Abstract
Abstract Diffuse Large B-cell Lymphoma (DLBCL) represent a diverse group of lymphoid neoplasms with heterogeneous clinical, histological, immunophenotypic, cytogenetic and molecular genetic features. Approximately 50% of DLBCL patients are not cured by the standard combination chemotherapy regimens. DLBCL can be subclassified into GCB-like DLBCL which are characterized by expression of genes normally expressed in germinal center B cells, and having a significantly better overall survival (OS) than the ABC-like DLBCL, which are characterized by expression of genes induced during in vitro activation of normal B cells. At least two markers of the GCB-phenotype - BCL6 and HGAL - are IL-4 target genes, increased expression of which independently predicts better OS. These observations suggest that endogenous or exogenously administered IL-4 may influence behavior of DLBCL. IL-4 mRNA was detected at low levels in 5 of 7 GCB-like and in all 4 ABC-like DLBCL tumor specimens. Two of 7 GCB-like tumors showed high expression levels of IL-4 as determined by real-time RT-PCR. Examination of the effects of IL-4 on proliferation of GCB-like (SUDHL6, SUDHL4 and OCILY19) and ABC-like (OCILY10 and OCILY3) DLBCL cell lines showed that IL-4 mildly increased DNA synthesis, as assessed by thymidine incorporation, in all the GCB-like DLBCL. Conversely, IL-4 markedly decreased proliferation in the ABC-like DLBCL cell lines by inducing G1 arrest. IL-4 also differently affected the sensitivity of GCB-like and ABC-like DLBCL to doxorubicin. IL-4 reduced doxorubicin-induced cell death of ABC-like cell lines (20–50% reduction) while it markedly increased the killing of the GCB-like cells (40–80% induction). IL-4 also prevented serum starvation-induced cell death of the ABC-like DLBCL, but it increased cell death of the GCB-like DLBCL cell lines. Recently, Rituximab was shown to improve survival of DLBCL patients when added to the CHOP regimen. The precise mechanisms of its action are unknown; however present data suggest that it may affect lymphoma cells either by activation of complement lysis or by mediating ADCC. IL-4 reduced the complement mediated Rituximab cell lysis of the ABC-like cell lines, while it increased the complement mediated Rituximab cell lysis of the GCB-like DLBCL cell lines. Expression levels of surface markers that modulate complement cell lysis (CD46, CD55 and CD59) were not affected by IL-4 exposure. In contrast, IL-4 did not affect killing of GCB-like and ABC-like cells by ADCC. These observations suggest that DLBCL subtypes may respond differently to the in vivo cytokine milieu of the tumor. Different responsiveness to IL-4 may modulate tumor sensitivity to the current therapeutic modalities and can potentially be explored to augment response to chemotherapy and Rituximab.