Ibrutinib-triggered matriptase maintains extracellular CD19 and limits antigen escape in B-cell malignancy

Abstract

CD19-directed CART therapy has improved outcomes in B-cell malignancies, but durable responses remain limited by antigen escape, in which loss of surface CD19 can drive antigen-negative relapse. Ibrutinib (IB) has been reported to enhance CART activity, yet whether IB directly modulates tumor-cell antigen presentation remains unclear. Here, we identify matriptase (MTP, encoded by ST14) as a tumor-cell-intrinsic regulator of CD19 stability and a mediator of IB-enhanced CART efficacy. In an HT xenograft model, combined IB and CD19-CART treatment prolonged survival, suppressed tumor growth, and increased apoptosis compared with either monotherapy. IB treatment induced coordinated upregulation of MTP and CD19 in vivo. Analysis of patient-derived DLBCL datasets and tissue microarrays further showed that high ST14 expression correlated with MYC-associated aggressive disease features, poor prognosis, and CD19 protein expression. Mechanistically, ST14 knockout in Ramos cells reduced total and surface CD19, accelerated CD19 degradation, and impaired membrane localization, whereas exogenous activated MTP restored CD19 abundance. Loss of ST14 also increased susceptibility to IB- and CART-induced CD19 downregulation, attenuated CART-mediated cytotoxicity, and abolished the synergistic benefit of IB in vitro. Phosphoproteomic and transcriptomic analyses revealed that MTP deficiency impaired CK2 activity and reduced PAX5 expression, linking MTP to a CK2-PAX5-CD19 regulatory axis. Finally, direct MTP inhibition with an anti-MTP monoclonal antibody enhanced IB-mediated tumor suppression in a dual Ramos/HT xenograft model without overt systemic toxicity, but reduced CD19 availability and slightly compromised CART cytotoxicity when combined with CART alone. Collectively, our findings reveal a context-dependent role for MTP in B-cell lymphoma, whereby MTP stabilizes CD19 to sustain CART recognition while also contributing to aggressive biology.