This study compares second generation chimeric antigen receptors encoding signaling domains comprised of CD28, ICOS and 4-1BB. Here we report that certain CARs endow T cells with the ability to undergo long-term autonomous proliferation. Transduction of primary human T cells lentiviral vectors encoding some of the CARs resulted in sustained proliferation for up to three months following a single stimulation through the TCR. Sustained numeric expansion was independent of cognate antigen and did not require the addition of exogenous cytokines or feeder cells after a single stimulation of the TCR and CD28. Both gene array and functional assays link sustained cytokine secretion and expression of T-bet, EOMES and GATA-3 to the effect. Sustained expression of the endogenous IL-2 locus has not previously been reported in primary T cells. The growth is dependent on CAR structure and high expression of the CAR, which is necessary but not sufficient. The mechanism involves constitutive signaling through NF-kB, Akt, Erk and NFAT. The propagated CAR T cells retain a diverse TCR repertoire and transformation was not observed. The CARs with a constitutive growth phenotype displayed inferior antitumor effects and engraftment in vivo. Therefore the design of CARs that have a non-constitutive growth phenotype may be a strategy to improve efficacy and engraftment of CAR T cells. The identification of CARs that confer constitutive or non-constitutive growth patterns may explain observations that CAR T cells have differential survival patterns in clinical trials.
- Received October 1, 2014.
- Revision received December 23, 2014.
- Accepted December 26, 2014.
- Copyright © 2015, American Association for Cancer Research.