Rituximab plus CHOP (R-CHOP) overcomes PRDM1-associated resistance to chemotherapy in patients with diffuse large B-cell lymphoma.

The positive regulatory domain I (PRDM1) is a master regulator in the differentiation of mature B lymphocytes to plasma cells. It has 2 isoforms, PRDM1alpha and PRDM1beta, and is regulated by the transcriptional regulator nuclear factor kappa (NF)-kappaB. PRDM1 protein expression was recently demonstrated in a subset of diffuse large B-cell lymphoma (DLBCL) with aggressive behavior, a type of lymphoma for which rituximab associated with chemotherapy (R-CHOP) is now widely indicated. Using laser microdissection combined with reverse transcription-polymerase chain reaction (RT-PCR) amplification, PRDM1 gene expression was assessed in 82 DLBCL patients. The results showed that both PRDM1alpha and PRDM1beta transcripts were expressed in microdissected lymphoma cells only in the non-germinal center B-cell-like (non-GCB) subtype of DLBCL. PRDM1beta gene expression was correlated with short survival time in the non-GCB patients treated with CHOP but not with R-CHOP. In vitro, B-lymphoma cells resistant to chemotherapy expressed PRDM1beta. Rituximab suppressed PRDM1beta expression, which was concomitant with NF-kappaB inactivation. The value of PRDM1beta expression as a prognostic marker in non-GCB DLBCL might thus be considered. This study confirms the efficiency of rituximab on DLBCL and allows a better understanding of one of its biologic actions.