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Background Expression of immune checkpoints in the tumor microenvironment is one mechanism underlying paclitaxel (PTX) chemoresistance. This study aimed to investigate whether the addition of checkpoint blockade to PTX can improve the therapeutic efficacy against apparently disseminated intraperitoneal tumors.Methods We analyzed the in vivo expression of various immune checkpoints in CD3+CD8+ cytotoxic T cells from tumor-bearing mice treated with or without PTX and validated the tumor-killing activities of selected checkpoint-expressing T-cell subpopulations ex vivo. The regulation of selected checkpoints was investigated in vitro. The therapeutic effects of inhibition of a targeted checkpoint pathway with antibodies added to PTX therapy were examined.Results CD3+CD8+ T cells expressed with herpes virus entry mediator (HVEM), programmed cell death 1 (PD-1), and T-cell immunoglobulin domain and mucin domain 3 (TIM-3) in tumor-bearing hosts treated with PTX had effective tumoricidal activities. In addition to PTX and cytokines, B and T lymphocyte attenuator (BTLA) or homologous to lymphotoxin, exhibits inducible expression and competes with herpes simplex virus (HSV) glycoprotein D for binding to HVEM, a receptor expressed on T lymphocytes (LIGHT) interacting with HVEM can regulate the expression of PD-1 on CD3+CD8+ T cells. Interleukin (IL)-15 increased the percentage of HVEMhighgranzyme B (GZMB)+ cells among CD3+CD8+ T cells, which was suppressed by the BTLA/HVEM signal. LIGHT induced the percentage of HVEM+GZMB+ cells but not HVEMhighGZMB+ cells among CD3+CD8+ T cells. Expression of IL-15, BTLA, or LIGHT was detected in CD19+ B cells and regulated by damage-associated molecular patterns/Toll-like receptor interactions. In the tumor-bearing hosts treated with PTX, certain proportions of BTLA+ B or PD-1+ T lymphocytes were still noted. When dual inhibition of BTLA and PD-1 was added to PTX, the antitumor effects on intraperitoneally disseminated tumors can be significantly improved.Conclusions Dual blockade of BTLA on B cells and PD-1 on cytotoxic T cells may have clinical potential for enhancing the efficacy of PTX in the treatment of tumors with intraperitoneal spread, including epithelial ovarian carcinomas.

Abstract Background The standard treatment for epithelial ovarian carcinoma (EOC) is surgery followed by platinum/paclitaxel-based chemotherapy, but the overall survival rate is poor. The purpose of this study was to investigate the therapeutic potential of chemotherapy combined with inhibition of B and T lymphocyte attenuator (BTLA) for clinical use to treat EOC. Methods Initially, we evaluated the potential application of chemotherapy combined with anti-BTLA antibody in an animal model. We then analyzed the distribution and regulation of BTLA expression on immunocytes in vitro. Finally, we examined the correlation between BTLA expression levels in cancerous tissues and prognosis in 254 EOC cases. Results The combination of chemotherapy and anti-BTLA antibody for inhibiting BTLA significantly reduced peritoneal tumor volume and extended survival in tumor-bearing mice. In addition, BTLA could be identified mostly on B lymphocytes, especially on CD19hi B cells, rather than on T lymphocytes and natural killer cells. Under regulation of interleukins 6 and 10, more BTLA+CD19hi B lymphocytes could be induced through AKT and STAT3 signaling pathways. Detectable BTLA expression in ovarian cancerous tissues was associated with worse disease-free and overall survivals of EOC patients. Conclusions BTLA detected in cancerous tissues can predict poor outcome of EOC patients. Inhibition of BTLA combined with chemotherapy can elevate immune activation and generate potent anti-tumor effects. Thus, the combination of chemotherapy and anti-BTLA antibody may hold potential clinical application for the treatment of EOC patients. Trial registration The Trial Registration Number was NCT00854399.