Engraftment of Human Glioblastoma Cells in Immunocompetent Rats through Acquired Immunosuppression

Transplantation of glioblastoma patient biopsy spheroids to the brain of T cell-compromised Rowett (nude) rats has been established as a representative animal model for human GBMs, with a tumor take rate close to 100%. In immunocompetent littermates however, primary human GBM tissue is invariably rejected. Here we show that after repeated passaging cycles in nude rats, human GBM spheroids are enabled to grow in the brain of immunocompetent rats. In case of engraftment, xenografts in immunocompetent rats grow progressively and host leukocytes fail to enter the tumor bed, similar to what is seen in nude animals. In contrast, rejection is associated with massive infiltration of the tumor bed by leukocytes, predominantly ED1+ microglia/macrophages, CD4+ T helper cells and CD8+ effector cells, and correlates with elevated serum levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. We observed that in nude rat brains, an adaptation to the host occurs after several in vivo passaging cycles, characterized by striking attenuation of microglial infiltration. Furthermore, tumor-derived chemokines that promote leukocyte migration and their entry into the CNS such as CXCL-10 and CXCL-12 are down-regulated, and the levels of TGF-β2 increase. We propose that through serial in vivo passaging in nude rats, human GBM cells learn to avoid and or/ suppress host immunity. Such adapted GBM cells are in turn able to engraft in immunocompetent rats without signs of an inflammatory response.

将胶质母细胞瘤（glioblastoma）患者活检球状体移植至T细胞缺陷的Rowett裸鼠脑部，已被确立为人类GBM的代表性动物模型，其肿瘤接种率接近100%。然而，在免疫健全的同窝仔鼠中，原代人GBM组织会被完全排斥。本研究证实，经裸鼠体内多次传代后，人GBM球状体可在免疫健全大鼠的脑部生长。若成功定植移植，免疫健全大鼠体内的异种移植瘤会进行性生长，且宿主白细胞无法侵入肿瘤床，与裸鼠中的观察结果一致。与之相反，排斥反应伴随肿瘤床被大量白细胞浸润，主要为ED1+小胶质细胞/巨噬细胞、CD4+辅助性T细胞及CD8+效应T细胞，且与促炎细胞因子IL-1β、IL-18及TNF-α的血清水平升高显著相关。我们观察到，在裸鼠脑部，经数次体内传代后，肿瘤会适应宿主环境，其特征为小胶质细胞浸润显著减弱。此外，可促进白细胞迁移并侵入中枢神经系统（central nervous system, CNS）的肿瘤源性趋化因子，如CXCL-10与CXCL-12，其表达水平下调，而TGF-β2的含量升高。我们提出，经裸鼠体内连续传代后，人GBM细胞可获得规避或抑制宿主免疫的能力。此类经过适应性改造的GBM细胞可在免疫健全大鼠体内成功移植，且未出现炎症反应迹象。