Antibody targeting of surface P‐selectin glycoprotein ligand 1 leads to lymphoma apoptosis and tumorigenesis inhibition

Lymphomas are a heterogeneous group of diseases that originate from T, B or natural killer cells. Lymphoma treatment is based on chemotherapy, radiotherapy, and monoclonal antibody (mAb) or other immunotherapies. The P‐selectin glycoprotein ligand 1 (PSGL‐1) is expressed at the surface of hematological malignant cells and has been shown to have a pro‐oncogenic role in multiple myeloma and lymphoma. Here, we investigated the expression and therapeutic potential of PSGL‐1 in T and B cell lymphomas. By flow cytometry analysis, we found that PSGL‐1 was expressed in both T and B cell‐derived lymphoma cell lines but generally at higher levels in T cell lymphoma cell lines. For most T and B cell‐derived lymphoma cell lines, in vitro targeting with the PL1 mAb, which recognizes the PSGL‐1 N‐terminal extracellular region and blocks functional interactions with selectins, resulted in reduced cell viability. The PL1 mAb pro‐apoptotic activity was shown to be dose‐dependent, to be linked to increased ERK kinase phosphorylation, and to be dependent on the MAP kinase signaling pathway. Importantly, anti‐PSGL‐1 treatment of mice xenografted with the HUT‐78 cutaneous T‐cell lymphoma cell line resulted in decreased tumor growth, had no effect on in vivo proliferation, but increased the levels of apoptosis in tumors. Anti‐PSGL‐1 treatment of mice xenografted with a Burkitt lymphoma cell line that was resistant to anti‐PSGL‐1 treatment in vitro, had no impact on tumorigenesis. These findings show that PSGL‐1 antibody targeting triggers lymphoma cell apoptosis and substantiates PSGL‐1 as a potential target for lymphoma therapy.