The inhibition of T cell proliferation in a mixed lymphocyte reaction by Itolizumab (T1h) is associated with reduction in pro inflammatory cytokines and CD6 internalization. (52.27)

Abstract

Abstract We have shown previously that the CD6-ALCAM interaction in vitro induced a synergistic co-stimulation of normal human peripheral blood mononuclear cells (PBMCs), defined by Bliss analysis. The use of a CD6 membrane-distal domain (SRCR1)-specific non-depleting monoclonal antibody Itolizumab, inhibited the CD6-ALCAM induced proliferation of PBMCs. This is associated with reduction in pro inflammatory cytokines at the protein and mRNA level. In this study, we show that the antibody inhibits T cell proliferation in a typical mixed lymphocyte reaction wherein the matured dendritic cells over express ALCAM. The inhibition is associated with reduction in CD4 and CD25 surface expression in these T cells. A marked reduction in interferon-γ, tumour necrosis factor-α and IL-17 production is also observed. Using confocal microscopy we show that the receptor CD6 internalization occurs within minutes in T cells in the presence of Itolizumab and is not localized to the immunological synapse. Intriguingly, a deglycosylated antibody showed reduced inhibition of T cells in the mixed lymphocyte reaction. The deglycosylated antibody did not show any difference in binding to HuT 78 cell expressing CD6 as compared to the normal antibody. These results would suggest that the monoclonal antibody Itolizumab also prevents T cell proliferation induced in mixed lymphocyte reactions and there is a role for the Fc region glycosylation of the antibody to elucidate this function.