As shown in Fig. technology to mimic long-lasting PD-1 blockade. We constructed PD-1 steadily clogged chimeric antigen receptor altered T (CAR-T) cells, and with these cells we can clearly study the effects of PD-1 knockdown on T cell function. The anti-tumor function, proliferation ability and differentiation status of PD-1 silenced CAR-T cells were analyzed by in vitro and animal experiments. Results Relating to short-term in vitro results, it was reconfirmed the resistance to programmed death-ligand 1 (PD-L1)-mediated immunosuppression could be enhanced by PD-1 blockade. However, better anti-tumor function was not offered by PD-1 clogged CAR-T cells in vitro or in Bumetanide vivo experiments. It was found that PD-1 knockdownmight impair the anti-tumor potential of CAR-T cells because it inhibited T cells proliferation activity. In addition, we observed that PD-1 blockade would accelerate T cells early differentiation and prevent effector T cells from differentiating into effect memory space T cells, and this might become the reason behind the limited proliferation of PD-1 silenced CAR-T cells. Conclusion These results suggest that PD-1 might perform an important role in keeping the proper proliferation and differentiation of T cells, and PD-1 silencing would impair T cells anti-tumor function by inhibiting their proliferation activity. Electronic supplementary material The online version of this article (10.1186/s40425-019-0685-y) contains supplementary material, which is available to authorized users. Keywords: PD-1 blockade, Chimeric antigen receptor altered T cells, T cell proliferation, T cell differentiation, Persistence Background Chimeric antigen receptor altered T (CAR-T) cells show potent antitumor activity against hematological malignancies [1C4]. However, the translation of this success to solid tumors is Bumetanide still gloomy . In the treatment of solid tumors, CAR-T therapy is definitely faced with enormous difficulties, such as the immunosuppressive milieu [6, 7]. In the establishment of the suppressive milieu, programmed death-1 Bumetanide (PD-1)/ programmed death-ligand 1 (PD-L1) axis is definitely thought to play a key part [6, 8, 9]. As an inhibitory receptor, PD-1 inhibits T cells activity by interesting with its ligands [10, 11]. It has been widely confirmed that PD-1 obstructing antibodies could help cytotoxic T lymphocytes (CTL) resist immune suppression and enhance anti-tumor functions [12C14]. And PD-1 antibodies were also reportedly able to save CAR-T cells from exhaustion and senescence [15, 16]. In addition to antibodies, intrinsic PD-1 obstructing by genetic changes was also proved to be effective [17, LEFTY2 18]. Consequently, PD-1 blockade is considered to be a promising method to improve CAR-T cell function and is explored in many ongoing clinical tests. Although this concept offers solid theoretical basis, so far few medical results clearly show its authenticity. This dilemma influenced us to re-cognize PD-1 blockade. In fact, the conclusion that PD-1 blockade can improve T cell function is mostly based on the results of short-term experiments or observations; however, the PD-1 obstructing in medical practice is usually long-lasting. This means that there is a cognitive space between our knowledge and medical practice, and the missing link is definitely that we still dont know how long-lasting PD-1 blockade will affect T cell function. Actually, some studies possess suggested that long-lasting PD-1 blockade might induce bad opinions regulations. It has been reported that persistently obstructing PD-1 Bumetanide (both with antibodies and with genetic changes) would up-regulate T cell immunoglobulin and mucin-domain comprising-3 (TIM-3) and lymphocyte activation gene-3 (LAG-3) [19, 20], which forms an important mechanism to resist PD-1 blockade. Inside a portion of individuals, a novel pattern of hyperprogressive disease (HPD) induced by anti-PD-1 treatment was observed [21, 22]. It has also been reported that PD-1 knockout would promote exhaustion of CD8-positive T cells, and PD-1 was believed to play an important part in avoiding T cells from overstimulation and senescence . Although these studies shown the possibility of the bad rules, the effects of long-lasting PD-1 blockade on T cell functions have not been systematically evaluated, which we think is very necessary. To this end, we constructed dual-promoter lentivirus vectors which allowed us to simultaneously communicate the PD-1 focusing on short hairpin RNA (shRNA) and CAR molecule (ZsGreen adopted). With this approach, we could clearly analyze.