Background

Immune-targeted therapies are being successfully implemented into cancer clinical practice. In particular checkpoint inhibitors are employed to modulate the immune microenvironment of solid tumors. We sought to determine the expression of PD-L1, HVEM, and B7H3 in human and canine osteosarcoma, and correlate expression with clinical features and tumor infiltrating lymphocytes in naturally-occurring canine osteosarcoma.

Methods

Flow cytometry was used to measure ligand surface expression of five human and three canine cell lines. Immunohistochemistry was utilized for expression of ligands and lymphocyte markers in thirty-seven treatment-naïve canine osteosarcoma patients.

Results

All cell lines expressed all three ligands at variable levels in both species. Metastatic lesions were associated with higher expression of all three ligands in patient tumor samples. PD-L1 expression strongly correlated with B7H3 and HVEM expression, while HVEM and B7H3 were weakly correlated. Whereas peritumoral T-cell expression positively correlated with PD-L1 and HVEM tumor expression, the presence of T-cells intratumorally were rare. Furthermore, intratumor penetration by T-cells was greatest in metastatic lesions, despite log-fold increases in peritumoral T-cells.

In summary, PD-L1, HVEM, and B7H3 are expressed in osteosarcoma, with metastatic disease lesions expressing higher levels. We show for the first time that these ligands expressed on osteosarcoma cells positively correlate with each other and the presence of peritumoral T cell infiltration. Furthermore, osteosarcoma appears to be an intratumoral immune desert with significant resistance to effector T cells. Multiple agents targeting checkpoints are in clinical practice, and may have immune modulating benefit in osteosarcoma.

中文翻译：

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犬骨肉瘤检查点表达与转移和T细胞浸润相关

背景

免疫靶向疗法已成功地应用于癌症临床实践。特别地，检查点抑制剂用于调节实体瘤的免疫微环境。我们试图确定PD-L1，HVEM和B7H3在人和犬骨肉瘤中的表达，并将其与自然存在的犬骨肉瘤中的临床特征和肿瘤浸润淋巴细胞相关联。

方法

流式细胞仪用于测量五个人和三个犬细胞系的配体表面表达。免疫组织化学被用于在三十七名未接受过治疗的犬骨肉瘤患者中表达配体和淋巴细胞标志物。

结果

所有细胞系在两个物种中均以可变水平表达所有三个配体。转移性病变与患者肿瘤样品中所有三种配体的较高表达有关。PD-L1表达与B7H3和HVEM表达密切相关，而HVEM和B7H3呈弱相关。肿瘤周围的T细胞表达与PD-L1和HVEM肿瘤表达呈正相关，而肿瘤内T细胞的存在却很少。此外，尽管肿瘤周围T细胞的对数倍增加，但在转移性病变中T细胞的肿瘤内渗透最大。

总之，PD-L1，HVEM和B7H3在骨肉瘤中表达，而转移性疾病病变表达更高。我们首次表明，这些在骨肉瘤细胞上表达的配体彼此正相关，并且与肿瘤周围T细胞浸润有关。此外，骨肉瘤似乎是肿瘤内免疫性沙漠，对效应T细胞具有明显的抵抗力。针对检查点的多种药物正在临床实践中，并且在骨肉瘤中可能具有免疫调节作用。