Department of Radiation Oncology, Emory University, Atlanta, Georgia, USA.
Emory Vaccine Center, Department of Microbiology and Immunology, Emory University, Atlanta, Georgia, USA.
J Immunother Cancer. 2020 Oct;8(2). doi: 10.1136/jitc-2020-000867.
Radiotherapy (RT) has been shown to stimulate an antitumor immune response in irradiated tumors as well as unirradiated distant sites (abscopal effect). Previous studies have demonstrated a role for the tumor-draining lymph node (LN) in mediating an anti-programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) stimulated antitumor immune response. Here, we investigated whether the LN is also important in mediating a RT alone stimulated abscopal response.
We used a subcutaneous modified B16F10 flank tumor model injected bilaterally. Our B16F10 cell line has an inserted viral glycoprotein which facilitated identification of tumor-specific T-cells. RT was directed at one flank tumor alone or one flank tumor and the tumor-draining LN. We evaluated response by tumor growth measurements and flow cytometry of both tumor-infiltrating and LN T-cells.
We show that local tumor irradiation improves distant tumor control (abscopal effect). Depletion of CD8 T-cells significantly reduced this abscopal response. We have previously shown, in a chronic lymphocytic choriomeningitis virus (LCMV) infection, that the T-cell proliferative burst following blockade of PD-1/L1 is provided by a 'stem-like' CD8 T-cell subset which then differentiate into terminally differentiated effectors. These terminally differentiated effectors have the potential to kill virally infected or tumor cells following PD-1/L1 blockade. In the chronic LCMV infection, stem-like CD8 T-cells were found exclusively in secondary lymphoid organs. Similarly, here we found these cells at high frequencies in the tumor-draining LN, but at low frequencies within the tumor. The effect of RT on this T-cell subset in unknown. Interestingly, tumor irradiation stimulated total CD8 and stem-like CD8 T-cell proliferation in the LN. When the LN and the tumor were then targeted with RT, the abscopal effect was reduced, and we found a concomitant reduction in the number of total tumor-specific CD8 T-cells and stem-like CD8 T-cells in both the irradiated and unirradiated tumor.
These correlative results suggest the tumor-draining LN may be an important mediator of the abscopal effect by serving as a stem-like CD8 T-cell reservoir, a site for stem-like T-cell expansion, and a site from which they can populate the tumor.
放射治疗（RT）已被证明可在照射肿瘤以及未照射的远处部位（远隔效应）中刺激抗肿瘤免疫反应。先前的研究表明，肿瘤引流淋巴结（LN）在介导抗程序性死亡-1（PD-1）/程序性死亡配体-1（PD-L1）刺激的抗肿瘤免疫反应中起作用。在这里，我们研究了 LN 是否在介导单独 RT 刺激的远隔反应中也很重要。
我们使用双侧皮下改良 B16F10 肋部肿瘤模型。我们的 B16F10 细胞系具有插入的病毒糖蛋白，这便于鉴定肿瘤特异性 T 细胞。RT 仅针对一侧的肿瘤或一侧的肿瘤和肿瘤引流 LN。我们通过肿瘤生长测量和肿瘤浸润和 LN T 细胞的流式细胞术来评估反应。
我们表明，局部肿瘤照射可改善远处肿瘤控制（远隔效应）。CD8 T 细胞耗竭显著降低了这种远隔反应。我们之前在慢性淋巴细胞性脉络丛脑膜炎病毒（LCMV）感染中表明，PD-1/L1 阻断后 T 细胞增殖爆发是由“干细胞样”CD8 T 细胞亚群提供的，然后这些细胞分化为终末分化效应器。这些终末分化的效应物在 PD-1/L1 阻断后有潜力杀死病毒感染或肿瘤细胞。在慢性 LCMV 感染中，干细胞样 CD8 T 细胞仅在次级淋巴器官中发现。同样，在这里，我们在肿瘤引流 LN 中以高频率发现这些细胞，但在肿瘤中以低频率发现这些细胞。RT 对该 T 细胞亚群的影响尚不清楚。有趣的是，肿瘤照射刺激 LN 中总 CD8 和干细胞样 CD8 T 细胞的增殖。当 LN 和肿瘤随后接受 RT 治疗时，远隔效应降低，我们发现辐照和未辐照肿瘤中总肿瘤特异性 CD8 T 细胞和干细胞样 CD8 T 细胞的数量均减少。
这些相关结果表明，肿瘤引流 LN 可能是通过充当干细胞样 CD8 T 细胞库、干细胞样 T 细胞扩增的部位以及它们可以从中填充肿瘤的部位来介导远隔效应的重要介质。
