Question

1. What are the differences between first, second, and third generation CAR-T receptors. Discuss whether the different intracellular domains of the receptors represent signal 1 or signal 2. Typed Answers only, thank you.

Answer 1

1. FIRST GENERATION- single structure from the CD3 ζ- chain or FcεRIγ from the intracellular domain for the first generation of CARs is the typical characteristics, which is the primary transmitter of signals from endogenous T cell receptor (TCR) . However, these CAR-T cells could not produce enough interleukin-2 (IL-2), so in order to kill tumor cells it was necessary to administer exogenous IL-2. Therefore, the first generation of CAR-T cell therapy transfected with single-chain receptors benefitted substantially from the accompanying administration of cytokines

2. Second generation

   Dual signal was the typical characteristics for T cell activation. Three different receptor types including the T-cell antigen receptors, cytokine receptors and co-stimulatory receptors are included in this progression. The first signal is the special signal that, triggered by the TCR, recognizes the antigenic peptide-MHC complex on the surface of antigen-presenting cells. The second signal is the co-stimulatory signal, produced by a co-stimulatory molecule such as CD28/B7, which promotes the IL-2 synthesis to complete the activation of T cells and avoid apoptosis.

3. Third generation

   The third-generation CARs were made by combining multiple signaling domains, such as CD3ζ-CD28-OX40 or CD3ζ-CD28-41BB, to augment potency with stronger cytokine production and killing ability. These scFv CD20-CD28-CD137-CD3ζ-CAR-T cells and HER2-CAR-T cells were used to treat lymphoma and colon cancer; however, outcomes were not improved relative to the second generation .The reason may be that the number of cases studied was small. Therefore, further studies are needed to explore the safety and efficacy of these treatments, and the selection of co-stimulatory molecules is also important.

the transmembrane domain and a CD3ζ signaling domain, which provides “signal 1” necessary for T-cell activation, paved its way as first-generation CAR T cells. Preclinical studies using first-generation CAR T cells directed against CD19 expressing B-cell malignancies and HER2/Neu showed promising results.

the second-generation CAR T cells were developed by coupling the intracellular portion of the construct with additional costimulatory signaling domains such as CD28 or 4–1BB, which provided “signal 2” for T-cell activation and further improved the efficacy of CAR T cells.