CD4 and acute lymphoblastic leukemia: T-ALL diagnosis relies on cytoplasmic and/or membrane CD3 positivity, while other T-cell antigens, such as terminal deoxynucleotidyl transferase (TdT), and CD7, CD2, CD5, CD1a, CD3, CD4, and CD8, are variably expressed during each step of development from pro-T to pre-T, cortical-T, and mature-T cells [3].