What is the utility of detecting CD52 expression on T cell neoplasms by flow cytometry?
CD52 is a glycosylphophatidylinositol (GPI) anchored low molecular weight glycoprotein (21-28 kDa) expressed on the surface of normal B and T lymphocytes, natural killer (NK) cells, monocytes, macrophages, and some dendritic cells, but not on plasma cells, granulocytes, erythrocytes, platelets, or hematopoietic progenitor cells. CD52 has been shown to be a valuable target for antibody therapy in lymphoid neoplasia because of its abundant cell surface expression, close apposition to the cell membrane, and lack of modulation after antibody binding. CD52 exists in two forms, CD52-I and CD52-II. Both forms are recognized by alemtuzumab (Campath-1H), a "humanized" murine IgG1 monoclonal antibody. Upon binding to the cell surface CD52, alemtuzumab induces cell destruction via activation of complement dependent cytotoxicity, antibody-dependent cellular cytotoxicity, and induction of apoptosis. While all three activities have been demonstrated in vitro, the mechanism of in vivo cell killing remains unclear.
While alemtuzumab (Campath-1H) demonstrates excellent therapy effect on various B cell lymphomas and acute lymphoblastic leukemia/lymphoma, several clinical trials including alemtuzumab as a single agent or in combination with other chemotherapeutic agents in treatment of T cell neoplasia have demonstrated promising outcomes which have generated great interest and attention.
There are some studies utilizing immunohistochemical (IHC) studies to examine CD52 expression; however, IHC did carry quite a few limitations. Many low-grade B cell lymphomas or T/NK cell lymphomas carry minimal or mild cytological atypia and/or abundant reactive cells (i.e. lymphocytes or macrophages) in the background, which makes assessment of neoplastic lymphocytes difficult on IHC slides. A fibrotic background may interfere with antibody's ability to bind to its target antigen on the formalin-fixed paraffin-embedded tumor cells. In addition, there is the possibility of antigen loss through formalin fixation and paraffin embedding, which may diminish the sensitivity of the study. Furthermore, CD52 must be expressed on the cell surface for alemtuzumab to be effective and IHC cannot determine if a membrane associated antigen is on the external or internal cell membrane. Lastly low level CD52 expression may not be detected by IHC due to decreased sensitivity of the technique. In contrast, flow cytometry can readily detect these cell populations and distinguish neoplastic populations from the background normal cells with higher sensitivity for low level expression. Therefore, we believe that flow cytometry analysis on fresh specimen offers clear advantages in evaluating CD52 expression for patients being considered for alemtuzumab therapy.
Jiang, et al studied the expression of CD52 in seventy-eight cases of various mature T cell and NK cell neoplasms; the highest expression rate (100%) was observed in angioimmunoblastic T-cell lymphoma, hepatosplenic T-cell lymphoma, and T prolymphocytic leukemia; followed by adult T-cell leukemia/lymphoma (94.1%), peripheral T cell lymphoma (92.3%) and cutaneous T-cell lymphoma (87.5%). Examples 1 and 2 demonstrate CD52 expression in adult T cell lymphoma/leukemia and cutaneous T cell lymphoma (mycosis fungoides/Sezary syndrome), respectively.
Since CD52 is ubiquitously present on many normal lymphocytes or other cells, it carries little diagnostic value for the detection or classification of lymphoma, and its inclusion in initial diagnostic screening panels may be of limited value. . Once a diagnosis is made and the diagnosis of lymphoma is established, however, running a small panel that includes CD52 may be useful to help determine potential eligibility for anti-CD52 directed therapy. The panel of CD19/CD3/CD52/CD45 is often sufficient.
Example #1:
These dot-plots are from flow cytometry analysis of peripheral blood from patient with adult T cell leukemia/lymphoma with atypical lymphocytosis in the peripheral blood and positive serology testing for HTLV-1. The neoplastic T-cell population showed the following immunophneotype: CD3 dim+, CD4+, CD8-, CD7-, CD25+, and CD52+
Example #2:
These dot-plots are from flow cytometry analysis of peripheral blood from patient with mycosis fungoides with atypical lymphocytosis in the peripheral blood. The neoplastic T-cell population showed the following immunophneotype: CD3+, CD5+, CD4+, CD8-, and CD52+.
References:
[1] Jiang L, Yuan CM, Hubacheck J, Janik JE, Wilson W, Morris JC, Jasper GA, Stetler-Stevenson M: Variable CD52 expression in mature T cell and NK cell malignancies: implications for alemtuzumab therapy. Br J Haematol 2009, 145:173-9.
[2] Buckstein R, Fraser G, Cheung M, et al. Alemtuzumab and CHOP Chemotherapy for the Treatment of Aggressive Histology Peripheral T Cell Lymphomas: A Multi-Center Phase I Study. Clin Lymphoma Myeloma Leuk. 2016;16(1):18?28.
[3] Arlindo EM, Marcondes NA, Fernandes FB, Faulhaber GAM. Quantitative flow cytometric evaluation of CD200, CD123, CD43 and CD52 as a tool for the differential diagnosis of mature B-cell neoplasms. Rev Bras Hematol Hemoter. 2017;39(3):252?258.
[4] DeAngelo DJ. The use of novel monoclonal antibodies in the treatment of acute lymphoblastic leukemia. Hematology Am Soc Hematol Educ Program. 2015;2015:400?405.
