Inhibition Of Indoleamine 2, 3-Dioxygenase In CD20+ Diffuse Large B Cell Lymphoma Cell Correlates With Rituximab-mediated Antibody-dependent Cell-mediated Cytotoxicity

Background and Objective: Diffuse large B-cell lymphoma(DLBCL) is a common subtype of non-Hodgkin lymphoma(NHL). The incidence in china is remarkably higher than that in foreign countries. The exact mechanisms of its action have not been unambiguously explained. Clinical application of rituximab in combination with chemotherapy has significantly improved the treatment outcome in the patients with DLBCL. However, in the state of tumor progression, the host fails to reject tumors that have evolved ways to escape immune surveillance. With the research developed, people begin to realize the correlations between abnormal expression of gene protein and the immune tolerance, which has become a hot topic in this field. Recent studies have suggested that one mechanism of immune escape could be tryptophan catabolism, via indoleamine 2, 3-dioxygenase(IDO). IDO is an enzyme that degrades the essential amino acid tryptophan along the kynurenine pathway. IDO can also be expressed by cancer cells in a variety of human malignancies. It was involved in protecting tumors from attack by tumor-associated antigen-specific host cytotoxic T cells. The IDO inhibitor is being developed for clinical trials. And, several findings had support that the use of IDO inhibition to block host-mediated immunosuppression can enhance antitumor immunity in the setting of combined chemo-immunotherapy regimens. This study was therefore aimed to confirm that inhibition of indoleamine2 3-Dioxygenase in CD20+ diffuse large B cell lymphoma cell correlates with Rituximab-mediated cytotoxic effect.Methods: The expression of IDO was tested by the Western blot, when Raji and K562 cells were grown with the inhibitor of IDO or not, after 24 hours. Mononuclear cell were isolated by Ficoll density-gradient centrifugation and were classified as effector cells. The activity of rituximab was tested in vitro on Raji and K562 cells using the LDH release assay at various ratios of effecter cells to target cells(1:1, 5:1, and 10:1). Raji and K562 cells were divided into E/T group, E/T+R group, E/T+R+CQ group, E/T+R+1-MT group, and E/T + R + IFN-γ group.Results: Western blot: 1.With the treatment of different concentrations of Chloroquine, the expression of IDO was significantly knocked down(P<0.05). 2. The expression of IDO was been knocked down, when treatment with 1-MT. 3. With the treatment of IFN-γ, the expression of IDO was significantly up-regulated(P<0.05). LDH release assay: 1. The killing activity of lymphocyte cells rises obviously in vivo, when the expression of IDO was been knocked down(P<0.05). 2. The killing activity of lymphocyte cells is lower in vivo, when the expression of IDO was been up-regulated, but there was no statistically significant(P<0.05).Conclusion: 1. The increase of IDO in CD20+ DLBCL is one of the molecular mechanisms of Rituxima resistance; 2. According to our results, inhibition of IDO in CD20+ diffuse large B cell lymphoma cell can increase the cytotoxic effect of Rituximab; 3. The combination of IDO inhibitor and Rituximab may be an effective way to avoid IDO mediated resistance of Rituximab in DLBCL.