CD7 is a 40 kDA transmembrane single-chain glycoprotein belonging to the immunoglobulin superfamily. CD7 is the earliest marker antigen of T-cell lineage, which is expressed throughout T-lymphocyte differentiation. It is found on T-cell precursors in the fetal liver and thorax prior to thymic colonization, and in the thymus and bone marrow. CD7 is expressed on the pluripotent hematopoietic cells, most human thymocytes, and a major subset of peripheral blood CD4+ and CD8+ T-cells, and natural killer (NK) cells. It is also present in reduced density on monocytic cells. The expression of the T-cell lineage marker CD7 on myeloid blasts is associated with an unfavorable outcome of myeloid malignancies