CD4 and acute lymphoblastic leukemia: Reinherz originally proposed that T-ALL be classified along the lines of CD1 and CD3 expression with stage I (early thymocyte) expressing CD2, CD5, CD7, and no CD1, CD4, CD8, or CD3; stage 2 (intermediate) expressing CD1, CD2, CD5, and CD7 with variable 4 and 8, and weak CD3; and stage 3 (mature) expressing CD2, CD3, CD5, CD7, and CD4 or CD8 (usually only one or the other) (6, 7).