Immunophenotypic analysis of hematogones (B-lymphocyte precursors) in 662 consecutive bone marrow specimens by 4-color flow cytometry.

Bone marrow hematogones (B-lymphocyte precursors) may cause problems in diagnosis because of their morphologic and immunophenotypic similarities to neoplastic lymphoblasts. The purposes of this prospective, multiparametric flow cytometry study were to quantify hematogones across age groups and a spectrum of clinical conditions, to identify factors that affect the relative quantity of hematogones, and to compare their immunophenotype with that of neoplastic lymphoblasts. A total of 662 consecutive marrow specimens were analyzed for hematogones using one of two 4-color antibody combinations; hematogones were identified in 528 (79.8%). There was a significant decline in hematogones with increasing age (P <.001), but a broad range was found at all ages and many adults had a relatively high number. Specimens processed by density gradient had a higher mean percent hematogones than those processed by erythrocyte lysis (P <.001). There was a direct decline in hematogones with increasing marrow involvement with neoplastic cells. A total of 8% of the 662 specimens contained 5% or more hematogones: 24.6% of specimens from patients aged less than 16 years and 6.3% from those 16 and older (P <.000 01). Increased hematogones were observed most often in patients with lymphoma, marrow regenerative states, immune cytopenias, and acquired immunodeficiency syndrome. Hematogones always exhibited a typical complex spectrum of antigen expression that defines the normal antigenic evolution of B-cell precursors and lacked aberrant expression. In contrast, lymphoblasts in 49 cases of precursor B-ALL showed maturation arrest and exhibited 1 to 11 immunophenotypic aberrancies. Four-color flow cytometry with optimal combinations of antibodies consistently distinguishes between hematogones and neoplastic lymphoblasts.

Absence of CD26 expression is a useful marker for diagnosis of T-cell lymphoma in peripheral blood.

We report flow cytometric characterization of surface CD26 expression in 271 peripheral blood samples from 154 patients evaluated for the presence of a T-cell lymphoproliferative disorder, primarily mycosis fungoides/Sézary syndrome (MF/SS). The presence of morphologically identifiable tumor cells on peripheral blood smears was the criterion for lymphomatous involvement. In 66 of 69 samples from 28 patients, we identified an abnormal CD26-/dim T-cell population that was distinct from the variable CD26 expression seen in normal peripheral blood T cells. This population was CD26- in 23 patients and weakly CD26+ in 5 patients. CD7 was more variably expressed in MF/SS tumor cells, allowing recognition of a distinct, quantifiable abnormal T-cell population in only 34 of 69 involved samples. An increased CD4/CD8 ratio and lower surface expression of CD4 in tumor cells also helped separate the CD26-/dim atypical population for quantification. In 35 blood samples from other types of T-cell tumors, tumor cells in 10 of 11 morphologically involved cases showed absent/dim CD26. Although capable of detecting abnormalities in most cases of MF/SS, CD7 expression does not provide as clear a separation of the neoplastic population and can be replaced by CD26 staining in routine peripheral blood flow cytometric screening of MF/SS patients.