B-lymphocyte suppression in multiple myeloma is a reversible phenomenon specific to normal B-cell progenitors and plasma cell precursors

The reduced levels of normal immunoglobulin in patients with myeloma may be due to suppression of normal B-cell differentiation. However, reports on the numbers of B cells vary, with some finding decreases consistent with immunoparesis, and others reporting expansions of phenotypically aberrant cells. We have therefore assessed the phenotype and levels of B lymphocytes in patients at presentation (n = 23), in plateau or complete remission (PB n = 42, BM n = 18), and in relapse (PB n = 17, BM n = 14), in comparison to normal individuals (n = 10). Phenotypic analysis was performed using five-parameter flow cytometry, with CD14 used to exclude monocytes where necessary.

We found no evidence of a phenotypically distinctive blood or marrow B-cell population in patients with myeloma, nor of an increase in the levels of any B-cell subset. Numbers of blood CD19⁺38⁺ normal plasma cell precursors were significantly reduced in presentation/relapse patients, but not in patients in plateau/remission. Total CD19⁺ cells were significantly reduced only in patients with circulating myeloma cells, detected by IgH-PCR. In the marrow, CD19⁺ B cells expressing CD5, CD10, CD34, CD38, CD45^low and Syndecan-1 were significantly decreased at presentation/relapse, but not in patients in plateau/remission. The majority of these antigens are expressed by normal B-cell progenitors, indicating that myeloma also affects the early stages of B-cell development. The suppression of progenitor cells was not restricted to B-lymphoid differentiation, as total CD34⁺ cells were also significantly reduced in the marrow of myeloma patients at presentation.

These results indicate that, if neoplastic B cells are present in myeloma, they are low in number and have a phenotype similar to their normal counterparts. Furthermore, there is a reversible suppression of CD19⁺ B lymphocytes that correlates inversely with disease stage, and specifically affects the early and late stages of normal B-cell differentiation.