Michael J. Walsh

Tumor-infiltrating lymphocyte (TIL) therapy has demonstrated that endogenous T cells can be harnessed to initiate effective antitumor responses. Despite clinical promise, current TIL production protocols involve weeks-long ex vivo expansions that can affect treatment efficacy. Therefore, additional tools are needed to engineer TILs to have increased potency while mitigating manufacturing challenges. Here, we present a strategy for pseudotyping retroviruses with peptide–major histocompatibility complexes (pMHCs) for antigen-specific gene delivery to CD8 T cells and validate therapeutic impact in immunocompetent mouse models. We demonstrate that pMHC-targeted viruses specifically deliver function-enhancing cargos while simultaneously activating and expanding antitumor T cells. This targeting precision enables in vivo engineering of tumor-specific T cells, resulting in improved overall survival in B16F10-bearing mice. Together, we have established that pMHC-targeted viruses are efficient vectors for reprogramming and expanding tumor-specific T cells directly in vivo, with the potential to substantially streamline engineered cell therapy production.

Long-standing goals of cancer immunotherapy are to activate cytotoxic antitumor T cells across a range of affinities for tumor antigens while suppressing regulatory T cells. Computational protein design has enabled the precise tailoring of proteins to meet specific needs. Here, we report a de novo designed IL-21 mimic, 21h10, with high stability and signaling potency in humans and mice. In murine and ex vivo human organotypic tumor models, 21h10 showed robust antitumor activity, with more prolonged signaling and stronger antitumor activity than native IL-21. 21h10 induced pancreatitis that could be mitigated by TNF blockade without compromising antitumor efficacy. Although antidrug antibodies to 21h10 formed, they were not neutralizing. 21h10 induced highly cytotoxic T cells with a range of affinities, robustly expanding intratumoral low-affinity cytotoxic T cells and driving high expression of IFN-γ and granzyme B compared with native IL-21, while increasing the frequency of IFN-γ ⁺ T helper 1 cells and reducing regulatory T cells. The full human-mouse cross-reactivity, high stability and potency, and low-affinity antitumor responses support the translational potential of 21h10.