Chimeric antigen receptor (CAR) T cell therapy has achieved extraordinary success in eliminating B cell malignancies; however, so far, it has shown limited efficacy in the treatment of solid tumors, which is thought to be due to insufficient CAR T cell activation. We hypothesized that the transcription factor PU.1, a master regulator of innate cell functionality, may augment pro-inflammatory CAR T cell activation. T cells were engineered with a CEA-specific CAR together with the constitutive expression of PU.1. CAR-redirected T cell activation was recorded for canonical functionality in vitro under conditions of prolonged repetitive antigen exposure. Ectopic PU.1 expression in CAR T cells upregulated the costimulatory receptors CD40, CD80, CD86, and CD70, which, unexpectedly, did not augment effector functions but hampered the upregulation of 4-1BB, decreased IL-2 production, reduced CAR T cell proliferation, and impaired their cytotoxic capacities. Under “stress” conditions of repetitive engagement of cognate tumor cells, CAR T cells with ectopic PU.1 showed reduced persistence, and finally failed to control the growth of cancer cells. Mechanistically, PU.1 caused CAR T cells to secrete IFN-β, a cytokine known to promote CAR T cell attrition and apoptosis. Collectively, PU.1 can polarize the functional capacities of CAR T cells towards innate cells.
嵌合抗原受体（CAR）T细胞疗法在清除B细胞恶性肿瘤方面取得了显著成功；然而，迄今为止，其在实体瘤治疗中疗效有限，这被认为与CAR T细胞活化不足有关。我们假设转录因子PU.1（一种先天细胞功能的主调控因子）可能增强CAR T细胞的促炎性活化。通过构建同时表达CEA特异性CAR与组成型PU.1的工程化T细胞，在长期重复抗原暴露条件下，于体外记录了CAR导向T细胞活化的典型功能特征。PU.1在CAR T细胞中的异位表达上调了共刺激受体CD40、CD80、CD86和CD70，但意外的是，这并未增强效应功能，反而阻碍了4-1BB的上调，降低了IL-2的产生，减少了CAR T细胞增殖并削弱其细胞毒性能力。在重复接触同源肿瘤细胞的“应激”条件下，异位表达PU.1的CAR T细胞持续性下降，最终未能抑制癌细胞生长。机制研究表明，PU.1促使CAR T细胞分泌IFN-β——一种已知会促进CAR T细胞耗竭和凋亡的细胞因子。综上所述，PU.1可将CAR T细胞的功能特性极化向先天细胞方向转变。
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