Ng, Tay, and Li et al. tested the antitumor efficacy of T cells transduced to stably express a second generation CAR consisting of NKG2D ectodomain linked to 4-1BB and the cytoplasmic domain of human DAP-12. The inclusion of 4-1BB enhanced long-term T cell expansion, decreased the expression of exhaustion markers, enhanced the formation of memory subsets, and increased tumor control. The inclusion of DAP12 (versus CD3ζ) showed similar antitumor efficacy, but led to lower production of cytokines both in vitro and in tumor-bearing mice, and did not induce xenogeneic GVHD, suggesting that the inclusion of DAP12 could mitigate the effects of CRS.
Contributed by Lauren Hitchings
ABSTRACT: Cytokine-related toxicity associated with the use of highly active chimeric antigen receptor T cells (CAR-T cells) is a significant clinical problem. By fusing the natural killer group 2D (NKG2D) ectodomain to 4-1BB and the DAP12 cytoplasmic domain containing only one immunoreceptor tyrosine-based activation motif, we have developed a 2nd-generation (2nd-Gen) NKG2D CAR for stable expression in human T cells. When compared to T cells modified with NKG2D CAR containing the commonly used CD3ζ activation domain, T cells expressing the NKG2D-DAP12 CAR stimulated lower level release of interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin (IL)-2 during tumor cell lysis and their proliferative activity was lower upon repeated antigen stimulation, although no difference between the two CARs was observed in mediating in vitro tumor cell lysis. In tumor-bearing NSG mice, both types of CAR-T cells displayed similar anti-tumor activity, being able to completely eradicate established solid tumor xenografts. However, treatment with the NKG2D-CD3ζ CAR-T cells led to the death of most mice from xenogeneic graft versus host disease starting 30 days post-CAR-T cell injection, which was associated with a higher level of cytokine release, whereas all the mice treated with the NKG2D-DAP12 CAR-T cells survived well. Thus, the incorporation of the DAP12 activation domain in a CAR design may possibly provide a potential clinical advantage in mitigating the risk of cytokine release syndrome (CRS).