Potent antitumor activity of a designed interleukin-21 mimic

Abstract

Long-standing goals of cancer immunotherapy are to activate cytotoxic antitumor T cells across a broad range of affinities while dampening suppressive regulatory T (Treg) cell responses, but current approaches achieve these goals with limited success. Here, we report a de novo IL-21 mimic, 21h10, designed to have augmented stability and high signaling potency in both humans and mice. In multiple animal models and in ex vivo organotypic human melanoma, 21h10 showed robust antitumor activity. 21h10 generates significantly prolonged STAT signaling in vivo compared with native IL-21, and has considerably stronger anti-tumor activity. Toxicities associated with systemic administration of 21h10 could be mitigated by TNFα blockade without compromising antitumor efficacy. In the tumor microenvironment, 21h10 induced highly cytotoxic antitumor T cells from clonotypes with a range of affinities for endogenous tumor antigens, robustly expanding low-affinity cytotoxic T cells and driving high expression of interferon-𝛾 (IFN-𝛾) and granzyme B compared to native IL-21, while increasing the frequency of IFN-𝛾+ Th1 cells and reducing that of Foxp3+ Tregs. Thus, 21h10 is a highly stable and active IL-21 mimic with full human/mouse cross-reactivity that potentiates low-affinity antitumor responses and has considerable translational potential.