Purpose: TIGIT blockade in our ex vivo models of bone marrow (BM) reduced the number of malignant plasma cells (PCs) in only half of patients with multiple myeloma (MM). Here we wanted to investigate whether increased expression of TIGIT ligands may inhibit T cell immune response promoting resistance to TIGIT blockade. Experimental Design: We first characterized the number and phenotype of BM macrophages in the different stages of disease by multi-parameter flow cytometry. We assessed the effect of TIGIT ligands on PC survival performing experiments with ex vivo BM model and analyzed changes in gene expression by using Nanostring technology and real-time PCR. Results: Frequency of BM macrophages was significantly decreased in MM which was accompanied by changes in their immunophenotype. Moreover, we found a higher number of malignant PCs in ex vivo BM cells cultured onto PVR and nectin-2 compared to control, suggesting that both ligands may support PC survival. In addition, presence of PVR, but not nectin-2, overcame the therapeutic effect of TIGIT blockade or exogenous IL-2. Furthermore, presence of exogenous IL-2 increased TIGIT expression on both CD4+ and CD8+ T cells and, indirectly, PVR on BM macrophages. Consistently, PVR reduced the number of cytotoxic T cells and promoted a gene signature with reduced effector molecules. Conclusions: IL-2 induced TIGIT on T cells in the BM where increased PVR expression resulted in cytotoxic T cell inhibition promoting PC survival and resistance to TIGIT blockade.

中文翻译：

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骨髓巨噬细胞 PVR 表达增加可能促进多发性骨髓瘤对 TIGIT 阻断的耐药性


目的：在我们的离体骨髓 (BM) 模型中，TIGIT 阻断仅减少了一半多发性骨髓瘤 (MM) 患者的恶性浆细胞 (PC) 数量。在这里，我们想要研究 TIGIT 配体表达的增加是否可能抑制 T 细胞免疫反应，从而促进对 TIGIT 阻断的抵抗。实验设计：我们首先通过多参数流式细胞术表征了疾病不同阶段的BM巨噬细胞的数量和表型。我们通过离体 BM 模型进行实验评估了 TIGIT 配体对 PC 存活的影响，并使用 Nanostring 技术和实时 PCR 分析了基因表达的变化。结果：MM中BM巨噬细胞的频率显着降低，并伴有免疫表型的变化。此外，我们发现与对照相比，在体外培养的 PVR 和 nectin-2 上的 BM 细胞中，恶性 PC 的数量更高，这表明两种配体可能支持 PC 存活。此外，PVR（而非nectin-2）的存在克服了TIGIT阻断或外源IL-2的治疗效果。此外，外源性IL-2的存在增加了CD4+和CD8+T细胞上的TIGIT表达，并间接增加了BM巨噬细胞上的PVR。一致的是，PVR 减少了细胞毒性 T 细胞的数量，并通过减少效应分子促进了基因特征。结论：IL-2 诱导 BM 中 T 细胞上的 TIGIT，其中 PVR 表达增加导致细胞毒性 T 细胞抑制，促进 PC 存活和对 TIGIT 阻断的抵抗。