Abstract 719: A tumor-activated PD1/IL2 bispecific molecule, designed to overcome IL-2 receptor-mediated clearance, improve tolerability and stimulate antigen-experienced CD8+ T cells in the tumor microenvironment of murine models

Abstract PD-1/PD-L1 therapies have shown significant activity across a range of tumor types, however, 70-90% of patients do not derive durable benefit. In preclinical settings, delivery of PD-1 blockade and IL-2 agonism in cis via a bispecific molecule, comprising a PD-1 antibody fused to IL-2, has demonstrated superior activity compared to delivery of individual components or their combination. Targeting of IL-2 to PD-1+ cells in cis has been shown to drive a unique differentiation path endowing CD8+ T cells with enhanced functionality. However, we show that the IL-2 component in an unmasked PD1/IL2 bispecific molecule dominates its pharmacology, driving marked peripheral activation of immune cells, rapid IL-2 receptor-mediated clearance and systemic toxicity. To address these challenges and enable tumor-specific activity, we designed a PD1/IL2 bispecific molecule that incorporates a single domain antibody-based mask to bind to the IL-2 component and maintain it in a quiescent state until activated by prevalent and dysregulated proteases in the tumor microenvironment (TME). In preclinical models, the affinity-optimized mask prevented peripheral IL-2 receptor binding, associated toxicity and receptor-mediated clearance. Improved pharmacokinetics of our tumor-activated PD1/IL2 enabled PD1 antibody-like exposures and is projected to achieve complete blockade of PD1 signaling. Tumor-activated PD1/IL2 significantly inhibited tumor growth compared to anti-PD-1 alone or vehicle and demonstrated improved tolerability compared to an unmasked PD1/IL2 bispecific in mouse models. In addition, pharmacodynamic activity of tumor-activated PD1/IL2 was restricted to the TME. Consistent with the masked design, we observed no significant change in CD8+ T cells in the periphery and significant increases in antigen specific CD8+ T cells, memory CD8+ T cells and TCF1+ stem-like CD8+ T cells in the TME. Ex vivo protease cleavage assays performed in human samples demonstrated efficient activation of tumor-activated PD1/IL2 by multiple tumor types and minimal activation in human plasma. In non-human primates, tumor-activated PD1/IL2 achieved tolerable exposures that were comparable to those of existing PD-1 blocking immunotherapies. Taken together, these preclinical data suggest that tumor-activated PD1/IL2 has the potential to improve upon existing PD-1/PD-L1 immunotherapies by inhibiting PD-1/PD-L1 axis and simultaneously directing immunostimulatory IL-2 to antigen-experienced effector cell populations in the TME. Citation Format: Ertan Eryilmaz, Wilson Guzman, Stephanie Hsiao, Parker Johnson, Lisa Quinn, Jimit Lakhani, Brendan Whalen, Rosa Quiroz, Kurt Jenkins, Bernard Lanter, Oleg Yerov, Will Scott, Justin Greene, Zhen Liu, Jason Hedges, Megan McLaughlin, Sallyann Vu, Chelsea Turcotte, Jacob Taylor, Caitlin O'Toole, Magali Pederzoli-Ribeil, Haley Duprey, Natalia Malkova, Damiano Fantini, David Crowe, Kyle Smith, Joseph Card, Janice Lee, Kerri Smith, Benjamin Nicholson, Jennifer O'Neil, Carl U. Bialucha. A tumor-activated PD1/IL2 bispecific molecule, designed to overcome IL-2 receptor-mediated clearance, improve tolerability and stimulate antigen-experienced CD8+ T cells in the tumor microenvironment of murine models [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 719.