This week journal Cell published new article from Wendell Lim's lab at UCSF (also a founder of Cell Design Labs) that reads like a science fiction story. It was a continuation of previous work that focused on developing customized molecular architecture based on Notch core regulatory domain attached to synthetic extracellular recognition and intracellular transcriptional domains (SynNotch). By changing extracellular and intracellular domains one can design T cells producing molecule of interest upon engagement with specific ligand.
For this new paper, the authors managed to transform T cells into cellular factories which upon specific SynNotch stimulation were making and expressing (a) cytokines (b) checkpoint inhibitors (c) bi-specific antibodies (d) CARs (e) transcriptional factors (f) lytic granules.
Basically, T cells are transfected with vector containing SynNotch module linked to promoter encoding molecule of interest. The most of the experiments were done in vitro. One in vivo experiment the authors put in paper was similar in overall design to one previously reported. In short, NSG mice were injected with K562 tumor expressing GFP + CD19 or only CD19. Afterwards T cells containing SynNotch module designed to recognize GFP were infused. Upon GFP recognition these T cells could start expressing soluble Blinatumomab, a-CD19/CD3 BiTE molecule that in turn can engage conventional TCR and produce T cell activation. Indeed, the authors showed that only tumor cells expressing both GFP and CD19 were efficiently controlled by engineered T cells (though its is not clear why soluble BiTE antibodies would not diffuse freely and engage single CD19+ tumors as well).
While all these results look very impressive, it nonetheless lack some of the critical elements that are required to properly analyze beneficial effect of SynNotch. For example, in vivo experiments were done in mice that does not express tumor antigens naturally (anti-CD19 here was human in origin). So we can't tell how such T cells would behave in "human-like" environment. Similarly, in vitro experiments with SynNotch-anti-HER2 expressing T cells are of dubious value without testing it at least in humanized mouse models.