Figure 2.

Structures of signaling transduction triggered by TCR, CAR, and bsAb. (A) In natural T cell, tumor antigen peptide is presented by APC and recognized by TCR. The associated CD3 molecule in TCR-CD3 complex will provide Signal 1 to T cell. The costimulatory signal (Signal 2) is provided by costimulatory molecules, such as CD28, 4-1 BB, etc. (B) In CAR-T cell, target antigens are directly recognized by CAR molecule’s scFv. Signal 1 and Signal 2 are provided by CD3ζ and costimulatory domain relatively in CAR’s intracellular domain. (C) In bsAb-T cell, bsAbs simultaneously recognize tumor antigen and CD3ϵ chain, and form a bridge between tumor cell and T cell. Similar to natural T cell, Signal 1 is still provided by TCR-CD3 complex. However, Signal 2 is lack in bsAb-mediated activation.