LAG3 regulates antibody responses in a murine model of kidney transplantation

Lymphocyte activation gene-3 (LAG3) is a coinhibitory receptor expressed by a range of immune cells. While immunomodulatory potential of LAG3 is being actively explored in cancer and autoimmunity fields, there is no information on how this pathway affects alloreactive immune responses following organ transplantation. The goal of this study was to investigate the functions of recipient LAG3 in a mouse model of renal allograft rejection. We found that mice deficient in LAG3 expression have elevated heterologous immunity against a panel of alloantigens prior to transplantation. Recipient LAG3 deficiency results in rapid rejection of MHC-mismatched renal allografts that are spontaneously accepted by WT recipients, with graft histology characteristic of antibody mediated rejection (ABMR). Depletion of recipient B cells but not CD8+ T cells significantly extended kidney allograft survival in LAG3-/- recipients further supporting ABMR as the main mechanism of graft loss. Treatment of WT recipients with an antagonistic LAG3 antibody enhanced anti-donor immune responses and induced kidney damage associated with chronic rejection. The experiments using conditional LAG3 knockout recipients demonstrated that LAG3 expression on either T or B cells is sufficient to regulate anti-donor humoral immunity. These results are the first to identify LAG3 as a regulator of both T and B cell responses to kidney allografts and a potential therapeutic target for ABMR prevention and treatment.