CD7

The CD7 antigen is a cell surface glycoprotein found on thymocytes and mature T cells. It is one of the earliest antigens to appear on cells of the T-lymphocyte lineage and the most reliable clinical marker of T-cell acute lymphocytic leukemia. CD7 is a member of immunoglobulin superfamily at 17q25.2-25.3

The gene comprises 4 exons that span 3.5 kb. Comparison of the organization of the CD7 gene with that of other members of the immunoglobulin gene superfamily revealed that the human CD7 gene most closely resembles the murine Thy-1 gene (MIM.188230). Both genes have 4 exons and promoters with no TATA boxes.

Functions

 CD7 has costimulatory activity for T cells.
 It plays important role in T cell-B cell interaction in early lymphoid development.

Expression in normal cells

 thymocytes and mature T lymphocytes (85%)

• The CD7 antigen is a cell surface glycoprotein found on thymocytes and mature T cells. It is one of the earliest antigens to appear on cells of the T-lymphocyte lineage and the most reliable clinical marker of T-cell acute lymphocytic leukemia.
• Membrane expression appears early during T cell development, before TCR rearrangement; it persists until terminal stages of T cell development.

 NK cells (majority)
 pluripotent hematopoietic progenitor cells
 early myeloid cells
 pre-B lymphocytes

Pathology

 CD7 is downregulated in infectious mononucleosis.

 Loss of CD7 expression and altered cellular glycosylation may contribute to apoptosis resistance of malignant T cells in mycosis fungoides.

Expression in tumors

 T-cell lymphoma

• extranodal NK/T cell lymphoma-nasal type
• intestinal T cell lymphoma

 T-ALL
 malignant immature T cells
 NK lymphomas
 rarely B cell lymphomas
 AML
 chronic myelogenous leukemia
 Down’s syndrome associated transient myeloproliferative disorder and AML
 lymphocyte rich thymoma

 miscellaneous

• pancreatic ductal carcinoma
• cholangiocarcinoma
• epithelioid sarcoma

No expression in :

 mature B cells
 granulocytes
 B cell ALL
 mycosis fungoides
 adult T cell leukemia/lymphoma
 Reed-Sternberg cells in Hodgkin lymphomas