CD40L and IL-4 suppress NK cell-mediated antibody-dependent cellular cytotoxicity through the HLA-E:NKG2A axis

Anti-CD20 antibodies are first-line treatments for B cell malignancies. Natural killer (NK) cells are important mediators of anti-CD20 antibody efficacy in humans through antibody-dependent cellular cytotoxicity (ADCC). In B cell malignancies, the lymph nodes are a critical site of pathology and the T cell-derived signals CD40L and IL-4 within the lymph node microenvironment can mediate tumour proliferation, survival and resistance to pro-apoptotic therapy. CD40L and IL-4 have recently been shown to inhibit NK cell activation against chronic lymphocytic leukaemia (CLL) cells via the HLA-E:NKG2A immune checkpoint axis. However, the effect of these signals on NK cell-mediated ADCC of malignant B cells is unclear.

Using a combination of clinical samples, murine models, flow cytometry, immunoblotting, immunohistochemistry, ELISA, bioinformatics and functional assays, we examined the impact of lymph node-mimicking conditions on NK cell-mediated ADCC against malignant B cells. Exogenous CD40L and IL-4 were used to mimic T-B cell interactions in 2D malignant B cell cultures, in addition to a 3D spheroid model of T cell-dependent CLL proliferation.

CD40L and IL-4 increased HLA-E expression on the surface of primary CLL cells and non-Hodgkin's lymphoma (NHL) cell lines, and this decreased NK cell-mediated ADCC via ligation of the inhibitory receptor NKG2A. High HLA-E surface expression was observed in lymph node FFPE sections of CLL and NHL patients and in a 3D ex vivo lymph node-mimicking model of CLL. NKG2A blockade potentiated NK cell-mediated ADCC against malignant B cells treated with CD40L and IL-4 and improved anti-CD20 antibody therapy in a murine model of B cell lymphoma.

These results reveal a novel mechanism of resistance to anti-CD20 therapy in B cell malignancies and demonstrate that the combination of anti-NKG2A with anti-CD20 could improve the treatment of patients with CLL or NHL.