Marrow B-cell precursors are increased in lymphomas or systemic diseases associated with B-cell dysfunction

Marrow regeneration is known to be associated with an increase in immature B cells, including CD10⁺ cells. A similar phenotype has been seen in some children with unusual cytopenias. This article describes 21 adult patients not recovering from chemotherapy, who had increased CD10⁺ cells in their marrows. These cells had the relatively uniform scatter properties of small lymphocytes by flow cytometry, and by multiparameter analysis were found to have a distinct phenotype in that they were CD19⁺, lacked surface immunoglobulin, and heterogeneity expressed CD20. In two of three patients tested, some but not all of these early B cells were TdT⁺. CD10⁺ cells accounted for 10-76% of total mononuclear cells. All 21 patients had some systemic illness. Thirteen patients had a diagnosis of lymphoma (three Hodgkin's, ten non-Hodgkin's); all ten of the latter were extranodal and seven of seven phenotyped cases were B-cell lymphomas. Seven patients had autoimmune disease (one also had lymphoma) and one had the acquired immunodeficiency syndrome with mycobacterial infection of the marrow. One patient with a history of a 'viral illness' had a lymph node showing atypical lymphoid hyperplasia with progressive transformation of germinal centers. Examination of marrow core biopsies in these patients showed a proliferation of small lymphocytes ranging from a barely perceptible diffuse increase to numerous lymphoid aggregates. The extensive lymphocytosis seen in two marrows suggested a diagnosis of lymphoma on morphologic grounds alone, but neither these patients nor any others had B-cell clonal excess. The presence of this phenotype suggests nonspecific stimulation of marrow B-cell precursors associated with systemic B-cell activation in either an immunologic or neoplastic disorder. Presence of this unusual phenotype does not imply involvement of marrow by B-cell neoplasia.