CD4 and leukemia: Of interest, the presence of the 11-mer peptide along with 13.9 and 14.9 epitopes allowed the stimulation of leukemia-specific CD4+ T cells, which have previously been shown to directly induce potent anti-tumor, HLA class II-mediated, cytotoxic responses in vivo, in addition to providing help to CD8+ CTLs [19,26].