Today journal Immunity published new [short] study from Carl June's lab describing some functional and metabolic differences between CAR-T cells expressing CD28 or 4-1BB costimulatory domains.
It is not a particularly cutting-edge study. But since its focus is human CAR-T cells such limited experiments are still expected. Though I will anticipate that soon publications of in vitro studies on human primary cells [in top journals] will require incorporation of specific gene targeting experiments using CRISPR-Cas9 technology. Such experiments are now technically feasible and will be more informative.
In short, for this study the authors compared proliferation/expansion and metabolic/energy source of two CAR constructs, one with CD28 and another with 4-1BB (aka CD137) signaling domains, as shown below. FMC63 is anti-CD19 scFv and SS1 is anti-mesothelin scFv.
Human primary T cells were electroporated with these two CAR constructs. Efficacy of CAR expression was 90%.
Then, these transduced CAR-T cells were stimulated with magnetic beads coated with a recombinant anti-CD19 or mesothelin-Fc (such stimulation allowed selective activation of CAR-T cells via CAR construct). It revealed that CAR construct with 4-1BB domain imparted superior long-term expansion functionality on CAR-T cells.
Metabolic analysis revealed that unlike CD28 construct, 4-1BB CAR-T cells showed enrichment for genes responsible for lipid oxidation, implying 4-1BB signaling activates metabolic pathway resembling that of naive and memory T cells (involving mitochondrial oxidation of free fatty acids).
Indeed, transmission electron microscopy data confirmed that 4-1BB CAR-T cells were enriched for mitochondria.
In summary, this study provided supporting evidence that 4-1BB CAR construct endows T cells with superior expansion/persistence quality. Initial studies on this topic suggested that CD28 CAR construct displayed superior "effector" activity against tumor, while 4-1BB CAR construct showed longer survival [superior memory function]. Subject is not settled, but in discussion section, the authors do note that mixing both CAR constructs could provide better outcome compared to individual construct.