Here, we have developed and characterized a cytotoxic LAG-3 chimeric antibody (chimeric A9H12), and evaluated its potential as a selective therapeutic depleting agent in a non-human primate model of delayed-type hypersensitivity (DTH). Chimeric A9H12 showed

a high affinity to its antigen and depleted both cytomegalovirus (CMV)-activated CD4+ and CD8+ human T lymphocytes in vitro. In vivo, a single intravenous injection at either 1 or 0·1 mg/kg was sufficient to deplete LAG-3+-activated T cells in lymph nodes and to prevent the T helper type 1 (Th1)-driven skin inflammation NVP-BGJ398 order in a tuberculin-induced DTH model in baboons. T lymphocyte and macrophage infiltration into the skin was also reduced. The in vivo effect was long-lasting, as several weeks to months were required after injection to restore a positive reaction after antigen challenge. Our data confirm that LAG-3 is a promising therapeutic target for depleting antibodies that might lead to higher therapeutic indexes compared to traditional immunosuppressive agents in autoimmune diseases and transplantation. Selectively inhibiting or deleting activated T lymphocytes represents a promising therapeutic approach as an alternative to current immunosuppressive treatments in autoimmunity and transplantation. One strategy might be the use of depleting antibodies that target specific antigens on activated T cells. This provides a competitive

advantage of targeting only pathogeneic T cells that are specific for auto- or alloantigens without modifying RG7420 manufacturer the protective immunity directed against third-party antigens [1]. The proof of concept for selective depletion of pathogeneic T lymphocytes has been demonstrated in an engineered mouse model, whereby their T cells express a viral thymidine kinase suicide gene that metabolizes the non-toxic prodrug ganciclovir into a metabolite that is toxic only to dividing cells. The result was a significant delay in the rejection of skin and heart grafts and the induction of an immune tolerance in a fraction of the recipient mice [2]. However,

the Rolziracetam therapeutic translation of this strategy requires the targeting of an antigen that is highly specific for activated T cells. So far, few molecules that are expressed selectively by activated T cells have been identified. Among these are CD25, CD152, CD154 and CD223 (lymphocyte-activation gene-3; LAG-3[3]). LAG-3 is an important regulator of T cell homeostasis [4] that is related evolutionarily to CD4 and, like CD4, is associated with the T cell receptor. It has retained an affinity 2 logs higher than CD4 for their common ligand, major histocompatibility complex (MHC) class II. LAG-3 is a transmembrane protein that forms dimers at the surface of both CD4+ and CD8+ T lymphocytes [3,5] residing in inflamed secondary lymphoid organs or tissues (i.e. human tumours or rejected allograft), but not in spleen, thymus or blood.