |    |                                        |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | Total protocol enrollment is up to 25 subjects                                                                                                       |    |                                        |
| Amendment 5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 6 Mar 2020                                                                                                                                           |    |                                        |
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signature page sponsor-investigator signature

I have read and agree to the protocol, as detailed in this document. I am aware of my responsibilities as an Investigator under the guidelines of Good Clinical Practice (GCP),1the Declaration of Helsinki,2the Code of Federal Regulations (CFR) Title 21,3the applicable regulations of the relevant entities (Stanford University, Stanford Hospitals and Clinics), and the clinical trial protocol. I agree to conduct the trial according to these regulations and guidelines and to appropriately direct and assist the staff under my control, who will be involved in the trial, and ensure that all staff members are aware of their clinical trial responsibilities.  
| Investigator's Name:   | George W Sledge, Jr, MD   |
|------------------------|---------------------------|  
Name of Site: Stanford Hospitals and Clinics, Stanford University Investigator's Signature: __________________________________________  
1 FDA Guidance for Industry: E6 Good Clinical Practice Guidelines, April 1996. 2 World Medical Association , Declaration of Helsinki - Ethical Principles for Medical Research Involving Human Patients. 3 United States Code of Federal Regulations (CFR), Title 21, Food and Drugs.  
| TABLE OF CONTENTS Section                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | Page Number   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|
| Protocol Synopsis 7 Study Schema 13 1. BACKGROUND 16 1.1 4-1BB Target Biology and Mechanism of Action 16 1.2. Preclinical Profiles of PF-05082566 17 1.2.1. In vitro Data 17 1.2.2. In vivo Data 18 1.2.3. Clinical Experience 18 1.3. Trastuzumab and Ado-Trastuzumab Emtansine 30 1.4. Study Rationale 31 1.4.1. Rationale for the Combination of Utomilumab with Ado-Trastuzumab  and Trastuzumab 31 1.4.2. Rationale for Utomilumab and Ado-Trastuzumab/Trastuzumab Doses 34 1.4.2.1. Utomilumab 34 1.4.2.2. Ado-Trastuzumab / Trastuzumab 36 2. STUDY OBJECTIVES; ENDPOINTS; AND OUTCOMES 36 2.1. Objectives 36 2.2. Endpoints 37 2.3. ClinicalTrials.gov Outcomes 38 3. PARTICIPANT SELECTION 38 3.1. Inclusion Criteria 39 3.2. Exclusion Criteria 42 3.3. Informed Consent Process 45 3.4. Study Timeline 45 4. STUDY DESIGN 45 4.1. Starting Dose Selection Strategy 45 4.2. Criteria for Dose-Escalation 45 4.3. Expansion Phase 1B Cohorts 1 and 2 48 4.4. Dose-limiting Toxicity (DLT) Definition 48 4.5. Maximum-tolerated Dose (MTD) Definition 49 4.6. Recommended Phase 2 Dose (RP2D) Definition 49 |               |  
| 4.7.                                                                                                                                          | Concomitant Medication and Supportive Care Guidelines ..........................................49                                                |
|-----------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------|
| Criteria for Removal From Study  ..............................................................................................50             |                                                                                                                                                   |
| 4.8.                                                                                                                                          | Alternatives to study participation......................................................................................................51       |
| 4.9.                                                                                                                                          |                                                                                                                                                   |
| INVESTIGATIONAL AGENT INFORMATION                                                                                                             |                                                                                                                                                   |
| Physical, Chemical, and Pharmaceutical Properties and Formulation  ...................51                                                      |                                                                                                                                                   |
| 5.1                                                                                                                                           | Formulation of utomilumab Solution for Intravenous administration ....................51                                                          |
| 5.2                                                                                                                                           | Agent Accountability .                                                                                                                            |
| 5.3                                                                                                                                           | Drug Storage and Accountability ...........................................................................................................52     |
| 5.4                                                                                                                                           | Drug Administration                                                                                                                               |
| 5.5                                                                                                                                           |                                                                                                                                                   |
| DOSE MODIFICATIONS .                                                                                                                          |                                                                                                                                                   |
| ASSESSMENTS                                                                                                                                   |                                                                                                                                                   |
| Se                                                                                                                                            |                                                                                                                                                   |
| 7.1                                                                                                                                           | Adverse Events ................................................................................................................................57 |
| 7.1.1                                                                                                                                         |                                                                                                                                                   |
| 7.1.2                                                                                                                                         | Laboratory Safety Assessments .........................................................................................57                         |
| 7.1.3                                                                                                                                         | Vital Signs and Physical Examination .........................................................................57                                  |
| EG Assessments                                                                                                                                |                                                                                                                                                   |
| 7.1.4                                                                                                                                         |                                                                                                                                                   |
| Tumor Response Assessments ...........................................................................................................58      |                                                                                                                                                   |
| 7.2                                                                                                                                           |                                                                                                                                                   |
| 7.3                                                                                                                                           | Pharmacokinetic Assessment .                                                                                                                      |
| Immunogenicity Assessment                                                                                                                     |                                                                                                                                                   |
| 7.4                                                                                                                                           |                                                                                                                                                   |
| 7.5                                                                                                                                           | Pharmacodynamic Assessments .........................................................................................................59           |
| 7.5.1. Blood for Immunomodulation/Cytokine Release Biomarkers ....................59                                                          |                                                                                                                                                   |
| 7.5.2. Pharmacodynamic Assessment of Lymphocyte Subpopulations ..................60                                                           |                                                                                                                                                   |
| 7.5.3. T-cell receptor assessment........................................................................................60                   |                                                                                                                                                   |
| 7.6                                                                                                                                           | Tumor Biopsies.............................................................................................................................60     |
| ADVERSE EVENT REPORTING ....................................................................................................60                |                                                                                                                                                   |
| 8.1                                                                                                                                           | Reporting Period ..............................................................................................................................61 |
| Definition of an Adverse Event ...................................................................................................61          |                                                                                                                                                   |
| 8.2                                                                                                                                           |                                                                                                                                                   |
| 8.3                                                                                                                                           | Abnormal Test Findings............................................................................................................62              |
| 8.4                                                                                                                                           | Serious Adverse Events .................................................................................................................62        |
| Causality Assessment.......................................................................................................................62 |                                                                                                                                                   |
| 8.5                                                                                                                                           | Risks Associated with Trastuzumab ...................................................................................63                           |
| 8.6                                                                                                                                           |                                                                                                                                                   |
| 8.7                                                                                                                                           | Risks Associated with Ado-Trastuzumab Emtansine ....................................................64                                            |
| Infusion-Related Symptoms with Hypersensitivity Reactions .....................................65                                             |                                                                                                                                                   |
| 8.8                                                                                                                                           |                                                                                                                                                   |  
5.  
6.  
7.  
8.  
| 8.9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | Rationale for Continued Dosing 66                                                                                                                                                                                                                                                                                     |
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| 9.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | CORRELATIVE/SPECIAL STUDIES 66 9.1 Biomarkers 66                                                                                                                                                                                                                                                                      |
| 10.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | REGULATORY CONSIDERATIONS 66 10.1 Institutional Review of Protocol 66 10.2 Clinical Site Selection for Stanford Sponsored Clinical Investigation 67 10.3 Site Communication 68 10.4 Subject Registration 68 10.5 Data and Safety Monitoring Plan 69 10.6 Data Management Plan 69 10.7 Ethical Conduct of the Study 69 |
| 11. STUDY DISCONTINUATION CRITERIA 69 12. PUBLICATIONS BY INVESTIGATORS 70 13. DATA ANALYSIS/STATISTICAL METHODS 70 13.1 Analysis Sets 70 13.2 Statistical Methods and Sample Size Determination 71 13.3 Efficacy Analysis 71 13.4 Analysis of Pharmacokinetics and Pharmacodynamics 71 13.4.1 Analysis of Pharmacokinetics of Study Drugs 71 13.4.2. Analysis of Immunogenicity Data of Study Drugs 72 13.4.3. Analysis of Biomarker Endpoints 72 13.4.4. Population Pharmacokinetic Analysis or Pharmacokinetic / Pharmacodynamic (PK/PD) Modeling 72 13.5 Safety Analysis 72 13.5.1 Analysis of the Primary Endpoint 72 13.5.2 Analysis of Secondary Safety Endpoints 72 14. REFERENCES 74 Appendix 1 Determination of Efficacy - Solid Tumors 76 Appendix 2 ECOG Performance Status 80 Appendix 3 Schedule of Activities 81 Appendix 4 Tumor Biopsy Recommendations 85 Appendix 5 Correlative / Special Studies - Biomarkers 87 Appendix 6 List of Abbreviations 88 |                                                                                                                                                                                                                                                                                                                       |
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1. protocol synopsis

| FULL TITLE                                                                                                                                                                                                                                                                                                                                                                                                            | A Phase 1B Dose Escalation Trial of human anti-4-1BB  agonistic antibody utomilumab (PF-05082566) in combination  with ado-trastuzumab-emtansine or trastuzumab in patients with HER2-positive advanced breast cancer                                                                                                                          |
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| SHORT TITLE                                                                                                                                                                                                                                                                                                                                                                                                           | Phase 1B Trial of Utomilumab (PF-05082566) in Combination  with Ado-trastuzumab emtansine or Trastuzumab in HER2-positive  Advanced Breast Cancer                                                                                                                                                                                              |
| STUDY PHASE                                                                                                                                                                                                                                                                                                                                                                                                           | 1B                                                                                                                                                                                                                                                                                                                                             |
| INVESTIGATIONAL                                                                                                                                                                                                                                                                                                                                                                                                       | Fully human anti-4-1BB agonistic antibody utomilumab                                                                                                                                                                                                                                                                                           |
| PRODUCT                                                                                                                                                                                                                                                                                                                                                                                                               | Estimate the maximum-tolerated dose (MTD) and determine the                                                                                                                                                                                                                                                                                    |
| PRIMARY  OBJECTIVES                                                                                                                                                                                                                                                                                                                                                                                                   | recommended phase 2 dose (RP2D) of utomilumab in combination  with ado-trastuzumab emtansine (T-DM1) in subjects with  HER2-positive advanced breast cancer.                                                                                                                                                                                   |
| SECONDARY                                                                                                                                                                                                                                                                                                                                                                                                             | 1) Determine the objective tumor response rate (ORR)                                                                                                                                                                                                                                                                                           |
| OBJECTIVES                                                                                                                                                                                                                                                                                                                                                                                                            | 2) Determine the time-to-tumor response (TTR) 3) Determine the duration of response (DR) 4) Determine progression-free survival (PFS) 5) Assess the safety and tolerability of utomilumab in combination  with ado-trastuzumab emtansine or trastuzumab                                                                                        |
| EXPORATORY                                                                                                                                                                                                                                                                                                                                                                                                            | 1) Evaluate the pharmacokinetics (PK) of utomilumab and                                                                                                                                                                                                                                                                                        |
| OBJECTIVES                                                                                                                                                                                                                                                                                                                                                                                                            | ado-trastuzumab emtansine or trastuzumab when given in  combination                                                                                                                                                                                                                                                                            |
| 2) Evaluate the immunogenicity of utomilumab and  ado-trastuzumab emtansine or trastuzumab when given in  combination 3) Assess the presence of CD8+ T-cells in HER2-positive tumors  4) To evaluate the modulation of immune activity biomarkers by utomilumab in combination with ado-trastuzumab emtansine or  trastuzumab Analysis of samples from subjects who received utomilumab and  trastuzumab is optional. |                                                                                                                                                                                                                                                                                                                                                |
| ClinicalTrials.gov  PRIMARY  OUTCOME                                                                                                                                                                                                                                                                                                                                                                                  | Incidence of dose-limiting toxicities (DLTs) within the first  2 cycles (up to about 2 months) reported for Dose-finding  Cohorts 1 (ado-trastuzumab emtansine) and 2 (trastuzumab).  Subjects lost to follow-up before completion of first 2 cycles due to  reasons unrelated to treatment-related adverse events are not  evaluable for DLT. |  
| ClinicalTrials.gov  SECONDARY  OUTCOMES   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | Objective tumor response rate (ORR) after 2 cycles for subjects  in Expansion Phase 1B Cohort 1 (ado-trastuzumab emtansine),  per RECIST v1.1 (for solid tumors per Appendix 1)   |
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|                                          | Time-to-event measures, for subjects in Expansion Phase 1B  Cohort 1 (ado-trastuzumab emtansine) who have at least 1  on-study tumor assessment: o Time-to-tumor response (TTR), per RECIST v1.1 (see Appendix 1), in subjects that respond within 4 months. o Duration of response (DR), per RECIST v1.1 (see Appendix 1), in subjects that respond, through up  to 5 years after treatment.  o Progression-free survival (PFS) of subjects (percentage) who  initiate treatment, reported as the number who remain alive  without progression 6 months after treatment. Subjects  withdrawn for treatment-related AEs, or lost to follow-up  before 6 months, will report as the last date known alive |                                                                                                                                                                                   |
|                                          | Incidence of all adverse events (not including laboratory  abnormalities) while receiving treatment and within 30 days,  reported by treatment group for severity (as graded by NCI  CTCAE v5), seriousness (YES/no), and relationship to the study  treatments                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                   |
|                                          | Incidence of laboratory abnormalities reported by treatment  group for severity (as graded by NCI CTCAE v5)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                   |
| KEY ELIGIBILITY                           | Eligibility criteria are extensive. Eligible subjects are cancer                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                   |
| CRITERIA                                  | patients in otherwise general good health (ECOG 0 to 1), with a  history of biopsy-proven HER2-overexpressing breast cancer and  radiographic evidence of metastatic disease, or locally recurrent  unresectable disease. Acceptable methods of contraception  required.  See Eligibility Criteria and Participant Eligibility Checklist at  Section 3.1.                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                   |  
| TREATMENT   | Study Rationale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| SUMMARY     | Utomilumab is a new molecular entity that binds to human 4-1BB  with high affinity and specificity. In vitro and in vivo data  demonstrated significant immunomodulatory activity and  anti-tumor activity of utomilumab when dosed as a single agent and  in combination with ADCC-inducing antibodies. Preclinical and  the ongoing phase 1 first-in-human studies have shown favorable  PK properties and safety profiles suggest that it may be  well-tolerated when administered IV. Based upon the above considerations, this phase 1B study will  assess the safety and identify the recommended phase 2 dose  (RP2D) of utomilumab in subjects with advanced/metastatic  HER2-overexpressing breast cancer in combination with  ado-trastuzumab emtansine or trastuzumab. During  dose-escalation, consecutive dose cohorts of subjects will receive  utomilumab (20 or 100 mg) administered once every 3 weeks as an  IV infusion in conjunction with ado-trastuzumab emtansine or  trastuzumab. During dose-expansion, 2 cohorts (one for each  combination regimen) will accrue subjects to the selected dose of  utomilumab. Treatment with study drugs will continue until completion of  24 cycles of treatment (up to about 18 months), confirmed disease  progression, subject refusal, unacceptable toxicity, whichever  occurs first, or the study is prematurely terminated by the Sponsor,  or one of the other reasons for subject withdrawal as specified in  Section 4.8 will occur. Treatment beyond 24 cycles (18 months) will be allowed only if reviewed and approved by the Principal  Investigator.  Based on preclinical studies and the ongoing phase 1 trial, the  utomilumab dosing will begin at 20 mg, then step to 100 mg.  Given the scientific rationale and preclinical data suggesting  synergistic effect of utomilumab given in combination with  ADCC-inducing mAbs, this study will primarily assess the safety  and determine the utomilumab RP2D given in combination with  trastuzumab or ado-trastuzumab emtansine. In both dose-escalation  and expansion cohorts, subjects will be assessed for DLTs for the  first 2 cycles of treatment. PK and immunogenicity of utomilumab and ado-trastuzumab emtansine or trastuzumab will be assessed,  and pharmacodynamic (PD) markers of immunomodulatory activity  will be examined. |  
| SAMPLE SIZE   | Up to 30 subjects, to achieve 25 evaluable subjects.  Up to a maximum of 20 subjects in Cohort 1 (utomilumab plus ado-trastuzumab emtansine), consisting of 3 subjects who  receive utomilumab 20 mg IV, and up to 17 who receive  utomilumab 100 mg IV. Subject replacement shall not exceed 5  additional subjects.  5 subjects in Cohort 2 (utomilumab and trastuzumab).  Cohort 2 closed in January 2020.   |
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study schema

It is to note that other more complex adaptive trial designs were considered, however as just  
 2 doses of utomilumab will be tested in combination with ado-trastuzumab emtansine or trastuzumab, and as the safety of utomilumab IV has been well tolerated to date in combination with other ADCC-inducing mAbs (with defined PK), the following dosing scheme has been devised as an efficient means to arrive at the RP2D: Due to differences in eligibility between Cohort 1 and Cohort 2, dose-finding and dose-escalation are not dependent between cohorts, and may occur at different times. Accrual to both cohorts for dose-finding and dose-escalation will occur in parallel to optimize efficiency in dose-finding.
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cohort 1 ado-trastuzumab emtansine

Dose **Level** 1 - Utomilumab 20 mg IV + ado-trastuzumab emtansine (T-DM1) 3.6 mg/kg IV every 3 weeks. 3 subjects will be treated at this dose level. If no DLT events are recorded, then utomilumab dose will be increased to 100 mg (Dose Level 2, below). If 1 DLT is observed amongst the first 3 subjects, then Dose Level 1 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab will proceed to 100 mg (Dose Level 2). If 2 (or more) DLTs are recorded at Dose Level 1, enrollment in the ado-trastuzumab emtansine + utomilumab cohort will be terminated. Dose **Level** 2 - Utomilumab 100 mg IV + ado-trastuzumab emtansine 3.6 mg/kg IV every 3 weeks. 3 subjects will be dosed initially. If one DLT is observed, Dose Level 2 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab 100mg IV + ado-trastuzumab emtansine 3.6 mg/kg IV will be expanded to 9 subjects to gain further confidence in the RP2D determination. If no DLTs are observed in the first 3 subjects, then Dose Level 2 will also be expanded to 9 subjects total to define the RP2D. If more than 2 DLTs are recorded in Dose Level 2, then by definition the MTD will be exceeded, and dosing will be decreased to utomilumab 20 mg/kg IV (Dose Level 1), with enrollment to the Dose Level 1 cohort to a total of 9 subjects. If ≤ 2 DLTs are observed in 9 subjects at Dose Level 1 (utomilumab = 20 mg/kg IV), then utomilumab 20 mg/kg IV in combination with ado-trastuzumab emtansine 3.6 mg/kg IV will be the RP2D.
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cohort 2 trastuzumab (closed january

Dose **Level** 1 - Utomilumab 20 mg IV + trastuzumab 6 mg/kg IV every 3 weeks. 3 subjects will be treated at this dose level. If no DLT events are recorded, then utomilumab dose will be increased to 100 mg (Dose Level 2, below). If 1 DLT is observed amongst the first 3 subjects, then Dose Level 1 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab will proceed to 100 mg (Dose Level 2). If 2 (or more) DLTs are recorded at Dose Level 1, enrollment in the trastuzumab + utomilumab cohort will be terminated. Dose **Level** 2 - Utomilumab 100 mg IV + trastuzumab 6 mg/kg IV every 3 weeks. 3 subjects will be dosed initially. If one DLT is observed, Dose Level 2 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab 100 mg IV + trastuzumab 6 mg/kg IV will be expanded to 9 subjects to gain further confidence in the RP2D determination. If no DLTs are observed in the first 3 subjects, then Dose Level 2 will also be expanded to 9 subjects total to define the RP2D. If more than 2 DLTs are recorded in Dose Level 2, then by definition the MTD will be exceeded, and dosing will be decreased to utomilumab 20 mg/kg IV, with enrollment to the Dose Level 1 cohort to a total of 9 subjects. If ≤ 2 DLTs are observed in 9 subjects at Dose Level 1 (utomilumab = 20 mg/kg IV), then utomilumab 20 mg/kg IV in combination with trastuzumab 6 mg/kg IV will be the RP2D.
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expansion phase 1b cohort 1

RP2D in combination with ado-trastuzumab emtansine 3.6 mg/kg IV, will be based on Minimax Simon 2 Stage Design. The null hypothesis that the true response rate is 5% will be tested against a one-sided alternative. In 17 response-evaluable subjects, if there are no responses, the study will be terminated. If 1 or more responses are observed, it will be recommended to conduct a future formal phase 2 trial of the combination under a separate study protocol. Expansion Phase 1B Cohort 2 **(trastuzumab)** - Utomilumab given IV at the RP2D in combination with trastuzumab 6.0 mg/kg IV, will be based on Minimax Simon 2 Stage Design. The null hypothesis that the true response rate is 5% will be tested against a one-sided alternative. In 17 response-evaluable subjects, if there are no responses, the study will be terminated. If 1 or more responses are observed, it will be recommended to conduct a future formal phase 2 trial of the combination under a separate study protocol.
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additional considerations in the design

Subjects will continue treatment at the assigned dose level and schedule until unacceptable toxicity, subject's voluntary withdrawal, or documentation of progressive disease as determined by RECIST v1.1 criteria (see Section 7.2 regarding clinical interpretation of potential "flare" tumor responses seen with immunotherapeutic drugs, such as utomilumab). If ado-trastuzumab emtansine (T-DM1) or trastuzumab must be discontinued (eg, for toxicity), the patient may remain on single-agent utomilumab until disease progression. The converse is also true (ie, if utomilumab is discontinued, the patient may remain on ado-trastuzumab emtansine or trastuzumab until disease progression. Administration of the study drug utomilumab may continue for up to 24 cycles (18 months).
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1. background 1.1. 4-1bb target

4-1BB (CD137, TNFRSF9), first identified as an inducible costimulatory receptor expressed on  
 activated T-cells, is a membrane spanning glycoprotein of the tumor necrosis factor (TNF) receptor superfamily. Current understanding of 4-1BB indicates that expression is generally activation dependent and encompasses a broad subset of immune cells including activated NK and NKT cells; regulatory T-cells; dendritic cells (DC) including follicular DC; stimulated mast cells, differentiating myeloid cells, monocytes, neutrophils, eosinophils (Wang, et al, 2009), and activated B-cell s (Zhang, et al, 2011)(Figure 1). 4-1BB expression has also been demonstrated on tumor vasculature (Broll, et al, 2001, Seaman, et al, 2007) and atherosclerotic endothelium (Olofsson, et al, 2008). The ligand that stimulates 4-1BB (4-1BBL) is expressed on activated antigen-presenting cells (APCs); myeloid progenitor cells; and hematopoietic stem cells.
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figure 1. mechanism of cd137

4-1BB is undetectable on the surface of naive T-cells but expression increases upon activation. Based on homology to other members of the TNFRSF, ligand binding is expected to induce receptor trimerization resulting in activation (Chan, et al, 2007). Some members of the TNFRSF can cleave the extracellular domain from the cell surface and exist in a soluble form. Soluble 4-1BB and soluble 4-1BBL have been demonstrated in the serum of some patients with autoimmune diseases and cancers (Michel, et al, 1998; Furtner, et al, 2005; Hentschel, et al, 2006). Upon 4-1BB activation, TRAF1 and TRAF2, pro-survival members of the TNFR-associated factor (TRAF) family are recruited to the 4-1BB cytoplasmic tail resulting in downstream activation of NFkB and the Mitogen Activated Protein (MAP) Kinase cascade including Erk, Jnk, and p38 MAP kinases. NFkB activation leads to upregulation of Bfl-1 and Bcl-XL, pro-survival members of the Bcl-2 family. The pro-apoptotic protein Bim is downregulated in a TRAF1 and Erk dependent manner (Sabbagh, et al, 2008). Numerous studies of murine and human T-cells indicate that 4-1BB promotes enhanced cellular proliferation, survival, and cytokine production (Croft 2009). Reports have shown that 4-1BB agonist mAbs increase costimulatory molecule expression and markedly enhance cytolytic T lymphocyte responses, resulting in anti-tumor efficacy in various models. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings and both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T-cell memory responses (Lynch 2008). 4-1BB agonists also inhibit autoimmune reactions in a variety of autoimmunity models (Vinay, et al, 2006). This dual activity of 4-1BB offers the potential to provide anti-tumor activity while dampening autoimmune side effects that can be associated with immunotherapy approaches that break immune tolerance. utomilumab, an intravenous (IV) fully-human IgG2 monoclonal antibody (mAb), binds to the extracellular domain of human 4-1BB with high affinity and specificity and is capable of 4-1BB agonism. Injection with utomilumab has been shown to correlate with tumor cell line growth inhibition in xenogenic tumor models as a single agent. In addition, 4-1BB agonist mAbs demonstrate significant combinatorial efficacy with ADCC antibodies in lymphoma and breast cancer models. Preclinical studies support the use of this 4-1BB agonist mAb as a promising candidate for treatment of cancer, alone or in combination with ADCC-inducing mAbs.
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1.2. preclinical profiles of utomilumab

Utomilumab has shown immunomodulatory activity in various in *vitro* assays. In concert with a signal through the T-cell receptor, utomilumab has been shown to mediate ligation of 4-1BB, which results in release of soluble 4-1BB (sCD137), activation of NFkB, production of cytokines and chemokines (including IL2 and CCL22) and proliferation of antigen-specific CD8+ T-cells (Fisher et al., 2012). Interaction of 4-1BB on activated normal human B-cell s with its ligand at the time of B-cell receptor engagement stimulates proliferation and enhances survival (Zhang, et al, 2011). The potential impact of 4-1BB engagement in B-cell lymphoma has been investigated in 2 published studies. Evaluation of several types of human primary NHL samples indicated that 4-1BB was expressed predominantly on infiltrating T-cells rather than the lymphoma cells (Houot, et al, 2011). The addition of 4-1BB agonists to in *vitro* cultures of B lymphoma cells with rituximab and NK cells resulted in increased lymphoma killing (Kohrt, et al, 2010). In addition, B-cell immunophenotyping was performed in two experiments using utomilumab in cynomolgus monkeys with doses from 0.001-100 mg/kg; in these experiments peripheral blood B-cell numbers were either unchanged or decreased.
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1.2.2. in vivo data

In pre-clinical studies, utomilumab has exhibited the ability to increase lymphocyte proliferation.  
 In small animal models developed to test the in *vivo* function of utomilumab, utomilumab was able to enhance expansion of human leukocytes in a dose-dependent manner as evidenced by an increase in the proportion of human CD45+ cells in the peripheral blood of engrafted mice. Similarly, a dose-dependent increase in the proportion of human leukocytes expressing the proliferation marker Ki-67 was noted. In addition, utomilumab treatment of cynomolgus monkeys in single or multiple dose studies increased proliferation among cytotoxic central memory T-cells (CD8 TCM) in PBMC samples. Taken together, these data demonstrate evidence of utomilumab's ability to enhance lymphocyte response in *vivo* with human PBMC from a healthy volunteer donor prior to injection in all cases. Once tumors were established, animals were treated with utomilumab. Utomilumab was found to be efficacious against all 3 tumor types. An example growth curve demonstrating the response to a prostate carcinoma is shown in Figure 2. (Fisher, et al, 2012).
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1.2.3. clinical experience

Utomilumab has been administered to a total of 390 subjects (see Table 1). In Study B1641001, 180 subjects with advanced solid tumors and hematological malignancies received utomilumab in a dose range between 0.006 and 10.0 mg/kg. In this study, 114 subjects, mainly with advanced solid tumors, received single-agent utomilumab and 66 subjects with non-Hodgkin's lymphoma (NHL) received utomilumab in combination with rituximab. In Study B1641003, utomilumab has been administered to 23 subjects with advanced solid tumors in a dose range between 0.45 mg/kg and 5.0 mg/kg in combination with pembrolizumab. In Study B1641004, utomilumab has been administered to 24 subjects with advanced solid tumors, in a dose range between 1.2 mg/kg and 5 mg/kg in combination with mogamulizumab. In Study B9991004, 153 subjects received utomilumab at dose levels of 20 mg, 100 mg, and 500 mg in combination with avelumab. In Study B0601002, utomilumab has been administered to 10 subjects at 20 mg in combination with PF-04518600. The ongoing first-in-patient clinical Study B1641001 is a phase 1, open–label, dose-escalation study. In study Portion A, utomilumab is administered as a single agent in subjects with advanced solid tumors or relapsed or refractory B-cell lymphoma, and in study Portion B, utomilumab is given in combination with rituximab in subjects with relapsed or refractory CD20+ NHL. The key study parameters assessed include: safety, tolerability PK/PD markers of activity, and preliminary utomilumab anti-tumor activity. Study B1641003, a phase 1, open-label, dose-escalation study designed to evaluate the safety, and PK/PD of utomilumab administered in combination with pembrolizumab to adults with advanced solid tumors, has been completed. The study also aimed to: assess preliminary anti-tumor activity, estimate the MTD and select the RP2D for the combination. The study was halted following completion of the dose-escalation phase. The dose expansion phase of the study was not conducted. The decision to terminate the study was made for strategic reasons, and was not due to any safety or efficacy concerns related to the combination treatment. A completed CSR is available for Study B1641003. The ongoing clinical Study B1641004 is a phase 1b, open label, multi-center, multi-dose, dose-escalation study designed to evaluate the safety, and PK/PD of utomilumab administered in combination with mogamulizumab to adults with defined advanced solid tumors. The study will assess preliminary anti-tumor activity, and will estimate the MTD and RP2D for the combination. The ongoing clinical Study B9991004 is a phase 1b/2, open label, multi-center, multiple dose, study designed to evaluate the safety, clinical activity, PK/PD of avelumab in combination with increasing dose levels of other immune modulators in adult subjects with locally advanced or metastatic solid tumors. Combination A of this study includes utomilumab in combination with avelumab. The study aims to determine the RP2D(s) of the combination of utomilumab and avelumab in subjects with NSCLC. The phase 2 component of the study evaluates efficacy and further evaluates safety of the combination in subjects with NSCLC, melanoma, head and neck cancer, triple negative breast cancer, and small cell lung cancer. The ongoing clinical Study B0601002 is a phase 1, open label, multi-center, multiple-dose, dose-escalation, safety, and PK/PD study that in Part A evaluates the single agent activity of PF-04518600 (OX-40 agonist) and in Part B evaluates the combination of PF-04518600 and utomilumab in subjects with select locally-advanced or metastatic carcinomas. The primary objective is to assess safety and tolerability at increasing dose levels of PF-04518600 in combination with utomilumab and to estimate the MTD of the combination. Secondary objectives include the overall safety profile, PK/PD, and anti-tumor effects of the combination. The clinical data reported in the following sections are based on all available data as of the data cut-off of 06 July 2017 for Studies B1641001, B1641003, and B1641004.
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table 1. clinical studies of

| Subjects                                                                                                                                                |           |         |           |        |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|-----------|---------|-----------|--------|
| Protocol                                                                                                                                                | Title     | Planned | Treated   | Status |
| A Phase 1 Study of PF-05082566 as a Single Agent in Patients                                                                                            |           |         |           |        |
| B1641001 with Advanced Cancer, and in Combination with Rituximab in                                                                                     | 72 to 161 | 180     | Ongoing   |        |
| Patients with Non-Hodgkin's Lymphoma (NHL) A Phase 1 Study of the 4-1BB Agonist PF-05082566 in                                                          |           |         |           |        |
| B1641003 Combination With the PD-1 Inhibitor MK-3475 in Patients with                                                                                   | 45 to 75  | 23      | Completed |        |
| Advanced Solid Tumors A Phase 1b Study of PF-05082566 in Combination With                                                                               |           |         |           |        |
| B1641004 Mogamulizumab (KW-0761) in Patients With Advanced Solid                                                                                        | 70        | 24      | Ongoing   |        |
| Tumors A Phase 1b/2 Open-Label Study to Evaluate Safety, Clinical  Activity, Pharmacokinetics and Pharmacodynamics of Avelumab                          |           |         |           |        |
| B9991004 (MSB0010718C) in Combination with Other Cancer  Immunotherapies in Patients with Advanced Malignancies  (Avelumab IB version 7, 31 March 2017) | 317       | 153     | Ongoing   |        |
| A Phase 1 Open Label, Dose Escalation Study of PF-04518600 as  a Single Agent and in Combination with PF-05082566 in Patients                           |           |         |           |        |
| B0601002 with Selected Locally Advanced or Metastatic Carcinomas  (PF-04518600 IB December 2016)                                                        | 190       | 10      | Ongoing   |        |
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safety and efficacy

As of the data cut-off date of 06 July 2017, the safety and efficacy of utomilumab are being evaluated in 3 studies within the utomilumab clinical program, 2 of which are ongoing (B1641001 and B1641004) and 1 is completed (B1641003). Utomilumab is being evaluated both as a single agent (B1641001 Portion A) and in combination with other anti-cancer treatments (B1641001 Portion B, B1641003, and B1641004). For B1641001, safety and efficacy data were recorded for 114 subjects in Portion A (74 [64.9%] male and 40 [35.1%] female; mean age of 60.9 years) treated with utomilumab in dose levels between 0.006 and 10 mg/kg, and 66 subjects in Portion B (37 [56.0%] male and 29 [43.9%] female; mean age of 62.1 years) treated with utomilumab in dose levels between 0.03 and 10 mg/kg in combination with rituximab at 375 mg/m2.  
For B1641003, safety and efficacy data were recorded for 23 subjects (14 [60.9%] males and 9 [39.1%] females; mean age of 58.0 years) treated with utomilumab in dose levels between 0.45 and 5.0 mg/kg in combination with 2 mg/kg of pembrolizumab. For B1641004, safety and efficacy data were recorded for 24 subjects (19 [79.1%] males and 5 [20.8%] females; mean age of 63.9 years) treated with utomilumab in dose levels between 1.2 and 5 mg/kg, in combination with 1 mg/kg of mogamulizumab. Since Studies B1641001 and B1641004 are ongoing, the available data are subject to change. Study B1641003 is completed and the final clinical study report (CSR) is available.
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dose-limiting toxicities

There were no dose-limiting toxicities (DLTs) in Study B1641001 either for utomilumab as a single agent in Portion A or in combination with rituximab in Portion B. There were no DLTs reported in Studies B1641003 nor B1641004. A summary of treatment emergent adverse events (TEAEs) occurring or worsening during the time from the first dose of study treatment to at least 30 days after the last dose of study treatment by System Organ Class (SOC), Medical Dictionary for Regulatory Activities (MedDRA), Preferred Term (PT), and maximum CTCAE Grade (all-causality and treatment-related) for Portion A is as follows. The most commonly reported TEAEs (88.6% of subjects, all grades), regardless of causality, were in the SOCs of gastrointestinal disorders (51.8%); general disorders and administration site conditions (46.5%); nervous system disorders (28.9%); musculoskeletal and connective tissue disorders (24.6%); metabolism and nutrition disorders (22.8%); respiratory; thoracic and mediastinal disorders (19.3%); skin and subcutaneous tissue disorders (17.5%); infections and infestations (15.8%); investigations (14.0%); and blood and lymphatic system disorders (13.2%). The most frequently reported TEAEs (≥ 10% of all subjects, all grades) regardless of causality were: fatigue (29.8%); nausea (21.1%); abdominal pain (14.9%); decreased appetite (14.9%); vomiting (14.0%); diarrhea (12.3%); dizziness (12.3%); pyrexia (11.4%); anemia (10.5%); and constipation (10.5%). There were four Grade 5 AEs reported (disease progression [2 subjects], respiratory failure and malignant neoplasm progression [1 subject each]), which were considered to be not related to the study drug. The most commonly reported TEAEs (≥ 10% of all subjects; all grades) that were considered treatment-related were in the SOCs of general disorders and administration site conditions (21.1%); gastrointestinal disorders (17.5%); and skin and subcutaneous tissue disorders (10.5%). The most frequently observed treatment-related TEAE (41.2% of subjects; all grades) was fatigue (14.0%). Treatment-related TEAEs were mostly Grade 1 or 2 with only four Grade 3/4 AEs reported (colitis; diarrhea; fatigue; hyperbilirubinemia and hyponatremia); Grade 3/4 colitis and diarrhea were observed in the same subject. No Grade 5 treatment-related AEs were observed. A summary of TEAEs by SOC, MedDRA PT, and maximum CTCAE Grade (all-causality and treatment-related) for Portion B is as follows. The most commonly reported TEAEs (≥10% of subjects; all grades), regardless of causality, were in the SOCs of general disorders and administration site conditions (48.5%); gastrointestinal disorders (45.5%); musculoskeletal and connective tissue disorders (39.4%); respiratory; thoracic and mediastinal disorders (36.4%); injury; poisoning and procedural complications and nervous system disorders (30.3% each); infections and infestations (27.3%); skin and subcutaneous tissue disorders (25.8%); investigations (24.2%); blood and lymphatic system disorders (16.7%); psychiatric disorders (12.1%). The most frequently reported TEAEs (≥10% of subjects; all grades) regardless of causality were: fatigue (28.8%); infusion-related reaction (21.2%); cough (16.7%); pyrexia (13.6%); upper respiratory tract infection (13.6%); diarrhea (12.1%); headache (10.6%); and blood creatinine increased (10.6%). There was one Grade 5 AE (death) reported (due to disease progression), which was considered not-related to the study drug. The most commonly reported TEAEs (all grades) that were considered treatment-related were in the SOCs of general disorders and administration site conditions (28.8%); gastrointestinal disorders (25.8%); injury, poisoning and procedural complications (24.2% ); nervous system disorders (16.7%); and skin and subcutaneous tissue disorders (15.2%). The most commonly reported treatment-related TEAEs (75.8% of subjects; all grades) that were considered treatment-related were infusion-related reaction (21.2%) and fatigue (19.7%). Note that all of the infusion reactions were associated with rituximab infusion. Treatment-related TEAEs were mostly Grade 1 or Grade 2. Grade 3/4 AEs were reported in 6 subjects: infusion-related reaction and neutropenia (2 subjects each), lymphocyte count decreased and neutrophil count decreased (1 subject each). All Grade 3/4 AEs were related to rituximab treatment only, per Investigator assessment. Two of the Grade 3 AEs were related to PF-05082566 (diarrhea and neutropenia). No Grade 5 treatment-related AEs were observed.  
Twenty-three (23) solid tumor subjects were treated with the combination of PF-05082566 and pembrolizumab at the fixed dose of 2 mg/kg. PF-05082566 was administered at different dose levels as follows: 5 subjects received 0.45 mg/kg, 3 subjects each received 0.9 mg/kg; 1.8 mg/kg; and 3.6 mg/kg; and 9 subjects received 5 mg/kg. A summary of TEAEs by SOC, MedDRA PT, and maximum CTCAE grade (all-causality and treatment-related) for B1641003 is as follows. The most commonly reported TEAEs, regardless of causality, were in the SOCs of gastrointestinal disorders (69.6%); general disorders and administration site conditions (65.2%); skin and subcutaneous tissue disorders (60.9%); respiratory; thoracic and mediastinal disorders (56.5%); metabolism and nutrition disorders; and musculoskeletal and connective tissue disorders (52.2% each); infections and infestations (43.5%); nervous system disorders (39.1%); investigations (34.8%); blood and lymphatic system disorders (26.1%); injury, poisoning and procedural complications (21.7%); endocrine disorders (17.4%); ear and labyrinth disorders (8.7%); cardiac disorders; eye disorders; hepatobiliary; neoplasms benign; malignant and unspecified (includes cysts and polyps); product issues; reproductive system and breast disorders; and vascular disorders (4.3% each). The most frequently reported TEAEs (100% of subjects; all grades) regardless of causality, were fatigue (43.5%); cough; nausea (34.8% each); decreased appetite (30.4%); constipation; pruritus; rash maculo-papular and vomiting (26.1% each); anemia; pyrexia (21.7% each); back pain; dyspepsia; rash; and upper respiratory tract infection (17.4% each); alanine aminotransferase increased; arthralgia; asthenia; dry mouth; dry skin; dyspnea; fall; hemoptysis; hypokalemia; hyponatremia; muscle spasms; musculoskeletal chest pain; edema peripheral; pleural effusion; pneumonia; sinusitis; and stomatitis (13.0% each). There was one Grade 5 AE (death) reported, (due to disease progression), which was considered not related to the study drug. The most frequently observed treatment-related TEAEs (all grades) were in the SOCs of skin and subcutaneous tissue disorders (52.2%); general disorders; and administration site conditions (47.8%); gastrointestinal disorders (34.8%); and metabolism and nutrition disorders (21.7%). The most frequently observed treatment-related TEAEs (78.3% of subjects; all grades) were fatigue (34.8%); rash maculo-papular (26.1%); pruritus (21.7%); pyrexia (17.4%); nausea; decreased appetite; dry skin; dry mouth (13.0% each). Treatment-related TEAEs were mostly Grade 1 or Grade 2. There were only 2 treatment-related (PF-05082566 and pembrolizumab) Grade 3 AEs reported in 2 subjects: adrenal insufficiency (no evidence of associated hypophysitis reported) and hypokalemia (1 subject each). No Grade 4 or 5 treatment-related AEs were observed. Twenty four (24) solid tumor subjects were treated with the combination of PF-05082566 and mogamulizumab at 1 mg/kg. PF-05082566 was administered at 4 dose levels as follows: 11 subjects received 1.2 mg/kg; 4 subjects received 2.4 mg/kg; 3 subjects received 5 mg/kg; and 6 subjects received 100 mg. A summary of TEAEs by SOC, MedDRA PT, and maximum CTCAE Grade (all-causality and treatment-related) for B1641004 is as follows. The most frequently observed TEAEs, regardless of causality, were in the SOCs of general disorders and administration site conditions (66.7%), gastrointestinal disorders (62.5%), skin and subcutaneous tissue disorders (58.3%), respiratory, thoracic and mediastinal disorders (54.2%), infections and infestations (45.8), metabolism and nutrition disorders (41.7%). The most frequently observed TEAEs (100% of subjects; all grades)
regardless of causality, were fatigue (41.7%); rash (29.2%); constipation; nausea; diarrhea and pyrexia (20.8% each); decreased appetite, pruritus, anemia, dyspnea, and headache (16.7% each); abnormal dreams, chills, cough, dehydration, infusion related reaction, insomnia, lymphocyte count decreased, and rhinorrhea (12.5% each). There were no Grade 5 AEs reported in this study. The most frequently observed treatment-related TEAEs (all grades) were in the SOCs of skin and subcutaneous tissue disorders (50%), general disorders and administration site conditions (41.7%), gastrointestinal disorders (37.5%), metabolism and nutrition disorders (25.0%). The most frequently observed treatment-related TEAEs (83.3% of subjects; all grades) were fatigue; rash (25.0% each); diarrhea (20.8%); nausea; pyrexia; abnormal dreams; infusion related reaction and pruritus (12.5% each). Most treatment-related TEAEs were Grade 1/2 in severity. No Grade 5 treatment-related AEs were observed.
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discontinuations due to adverse events

In Portion A, there were 15 adverse events reported in 13 subjects that led to permanent discontinuation from treatment with utomilumab. Only 1 subject with metastatic melanoma treated at 1.2 mg/kg permanently discontinued treatment with utomilumab for a Grade 2 AE of enterocolitis that was considered related to study drug per Investigator assessment. There were no AEs leading to permanent treatment discontinuation reported for subjects treated in Portion B. No subject permanently discontinued from the study treatment due to a treatment-related AE in the pembolizumab plus utomilumab trial. In the utomilumab and mogamulizumab at 1 mg/kg trial, 1 subject permanently discontinued from the study treatment due to treatment-related Grade 3 pneumonitis.
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serious adverse events

A total of 41 SAEs (all-causality) were reported in the safety database for 34 subjects who received utomilumab in Portion A or Portion B. One (1) event each of colitis, diarrhea, enterocolitis, hyperbilirubinemia, decreased appetite, dehydration and pneumonitis were reported as treatment-related in 5 subjects. In one case, Pfizer (the manufacturer of utomilumab) does not consider a reasonable possibility that hyperbilirubinemia may be attributed to the study drug. The event occurred approximately 43 days after the first dose of study drug in a subject who had an ongoing abdominal ascites. Significant tests, including baseline bilirubin and liver enzyme levels, abdominal imaging results, were not available to determine the causality of the event. Progression of the underlying disease may provide the most plausible cause; of note, recent MRI showed brain metastases. A total of 14 SAEs (all-causality) were reported in the safety database for 10 subjects who received utomilumab and pembrolizumab. None of these SAEs were considered related to utomilumab per Investigator assessment. There was 1 SAE (Grade 2 inflammation) that was determined by the investigator as related to pembrolizumab treatment. There was 1 SAE of special interest, a Grade 3 hyperbilirubinemia in the utomilumab 5 mg/kg + pembrolizumab 2 mg/kg treatment group, which was considered not related to treatment.  
The MTD of utomilumab once every 3 weeks (q3wks) in combination with 2 mg/kg of pembrolizumab q3wks was determined to be at least 5 mg/kg (the highest dose evaluated). Doses up to utomilumab 5 mg/kg q3wks when combined with pembrolizumab 2 mg/kg q3wks were safe and well-tolerated in subjects with advanced solid cancer. The dose expansion phase of the study was not initiated by Pfizer for strategic reasons and therefore, there was insufficient information to determine the RP2D. In the utomilumab plus mogamulizumab at 1 mg/kg trial, a total of 13 SAEs (all-causality) in 10 subjects were reported in the safety database. None of these SAEs were considered treatment-related.
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deaths

A total of 13 deaths were reported in the safety database for subjects in Portion A or in Portion B who received treatment with utomilumab. One (1) subject in Portion B died of disease progression after receiving the first dose of rituximab but was not dosed with utomilumab. None of the deaths were attributed to study treatment. A total of 5 deaths were reported in the safety database in the pembrolizumab plus utomilumab trial. None of these were considered related to the treatment with utomilumab. In the utomilumab plus mogamulizumab trial, a total of 3 deaths were reported in the safety database. None of these deaths were considered related to the treatment with utomilumab. One (1) subject died of sepsis and 2 subjects died due to neoplasm progression. None of the deaths were attributed to study treatment.
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laboratory abnormalities

Note: As many abnormal laboratory values are not necessarily considered as AEs, the numbers presented in this section do not precisely match those in the corresponding AE sections above. For subjects who received utomilumab in Portion A, Grade 3 hematology laboratory test abnormalities reported were: lymphopenia (21 subjects; 18.9%), anemia (3 subjects; 2.7%), neutrophils (absolute) (1 subject; 0.9%). The Grade 4 hematology laboratory test abnormalities reported were: lymphopenia (2 subjects; 1.8%), neutrophils (absolute) (0 subjects; 0.0%), and white blood cells (0 subjects; 0.0%). The Grade 3 abnormal serum chemistry abnormalities reported were: hyponatremia (7 subjects; 6.3%), hypophosphatemia (4 subjects; 3.8%), hyperglycemia (3 subjects; 2.7%), alkaline phosphatase increased, hypokalemia, and hypoalbuminemia (2 subjects each; 1.8%), and hypomagnesemia (1 subject each; 0.9%). The only Grade 4 abnormal serum chemistry values were: hypercalcemia (1 subject; 0.8%) and hypokalemia (1 subject; 0.9%). In Portion B, Grade 3 hematology laboratory test abnormalities reported were: lymphopenia (22 subjects; 34.9%), neutrophil count decreased (4 subject each; 6.3%), white blood cell count decreased (3 subjects; 4.7%), platelet count decreased (1 subject; 1.5%). The Grade 4 hematology laboratory test abnormalities reported were: lymphopenia (4 subjects; 6.3%), and neutrophil count decreased (3 subjects; 4.7%). The Grade 3 abnormal serum chemistry values reported were: hyperglycemia and hypophosphatemia (2 subjects each; 4.4%); ALT increased, hyperkalemia, hypomagnesemia, hypoglycemia, and hyponatremia (1 subject each; 1.5%). Laboratory test abnormalities for subjects who received utomilumab and pembrolizumab are summarized by maximum CTCAE Grade, as follows. The Grade 3 hematology laboratory test abnormalities reported were: lymphopenia (6 subjects; 26.1%) and anemia (3 subjects; 13.0%). The only Grade 4 hematology laboratory test abnormalities reported was lymphopenia (1 subject; 4.3%). This was not reported as an AE by the Investigator. The Grade 3 abnormal serum chemistry abnormalities reported were: hypoalbuminemia and hyponatremia (3 subjects each; 13.0%), hyperglycemia, hypokalemia, and hypophosphatemia (2 subjects each; 8.7%), alkaline phosphatase increased and bilirubin increased (1 subject each; 4.3%). Both alkaline phosphatase increased and bilirubin increased were considered related to metastatic disease. The only Grade 4 abnormal serum chemistry values reported was hyponatremia (1 subject; 4.3%). This hyponatremia occurred in the subject with adrenal insufficiency. Laboratory test results for subjects who received utomilumab and mogamulizumab in B1641004 is summarized by maximum CTCAE Grade. The Grade 3 hematology laboratory test abnormalities reported were: lymphopenia (7 subjects; 29.2%) and anemia (2 subjects; 8.3%); and in Grade 4 only lymphopenia (1 subject; 4.1%) was reported. The Grade 3 serum chemistry abnormalities reported were: hyperglycemia (3 subjects; 12.5%), hypophosphatemia (2 subjects; 8.3%), and hyponatremia (1 subject; 4.1%). There were no Grade 4 hematology or Grade 3/4 serum chemistry abnormalities reported.
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ecg and vital signs

In both Portion A and B, as well as the pembrolizumab plus utomilumab combination, and in the utomilumab plus mogamulizumab combination, there were no observed QTc prolongations (≥ 500 msec) or changes from baseline QTcF (≥ 60 msec) that were considered clinically significant per Investigator assessment. In both Portion A and B, as well as the utomilumab plus pembrolizumab combination, there were no observed heart rates (< 50 bpm and > 120 bpm) or change in heart rate (decrease/increase from baseline ≥ 30 bpm) that were considered clinically significant, per Investigator assessment. In both Portion A and B, there were no observed blood pressure measurements (decrease/increase baseline systolic ≥ 30 m Hg or baseline diastolic blood pressure ≥ 20 mm Hg) that were considered clinically significant per Investigator assessment.
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safety summary

In summary, the observed safety profile, based on a data cut-off date of 06 July 2017 for B1641001, support the use of utomilumab both as a single agent and in combination with rituximab. Treatment-related AEs were generally mild or moderate with four Grade 3/4 AEs (colitis; diarrhea; hyponatremia; hyperbilirubinemia; and fatigue) reported as related to PF-5082566 in Portion A. The observed safety profile supports utomilumab use in combination with pembrolizumab. Treatment-related AEs were generally mild or moderate, with only two Grade 3 AEs reported as treatment-related to both utomilumab and pembrolizumab. In addition, the observed safety profile, based on a data cut-off date of 06 July 2017 for B1641004, supports utomilumab in combination with mogamulizumab. Treatment-related AEs were generally mild or moderate and Grade 1 or Grade 2 in severity.
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pharmacokinetics and product metabolism in

Study B1641001: A Phase I Study of PF-05082566 As A Single Agent In Subjects With Advanced Cancer, And In Combination With Rituximab In Patients With Non-Hodgkin's Lymphoma (NHL). The phase 1 first in human (FIH) study of utomilumab is currently ongoing. This is an open-label, multi-center, multiple-dose study of single agent utomilumab in subjects with solid tumors or relapsed or refractory B-cell lymphoma (Portion A) and of utomilumab in combination with rituximab in subjects with relapsed or refractory CD20 positive NHL (Portion B). Preliminary median utomilumab concentration versus time profiles for subjects in Portion A (utomilumab alone) and Portion B (utomilumab + rituximab) after single dose (Cycle 1) are depicted in Figure 3. The utomilumab exposure after single dose appeared to increase with increasing doses. The utomilumab terminal half-life (t1/2) ranged from 208 to 349 hours in Portion A and from 274 to 550 hours in Portion B, respectively. The utomilumab AUCinf was slightly higher in Portion B than that in Portion A at corresponding dose levels.
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population pharmacokinetic modeling

Preliminary population PK analysis has been conducted using data from 68 subjects (n = 41 in Portion A and n = 27 from Portion B) receiving doses from 0.006 to 5 mg/kg Q4W using serial and sparse PK samples in Study B1641001. A two-compartment model with linear elimination best described these data. Among the covariates tested, both baseline body weight and treatment portion had statistically significant effect on clearance (CL). Baseline body surface area and gender were found to significantly correlate with central volume of distribution (Vc). No other covariates had a statistically significant effect on either CL or Vc. Simulations were performed at various dosing schedules which indicated that the exposure at dose levels higher than 0.12 mg/kg was above the assumed efficacious concentration (Ceff, 1730 ng/mL) with both once every 3 weeks (Q3W) and once Q4W schedule. Although body weight was identified as a significant covariate on CL, it accounted for only a small percentage (~< 7%) of the inter-individual variability in serum utomilumab exposure. In addition, simulations indicated that utomilumab exposure is similar between body weight based and fixed dosing regimens. Therefore, this suggests the possibility of using a fixed dosing regimen in future utomilumab clinical studies.
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immunogenicity

Anti-drug antibodies (ADA) to utomilumab in human serum were determined by a validated, quasi-quantitative bridging electro chemi-luminescence method. Preliminary analyses based on quality-controlled, non-quality-assured data are presented. In Portion A, 9 of 61 subjects (14.8%) exhibited positive ADA prior to treatment with utomilumab. 35 of 61 subjects (57.4%) were positive for ADA for at least 1 time point regardless of baseline ADA status. Among 35 ADA-positive subjects, 7 (20%) exhibited positive neutralizing antibody (Nab) against utomilumab. In Portion B, 2 of 41 subjects (4.9%) exhibited positive ADA against utomilumab prior to treatment with utomilumab plus rituximab. 3 of 41 subjects (7.3%) were positive for ADA for at least 1 time point regardless regardless of baseline ADA status when administered in combination with rituximab. Among 3 ADA-positive subjects, 1 (33.3%) exhibited positive Nab against utomilumab. The impact of ADA on PK of utomilumab was characterized. ADA-negative subjects were defined as those with negative antibody status for all samples collected during the study including baseline (pre-treatment). ADA-positive subjects were defined as those with at least 1 positive ADA sample anytime during the study including baseline (pre-treatment). Utomilumab clearance (CL) was similar in ADA-negative and ADA-positive subjects suggesting  
  
 that ADA status had minimal impact on the PK of utomilumab (see Figure 4). In study B1641003, 2 out of 23 (8.7%) subjects exhibited positive ADA against utomilumab prior to treatment with utomilumab plus pembrolizumab. The presence of positive ADA at baseline was likely due to pre-existing host antibodies that were cross-reactive with utomilumab. Seventeen out of 23 subjects (73.9%) were positive for ADA for at least 1 time point regardless of baseline ADA status when administered in combination with pembrolizumab. The overall incidence of treatment-induced ADA was 65.2% (15/23 subjects); 7 out of 23 (30.4%) subjects exhibited positive Nab against utomilumab. Similar utomilumab exposure (eg, AUCtau (dn) and Cmax (dn)) was observed in subjects with treatment-induced ADA and ADA-negative subjects. While mean Cmax (dn) appeared to be lower in subjects with positive NAb, AUCτ (dn) was similar in subjects with positive and negative NAb. There were 2 (13.3%) out of 15 ADA-positive subjects and 1 (12.5%) out of 8 ADA-negative subjects who experienced treatment-emergent, all causalities hypersensitivity/infusion reactions. There was 1 (14.3%) out of 7 NAb-positive subjects and there were 2 (12.5%) out of 16 NAb-negative subjects who experienced treatment-emergent, all causalities hypersensitivity/infusion reactions. In addition, the presence of ADA against utomilumab did not preclude subjects from responding to the combination treatment. The response rate was 25% (2 responders out of 8 ADA-negative subjects) and 26.7 % (4 responders out of 15 ADA-positive subjects) for ADA-negative and ADA-positive subjects, respectively. The response rate was 25% (4 responders out of 16 NAb-negative subjects) and 28.6% (2 responders out of 7 NAb-positive subjects) for NAb-negative and NAb-positive subjects, respectively. Overall, there was no detectable impact of ADA/NAb on PK, safety and efficacy. In study B1641004, among 10 subjects tested for ADA analysis, none of them exhibited positive ADA against utomilumab prior to treatment with utomilumab plus mogamulizumab. Five out of 10 subjects (50%) were positive for ADA against utomilumab for at least 1 time point when administered in combination with mogamulizumab.
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efficacy

Study B1641001: The anti-tumor activity of single-agent utomilumab in subjects with advanced malignancies and utomilumab in combination with rituximab in subjects with CD20-positive NHL is being assessed in the Study B1641001. In this study, tumor responses are reported by Investigators per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 for Portion A subjects and irRECIST for subjects enrolled in the expansion cohort of Portion A or International Working Group (IWG) criteria for Portion B. For Portion A, BOR observed was 1 CR (0.24 mg/kg; MCC) and 2 PR in MCC subjects (1 at 0.24 mg/kg, and 1 at 0.60 mg/kg). One of the PR observed in MCC subject had prior IO-experience (0.24 mg/kg). In the 59 melanoma subjects there were no CR but 1 PR (0.24 mg/kg) was observed. There were no confirmed PR and CR in NSCLC subjects. The irRECIST exploratory analysis was consistent with analysis using RECIST 1.1. For Portion B, in NHL subjects 4 CR (1 at 0.03 mg/kg, 1 at 0.12 mg/kg, and 2 at 1.20 mg/kg) and 9 PR (2 at 0.18 mg/kg, 3 at 1.20 mg/kg, 1 and 1 at 5.0 mg/kg) were observed. In follicular lymphoma subjects, 4CR (1 at 0.03 mg/kg, 1 at 0.12 mg/kg, and 2 treated at 1.20 mg/kg) and 6 PR (2 at 0.18 mg/kg, 5 at 1.20 mg/kg, 1 at 2.40 mg/kg and 1 at 5.0 mg/kg) was observed. Study B1641003: The anti-tumor activity of utomilumab in combination with pembrolizumab in subjects with advanced solid tumors was assessed in B1641003. In this study, tumor responses are reported by Investigators per RECIST 1.1 (Eisenhauer, et al, 2009). The tumor responses reported below were confirmed by the Investigator on at least 2 consecutive scan evaluations. Among the 23 subjects treated, 6 had confirmed objective response providing an objective response rate (ORR) of 26.1%. Two (2) subjects had a confirmed CR (1 subject with RCC treated at 1.8 mg/kg and 1 subject with SCLC treated at 5.0 mg/kg). Four (4) subjects achieved a PR: 1 subject with RCC and 1 subject with NSCLC treated at 0.45 mg/kg; 1 subject with anaplastic thyroid disease treated at 3.6 mg/kg, and 1 subject with SCCHN treated at 5 mg/kg. Study B1641004: Efficacy assessments are ongoing for Study B1641004. Out of 24 subjects evaluated during the utomilumab dose-escalation phase of the study, no RECIST-defined complete responses were observed. One (1) subject had BOR of PR and 9 subjects achieved a BOR of SD.
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1.3. trastuzumab and ado-trastuzumab emtansine

Trastuzumab is a recombinant DNA-derived humanized monoclonal antibody that selectively binds with high affinity in a cell-based assay (Kd = 5 nM) to the extracellular domain of the human epidermal growth factor receptor 2 protein, HER2. The antibody is an IgG1 kappa that contains human framework regions with the complementarity-determining regions of a murine antibody (4D5) that binds to HER2. The HER2 (or c-erbB2) proto-oncogene encodes a transmembrane receptor protein of 185 kDa, which is structurally related to the epidermal growth factor receptor (EGFR, aka HER1). HER2 protein overexpression is observed in 25% to 30% of primary breast cancers. HER2 protein overexpression can be determined using an immunohistochemistry-based assessment of fixed tumor blocks, and HER2 gene amplification status can be measured by fluorescence in situ hybridation (FISH) in archival formalin-fixed, paraffin-embedded breast tumor tissue specimens. Trastuzumab has been shown, in both in *vitro* assays and in animals, to inhibit the proliferation of human tumor cells that overexpress HER2. Trastuzumab is a mediator of antibody-dependent cellular cytotoxicity (ADCC). In *vitro*, trastuzumab-mediated ADCC has been shown to be preferentially exerted on HER2 overexpressing cancer cells compared with cancer cells that do not overexpress HER2. In HER2+ metastatic breast cancer trastuzumab is indicated: 1) in combination with paclitaxel for first-line treatment of HER2-overexpressing metastatic breast cancer, or 2) as a single-agent for treatment of HER2-overexpressing breast cancer in patients who have received one or more chemotherapy regimens for metastatic disease. Ado-trastuzumab emtansine is a HER2-targeted antibody-drug conjugate. The antibody is the humanized anti-HER2 IgG1, trastuzumab. The small molecule cytotoxin, DM1, is a microtubule inhibitor that is covalently linked to trastuzumab via the stable thioether linker MCC (4-[N-maleimidomethyl] cyclohexane-1-carboxylate). Upon binding to sub-domain IV of the HER2 receptor, ado-trastuzumab emtansine undergoes receptor-mediated internalization and subsequent lysosomal degradation, resulting in intracellular release of DM1-containing cytotoxic catabolites. Binding of DM1 to tubulin disrupts microtubule networks in the cell, which results in cell cycle arrest and apoptotic cell death. In addition, in *vitro* studies have shown that similar to trastuzumab, ado-trastuzumab emtansine inhibits HER2 receptor signaling, mediates antibody-dependent cell-mediated cytotoxicity and inhibits shedding of the HER2 extracellular domain in human breast cancer cells that overexpress HER2. Ado-trastuzumab emtansine as a single agent, is indicated for the treatment of patients with HER2-positive, metastatic breast cancer who previously received trastuzumab and a taxane, separately or in combination. Patients should have either received prior therapy for metastatic disease, or developed disease recurrence during or within six months of completing adjuvant therapy.
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1.4. study rationale 1.4.1. rationale

Antibody dependent cellular cytotoxicity (ADCC) has been hypothesized as a mechanism of tumor destruction resulting in direct antigen presentation and in the induction of tumor antigen specific T-cell responses ('cross-priming"). This is supported by preclinical experiments demonstrating that the therapeutic efficacy of an anti-HER2/neu antibody depends on both innate and adaptive immunity (Park, et al, 2010). The combinatorial anti-tumor activity of ADCC inducing mAb with 4-1BB agonist mAbs was  
  
 assessed in both lymphoma and HER2+ breast cancer models. A mouse anti-mouse CD20 antibody with ADCC inducing activity was selected as a surrogate mAb for rituximab. MAB9371 was selected as a surrogate for utomilumab, as utomilumab does not cross react with murine 4-1BB. MAB9371 is a commercially available rat anti mouse 4-1BB agonist mAb (R & D Systems, Minneapolis MN). The binding affinity of MAB9371 for murine 4-1BB is similar to the affinity of utomilumab for human 4-1BB. In both models, treatment with a combination of surrogate mAbs at concentrations with limited single agent efficacy, showed significant tumor growth inhibition (A20 model) and/or enhanced survival (Em-myc model) (Figure 5).  
spontaneous lymphoma models. A) A20 murine lymphoma cells were implanted on the flank of Balb/C mice.  
Group mean tumor volume measurements at the indicated times are shown above. Error bars represent SEM.  
Untreated vs single agent p = not significant, untreated vs combination p < 0.01. B) Survival days post treatment. Median survival was calculated using Graph Pad Prism CD20 = 15 days, 1mpk 4-1BB = 23.5 days, CD20+0.1mpk 4-1BB = 25.5 days, CD20+1mpk 4-1BB = 34 days. Statistical significance of the 4-1BB
treatment or combination treatment versus CD20 group was determined using a Log Rank (Mantel-Cox) test using Graph Pad Prism software, CD20 vs 4-1BB p < 0.02, CD20 vs CD20 + 0.1mpk 4-1BB p = not significant, CD20 vs CD20 + 1mpk 4-1BB p < 0.001.  
Anti-4-1BB agonistic mAb enhances anti-breast cancer activity of trastuzumab in *vivo* (Kohrt, et al, 2012). The in *vivo* ability of anti-4-1BB mAbs to enhance trastuzumab's activity was tested in a xenotransplanted human breast cancer (BT474M1 cell line) model in athymic mice. These mice have fully competent NK cells while lacking functional T-cells.  
Anti-4-BB mAb alone had no effect on tumor growth, while trastuzumab had a modest effect
(Figures 6A and 6C). Simultaneously, Kohrt explored the effect of trastuzumab and anti-4-1BB mAb in various schedules. Since maximal upregulation of CD137 required 24 hours of NK cell exposure to trastuzumab-coated cells in *vitro*, investigators aimed to determine the importance of injection sequence. Trastuzumab was injected on Day 3 (post-tumor inoculation) and anti-4-1BB mAb was injected either on Day 2, 3 or 4. Treatment was repeated in all groups 14 days following the first injection. Of the three combination sequences tested, trastuzumab followed by anti-4-1BB mAb resulted in the greatest reduction in tumor size and mortality with the opposite order, anti-4-1BB mAb followed by trastuzumab having the least effect both in tumor growth (Figure 6A) and survival (Figure 6B). Since trastuzumab followed by anti-4-1BB antibodies demonstrated more potent antitumor activity in *vivo*, this injection schedule was chosen for subsequent experiments. When the treatment regimen was repeated weekly for 3 weeks the combination treatment resulted in prolonged control of tumor growth and a significant improvement in survival (Figures 6C and 6D). Enhancement of the therapeutic activity of trastuzumab by anti-4-1BB mAb is specific to HER2-expressing tumors. To determine if the synergy between anti-HER2 and anti-4-1BB mAbs requires specific recognition by the anti-tumor antibody, two tumors differing in HER2 expression were inoculated subcutaneously in individual mice. On the left flank, mice were inoculated with MCF7 cells, which are HER2 low to negative. On the right flank, mice were inoculated with HER18 cells, a transduced derivative of MCF7 cells that stably overexpress HER2 (Figure 7A)(12). Mice then received either trastuzumab monotherapy on Day 3 or the combination of trastuzumab on Day 3 and anti-4-1BB mAb on Day 4. This sequential therapy was repeated weekly for 3 successive weeks. As expected, only the HER2-overexpressing tumors responded to monotherapy with trastuzumab. The addition of anti-4-1BB mAb resulted in an enhanced therapeutic effect but only against the HER2-positive tumor that could be targeted by the anti-HER2 mAb (Figures 7B-C). Anti-4-1BB mAb enhances the therapeutic activity of trastuzumab against a human HER2-overexpressing primary breast tumor. Since the combination of trastuzumab and anti-4-1BB antibodies demonstrated increased efficacy against HER2-overexpressing cell lines, we next aimed to assess efficacy of the combination therapy using a primary patient  
   
xenotransplant model. A primary HER2-overexpressing-breast tumor was successfully engrafted into sub-lethally irradiated SCID mice. After tumors were established the mice were randomized into treatment groups that received either: rat IgG control, trastuzumab, anti-4-1BB mAb, or trastuzumab followed 24 hours later by anti-4-1BB mAb and repeated weekly for a total of 3 weeks. The combination of trastuzumab and anti-4-1BB mAb was superior to trastuzumab alone, significantly reducing tumor growth and prolonging survival (Figures 7D-E). The enhanced efficacy of trastuzumab in combination with anti-4-1BB has been recently confirmed with ado-trastuzumab emtansine, which has been previously shown to retain ADCC capacity as a mechanism of action in *vitro* and in *vivo* (Junttila, et al, 2011; Barok, et al, 2011; English, et al, 2014). Two murine models have been performed which confirm the synergy observed with anti-4-1BB and ado-trastuzumab emtansine combination therapy including a HER18 xenograft model and an SU-258 primary breast model (data not shown).  
Overexpression of HER2 is observed in approximately 20% of human breast cancers and is implicated in the aggressive growth and poor clinical outcomes associated with these tumors. While the development of trastuzumab, pertuzumab, lapatinib and ado-trastuzumab emtansine provided patients with HER2-positive tumors a markedly better outcome than with chemotherapies, virtually all patients with HER2-positive MBC will eventually progress despite these available therapies, leading to mortality. Opportunities remain to improve outcomes for patients with MBC. Ado-trastuzumab emtansine and trastuzumab have individually demonstrated activity in patients *with HER2-positive MBC*, and additionally, nonclinical data showing synergy with the combination of ado-trastuzumab emtansine and anti-4-1BB mAb, and between trastuzumab and anti-4-1BB mAb, suggest that investigation of ado-trastuzumab emtansine or trastuzumab in combination with anti-4-1BB mAb in patients with HER2-positive, locally advanced (unresectable) or metastatic breast cancer is warranted. Such patients represent the patient population eligible for study enrollment.
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1.4.2. rationale for utomilumab and

Preliminary population PK analysis showed that body weight accounts for only a small percentage (~7%) of the variability in drug exposure. Simulations indicated that utomilumab exposure profiles are similar in both body weight and flat utomilumab dosing regimens. Therefore, it is suggested a fixed dosing regimen be utilized for ease of use and to minimize potential medication errors. Active doses for utomilumab ranged from 0.24 mg/kg to 0.6 mg/kg (approximately 20 to 50 mg) in Merkel cell carcinoma (MCC) as a single agent. It is not clear if higher doses might be active as limited number of MCC patients were treated at higher doses. Responses were also observed with the combination of utomilumab and rituximab (R) in R-refractory NHL as low as 0.03 mg/kg with highest active dose of 2.4 mg/kg. These data suggest that the active dose range of utomilumab is quite broad, spanning an approximate 100-fold dose range. Flat utomilumab doses of 20 (approximately 0.24 mg/kg), 100 (approximately 1.2 mg/kg), and 500 mg (approximately 6 mg/kg) are being tested in Pfizer Study B9991004. In this study, two dose levels of utomilumab (20 mg IV, and 100mg IV) will be tested in combination with ado-trastuzumab or trastuzumab.  
  
HER2+ primary breast tumor cells (SU-258) by intramammary injection 24 hours after 200 cGy total body irradiation (TBI) (D-E). On Day 40 mice were randomized to 1 of 4 groups (5 mice per group) including IgG control with treatment on Day 40 (●),
trastuzumab on Day 40 ( ), anti-4-1BB mAb on Day 41 ( ♦ ), or trastuzumab on Day 40 and anti-4-1BB mAb on Day 41 ( ▲ ).  
Treatment was repeated weekly in each group for a total of 3 treatments.  Mice were monitored for tumor growth (D, *p = .016)
and overall survival (E, *p = .002).
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1.4.2.2. ado-trastuzumab/trastuzumab

The dose selection for ado-trastuzumab emtansine (3.6 mg/kg IV q 3 weeks) in this protocol is the full FDA-approved dose for patients with HER2+ metastatic breast cancer, and the dose selection of trastuzumab (6 mg/kg IV q3 weeks) is the full FDA-approved drug dose for treatment of HER2+ metastatic breast cancer.
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2. study objectives endpoints and

Estimate the maximum tolerated dose (MTD) and determine the recommended dose
(RP2D) of utomilumab in combination with ado-trastuzumab emtansine (T-DM1) in subjects with HER2-positive advanced breast cancer.
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secondary objectives

Determine the objective tumor response rate (ORR)
Determine the time-to-tumor response (TTR)
Determine the duration of response (DR)  
Determine progression-free survival (PFS)
Assess the safety and tolerability of utomilumab in combination with ado-trastuzumab emtansine or trastuzumab
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exploratory objectives

Evaluate the pharmacokinetics (PK) of utomilumab and ado-trastuzumab emtansine or trastuzumab when given in combination  
Evaluate preliminary evidence of antitumor activity of utomilumab in combination with ado-trastuzumab emtansine or trastuzumab
Evaluate the immunogenicity of utomilumab and ado-trastuzumab emtansine or trastuzumab when given in combination Assess the presence of CD8+ T-cells in HER2-positive tumors Evaluate the modulation of immune activity biomarkers by utomilumab in combination with ado-trastuzumab emtansine or trastuzumab.  
Analysis of samples from subjects who received utomilumab and trastuzumab is optional.
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secondary endpoints

Objective tumor response rate (ORR) per RECIST v1.1 Time-to-event measures:
o Time-to-tumor response (TTR)
o Duration of response (DR)
o Progression-free survival (PFS)
Adverse events (not including laboratory abnormalities) as characterized by types, severity
(as graded by NCI CTCAE v5), timing, seriousness, and relationship to study treatments  
Laboratory abnormalities as characterized by type, severity (as graded by NCI CTCAE v5) and timing
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exploratory endpoints

Ctrough and Cmax of utomilumab, ado-trastuzumab emtansine, or trastuzumab Anti-drug antibody level and incidence Tumor tissue biomarkers (including number and percentage of CD8+ T-cells)  
Peripheral blood and additional tumor tissue biomarkers consisting of the levels of cells, DNA, RNA or proteins, such as CD8 T-cells, PD-L1, TCR sequence changes, and
biomarkers of the IFN pathway, that may be related to anti-tumor immune response and/or response to or disease progression on utomilumab in combination with trastuzumab or ado-trastuzumab emtansine.  
Analysis of samples from subjects who received utomilumab and trastuzumab is optional.
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2.3. clinicaltrials.gov outcomes primary outcome

Incidence of dose-limiting toxicities (DLTs) within the first 2 cycles (up to 2 months) reported for the Dose-finding Cohorts 1 (ado-trastuzumab emtansine) and 2 (trastuzumab). Subjects lost to follow-up before completion of first 2 cycles due to reasons unrelated to treatment-related adverse events are not evaluable for DLT.
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secondary outcomes

1. Objective tumor response rate (ORR) after 2 cycles for subjects in Expansion Phase 1B
Cohort 1 (ado-trastuzumab emtansine), per RECIST v1.1 (see Appendix 1)  
2. Time-to-event measures, for subjects in Expansion Phase 1B
Cohort 1 (ado-trastuzumab emtansine) who have at least 1 on-study tumor assessment:
o Time-to-tumor response (TTR), per RECIST v1.1 (see Appendix 1), in subjects that respond within 4 months o Duration of response (DR), per RECIST v1.1 (see Appendix 1), in subjects that respond, through up to 5 years after treatment o Progression-free survival (PFS) of subjects (percentage) who initiate treatment, reported as the number who remain alive without progression 5 years after treatment. Subjects withdrawn for treatment-related AEs, or lost to follow-up before 5 years, will report as the last date known alive 3. Incidence of adverse events (not including laboratory abnormalities) while receiving treatment and within 30 days, reported by treatment group for severity (as graded by NCI CTCAE v5), seriousness (YES/no), and relationship to the study treatments 4. Incidence of laboratory abnormalities reported by treatment group for severity (as graded by NCI CTCAE v5)
3. **PARTICIPANT SELECTION** The Inclusion and Exclusion Criteria are provided on the Participant Eligibility Checklist following, which must be completed in its entirety for each subject prior to registration (see Section 10.4 Subject Registration). The checklist may be extracted from this document for use in screening potential subjects. The completed, signed, and dated checklist must be retained in the subject's study file, and the study's Regulatory Binder. Pursuant to Stanford Medicine SOP "Confirmation of Participant Eligibility in Clinical Trials," the treating Physician (investigator); the Study Coordinator; and an Independent Reviewer will verify that the subject's eligibility is accurate; complete; and legible in source records. A description of the eligibility verification process should be included in the EPIC or other Electronic Medical Record progress note.  
| Protocol Title:                                        | A Phase 1B Dose Escalation Trial of human anti-4-1BB agonistic  antibody Utomilumab (PF-05082566) with ado-trastuzumab-emtansine  or trastuzumab in patients with HER2-positive advanced breast cancer   |
|--------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Protocol Number:                                       | IRB-37299 / BRS0070                                                                                                                                                                                      |
| Principal Investigator:                                | George W Sledge, Jr, MD                                                                                                                                                                                  |
| II. Subject Information: Subject Name/ID: Gender: Male | Female                                                                                                                                                                                                   |
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iii. study information

SRC-Approved IRB-Approved Contract signed IV. Inclusion / Exclusion Criteria  
| Inclusion Criteria (From IRB-approved protocol)   | Yes                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | No   | Supporting Documentation*   |
|---------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------|-----------------------------|
| 1.                                                | History of biopsy-proven HER2-overexpressing  breast cancer and radiographic evidence of  metastatic disease, or locally-recurrent unresectable  disease. The HER2 status can be determined either  by immunohistochemistry (IHC) [IHC score, 3+] or  by fluorescence in situ hybridization (FISH) [as  defined by HER2/CEP-17 ratio ≥ 2.0, or HER2 copy  number ≥ 6], or as otherwise defined by 2018  ASCO/CAP guidelines. oCohort 1 subjects must have received trastuzumab  and a taxane separately or in combination. oSubjects in Cohort 2 (closed January 2020) must  have received at least 1 prior therapy, including  ado-trastuzumab emtansine. o Subjects who discontinued prior trastuzumab or  ado-trastuzumab emtansine due to progressive or  refractory disease are eligible for enrollment. |      |                             |  
| Inclusion Criteria (From IRB-approved protocol)   | Yes                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | No   | Supporting Documentation*   |
|---------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------|-----------------------------|
| 2.                                                | Available tumor samples. For eligibility, if no  unstained slides remain, stained pathology slides  may be reviewed at the treating institution.  However, a tumor sample is required for research  evaluations per the following (any of Item 1;  2; or 3, in order of preference).  1. A FFPE tumor tissue block from a de novo fresh  tumor biopsy obtained during screening will be  requested, though not mandated.  2. A recently-obtained archival FFPE tumor tissue  block (or 10 to 15 unstained slides) from a  primary or metastatic tumor resection or biopsy  if the following criteria are met:  A. The biopsy or resection was performed  within 1 year of enrollment  OR B. The subject has not received any  intervening systemic anti-cancer  treatment from the time the tissue was  obtained and enrolled onto the current  study. OR 3. Any archival FFPE tumor tissue block (or  unstained slides) from primary tumor resection  specimen (if not provided per above). The  archival sample may have been collected at any  time prior to the current study, regardless of any  intervening therapy. If an FFPE tissue block  cannot be provided, a minimum of 10 unstained  slides (15 preferable) will be acceptable. |      |                             |
| 3.                                                | Subjects must have evaluable OR measurable  disease, as defined by RECIST v1.1.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |      |                             |
| 4.                                                | Women or men, age ≥ 18 years old.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |      |                             |
| 5.                                                | Performance status 0 to 1 (by Eastern Cooperative  Oncology Group [ECOG] scale).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |      |                             |  
| Inclusion Criteria (From IRB-approved protocol)   | Yes                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | No   | Supporting Documentation*   |
|---------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------|-----------------------------|
| 6.                                                | Laboratory parameters (must satisfy all):  Absolute neutrophil count (ANC) ≥ 1.5 × 109 /L   (≥ 1500/µL)  Platelet count ≥ 100 × 109 /L (≥ 100,000/µL)  Hemoglobin ≥ 9.0 g/dL; subjects on therapeutic   anticoagulation are eligible if there is no bleeding   and they are on a stable dose of anticoagulation   therapy (eg, on Coumadin with an INR of 2 to 3)   for at least 7 days before registration (prior to the   start of therapy, or stable heparin or Factor Xa   inhibitor dose) Serum creatinine ≤ 1.5 × the ULN or calculated   creatinine clearance (by Cockcroft-Gault formula)   ≥ 60 mL/min  Aspartate aminotransferase (AST) ≤ 2.5 × ULN  Alanine aminotransferase (ALT) ≤ 2.5 × ULN  Bilirubin ≤ 1.5 × ULN |      |                             |
| 7.                                                | Subjects must not be pregnant or breastfeeding.  A pregnancy test will be obtained if the subject is a  woman of child-bearing potential, defined as a  sexually-mature woman who has not undergone a  hysterectomy or and/or bilateral oophorectomy or  who has not been naturally postmenopausal for at  least 24 consecutive months (ie, who has had menses  at any time in the preceding 24 consecutive months)  with 2 pregnancy tests, one at screening, and another  immediately preceding the initiation of treatment.                                                                                                                                                                                                   |      |                             |
| 8.                                                | Subjects must have signed an informed consent  document stating that they understand the  investigational nature of the proposed treatment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |      |                             |
| 9.                                                | Left ventricular ejection fraction determined by  echocardiogram or multiple-gated acquisition scan  (MUGA) (cardiac scan) must be 50% or higher                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |      |                             |  
| Exclusion Criteria (From IRB-approved protocol)   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 1.                                                | Previously discontinued either trastuzumab or  ado-trastuzumab emtansine due to intolerance.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| 2.                                                | Received any other investigational agents within  30 days of registration.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| 3.                                                | Central nervous system (CNS) metastases, unless  previously treated by either radiation therapy and/or surgical resection, clinically-stable for at least 60 days  and on a stable corticosteroid dose of ≤ 4 mg/day  decadron (or equivalent steroid regimen) for at least  1 month. Subjects with a history of CNS metastases  that are both treated and stably-controlled are eligible  if all of the following apply:  o Therapy has been administered (surgery and/or  radiation therapy);  o There is no additional treatment planned for brain  metastases; o The subject is clinically-stable;  o The subject is on a stable corticosteroid dose of  ≤ 4 mg/day decadron (or equivalent steroid  regimen) for at least 1 month. |
| 4.                                                | Prior malignancy (other than in situ cervical cancer, or  basal cell or squamous cell carcinoma of the skin),  unless treated with curative intent and without  evidence of disease for 3 years or longer                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| 5.                                                | Administration of other prior anticancer therapies  within 4 weeks of enrollment, except ongoing  administration of a bisphosphonate drug or  denosumab as treatment for bone metastasis                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| 6.                                                | Toxicities related to prior anticancer treatment (except  alopecia) that have not resolved to ≤ Grade 1  according to common terminology criteria for adverse  events (CTCAE v5) before registration or prior to start  of therapy                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| 7.                                                | Currently receiving systemic antibiotic, antiviral, or  antifungal therapy for the treatment of an active  infection                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |  
| Exclusion Criteria (From IRB-approved protocol)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 8.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Systemic corticosteroid therapy at doses of greater  than prednisone 5 mg daily (or dose-equivalent  chronic steroid regimen) for therapeutic and not  adrenal replacement indications (maintenance steroid  use for adrenal insufficiency is permitted). Acute  emergency administration, topical applications,  inhaled sprays, eye drops or local injections of  corticosteroids are allowed. |
| 9.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | History of bleeding diathesis                                                                                                                                                                                                                                                                                                                                                                    |
| 10. Any co-morbid medical condition deemed by the  treating or principal investigator to possibly put the  subject at significant risk for toxicity. 11. Subject has known sensitivity to any of the products to  be administered during dosing 12. Subject has any kind of disorder that compromises the  ability of the subject to give written informed consent  and/or to comply with study procedures 13. Uncontrolled intercurrent illness including, but not  limited to, symptomatic congestive heart failure,  unstable angina pectoris, cardiac arrhythmia, or  psychiatric illness/social situations that would limit  compliance with study requirements 14. History of venous thromboembolism within prior  6 months.  15. Subject with reproductive potential who will not agree  to use, during the study and for 60 days after the last  dose of utomilumab or 6 months for ado-trastuzumab  emtansine or trastuzumab 2 highly effective method of  contraceptive such as:  o Implants o Injectables o Intrauterine devices (IUDs) such as copper T or  levonorgestrel-releasing intrauterine system  (LNG-IUS) o Sexual abstinence o Vasectomized partner o Condom or occlusive cap (diaphragm or  cervical/vault cap) supplemented with the use of a  spermicide during treatment. |                                                                                                                                                                                                                                                                                                                                                                                                  |  
*All subject files must include supporting documentation to confirm subject eligibility. The method of confirmation can include, but is not limited to, laboratory test results, radiology test results, subject self-report, and medical record review.
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iv. statement of eligibility

By signing this form of this trial I verify that this subject is [ eligible / **ineligible**] for participation in the study. This study is approved by the Stanford Cancer Institute Scientific Review Committee, the Stanford IRB, and has finalized financial and contractual agreements as required by Stanford School of Medicine's Research Management Group.  
  
 Printed Name:  
  
Secondary Reviewer Signature: Date:  
  
  
  
Printed Name:  
| Stanford Designate Signature:   | Date:   |
|---------------------------------|---------|
| Printed Name:                   |         |
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3.3. informed consent process

All participants must be provided a consent form describing the study with sufficient information for participants to make an informed decision regarding their participation. Participants must sign the IRB approved informed consent prior to participation in any study specific procedure. The participant must receive a copy of the signed and dated consent document. The original signed copy of the consent document must be retained in the medical record or research file.
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3.4. study timeline

It is anticipated that the study will reach primary completion (final subject enrollment and treatment) within 48 months from the time the study opens to accrual. The study is estimated to reach completion 60 months from the time the study opens to accrual. Treatment with study drugs will continue until completion of 24 cycles of treatment (up to about 18 months), confirmed disease progression, subject refusal, unacceptable toxicity, whichever occurs first, or the study is prematurely terminated by the investigator, or one of the other reasons for subject withdrawal as specified in Section 4.8 will occur.
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4. study design

This is a parallel cohort, open-label, non-randomized treatment study. The cohorts are:  
1. Ado-trastuzumab emtansine 3.6 mg/kg IV Q3W plus utomilumab (Cohort 1, with utomilumab administered at 20 mg or 100 mg), or 2. Trastuzumab 6 mg/kg IV Q3W plus utomilumab (Cohort 2, with utomilumab administered at 20 mg or 100 mg. Cohort closed January 2020)
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4.1. starting dose selection strategy

In the ongoing first-in-human phase 1 study B1641001, utomilumab has been well-tolerated up to 10 mg/kg once every 4 weeks with no dose-limiting toxicity. However, in order to minimize the potential risk of synergistic toxicity due to the combination, a starting dose of utomilumab 20 mg (0.24 mg/kg) [which is 41.6-fold lower than the 10 mg/kg dose found to be well-tolerated with no dose-limiting toxicity in protocol B1641001] was chosen for this protocol, as this dose is 1) safe, and 2) exposure is adequate based on the cumulative data in the B1641001 study. The starting dose for ado-trastuzumab emtansine (3.6 mg/kg IV q 3 weeks) in this protocol is the full FDA-approved dose for subjects with HER2+ metastatic breast cancer, and the starting dose of trastuzumab (6 mg/kg IV q3 weeks) is the full FDA-approved drug dose for treatment of HER2+ metastatic breast cancer.
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4.2. criteria for dose escalation

For Cohort 1, utomilumab at escalating doses of 20 mg and 100 mg will be given intravenously in combination with the FDA-approved dose and schedule of ado-trastuzumab emtansine (3.6 mg/kg IV) every 3 weeks. On Cycle 1, ado-trastuzumab emtansine will be administered on Day 0, followed by utomilumab on Day 1. On all subsequent cycles (because of the known long half-life of ado-trastuzumab emtansine), ado-trastuzumab emtansine and utomilumab will be administered on the same day, with utomilumab being administered following the end of ado-trastuzumab emtansine infusion. Initially, 3 subjects will be treated at each dose level. For the first 3 subjects at each utomilumab dose level, there will be a minimum 7-day window between the first dose of subject 1 and the first dose of subject 2. For all subsequent subjects enrolled in dose-escalation stages, a minimum 72-hour window will apply between first doses. For the expansion cohort combination of ado-trastuzumab emtansine plus utomilumab at the RP2D dose, no fixed time interval between subject enrollment and treatment need apply. As indicated in the Protocol Synopsis Schema section above, it is to note that other more complex adaptive trial designs were considered, however as just 2 doses of utomilumab will be tested in combination with ado-trastuzumab emtansine or trastuzumab, and as the safety of utomilumab IV has been well tolerated to date in combination with other ADCC-inducing mAbs (with defined PK), the present dosing scheme has been devised as an efficient means to arrive at the RP2D. Accordingly, the criteria for dose-escalation will be based on a modified 3+3 dose-escalation procedure (with expansion of the RP2D dose levels to a total of 9 subjects to gain further confidence in the RP2D determination). However, if a DLT is observed in 1 of the initial 3 treated subjects, 3 additional subjects will be enrolled and treated at the same dose level. If no further DLT is observed, the next dose level will be opened. Subsequent dose levels will not be opened until all subjects entered at the current dose level have been treated and observed for at least 21 days after the 1 st dose in Cycle 2 is given, and the number of DLTs among those subjects in their first two cycles has been determined. If a subject in a cohort drops out of study during the DLT observation period due to reasons other than a dose limiting toxicity (eg, progression of disease; no longer willing to participate; etc), another subject (ie, replacement) will be enrolled. Dose-escalation will continue until DLTs are observed in at least 2 of the 3 to 6 subjects treated at a dose level, leading to the conclusion that the MTD has been exceeded and thereby ending dose-escalation (or until utomilumab 100 mg IV dose cohorts with ado-trastuzumab emtansine and trastuzumab are filled). Doses of utomilumab higher than 100 mg will not be tested in either Cohort 1 or Cohort 2, even if the MTD of utomilumab in combination with either ado-trastuzumab emtansine or trastuzumab is not exceeded. If a dose exceeding the MTD has been identified, the next lower dose is declared the MTD, provided that 6 subjects have already been treated at that dose with 0 or 1. DLTs experienced in total. [3 additional subjects may need to be enrolled at this dose level for a total of 6]. If 2 or more subjects are deemed to have DLTs, the dose will be further de-escalated and the dosing interval will be adjusted based on the observed DLTs. When 6 subjects have been treated at the MTD dose, the MTD dose cohort will be further expanded to a total N = 9 subjects in order to further characterize the safety at that dose level. If 3 or more subjects at the expanded MTD experienced DLT, the dose will be de-escalated. The MTD/RP2D will be defined as the utomilumab dose in combination with standard dose ado-trastuzumab emtansine in which no more than 2 of 9 subjects experience DLT. The expansion cohort may be selected at this dose or at a lower dose based on observed clinical activity. For Cohort 2, Dose Level 1 - Utomilumab 20 mg IV + trastuzumab 6 mg/kg IV every 3 weeks. 3 subjects will be treated at this dose level. If no DLT events are recorded, then utomilumab dose will be increased to 100 mg (Dose Level 2, below). If 1 DLT is observed amongst the first 3 subjects, then Dose Level 1 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab will proceed to 100 mg (Dose Level 2). If 2 (or more) DLTs are recorded at Dose Level 1, enrollment in the trastuzumab + utomilumab cohort will be terminated. Dose Level 2 - Utomilumab 100 mg IV + trastuzumab 6 mg/kg IV every 3 weeks. 3 subjects will be dosed initially. If 1 DLT is observed, Dose Level 2 will be expanded to 6 subjects. If no further DLTs are observed, then utomilumab 100 mg IV + trastuzumab 6 mg/kg IV will be expanded to 9 subjects to gain further confidence in the RP2D determination. If no DLTs are observed in the first 3 subjects, then Dose Level 2 will also be expanded to 9 subjects total to define the RP2D. If more than 2 DLTs are recorded in Dose Level 2, then by definition the MTD will be exceeded, and dosing will be decreased to utomilumab 20 mg/kg IV, with enrollment to the Dose Level 1 cohort to a total of 9 subjects. If ≤ 2 DLTs are observed in 9 subjects at Dose Level 1 (utomilumab = 20 mg/kg IV), then utomilumab 20 mg/kg IV in combination with trastuzumab 6 mg/kg IV will be the RP2D. Due to differences in eligibility between Cohort 1 and Cohort 2, dose-finding and dose-escalation are not dependent between cohorts, and may occur at different times. Accrual to both cohorts for dose-finding and dose-escalation will occur in parallel to optimize efficiency in dose-finding. On Cohort 2, Cycle 1, trastuzumab will be administered on Day 0, followed by utomilumab on Day 1. On all subsequent cycles, trastuzumab and utomilumab will be administered on the same day, with utomilumab being administered following the end of trastuzumab infusion. Initially, 3 subjects will be treated at each dose level (utomilumab at RP2D). For the first cohort (utomilumab given at RP2D), there will be a minimum 7-day window between the first dose of subject 1 and the first dose of subject 2. For all subsequent subjects enrolled, a minimum 72-hour window will apply between first doses. Utomilumab doses above 100 mg will not be tested in this protocol, even if an MTD in combination with trastuzumab 6 mg/kg every 3 weeks is not observed. If a subject in a cohort drops out of study during the DLT observation period due to reasons other than a dose-limiting toxicity (eg, progression of disease, no longer willing to participate, etc), another subject (ie, replacement) may be enrolled. For reference, the study schema is presented again in Figure 9.
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figure 9. protocol schema

4.3. Expansion Phase 1B Cohorts 1 And 2  
Utomilumab will be given IV at the RP2D in combination with ado-trastuzumab emtansine (Cohort 1) or trastuzumab (Cohort 2, closed January 2020), based on Minimax Simon 2 Stage Design. The null hypothesis that the true objective response rate is 5% will be tested against a one-sided alternative. In 17 response-evaluable subjects (including the 9 subjects already treated at the RP2D in the dose-escalation stage), if there are no objective responses the study will be terminated. If 1 or more responses are observed, it will be recommended to conduct a future formal phase 2 study of the utomilumab combination under a separate protocol document.
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4.4. dose-limiting toxicity (dlt) definition

Severity of AEs will be graded according to CTCAE version 5. For the purpose of dose-escalation, any of the following adverse events occurring during the DLT observation period (first 2 Cycles, ie, 6 weeks) that are attributable to one or both study drugs will be classified as DLTs:
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hematologic

Grade 4 neutropenia lasting > 7 days Febrile neutropenia, defined as absolute neutrophil count (ANC) < 1000/mm3 with a single temperature of > 38.3 degrees C (101 degrees F) or a sustained temperature of ≥ 38 degrees C (100.4 degrees F) for more than 1 hour;  
Grade ≥ 3 neutropenic infection Grade ≥ 3 thrombocytopenia with bleeding Grade 4 thrombocytopenia. Non-Hematologic:
Grade ≥ 3 non-laboratory toxicities, except for nausea, vomiting and diarrhea that has been treated and recovered to < Grade 2 within 48 hours.  
Grade ≥ 3 laboratory abnormalities [other than aspartate aminotransferase/ alanine aminotransferase (AST/ALT)] if:
o Medical intervention is required to treat the subject, or  
o The abnormality leads to hospitalization, or o Lasts more than 24 hours
Grade 4 AST and ALT increase Criteria for Hy's Law is met:  
o ALT or AST > 3 × ULN
o Total bilirubin > 2 × ULN, with no elevation of alkaline phosphatase o No other reason for these abnormalities or pre-existing liver disease
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4.5. maximum-tolerated dose (mtd) definition

The MTD estimate is the highest dose associated with the occurrence of DLTs, as pre-specified in the DLT Definition section, in < 33% of DLT-evaluable subjects. In practice using the modified 3+3 design, the MTD estimate is the dose level at which 0 of 6; 1 of 6; or 2 of 9 DLT-evaluable subjects experience a DLT during the first two cycles with the next higher dose having at least 2 of 3 to 6 or at least 3 of 9 DLT-evaluable subjects experiencing DLTs.
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4.6. recommended phase 2 dose

The recommended phase 2 dose (RP2D) is the dose chosen for further study based on phase 1 results. If the MTD proves to be clinically feasible for long term administration in a reasonable number of subjects, such dose usually becomes the RP2D. Further experience with the MTD may result in a RP2D dose lower than the MTD.
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4.7. concomitant medication and supportive

Administration of other prior anticancer therapies within 4 weeks of enrollment, except ongoing administration of a bisphosphonate drug or denosumab as treatment for bone metastasis, is prohibited. Additionally, the concurrent use of vitamins or herbal supplements should be considered with caution. Concomitant treatment considered necessary for the subject's well-being may be given at discretion of the treating physician. All concomitant medications, blood products, as well as interventions (eg, paracentesis, etc) received by subjects from screening until the end of study visit will be recorded in the CRF. Palliative radiotherapy on study is permitted for the treatment of painful bony lesions providing the lesions were known at the time of study entry and the investigator clearly indicates that the need for palliative radiotherapy is not indicative of disease progression. In view of the current lack of data about the interaction of utomilumab with radiotherapy, utomilumab treatment should be interrupted during palliative radiotherapy, resuming utomilumab treatment after recovery to ≤ Grade 1 radiotherapy-related toxicity. Primary prophylactic use of granulocyte-colony stimulating factors is not permitted during the first two cycles of treatment but they may be used to treat treatment emergent neutropenia as indicated by the current American Society of Clinical Oncology (ASCO) guidelines. (J Clin *Oncol*. 2006;24(19):3187-3205). Erythropoietin may be used at the investigator's discretion for the supportive treatment of anemia. Chronic, systemic corticosteroid use of more than 5 mg/day prednisone (or equivalent corticosteroid regimen) for palliative or supportive purpose is not permitted. Use of short course corticosteroids as symptomatic treatment for acute medical conditions may be allowed on individual basis, if no acceptable alternatives are available. Acute emergency administration, topical applications, inhaled sprays, eye drops or local injections of corticosteroids are allowed.
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4.8. criteria for removal from

Subjects may withdraw from treatment at any time at their own request, or they may be withdrawn at the discretion of the investigator for safety, behavioral, or administrative reasons. Reasons for subject discontinuation of study treatment may include:
Objective disease progression according to RECIST criteria v1.1; Global deterioration of health status requiring discontinuation; Unacceptable toxicity which may also be an adverse event; Significant protocol violation; Lost to follow-up; Subject refused further treatment; Study terminated by the investigator or Pfizer; Death; Pregnancy Reasons for subject withdrawal from study follow-up may include:
Completed study follow-up; Study terminated by the PI or Pfizer; Lost to follow-up; Refusal for further follow-up for survival; Start of an alternative treatment regimen; Death.  
If a subject does not return for a scheduled visit, every effort should be made to contact the subject. In any circumstance, every effort should be made to document subject outcome, if possible. The investigator should inquire about the reason for withdrawal, request the subject to return for a final visit, and follow-up with the subject regarding any unresolved adverse events. The early termination final visit should include all assessments listed for the End of Treatment visit. If the subject withdraws consent for disclosure of future information, no further study specific evaluations should be performed, and no additional data should be collected. The PI may retain and continue to use any data collected before such refusal for further follow-up.
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4.9 alternatives to study participation

For patients assigned to the ado-trastuzumab emtansine cohort, the current FDA-approved standard of care is single agent ado-trastuzumab emtansine. For patients assigned to the trastuzumab cohort, the current standard of care is trastuzumab plus chemotherapy. There are numerous chemotherapy options commonly used in combination with trastuzumab in this clinical setting (eg, vinorelbine, capecitabine, gemcitabine, taxanes, and eribulin).
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5. investigational agent information 5.1

Name: Utomilumab Laboratory Nomenclature: PF-05082566 Molecular Weight: 145 kDa Antibody Type: Recombinant fully-human IgG2 monoclonal antibody Physical Description: Clear to opalescent solution
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5.2 formulation of utomilumab solution

Utomilumab Injection, 10 mg/ml is presented as a sterile solution for intravenous administration in a 10 mL clear glass vial with an appropriate stopper and aluminum overseal. The formulation contains of the active substance utomilumab in a buffered solution containing precedented excipients. The drug product should be stored at 2 to 8ºC (36-46ºF). Protect from light. Each vial contains nominal 100 mg of utomilumab in a 10 mL solution. To ensure that the exact volume can be withdrawn by syringe, there is a small amount of overfill in the vial.
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5.3 agent accountability

Utomilumab drug product will be supplied by Pfizer. Utomilumab drug product is a solution and should be stored refrigerated at 2 to 8°C. Utomilumab drug product will be supplied in glass vials at a 10 mg/mL concentration and labeled as open supplies. Each vial is packed in an individual carton. Each vial has a unique container number. For packaging and labeling information on ado-trastuzumab emtansine and trastuzumab, refer to the most recent version of the local product labeling. Only qualified personnel who are familiar with procedures that minimize undue exposure to them and to the environment will undertake the preparation, handling, and safe disposal of investigational and cytotoxic (or monoclonal antibody) agents. Specific preparation and dispensing instructions are provided in the Dosage Administration Instruction located in the Study Manual. Refrigerated utomilumab drug product will be equilibrated to ambient temperature before preparation and administration.
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5.4 drug storage and accountability

Utomilumab will be shipped and stored at a temperature between 2° and 8°C. Ado-trastuzumab-emtansine and trastuzumab should be stored according to product instructions. The storage conditions stated in the investigator brochure may be superseded by the label storage. The storage conditions and stability of the reconstituted product are detailed in the Dosing Administration Instructions. If a deviation to the storage condition occurs, contact Pfizer. The Investigator or an approved representative (eg, research pharmacist) will ensure that all investigational product is stored in a strictly controlled, secure area, at appropriate temperatures and in accordance with applicable regulatory requirements. The Investigator or designated personnel must maintain adequate records documenting the receipt, use, loss or other disposition of the investigational product(s). Pfizer *may* supply drug accountability forms that must be used or may approve use of standard institution forms. In either case, the forms must identify the investigational product, including batch or code numbers, and account for its disposition on a subject by subject basis, including specific dates and quantities. The forms must be signed by the individual who dispensed the drug and copies must be provided to Pfizer when directed. At the end of the trial, Pfizer will provide instructions as to disposition of any unused investigational product. If Pfizer authorizes destruction at the trial site, the Investigator must ensure that the materials are destroyed in compliance with applicable environmental regulations, institutional policy and any special instructions provided by Pfizer. Destruction must be adequately documented.
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5.5 drug administration

Subjects will receive doses of utomilumab on Day 1 every 3 weeks (one cycle). A cycle is defined as the time from Day 1 dose to the next Day 1 dose. If there are no treatment delays, a cycle will be 3 weeks in duration. An every 3-week schedule of utomilumab (instead of every 4 weeks in prior studies) is deliberately chosen for 1) clinical feasibility to match the treatment schedule for ado-trastuzumab emtansine in Cohort 1 and trastuzumab in Cohort 2, and 2) to avoid a staggered dosing schedule (every 4 week) of utomilumab as compared to the trastuzumab and ado-trastuzumab emtansine (which are every 3 weeks), which would add considerable complexity to the PK analysis. Pre-medication is allowed for all subjects, and may include an antihistamine, an antiemetic, an anti-inflammatory agent and/or pain reliever. The anticipated duration of utomilumab infusion is 1 hour (± 15 minutes). The infusion rate should be reduced or interrupted in the case of symptoms of infusion reaction, and symptomatic treatment administered. The infusion may be continued at one-half the previous rate upon improvement of symptoms. If symptoms persist or worsen, the infusion should be discontinued. For the administration of ado-trastuzumab emtansine and trastuzumab, refer to the most recent version of the FDA-approved product labeling. Ado-trastuzumab emtansine or trastuzumab administration: Treatment will be administered in a 3-week cycle (ie, 21-day cycle), by intravenous infusion. The first infusion of ado-trastuzumab emtansine or trastuzumab on-study will be over 90 minutes (± 30 minutes), on Cycle 1 Day 0. Subsequent infusions will be administered over 30 ± 15 minutes as tolerated (see Appendix 3, Study Schedule of Activities, footnote 16). Given the known side effects of ado-trastuzumab emtansine and trastuzumab, and the pre-clinical safety data for utomilumab, it is not anticipated that overlapping severe side effects will occur. Subjects will be treated with ado-trastuzumab emtansine (Cohort 1) or trastuzumab (Cohort 2) one day prior to the initiation of utomilumab on Cycle 1 to assess for ado-trastuzumab emtansine-or trastuzumab-specific side effects. Subjects should be monitored carefully, however, for potential infusion reactions, particularly for the earlier cycles of utomilumab. The safety monitoring as dictated per protocol is consistent with that recommended for subjects receiving ado-trastuzumab emtansine or trastuzumab.
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6. dose modifications

Every effort should be made to administer study treatment on the planned dose and schedule. In the event of significant toxicity dosing may be delayed and/or reduced as described below. In the event of multiple toxicities, dose modification should be based on the worst toxicity observed. Subjects are to be instructed to notify Investigators at the first occurrence of any adverse symptom. Subjects who experience an adverse event meeting the definition of a DLT should be removed from treatment. Dose modifications may occur in 3 ways:  
Within a cycle: dose interruption/reduction until adequate recovery during a given treatment cycle; Between cycles: next cycle administration may be postponed due to toxicity in the previous cycle; In the next cycle: dose reduction based on worst toxicity in the previous cycle.
Ado-trastuzumab emtansine *dose should not be re-escalated after a dose reduction is made.* The infusion rate of ado-trastuzumab emtansine or trastuzumab should be slowed or interrupted as stated in the label if the subject develops an infusion-related reaction. Permanently discontinue ado-trastuzumab emtansine or trastuzumab for life-threatening infusion-related reactions. Management of increased serum transaminases, hyperbilirubinemia, left ventricular dysfunction, thrombocytopenia, pulmonary toxicity or peripheral neuropathy may require temporary interruption, dose reduction or treatment discontinuation of ado-trastuzumab emtansine as per guidelines provided in Tables 2 to 5.  
| Dose Reduction Schedule                | Dose Level            |
|----------------------------------------|-----------------------|
| Starting dose                          | 3.6 mg/kg             |
| First dose reduction                   | 3 mg/kg               |
| Second dose reduction                  | 2.4 mg/kg             |
| Requirement for further dose reduction | Discontinue treatment |
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hepatotoxicity

A reduction in the dose of ado-trastuzumab emtansine is recommended in the case of hepatotoxicity exhibited as increases in serum transaminases and/or hyperbilirubinemia (see Tables 3 and 4).
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table 4. dose modification guidelines

Permanently discontinue ado-trastuzumab emtansine treatment in subjects with serum transaminases > 3 × ULN and concomitant total bilirubin > 2 × ULN. Permanently discontinue ado-trastuzumab emtansine in subjects diagnosed with nodular regenerative hyperplasia (NRH).
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thrombocytopenia

A reduction in dose is recommended in the case of Grade 4 thrombocytopenia (platelets
< 25,000/mm3(see Table 5).  
Table 5. Dose Modification Guidelines for Thrombocytopenia
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pulmonary toxicity

Ado-trastuzumab emtansine should be permanently discontinued in subjects diagnosed with interstitial lung disease (ILD) or pneumonitis.
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peripheral neuropathy

Ado-trastuzumab emtansine should be temporarily discontinued in subjects experiencing Grade 3 or 4 peripheral neuropathy until resolution to ≤ Grade 2.
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left ventricular dysfunction dose modifications

For symptomatic congestive heart failure, ado-trastuzumab emtansine, trastuzumab and Utomilumab will be permanently discontinued and subjects removed from the study. If the left ventricular ejection fraction decreases to less than 50% and is ≥ 10% points from baseline, ado-trastuzumab emtansine, trastuzumab, and utomilumab should be held, with repeat LVEF assessment within 3 to 4 weeks. If the LVEF has not recovered to within 10% points from baseline, ado-trastuzumab emtansine, trastuzumab and utomilumab will be permanently discontinued and subjects removed from the study. If the LVEF decreases to less than 50%, but is within 10% points from baseline and the subject is asymptomatic with respect to cardiac signs/symptoms, continue medical treatment with reassessment of the LVEF within 3 weeks.
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dose interruptions/delay

A new cycle of treatment may begin only if:  
ANC ≥ 1,000/µL;
Platelets count ≥ 75,000/µL;
Non-hematologic toxicities have returned to baseline or Grade ≤ 2 severity. If these conditions are not met, treatment must be delayed by 1 week. If, after a 1-week delay, all toxicities have recovered within the limits described above treatment with utomilumab or ado-trastuzumab emtansine or trastuzumab, as applicable, can be resumed. Both study drugs should be delayed simultaneously if applicable. If the subject has not recovered after 1 week of delay, treatment may be delayed by 1 more week. However, initiation of the next cycle can only be delayed by a maximum of 2 weeks. Therefore, if persisting toxicity does not allow for the resumption of treatment, the subject will be permanently discontinued.
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dose reductions

Subjects who experience a DLT will be removed from the study. After the first two cycles dose reductions may be required based on the worst toxicity experienced in the previous cycle. Subjects experiencing recurrent and intolerable Grade 2 toxicity may resume dosing at the next lower dose level once recovery to ≤ Grade 1 or baseline is achieved. Dose reduction for utomilumab-related serious adverse events is not allowed. In such cases the subject should discontinue treatment with this drug. In Cohort 2, no dose reductions of trastuzumab will be allowed. Once a subject has a dose reduction for a drug-related toxicity, the dose for that drug will not be re-escalated. For subjects requiring more than 2 dose reductions of ado-trastuzumab emtansine for treatment-related toxicity, ado-trastuzumab emtansine will be discontinued as per the approved package insert. At the investigator's discretion, utomilumab may be continued until disease progression or cumulative dose-limiting toxicity.
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infusion-related reactions hypersensitivity reactions in

Treatment with ado-trastuzumab emtansine has not been studied in subjects who had trastuzumab permanently discontinued due to infusion-related reactions (IRR) and/or hypersensitivity; treatment with ado-trastuzumab emtansine is not recommended for these subjects. Infusion-related reactions, characterized by one or more of the following symptoms − flushing, chills, pyrexia, dyspnea, hypotension, wheezing, bronchospasm, and tachycardia have been reported in clinical trials of ado-trastuzumab emtansine. In a randomized FDA-registrational trial, the overall frequency of IRRs in subjects treated with ado-trastuzumab emtansine was 1.4%. In most subjects, these reactions resolved over the course of several hours to a day after the infusion was terminated. Ado-trastuzumab emtansine treatment should be interrupted in subjects with severe IRR. Ado-trastuzumab emtansine treatment should be permanently discontinued in the event of a life-threatening IRR. Subjects should be observed closely for IRR reactions, especially during the first infusion. One case of a serious, allergic/anaphylactic-like reaction has been observed in clinical trials of single-agent ado-trastuzumab emtansine. Medications to treat such reactions, as well as emergency equipment, should be available for immediate use. Management of Infusion Reactions, Cohort 2: During the first infusion with trastuzumab, a symptom complex most commonly consisting of chills and/or fever was observed in about 40% of subjects in clinical trials. The symptoms were usually mild to moderate in severity and were treated with acetaminophen, diphenhydramine, and meperidine (with or without reduction in the rate of trastuzumab infusion). Trastuzumab discontinuation was infrequent. Other signs and/or symptoms may include nausea, vomiting, pain (in some cases at tumor sites), rigors, headache, dizziness, dyspnea, hypotension, rash and asthenia. The symptoms occurred infrequently with subsequent trastuzumab infusions.
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7. assessments

Every effort should be made to ensure that the protocol required tests and procedures are completed as described. However it is anticipated that from time to time there may be circumstances, outside of the control of the investigator, that may make it unfeasible to perform the test. In these cases the investigator will take all steps necessary to ensure the safety and well being of the subject. When a protocol required test cannot be performed the investigator will document the reason for this and any corrective and preventive actions which he/she has taken to ensure that normal processes are adhered to as soon as possible. The IRB will be informed of these incidents in a timely fashion, according to governing IRB requirements.
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7.1 safety assessment

Safety assessments will include collection of AEs, SAEs, vital signs and physical examination, ECG (12 lead), laboratory assessments, including pregnancy tests and verification of concurrent medications.
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7.1.1 adverse events

Assessment of adverse events will include the type, incidence, severity (graded by the National Cancer Institute Common Terminology Criteria for Adverse Events [NCI CTCAE] version 5) timing, seriousness, and relatedness. Baseline signs and symptoms will be recorded at baseline and then reported as adverse events during the trial if they worsen in severity or increase in frequency. Adverse events will be collected at every study visit, whether scheduled or unscheduled; at end-of-treatment; and through the Day 60 follow-up. In addition, if subjects continuing to experience toxicity (ie, treatment-related adverse events) following discontinuation of study treatment, adverse events will be collected at least every 3 weeks until resolution or determination, in the clinical judgment of the Investigator, that no further improvement is expected. Adverse events will not be collected after resolution of treatment-related toxicities or 60 days after last dose of study treatment, whichever is later. Due to pre-clinical results and human experience with compounds of a similar nature, subjects will be assessed at baseline and as medically-indicated by medical history, physical examination, and routine laboratory parameters (eg, blood chemistries) for endocrine function (including but not limited to TSH, ACTH, and cortisol levels, and may include assessment for hypopituitarism and hypoadrenalism) and hepatic events. Laboratory evaluation of hypopituitarism or hypoadrenalism should be considered in subjects who develop signs and symptoms that may include unexplained loss of body and facial hair, decreased blood pressure, and hyponatremia with hyperkalemia. In the presence of clinical suspicion, laboratory testing should include one or more of the following: TSH, ACTH, and cortisol levels before and 30 to 60 minutes after corticotrophin stimulation. Referral to an endocrinologist should be considered.
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7.1.2 laboratory safety assessments

Blood and/or urine for hematology, chemistry, coagulation, hepatitis B and C, endocrine function (as clinically indicated), urinalysis and pregnancy testing will be collected at the time points described in the Schedule of activities (Appendix 3), and analyzed at local laboratories.
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7.1.3 vital signs and physical

Subjects will have a physical exam to include weight, blood pressure, heart rate, assessment of ECOG status and height; height will be measured at baseline only. Physical examinations will be performed at the time points described in the Schedule of activities (Appendix 3).
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7.1.4 ecg assessments

Electrocardiogram (ECG): A 12-lead tracing in the supine position will be used for all ECGs at each time point (see the Schedule of Activities, Appendix 3). It is preferable that the machine used has a capacity to calculate the standard intervals automatically. If the QTc is prolonged (> 500 msec, ie, ≥ CTCAE Grade 3), then the ECGs should be re-evaluated by a qualified person at the site for confirmation as soon as the finding is made, including verification that the machine reading is accurate. If manual reading verifies a QTc of > 500 msec, immediate correction for reversible causes (including electrolyte abnormalities, hypoxia and concomitant medications for drugs with the potential to prolong the QTc interval) should be performed at the discretion of the treating physician. In addition, repeat ECGs should be performed until the QTc interval falls below 500 msec. If QTc interval reverts to less than 500 msec, and in the judgment of Investigator(s) is determined to be due to cause(s)
other than study drug, treatment may be continued with regular ECG monitoring. If in that timeframe the QTc intervals rise above 500 msec the study drug will be held until the QTc interval decreases to ≤ 500 msec. Subjects will then re-start the study drug at the next lowest dose level. If the QTc interval has still not decreased to < 500 msec after 2-weeks, or if at any time a subject has a QTc interval > 515 msec or becomes symptomatic, the subject will be removed from the study. Additional triplicate ECGs may be performed as clinically indicated. Prior to concluding that an episode of prolongation of the QTc interval is due to study drug, thorough consideration should be given to potential precipitating factors (eg, change in subject clinical condition, effect of concurrent medication, electrolyte disturbance) and possible evaluation by specialist. If subject experiences a cardiac or neurologic AE (specifically syncope, dizziness, seizures, or stroke), an ECG should (ideally) also be obtained at the time of the event.
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7.2 tumor response assessments

Tumor assessments will include all known or suspected disease sites. Imaging may include chest, abdomen and pelvis CT or MRI scans; brain CT or MRI scan for subjects with known or suspected brain metastases; bone scan; PET scan; CT/PET scan; and/or bone x-rays for subjects with known or suspected bone metastases. During screening period within 28 days of Cycle 1 Day 0, tumor assessment is required using CT scan with contrast (chest, abdomen, + pelvis), plus radionuclide bone scan or CT/PET with contrast. If central nervous system (CNS) metastasis are present, CNS imaging is required by CT or MRI.  
17 The same imaging technique used to characterize each identified and reported lesion at baseline should ideally be employed in the following tumor assessments. However, in certain clinical circumstances (eg, IV contrast allergy or nephrotoxicity from IV contrast), the most suitable imaging modality for an individual patient may be used at the discretion of the treating physician. Antitumor activity will be assessed through radiological tumor assessments conducted at baseline, during treatment as specified in the Schedule of Activity (Appendix 3), whenever disease progression is suspected (eg, symptomatic deterioration), and at the time of withdrawal from the study (if not done in the previous 6 weeks). Subjects will be followed up to 6 months from the date of the last dose of the study drug, with follow-up ending at death; disease progression; or initiation of a new anticancer therapy. During this follow-up period, subjects will have disease assessments performed every 9 weeks (± 7 days). Utomilumab is thought to stimulate patients' immune systems to attack their tumors, rather than to have a direct and immediate effect on tumor cells. In addition, drugs with a similar mechanism have been observed to have a delayed effect on tumors. It is possible that new lesions may appear early after treatment begins, before an effective immune response is induced. In addition, it is postulated that there may be initial increase in size of lesions due to infiltration of inflammatory cells, which is later followed by tumor regression. In some cases, this inflammation could make an undetectable lesion increase in size so that it appears to be a new lesion. In addition, subjects may have mixed responses, in which some lesions respond while other lesions progress or new lesions appear. There may be cases where, in the judgment of the Sponsor-investigator, a patient with a mixed response appears to be deriving benefit from the treatment. In such cases, at the discretion of the Sponsor-investigator, subjects may continue treatment until clinical benefit is no longer present in the opinion of the Investigator. Assessment of response will be made using RECIST v1.1 (for solid tumors). All subjects' files and radiologic images must be available for source verification and for potential peer review.
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7.3 pharmacokinetic assessment

PK samples will be collected as specified in the Schedule of Activity (Appendix 3), and assayed for utomilumab, ado-trastuzumab emtansine or trastuzumab using a validated analytical assay. Analysis of samples from subjects who received utomilumab and trastuzumab is optional. Details regarding the collection, processing, storage and shipping of the blood samples will be provided in the Laboratory Manual. All efforts will be made to obtain the pharmacokinetic samples at the scheduled nominal time relative to dosing. However, samples obtained within 10% of the nominal time (eg, within ± 6 minutes of a 60-minute sample) will be considered protocol compliant, and the exact time of the sample collection noted on the CRF. Wherever possible or applicable, blood samples for utomilumab concentrations should be collected at as close to the same time a pharmacodynamic biomarker samples or tumor biopsy is collected.
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7.4 immunogenicity assessment

Blood samples will be collected as specified in the Schedule of Activity (Appendix 3), and assayed for anti-drug antibodies (ADA) including, anti-utomilumab, and anti-ado-trastuzumab-emtansine or anti-trastuzumab using a validated analytical method. Analysis of samples from subjects who received utomilumab and trastuzumab is optional. Samples that are positive for ADA may also undergo characterization for neutralizing antibodies.
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7.5 pharmacodynamic assessments 7.5.1. blood

Blood will be analyzed for immune-related biomarkers that may include TNFα; IFNγ; IL10; IL-8; IL-6; IL-4; IL-2; IL-1b; IL-12p70; sFasL; CRP; sCD25; CXCL9; CXCL10; and Neopterin, etc. The specific biomarkers in the immunomodulation/cytokine release biomarker panel is subject to change based upon technical updates to the panel made by the Stanford Human Immune Monitoring Core Facility. Analysis of samples from subjects who received utomilumab and trastuzumab is optional.
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7.5.2. pharmacodynamic assessment of lymphocyte

Blood and available tumor will be analyzed for biomarkers indicative of key immune cell populations, including T-cell, NK cells, and B-cells. Analysis of samples from subjects who received utomilumab and trastuzumab is optional.
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7.5.3. t-cell receptor assessment

Blood and available tumor will be collected for future analysis of T-cell receptor frequencies using targeted sequencing. Analysis of samples from subjects who received utomilumab and trastuzumab is optional.
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7.6 tumor biopsies

Tumor biopsies will be requested, though not mandated, pre-treatment and after at least one dose of utomilumab (as clinically feasible) for CD8+ T-cells and other markers of tumor infiltrating lymphocytes, such as CD3; CD4; PD-1; 4-1BB; FoxP3; and PD-L1.
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8. adverse event reporting

Adverse events will be graded according to CTCAE v5. Both Serious and Non-Serious Adverse Events will be clearly noted in source documentation and listed on study-specific Case Report Forms (CRFs). The Principal Investigator or designee will assess each Adverse Event (AE) to determine whether it is unexpected according to the Informed Consent, Protocol Document, or Investigator's Brochure, and related to the investigation. All Serious Adverse Events (SAEs) will be tracked until resolution, or until 30 days after the last dose of the study treatment. SAEs CTCAE Grade 3 and above, and all subsequent follow-up reports will be reported to the Stanford Cancer Institute Data and Safety Monitoring Committee (DSMC) using the study specific CRF regardless of the event's relatedness to the investigation. Following review by the DSMC, events meeting the IRB definition of "Unanticipated Problem" will be reported to the IRB using eProtocol within 10 working days of DSMC review, or within 5 working days for deaths or life-threatening experiences. All observed or volunteered adverse events regardless of treatment group or suspected causal relationship to the investigational product(s) will be reported as described in the following sections. For all adverse events, the local Principal Investigator (treating physician) must pursue and obtain information adequate both to determine the outcome of the adverse event and to assess whether it meets the criteria for classification as a serious adverse event requiring immediate notification to the Sponsor-investigator (IND-holder or designate). For all adverse events, sufficient information should be obtained by the local Principal Investigator to determine the causality of the adverse event. The local Principal Investigator and/or the Sponsor-investigator will assess causality. Follow-up by the local Principal Investigator may be required until the event or its sequelae resolve or stabilize at a level acceptable to the investigator.