PTPN2/PTPN1 inhibition enhances ex vivo T- cell responses and potentiates mosunetuzumab activity in chronic lymphocytic leukemia

Background Chronic lymphocytic leukemia (CLL) is characterized by T-cell dysfunction that limits the efficacy of immunotherapies, including CD20×CD3 bispecific antibodies. Protein tyrosine phosphatases non-receptor type 2/1 PTPN2/PTPN1 are central intracellular negative regulators of T-cell activation. Preclinical studies show that deletion or PTPN2/PTPN1 inhibition increased T-cell activation, proliferation, and antitumor activity. This study aimed to investigate the potential of PTPN2/PTPN1 inhibition in combination with the bispecific antibody mosunetuzumab as a therapeutic approach for CLL. Methods Peripheral blood mononuclear cells (PBMCs) obtained from CLL patients were used in all experiments. The effects of PTPN2/PTPN1 inhibition in combination with mosunetuzumab, were evaluated using flow cytometry, confocal microscopy, ELISA, and Incucyte Live-Cell Analysis to assess T-cell activation, immune synapse formation and cytotoxic activity. Results Pretreatment with the PTPN2/PTPN1 inhibitor ABBV-CLS-484 (AC484) enhanced T-cell activation following CD3/CD28 stimulation, as demonstrated by increased expression of the activation markers CD69 and CD25. Confocal microscopy revealed increased CD8+ T-cell size, enhanced granzyme B expression and release, and more robust immune synapse formation following treatment with mosunetuzumab +/-AC484. Incucyte imaging of CLL-T-cell co-cultures demonstrated enhanced T-cell proliferation, increased CLL-T-cell clustering, and a modest increase in cytotoxicity with the combination of AC484 and mosunetuzumab. Consistent with these findings, ELISA assays showed increased secretion of granzyme B and IFN-γ. Conclusion Combining the PTPN2/PTPN1 inhibitor AC484 with mosunetuzumab enhanced T-cell activation, proliferation, granzyme B and IFN-γ secretion, and anti-CLL cytotoxicity in CLL samples, supporting further evaluation of PTPN2/PTPN1 inhibition as a strategy to enhance the efficacy of CLL immunotherapy.