Engineering T cells to cellular factories with synthetic Notch receptors

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.

David Usharauli

Experimental malaria vaccine shows 55% efficacy in small trial

This week Nature Medicine published results from small trial involving controlled human malaria infection (CHMI) and experimental malaria vaccine developed by Sanaria (Sanaria Inc., Rockville, Maryland, USA). This vaccine based on attenuated Plasmodium falciparum sporozoite (abbreviated as PfSPZ vaccine) showed 55% efficacy at 1 year post-immunization.

Currently, only malaria vaccine available on market, RTS,S, has efficacy of ~ 22%. In this new study, scientists tested different dosages and routes of immunization for new PfSPZ vaccine as follows:

The results of the controlled human malaria infection are shown below. Here, healthy malaria-naive volunteers were first vaccinated and then received malaria infection from actual mosquitoes bites that carry malaria clone 3D7. The best outcomes were achieved with groups 4 and 5 (i.v. administration, 4 doses of 2.7 × 10⁵ PfSPZ).

Next step was to understand immunological correlates of protection. However, this task was quite challenging, as it turned out. All vaccination protocols, with the exception of i.m. immunization, induced anti-malaria Ab or T cell responses. However, when vaccine trial participants were divided based on blood parasitemia following malaria challenge, it was observed that participants without parasitemia developed higher levels of anti-malaria serum Abs.

At the cellular level, however, the only marker that correlated with vaccine efficacy was frequency of unstimulated Vγ9+Vδ2+ γδ T cells which comprises ~75% of γδ T cells in blood. Actually, the frequency of Vγ9+Vδ2+ γδ T cells in pre-vaccinated individuals was the only marker that correlated with vaccine efficacy in challenge model.

In summary, this study showed that there is still room to improve malaria vaccine. Vaccine efficacy of 55% in 1-year followup is a significant progress when considering that In 2015 there were an estimated 214 million clinical cases of malaria in the world. Another outcome of this study is that fact that it is quite hard to find or define immune correlates of protection and this is especially true for parasitic infection such as malaria or dengue.

David Usharauli

Genentech's Trojan horse destroys cocooned Staphylococcus aureus

Genentech did it again. It is truly amazing that since its inception in late 70s, Genentech, a bona fide biotech company, keeps its original spirit alive and encourages and supports R&D scientists to conduct and produce quality research befitting publication in top journals. I think in this regard Genentech does not have a single peer in whole of biotech industry.  

Just this week journal Nature published results from Genentech showing that it is possible to design anti-microbial antibody-antibiotic complexes capable of elimination of hard to reach intracellular microbes.

First, they showed that unlike freely floating extracellular S. aureus, intracellularly entrenched, hard to reach S. aureus are of clinical relevance. 

Indeed, in vitro experiments confirmed that intracellular S. aureus are resistance to conventional antibiotic application.

To overcome this resistance, Genentech's team designed antibody-antibiotic complex, called rifalogue, that was made of anti-S. aureus antibody and antibiotic rifampicin complex. The authors first showed that in vitro once rifalogue attached to S. aureus is internalized by cells rifampicin is released from complexes [in endosomes] and destroys S. aureus.

Finally, the authors confirmed effectiveness of this strategy against S. aureus in in vivo experiments as well.

In summary, these results (re)-opens the door for immunotherapy against infectious agents.

I would admit that for me data seems extremely clear-cut. This is a little bit concerning. I want to see these results confirmed in other labs. Another puzzling point is its mechanism of action. The model proposes that rifalogue works by engaging S. aureus with its Fab part and mammalian cells by its FcR. This suggests that rifalogue can't access or destroy S. aureus already cocooned within cells, but it could prevent freely floating S. aureus becoming intracellular. But regular rifampicin is capable of destroying freely floating S. aureus too. So this is a paradox for me [because results showed that rifalogue was still highly effective, even after delay of 24h, against "potentially" intracellular S. aureus]. 

David Usharauli