PTPN22 as a novel therapeutic target: a key intracellular checkpoint for NK cell therapy

Background PTPN22, a protein tyrosine phosphatase (PTP) family member, has recently emerged as an intracellular regulator in adaptive immune cells. However, its function in natural killer (NK) cells remains unclear despite its high expression in innate immune cells. Methods We analyzed single-cell RNA-sequencing (scRNA-seq) datasets and The Cancer Genome Atlas (TCGA) to evaluate PTPN22 expression in NK cells and its association with clinical outcomes. We established a CRISPR-mediated PTPN22 knockout platform for NK cell gene editing and evaluated PTPN22 function using both genetic deletion and pharmacological inhibition across multiple NK cell platforms. Cytotoxicity and cytokine production were assessed against hematologic and solid tumor targets, including CD19 + and mesothelin-positive (MSLN + ) cancer cells. PTPN22 knockout (PTPN22 KO ) anti-CD19/CAR-NK92 cells were tested in Nalm6 xenograft models. Results Published scRNA-seq datasets showed that PTPN22 was highly expressed in tumor-infiltrating NK cells. PTPN22 high NK cells exhibited stress and dysfunction signatures within inflammatory and immunosuppressive tumor microenvironments (TME), with elevated PTPN22 expression in TCGA associated with poorer patient survival. Genetic deletion of PTPN22 or pharmacological inhibition enhanced NK-cell cytotoxicity and pro-inflammatory cytokine release and improved the antitumor activity of chimeric antigen receptor (CAR)-NK cells against CD19 + and MSLN + targets. PTPN22 KO preserved CAR-NK cell function under cytokine-based TME-like conditions and improved the functional persistence of primary anti-CD19 CAR-NK cells during prolonged tumor exposure. PTPN22 KO NK and CAR-NK cells showed increased or preserved signal transducer and activator of transcription 3 (STAT3) phosphorylation and reduced FAS expression under inflammatory conditions. Notably, PTPN22 KO anti-CD19/CAR-NK92 cells demonstrated superior anti-leukemic activity and significantly prolonged survival compared with non-knockout controls in vivo. Conclusions These findings identify PTPN22 as a novel intracellular checkpoint that limits NK and CAR-NK cell function. Targeted deletion of PTPN22 represents a promising strategy to enhance the therapeutic efficacy and persistence of both unmodified and CAR-engineered NK cells for cancer immunotherapy.