Description
Adoptive transfer of anti-CD19 chimeric antigen receptor (CAR)-engineered T cells has shown impressive clinical responses in patients with refractory B-cell malignancies. However, therapeutic effects of CAR-T cells targeting other hematologic malignancies and solid tumors are not yet satisfactory. Although inefficient tumor trafficking and multiple immunosuppressive molecules impede CAR-T cell effector responses, signals delivered by the current CAR constructs may still be insufficient to fully activate antitumor T cell functions. Optimal T cell activation and proliferation requires multiple signals including T cell receptor (TCR) engagement (signal 1), costimulation (signal 2), and cytokine engagement (signal 3). CAR genes developed to date contain a CD3z domain and costimulatory domain(s), but not a domain to transmit signal 3.