Immunotherapy with CAR-Modified T Cells: Toxicities and Overcoming Strategies

Figure 3

Summary of the targeted activation strategies for T cells to overcome toxicities. (a) In the dual targeting CAR-modified T cells, the T cells are transduced with both a CAR that provides suboptimal activation upon binding of one antigen and a chimeric costimulatory receptor (CCR) that recognizes a second antigen. (b) T cells are designed with a bispecific tandem CAR (TanCAR), in which two distinct antigen recognition domains are present in tandem by a Gly-Ser linker. (c) T cells can be engineered with an inhibitory receptor, carrying an intracellular domain from PD1 or CTLA-4, which can be triggered by an antigen expressed on normal cells, allowing T-cell inhibition outside the tumor. (d) Design of a synNotch AND-gate circuit that requires T cells to sense two antigens to activate. It works in two sequential steps: (1) The synNotch receptor is engineered to allow the T cell to recognize TAA1. Upon ligand recognition by the synNotch receptor, an orthogonal transcription factor is cleaved from the cytoplasmic tail, and (2) the T cell expresses a CAR directed towards TAA2. The cleaved transcription factor primes CAR expression. If A and B are present, the T cells can activate and kill the target tumor. (e) The on-switch CAR design distributes key components from the conventional CAR into two physically separate polypeptides that can be conditionally reassembled when a heterodimerizing small-molecule agent is present. Only in the presence of a heterodimerizing small molecule can they conditionally reassemble. (f) Antibody-based switches are engineered by the introduction of peptide neo-epitopes (PNE) at defined locations in an antigen-specific antibody. Given that the PNE is not an endogenous tissue or antigen , the activation of the sCAR-T cell is therefore strictly dependent on the presence of the switch. scFV: single-chain variable fragment of antibody; CM: costimulatory molecule; ITAM: immune-receptor tyrosine-based activation motif; TAA: tumor-associated antigen; NTA: normal tissue antigen; CAR: chimeric antigen receptor; CCR: chimeric costimulatory receptor; iCAR: inhibitory CAR; TanCAR: tandem CAR; synNotch CAR: synthetic notch CAR; TF: transcription factor; PNE: peptide neo-epitope; Fab: fragment of antigen binding.

(a) CAR + CCR

(b) TanCAR

(c) CAR + iCAR

(d) synNotch CAR

(e) On-switch CAR

(f) Antibody-based CAR