Human T and B lymphocytes develop in these mice, but the mice do not succumb to xeno-GVHD as the differentiated human lymphocytes recognize mouse antigens as “self.” The treatment of these mice with 2B010 resulted in a transient loss of CD25 expression on day 3 on both CD4+CD25+Foxp3− and CD4+CD25+Foxp3+ T cells which did not reach statistical significance. This evidence concerns the gene FOXP3 and graft versus host disease.