Tumor protein encoding [negatively charged] RNA-nanoparticles induced robust anti-tumor response

This week journal Nature published study that showed that negatively charged [cancer antigen encoding] RNA-nanoparticles are selectively take up by antigen-presenting cells in lymphoid tissues and induced robust type I IFN driven anti-tumor immune response to all tumors tested.

In earlier studies for in vivo delivery of RNA/DNA nucleic acids into antigen-presenting cells scientists have used positively charged [cationic] nanoparticles. However, such particles were mostly trapped within lungs rather than lymphoid tissues where most antigen-presenting cells, such as dendrtic cells, reside. Surprisingly, here the authors showed that negatively charged RNA-nanoparticles selectively accumulated in spleen within antigen-presenting cells after in vivo injection.

Strangely, accumulation of RNA-nanoparticles were reduced when mice were depleted of conventional DCs (cDCs) after diphtheria toxin injection (CD11-DRT BM chimera mice), even though these mice retain both plasmacytoid DCs (pDCs) and macrophages which can themselves capture RNA-nanoparticles.

RNA-nanoparticle injection was associated with rapid IFN-α secretion in a manner that depended on TLR7 expression.

In addition, RNA-nanoparticles induced robust priming of antigen-specific adaptive immune response.

More importantly, injection of tumor protein encoding RNA-nanoparticles delivered incredibly robust prophylactic and therapeutic anti-tumor effect (article has some preliminary  results from phase I study showing T cell priming in cancer patient after RNA-nanoparticle delivery).

In summary, the authors of this study believe that they found universal antigen delivery RNA-nanoparticle construct that induces robust adaptive immune response.

There is one thing that is puzzling about this study which the authors did not tried explain: in mice depletion of cDCs eliminated RNA-nanoparticle uptake and T cell priming. However, pDCs are not depleted in CD11c-DTR chimera mice and the data showed that pDCs are themselves could capture RNA-nanoparticles and are the main source of type I IFNs. So, the question then is why cDCs depletion has such disproportional effect?

David Usharauli

TH17-derived IL-26 punches holes in bacteria

T_H17 cells have been implicated in host's protection against extracellular bacteria. It is thought that T_H17 cells recruit neutrophils and other granulocytes to the site of bacterial infection who do the job.

However, a new study in Nature Immunology provided evidence that human T_H17 cells can directly eliminate extracellular bacteria via release of IL-26, a cationic peptide that punches holes in bacterial membrane.  

This is actually very well done study. Initially the authors showed that recombinant human IL-26 (rhIL-26) had a direct bactericidal activity in vitro.

Next, the authors showed that rhIL-26 had bactericidal activity in vivo as well.

The authors found that in humans IL-26 expression was restricted to T cells and that out of T cells, T_H17 cells expressed high level of IL-26 and that T_H17 cell supernatant showed IL-26 dependent bactericidal activity.

In addition to its direct bactericidal activity, rhIL-26 could activate human plasmacytoid DCs (pDCs) when combined with dying bacterial DNA.

Interestingly, the authors showed that rhIL-26 could also combine with human DNA and activate pDCs and to a lesser extent monocytes.

Further experiments revealed that rhIL-26 + human DNA conjugate were taken up by pDCs and could signal through TLR9.

Finally, the authors showed that T_H17 cells could activate human pDCs to produce IFN-α via IL-26 + DNA conjugate formation.

In summary, these results provided mechanistic model for direct bactericidal activity of T_H17 cells against extracellular bacteria. In addition, results with IL-26 + hDNA conjugates and pDCs activation revealed how T_H17 cells could be involved in amplification of immune response during autoimmune conditions.    

David Usharauli

Mutation in human interferon regulatory factor-7 (IRF7) predisposes to severe flu infection

Many times, unexpected reactions to infections (as in severe influenza) or innocuous agents (as in allergy) are based on unsuspected mutations in proteins relevant in immune regulation. 

New study in journal Science described the patient with inherited mutation in interferon regulatory factor-7 (IRF7) who developed severe inflammatory reaction to type A influenza (pandemic H1N1).

The authors showed that the patient inherited one mutated copy of IRF7 from each parent. Functionally, the patient's derived IRF7 lacked the ability to induce IFN-α in a reporter assay (parents were heterozygous and had normal IRF7 functions).

In ex vivo experiments the authors showed that patient's derived plasmacytoid dendritic cells (IFN-producing cells) did not respond to H1N1 infection by up-regulating IFN-α system (though small amount of IFN-β was produced).

Furthermore, the authors showed that the patient's derived fibroblast were highly susceptible in a viral replication assay compared to control fibroblast samples, suggesting that high viral titre in this patient could have produced clinical signs of severe flu.

In summary, this short and simple study provides molecular basis in understanding the disease outcome. In the future, when every newborn will have their DNA sequenced, the parents will be in a better position to carry out necessary prophylaxis and avoid any complications from infections or allergy.

David Usharauli