CLL cell-derived soluble factors do not influence the functionality of normal B cells

Humoral immunodeficiency is frequently observed in patients affected by chronic lymphocytic leukemia (CLL). The reasons for the compromised B-cell responses are only partly understood. We hypothesized that the normal residual B cells in CLL patients are negatively influenced in their functionality by soluble factors produced by CLL cells.

We performed functional B-cell assays to analyze the influence of serum from CLL patients or conditioned medium from CLL cells cultivated with stromal cells on B cells from healthy donors. Serum from healthy individuals or conditioned medium from normal B cells was used as controls, respectively. We stimulated the B cells in a T-cell-dependent fashion and incubated them in the respective serum or conditioned medium for 5 days. We measured plasma cell differentiation, proliferation, cell death, and B-cell activation, the latter using the markers CD80, CD86, and CD25.

We did not detect significant differences supporting the hypothesis that CLL-derived soluble factors negatively influence the proliferation, activation, or cell death levels of normal B cells from healthy individuals in in vitro coculture.

Our analysis suggests no major direct inhibitory effects of CLL-derived soluble factors on normal mature B cells. Thus, it is likely that other factors lead to the known B-cell dysfunction in CLL.