Abstract 4070: CIS-demasking cytokine linker technology allows a selective cytokine delivery to activated immune cells while sparing others and peripheral toxicity

Abstract Immunocytokines are promising new therapeutic approaches to enhance T-cell response by delivering interleukins into the tumoral site. Fusion of wild-type or attenuated interleukins to anti-PD-1 antibody has shown some efficacy to preferentially cis-activate PD1-expressing T-cells but on-target/off-tumor activity on PD-1-negative cells is still observed due to the high affinity of the cytokine to its receptor leading a broad systemic effect, toxicity, high clearance and low tumor biodistribution limiting the potential of some immunocytokines (e.g. anti-PD-1/IL-2/IL-15/IL-21). Various strategies have emerged to achieve localized cytokine activation using conditional strategies (e.g. allosteric modulators, MMP-cleavable linkers or pH-dependent binding) that remain challenging due to high dependency to specific TME composition (MMP, acidosis...). We developed the OSE-Cytomask® Platform, a universal and innovative linker technology allowing exclusive cytokine CIS-demasking upon binding of the fused antibody to its target without TRANS-activation associated with undesired effects (e.g. Toxicity). A series of different linkers were screened for optimal cis-activation of cytokine on PD1-expressing vs PD1-negative T-cells using different cytokines fused to a high-affinity anti-PD1. OSE-Cytomask® linker technology decreases IL-2 or IL-15 cytokine activity (pSTAT5 signaling) on PD1-negative cells while maintaining high activation of PD1-transduced T-cells even in co-culture. We confirmed activity of OSE-Cytomask® Immunocytokine on (PD1+) human T-cells while very low activation has been observed in naïve T-cells. Importantly, Cytomask® linker technology does not induce TRANS-activation on PD1-negative T-cells illustrating an innovative and strict CIS-demasking mechanism of action. In vivo, Anti-PD-1/IL-15 and/or anti-PD1/IL-2 OSE-Cytomask® molecules illustrated reduced toxicity after single or multiple injections (2mg/kg). High T-cell proliferation has been observed in tumor-micro-environment where PD1-expressing T cells are located. Low T-cell proliferation in periphery was seen, illustrating the potential of CIS-demasking technology to target the right T-cells at the right place. Altogether, OSE-Cytomask® linker technology illustrates specific intrinsic property to mask cytokine on naïve peripheral immune cells not expressing the target of the antibody while allowing selective CIS-demasking of the cytokine and CIS-activation of activated immune cells expressing (e.g. PD-1). This linker technology could be used with a broad range of cytokine to abrogate OFF-tumor cytokine activity associated with toxicity while selectively CIS-activating activated immune cells in the TME. Citation Format: Aurore Morello, Caroline Mary, Virginie Thepenier, Margaux Seité, Justine Durand, Cécile Batty, Kévin Biteau, Julien Taurelle, Géraldine Teppaz, Amandine Georges, Nicolas Poirier. CIS-demasking cytokine linker technology allows a selective cytokine delivery to activated immune cells while sparing others and peripheral toxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4070.