Clinical trial NCT03214666
Conditions: High-risk Myelodysplastic Syndromes Acute Myelogenous Leukemia Systemic Mastocytosis Mast Cell Leukemia
Keywords: Myelodysplastic Syndromes (MDS) Acute Myeloid Leukemia (AML)
Sponsor: GT Biopharma, Inc.
Start date: 2020-01-01; Completion date: 2021-09-29
Enrollment: 12 participants; Allocation: NON_RANDOMIZED; Intervention model: SEQUENTIAL

Brief summary:
This is a multi-center Phase I/II clinical trial of GTB-3550 (CD16/IL-15/CD33) tri-specific killer cell engager (TriKE®) for the treatment of CD33-expressing high risk myelodysplastic syndromes, refractory/relapsed acute myeloid leukemia or advanced systemic mastocytosis. The hypothesis is that GTB-3550 TriKE® will induce natural killer cell function by targeting malignant cells as well as CD33+ myeloid derived suppressor cells (MDSC) which contribute to tumor induced immunosuppression. Because CD16 is the most potent activating receptor on natural killer (NK) cells, this single agent may induce a targeted anti-CD33+ tumor response.

Detailed description:

Arms: arm 1: Patients receive a single course of GTB-3550 TriKE® at their assigned dose as 3 weekly treatment blocks. Each block consists of four consecutive 24 hour continuous infusions (over approximately 96 hours) of GTB-3550 TriKE® followed by a 72 hour break after Block #1 and #2. All treatment is given as an inpatient. The assigned dose will be calculated on a weight obtained within 5 days prior to or on day of the 1st dose. The dose is not be recalculated for subsequent treatment blocks. arm 2: The treatment schedule is identical to the dose finding component. The extended component uses a Simon's MiniMax two-stage design for continued enrollment using the maximum tolerated dose (MTD) established during Phase I with monitoring guidelines to stop the study early for excessive toxicity.
Interventions: intervention 1: GTB-3550 TriKE® Phase I intervention 2: GTB-3550 TriKE® Phase II
Intervention descriptions: intervention 1: The 1st two patients will be assigned Dose Level 1. The study statistician will assign each new cohort of 2 patients to the most appropriate dose level based on updated toxicity probabilities.

* Dose Level 1 - 5 μg/kg/day
* Dose Level 2 - 10 μg/kg/day
* Dose Level 3 - 25 μg/kg/day
* Dose Level 4 - 50 μg/kg/day
* Dose Level 5 - 100 μg/kg/day
* Dose Level 6 - 150 μg/kg/day
* Dose Level 7 - 200 μg/kg/day intervention 2: Patients will receive the maximum tolerated dose (MTD) established during Phase I with monitoring guidelines to stop the study early for excessive toxicity.

Protocol documents:
Prot_SAP_000.pdf: 




















 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 11 of 79 
 
7.3.4 
Neurotoxicity ........................................................................................................36 
7.3.5 
Pulmonary Toxicity...............................................................................................36 
7.3.6 
Cytokine Release Syndrome (CRS) or CRS-Like Symptoms ...............................36 
7.4 
Opportunity for Re-Treatment .....................................................................................36 
7.5 
Duration of Study Treatment .......................................................................................37 
7.6 
Duration of Study Participation ....................................................................................37 
8 
Schedule of Patient Activities .............................................................................................38 
8.1 
Required Standard of Care .........................................................................................39 
8.2 
Research Related Testing, Assessments, and Sample Collections .............................41 
8.3 
Re-Treatment Research Related Testing, Assessments, and Sample Collections ......43 
8.4 
Overview of Planned Correlative Studies ....................................................................44 
9 
GTB-3550 TriKE Description, Supply, Preparation, and Potential Toxicities .......................45 
9.1 
Product Description .....................................................................................................45 
9.2 
Product Manufacturing ................................................................................................45 
9.3 
Product Formulation ....................................................................................................45 
9.4 
How Supplied ..............................................................................................................45 
9.5 
Study Site Storage and Product Stability .....................................................................46 
9.6 
Preparation and Administration ...................................................................................46 
9.7 
Potential Toxicities ......................................................................................................47 
10 Event Monitoring, Documentation and Reporting ...............................................................48 
10.1 Definitions ...................................................................................................................48 
10.2 Event Documentation ..................................................................................................50 
10.3 Dose Limiting Toxicity Documentation and Reporting (Phase I Dose Finding) ............51 
10.4 Early Study Stopping Rules - Event Documentation and Reporting (Phase II Dose 
Expansion) ............................................................................................................................52 
10.5 Documentation of Death and Reporting Requirements ...............................................53 
10.6 Participating Sites Event Reporting Table ...................................................................54 
10.7 UMN Required Reporting: UMN IRB, GT Biopharma, 
, and Masonic Cancer 
Center’s SAE Coordinator .....................................................................................................54 
11 Study Data Collection and Monitoring ................................................................................55 
11.1 Data Management ......................................................................................................55 
11.2 Case Report Forms .....................................................................................................55 
11.3 Data and Safety Monitoring .........................................................................................55 
11.4 UMN Led Teleconferences – Participating Sites, GT Biopharma and 
 ...................56 
11.5 Record Retention ........................................................................................................56 
12 Statistical Considerations ...................................................................................................57 
12.1 Study Design and Endpoints .......................................................................................57 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 12 of 79 
 
12.2 Statistical Analysis ......................................................................................................59 
12.3 Sample Size Justification ............................................................................................59 
12.4 Monitoring Guidelines (Study Stopping Rule Events) ..................................................60 
13 Conduct of the Study .........................................................................................................61 
13.1 Good Clinical Practice .................................................................................................61 
13.2 Ethical Considerations ................................................................................................61 
13.3 Informed Consent .......................................................................................................61 
14 References ........................................................................................................................62 
Appendix I - Karnofsky Performance Status ..............................................................................65 
Appendix II - Revised International Prognostic Scoring System (IPSS-R) for Myelodysplastic 
Syndromes and Risk Assessment Calculator Link ....................................................................66 
Appendix III - Response Criteria ...............................................................................................68 
Appendix IV - P450 Drug Interactions .......................................................................................69 
Appendix V - Combined List of Drugs That Prolong QT/QTc .....................................................74 
Appendix VI - Targeted Expected Toxicities Worksheet ............................................................79 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 13 of 79 
 
Key Abbreviations 
ADCC 
antibody-dependent cell-mediated cytotoxicity 
AE 
Adverse event 
ALC 
Absolute lymphocyte count 
AML 
Acute myeloid (myelogenous) leukemia 
CAR 
chimeric antigen receptor 
CI 
Continuous infusion 
CNS 
Central nervous system 
CR 
Complete remission 
CRi 
Complete remission with incomplete hem recovery 
CRM 
continual reassessment method 
CRp 
Complete remission without platelet recovery 
CRS 
Cytokine Release Syndrome 
CTCAE 
Common Terminology Criteria for Adverse Events 
CTO 
Clinical Trials Office 
DLT 
dose limiting toxicity 
DSMC 
Data and Safety Monitoring Council 
e-CRF 
electronic case report form 
FDA 
Food and Drug Administration 
GVHD 
Graft versus host disease 
HI 
hematologic improvement 
IND 
investigational new drug 
IPSS-R 
Revised International Prognostic Scoring System 
IRB 
Institutional Review Board 
IV 
Intravenous (into a vein) 
LIMS 
Laboratory Information Management System 
mAB 
monoclonal antibodies 
MCC 
Masonic Cancer Center 
MDS 
myelodysplastic syndrome 
MDSC 
myeloid derived suppressor cells 
MTD 
maximum tolerated dose 
NK 
natural killer 
 
 
OS 
overall survival 
PFT 
pulmonary function tests 
PK/PD 
pharmacokinetic/pharmacodynamics 
PO 
per os (by mouth) 
SAE 
serious adverse event 
TriKE 
Tri-Specific Killer Engager 
TTL 
Translational Therapy Laboratory 
UMN 
University of Minnesota 
WPSS 
WHO Based Prognostic Scoring System 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 14 of 79 
 
Protocol Synopsis 
GTB-3550 (CD16/IL-15/CD33) Tri-Specific Killer Engager (TriKE™) for the Treatment of High Risk 
Myelodysplastic Syndromes, Refractory/Relapsed Acute Myeloid Leukemia and Advanced 
Systemic Mastocytosis 
 
Study 
Design: 
This is a multisite Phase I/II clinical trial of GTB-3550 (CD16/IL-15/CD33) tri-specific killer cell 
engager (TriKE™) for the treatment of CD33-expressing high-risk myelodysplastic 
syndromes, refractory/relapsed acute myeloid leukemia or advanced systemic mastocytosis. 
Up to 10 sites may participate. The hypothesis is that GTB-3550 TriKE will induce natural killer 
cell function by targeting malignant cells as well as CD33+ myeloid derived suppressor cells 
(MDSC) which contribute to tumor induced immunosuppression. Because CD16 is the most 
potent activating receptor on NK cells, this single agent may induce a targeted anti-CD33+ 
tumor response.  
 
Patients receive a single course of GTB-3550 TriKE given as 3 weekly treatment blocks. Each 
block consists of four consecutive 24 hour continuous infusions of GTB-3550 TriKE followed 
by a 72 hour break after Block #1 and #2. All treatment is given as an inpatient.  
 
Disease response is assessed by bone marrow biopsy performed between Day 21 and Day 
42 after the start of the 1st infusion. Follow-up for response and survival continues through 6 
months from treatment start. Patients experiencing lack of disease progression or evidence of 
clinical improvement and no unacceptable side effects may be considered for a 2nd course of 
GTB-3550 TriKE on a compassionate basis. 
  
The study consists of two components. The dose finding component is a modified version of 
a Phase I trial and the extended component is a modified Phase II trial.  
 
Phase I Dose Finding Component:   
The Phase I component uses a continual reassessment method (CRM) to determine the 
maximum tolerated dose (MTD) of GTB-3550 TriKE. Up to 7 doses levels will be tested. The 
goal of the CRM is to identify the dose level which most closely corresponds to the targeted 
dose limiting toxicity (DLT) rate of 20%. Patients are enrolled in cohorts of 2 beginning at Dose 
Level 1. A minimum of 1 week must separate each patient. Both patients within a cohort must 
reach Day 28 (end of the DLT assessment period) prior to enrollment of a subsequent cohort. 
The study statistician assigns each new cohort of 2 patients to the most appropriate dose level 
based on updated toxicity probabilities. As enrollment proceeds, each cohort is assigned to 
an increased, decreased or equivalent dose level based on prior data in the trial until the study 
sample reaches 30. At this time, the last dose is declared the MTD and becomes the GTB-
3550 TriKE dose for the extended component.  
 
Phase II Extended Component:   
The primary goal of the extended component is to study the potential efficacy of GTB-3550 
TriKE in this patient population. Efficacy is measured using rates of complete and partial 
remission. A Simon’s MiniMax two-stage design is used in this phase. Stage 1 will enroll 13 
patients, including all patients treated at the MTD defined during the dose finding component. 
If 3 or more of these 13 patients experience a clinical response by Day 42, the trial moves to 
Stage 2 and enrolls an additional 17 patients. If at least 10 of the 30 patients have a disease 
response, GTB-3550 TriKE will be considered for further investigation. There is no staggering 
of enrollment for this cohort. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 15 of 79 
 
 
Primary 
Objectives: 
Phase I Dose Finding:  To identify the maximum tolerated dose (MTD) of GTB-3550 TriKE 
defined as the dose level that most closely corresponds to a dose limiting toxicity rate (DLT) 
of 20%.  
Phase II Extension:  To determine preliminary efficacy as measured by the rates of “best” 
clinical response by Day 42 day after the start of the 1st infusion. For AML clinical response 
includes complete remission with or without hematologic or platelet recovery (CR, CRi or 
CRp) or partial response. For MDS clinical response includes complete remission, marrow 
CR (with incomplete peripheral blood count normalization), partial response or hematologic 
improvement (HI). For advanced systemic mastocytosis response is considered a decrease 
in mast cell burden in bone marrow or serum tryptase level by at least 30%.  
 
Secondary 
Objectives: 
• To evaluate the safety of GTB-3550 TriKE when administered on this schedule 
• To estimate overall survival (OS) at 6 months 
 
Correlative 
Objectives: 
• To monitor the number, phenotype, activation status and function of NK cells, T cells, 
T regulatory cells and MDSCs pre- and post-therapy (
 
)  
• To evaluate the pharmacokinetics and dynamics of the TriKE reagent 
• To monitor for the development of human anti-TriKE antibodies 
• To monitor the occurrence of antigen negative escape variants (
) in patients 
without response 
 
Eligible 
Diseases: 
Diagnosis of one of the following CD33-expressing myeloid malignancies with greater than 
or equal to 50% CD33+ target cells with no good standard of care treatment options 
including: 
High Risk Myelodysplastic Syndromes (MDS) progressive on two or more prior regimens 
and requiring treatment that meets at least one of the following: 
• 
IPSS-R High or Very High Risk  
• 
WHO Classification: RAEB-1 or RAEB-2 
• 
Poor and very poor risk cytogenetic abnormality as defined by the IPSS-R 
cytogenetic classifications 
• 
WHO Based Prognostic Scoring System (WPSS): High or Very High Risk 
Therapy related MDS and not a candidate for induction chemotherapy or had an inadequate 
treatment response after induction chemotherapy 
  
Acute Myelogenous Leukemia (AML) meeting at least one of the following:  
• 
Refractory AML defined as failure to achieve remission after at least 3 induction 
attempts  
o 
Elderly AML not fit for induction therapy can be enrolled after 2 failed 
inductions 
• 
Relapsed AML meeting one of the following: 
• 
Not a candidate for hematopoietic stem cell transplant (HSCT), at least one re-
induction attempt required  
• 
Prior HSCT relapse beyond 3 months may be included only if off 
immunosuppression for a minimum of 4 weeks and do not have GVHD 
 
Advanced systemic mastocytosis (defined as mast cell leukemia, aggressive systemic 
mastocytosis, and systemic mastocytosis associated with hematologic neoplasm) may enroll 
without any prior treatment, given there is no standard established therapy. 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 16 of 79 
 
Key 
Inclusion 
Criteria: 
• Age ≥ 18 years of age, Karnofsky performance status ≥ 70% 
• Adequate renal, hepatic, cardiac and lung function 
• Absolute lymphocyte count (ALC) ≥ 200 cells/mm³ OR absolute circulating CD56+/CD3- 
NK cell count >25 cells/µL within the 14 days prior to start of therapy 
 
 
Enrollment: 
Dose Finding Component: 30 patients enrolled in cohorts of 2 testing up to 7 GTB-3550 
TriKE dose levels 
 
Extended Component: 
Stage 1: enroll 13 patients at the MTD (including any from the dose finding component 
treated at the MTD) – If 3 or more of these 13 patients experience a clinical response by 
Day 42, the trial will move to Stage 2 
 
Stage 2: enroll 17 additional patients at the MTD established during the dose finding 
component 
 
If the Phase I component enrolls more than 13 patients at the MTD, the futility rule for the 
two stage design will be adjusted with the given number of patients enrolled at the MTD. 
 
 
 




 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 18 of 79 
 
• 
Hematologic Toxicity - Given that AML and MDS inherently leads to low neutrophils and platelets, standard 
grading cannot be used as many of these patients technically meet criteria for “grade 4” neutropenia or 
thrombocytopenia at baseline. Thus, the hematologic DLTs are listed below: 
o AML: 
 Grade 4 neutrophil count (<500/µL) lasting ≥ 29 days from start of cycle in absence of evidence of 
active leukemia 
 Grade 4 platelet count (<25,000/µL) lasting ≥ 29 days from start of cycle in the absence of active 
leukemia 
 Any clinically significant bleeding that is not controllable with transfusion support 
o MDS/mast cell diseases: 
 Grade 4 neutrophil count (<500/µL) lasting ≥ 29 days from start of cycle in absence of evidence of 
active MDS/mast cell disease 
 Grade 4 platelet count (<25,000/µL) lasting ≥ 29 days from start of cycle in the absence of active 
MDS/Mast cell disease 
 Any clinically significant bleeding that is not controllable with transfusion support 
 Grade 4 anemia, unexplained by the underlying disease 
• 
Grade 3 infusion related, treatment related reaction including cytokine release syndrome which does not 
resolve within 72 hours despite best medical management (refer to Section 10 for modified CRS grading) 
• 
Grade 3 or 4 Tumor Lysis Syndrome that does not resolve within 7 days with or without intervention 
• 
Inability to complete at least one block of three 24 hour infusions due to any treatment emergent, treatment 
related toxicity 
 
Maximum Tolerated Dose (MTD) is defined as the dose level that most closely corresponds to the target DLT 
rate of 20%. 
 
Additional Dose Escalation Parameters (Phase I Only): 
In addition to monitoring for dose limiting toxicity, patients enrolled in the Phase I component will be monitored 
for signs of immune activation using treatment related tachycardia and fever as clinical markers of transient 
bioactivity resulting from endogenous cytokine release. If detected in a single patient, subsequent dose levels 
will increase by 50% instead of the planned doubling (100% increase). 
 
Extended Phase II Component: 
Patients will receive three consecutive blocks of four 24 hour continuous infusions of GTB-3550 TriKE at the 
Phase I MTD separated by a 72 hour rest. There is no staggering of enrollment for this component.  
 
Stage 1: Enroll a total of 13 patients (including all treated at the MTD in Phase I). If 3 or more of these patients 
have clinical response by Day 42 the trial will continue to Stage 2. If the Phase I component enrolls more than 
13 patients at the MTD, the futility rule for the two-stage design will be adjusted with the given number of patients 
enrolled at the MTD. 
 
Stage 2: Enroll an additional 17 patients. If 10 of 30 patients have a clinical response by Day 42, GTB-3550 
TriKE will be considered promising for further investigation. 
 
Monitoring for Safety (Phase II Extended): 
• Grade 4-5 non-hematologic, non-relapse, non-infectious toxicity (except fever) by 42 days after the start of the 
first GTB-3550 TriKE treatment block  
• Non-relapse, non-infectious treatment related mortality within 60 days of the 1st dose of GTB-3550 TriKE  
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 19 of 79 
 
1 Objectives 
1.1 Primary Objective 
Phase I Dose Finding: To identify the maximum tolerated dose (MTD) of GTB-3550 
TriKE defined as the dose level that most closely corresponds to a dose limiting 
toxicity rate (DLT) of 20%. 
Phase II Extension: To determine preliminary efficacy as measured by the rates of 
“best” clinical response by Day 42 after the start of the 1st infusion.  
For AML clinical response includes complete remission with or without hematologic 
or platelet recovery (CR, CRi or CRp) or partial response. For MDS clinical response 
includes complete remission, marrow CR (with incomplete peripheral blood count 
normalization), partial response or hematologic improvement (HI). For advanced 
systemic mastocytosis response is considered a decrease in mast cell burden in 
bone marrow or serum tryptase level by at least 30%.  
1.2 Secondary Objectives 
• To evaluate the safety of GTB-3550 TriKE when administered on this schedule 
• To estimate overall survival (OS) at 6 months 
1.3 Correlative (Research) Objectives 
• 
 
 
  
• To evaluate the pharmacokinetics and dynamics of the TriKE reagent 
• 
 
• To monitor the occurrence of antigen negative escape variants (CD33- blasts) 
in patients without response 
2 Background 
Acute myeloid leukemia (AML) is a heterogeneous hematologic stem cell malignancy in 
adults with incidence rate of 3–5% per 100,000 populations. The median age at the time 
of diagnosis is 65–69 years.1,2 AML is an aggressive disease and is fatal without 
anti-leukemic treatment. Myelodysplastic syndromes (MDS) are a heterogeneous group 
of 
myeloid 
neoplasms 
characterized 
by 
dysplastic 
features 
of 
erythroid/myeloid/megakaryocytic lineages, progressive bone marrow failure, a varying 
percentage of blast cells, and enhanced risk to evolve into acute myeloid leukemia3. The 
incidence of MDS is rising especially in states like Minnesota for unknown reasons.  There 
are few established treatments for MDS so a drug that could be successfully employed 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 20 of 79 
 
to treat AML and MDS would be extremely valuable. The expression of cell surface 
markers in MDS is complicated by its heterogeneous nature and has only been recently 
brought to light with the work of the First Workshop on Standardization of Flow Cytometry 
in MDS convened in Amsterdam bringing together experts from Europe, Japan, and the 
USA4. The workshop found that a majority of MDS cases showed an abnormally high 
expression of HLA-DR, CD64, and CD33. We believe that CD33 is a validated target in 
AML and can also target MDS cells to promote a novel targeted immunotherapy approach 
for these diseases. 
Targeted cancer immunotherapies are currently a subject of great clinical interest and 
potential 5. While a great deal of interest has recently been placed upon generation of 
chimeric antigen receptor (CAR) expressing T cells from monoclonal antibodies shown to 
target human malignancies 6, and more even more recently upon generation of 
CAR-expressing natural killer (NK) cells 7,8, these approaches require a personalized 
approach that is expensive, time consuming, and difficult to apply on a large scale. There 
is a clear need for targeted off-the-shelf therapies that augment the current monoclonal 
antibody approach. To accomplish this goal, we focus on generation of tri-specific killer 
engagers (TriKEs) meant to target NK cells to the tumor synapse and induce their 
activation at that site. Unlike full-length tri-specific antibodies,
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In human NK cells,
 
 
 
 
 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 21 of 79 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 The efficacy of therapeutic mAbs in vivo, in contrast 
to their high ADCC efficacy in vitro, is further attenuated by the presence of physiologic 
serum IgG levels in plasma. In the in vivo setting, ADCC potency is diminished by 
saturation of CD16 receptors, thus competing for binding with the therapeutic mAb 36. 
Such competition for binding of the therapeutic Fc portion of antibodies requires high 
serum levels of the mAb to be sustained over several months of treatment in order to 
achieve in vivo efficacy 37,38.
 
 
 
 
 
These attributes make them an ideal pharmaceutical platform for potentiated NK cell-
based immunotherapies. 
3 Summary and Rationale 
The most important aspects of the humoral (antibody) response against cancer is 1) the 
ability of antibody to mediated antibody dependent cellular cytotoxicity (ADCC) through 
CD16, 2) the ability to mediate in vivo expansion of the immune population to recruit more 
killers to generate an anti-cancer response (the IL-15 linker) and 3) recognition of a target 
antigen (like CD33 being tested here). 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 22 of 79 
 
 
 
 
 
 
 
 
 
  
The Trispecific Killer Engager (TriKE) designated GTB-3550 was designed as a 
straightforward off-the-shelf product that can be used to treat CD33+ AML/MDS patients 
in a manner similar to the way rituximab is used to treat B cell malignancies. We believe 
that a major advantage of our drug as compared to chimeric antigen receptor (CAR) 
transduced T cells that require cell and gene therapy is the simplicity of our approach. 
 
 
 The MTD of exogenous IL-15 
in humans following continuous IV infusion is 2 ug/kg/day for a total of 10 days 
(240 hours). 
 
4 Study Design 
This is a multisite Phase I/II clinical trial of GTB-3550 (CD16/IL-15/CD33) tri-specific killer 
cell engager (TriKE) for the treatment of CD33-expressing high risk myelodysplastic 
syndromes, refractory/relapsed acute myeloid leukemia or advanced systemic 
mastocytosis. Up to 10 study centers may take part in this trial.  
Patients receive a single course of GTB-3550 TriKE given as 3 weekly treatment blocks. 
Each block consists of four consecutive 24 hour continuous infusions of GTB-3550 TriKE 
followed by a 72 hour break after Block #1 and #2. All treatment is given as an inpatient.  
Toxicities are monitored through Day 28 (as assessed on Day 29) with continued toxicity 
assessment through Day 60. Disease response is assessed by bone marrow biopsy 
performed between Day 21 and 42 after the start of the 1st infusion. Follow-up for 
response and survival continues through 6 months from study treatment start. 
The study consists of two components. The dose finding component is a modified version 
of a Phase I trial and the extended component is a modified Phase II trial. 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 23 of 79 
 
Dose Finding Component: The Phase I component uses a continual reassessment 
method (CRM) to determine the maximum tolerated dose (MTD) of GTB-3550 TriKE. Up 
to 7 doses levels will be tested. The goal of the CRM is to identify the dose level which 
most closely corresponds to the targeted dose limiting toxicity (DLT) rate of 20%.  
 
Patients are enrolled in cohorts of 2 beginning at Dose Level 1. A minimum of 1 week 
must separate each patient. Both patients within a cohort must reach Day 28 (end of the 
DLT assessment period) prior to enrollment of a subsequent cohort. The study statistician 
assigns each new cohort of 2 patients to the most appropriate dose level based on 
updated toxicity probabilities. As enrollment proceeds, each cohort is assigned to an 
increased, decreased or equivalent dose level based on prior data in the trial until the 
study sample reaches 30. At this time, the last dose is declared the MTD and the GTB-
3550 TriKE dose for the extended component.  
 
Extended Component: The primary goal of the extended component is to study the 
potential efficacy of GTB-3550 TriKE in this patient population. Efficacy is measured using 
rates of complete and partial remission. A Simon’s MiniMax two-stage design is used in 
this phase. Monitoring guidelines are in place to stop the study early for excessive toxicity. 
 
Stage 1 enrolls 13 patients, including all patients treated at the MTD defined during the 
dose finding component. If 3 or more of these 13 patients have a clinical response to 
GTB-3550 TriKE, the trial moves to Stage 2 and enrolls an additional 17 patients. If the 
Phase I component enrolls more than 13 patients at the MTD, the futility rule for the 
two-stage design will be adjusted with the given number of patients enrolled at the MTD.  
 
If at least 10 of the 30 patients have a clinical response, GTB-3550 TriKE will be 
considered for further investigation.  
 
Patients experiencing clinical benefit (defined as stable or better) at the time of the 1st 
disease reassessment may be considered for a 2nd course of GTB-3550 TriKE on a 
compassionate basis provided they experienced no side effects equivalent to a DLT and 
continue to meet relevant study inclusion/exclusion criteria. Refer to Section 7.4 for 
additional information. 
 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 24 of 79 
 
5 Patient Selection 
Study entry is open to adult patients 18 years of age and older regardless of gender, race, 
or ethnic background. While there will be every effort to seek out and include women and 
minority patients, the patient population is expected to be no different than that of other 
high risk malignancies studies at the University Of Minnesota and other participating 
institutions.  
A potential participant must meet all of the inclusion and exclusion criteria to be 
considered eligible for study participation.  
5.1 Eligible Diseases 
Diagnosis of one of the following CD33-expressing myeloid malignancies with 
greater than or equal to 50% CD33+ target cells with no good standard of care 
treatment options including: 
 
High Risk Myelodysplastic Syndromes (MDS) progressive on two or more prior 
regimens and requiring treatment that meets at least one of the following: 
• IPSS-R High or Very High Risks 
• WHO Classification: RAEB-1 or RAEB-2 
• Poor and very-poor risk cytogenetic abnormality as defined by the IPSS-R 
cytogenetic classifications 
• WHO Based Prognostic Scoring System (WPSS): High or Very High Risk 
 
Therapy related MDS and not a candidate for induction chemotherapy or had an 
inadequate treatment response after induction chemotherapy. 
 
Refractory or Relapsed Acute Myelogenous Leukemia (AML) meeting at least one 
of the following:  
• Refractory AML defined as failure to achieve remission after at least 3 induction 
attempts 
o Elderly AML not fit for induction therapy can be enrolled after 2 failed 
inductions 
• Relapsed AML 
o Not a candidate for hematopoietic stem cell transplant (HSCT), at least one 
re-induction attempt required  
o Prior HSCT relapse beyond 3 months may be included only if off 
immunosuppression for a minimum of 4 weeks and do not have GVHD 
Notes: 
1) For hypomethylating agents (i.e. decitabine, azacititdine) to count as an induction/re-induction 
attempt, the patient must have completed a minimum of 3 monthly cycles 
2) For targeting agents (i.e. sorafenib) to count as an induction/re-induction attempt, the patient 
must have completed a minimum of 1 month without attaining CR 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 25 of 79 
 
Advanced systemic mastocytosis (defined as mast cell leukemia, aggressive 
systemic mastocytosis, and systemic mastocytosis associated with hematologic 
neoplasm) may enroll without any prior treatment, given there is no standard 
established therapy. 
5.2 Age, Performance Status, Organ Function, Contraception Use 
• At least 18 years of age 
• Karnofsky score ≥ 70% (Appendix I) 
• Adequate organ function within 14 days (30 days for cardiac and pulmonary) of 
study enrollment defined as: 
o Renal: an estimated glomerular filtration rate ≥ 60 mL/min/1.73 m2  
o Hepatic: AST, ALT, alkaline phosphatase and total bilirubin within normal 
range   
o Pulmonary function: DLCO corrected (ml/min/mm Hg) defined as no more 
than 5 units below lower limit of normal (CTCAE v5 Grade 1 carbon 
monoxide diffusing capacity decreased) based on patient’s height, weight, 
and gender as reported by the institutional pulmonary function lab. 
o Cardiac: Absence of decompensated congestive heart failure, or 
uncontrolled arrhythmia; left ventricular ejection fraction ≥ 45% by 
echocardiogram, MUGA or cardiac MRI. 
• Absolute lymphocyte count (ALC) ≥ 200 cells/mm³ OR absolute circulating 
CD56+/CD3- NK cell count >25 cells/µl within the 14 days prior to start of therapy  
• Sexually active females of childbearing potential and males with partners of 
child-bearing potential must agree to use adequate birth control during study 
treatment 
• Participant provides voluntary written consent signed before performance of any 
study-related procedure not part of normal medical care 
5.3 Exclusion Criteria 
• New or progressive pulmonary infiltrates on screening chest x-ray or chest CT 
scan unless cleared for study by Pulmonary. Infiltrates attributed to infection 
must be stable/improving with associated clinical improvement after 1 week of 
appropriate therapy (4 weeks for presumed or documented fungal infections).  
• Uncontrolled bacterial, fungal or viral infections, known history of HIV  
• Active Hepatitis B or Hepatitis C (virus detectable by PCR) - chronic 
asymptomatic viral hepatitis is allowed 
• Other concurrent active cancer within the last year (excluding non-melanoma 
skin cancers) 
• Severely clinically obese patients, BMI >38 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 26 of 79 
 
• Currently taking any over-the-counter [OTC], vitamin, mineral, or dietary 
supplement within 14 days prior to study drug administration on Day 1 and 
during study conduct that may confound study safety goals (e.g. St. John’s 
wort). Questions should be discussed with GT Biopharma. 
• Pregnant or breast feeding. The effect of GTB-3550 TriKE on the fetus is 
unknown. Females of childbearing potential must have a blood test within 7 days 
prior to enrollment to rule out pregnancy - must be repeated if not within 7 days 
of treatment initiation 
• History of central nervous system malignancy or symptoms of active CNS 
disease 
• A family history of long QT syndrome or with a QTc interval > 480 msec at 
screening 
• Currently taking medications known to prolong QT/QTc interval as the potential 
risk of QT/QTc prolongation is unknown in humans (refer to Appendix V for a 
list of prohibited medications for eligibility) 
• A candidate for potentially curative therapy, including hematopoietic cell 
transplant 
• Unwilling to remain within a 90 minute drive of the study center through at least 
Day 29 
6 
Patient Screening and Study Enrollment 
Written consent must be obtained prior to the performance of any research related 
tests or procedures. Consent is usually obtained before final eligibility is determined. 
6.1 Consent and Study Screening in 
  
Any patient who has been consented is to be entered in 
 by the Study 
Coordinator or designee. If a patient is consented but is not enrolled in the study 
treatment, the patient’s record is updated in 
 as a screen failure and reason 
for exclusion recorded.  
6.2 Prior and Concomitant Therapy:  
All non-study medications, including prescription, OTC, or herbal therapies, used 
by the patient will be documented (i) for the 14 days prior to screening (prior 
medications), (ii) during screening, and (iii) throughout the study (concomitant 
medications). The Investigator in communication with the Sponsor will review and 
determine if prior/concomitant medication(s) affect the patient’s eligibility to 
participate or continue to participate in the study. 
Administering medications known to elevate Liver Function Tests (LFTs) during 
the treatment interval and the week before should be avoided. Azole antifungal 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 27 of 79 
 
agents frequently increase liver function tested in >10% of subjects. For 1 week 
prior to and concurrent with GTB-3550 administration, patients should be treated 
with micafungin if medically indicated. 
6.3 Study Enrollment and GTB-3550 TriKE Dose Level  
To be eligible for this study, the patient must sign the treatment consent and meet 
each inclusion criteria and none of the exclusion criteria listed on the eligibility 
checklist based on the eligibility assessment documented in the patient’s medical 
record. 
To complete enrollment in 
, the Study Coordinator or designee records the 
GTB-3550 TriKE dose level assignment. 
6.4 Inability to Begin Study Treatment 
If a patient is enrolled to the study, and is later found not able begin the study 
treatment, for whatever reason, the patient will be taken off study and treated at 
the physician’s discretion. The Study Coordinator or designee will update 
 
of the patient’s non-treatment status. The patient will be replaced to fulfill 
enrollment requirements. 
6.5 Re-Treatment Enrollment onto 2015LS167R 
Any patient, in the judgement of the Principal Investigator, who experiences lack 
of disease progression or evidence of clinical improvement after completion of the 
1st treatment course may be considered for retreatment per Section 7.4. To be 
eligible for re-treatment the patient must sign the re-treatment consent and meet 
each inclusion criteria and none of the exclusion criteria listed on the eligibility 
checklist based on the eligibility assessment documented in the patient’s medical 
record. Any qualifying patient who has signed the re-treatment consent is entered 
onto the re-treatment protocol (
) in 
 by the Study Coordinator 
or designee. 
7 Treatment Plan 
In order to provide optimal patient care and to account for individual medical 
conditions, investigator discretion may be used in the prescribing of all supportive care 
drug therapy (i.e. acetaminophen, diphenhydramine, G-CSF, antimicrobials, etc.). 
7.1 GTB-3550 TriKE Administration 
Patients receive a single course of GTB-3550 TriKE at their assigned dose as 3 
weekly treatment blocks. Each block consists of four consecutive 24 hour 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 28 of 79 
 
continuous infusions (over approximately 96 hours) of GTB-3550 TriKE followed 
by a 72 hour break after Block #1 and #2. All treatment is given as an inpatient.  
The assigned dose will be calculated on a weight obtained within 5 days prior to 
or on day of the 1st dose. The dose is not be recalculated for subsequent treatment 
blocks. 
 
The institutional Investigational Pharmacy will prepare each 24 hour bag for 
infusion per Section 9.6 based on the patient’s assigned GTB-3550 TriKE dose. 
Each assigned dose will be administered as a 100 mL infusion over 24 hours 
period at 4.17 mL/hour rate. Note: actual bag volume is 130 ml to allow for the 
product sample collection before and after infusion. 
Pre-meds: 
Pre-meds: 30 minutes prior to each infusion, patients will receive acetaminophen 
325 mg PO and diphenhydramine 25mg PO/IV. Repeat prn. 
 
IV Fluid Management: 
IV fluids should be administered at a minimum rate of 50 cc/hour additional fluids 
given based on the clinical status of the patient. 
 
Infusion Related Reactions: 
If Grade 2 infusion related reaction occurs, interrupt the infusion and treat 
symptomatically with antihistamines, NSAIDS, narcotics, IV fluids as medically 
appropriate. Any patient experiencing a second Grade 2 infusion related reaction 
after restarting, despite pre-medication or a Grade 3 or 4 infusion related reaction 
will be permanently discontinued from GTB-3550 TriKE. 
Administration of glucocorticoids is prohibited during the TriKE treatment period as 
the use of systemic steroid medications may result in loss of therapeutic effects of 
the study drug. They should be avoided except in the event of a severe toxicity.  
Any Grade 3 or 4 infusion related reaction will result in permanent discontinuation 
of study drug with appropriate medical intervention.  
Post-Infusion TriKE Sample Collection (Week 1 infusions only): 
Upon completion of each infusion during Week 1 only, the nursing staff will 
disconnect the infusion bag and tubing from the patient. Prior to discarding the bag 
and tubing, two pre-labeled 1.8 ml cryo-vial (containing wording "Post-Infusion" as 
well as dose and date when bag was prepared) will be filled with a minimum of 
1 ml of drug each. This may be done on the unit or the bag/tubing transferred to 
the institutional research lab and samples collected there. Regardless, the vials or 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 29 of 79 
 
infusion bag/tubing must be refrigerated while awaiting transfer to the research lab. 
The research lab will freeze samples for later batch shipping to UMN TTL (if 
applicable) and testing. Refer to Section 8.2 for additional details. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 30 of 79 
 
7.1.1 Monitoring Requirements During TriKE Infusions 
Monitoring during the 1st infusion of each continuous infusion (CI) block: 
Vital signs including blood pressure, pulse, temperature, respirations, and 
pulse oximetry will be measured as follows: 
• prior to the infusion start 
• every 15 minutes (±10 minutes) during the 1st hour  
• every 30 minutes (±10 minutes) during the 2nd hour 
• every 60 minutes (±10 minutes) for the next 2 hours 
• then every 4 hours (±20 minutes) for the remainder of the infusion 
 
Monitoring during the infusion 2, 3, and 4 of each CI block:  
Vital signs including blood pressure, pulse, temperature, respirations, and 
pulse oximetry will be measured as follows: 
• every 15 minutes (±10 minutes) during the 1st hour  
• then every 4 hours (±20 minutes) for the remainder of the infusion 
 
Targeted toxicities (Appendix VI) and unexpected adverse events will be 
collected at the time points listed in Section 10.2. 
7.1.2 Monitoring for Signs of Immune Activation (Phase I Patients): 
In addition to monitoring as above, patients enrolled in Phase I will be 
monitored for clinical signs of immune activation: 
• treatment related tachycardia defined as a heart rate of >30 BPM than 
baseline heart rate measured each cycle pre-infusion and persists for 4 
hours 
• fever defined as Grade 2 (>39.0 - 40.0 degrees C [102.3 - 104.0 degrees 
F]) and persists for 4 hours 
 
If a patient meets either of the above criteria, no dose adjustment will be made 
unless a dose limiting toxicity (DLT) occurs. Refer to Section 7.2.1 for impact 
on subsequent dose level escalation. 
7.1.3 Supportive Care/Concomitant Medications  
Supportive measures may include acetaminophen for fevers, meperidine for 
chills, anti-emetics for nausea and vomiting, normal saline or furosemide to 
maintain fluid balance/blood pressure/pulmonary function, and electrolyte 
replacement. Use of G-CSF is permitted as clinically indicated. Refer to 
Section 7.3 for management of selected toxicities. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 31 of 79 
 
Administration of glucocorticoids is prohibited during the TriKE treatment period 
as the use of systemic steroid medications may result in loss of therapeutic 
effects of the study drug. They should be avoided except in the event of a 
severe toxicity. 
The potential risk of QT/QTc prolongation is unknown in humans receiving 
TriKE. Persons with a family history of long QT syndrome, with a QTc interval 
> 480 msec at screening, or taking concurrent medications known to prolong 
QT/QTc interval are not eligible for this study. The use of medications known 
to prolong QT/QTc interval (refer to Appendix V) are prohibited between 
screening and the end of treatment visit if at all possible. 
The interactions between TriKE and the P450 system are unknown. The IL-15 
component may affect substrates of CYP3A4 and CYP2D6 substrates. See 
Appendix IV for a list of drugs which may be affected. Patients with unexpected 
toxicity should have a review of their con-meds to determine whether there are 
any potential interactions. The PI or treating physician should consider 
discontinuing these medications as clinically indicated. 
All concomitant medications, with a start and stop date must be documented 
relative to administration of GTB-3550 TriKE. 
7.1.4 Dose Modifications 
No individual patient dose modifications are permitted other than as described 
in Section 7.3.3 for elevated liver enzymes. 
7.1.5 Criteria to Continue with GTB-3550 TriKE Block #2 and #3 
A dose limiting toxicity (for any patient, not just dose finding) during the previous 
block’s infusions (defined in Section 7.2.1) will disqualify a patient from 
receiving further therapy. 
 
Disease based treatment decisions: If after completing Block #1 and Block 
#2, the patient has clear evidence of disease progression they will be 
discontinued from study treatment and further treatment with study drug is to 
be discontinued. Such patients remain fully evaluable for efficacy and toxicity. 
  
To begin a new block, on the day of the planned treatment the patient must: 
 not currently meet any disease specific hematologic dose limiting toxicity 
as defined in Section 7.2.1. 
 have an estimated glomerular filtration rate ≥ 60 mL/min/1.73 m2  
 have a total bilirubin of ≤1.5 times the ULN 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 32 of 79 
 
 have AST and ALT ≤ 3 x upper limit of normal, and alkaline phosphatase 
levels ≤ 2.5 x upper limit of normal  
 be afebrile (defined as a temperature of ≤ 101ºF) 
 have room air 02 saturation ≥ 88% 
 have a blood pressure ≥ 100/65 mm/Hg 
 have no signs or symptoms of infection 
 
If the above criteria is not met, treatment must be delayed for appropriate 
supportive care and clinical assessment. The study drug may begin the 
following day, if the above criteria are met and, in the opinion of the clinical 
provider it is safe to proceed. Otherwise delay 1 week from the planned start 
and reassess at that time.  
 
Patients unable to begin treatment after a 1 week delay will be permanently 
discontinued from treatment and followed per Section 7.6. 
 
The start of Block #2 or Block #3 may be delayed for up to 1 week (i.e. start 
1 week later than planned) to allow for the resolution of any treatment or 
non-treatment issues (i.e. URI, UTI, etc.) or for holiday/scheduling issues. 
 
7.2 GTB-3550 TriKE Dose Levels 
7.2.1 Dose Finding Component (Phase I) 
The 1st two patients will be assigned dose level 1. The study statistician (UMN 
biostatistician Todd DeFor or designee) will assign each new cohort of 2 
patients to the most appropriate dose level based on updated toxicity 
probabilities. Both patients within a dose cohort must reach Day 28 (end of the 
DLT assessment period) prior to enrollment of a subsequent cohort. Enrollment 
continues until 30 evaluable patients are accrued. 
 
Dose 
Level 
GTB-3550 TriKE Dose 
daily continuous infusion 
(CI) dose (µg/kg/day) 
1 
5 
2 
10 
3 
25 
4 
50 
5 
100 
6 
150 
7 
200 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 33 of 79 
 
Dose Limiting Toxicity (DLT) is defined as any of the following related 
treatment emergent toxicity with the exception of those that are clearly and 
incontrovertibly due to extraneous causes within 28 days (as assessed on Day 
29) of the first dose of TriKE for the following criteria based on CTCAE v5: 
 
• Any Grade 4 or 5 non-hematologic events  
• Grade 3 non-hematologic adverse events lasting more than 72 hours, 
except the following:  
o Non-sustained (< 7 days) Grade 3 liver function tests (ALT/AST, alkaline 
phosphatase, total or direct bilirubin) abnormalities in the absence of 
clinical signs of hepatic dysfunction (lethargy, confusion, anorexia, 
pruritus or tremors). 
o Non-sustained Grade 3 QTc prolongation (< 72 hours) in the absence of 
cardiac arrhythmia 
o Grade 3 electrolyte disturbances that resolve, with or without intervention, 
to < Grade 2 levels within 72 hours 
o Grade 3 fatigue 
o Grade 3 anorexia 
o Grade 3 fever 
o Grade 3 infection 
• Hematologic Toxicity - Given that AML and MDS inherently leads to low 
neutrophils and platelets, standard grading cannot be used as many of 
these patients technically meet criteria for “Grade 4” neutropenia or 
thrombocytopenia at baseline. Thus, the hematologic DLTs are listed 
below: 
o AML 
 Grade 4 neutrophil count (< 500/µL) lasting ≥ 29 days from start of cycle 
in absence of evidence of active leukemia 
 Grade 4 platelet count (< 25,000/uL)  lasting ≥ 29 days from start of cycle 
in absence of evidence of active leukemia  
Any clinically significant bleeding that is not controllable with transfusion 
support 
o 
MDS/mast cell diseases: 
 Grade 4 neutrophil count (<500/µL) lasting ≥ 29 days from start of cycle 
in absence of evidence of active MDS/mast cell disease 
 Grade 4 platelet count (<25,000/µL) lasting ≥ 29 days from start of cycle 
in the absence of active MDS/Mast cell disease 
 Any clinically significant bleeding that is not controllable with transfusion 
support 
 Grade 4 anemia, unexplained by the underlying disease 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 34 of 79 
 
• Grade 3 infusion related, treatment related reaction including cytokine 
release syndrome which does not resolve within 72 hours despite best 
medical management (refer to Section 10 for modified CRS grading) 
• Grade 3 or 4 Tumor Lysis Syndrome that does not resolve within 7 days 
with or without intervention 
• Inability to complete at least one block of three 24 hour infusions due to any 
treatment emergent, treatment related toxicity.  
 
Maximum Tolerated Dose (MTD) is defined as the dose level that most closely 
corresponds to the target DLT rate of 20%. 
 
Additional Dose Escalation Parameters (Phase I Only): 
In addition to monitoring for dose limiting toxicity, patients enrolled in the 
Phase I component will be monitored for signs of immune activation using 
treatment related tachycardia and fever as clinical markers of transient 
bioactivity. Refer to Section 7.1.2 Monitoring for Signs of Immune Activation 
(Phase I patients) for the definition of tachycardia and fever thresholds. 
If detected in a single patient (fever or tachycardia lasting > 4 hours OR meets 
criteria for any DLT) subsequent dose levels will increase by 50% instead of 
the planned doubling (100% increase). For example, if signs of immune 
activation occurred at Dose Level 4 (50 µg/kg/day), Dose Level 5 would be 
adjusted to 75 µg/kg/day rather than 100 µmg/kg/day and Dose Level 6 would 
be 115 µg/kg/day (75 x 1.5 rounded up to the nearest 5) rather than 200 
µg/kg/day. 
7.2.2 Extended Component (Phase II) 
The treatment schedule is identical to the dose finding component. The 
extended component uses a Simon’s MiniMax two-stage design for continued 
enrollment using the maximum tolerated dose (MTD) established during 
Phase I with monitoring guidelines to stop the study early for excessive toxicity. 
 
In Stage 1, a total of 13 patients (including all treated at the MTD in part 1) will 
be enrolled. If 3 or more of these have clinical response the trial will continue 
to Stage 2. If the phase I component enrolls more than 13 patients at the MTD, 
the two-stage design will be adjusted with the given number of patients enrolled 
at the MTD. 
 
In Stage 2, an additional 17 patients will be enrolled for a total of 30 patients 
treated at the MTD.  


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 35 of 79 
 
7.3 Management of Selected GTB-3550 TriKE Toxicities  
Throughout the study, the investigator may prescribe any concomitant medications 
or treatment deemed necessary to provide adequate supportive care. Supportive 
care may include antibiotics, anti-fungals, analgesics, transfusions, and 
G-CSF/cytokines. 
Note: Any patient experiencing a DLT equivalent toxicity must discontinue 
treatment per Section 7.5 and is not eligible for retreatment. 
Please refer to Section 9.7 for potential toxicities. 
7.3.1 Tumor Lysis Syndrome 
Tumor lysis syndrome is a possible risk associated with therapy of active 
leukemia. All patients (except those with known allergy) will begin on 
prophylactic allopurinol 300 mg po before the 1st dose of GTB-3550 TriKE and 
continue daily as clinically indicated. 
7.3.2 Infusion Related Reaction 
Patients will be monitored for the occurrence of hypotension, dyspnea and 
angioedema during the infusion. The infusion will be stopped and the reaction 
treated per Section 7.1. A Grade 3 or Grade 4 infusion related reaction will 
result in permanent discontinuation of the infusion. 
7.3.3 Increase in Liver Function Tests 
Liver function tests will be monitored three times weekly during each CI block 
and at Day 22, 29, and 60 visits. 
Elevated liver function tests (ALT, AST and/or total bilirubin) guidelines based 
on CTCAE v 5 grading: 
 
Grade 1 or 2: continue therapy per protocol 
Grade 3: discontinue treatment for the current block after completion of the 
currently hung infusion bag, if applicable. Missed doses are not made up. 
 
At the time of next scheduled treatment, if LFTs return to Grade 0 in two weeks 
or less, initiate the next block of treatment; however, reduce the TriKE dosing 
by 1 dose level.  
 
Grade 4 or recurrence of a Grade 3: permanently discontinue therapy 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 36 of 79 
 
7.3.4 Neurotoxicity 
A neurological assessment including basic motor (gait), coordination 
(steadiness) and cognitive function (alert and oriented) should be performed 
daily during each CI block. Any abnormalities should be followed up with a 
detailed neurologic exam and appropriate clinical care. 
7.3.5 Pulmonary Toxicity 
Patients will be monitored for clinical signs and symptoms of pulmonary toxicity 
through routine daily patient assessments and via the Targeted Toxicities 
Worksheet (Appendix VI). O2 saturation levels will be checked per routine 
in-patient assessments (minimum of once every nursing shift).  
Any new hypoxia will be evaluated with a chest x-ray or other imaging as 
clinically indicated.  
Grade 3 hypoxia (decreased oxygen saturation at rest [e.g., pulse oximeter < 
88%]) or higher is a dose limiting toxicity. In this situation, discontinue treatment 
for per Section 7.5 after completion of the currently hung infusion bag, if 
applicable.  
7.3.6 Cytokine Release Syndrome (CRS) or CRS-Like Symptoms 
While CRS is a clearly defined syndrome in T cell therapy, it is not known to 
occur to the full extent in NK cell therapies. However, we have seen immune 
activation syndromes with other IL-15 products that include fever, and rash. If 
symptoms occur, CRP, IL-6 and ferritin levels will be assessed. If indicated by 
the presence of medically significant symptoms and/or high IL-6 levels or any 
symptoms requiring intervention, steroids are the first line of treatment.  
 
Patients will be monitored for clinical signs and symptoms of CRS through 
routine daily patient assessments and via the Targeted Toxicities Worksheet 
(Appendix VI). Refer to Section 10 for the revised CRS grading system that will 
be used for this study. 
 
7.4 Opportunity for Re-Treatment 
If a patient completes the planned 3 blocks of TriKEs treatment per protocol with 
lack of disease progression or evidence of a clinical improvement, re-treatment 
may be an option after discussion with the institutional PI or designee. The patient 
must continue to fulfill the relevant eligibility criteria in Section 5 and have had no 
toxicity equivalent to a DLT with the 1st treatment course. Participants would sign 
a re-treatment consent and be enrolled onto the retreatment protocol CPRC 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 37 of 79 
 
#2015LS167R, while continuing to be followed for the main study’s endpoints as 
planned. 
Eligible patients will receive TriKE at the same or a lower dose level and on the 
same schedule as initially treated. Treatment must begin within 2 to 4 weeks after 
completion of the 1st course. Treatment guidelines will be followed per Section 7. 
Re-treatment patient events will not apply toward dose limiting toxicities (DLTs) or 
early stopping rule events. Tests and evaluations (with a limited research related 
sample collection plan) during and after treatment would follow those in Section 8.1 
and Section 8.3. This includes frequent assessments for toxicity and survival 
follow-up through 6 months from the 1st dose of the re-treatment. 
Such situations are considered compassionate and would not be included in the 
statistical analysis. 
7.5 Duration of Study Treatment 
Patients will receive one treatment course consisting of three sets (blocks) of four 
consecutive 24 hour continuous infusions GTB-3550 TriKE unless:  
• the patient experiences the equivalent of a dose limiting toxicity (see 
Section 7.2.1 for definition),  
• the patient is unable to start Block #2 or #3 within 1 week of the planned 
date,  
• the patient refuses further treatment, 
• Disease based treatment decisions: If after completing Block #1 and 
Block #2, the patient has clear evidence of disease progression they will be 
discontinued from study treatment and further treatment with study drug is 
to be discontinued.  
• In the opinion of the treating investigator, continuing treatment is not in the 
best interest of the patient.  
For patients discontinuing prior to completing 3 blocks, post-treatment activities 
at Day 22 and Day 29 are shifted earlier to maintain the timing (i.e. 1 and 2 
weeks from the start of the final block). 
7.6 Duration of Study Participation 
Direct study participation ends with the end of treatment visit at Day +60 (±1 week) 
or earlier, if a new treatment is started. For patients not receiving all 3 blocks, the 
end of treatment visit occurs approximately 6 weeks (±1 week) from the start of the 
last block. 
Further treatment, independent of the study, will be at the treating physician’s 
discretion. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 38 of 79 
 
Follow-up will continue for overall survival continues on all evaluable patients 
through 6 months from the 1st treatment by record review or other means.  
8 Schedule of Patient Activities 
Scheduled evaluations after screening may be performed ±1 day from the targeted 
date through Day 29; unless otherwise noted. A disease reassessment will occur 
between Days 21 and 42. A ±7 day window is permitted for the end of treatment (EOT) 
visit. If a patient discontinues treatment before receiving all 3 blocks, subsequent time 
points are adjusted to maintain timing (i.e. Day 22 is moved to 1 week after the start 
of the last block). 
In addition, targeted days may be altered as clinically appropriate. Follow-up visits are 
per standard of care with disease status and survival status abstracted from the 
medical record. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 39 of 79 
 
8.1 Required Standard of Care 
Standard of care procedures should be followed for all enrolled patients, including 
those who are enrolled for retreatment. 
Activity 
Screening 
within 30 
days of 
enrollment 
(within 14 days 
if for eligibility) 
Day 1, 
Day 8, and 
Day 15 
(start of 
treatment 
block) 
Daily 
during 
infusions 
(i.e. Day 2-5, 
9 12, 16-19) 
Day 
22 
Day 
29 
Anytime 
between 
Day 21 
through 
Day 42 
End of 
Treatment 
Visit 
Day 60  
(±7 days) 
FU for 
overall 
survival 
(through 
Month 6) 
consent 
X 
 
 
 
 
 
 
 
baseline 
assessment 
X 
 
 
 
 
 
 
 
medical history 
X 
X 
 
X 
X 
 
X 
 
concomitant meds7 
X 
X 
X  
 
X 
X 
 
X 
 
physical exam 
X 
X 
 
X 
X 
 
X 
 
vital signs including 
pulse oximetry 
X 
X 
per 
Section 7.1.1 
X 
X 
 
X 
 
neurologic 
assessment 
 
X2 
X 
 
 
 
 
 
provider assessment 
 
 
X 
 
 
 
 
 
survival status 
 
 
 
 
 
 
X5 
X 
assessment of toxicity 
 
X 
X 
X 
X 
 
X 
 
Karnofsky PS 
X 
 
 
 
X 
 
X 
 
height 
X 
 
 
 
 
 
 
 
weight 
 
X (- 5 days) 
 
 
 
 
 
 
CBC/diff/plt 
X 
X 
X 
X 
X 
 
X 
 
basic metabolic 
panel  
 
 
X 
 
 
 
 
 
comprehensive 
metabolic panel3, 
magnesium and 
phosphorus 
X 
X 
 
X 
X 
 
X 
 
ALT, AST, total bili, 
albumin4 
 
 
2 times 
 
 
 
 
 
hepatitis B and C 
screening  
X 
 
 
 
 
 
 
 
INR8 
X 
 
 
 
 
 
 
 
eGFR  
X 
 
 
 
 
 
 
 
Serum pregnancy test 
for FOCBP within 7 
days of treatment start
X 
 
 
 
 
 
 
 
Disease assessment 
X 
 
 
 
 
X 
 
 
BM biopsy1  
X 
 
 
 
 
X 
 
 
Electrocardiogram 
X 
 
 
 
 
 
 
 
Echocardiogram, 
cardiac MRI or 
MUGA 
X 
 
 
 
 
 
 
 
Chest/abdomen CT 
X 
 
 
 
 
 
 
 
assessment of 
response 
 
 
 
 
 
X 
 
X6 
1 - sample to TTL per Section 8.2 at time of each SOC bone marrow biopsy 
2 - Neurological assessment daily including basic motor (gait), coordination (steadiness) and cognitive function (alert 
and oriented) - any abnormalities should be followed up with a detailed neurologic exam. 
3 - Albumin, alkaline phosphatase, ALT, AST, bilirubin (total), calcium, chloride, CO2, creatinine, glucose, potassium, 
protein (total), sodium, urea nitrogen 
4 - perform LFTs and albumin twice more during infusion week (in addition to Day of infusion start CMP) = three times 
during infusion week 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 40 of 79 
 
5 - survival status at Day 60 for early study stopping rule for expansion component only 
6 - until relapse/progression or start of a new therapy, then survival only 
7 - document all concomitant medications, including start and stop dates, relative to administration of GTB-3550 TriKE 
8-  Measure and report prior to commencement of GTB-3550 therapy for information only and not as criteria for 
inclusion. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 41 of 79 
 
8.2 Research Related Testing, Assessments, and Sample Collections 
Sample collections and other procedures after the end of the infusions will coincide 
with outpatient clinic visits which may not occur on the targeted day. 
 
Screen/ 
Baseline 
Pre Dose 1  
each Block 
(Day 1, 8, 15) 
Daily during infusions 
(i.e. Day 2-5, 9-12, 16-
19) 
PK/PD 
sampling at end
of each infusion
block  
Day 
22 
Day 
29 
Day of SOC 
Disease 
Reassessmen
t (Day 21 – 
Day 42) 
Toxicity Assessment 
 
Refer to Section 10.2 for details 
Assessment for dose 
limiting toxicity 
 
By Day 29 – report as DLT for Phase I only; however any patient 
experiencing a DLT is not eligible to continue treatment per Section 7.5 
 
Assessment for 
stopping rules 
 
Expansion component only through Day 42 for non-hematologic, non-relapse, non-
infectious toxicity (except fever), Day 60 for TRM,  
Monitoring for signs of 
immune activation  
 
Pre and during TriKE infusions – all 
patients 
 
CRP, ferritin4 
X 
X 
X (Day 5 only) 
 
 
 
 
Pulmonary Function 
Testing 
X 
 
 
 
 
 
 
EKG 
 
X 
(At 4 hours 
(±15 min) into 
the infusion) 
X  
(at 4 hours (±15 min) 
into each daily infusion 
and at 4 hours (±15 
min) after disconnect 
at block end) 
 
 
 
 
T Cell Subset 
Extended Profile4 
X 
 
 
 
 
 
 
5 - 10 ml green top 
tubes and 1- 10 ml red 
top tube 
X 
X 
X  
(Day 3, 10, and 17, 
only)5 
 
X 
X 
X3 
antibody testing 
(sample obtained from 
the 10 ml red top 
collected in previous 
row) 
X2 
X (Day 15 
only) 
 
 
X 
X 
X3 
5 ml red top for each 
PK/PD time point  
 
X 
X 
X1 
 
 
 
30 ml or as much as able
to obtain of heparinized 
bone marrow aspirate at 
time of SOC bm bx 
X3 
 
 
 
 
 
X6 
Pre- and Post-TriKE drug product concentrations levels samples – each drug bag during Week 1 only 
TriKE pre-infusion 
sample - 2 ml of drug 
split between two pre-
labeled 1.8 ml cryo-vials 
 
Each drug bag during Week 1 only per 
Section 9.6 – collected after drug 
preparation is complete and before bag 
sent to floor, – keep refrigerated until 
pick-up  
 
 
 
 
TriKE post-infusion 
sample collection ~2 ml 
of drug split between two 
pre-labeled 1.8 ml cryo-
vials 
 
Each drug bag during Week 1 only – per 
Section 7.1 after infusion end and prior to 
discarding bag and tubing - keep 
refrigerated until samples are collected 
 
 
 
 
1. 
PK/PD time points in association with the end of each infusion block (i.e. Day 5, 12, and 19 or at the 
discontinuation of the block’s infusions, if prior to 96 hours) - 1 hour post (±5 min), 2 hours post (±10 min), 
3 hours post (±10 min), 4 hours post (±10 min) and optional 10 hours (±30 min)  
2. 
Antibody testing will not be performed in real time nor affect a patient’s initial eligibility or ongoing treatment  
3. 
Baseline sample if feasible (repeat marrow is not required solely for research sample)  


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 42 of 79 
 
4. 
To Institution’s clinical lab, charge to research 
5. 
A +2 day window is permitted for this time point (Day 3 (window of days 3- 5), Day 10 (window of 
days 10-12) and Day 17 (window of days 17-19) 
6. 
At time of post-treatment bone marrow biopsy or at Day 60 (End of Treatment visit) 
 
For UMN patients: All samples unless otherwise noted go to Masonic Cancer 
Center Translational Therapy Laboratory (TTL) - Call 
 for sample pick-up. 
For non-University of Minnesota sites: 
• The 5 green top and 1 red top samples are shipped the day of collection 
(Monday-Thursday) for next day delivery to the Masonic Cancer Center’s 
Translational Therapy Lab (MCC TTL).  
• PK/PD samples are stored frozen and batched shipped to MCC TTL at the 
end of the patient’s treatment. 
• TriKE pre and post infusion samples (Week 1 only) are stored frozen and 
batch shipped to MCC TTL during Week 2. 
• Bone marrow aspirate is collected at the time of standard of care bone 
marrow prior to treatment start and at the time of the post-treatment bone 
marrow biopsy. Ship day of collection to MCC TTL. 
Refer to the Laboratory Manual for additional details. 
It is recognized that with novel therapies as used in this study, the timing of protocol 
directed research samples may miss important patient specific events. For this 
reason, additional sets of research samples may be drawn at up to 3 time points 
that are not specified above. 
Note: if a patient is not abiding by the standard of care study calendar (Section 8.1), 
collection of the research related samples (and targeted toxicities) may be altered 
or discontinued on an individual patient basis, as appropriate.  
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 43 of 79 
 
8.3 Re-Treatment Research Related Testing, Assessments, and Sample 
Collections 
All standard of care procedures described in Section 8.1 are also required for 
retreatment. Sample collections and other procedures after the end of the infusions 
will coincide with outpatient clinic visits (and may not occur on the targeted day). 
 
Screen/ 
Baseline 
Block 1 only 
Pre and during 
TriKE infusions 
Day 22 or 1 
week after 
the start of 
the last block 
Day of SOC 
Disease 
Reassessment 
(Day 21 – Day 
42) 
Pre Dose 1 
Day 5 
Toxicity 
Assessment 
 
 
 
Refer to Section 10.2 for details 
Monitoring for signs 
of immune 
activation  
 
 
 
Pre and during TriKE infusions – all patients 
CRP, ferritin1 
X 
X 
X 
 
 
 
Pulmonary 
Function Testing 
X 
 
 
 
 
 
T Cell Subset 
Extended Profile1 
X 
 
 
 
 
 
5 - 10 ml green top 
tubes and 1- 10 ml 
red top tube 
 
X 
 
 
X 
 
antibody testing  
5 ml red top tube 
(sample obtained 
from the 10 ml red 
top collected in 
previous row) 
X2 
 
 
 
X 
 
30 ml or as much 
as able to obtain of 
heparinized bone 
marrow aspirate at 
time of SOC bm bx 
X3 
 
 
 
 
 
X 
1- 
To Institutional Lab, but charge to research 
2- 
Antibody testing will not be performed in real time nor affect a patient’s initial eligibility or ongoing treatment  
3- 
May be same sample as reassessment from 1st treatment course 
For UMN patients, all samples unless otherwise noted go to Masonic Cancer 
Center Translational Therapy Laboratory (TTL) - Call 
 for sample pick-up.  
For non-University of Minnesota sites, refer to Section 8.2 for shipping information. 
All “rules” of sample collection found in Section 8.2 also apply to the re-treatment 
research samples (i.e., windows, missed samples, extra samples). 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 44 of 79 
 
8.4 Overview of Planned Correlative Studies 
A number of correlative studies are performed to understand the safety and ability 
of the GTB-3550 TriKE to activate the immune response. Immune monitoring is a 
critical component of the GTB-3550 TriKE clinical trial to understand the drug 
pharmacokinetic/pharmacodynamic (PK/PD), its in vivo functional activity and 
clinical tolerance.  
1. PK sampling to determine TriKE levels and secondary cytokines. In association 
with each TriKE treatment block, TriKE concentrations will be determined at 
multiple time points by standard IL-15 ELISA to detect the IL-15 linker in the 
TriKE as we have already validated. Samples will also be contract tested for 
IFNα, IL-6, IL-10 and TNF (and other inflammatory cytokines determined 
informative). This will allow us to determine drug PK/PD and immediate 
secondary cytokine responses in vivo. 
2. Determine the absolute number and proportion of NK cells, T cells and their 
subsets. We have designed multi-color flow cytometry panels to look at basic 
lymphocytes in whole blood as well as in more detail on ficolled mononuclear 
cells to determine lymphocyte (and subset) proliferation as measured by Ki-67, 
inhibitory cells [Treg and CD33+ myeloid-derived suppressor cells] and a 
number of established NK cell subsets defining adaptive or conventional NK 
cells. 
3. NK cell function induced by GTB-3550 TriKE. CD107A degranulation and 
cytokine production against K562 (to measure natural cytotoxicity) and CD33+ 
HL60 targets (± exogenous TriKE) will be performed. 
4. 
 
 
 
 
 
5. Pre- and Post- TriKE drug product concentrations levels samples will be stored 
in TTL frozen at < -70ºC for future batch testing. 
The marrow will be used in the research lab to study CD33 expression and 
targeting by allogeneic and autologous lymphocytes. 




 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 46 of 79 
 
9.5 Study Site Storage and Product Stability 
  
  
9.6 Preparation and Administration 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 47 of 79 
 
• 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
9.7 Potential Toxicities 
Although blinatumomab, a bi-specific T cell engager (BiTE), is conceptually similar to 
our NK cell GTB-3550 TriKE, there are important differences. Blinatumomab’s toxicity 
is presumed related to the anti-CD3 moiety that acts as a potent stimulus for CD3+ T 
cells. The TriKE is different since the anti-CD16 moiety does not deliver a proliferative 
stimulus and in fact, we do not expect that promotion of an immune synapse alone 
will lead to toxicity much like natural engagement of CD16 by FDA-approved 
monoclonal antibodies such as trastuzumab or rituximab. Instead, we expect the 
toxicities of GTB-3550 TriKE may be similar to those seen with blinatumomab and/or 
IL-15. Other than the intramural center at the NCI in Washington DC, we probably 
have the most experience administering IL-15 to patients as a single agent and in 
combination with chemotherapy and NK cells.  
 
 
 
Most of the side effects of IL-15 are related to 
immune activation including fevers, chills and some degree of immune activation. We 
have a prospective plan to monitor patients for these immune side effects to 
characterize the safety profile of the TriKE. In addition, we will use fever and 
tachycardia as validated clinical markers to measure early signs of immune activation 
to modify our dose escalation plan if needed. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 48 of 79 
 
10 
Event Monitoring, Documentation and Reporting 
Toxicity and adverse events will be classified according to NCI's Common 
Terminology Criteria for Adverse Events version 5 (CTCAE v5). A copy of the CTCAE 
can be downloaded from the CTEP home page at 
https://ctep.cancer.gov/protocoldevelopment/electronic_applications/docs/CTCAE_v
5_Quick_Reference_5x7.pdf  
 
An exception to the use of CTCAE will be for the assessment of cytokine release 
syndrome (CRS). Individual adverse events which are associated with CRS will be 
graded per CTCAE; however the ultimate assessment will be made using a revised 
grading system for CRS as presented by Lee et al43. 
 
CRS Revised Grading System (replaces CTCAE v4 CRS grading) 
Grade 
Toxicity Description 
Grade 1 
Symptoms are not life threatening and require symptomatic treatment only, e.g., fever, nausea, 
fatigue, headache, myalgias, malaise 
Grade 2 
Symptoms require and respond to moderate intervention - Oxygen requirement < 40% or 
Hypotension responsive to fluids or low dose of one vasopressor or Grade 2 organ toxicity 
Grade 3 
Grade 3 Symptoms require and respond to aggressive intervention - Oxygen requirement ≥40% 
or Hypotension requiring high dose  or multiple vasopressors or Grade 3 organ toxicity or grade 
4 transaminitis 
Grade 4 
Life-threatening symptoms - Requirement for ventilator support or Grade 4 organ toxicity 
(excluding transaminitis) 
Grade 5 
Death 
Grades 2-4 refer to CTCAE v4.0 grading. 
 
10.1 Definitions 
The following definitions are based on the Code of Federal Regulations Title 21 
Part 312.32 (21CFR312.32(a)). 
Adverse Event:  Any untoward medical occurrence associated with the use of a 
drug in humans, whether or not considered drug related.  
Suspected Adverse Reaction:  Any adverse event for which there is a 
reasonable possibility that the drug caused the adverse event. For the purposes 
of IND safety reporting, "reasonable possibility" means there is evidence to 
suggest a causal relationship between the drug and the adverse event. Suspected 
adverse reaction implies a lesser degree of certainty about causality than adverse 
reaction, which means any adverse event caused by a drug. 
Life-Threatening Adverse Event Or Life-Threatening Suspected Adverse 
Reaction: An adverse event or suspected adverse reaction is considered 
“life-threatening” if, in the view of either the investigator or sponsor, its occurrence 
places the patient or subject at immediate risk of death. It does not include an 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 49 of 79 
 
adverse event or suspected adverse reaction that, had it occurred in a more severe 
form, might have caused death. 
Serious Adverse Event or Serious Suspected Adverse Reaction:  An adverse 
event or suspected adverse reaction is considered “serious” if, in the view of either 
the investigator or sponsor, it results in any of the following outcomes:  
• 
Death 
• 
A life-threatening adverse event 
• 
Inpatient hospitalization or prolongation of existing hospitalization 
• 
A persistent or significant incapacity or substantial disruption of the ability 
to conduct normal life functions 
• 
A congenital anomaly/birth defect 
• 
An important medical event 
Important medical events that may not result in death, be life-threatening, or 
require hospitalization may be considered serious when, based upon appropriate 
medical judgment, they may jeopardize the patient or subject and may require 
medical or surgical intervention to prevent one of the outcomes listed in this 
definition 
If either the IND sponsor or the investigator believes the event is life-threatening 
or serious, the event must be evaluated by the sponsor for expedited reporting 
(21CRF 312.32(a)).  
Unexpected adverse event or unexpected suspected adverse reaction: An 
adverse event or suspected adverse reaction is considered “unexpected” if it is not 
listed in the investigator brochure or is not listed at the specificity or severity that 
has been observed; or, if an investigator brochure is not required or available, is 
not consistent with the risk information described in the general investigational plan 
or elsewhere in the current application, as amended.  
Expedited (Rapid) Reporting: Certain events may require rapid notification to 
entities providing patient safety oversight (e.g. IRB) as detailed in Section 10.5.  
The categories for AE attribution to study treatment are as follows:  
• 
Definite – clearly related 
• 
Probable – likely related 
• 
Possible – may be related 
• 
Unlikely – doubtfully related 
• 
Unrelated – clearly not related 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
June 4, 2021 
Page 50 of 79 
 
The following definitions are from the Masonic Cancer Center’s Standard 
Operating Procedure (SOP) Deviation Reporting: 
 
Major Deviation: A deviation or violation that impacts the risks and benefits of the 
research; may impact subject safety, affect the integrity of research data and/or 
affect a subject’s willingness to participate in the research. Deviations that place a 
subject at risk, but do not result in harm are considered to be major deviations. 
 
Minor Deviation: A deviation or violation that does not impact subject safety, 
compromise the integrity of research data and/or affect a subject’s willingness to 
participate in the research. 
10.2 Event Documentation 
Event monitoring and documentation begins with the 1st dose of TriKEs.  
 
For the purposes of this study, selected expected adverse events will be assessed 
using the Targeted Toxicity Worksheet (Appendix VI) and any unexpected events 
will be collected at the following time points in relation to the GTB-3550 TriKE 
infusions through Day 29:  
• 
Prior to the infusion start of each 24 hour infusion (i.e. Day 1, 2, 3, 4, and 
Day 8, 9, 10, 11, and Day 15, 16, 17, 18) 
• 
At the end of the final infusion of each block (i.e. Day 5, Day 12, Day 19) 
• 
Day 22 
• 
Day 29 
At each time point, the worst grade of the targeted toxicity since the last 
assessment or the previous 24 hours (whichever is shorter) will be recorded in 
addition to any unexpected toxicities felt at least possibly related the study 
treatment. 
 
If a patient discontinues study therapy early or otherwise does not receive 
treatment as planned, the targeted toxicity assessment time points may be 
adjusted or eliminated; however, patients must be assessed for a minimum of 28 
days from the 1st dose of study drug. 
 
If a patient is not abiding by the standard of care study calendar (Section 8.1), 
collection of the corresponding targeted events (and research related samples) 
also may be altered or discontinued on an individual patient basis, as appropriate.  
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 51 of 79 
 
Monitoring for adverse events will end after the last targeted assessment; however, 
the investigator is obligated, upon knowledge of, to report any event meeting the 
criteria in Section 10.5. 
10.3 Dose Limiting Toxicity Documentation and Reporting (Phase I Dose 
Finding) 
The following events count toward dose limiting toxicity (DLT) during the Phase I 
dose finding component and must be reported the UMN Multisite Program 
Manager per Section 10.6.  
 
Note: DLT events are only reported for patients enrolled in the Phase I portion of 
the trial; however, any patient experiencing a DLT is not eligible to continue 
treatment per Section 7.5. 
 
A DLT is defined as a related treatment emergent toxicity that occurs within 28 
days after the 1st TriKE dose with the exception of those that are clearly and 
incontrovertibly due to extraneous causes: 
• Any Grade 4 or 5 non-hematologic events  
• Grade 3 non-hematologic adverse events lasting more than 72 hours, except 
the following:  
o Non-sustained (< 7 days) Grade 3 liver function tests (ALT/AST, alkaline 
phosphatase, total or direct bilirubin) abnormalities in the absence of clinical 
signs of hepatic dysfunction (lethargy, confusion, anorexia, pruritus or 
tremors). 
o Non-sustained Grade 3 QTc prolongation (< 72 hours) in the absence of 
cardiac arrhythmia 
o Grade 3 electrolyte disturbances that resolve, with or without intervention, to 
< Grade 2 levels within 72 hours 
o Grade 3 fatigue 
o Grade 3 anorexia 
o Grade 3 fever 
o Grade 3 infection 
• Hematologic Toxicity - Given that AML and MDS inherently leads to low 
neutrophils and platelets, standard grading cannot be used as many of these 
patients technically meet criteria for “grade 4” neutropenia or thrombocytopenia 
at baseline. Thus, the hematologic DLTs are listed below: 
o 
AML 
 Grade 4 neutrophil count (< 500/µL) lasting ≥ 29 days from start of cycle 
in absence of evidence of active leukemia 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 52 of 79 
 
 Grade 4 platelet count (< 25,000/µL) lasting ≥ 29 days from start of cycle 
in absence of evidence of active leukemia  
 Any clinically significant bleeding that is not controllable with transfusion 
support  
 
o MDS/mast cell diseases: 
 Grade 4 neutrophil count (<500/µL) lasting ≥ 29 days from start of cycle 
in absence of evidence of active MDS/mast cell disease 
 Grade 4 platelet count (<25,000/µL) lasting ≥ 29 days from start of cycle 
in the absence of active MDS/Mast cell disease 
 Any clinically significant bleeding that is not controllable with transfusion 
support 
 Grade 4 anemia, unexplained by the underlying disease 
• Grade 3 infusion related, treatment related reaction including cytokine release 
syndrome which does not resolve within 72 hours despite best medical 
management (refer to Section 10 for modified CRS grading) 
• Grade 3 or 4 Tumor Lysis Syndrome that does not resolve within 7 days with or 
without intervention 
• Inability to complete at least one block of three 24 hour infusions due to any 
treatment emergent, treatment related toxicity.  
10.4 Early Study Stopping Rules - Event Documentation and Reporting 
(Phase II Dose Expansion) 
Early study stopping rules for the Phase II dose expansion component patients 
are: 
• Grade 4-5 non-hematologic, non-relapse, non-infectious toxicity (except fever) 
by 42 days after the start of the first GTB-3550 TriKE treatment block 
• Non-relapse, non-infectious treatment related mortality (TRM) within 60 days of 
starting GTB-3550 TriKE treatment 
 
Meeting either stopping rule criterion temporarily will halt study enrollment until the 
event is fully evaluated and the Principal Investigator and GT Biopharma make a 
decision regarding the continuation of the trial. Any patients currently receiving 
treatment may continue after discussion with the study PI and GT Biopharma.  
 
Events that count toward dose limiting toxicity and early stopping rules do not 
necessarily constitute a serious adverse event requiring expedited reporting and 
should be reported as such only if they meet the criteria for expedited reporting as 
defined in Section 10.6. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 53 of 79 
 
10.5 Documentation of Death and Reporting Requirements 
Deaths during treatment and the follow-up period, including death due to disease, 
will be recorded as an SAE and reported per Section 10.6. Deaths due to disease 
should be recorded as a Grade 5 Neoplasm. 
In addition, even after the follow-up period ends, the death date must be 
documented in the patient follow-up tab in 
 upon knowledge using the 
comment field in survival status section to record the cause.  
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 54 of 79 
 
10.6 Participating Sites Event Reporting Table 
Event Type 
 
Reporting Timeframe 
Form to Use 
Email to 
Any event meeting the 
definition of serious 
Within 24 hours of 
knowledge 
Paper SAE Report Form 
 
Masonic Cancer Center (MCC) 
Multisite Program Manager  
  
 
Dose Limiting Toxicity 
Event 
Within 24 hours of 
knowledge 
DLT Event Form 
Stopping Rule Event 
Within 24 hours of 
knowledge 
Stopping Rule Event 
Form 
Major Deviations, as 
defined in Section 10.1. 
Within 5 working days of 
knowledge 
Record in Deviations 
Tab, generate report and 
have PI sign 
Minor Deviations, as 
defined in Section 10.1. 
Reporting not applicable 
Record in Deviations 
Tab – signed report not 
required 
Not applicable 
Participating Sites are responsible for reporting to Local institutional IRB or other 
entities per institutional policies and guidelines. 
The Multisite Program Manager will forward all reports to GT Biopharma and 
 
within 3 business hours.  
GT Biopharma/
 is responsible for submission of IND safety reports to the FDA 
per federal regulations. 
10.7 UMN Required Reporting: UMN IRB, GT Biopharma, 
, and 
Masonic Cancer Center’s SAE Coordinator 
Entity 
Reported To: 
Criteria for reporting 
Timeframe 
Form to Use 
Report to 
U OF MN IRB 
Information that indicates a new or increased 
risk, or safety issue. 
Unexpected Death per UMN requirements. 
5 business 
days 
Ethos Reportable 
New Information 
(RNI) 
Via 
 
 with copy 
GT Biopharma* 
Clinical deviations per current IRB reporting 
requirements (UMN patients only) 
 Deviation 
Report and 
 
 
GT 
Biopharma 
and 
* 
Any event meeting the definition of serious 
regardless of attribution 
Within 24 hours 
of knowledge  
CTO SAE Report 
Form 
GT Biopharma and 
  
Events that count toward dose limiting toxicity 
during the dose finding component or an 
early study stopping rule during the 
expanded component 
At time of 
reporting 
Appropriate form 
*GT Biopharma/
 is responsible for submission of IND safety reports to the FDA per 
federal regulations. 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 55 of 79 
 
11 Study Data Collection and Monitoring 
11.1 Data Management 
This study will collect regulatory and clinical data using
 
 
  
The 
 database resides on dedicated secure and PHI compliant hardware 
consisting of 3 physical servers: dev, DR, and production. All the data servers are 
managed by the 
 All 
relevant 
 procedures related for PHI compliant servers (as required by the 
Center of Excellence for HIPAA Data) apply to 
 databases. 
The integrated data will be stored in PHI compliant servers managed by 
 
with access given to those authorized users in the Clinical and Translation Science 
Institute Informatics team (CTSI BPIC and MCC CISS). 
 
 
 
  
 
 
Key study personnel are trained on the use of 
 and will comply with protocol 
specific instructions embedded within the 
. 
11.2 Case Report Forms 
Participant data will be collected using protocol specific electronic case report 
forms (e-CRF) developed 
 based on its 
library of standardized forms. The e-CRFs will be approved by the lead center PI 
and the UMN biostatistician prior to release for use. The Study Coordinator or 
designee will be responsible for registering the patient into 
 at time of study 
entry, completing e-CRF based on the patient specific calendar, and updating the 
patient record until patient death or end of required study participation.  
11.3 Data and Safety Monitoring 
The study will be in compliance with the 
 
 
  


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 56 of 79 
 
The site PI will comply with at least twice yearly monitoring of the project by their 
site’s internal monitoring staff. Monitoring reports are forwarded to the U of MN 
Multisite Program Manager who will forward to the reports to GT Biopharma 
 
 Refer to the Procedures Manual for Participating Sites for additional 
information. 
 
All sites must permit study-related monitoring, audits, and inspections by the IND 
Sponsor (GT Biopharma and/or their designee), IRB, government regulatory 
bodies, and compliance groups. The investigator will make available all study 
related documents (e.g. source documents, regulatory documents, data collection 
instruments, study data, etc.). The investigator will ensure the capability for 
inspections of applicable study-related facilities (e.g. pharmacy, diagnostic 
laboratory, etc.) will be available for trial related monitoring, audits, or regulatory 
inspections. 
11.4 UMN Led Teleconferences – Participating Sites, GT Biopharma 
 
 
Regular teleconferences will be held to facilitate communication between the 
participating sites and IND sponsor/representative regarding the study’s progress, 
including patient updates, a summary of safety reports, dose level/patient slot 
availability, case report form completion, and other issues for discussion. The 
Masonic Cancer Center Multisite Program Manager is responsible for arranging 
these teleconferences and preparing the agenda. Meetings occur every 2 weeks; 
however, they may be scheduled more or less frequently at the discretion of the 
lead institution. Participation of a minimum of one representative from each 
participating clinical site is expected. Attendance by 
 GT Biopharma is 
agenda driven. 
These teleconferences are in addition to other previously described site 
interactions including centralized patient registration, institutional and MCC 
required reporting of safety related issues, and case report form completion in the 
study’s central database 
 
11.5 Record Retention 
The investigator will retain essential documents (e.g. study records including 
source data, copies of case report form, consent forms, HIPAA authorizations, and 
all study correspondence) until at least 2 years after the last approval of a 
marketing application in an ICH region and until there are no pending or 
contemplated marketing applications in an ICH region or at least 2 years have 
elapsed since the formal discontinuation of clinical development of the 
investigational product. These documents should be retained for a longer period 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 57 of 79 
 
however if required by the applicable regulatory requirements or by an agreement 
with the sponsor.  
It is the responsibility of the sponsor (GT Biopharma) to inform the 
investigator/institution as to when these documents no longer need to be retained.  
12 Statistical Considerations 
12.1 Study Design and Endpoints 
This is a multisite Phase I/II study of GTB-3550 trispecific killer cell engager (TriKE) 
for the treatment of high risk MDS and relapsed AML. Once the MTD is identified, 
the objective will be to confirm safety and obtain preliminary estimates of efficacy 
as measured by the objective response, the primary trial endpoint as assessed 
between Day 21 and Day 42. For AML clinical response includes complete 
remission with or without hematologic or platelet recovery (CR, CRi or CRp) or 
partial response. For MDS clinical response includes complete remission, marrow 
CR (with incomplete peripheral blood count normalization), partial response or 
hematologic improvement (HI). For advanced systemic mastocytosis response is 
considered a decrease in mast cell burden in bone marrow or serum tryptase level 
by at least 30%.  
 
All patients completing Block #1 will be evaluable for DLTs and toxicities. Patients 
who discontinue therapy prior to completion of both Block #1 and Block #2 will be 
replaced.  Patients completing Block #1 and Block #2, but come off treatment for 
disease progression, will still be evaluable for efficacy and will not be replaced. If 
needed a subgroup of patients receiving all 3 blocks will also be evaluated for 
response as a secondary population. We expect that the number of patients 
coming off therapy after only completing block #1 will be minimal.  
 
Secondary trial endpoints will include toxicity through Day 29 and overall survival 
(OS) at 6 months from 1st dose of study drug. 
 
Phase I component: Estimating the MTD of GTB-3550 TriKE:  
The first phase is a dose finding study with the aim of establishing the MTD of 
GTB-3550 TriKE when given as a block of four 24 hour infusions with a 72 hour 
break for 3 consecutive weekly courses in patients with CD33-expressing high risk 
myelodysplastic syndromes, refractory/relapsed acute myeloid leukemia or 
advanced systemic mastocytosis. The MTD will be identified using the continual 
reassessment method (CRM)44.  
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 58 of 79 
 
The MTD will be defined as the dose that most closely corresponds to a dose 
limiting toxicity (DLT) rate of 20%. Dose limiting toxicity (DLT) is defined 
Section 7.2.1. Determination of the target rate of 20% was based on clinical input 
and acceptability.  
 
Seven dose levels of GTB-3550 TriKE will be tested (5.0 µg/kg, 10.0 µg/kg, 25.0 
µg/kg; 50.0 µg/kg, 100.0 µg/kg, 150 µg/kg, and 200 µg/kg daily dose). The CRM 
uses a Bayesian framework that combines experience from patients in the earlier 
part of the trial with clinicians’ initial best probability estimates of DLT at each dose. 
We are using a one parameter power model for the probability of DLT, where the 
probability at each dose i, is modeled as F(d, α)=diexp(α) where α is distributed a 
priori as a normal random variable with mean 0 and variance 0.5. The variance of 
the prior distribution, 0.5, was determined through simulations to balance accuracy 
and patient safety.  
 
Revision 5/5/2021: Seven dose levels of GTB-3550 TriKE are now being tested 
per 7.2.1 (5.0 µg/kg, 10.0 µg/kg, 25.0 µg/kg, 50.0 µg/kg, 100.0 µg/kg, 150.0 µg/kg 
and 200 µg/kg daily dose) using an expected “true” probability of 17% for DLTs at 
150.0 µg/kg (median probability between 100 and 200 µg/kg daily dose) and the 
same target DLT rate of 20%. 
 
The prior mean for the probability of DLT for the six doses (i.e. the power model 
skeleton) are 3%, 5%, 7%, 10%, 14% and 20%, respectively. As the study 
progresses, updated probabilities of DLT are computed before each new cohort of 
patients is enrolled and both patients of each cohort have reached Day 28 (end of 
the DLT assessment period) prior to enrollment of a subsequent cohort. Each 
subsequent cohort will be assigned to the most appropriate dose based on these 
updated probabilities. Eventually the final dose (within our proposed sample of 
30 patients) will be identified as the dose most closely associated with a DLT rate 
of 20%. To promote patient safety: 1) we will enroll cohorts of 2 patients starting at 
the 1st dose; and 2) dose levels will not be skipped when escalating. 
 
 
 
 
Phase II Extension: Studying the efficacy of GTB-3550 TriKE for the endpoint 
of objective response:  
After completion of the dose finding trial, the final dose will be carried forward into 
an uncontrolled two-stage Phase II extension trial to confirm safety and make a 
preliminary determination of the activity level. For advanced MDS/AML, the lack of 




 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 60 of 79 
 
 
If fewer than 14 patients are enrolled at the MTD, the Phase II extension trial using 
the Simon’s two-stage design will require 30 patients to test the null hypothesis 
that the response rate is <20% versus the alternative that the response rate is 
≥40% after assuming 80% power and a significance level of 0.05.  
 
If the Phase I trial enrolls more than 13 patients at the MTD, we will adjust the 
futility rule of the two-stage design while maintaining the constraints of 80% power, 
a significance level of 0.05 and using a maximum of 30 patients. We will choose 
the rule that minimizes the expected sample size given a true response rate 
equivalent to the null hypothesis. We expect that approximately 44 patients will be 
required due to use of patients from the Phase I trial in the Phase II extension but 
the sample size may be as high as 57. Enrollment is expected to be 1-2 patients 
per month.  
12.4 Monitoring Guidelines (Study Stopping Rule Events) 
During the CRM, the trial will stop if the posterior probability that the lowest dose 
is more toxic than the target is greater than 90%.  
 
After the MTD has been established stopping rules will also be employed to 
monitor excess toxicity outside of the Phase I trial47.  
 
Meeting either stopping rule criteria temporarily will halt enrollment per Section 
10.4.  
 
(1) Grade 4-5 non-hematologic, non-relapse, non-infectious toxicity (except 
fever) by 42 days after the start of the first GTB-3550 TriKE treatment block: 
We will construct a boundary such that the probability of early stopping is at most 
10% if the toxicity rate is equal to 10%. Assuming 27 additional patients are 
enrolled after phase I, the upper stopping boundary for toxicity would be 2/3, 3/8, 
4/13, 5/20, 6/26 or 7 events. 
(2) Non-relapse, non-infectious treatment related mortality within 60 days of 
starting GTB-3550 TriKE treatment: Assuming the same parameters as in (1), the 
upper stopping boundary for TRM will be 2/3, 3/8, 4/13, 5/20, 6/26 or 7 events. If 
the true rates of both toxicity and TRM are 30%, the probability of early stopping 
will be 88% for each guideline. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 61 of 79 
 
13 Conduct of the Study 
13.1 Good Clinical Practice 
The study will be conducted in accordance with the appropriate regulatory 
requirement(s). Essential clinical documents will be maintained to demonstrate the 
validity of the study and the integrity of the data collected. Master files should be 
established at the beginning of the study, maintained for the duration of the study 
and retained according to the appropriate regulations. 
13.2 Ethical Considerations 
The study will be conducted in accordance with ethical principles founded in the 
Declaration of Helsinki. The IRB will review all appropriate study documentation in 
order to safeguard the rights, safety and well-being of the patients. The study will 
only be conducted at sites where IRB approval has been obtained. The protocol, 
consent, written information given to the patients, safety updates, annual progress 
reports, and any revisions to these documents will be provided to the IRB by the 
investigator.  
13.3 Informed Consent 
All potential study participants will be given a copy of the IRB-approved consent to 
review. The investigator or designee will explain all aspects of the study in lay 
language and answer all questions regarding the study. If the participant decides 
to participate in the study, he/she will be asked to sign and date the consent 
document. Patients who refuse to participate or who withdraw from the study will 
be treated without prejudice. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 62 of 79 
 
14 References 
1. Taylor PR, Reid MM, Stark AN, Bown N, Hamilton PJ, Proctor SJ. De novo acute myeloid 
leukaemia in patients over 55-years-old: a population-based study of incidence, treatment and 
outcome. Northern Region Haematology Group. Leukemia. 1995;9(2):231-237. 
2. Ostgard LS, Kjeldsen E, Holm MS, et al. Reasons for treating secondary AML as de novo 
AML. Eur J Haematol. 2010;85(3):217-226. 
3. Vardiman JW, Thiele J, Arber DA, et al. The 2008 revision of the World Health Organization 
(WHO) classification of myeloid neoplasms and acute leukemia: rationale and important 
changes. Blood. 2009;114(5):937-951. 
4. Mufti GJ, Bennett JM, Goasguen J, et al. Diagnosis and classification of myelodysplastic 
syndrome: International Working Group on Morphology of myelodysplastic syndrome (IWGM-
MDS) consensus proposals for the definition and enumeration of myeloblasts and ring 
sideroblasts. Haematologica. 2008;93(11):1712-1717. 
5. Masters GA, Krilov L, Bailey HH, et al. Clinical cancer advances 2015: Annual report on 
progress against cancer from the American Society of Clinical Oncology. J Clin Oncol. 
2015;33(7):786-809. 
6. Caruana I, Diaconu I, Dotti G. From monoclonal antibodies to chimeric antigen receptors for 
the treatment of human malignancies. Semin Oncol. 2014;41(5):661-666. 
7. Hermanson DL, Kaufman DS. Utilizing chimeric antigen receptors to direct natural killer cell 
activity. Front Immunol. 2015;6:195. 
8. Glienke W, Esser R, Priesner C, et al. Advantages and applications of CAR-expressing natural 
killer cells. Front Pharmacol. 2015;6:21. 
9. Vivier E, Raulet DH, Moretta A, et al. Innate or adaptive immunity? The example of natural 
killer cells. Science. 2011;331(6013):44-49. 
10. Velardi A. Natural killer cell alloreactivity 10 years later. Curr Opin Hematol. 2012;19(6):421-
426. 
11. Anegon I, Cuturi MC, Trinchieri G, Perussia B. Interaction of Fc receptor (CD16) ligands 
induces transcription of interleukin 2 receptor (CD25) and lymphokine genes and expression 
of their products in human natural killer cells. J Exp Med. 1988;167(2):452-472. 
12. Ravetch JV, Bolland S. IgG Fc receptors. Annu Rev Immunol. 2001;19:275-290. 
13. Selvaraj P, Carpen O, Hibbs ML, Springer TA. Natural killer cell and granulocyte Fc gamma 
receptor III (CD16) differ in membrane anchor and signal transduction. J Immunol. 
1989;143(10):3283-3288. 
14. Perussia B, Ravetch JV. Fc gamma RIII (CD16) on human macrophages is a functional 
product of the Fc gamma RIII-2 gene. Eur J Immunol. 1991;21(2):425-429. 
15. Klaassen RJ, Ouwehand WH, Huizinga TW, Engelfriet CP, von dem Borne AE. The Fc-
receptor III of cultured human monocytes. Structural similarity with FcRIII of natural killer cells 
and role in the extracellular lysis of sensitized erythrocytes. J Immunol. 1990;144(2):599-606. 
16. Nishikiori N, Koyama M, Kikuchi T, et al. Membrane-spanning Fc gamma receptor III isoform 
expressed on human placental trophoblasts. Am J Reprod Immunol. 1993;29(1):17-25. 
17. Ravetch JV, Perussia B. Alternative membrane forms of Fc gamma RIII(CD16) on human 
natural killer cells and neutrophils. Cell type-specific expression of two genes that differ in 
single nucleotide substitutions. J Exp Med. 1989;170(2):481-497. 
18. Lanier LL, Ruitenberg JJ, Phillips JH. Functional and biochemical analysis of CD16 antigen 
on natural killer cells and granulocytes. J Immunol. 1988;141(10):3478-3485. 
19. Wirthmueller U, Kurosaki T, Murakami MS, Ravetch JV. Signal transduction by Fc gamma 
RIII (CD16) is mediated through the gamma chain. J Exp Med. 1992;175(5):1381-1390. 
20. Cooper MA, Fehniger TA, Caligiuri MA. The biology of human natural killer-cell subsets. 
Trends Immunol. 2001;22(11):633-640. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 63 of 79 
 
21. Beziat V, Duffy D, Quoc SN, et al. CD56brightCD16+ NK cells: a functional intermediate stage 
of NK cell differentiation. J Immunol. 2011;186(12):6753-6761. 
22. Vivier E, Nunes JA, Vely F. Natural killer cell signaling pathways. Science. 
2004;306(5701):1517-1519. 
23. Vivier E, Morin P, O'Brien C, Druker B, Schlossman SF, Anderson P. Tyrosine 
phosphorylation of the Fc gamma RIII(CD16): zeta complex in human natural killer cells. 
Induction by antibody-dependent cytotoxicity but not by natural killing. J Immunol. 
1991;146(1):206-210. 
24. Nimmerjahn F, Ravetch JV. Fcgamma receptors as regulators of immune responses. Nat Rev 
Immunol. 2008;8(1):34-47. 
25. Bryceson YT, Ljunggren HG, Long EO. Minimal requirement for induction of natural 
cytotoxicity and intersection of activation signals by inhibitory receptors. Blood. 
2009;114(13):2657-2666. 
26. Shore SL, Nahmias AJ, Starr SE, Wood PA, McFarlin DE. Detection of cell-dependent 
cytotoxic antibody to cells infected with herpes simplex virus. Nature. 1974;251(5473):350-
352. 
27. Laszlo A, Petri I, Ilyes M. Antibody dependent cellular cytotoxicity (ADCC)-reaction and an in 
vitro steroid sensitivity test of peripheral lymphocytes in children with malignant 
haematological and autoimmune diseases. Acta Paediatr Hung. 1986;27(1):23-29. 
28. Natsume A, Niwa R, Satoh M. Improving effector functions of antibodies for cancer treatment: 
Enhancing ADCC and CDC. Drug Des Devel Ther. 2009;3:7-16. 
29. Albertini MR, Hank JA, Sondel PM. Native and genetically engineered anti-disialoganglioside 
monoclonal antibody treatment of melanoma. Cancer Chemother Biol Response Modif. 
2005;22:789-797. 
30. Garcia-Foncillas J, Diaz-Rubio E. Progress in metastatic colorectal cancer: growing role of 
cetuximab to optimize clinical outcome. Clin Transl Oncol. 2010;12(8):533-542. 
31. Garnock-Jones KP, Keating GM, Scott LJ. Trastuzumab: A review of its use as adjuvant 
treatment in human epidermal growth factor receptor 2 (HER2)-positive early breast cancer. 
Drugs. 2010;70(2):215-239. 
32. Navid F, Santana VM, Barfield RC. Anti-GD2 antibody therapy for GD2-expressing tumors. 
Curr Cancer Drug Targets. 2010;10(2):200-209. 
33. Winter MC, Hancock BW. Ten years of rituximab in NHL. Expert Opin Drug Saf. 
2009;8(2):223-235. 
34. Congy-Jolivet N, Bolzec A, Ternant D, Ohresser M, Watier H, Thibault G. Fc gamma RIIIa 
expression is not increased on natural killer cells expressing the Fc gamma RIIIa-158V 
allotype. Cancer Res. 2008;68(4):976-980. 
35. Moore GL, Bautista C, Pong E, et al. A novel bispecific antibody format enables simultaneous 
bivalent and monovalent co-engagement of distinct target antigens. MAbs. 2011;3(6):546-
557. 
36. Preithner S, Elm S, Lippold S, et al. High concentrations of therapeutic IgG1 antibodies are 
needed to compensate for inhibition of antibody-dependent cellular cytotoxicity by excess 
endogenous immunoglobulin G. Mol Immunol. 2006;43(8):1183-1193. 
37. Baselga J, Albanell J. Mechanism of action of anti-HER2 monoclonal antibodies. Ann Oncol. 
2001;12 Suppl 1:S35-41. 
38. Berinstein NL, Grillo-Lopez AJ, White CA, et al. Association of serum Rituximab (IDEC-C2B8) 
concentration and anti-tumor response in the treatment of recurrent low-grade or follicular 
non-Hodgkin's lymphoma. Ann Oncol. 1998;9(9):995-1001. 
39. Holliger P, Hudson PJ. Engineered antibody fragments and the rise of single domains. Nat 
Biotechnol. 2005;23(9):1126-1136. 
40. Chames P, Van Regenmortel M, Weiss E, Baty D. Therapeutic antibodies: successes, 
limitations and hopes for the future. Br J Pharmacol. 2009;157(2):220-233. 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 64 of 79 
 
41. Scott AM, Wolchok JD, Old LJ. Antibody therapy of cancer. Nat Rev Cancer. 2012;12(4):278-
287. 
42. Vallera DA, Felices M, McElmurry D. IL15 Trispecific Killer Engagers (TriKE) Make Natural 
Killer Cells Specific to CD33þ Targets While Also Inducing Persistence, In Vivo Expansion, 
and Enhanced Function. Clin Cancer Res; 22(14) July 15, 2016. 
43. Lee DW, Gardner R, Porter DL, et al. Current concepts in the diagnosis and management of 
cytokine release syndrome. Blood. 2014;124(2):188-195.  
44. O'Quigley J, Pepe M, Fisher L. Continual reassessment method: a practical design for phase 
1 clinical trials in cancer. Biometrics. 1990;46(1):33-48. 
45. Simon R. Optimal two-stage designs for phase II clinical trials. Control Clin Trials. 
1989;10(1):1-10. 
46. Cheung YK. Sample size formulae for the Bayesian continual reassessment method. Clin 
Trials. 2013;10(6):852-861. 
47. Ivanova A, Qaqish BF, Schell MJ. Continuous toxicity monitoring in phase II trials in oncology. 
Biometrics. 2005;61(2):540-545. 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 65 of 79 
 
Appendix I - Karnofsky Performance Status 
 
Karnofsky Performance Scale 
Percent 
Description 
100 
Normal, no complaints, no evidence of disease. 
90 
Able to carry on normal activity; minor signs or symptoms of disease. 
80 
Normal activity with effort; some signs or symptoms of disease. 
70 
Cares for self, unable to carry on normal activity or to do active work. 
60 
Requires occasional assistance, but is able to care for most of his/her needs. 
50 
Requires considerable assistance and frequent medical care. 
40 
Disabled, requires special care and assistance. 
30 
Severely disabled, hospitalization indicated. Death not imminent. 
20 
Very sick, hospitalization indicated. Death not imminent. 
10 
Moribund, fatal processes progressing rapidly. 
0 
Dead. 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 66 of 79 
 
Appendix II - Revised International Prognostic Scoring System 
(IPSS-R) for Myelodysplastic Syndromes and Risk Assessment 
Calculator Link 
Developed by the International Working Group for the Prognosis of MDS (IWG-PM) under the aegis of the 
MDS Foundation, Inc. 
https://www.mds-foundation.org/ipss-r-calculator/ 
 
IPSS-R Cytogenetic Risk Groups*,** 
Cytogenetic prognostic 
subgroups 
Cytogenetic abnormalities 
Very good 
-Y, del(11q) 
Good 
Normal, del(5q), del(12p), del(20q), double including del(5q) 
Intermediate 
del(7q), +8, +19, i(17q), any other single or double independent clones 
Poor 
-7, inv(3)/t(3q)/del(3q), double including -7/del(7q), Complex: 3 
abnormalities 
Very poor 
Complex: >3 abnormalities 
 
IPSS-R Prognostic Score Values* 
Prognostic 
variable 
0 
0.5 
1 
1.5 
2 
3 
4 
Cytogenetics 
Very 
Good 
Good 
Intermediate 
Poor 
Very Poor 
BM Blast % 
≤2 
>2-
<5% 
5-10% 
>10% 
Hemoglobin 
≥10 
8-<10 
<8 
Platelets 
≥100 
50-
<100 
<50 
ANC 
≥0.8 
<0.8 
 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 67 of 79 
 
IPSS-R Prognostic Risk Categories/Scores* 
RISK CATEGORY 
RISK SCORE 
Very Low 
≤1.5 
Low 
>1.5 - 3 
Intermediate 
>3 - 4.5 
High 
>4.5 - 6 
Very High 
>6 
*Greenberg, Tuechler, Schanz et al, Revised International Prognostic Scoring System (IPSS-R) for Myelodysplastic Syndrome, 
Blood 120: 2454, 2012 
**Schanz J et al, J Clin Oncology 2012; 30:820. 
 
 


 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 68 of 79 
 
Appendix III - Response Criteria 
 
Acute Leukemias: 
• 
Morphologic complete remission (CR): ANC ≥ 1,000/mcl, platelet count ≥ 100,000/mcl, < 5% 
bone marrow blasts, no Auer rods, no evidence of extramedullary disease. (No requirements for 
marrow cellularity, hemoglobin concentration).  
• 
Morphologic complete remission with incomplete platelet recovery (CRp): Same as CR 
platelet count < 100,000/mcl. 
• 
Morphologic complete remission with incomplete blood count recovery (CRi): Same as CR 
but ANC may be < 1,000/mcl and/or platelet count < 100,000/mcl.  
• 
Partial remission (PR): ANC ≥ 1,000/mcl, platelet count > 100,000/mcl, and at least a 50% 
decrease in the percentage of marrow aspirate blasts to 5-25%, or marrow blasts < 5% with 
persistent Auer rods.  
 
Myelodysplastic Syndromes (MDS): 
 
Category 
Response criteria (responses must last at least 4 wk) 
Complete 
remission 
Bone marrow: ≤ 5% myeloblasts with normal maturation of all cell lines* 
• 
Persistent dysplasia will be noted*† 
Peripheral blood‡ 
• 
Hgb ≥ 11 g/dL 
• 
Platelets ≥ 100 x 109/L 
• 
Neutrophils ≥ 1.0 x 109/L† 
• 
Blasts 0% 
Partial remission 
All CR criteria if abnormal before treatment except: 
• 
Bone marrow blasts decreased by ≥ 50% over pretreatment but still > 5% 
Cellularity and morphology not relevant 
Marrow CR 
Bone marrow: ≤ 5% myeloblasts and decrease by ≥ 50% over pretreatment† 
Peripheral blood: if HI responses, they will be noted in addition to marrow CR† 
Stable disease 
Failure to achieve at least PR, but no evidence of progression for ≥ 8 weeks 
Cytogenetic 
response 
Complete 
• 
Disappearance of the chromosomal abnormality without appearance of new ones 
Partial 
• 
At least 50% reduction of the chromosomal abnormality 
Hematologic 
Improvement 
Erythroid response (pretreatment,< 11 g/dL): 
Hgb increase by 1.5 g/dL Relevant reduction of units of RBC transfusions by an absolute 
number of at least 4 RBC transfusions/8 wk compared with the pretreatment transfusion 
number in the previous 8 wk.  
 
Platelet response (pretreatment,< 100 X 109/L): 
Absolute increase of < 30 X 109/L for patients starting with 20 X 109/L platelets 
Increase from less than 20 X 109/L to greater than 20 X 109/L and by at least 100% 
 
Neutrophil response (pretreatment,< 1.0 X 109/L) 
At least 100% increase and an absolute increase0.5109/L 
 
MDS indicates myelodysplastic syndromes; Hgb, hemoglobin; CR, complete remission; HI, hematologic improvement; PR, partial 
remission; FAB, French-American-British; AML, acute myeloid leukemia; PFS, progression-free survival; DFS, disease-free survival. 
*Dysplastic changes should consider the normal range of dysplastic changes (modification). 
†Modification to IWG response criteria. 
‡In some circumstances, protocol therapy may require the initiation of further treatment (eg, consolidation, maintenance) before the 
4-week period. Such patients can be included in the response category into which they fit at the time the therapy is started. 
Transient cytopenias during repeated chemotherapy courses should not be considered as interrupting durability of response, as 
long as they recover to the improved counts of the previous course. 
 
Ref: Cheson BD, Greenberg DL, Bennett JM, et al. Clinical application and proposal for modification of the International Working 
Group (IWG) response criteria in myelodysplasia. Blood. 2006 108: 419-425. 
 
 






















 - GTB-3550 TriKE™ for MDS, Refractory/Relapsed AML and Advanced Systemic Mastocytosis 
 
 
 
June 4, 2021 
Page 79 of 79 
Appendix VI - Targeted Expected Toxicities Worksheet 
HM2015-39 
 
 
 
 
 
CTCAE v5            Refer to Section 10.2 for time points  
Patient Initials:  _______ 
Date of Assessment:  _________  Assessment Time Point:  _________ 
Toxicity 
Grade 0 
Grade 1 
Grade 2 
Grade 3 
Grade 4 
Infusion related 
reaction  
None 
Mild transient reaction; infusion 
interruption not indicated; 
intervention not indicated 
Therapy or infusion interrup ion 
indicated but responds promptly to 
symptomatic treatment (e.g., 
antihistamines, NSAIDS, narcotics, 
IV fluids); prophylactic medications 
indicated for ≤ 24 hrs 
Prolonged (e.g., not rapidly 
responsive to symptomatic 
medication and/or brief 
interrup ion of infusion); 
recurrence of symptoms following
initial improvement; hospitalizatio
indicated for clinical sequelae 
Life-threatening 
consequences; urgent 
intervention indicated 
Dyspnea 
None or 
no change 
Shortness of breath wi h 
moderate exertion 
Shortness of breath wi h minimal 
exer ion; limiting instrumental ADL 
Shortness of breath at rest; 
limiting self care ADL 
Life-threatening 
consequences; urgent 
intervention indicated 
Hypoxia 
None 
  
Decreased O2 saturation with 
exercise (e.g., pulse oximeter < 
88%) intermittent supplemental 
oxygen 
Decreased oxygen saturation 
at rest (e.g., pulse oximeter < 
88% or PaO2 ≤ 55 mm Hg) 
Life-threatening airway 
compromise; urgent 
intervention indicated (e.g., 
tracheotomy or intubation) 
Fever* 
None 
38.0 - 39.0◦ C (100.4 -102.2◦ F) 
> 39.0 - 40 0◦C (102.3 - 104.0◦F) 
> 40.0 ◦ C (>104.0◦ F) for ≤ 24 
hrs 
> 40.0 ◦ C (>104.0◦ F) for > 
24 hrs 
Tachycardia* 
None 
Asymptomatic, interven ion 
not indicated 
Non-urgent medical 
intervention indicated 
Medical intervention or 
hospitalization indicated 
Life-threatening and urgent 
intervention indicated 
Chills 
None 
Mild sensation of cold; shivering; 
chattering of teeth 
Moderate tremor of the entire body; 
narcotics indicated 
Severe or prolonged, not 
responsive to narcotics 
  
Hypertension 
None 
Pre-hypertension (systolic BP 
120 - 139 mm Hg or diastolic 
BP 80 - 89 mm Hg) 
Stage 1 hypertension (systolic BP 
140 - 159 mm Hg or diastolic BP 90 -
99 mm Hg); medical intervention 
indicated; recurrent or persistent ≥ 24
hrs); symptomatic increase by >20 
mm Hg (diastolic) or to >140/90 mm 
Hg if previously WNL; monotherapy 
indicated. 
Stage 2 hypertension (systolic 
BP ≥ 160 mm Hg or diastolic 
BP ≥ 100 mm Hg); medical 
intervention indicated; more 
than one drug or more 
intensive therapy than 
previously used indicated. 
Life-threatening 
consequences (e.g., 
malignant hypertension, 
transient or permanent 
neurologic deficit, 
hypertensive crisis); urgent 
intervention indicated. 
Hypotension 
None 
Asymptomatic, interven ion 
not indicated 
Non-urgent medical 
intervention indicated 
Medical intervention or 
hospitalization indicated 
Life-threatening and urgent 
intervention indicated 
Edema 
None 
Localized to dependent areas, 
no disability or functional 
impairment 
Moderate localized edema 
and intervention indicated; 
limi ing instrumental ADL 
Severe localized edema and 
intervention indicated; limiting 
self care ADL 
  
Pneumonitis 
None 
Asymptomatic; clinical or 
diagnostic observations only; 
intervention not indicated 
Symptomatic; medical 
intervention indicated; limiting 
instrumental ADL 
Severe symptoms; limiting self 
care ADL; oxygen indicated 
Life-threatening respiratory 
compromise; urgent 
intervention indicated (e.g. 
intuba ion or tracheotomy) 
Headache 
None 
Mild pain 
Moderate pain; limiting instrumental 
ADL 
Severe pain; limiting self care 
ADL 
  
Confusion 
(Altered Mental 
Status) 
None 
Mild disorientation 
Moderate disorientation; limiting 
instrumental ADL 
Severe disorientation; limiting 
self care ADL 
Life-threatening  
consequences; urgent 
intervention indicated 
Rash 
None 
Covering < 10% body surface 
area (BSA) 
Covering 10-30% body surface 
area (BSA) 
>30% body surface area (BSA) 
Generalized exfoliative, 
ulcera ive, or bullous 
dermatitis 
Gait 
Disturbance 
None 
Mild change in gait (eg, wide-
based, limping or hobbling) 
Moderate change in gait (eg, wide-
based, limping or hobbling); 
assistance device indicated;  
limi ing instrumental ADL 
Disabling; limiting self care ADL 
  
Ataxia 
(Incoordination) 
None 
Asymptomatic; clinical or 
diagnostic observations only; 
intervention not indicated 
Moderate symptoms; limiting 
instrumental ADL 
Severe symptoms; limiting self 
care ADL; mechanical 
assistance indicated 
  
*refer to Section 7.1.2 - Monitoring for Signs of Immune Activation if present in a Phase I patient 
Person Completing Form:  
 
 
 
 
 
 
ADL = activities of daily living