Simultaneous TCR and IL-2 agonism selectively enhances epitope-specific CD8 T-cell responses during chronic viral infection.

UNLABELLED: Interleukin-2 (IL-2) remains an attractive cytokine for enhancing antigen-specific CD8 T-cell responses in cancer immunotherapy, but systemic toxicity hinders its broad clinical application. To address this, various IL-2-based therapeutics have been engineered with altered IL-2 receptor bias or targeted delivery to tumors, the tumor microenvironment, or immune cell populations. Ideally, IL-2 signals should be selectively delivered to antigen-specific CD8 T cells, boosting their responses and promoting effector differentiation while sparing non-targeted populations. Immuno-STAT (Selective Targeting and Alteration of T cells) is a fusion protein platform comprising a bivalent peptide-major histocompatibility complex (MHC) class I complex and an affinity-attenuated IL-2 mutein that co-stimulates T-cell receptor and IL-2 signaling in epitope-specific CD8 T cells. Here, we investigated whether a DbGP33-41-targeted Immuno-STAT enhances DbGP33-specific CD8 T-cell responses in a mouse model of chronic lymphocytic choriomeningitis virus infection. Immuno-STAT treatment selectively expanded DbGP33-specific CD8 T cells with an effector-like phenotype. Non-targeted DbGP276-specific CD8 T cells showed little to no expansion in response to DbGP33-41-targeted Immuno-STAT therapy, underscoring the selectivity of this approach. However, minor changes in phenotypic markers, including increased expression of CD25 and CX3CR1, were observed in non-targeted CD8 T cells, likely reflecting bystander IL-2 signaling. Combining Immuno-STAT with PD-1 blockade augmented DbGP33-specific CD8 T-cell responses more effectively than PD-1 blockade alone, with minor effects on the non-targeted DbGP276-specific population. These findings inform the clinical development of Immuno-STAT and other IL-2 therapeutics and highlight the value of coordinated TCR and IL-2 stimulation during chronic antigen exposure, alone or in combination with PD-1 blockade.

IMPORTANCE: Interleukin-2 (IL-2) is a key cytokine for promoting effector differentiation of antigen-specific CD8 T cells and remains an attractive agent in cancer immunotherapy, but systemic toxicity limits its clinical use. This study addresses a central challenge in IL-2-based immunotherapy: delivering IL-2 to cognate antigen-specific CD8 T cells while minimizing activation of non-targeted populations. Using a mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection, we show that the Immuno-STAT (Selective Targeting and Alteration of T cells) platform selectively expands targeted virus-specific CD8 T cells and enhances their function while limiting effects on non-targeted populations. We also show that combining Immuno-STAT with PD-1 blockade further enhances targeted virus-specific CD8 T-cell responses during chronic LCMV infection. These findings provide mechanistic and preclinical support for integrating T-cell receptor specificity with IL-2 signaling to advance cancer immunotherapy and guide next-generation IL-2 therapeutics for cancer and chronic infection.