Abstract 1344: PTPN2/N1 inhibition drives a STAT3-mediated response in exhausted T cells and underscores targetable counter-regulatory mechanisms for T cell improvement.

Abstract New strategies to improve T cell function for immunotherapy and cell therapy are urgently needed. PTPN2 and PTPN1 are phosphatases that dephosphorylate members of the JAK–STAT signaling pathway and downstream TCR signaling kinases, positioning them as key negative regulators of cytokine signaling and T cell activation. Genetic deletion of PTPN2 or PTPN1 induces striking T cell–mediated anti–tumor immunity. However, despite the extensive knowledge on the enzymatic targets of PTPN2/N1, the signaling mechanisms leading to enhanced T cell function downstream of PTPN2/N1 loss are unclear. To address this, we performed transcriptional and phospho–proteomic profiling of human T cells treated with a PTPN2/N1 inhibitor (AC484) during chronic antigen stimulation. Using the CytoSig cytokine signaling inference method, we found that PTPN2/N1 loss drives robust activation of STAT3 signaling, accompanied by a counterintuitive inhibition of STAT5 activity. This pattern was consistent across both chronically stimulated human T cells and murine tumor–infiltrating T cells treated with AC484. Phospho–proteomic analyses confirmed a strong upregulation of phosphorylated STAT3, but a marked downregulation of JAK1/2/3 and STAT5 phosphorylation in PTPN2/N1 inhibitor–treated T cells. Conversely, acute PTPN2/N1 inhibition transiently increases STAT5 activity. Transcriptomic analyses further revealed potential mechanisms of feedback inhibition on JAK–STAT5 signaling, as several STAT3–driven counter regulatory factors were highly upregulated in chronically stimulated PTPN2/N1–deficient cells, such as SOCS3. SOCS3 is a well–established inhibitor of JAK1, JAK2, and TYK2, and can dampen STAT5 signaling; our results position SOCS3 as a strong candidate to mediate feedback inhibition. We hypothesize that PTPN2/N1 inhibition causes STAT3–mediated phenotypic changes in T cells, and while this is beneficial for enhancing T cell function, STAT3 also elicits upregulation of counter–regulatory factors that limit JAK–STAT5 signaling during chronic antigen stimulation and may ultimately restrain the persistence of PTPN2/N1–deficient T cells. Our next studies will elucidate the dynamic changes in signaling circuitry in PTPN2/N1–deficient T cells and leverage this knowledge to propose new strategies to counteract T cell exhaustion. These insights could inform the development of next–generation small molecule and cellular immunotherapies with improved efficacy and durability. Citation Format: Yaiza Senent, Kevin Bi, Hasmik Keshishian, Nikita Kormshchikov, Nelson Knudsen, Steven Carr, Debattama Sen, Kathleen Yates, Robert Manguso. PTPN2/N1 inhibition drives a STAT3-mediated response in exhausted T cells and underscores targetable counter-regulatory mechanisms for T cell improvement [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1344.