Immunophenotypic analysis of CD19(+) precursors in normal human adult bonemarrow: implications for minimal residual disease detection

Background and Objective. Normal B-cell differentiation has been characteri zed extensively, but discrepancies persist regarding the exact sequence of antigen expression. Few systematic studies focusing on identification of th e minor or undetectable B-cell subsets in normal human bone marrow (BM) whi ch are frequently found in leukemic cells have been performed. Such studies could help to monitor minimal residual disease (MRD) In precursor-B-acute lymphoblastic leukemia (precursor-B-ALL), The aim of the present study was to analyze the sequence of antigen expression among normal human CD19(+) a cells from adult BM. Our major goal was to identify infrequent and undetect able B-cell phenotypes that could be used for the detection of MRD in patie nts with precursor-B-ALL. Design and Methods. Adult BM samples from a total of 33 healthy volunteers were analyzed using triple stainings, and measured by flow cytometry, A sen sitive method based on the two-step acquisition procedure was used for the identification and characterization of cells present at very low frequencie s. Results. Five different subsets of CD19(+) cells were identified in normal BM samples according to their degree of maturation: 1) CD19(+)/CD34(+)/CD10 (-)/CD20(-)/CD22(dlm+) (0.5 +/- 0.4% B cells); 2) CD19(+)/CD34(-)/CD10(++) /CD20(-)/CD22(dlm+) (3.4 +/- 2.7%); 3) CD19(+)/CD34(-)/CD10(+)/CD20(-)/CD22 (dlm+) (3.5 +/- 2.2%); 4) CD19(+)CD34(-)/CD10(+)/CD20(+,++) /CD22(dlm+) (21 +/- 11%), and 5) CD19(+)/CD34(-)/CD10(-/)CD20(++)/CD22(+) (73 +/- 19%), We observed that several B-cell phenotypes are frequent among precursor-B-ALL , but are infrequent or undetectable in normal human B cell differentiation . Accordingly, in all normal BM samples analyzed, less than 4 x 10(-5) cell s co-expressed CD19 and CD117; CD20(strong+)/CD34(+) and CD22(strong+)/CD34 (+) events were found at frequencies less than 5 x 10(-4), while CD20(+)/CD 34(+) phenotypes were found in less than 1 x 10(-3) BM cells. Although both CD19(+)/CD13(+) and CD19(+)/CD33(+) events were found at frequencies of up to 3 x 10(-3), they never formed a well-defined population of cells and th erefore these latter phenotypic patterns could also be of use for MRD inves tigation in CD13(+) and/or CD33(+) precursor-B-ALL cases. Interpretation and Conclusions. Our results show that in adult BM normal B- cells display constant patterns of maturation as regards both their phenoty pic characteristics and their relative distribution. Abnormalities in these patterns provide a potentially useful tool for monitoring MRD in precursor -B-ALL patients who achieve cytomorphologic complete remission. (C) 1998, F errata Storti Foundation.