GT Biopharma Advances GTB-3650 to Higher Dose Level in Phase 1 Blood Cancer Trial
Key Insights
GT Biopharma successfully completed safety review for Cohort 3 of its Phase 1 GTB-3650 trial, with no safety or tolerability issues observed across six patients.
The company has advanced to Cohort 4 dosing at 10μg/kg/day, which represents a potential clinical efficacy threshold based on positive immunological biomarker trends.
GTB-3650 targets relapsed or refractory blood cancers expressing CD33 (search) protein, including acute myeloid leukemia (search) and high-risk myelodysplastic syndrome (search).
GT Biopharma has successfully completed the formal safety review for its ongoing Phase 1 clinical trial of GTB-3650's third dosing group (Cohort 3), with no safety or tolerability issues observed. This milestone has allowed the company to advance into Cohort 4, where patients will receive 10μg/kg/day, marking a significant step forward in the development of this novel immunotherapy for blood cancers.
The company is actively screening patients for Cohort 4 and anticipates initiating dosing in the coming weeks, with the next comprehensive update expected in the first quarter of 2026.
Trial Design and Patient Population
The Phase 1 study is testing GTB-3650 in patients battling relapsed or refractory blood cancers that express the CD33 (search) protein, specifically acute myeloid leukemia (search) (AML) and high-risk myelodysplastic syndrome (search) (MDS). These represent some of the most difficult cancer cases to treat, involving patients whose disease either came back after initial therapy or never responded to conventional treatment options.
GTB-3650 works by stimulating the patient's natural killer cells, a type of immune cell that naturally hunts down and destroys abnormal cells, to specifically target cancer cells. Patients receive the therapy through continuous infusions following a structured schedule: two weeks of treatment followed by two weeks of rest, repeating this cycle for up to four months based on how they respond.
Safety Profile and Dose Escalation
The six patients enrolled across Cohorts 1 through 3 have all been successfully treated with GTB-3650, demonstrating the therapy's tolerability at progressively higher dose levels. According to the company, the Cohort 4 dose level of 10μg/kg/day is more reflective of the potential clinical efficacy threshold. This assessment is based on positive trends observed across multiple immunological biomarkers from the previous six patients, the complete absence of dose-limiting toxicities throughout all three completed cohorts, and recognition that the earlier cohorts utilized lower dose levels that may have been below the therapeutic range where meaningful clinical benefit occurs.
The Phase 1 design calls for testing GTB-3650 in approximately 14 patients across seven cohorts, with two patients per cohort receiving progressively higher doses from 1.25μg/kg/day in Cohort 1 up to 100μg/kg/day in Cohort 7 if necessary. Beyond the current Cohort 4, three additional higher-dose cohorts remain available: Cohort 5 at 25μg/kg/day, Cohort 6 at 50μg/kg/day, and Cohort 7 at the maximum planned dose of 100μg/kg/day.
TriKE Platform Technology
Both GTB-3650 and the company's solid tumor candidate GTB-5550 utilize GT Biopharma's proprietary TriKE platform technology, which employs specialized antibody fragments originally found in camels and llamas. These molecules offer advantages over conventional antibodies due to their smaller size and greater stability. The company holds an exclusive worldwide license from the University of Minnesota for this technology.
Pipeline Expansion
Beyond blood cancers, the company is developing GTB-5550, which targets B7H3 (search), a protein commonly found across various solid tumor types including breast, lung, ovarian, pancreatic, bladder, and prostate cancers. GT Biopharma plans to file its regulatory application to begin human trials of GTB-5550 either in the fourth quarter of 2025 or in January 2026. GTB-5550 is being designed as a subcutaneous injection that patients might eventually self-administer at home.
Market Context
The hematologic malignancies treatment market reached $72 billion in 2025 and is projected to nearly double to $139 billion by 2034, driven by accelerating adoption of novel therapeutics. Scientists have engineered breakthrough cell therapies that can be mass-produced and stored ready-to-use, addressing key barriers in treatment access and cost. Researchers also discovered how tumors exhaust immune cells, revealing an entirely new pathway to revive cancer-fighting T cells and overcome treatment resistance.
The trial is measuring safety, pharmacokinetics, pharmacodynamics, in vivo expansion of endogenous patient natural killer cells, and clinical activity. This wide dosing range reflects the trial's goal of identifying where GTB-3650 delivers optimal therapeutic benefit while maintaining an acceptable safety profile.