CD33 and acute promyelocytic leukemia: APL is characterized by low or negative CD34 expression, the infrequent expression of HLA-DR and the lack of CD7, CD11a, CD11b, CD14 and CD18, strong positivity for CD33, the expression of CD13 and CD117 [59], and frequently show aberrant expressions of the T-cell-associated antigen CD2 which is associated with the microgranular variant morphology and increased leukocyte counts at presentation [17,58,60].