Rituximab-mediated Antibody-dependent Cytotoxicity Research Articles

Vitamin D-Dependent Induction of Cathelicidin in Human Macrophages Results in Cytotoxicity Against High Grade B-Cell Lymphoma

Infiltration by macrophages represents a characteristic morphological hallmark in high grade lymphatic malignancies such as Burkitt’s lymphoma (BL). Although macrophages can in principle target neoplastic cells and mediate antibody-dependent cytotoxicity (ADCC), tumor associated macrophages (TAMs) regularly fail to exert direct cytotoxic functions. The underlying mechanisms responsible for this observation remain unclear. Here we demonstrate that inflammatory M1 macrophages kill proliferating high grade B-cell lymphoma cells by releasing the antimicrobial peptide cathelicidin in a vitamin D-dependent fashion. Moreover, we show that cathelicidin directly induces cell death by targeting mitochondria of BL-cells. In contrast, anti-inflammatory M2 macrophages and M2-like TAMs in BL exhibit an altered vitamin D metabolism resulting in a reduced production of cathelicidin and consequently in inability to lyse BL cells. However, treatment of M2 macrophages with the bioactive form of vitamin D, 1,25D, or a vitamin D receptor agonist effectively induces cathelicidin production and triggers tumoricidal activity against BL cells. Furthermore, rituximab-mediated cytotoxicity of M2 macrophages is cathelicidin dependent and vitamin D treatment of 25D deficient volunteers improves rituximab-mediated ADCC against BL cells. These data indicate that activation of the vitamin D signaling pathway may activate antitumor activity of TAMs and improve the efficacy of ADCC. DisclosuresNo relevant conflicts of interest to declare.

Interleukin-15 enhances rituximab-dependent cytotoxicity against chronic lymphocytic leukemia cells and overcomes transforming growth factor beta-mediated immunosuppression

Chemoimmunotherapy with anti-CD20 monoclonal antibody rituximab is increasingly used for the treatment of patients with chronic lymphocytic leukemia (CLL). Antibody-dependent cytotoxicity (ADCC) is one of the most important mechanisms of action of rituximab against B-cell malignancies. We studied ways to increase the cytotoxic effect of rituximab on CLL cells by enhancing ADCC. Peripheral blood mononuclear cell (PBMC) or purified natural killer (NK) cells from healthy donors were activated with interleukin-15 (IL-15) and cultured with rituximab-coated CLL cells, and ADCC was evaluated using a (51)chromium release assay. The IL-15 significantly enhanced invitro ADCC against CLL cells, and this effect was mainly mediated by NK cells. The IL-15 treated effector cells with the low affinity FcγRIIIA receptor (158FF) had an ADCC comparable to those with the high affinity FcγRIIIA form (158VF). Inaddition, IL-15 enhanced rituximab-mediated ADCC of CLL cells in the presence of transforming growth factor-beta. The IL-15 increases rituximab-mediated ADCC against CLL, and supports the use of such agents with the goal of improving clinical response to chemoimmunotherapy in patients with CLL.

Supra-additive effect of IMO-4200, a novel TLR7 and TLR8 dual agonist, with rituximab and cytotoxics in preclinical models of hematologic malignancies.

e13076 Background: IMO-4200, a dual agonist of toll-like receptors (TLR) 7 and 8, induces potent Th-1 immune responses and exerts significant antitumor effects in a number of tumor models. In this study, we evaluated IMO-4200 in combination with rituximab and bendamustine or rituximab and fludarabine in human lymphoma xenograft models. Methods: Mice implanted IV with Ramos cells were treated with IMO-4200 50 mg/kg SC every other day x 5, rituximab 10 mg/kg IP every other day x 5, both agents or saline control starting at day 8. The addition of bendamustine 15 mg/kg IP daily x 3 was then tested. In a second experiment in human B-cell lymphoma Raji xenografts, we used fludarabine 250 mg/kg IP instead of bendamustine plus 4 additional IMO-4200 injections. In a third set of experiments conducted in vitro, we monitored the impact of IMO-4200 on rituximab-mediated antibody-dependent cytotoxicity (ADCC) and direct apoptosis of the tumor cells. Results: The table shows that IMO-4200 significantly increased survival when added to rituximab alone and when combined with both rituximab and either cytotoxic. In addition, IMO-4200 enhanced the ADCC of rituximab on Raji and Granta human lymphoma cell lines. It also sensitized human B-cell lymphoma Ramos cells to rituximab-induced apoptosis. Conclusions: IMO-4200 enhances the antitumor activity of rituximab and standard cytotoxic agents used in non-Hodgkin's lymphoma or other hematologic malignancies. IMO-4200 has been selected as the lead candidate for clinical development. Bendamustine Fludarabine Median survival (days) P value vs. control Median survival (days) P value vs. control Control 23 18 – IMO-4200 25 0.233 ND – Rituximab 36 <0.01 24 <0.01 IMO-4200 + rituximab 45 0.012* 29 <0.01* Cytotoxic agent + rituximab 49 <0.01* 32 <0.01* IMO-4200 + rituximab + cytotoxic agent 59 0.026† 37 0.012† * vs rituximab; † vs rituximab + cytotoxic agent; ND, not done.