The Role And Mechanism Of B7-h1and TLR4in The Immune Evasion Of Mantle Cell Lymphoma

MCL is a unique subtype of incurable B-cell neoplasm that accounts for about6%of non-Hodgkin lymphoma. It is characterized by monoclonal B cells that express CD5, CD19, CD20and CD22on their surface, but not CD23, and by a specific t (11;14)(q13; q32) translocation, causing overexpression of cyclin D1. Patients with MCL are quite heterogeneous in terms of their biological and clinical presentation, containing a leukemic component in20%-30%of patients. Most patients manifest with advanced stage disease at initial diagnosis, and the prognosis is poorest among B-cell lymphoma patients, with a median survival of approximately3-5years. Although progress has been made in MCL management in the past decade, persistent remissions are usually not achieved and management of relapsed or refractory MCL patients is still challenging. Therefore, novel treatment options are needed to improve clinical outcome in MCL patients.Vaccine-based immunotherapy often elicits strong T-cell responses in experimental models and some patients with mantle cell lymphoma (MCL). However, clinical trials have not yet delivered desirable results. The lack of clinical response may partly be related to the inhibitory machinery of tumor and its microenvironment but the underlying mechanisms remain largely unknown. In this study, we investigated the role of B7-H1, a member of the B7family of co-stimulatory/co-inhibitory ligands, in MCL-mediated immunosuppression. Our results showed that B7-H1was constitutively expressed by MCL cells including primary cells from patients and its expression can be further upregulated by IL-10, interferon-γ (IFN-γ) and toll-like receptor4(TLR4) ligand lipopolysacharide (LPS). B7-H1expressed on MCL cells was able to inhibit T-cell proliferation induced by the tumor cells, impair the generation of antigen-specific T-cell responses, and render MCL cells resistant to MCL-reactive T cell-mediated cytolysis. Antibody Blocking or knocking down B7-H1by short hairpin RNA (shRNA) on MCL cells enhanced T-cell responses and restored tumor-cell sensitivity to MCL-reactive T cell-mediated killing. Knocking down B7-H1on MCL cells primed more CD4+or CD8+memory effector T cells which displayed CD45RAlowCD45ROhighCD44highCD62Llow CD27lowCD28high phenotype. Thus, this study demonstrates for the first time that lymphoma cell-expressed B7-H1may lead to the suppression of host anti-tumor immune responses in MCL and targeting tumor cell B7-H1may represent a novel approach to improve the efficacy of immunotherapy in MCL patients.Toll-like-receptors (TLRs) initiate innate and adaptive immune responses against invading pathogens. Recent studies in solid tumors have demonstrated that TLRs take important role in tumor growth, tumor development and tumor biology. So we aimed to investigate TLR triggered responses in MCL cells including proliferation, anti-apoptosis and immune evasion. We showed that MCL cells expressed multiple TLRs and lipopolysacharide (LPS) induced proliferation of MCL cells.In addition, activation of TLR4signaling in MCL cells by LPS induced the synthesis of various soluble cytokines and surface proteins including interleukin-6(IL-6), interleukin-10(IL-10), vascular endothelial growth factor (VEGF), B7-DC, B7-H2and B7-H4, and resulted in inhibition of T cell proliferation and resistance of tumor cells to Cytotoxic T Lymphocytes (CTL) attack. In addition, Blockade of the TLR4pathway by TLR4shRNA reversed LPS induced tumor-mediated suppression of T cell proliferation and CTL activity, inhibited tumor growth and synthesis of various molecules stimulated by LPS. The above results were also observed in TLR4+MyD88+but not TLR4+MyD88-primary MCL cells. In conclusion, our study indicated that TLR4signaling triggered a cascade leading to MCL evasion from immune surveillance. These novel functions of TLR4in MCL biology provided a new therapeutic target for cancer therapy.In conclusion, one of the major hurdles for the success of cancer immunotherapy in human patients is tumor evasion of the immune system, i.e. MCL cells express special molecules including B7-H1and TLR4that disarm effector T cells. Therefore, a better understanding of the mechanism underlying tumor evasion is urgently needed to improve the efficacy of immunotherapy of cancers.