We further confirmed the hCD4-expression on HPB-ALL cells (Figure S1D) and the specific binding of both tracers to the target antigen by species-specific CD4+ and CD4-in vitro cell assays (Figure 1C, Figure S1E) and through CD4 blocking experiments using a 100-fold excess of unlabeled CD4-Mb. This evidence concerns the gene CD4 and acute lymphoblastic leukemia.