CD4 and leukemia: These data are consistent with idea that either the loss of helper function of CD4+ cells for CD8+ cells or failure in realization of the CD8+ killer effects in those mice engrafted with IRAK1 KO cells will allow the emergence of leukemia, which confirms a direct involvement of T cells in clearance of IRAK1 KO cells, further supporting a function for IRAK1 in modulating the immune system.