IL13 critically contributes to the antitumor activity of polyfunctional CD4+ T cells driven by constitutively active Stat5

The presence of polyfunctional T cells capable of concurrently producing multiple cytokines correlates with favorable clinical outcomes in patients with cancer. We previously reported that overexpression of constitutively active Stat5a (CASTAT5) confers polyfunctionality on tumor-specific CD4⁺ T cells, enabling durable antitumor immunity following adoptive cell therapy. However, the mechanisms underlying the enhanced antitumor effects of CASTAT5-modified T cells remain unclear. Here, we identify interleukin-13 (IL13) as a critical effector cytokine contributing to the multifaceted antitumor activity of CASTAT5-conditioned polyfunctional CD4⁺ T cells (C5-CD4). C5-CD4 T cells exhibit a prominent T helper 2 (Th2) cytokine profile, accompanied by extensive epigenomic remodeling at the Th2 cytokine loci, as revealed by Hi-C and histone-modification CUT&Tag assays. Neutralization of IL13 diminished the antitumor efficacy of C5-CD4 T cells. Furthermore, targeted Il13 disruption substantially impaired tumor control and was associated with reduced donor T cell expansion and persistence, diminished systemic cytokine and chemokine responses, and attenuated activation of endogenous tumor-reactive CD8⁺ T cells. Nonetheless, IL13 overexpression alone in donor CD4⁺ T cells failed to fully recapitulate the therapeutic activity of C5-CD4 T cells, indicating that IL13 is a critical contributor but is insufficient to account for the full antitumor activity conferred by CASTAT5. Single-cell RNA sequencing associated donor-derived IL13 with increased representation of tumor-infiltrating myeloid cells and IL13-signaling in monocytes and macrophages exhibiting tissue-repair-associated transcriptional programs. Moreover, Il13 disruption diminished the therapeutic efficacy of CASTAT5-expressing CD19-targeted CAR-T cells in a mouse B-cell lymphoma model. Reanalysis of a human CD19CAR-T infusion-product dataset further revealed an association between IL13 expression and type 2 cytokine signatures linked to prolonged clinical response, suggesting a potential contribution of IL13 to the efficacy of human CD19CAR-T therapy. Together, these findings uncover an unexpected antitumor role for IL13 and establish it as a critical node linking polyfunctional donor T cells with endogenous immune cells to promote sustained tumor immunity.