Abstract 3518: AB248 is a CD8+ T cell selective IL-2 designed for superior safety and anti-tumor efficacy

Abstract

Abstract High dose IL-2 was the first modern immunotherapy to show complete responses in a subset of cancer patients. The liabilities of IL-2 prompted development of second-generation molecules, which signal through the IL-2Rβγ (“not-α” IL-2 and IL-15 variants). Although these molecules avoid vascular leak syndrome, their clinical efficacy appears to be suboptimal compared to high dose IL-2 [1]. Furthermore, not-α IL-2s show biased expansion of NK cells over CD8+ T cells in patients due to their high expression of IL-2Rβ on NK cells, which can act as a sink and contribute to toxicity, and these molecules do not eliminate IL-2Rβγ-mediated activation of Tregs [2, 3]. To maximize the therapeutic potential of IL-2, we developed AB248, a cis-targeted IL-2 fusion protein that selectively signals on CD8+ T-cells with limited activity on the highly IL-2/IL-15-sensitive NK cells and immunosuppressive Tregs. We have previously shown that selective expansion of CD8+ T cells over NK cells and Tregs is achieved in vivo using muAB248, AB248’s murine surrogate. Furthermore, a single dose of muAB248 elicits strong efficacy in multiple tumor models without body weight loss. Here, we detail the properties of AB248, a fusion of a human CD8-targeting antibody that selectively binds to CD8+ T cells over NK cells, and an IL-2 mutein with reduced affinity to IL-2Rα and IL-2Rβ. In STAT5 assays, AB248 showed approximately 1000-fold preference for the activation of CD8+ T cells over NK cells and Tregs. AB248 mediated a dose-dependent selective expansion of CD8 T cells over NK and Tregs in non-human primates. Furthermore, AB248 reproduced the expected in vitro gene signatures of an IL2Rβγ agonist, demonstrating that AB248 recapitulates native IL-2Rβγ signaling selectively on CD8+ T cells.We previously demonstrated in mice that while the efficacy of not-α IL-2 was mediated by CD8+ T cells and not NK cells, toxicity as measured by body weight loss was dependent upon NK cells but not CD8+ T cells. Here, we show that human NK cells may also drive IL-2βγ agonist-induced toxicities. Both IL-2 and not-α IL-2 induced IFN-γ secretion from human PBMCs, whereas AB248 did not. Strikingly, depletion of CD56+ NK cells eliminated IL-2-induced cytokine secretion, demonstrating that human NK cells are capable of spontaneously secreting IFN-γ in response to IL-2 signaling. In the context of TCR stimulation, AB248 induced robust secretion of effector cytokines from CD8+ T cells, but no cytokine secretion was seen in absence of TCR activation. Our data suggest that while AB248 can induce antigen-independent expansion of CD8+ T cells, it only induces effector cytokine secretion in the context of an additional activating signal via the TCR. Collectively, these data show that AB248 demonstrates an improved safety and efficacy profile as compared to not-α IL-2 and is a promising immuno-oncology therapeutic. Ref: 1. Overwijk, Ann. Rev. Med., 2020; 2. Janku, AACR, 2021; 3. Italiano, JCO, 2021 Citation Format: Kelly D. Moynihan, Danielle Pappas, Terrence Park, Wei Chen, Irene Ni, Paul Bessette, Henry Nguyen, David Liu, Mike Chin, Ruth Lan, Aaron Arvey, Ton N. Schumacher, Yik Andy Yeung, Ivana Djuretic. AB248 is a CD8+ T cell selective IL-2 designed for superior safety and anti-tumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3518.