Characterization of bone marrow lymphoid infiltrates after immunochemotherapy for follicular lymphoma

We studied the distribution of lymphoid cells in the bone marrow of 10 follicular lymphoma (FL) cases in complete response after immunochemotherapy but with nodular lymphoid infiltrates mimicking persistent lymphoma nodules. Immunohistochemical analysis showed that most of these cells displayed a T-cell phenotype with important proportions of regulatory T cells (CD3+/CD4+/FOXP3+) and mast cells. These populations were also present before treatment. Whereas no CD20+ cells were observed, immature B cells (CD79a+/terminal deoxynucleotidyl transferase+/CD20-) were detected. These cells were scarce before immunochemotherapy, suggesting that immunochemotherapy enabled their expansion. Fluorescence in situ hybridization and quantitative polymerase chain reaction failed to detect residual lymphoma cells in 5 cases with the t(14;18) translocation. Our study describes 2 important features in bone marrow in FL following immunochemotherapy. It is probable that the accumulation of regulatory T cells has some role in the control of FL. The expansion of nonmalignant B cells reflects the regeneration of B-cell lineage following immunochemotherapy.