CD5 and cCLLa Expression in Chronic Lymphocytic Leukemia (CLL): Demonstration of Their Relative Prevalence and that of Other Common B-CLL Markers

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Abstract
Chronic lymphocytic leukemia (CLL) is a malignant lymphoproliferation most frequently involving B-cells. Characteristically, B-CLL cells express a number of surface antigens collectively known as CLL markers. Some of the most prevalent CLL markers have been used for the immunophenotypic diagnosis and for targeted immunotherapy of B-CLL. In order to ascertain the relative prevalence of CLL markers, we assessed the immunophenotypic profile of 112 consecutive B-CLL patients. Patients were diagnosed according to International CLL Workshop criteria extended to include preclinical B-CLL. Immunophenotypic profiles were based on fluorescence microscopy and flow cytometry. In decreasing order of frequency, the B-CLL clone was cCLLa +, CD19+, MosIg+ or CD5+ in 100%, 97%, 92% and 78% of patients, respectively. Likewise, in 14 CD5- patients the B-CLL clone was cCLLa, CD19+ and MosIg+ in 100%, 100% and 93% of patients, respectively. Co-expression of cCLLa, CD 19 and Moslgs by CD5- B-CLL cells was inferred from the high correlation (r > 0.99) among cell subsets expressing all three markers, and was confirmed by two color flow cytometry (n = 25). Except for a smaller circulating clone, CD5., B-CLL was clinically, hematologically and immunophenotypically indistinguishable from CD5+ B-CLL. These data indicate that a substantial fraction of B-CLL patients are CD5-. More prevalent CLL markers such as the cCLLa might be more suitable for targeted immunotherapy.