Enhancement of the Antigen-Presenting Cell Function of Mantle Cell Lymphomas (MCL) by Novel Molecularly Based Immunotherapeutic Strategies.

MCL is an aggressive and incurable B-cell malignancy with an intrinsic characteristic to relapse after an initial good response to treatment. Manipulation of the immune system to unleash its well-known specificity and long-lasting protective effect might provide a unique opportunity to induce more durable responses in MCL. In previous studies in an A20 B-cell lymphoma murine model we have demonstrated that augmentation of the antigen-presenting cell function of the malignant B-cell is required for elicitation of an effective anti-lymphoma immunity¹. Inhibition of Stat3 signaling, a negative regulator of inflammatory responses, and modulation of histone deacetylases function were identified as two novel targets to augment the immunogenicity of the malignant B-cell. In this study we determined therefore whether manipulation of these intracellular pathways in murine and human MCL cells could result in priming of antigen-specific T-cells and/or restoration of the responsiveness of tolerant T-cells. First, in vitro treatment of FC-muMCL1 cells - cell line derived from a MCL tumor that arise following pristine injection into Em-cyclin D1 transgenic mice- with increasing concentrations of the Stat3 inhibitors, Cucurbitacin I (CuI) or CPA-7 resulted in an enhanced presentation of OVA-peptide to naive CD4⁺ T-cells specific for a MHC class II restricted epitope of Ovalbumin (OT-II cells). Indeed, these antigen-specific T-cells produce higher levels of IL-2 and IFN-gamma compared to anti-OVA T cells that encountered cognate antigen in FC-muMCL1 cells treated with LPS alone. Similarly, we found that culture of the human MCL cells JEKO or Z138 with allogeneic human peripheral blood mononuclear cells in the presence of increasing concentrations of the Stat3 inhibitors also resulted in increased IL-2 production by T-cells. In the next set of experiments, we determined whether treatment of FC-muMCL1 cells with the hydroxamic acid analogue pan-HDAC inhibitor LAQ824 could influence their antigen-presenting capabilities and their ability to activate T-cell responses. Unlike, MCL cells treated with LPS alone, FC-muMCL1 cells treated with LPS and LAQ824 effectively prime antigen-specific CD4⁺ T-cells as determined by their production of both IL-2 and IFN-gamma in response to cognate peptide. Furthermore, in vitro treatment of Z138 MCL cells with LAQ824 also led to enhanced IFN-gamma production by allogeneic human PBMCs. Taken together, our findings points to inhibition of Stat3 signaling and inhibition of histone deacetylases as appealing molecularly based immunotherapeutic strategies to augment the immunogenicity of MCL cells.