Abstract Text: Administration of anti-CD45RC mAbs in preclinical models of transplant rejection, GVHD or APECED leads to amelioration and control of the disease. The anti-human CD45RC mAb (humanized IgG1) has a unique mechanism of action and induces CD45RChigh T and B cell death, while preserving and boosting CD45RClow/neg Tregs, inducing a long-lasting effect. Using in vitro studies, we demonstrated that anti-human CD45RC mAb induces CD45RChigh T and B cell death mainly by direct apoptosis through binding to CD45RChigh cells. Quantification of CD45RC surface level indicated that around 105 molecules per µm2 of membrane were expressed by CD45RChigh cells and 45 molecules per µm2 of membrane are required to reach EC50 of apoptosis. ADCC killing of CD45RChigh T cells mediated by NK cells and ADCP of CD45RChigh T and B cells mediated by monocytes also play an add-on role improving the effect of the anti-CD45RC mAb. Anti-CD45RC mAb does not induce CDC killing, as opposed to positive control Rituximab. We also showed improved apoptosis mediated by anti-CD45RC mAb in presence of cross-linking secondary antibodies. Finally, using in vivo studies in CD34+ immune humanized NSG mice, we showed killing of CD45RChigh T and B cells and not of CD45RClow/neg Tregs in a dose and time-dependent manner and we showed a dose dependent efficacy in a model of GVHD in PBMC-reconstituted NSG mice. Altogether our study demonstrates the mechanisms by which anti-human CD45RC mAb mediates CD45RChigh T and B cell death.
