Neutrophil elastase enhances antigen presentation by upregulating human leukocyte antigen class I expression on tumor cells

Neutrophil Elastase (NE) is an innate immune cell-derived inflammatory mediator that we have shown increases the presentation of tumor-associated peptide Antigens in Breast Cancer. In this study, we extend these observations to show that NE uptake has a broad effect on enhancing antigen presentation by Breast Cancer cells. We show that NE increases human leukocyte antigen (HLA) class I expression on the surface of Breast Cancer cells in a concentration and time-dependent manner. HLA class I upregulation requires internalization of enzymatically active NE. Western blots of NE-treated Breast Cancer cells confirm that the expression of total HLA class I as well as the antigen-processing machinery proteins TAP1, LMP2, and calnexin does not change following NE treatment. This suggests that NE does not increase the efficiency of antigen processing; rather, it mediates the upregulation of HLA class I by stabilizing and reducing membrane recycling of HLA class I molecules. Furthermore, the effects of NE extend beyond Breast Cancer since the uptake of NE by EBV-LCL increases the presentation of HLA class I-restricted viral Peptides, as shown by their increased sensitivity to lysis by EBV-specific CD8+ T cells. Together, our results show that NE uptake increases the responsiveness of Breast Cancer cells to adaptive immunity by broad upregulation of membrane HLA class I and support the conclusion that the innate inflammatory mediator NE enhances tumor cell recognition and increases tumor sensitivity to the host adaptive immune response.