CD40L and IL-4 lymph node-associated signals protect B cells from rituximab-induced ADCC via KIR and NKG2A.

Autoreactive B cells that remain in lymphatic tissue after anti-CD20 antibody therapy are considered a major contributing factor to relapse in patients with autoimmune diseases. Natural killer (NK) cells contribute to the depletion of autoreactive B cells by anti-CD20 antibodies via antibody-dependent cellular cytotoxicity (ADCC). However, the impact of germinal centre-associated signals CD40 ligand (CD40L) and interleukin-4 (IL-4) on ADCC was unknown. This study used a combination of flow cytometry, immunohistochemistry, and ex vivo functional assays using peripheral blood mononuclear cells to investigate how CD40L and IL-4 affect NK cell-B cell interactions. CD40L and IL-4 significantly upregulate human leukocyte antigen (HLA)-E and total HLA Class I expression on the surface of B cells from healthy donors, as well as patients with rheumatoid arthritis and systemic lupus erythematosus. The upregulation of HLA-E and total HLA functions to inhibit B-cell depletion by NK cell-mediated ADCC induced by rituximab via NKG2A and killer cell immunoglobulin-like receptors (KIR). Moreover, B cells that have differentiated through the germinal centre have higher expression of HLA-E and total HLA compared with naive B cells and are more resistant to depletion by rituximab. In accordance with this, blockade of NKG2A and inhibitory KIRs by monalizumab and lirilumab, respectively, increased antibody-dependent cellular cytotoxicity against autologous B cells in vitro. Overall, this study identifies a novel mechanism of resistance of B cells to NK cell cytotoxicity and indicates that blockade of the HLA-E:NKG2A and HLA:KIR checkpoint axes could be beneficial for improving B-cell depletion in patients with autoimmune diseases.