Immunophenotyping of chronic lymphoid leukemias.

The 1983 article entitled “Chronic lymphocytic leukemia and other chronic lymphoid proliferations: surface marker phenotypes and clinical correlations,” which is reprinted in this issue of the Journal of Clinical Oncology, was one of the first reporting the use of monoclonal antibodies to expand the phenotypic characterization of chronic lymphoid leukemia, and one of the earliest to examine clinical correlations associated with specific phenotypic subsets. This process continues today, not only with different combinations of monoclonal antibodies for immunophenotypic characterization, but also with cytogenetic differences reflected by karyotype or fluorescence in situ hybridization studies, mutations in the variable region of the heavy chain, and DNA microarray analyses as indicators of genotype. In the years after publication of this article, the cluster differentiation system (CD) for identifying leukocyte cellular antigens was developed based on a series of workshops initiated in response to the need for a common language to identify the various antigens that were being discovered by murine monoclonal antibodies. Today, antibodies that react with CD19 or CD20 are typically used instead of surface immunoglobulin (sIg) as an indicator of B-cell lineage, although intensity of sIg is still used to define subsets of monoclonal peripheral B-cell populations. Pan–T-cell–specific antibodies that react with CD2 or CD3 have replaced the cumbersome sheeperythrocyte-rosettes methodology to identify T lymphocytes. CD5 is the target of T65 (monoclonal antibody T101), which is generally a pan–T-cell marker, but is rarely coexpressed with B-cell markers on some lymphocytes. The Ia-like antigen is better known as HLA-DR. This was one of several papers appearing from 1982 to 1983 that identified the coexpression of CD5 and pan–B-cell markers as the phenotypic hallmark of classical chronic lymphocytic leukemia (CLL). Today, the coexpression of B-cell markers and CD5 is often used as one of the eligibility criteria in clinical protocols to assure a more homogeneous classical CLL population. Today, peripheral blood lymphocyte typing is commonly used in the evaluation of patients with a sustained lymphocytosis to determine whether it is reactive or due to malignant change. Lack of CD5 coexpression with CD19 or CD20 excludes B-cell CLL, and suggests the possibility of other B-cell lymphoproliferative disorders, including hairy-cell leukemia, leukemic manifestations of lymphoplasmacytic lymphomas, or follicular lymphoma. Modern multicolor flow cytometry makes it possible to determine the coexpression of several such antigens on specific cell populations, but differences in antibodies and gaiting procedures for flow cytometry have resulted in some lack of consensus regarding the expression of certain markers on malignant lymphocytes. Table 1 presents how combinations of these markers can be useful in helping to confirm a diagnosis. CLL is typically characterized as CD19 , CD5 , CD23 , CD22 , CD79b with weak expression of sIg. Small lymphocytic lymphoma cells also express this phenotype, but B-cell prolymphocytic leukemia cells typically express CD22. In clinical trials of CLL, the coexpression of such molecules on peripheral blood lymphocytes is being used as a marker for minimal residual disease. Coexpression of CD5 and B-cell markers is also a hallmark of mantle-cell lymphoma. In retrospect, it became clear that the patient described at the bottom of page 193 in the Discussion section of the original report had mantle-cell lymphoma, an entity that was not widely recognized at the time, and not well characterized for almost a decade. Donald Doll had referred this patient, and both of us immediately recalled the case when we saw each other after a lymphoma lecture I had given at the University of Missouri in July 2002. The phenotype of CD5 , CD19 , CD22 , CD23 is used to help distinguish CLL cells from mantle-cell lymphoma cells, which typically are CD19 , CD5 , CD22 , CD23 and express more sIg, and express cyclin D1. The presence of B-cell markers and lack of CD5 expression suggests the presence of a B-cell lymphoproliferative disease other than CLL/SLL or mantle-cell lymphoma. More expanded immunophenotyping can facilitate a more specific diagnosis. Examples include CD11 , CD19 , CD22 , CD25 , and CD103 for hairy-cell leukemia; CD19 ,CD22 , and FMC7 for splenic marginal zone lymphoma; B19 , CD5-, FMC7 , and CD38 for lymphoplasmacytic lymphoma; and CD19 , CD22 , CD23 , and CD10 for follicular lymphoma. One of the observations in the 1983 article was the association of paraproteinemia with B-cell lymphocytosis that was CD5 , and the suggestion that most of these patients had a lymphocytosis as an early manifestation of lymphoplasmacytic lymphoma, including Waldenstrom’s macroglobulinemia. There were six patients in the original report who were classified as negative for sIg and T-cell markers other than CD5, and were Ia . As suggested in the manuscript, these probably do represent a subset of CLL patients who have a low expression of sIg, but do express other B-cell markers. The apparent association with this phenotype and proteinuria was an interesting one, but to my knowledge, was never confirmed in other series. A subsequent report seemed to support the suggestion that these patients with little or no sIg may actually have a more indolent course. JOURNAL OF CLINICAL ONCOLOGY C E L E B R A T I N G 2 5 Y E A R S O F J C O VOLUME 26 NUMBER 8 MARCH 1