Issued on behalf of GT Biopharma, Inc.
Key Takeaways
- First patient dosed in Phase 1 trial of GTB-5550, a B7-H3-targeted natural killer (NK) cell engager — the third TriKE® program to enter clinical testing.
- Dose-escalation phase will focus primarily on prostate cancer patients, where B7-H3 is expressed in over 90% of metastatic castration-resistant tumors.
- Trial expansion will enroll up to seven solid tumor types: prostate, ovarian, breast, head and neck, non-small cell lung, pancreatic, and bladder cancer.
- First nanobody-based TriKE® tested with patient-friendly subcutaneous dosing rather than continuous infusion.
- Comes as NK cell-engaging therapies attract growing institutional interest, with peers across the space advancing manufacturing, autoimmune and oncology programs in 2026.
SAN FRANCISCO, May 14, 2026 - Baystreet.ca News Commentary - A new wave of immuno-oncology programs is putting the body's own natural killer (NK) cells at the center of cancer treatment strategy. After more than a decade of T-cell-dominated immunotherapy headlines, the natural killer cell — a faster-acting, MHC-independent arm of the innate immune system — is increasingly being engineered, recruited, and amplified against both blood cancers and solid tumors. The latest milestone arrives this week.
GT Biopharma, Inc. (NASDAQ: GTBP) announced that the first patient has been dosed in a Phase 1 dose-escalation basket trial evaluating GTB-5550, its B7-H3-targeted natural killer cell engager for solid tumors expressing B7-H3 [1]. The dosing event marks the third TriKE® (Tri-specific Killer Engager) program from GT Biopharma to enter clinical testing, and the first to be tested with subcutaneous administration rather than continuous intravenous infusion [1].
The Phase 1a dose-escalation portion will focus primarily on prostate cancer patients and evaluate up to six dose levels to identify the maximum tolerated dose (MTD). Phase 1b will then expand into up to seven distinct solid tumor types — castration-resistant prostate cancer, ovarian, breast, head and neck, non-small cell lung, pancreatic, and bladder cancer — to evaluate safety, tolerability and preliminary anti-tumor activity [1].
"Dosing the first patient in our GTB-5550 Phase 1 trial is a pivotal milestone for GT Biopharma and represents the natural evolution of our TriKE® platform into the broader opportunity of treating patients with a variety of solid tumors," said Michael Breen, Executive Chairman and Chief Executive Officer of GT Biopharma [1]. He added that ongoing Phase 1 progress with the company's earlier hematologic-malignancy program, GTB-3650, provided the confidence to advance the platform into B7-H3, which is broadly expressed across many of the most common and difficult-to-treat solid tumor cancers.
The choice of B7-H3 — and of prostate cancer as the lead indication — is grounded in the underlying biology. According to Dr. Nicholas Zorko, MD, PhD, of the University of Minnesota, patients with metastatic castration-resistant prostate cancer have B7-H3 expressed in over 90% of tumors, and PSA can serve as an early biomarker of therapeutic activity [1].
A Broader Push to Harness NK Cells
GTB-5550 enters the clinic at a moment when the NK cell engagement category is attracting substantial commercial-stage and clinical-stage activity across the United States.
ImmunityBio, Inc. (NASDAQ: IBRX), a commercial-stage immunotherapy company built around NK cell biology, announced in March 2026 that it had successfully completed manufacturing engineering programs establishing a scalable leukapheresis-to-manufacturing pathway for its autologous memory cytokine-enhanced NK cell therapy platform, with the ability to generate up to approximately 5 billion NK cells from a single apheresis collection — enough to yield up to 8–10 therapeutic doses within 12 days [2]. ImmunityBio's commercial product ANKTIVA®, an IL-15 receptor agonist designed to activate NK cells, T cells and memory T cells, is FDA-approved in combination with Bacillus Calmette-Guérin (BCG) for the treatment of adult patients with BCG-unresponsive non-muscle invasive bladder cancer (NMIBC) with carcinoma in situ (CIS), with or without papillary tumors; in early 2026 ImmunityBio also launched ResQ215B, a Phase 2 chemotherapy-free combination study pairing its CD19-targeted high-affinity NK (haNK) cell therapy with ANKTIVA® and rituximab in indolent B-cell non-Hodgkin lymphoma [3].
Artiva Biotherapeutics, Inc. (NASDAQ: ARTV), a clinical-stage company developing off-the-shelf NK cell therapies, illustrates the breadth of NK biology beyond oncology. In May 2026, Artiva reported that its lead candidate AlloNK® (AB-101), an off-the-shelf allogeneic cord-blood-derived NK cell therapy, had shown a 71% ACR50 response rate in refractory rheumatoid arthritis patients with at least six months of follow-up in a company-sponsored Phase 2a basket trial, with no patients relapsing or requiring new immunomodulatory agents [4]. Artiva also announced FDA alignment on a single Phase 3 registrational randomized controlled trial evaluating AlloNK plus rituximab versus rituximab alone in approximately 150 refractory RA patients, with trial initiation planned for the second half of 2026 [4]. The data underscore that NK cell engagement is being pursued across both oncology and autoimmune disease — a duality that the TriKE® platform's broader pipeline also reflects.
Purple Biotech Ltd. (NASDAQ: PPBT) is advancing a different but related strategy — multi-specific antibodies designed to engage both T cells and NK cells against tumors. Its lead program, the CAPTN-3 platform, is built around capped tri-specific antibodies that simultaneously target a tumor-associated antigen, the CD3 activating receptor on T cells, and NKG2A, an inhibitory receptor on NK and CD8⁺ T cells [5]. The platform's lead candidate, IM1240, targets 5T4 and is on track for Phase 1 initiation in the second half of 2026, with IND submission planned mid-2026 [5]. In April 2026, Purple Biotech reported new preclinical data showing that IM1240 induced mature tertiary lymphoid structures and increased CD8 T cell and NK cell abundances in a patient-derived non-small cell lung cancer tissue model [6].
Why Subcutaneous Dosing Matters
One element of the GTB-5550 trial design that distinguishes it within the NK cell engager landscape is its subcutaneous administration. GT Biopharma's announcement notes that GTB-5550 will be administered by subcutaneous (SQ) injection in the abdominal area for five consecutive days during Week 1 and Week 2, followed by two weeks of no treatment, with subsequent cycles dosed three times weekly for two weeks followed by two weeks off [1]. One treatment cycle is four weeks in duration, with a minimum of two cycles planned.
Subcutaneous dosing has become increasingly important across the broader immuno-oncology space as developers look to move treatments out of the infusion suite and into more outpatient-friendly settings — a trend already visible in ImmunityBio's subcutaneous ANKTIVA® regimens.
A Clinical Roadmap Into 2H 2026
GT Biopharma has indicated that it anticipates providing updates on the GTB-5550 trial throughout the second half of 2026 as enrollment progresses through the dose-escalation cohorts [1]. Patients in the trial are followed for 12 months to determine progression-free survival (PFS) and overall survival (OS), and the trial is registered on clinicaltrials.gov under the identifier NCT07541573 [1].
With three TriKE® programs now in the clinic, growing institutional activity around NK cell engagement, and a basket trial design that opens the door to multiple high-prevalence solid tumor types, the company's expansion into B7-H3-targeted therapy positions it within one of the most actively developed corners of next-generation immuno-oncology.
Continuing coverage of GT Biopharma, Inc. and the natural killer cell engager space is available at gtbiopharma.com.
Article Sources
1. GT Biopharma, Inc. — GT Biopharma Announces First Patient Dosed in Phase 1 Trial of GTB-5550 (May 14, 2026) — https://www.globenewswire.com/news-release/2026/05/13/
2. ImmunityBio, Inc. — ImmunityBio Achieves Milestone with Large-Scale NK Cell Production and Cryopreservation from Over 60 Healthy and Cancer Donors (March 13, 2026) — https://immunitybio.com/immunitybio-achieves-milestone-with-large-scale-nk-cell-production-and-cryopreservation-from-over-60-healthy-and-cancer-donors/
3. ImmunityBio, Inc. — ImmunityBio Launches Phase 2 Chemotherapy-Free CAR-NK Cell Therapy Trial with ANKTIVA® (ResQ215B) in Indolent Lymphomas (February 2, 2026) — https://immunitybio.com/immunitybio-launches-phase-2-chemotherapy-free-car-nk-cell-therapy-trial-with-anktiva-resq215b-in-indolent-lymphomas/
4. Artiva Biotherapeutics, Inc. — Artiva Biotherapeutics Reports First Quarter 2026 Financial Results and Recent Business Highlights (May 8, 2026) — https://www.sec.gov/Archives/edgar/data/0001817241/000119312526213239/d38160dex991.htm
5. Purple Biotech Ltd. — Purple Biotech Achieves Toxicology Milestone Demonstrating an Expanded Therapeutic Window for CAPTN-3 Platform Tri-specific Antibody, IM1240 (January 7, 2026) — https://www.globenewswire.com/news-release/2026/01/07/3214477/0/en/Purple-Biotech-Achieves-Toxicology-Milestone-Demonstrating-an-Expanded-Therapeutic-Window-for-CAPTN-3-Platform-Tri-specific-Antibody-IM1240.html
6. Purple Biotech Ltd. — Purple Biotech Announces New Data from CAPTN-3 Platform Tri-specific IM1240 (April 27, 2026) — https://www.stocktitan.net/news/PPBT/purple-biotech-announces-new-data-from-captn-3-platform-tri-specific-msgchjjy4dqv.html
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