Evaluation of costimulatory molecules in dogs with B cell high grade lymphoma

B cell high grade lymphoma is the most common hematopoietic malignancy in dogs. Although the immune checkpoint molecules, programmed death-1 (PD-1) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), and immune checkpoint inhibitors have been evaluated for the treatment of various human lymphoid malignancies, the expression of those molecules and their relationship with prognosis remain unknown in canine lymphoma. The objective of this study was to evaluate the expression of costimulatory molecules on peripheral blood lymphocytes and tumor infiltrating lymphocytes, in addition to associated ligand expression in the lymph nodes of patients with B cell multicentric high grade lymphoma. Eighteen patients diagnosed with B cell high grade lymphoma and nine healthy control dogs were enrolled. Flow cytometric analysis revealed that the expression of PD-1 on CD4+ peripheral and tumor infiltrating lymphocytes and CTLA-4 on CD4+ peripheral lymphocytes was significantly higher in the lymphoma group than in the control group. The expression level of CD80 mRNA was significantly lower in the lymphoma group than in the control group. In contrast, there were no significant differences in PD-L1, PD-L2, and CD86 expression between the groups. Dogs with CTLA-4 levels below the cutoff values, which were determined based on receiver operating characteristic curves, on peripheral CD4+, CD8+, and tumor infiltrating CD4+ lymphocytes had significantly longer survival than dogs with values above the cutoff. Although it is uncertain whether the expression of immune checkpoint molecules affect the biological behavior of canine lymphoma, one possible explanation is that PD-1 and CTLA-4 might be associated with the suppression of antitumor immunity in dogs with B cell high grade lymphoma, particularly through CD4+ T cells.

犬高级别B细胞淋巴瘤是犬类最常见的造血系统恶性肿瘤。尽管目前已针对多种人类淋巴恶性肿瘤，对免疫检查点分子（immune checkpoint molecules）、程序性死亡蛋白1（programmed death-1，PD-1）、细胞毒性T淋巴细胞相关抗原4（cytotoxic T-lymphocyte-associated antigen-4，CTLA-4）及免疫检查点抑制剂开展了治疗相关评估，但犬淋巴瘤中此类分子的表达情况及其与预后的关联仍未明确。本研究旨在评估多中心性高级别B细胞淋巴瘤患犬的外周血淋巴细胞（peripheral blood lymphocytes）、肿瘤浸润淋巴细胞（tumor infiltrating lymphocytes）表面共刺激分子（costimulatory molecules）的表达情况，同时检测其淋巴结中相关配体的表达水平。本研究共纳入18例经确诊的高级别B细胞淋巴瘤患犬与9只健康对照犬。流式细胞术分析结果显示，淋巴瘤组患犬CD4+外周血淋巴细胞及肿瘤浸润淋巴细胞表面PD-1的表达水平，与CD4+外周血淋巴细胞表面CTLA-4的表达水平，均显著高于对照组。淋巴瘤组患犬CD80 mRNA的表达水平显著低于对照组。与之相反，两组间PD-L1、PD-L2及CD86的表达水平均无显著差异。基于受试者工作特征曲线（receiver operating characteristic curves）确定临界值后，外周血CD4+、CD8+淋巴细胞以及肿瘤浸润CD4+淋巴细胞表面CTLA-4水平低于临界值的患犬，其生存时长显著高于CTLA-4水平高于临界值的患犬。尽管目前尚无法确定免疫检查点分子的表达是否会影响犬淋巴瘤的生物学行为，但一种可能的解释为：PD-1与CTLA-4可能与高级别B细胞淋巴瘤患犬的抗肿瘤免疫抑制相关，且该作用或主要通过CD4+ T细胞介导。