CD4 AND CD8 ANTIGEN COEXPRESSION - A FLOW CYTOMETRIC STUDY OF PERIPHERAL-BLOOD, BONE-MARROW, BODY-FLUID, AND SOLID LYMPHORETICULAR SPECIMENS

Objective.-CD4 and CD8 antigen coexpression occurs not only on blastic T-cell malignancies, but also on a small subset of mature lymphocytes . The aim of this study was to determine the prevalence of this popula tion of cells and to identify features that can be used to differentia te them from T lymphoblasts. Design.-All specimens submitted to the cl inical flow cytometry laboratory from August 1, 1994, through July 31, 1995, were analyzed for CD4 and CD8 coexpression. Main Outcome Measur e.-Percentage of lymphocytes coexpressing the CD4 and CD8 antigens. Re sults.-Four percent (22/526) of all specimens contained a population o f CD4/CD8 coexpressing cells. Five cases represented CD4 and CD8 antig en expression on neoplastic cells. In 17 cases, the CD4/CD8 coexpressi ng cells appeared to represent a population of mature lymphocytes with a normal phenotype. The immature cells of T-cell acute lymphocytic le ukemia and lymphoblastic lymphoma represented a dominant uniform popul ation of cells demonstrating strong staining with both the CD4 and CD8 antigens. Cases containing a mature population of CD4/CD8 coexpressin g cells were characterized by fewer coexpressing cells and variable ex pression of CD8. There were cases where distinction of this population of mature CD4/CD8 coexpressing lymphoid cells from a blastic malignan cy was not possible using immunophenotyping alone. Conclusion.-Correla tion of clinical, morphologic, and immunophenotypic data is recommende d to prevent the misdiagnosis of subtle involvement by a blastic T-cel l malignancy.