LAUSR

High-dose Interleukin-2 (IL-2) monotherapy induces complete responses in cancer patients but its use is limited by acute vascular toxicities including capillary leak syndrome and severe hypotension 1,2. IL-2 activates lymphocytes and NK-cells through the intermediate-affinity dimeric IL-2 receptor, IL-2Rβ/γ (CD122/CD132), while antigen activated T-cells and regulatory T-cells (Tregs) have increased sensitivity to IL-2 by expressing the high-affinity trimeric IL-2 receptor, IL-2Rα/β/γ (CD25/CD122/CD132)3. CD25-independent IL-2s (“non-α-IL-2s”) aim to increase the therapeutic efficacy of IL2 in cancer patients by avoiding Treg activation through selective binding to IL-2Rβ/γ 4. However, those molecules still are reported to induce fever and hypotension and have limited efficacy as a monotherapy or in combination with anti-PD-1 5,6. Here we show that a novel α/β-IL-2 agonist that was designed to preferentially bind to the IL-2Rα/β/γ receptor highly upregulated on antigen activated T-cells can greatly improve on the efficacy of IL-2 while avoiding the vascular toxicity commonly associated with IL-2 treatment. In syngeneic tumor models, this α/β-IL-2 agonist significantly reduced exhaustion of tumor infiltrating T cells compared to WT-IL-2 or a non-α-IL-2 leading to improved expansion of tumor antigen specific CD25+PD-1+CD8+ T cells systemically and in the tumor microenvironment. This resulted in complete responses and tumor immune memory with α/β-IL-2 monotherapy as well as improved outcomes in combination with anti-PD-1 therapy in PD-1 refractory syngeneic tumors. In contrast, WT-IL-2 reduced T cell exhaustion and drove antigen specific T cell responses to a lesser degree, resulting in reduced combinatorial efficacy with anti-PD-1, while the non-α-IL-2 failed to do either. Furthermore, the α/β-IL-2 agonist reduced intratumoral Tregs compared to treatment with WT-IL-2 or PBS improving the intratumoral CD8 to Treg ratio. In non-human primates and mice, WT-IL-2 and a non-α-IL-2 led to broad extravasation of lymphocytes and NK cells and activation of intra-pulmonal T cells resulting in systemic tissue inflammation and NK cell-mediated lethal capillary leak syndrome whereas the α/β-IL-2 agonist, which avoids binding the dimeric IL-2Rβ/γ expressed on NK cells, avoided systemic lymphocyte activation which facilitated continuous treatment without acute vascular toxicities. Overall, through selective engagement of CD25+ T cells, this α/β-IL-2 agonist demonstrated improved efficacy and tolerability of IL-2 in preclinical tumor models. Clinical trials with STK-012, a human α/β-IL-2 agonist, are in progress.1 Atkins, et al.; JCO 1999, 2 Dutcher, et al.; JITC 2014, 3 Liao, et al.; Immunity 2013, 4 Levin, et al.; Nature 2012, 5 Janku, et al.; Cancer Research 2021; 6 Diab, et al.; Cancer Disc. 2020 Citation Format: Martin Oft, Navneet Ratti, Sandro Vivona, Jan Emmerich, Romina Riener, Ievgen O. Koliesnik, Scott McCauley, Michele Bauer, Marie Semana, Deepti Rokkam, Bhargavi Jayaraman, Rene de Waal Malefyt, Paul-Joseph Aspuria, Michael Totagrande, Anita Mehta-Damani, Patrick J. Lupardus, Rob A. Kastelein. STK-012, an a/b-selective IL-2 activates tumor antigen specific CD25+ CD8 T cells to reject tumors without acute vascular toxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1801.