Adoptive cellular therapy is rapidly improving immunotherapy in hematologic malignancies and several solid tumors. Remarkable clinical success has been achieved in chimeric antigen receptor (CAR)-T cell therapy which represents a paradigm-shifting strategy for the treatment of hematological malignancies. However, many challenges such as resistance, antigen heterogeneity, poor immune cell infiltration, immunosuppressive microenvironment, metabolic obstructive microenvironment, and T cell exhaustion remain as barriers to broader application especially in solid tumors. Encouragingly, the development of new approaches such as multidimensional omics and biomaterials technologies was aided to overcome these barriers. Here, in this perspective, we focus on the most recent clinical advancements, challenges, and strategies of immune cellular therapy in solid tumor treatment represented by CAR-T cell therapy, to provide new ideas to further overcome the bottleneck of immune cell therapy and anticipate future clinical advances.
Programmed cell death 1 (PD-1)/programmed cell death 1 ligand (PD-L1) blockade has shown promising effects in cancer immunotherapy. Removing the so-called " brakes” on T cell immune responses by blocking the PD-1/PD-L1 check point should boost anti-tumor immunity and provide durable tumor regression for cancer patients. However, 30%–60% of patients show no response to PD-1/PD-L1 blockade. Thus, it is urgent to explore the underlying resistance mechanisms to improve sensitivity to anti-PD-1/PD-L1 therapy. We propose that the mechanisms promoting resistance mainly include T cell exclusion or exhaustion at the tumor site, immunosuppressive factors in the tumor microenvironment (TME), and a range of tumor-intrinsic factors. This review highlights the power of studying the cellular and molecular mechanisms of resistance to improve the rational design of combination therapeutic strategies that can be translated to the clinic. Here, we briefly discuss the development of PD-1/PD-L1 blockade agents and focus on the current issues and future prospects for potential combinatorial therapeutic strategies that include anti-PD-1/PD-L1 therapy, based upon the available preclinical and clinical data.
Chimeric antigen receptor-natural killer (CAR-NK) cells have emerged as another prominent player in the realm of tumor immunotherapy following CAR-T cells. The unique features of CAR-NK cells make it possible to compensate for deficiencies in CAR-T therapy, such as the complexity of the manufacturing process, clinical adverse events, and solid tumor challenges. To date, CAR-NK products from different allogeneic sources have exhibited remarkable anti-tumor effects on preclinical studies and have gradually been applied in clinical practice. However, each source has advantages and disadvantages. Selecting a suitable source may help maximize CAR-NK cell efficacy and increase the feasibility of clinical transformation. Therefore, this review discusses the development and challenges of CAR-NK cells from different sources to provide a reference for future exploration.
