The CD7 (HIT7) antibody recognizes a 40 kDa type-I single-chain transmembrane glycoprotein. CD7 antigen is considered as one of the earliest and immature T cell markers that is expressed on all thymocytes, most mature T cells, B-lineage progenitors, NK cells, monocytes (weakly) and some leukemia stem cells capable of multilineage differentiation. CD7 antigen may be considered as a marker of undifferentiated hemopoietic cells capable of giving rise to T, B and myeloid lineage cells under the appropriate microenvironment. CD7 is also present in the majority of T lymphoid leukemia cells and a subset of acute myeloid leukemia (AML) cells. Mature B lymphocytes and granulocytes do not express CD7 antigen.