Unlocking the Potential of GI101: Enhancing Tumor Immunotherapy through Bispecific Protein Targeting

The study introduces GI-101, a novel immunotherapy agent that combines the extracellular domain of CD80 as a CTLA-4 antagonist and an IL-2 variant that selectively binds the IL-2Rβ subunit. This fusion protein is designed to improve clinical outcomes, particularly for 'cold' tumors that do not respond to traditional immune checkpoint therapies.

The research utilized Surface Plasmon Resonance (SPR) to determine GI-101's binding affinity to IL2Rs, CTLA4, and CD28. The proliferation of immune cells was assessed using the CFSE assay, and the in vivo anti-tumor effects were evaluated using CT26, MC38, and B16F10 tumor models. Flow cytometry was employed to analyze the immune cell population in the tumor microenvironment (TME), and tumor-specific T cells were measured by splenocyte proliferation and IFN-γ ELISPOT assays. Additionally, RNA sequencing was conducted to understand the mechanism of action of GI-101.

Results showed that GI-101 has a high affinity for CTLA-4, enhancing the interaction between endogenous CD80 and CD28, which activates T cells. The bivalent IL-2 variant in GI-101 promotes the proliferation of CD8+ T and NK cells without affecting Tregs. The compound did not exhibit toxicity associated with IL-2 activity, such as vascular leakage syndrome or cytokine storm, in non-GLP monkey studies. GI-101 also restored immune function in vitro, and a dose-dependent tumor growth inhibition was observed in CT26 models without toxicity. Immune profiling indicated an increase in M1 macrophages, CD8+ Tcm, and Ki-67+ proliferating T cells in the TME. Tumor-specific T cells showed strong proliferation upon stimulation with CT26 neoantigens. Notably, GI-101 combined with anti-PD-1 resulted in significant tumor regression in MC38 tumor-bearing mice.

The study concludes that GI-101 offers a dual function of checkpoint blockade and IL2 activity, enhancing the proliferation and activation of T and NK cells. It is positioned as a potential superior alternative to first-generation ICBs, with promising clinical efficacy and safety profiles, even in 'cold tumor' models. The findings support further clinical investigation of GI-101 as a single agent or in combination with other immunotherapies.