Abstract
Much interest remains to harness the T cell-activating properties of high-dose (HD) IL-2 to promote antitumor immunity. Modifying IL-2 for cancer immunotherapy focused on targeting the intermediate-affinity IL-2R expressed on memory CD8+ T cells and NK cells to avoid high-affinity IL-2R-expressing Tregs. This does not selectively expand tumor-specific Teff cells, which we hypothesize to be the most effective at controlling tumor growth. Here, a novel IL-2 fused to CD25 (mIL-2/CD25), is evaluated for antitumor efficacy in syngeneic mouse models. HD mIL-2/CD25 outcompetes an intermediate-affinity IL-2R agonist in antitumor activity and in expanding CD8+ tumor-infiltrating lymphocytes (TILs). Intratumoral Treg numbers do not change with therapy, yet splenic Tregs expand 10-fold. CD8+ TILs are the major population amplified within the tumor microenvironment (TME) and the major driver of the mIL-2/CD25-induced antitumor response. HD mIL-2/CD25-treated CD8+ TILs expand locally, exhibit a lower exhaustion profile, elicit higher effector cytokine production, and support antitumor memory. The addition of PD-1 blockade promotes tumor clearance in almost all mice, even in late-stage tumors. During both mono- and combination therapy, scRNA and TCR repertoire sequencing of the TME reveals robust clonal expansion of unique CD8+ T cell subsets with high effector programming, yet Tregs undergo no detectable clonal expansion. This suggests that mIL-2/CD25 acts within the TME to support the expansion of unique CD8+ tumor-reactive Teff cells, while minimally impacting intratumoral Tregs. These studies serve to provide support for mIL-2/CD25 as a potential novel IL-2 candidate for combination with PD-1 checkpoint blockade to increase efficacy and decrease autoimmune-like side effects.