mAb14, a Monoclonal Antibody against Cell Surface PCNA: A Potential Tool for Sezary Syndrome Diagnosis and Targeted Immunotherapy

SIMPLE SUMMARY: We need better ways to detect and treat skin lymphoma, a type of skin cancer. Current treatments that enhance the body’s cancer-fighting abilities are not very effective, and the markers used for diagnosis are not specific. We’ve previously found a new marker called PCNA on the surface of various cancer cells. PCNA seems to stop immune cells from killing cancer cells. Investigating PCNA on skin lymphoma cells could help with diagnosis and improving treatment. To do this, we’re using a special homemade antibody called mAb14 to study PCNA on the outside of skin lymphoma cells. We’re also checking if blocking PCNA with mAb14 affects the immune cells’ ability to kill these cancer cells. Our research suggests that mAb14 could be a useful tool for detecting skin lymphoma cells in the blood of patients with advanced disease. It may also help boost the immune system’s fight against skin lymphoma through immunotherapy. ABSTRACT: Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common types of primary cutaneous T-cell lymphoma (CTCL). Proliferating cell nuclear antigen (PCNA) is expressed on the cell surface of cancer cells (csPCNA), but not on normal cells. It functions as an immune checkpoint ligand by interacting with natural killer (NK) cells through the NK inhibitory receptor NKp44, leading to the inhibition of NK cytotoxicity. A monoclonal antibody (mAb14) was established to detect csPCNA on cancer cells and block their interaction with NKp44. In this study, three CTCL cell lines and peripheral blood mononuclear cells (PBMCs) from patients with SS and healthy donors were analyzed for csPCNA using mAb14, compared to monoclonal antibody PC10, against nuclear PCNA (nPCNA). The following assays were used: immunostaining, imaging flow cytometry, flow cytometry, cell sorting, cell cycle analysis, ELISA, and the NK-cell cytotoxic assay. mAb14 successfully detected PCNA on the membrane and in the cytoplasm of viable CTCL cell lines associated with the G2/M phase. In the Sézary PBMCs, csPCNA was expressed on lymphoma cells that had an atypical morphology and not on normal cells. Furthermore, it was not expressed on PBMCs from healthy donors. In the co-culture of peripheral blood NK (pNK) cells with CTCL lines, mAb14 increased the secretion of IFN-γ, indicating the reactivation of pNK activity. However, mAb14 did not enhance the cytotoxic activity of pNK cells against CTCL cell lines. The unique expression of csPCNA detected by mAb14 suggests that csPCNA and mAb14 may serve as a potential biomarker and tool, respectively, for detecting malignant cells in SS and possibly other CTCL variants.