GT Biopharma Advances NK Cell Immunotherapy With Groundbreaking Nanobody-Based GTB-5550 for Solid Tumor Treatment

GT Biopharma has taken a significant step in its immunotherapy pipeline by filing an investigational new drug (IND) application with the U.S. FDA for GTB-5550, marking the company’s entry into solid tumor treatment using advanced NK cell engager technology. The innovative TriKE platform represents a departure from conventional cancer therapies, employing a sophisticated nanobody-based mechanism to harness natural killer cells against B7-H3 expressing malignancies.

The Solid Tumor Challenge and Market Opportunity

Solid tumors present one of oncology’s most persistent challenges, commanding a substantial segment of the estimated $362 billion global cancer market. B7-H3, an immune checkpoint protein present across prostate, ovarian, breast, lung, and pancreatic cancers, has emerged as a compelling therapeutic target. By redirecting NK cell activity toward B7-H3 positive tumors, GTB-5550 offers a potentially transformative treatment pathway for patients with restricted therapeutic alternatives.

TriKE Platform Architecture and Nanobody Innovation

The GTB-5550 candidate builds upon GT Biopharma’s proprietary TriKE technology, which employs a tri-specific nanobody configuration designed to coordinate multiple immune mechanisms simultaneously:

• A targeting nanobody that recognizes and binds B7-H3 on malignant cells • A CD16-engaging nanobody that activates NK cell cytotoxic functions • An IL-15 linker that enhances NK cell proliferation and persistence

This nanobody-based architecture distinguishes GTB-5550 as the company’s inaugural TriKE candidate eligible for subcutaneous administration, potentially enhancing patient tolerability and treatment convenience compared to conventional intravenous approaches.

Phase 1 Trial Strategy and Clinical Design

The upcoming Phase 1 basket trial, commencing in 2026, will evaluate GTB-5550 across seven metastatic disease cohorts with subcutaneous dosing protocols. The trial incorporates a dose-escalation phase to identify the maximum tolerated dose, followed by expansion phases assessing safety profiles and preliminary efficacy indicators. Clinical endpoints will track progression-free survival and overall survival metrics over a 12-month observation window.

Program Momentum and Financial Runway

GT Biopharma’s parallel Phase 1 program for GTB-3650 in myeloid malignancies is actively enrolling patients, with data anticipated in the first half of 2026. Insights from this hematologic program are expected to accelerate GTB-5550’s development trajectory within a substantially larger patient population. The company maintains a preliminary cash balance of approximately $7 million as of December 31, 2025, supporting operations through the third quarter of 2026.

Market Performance

GTBP stock has fluctuated between $0.54 and $3.85 over the preceding twelve months, currently trading at $0.71 with an 8.82% gain.