CD7 is the earliest antigen marker expressed in the T lineage, being found on T cell precursors in fetal liver and thorax prior to thymic colonization and in thymus and bone marrow. The function of CD7 antigen is unknown and the natural ligand for CD7 has not yet been identified. CD7 monoclonal antibodies co-stimulate T cell proliferation and induce second messengers, while soluble recombinant CD7 has been reported to inhibit antigen-specific proliferation and a mixed lymphocyte reaction. CD7 is a marker for pluripotential stem cell leukemias and T cell acute lymphocytic leukemia (T-ALL). The antigen is frequently lost on large cell T cell lymphomas. The CD7 antigen may also be expressed on myeloblastic leukemias.Synonyms: GP40, Leu-9, T-cell leukemia antigen, TP41