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Blog Series: NIAID-DVI

Pre-Clinical and clinical development of recombinant live attenuated tetravalent dengue vaccine (DENVax)
Jorge E Osorio
Takeda Vaccines

So Takeda Vaccines took over Inviragen and have been developing a tetravalent, live attenuated dengue vaccine called DENVax. It consists of a molecularly characterized, attenuated DENV-2 strain and three chimeras. The chimeras all have the backbone of the attenuated DENV-2 strain, but the prM and E genes have been swapped out with DENV-1, DENV-3 and DENV-4.





Rapid Fire:

•  DENVax has been shown safe in phase 1 clinical trials.
• Vaccine was highly immunogenic in non-human primates
• T cell responses with both T cell subsets producing proinflammatory cytokines, IFN-gamma, TNF-alpha and IL-2 one month after priming
• CD4+ and CD8+ T cells target structural and non-structural proteins.
• It is now in phase 1b clinical trial
• A clinical trial that usually tests a new treatment in a small number of patients in order to determine the safety and appropriate dose of the new treatment. Phase 1b trials may also test the treatment in combination with other drugs or agents. (source)
• Also being tested in phase 2 age-de-escalation clinical trial in four endemic countries.
• Phase 2: A clinical trial that usually tests a new treatment in a small number of patients who have the illness that the drug is designed to treat. Phase 2 trials measure efficacy as well as safety. (source)
• Prelim data suggests DENVax induced significant neutralizing antibody responses to all four dengue viruses after one or two administrations.
• Does not induce changes in serum chemistry or hematology
• No wildtype dengue challenge has been done yet with respect to this virus
• DENVax warrents further evaluation in Phase 2b/Phase 3 efficacy studies
• Phase 3: A clinical trial that definitively tests a new treatment, usually in a large number of patients who have the illness that the drug is designed to treat. Phase 3 trials measure efficacy as well as safety as compared to the standard of care. (source)

 Mels Thoughts:

• The backbone is an attentuated dengue 2 virus called PDK-53
• The phylogeneticist in me will probably tree that virus and compare it with other trees (if possible). Its a virus thats quite old, 1974 according to the accession on Genbank. Assuming I am looking at the right virus...viral strain S16803. This strain has also been passaged 53 times. Yowza! Great for attenuation...ok I get that but genetically Im sure quite far away from the currently circulating diversity of dengue. Perhaps this doesnt matter...perhaps it does.
• In the 53 passages 3 mutations were recorded, near the 5 UTR, NS1 and NS3 genes (indicated by black triangles in figure above). Surprising given the viruses Ive looked at like New Guinea C have several mutations relative to the Genbank reference. Specifically 9 non-synonymous mutations, 7 synonymous mutations, 1 gap and 2 bases which I had to call ambiguously because sanger and next generation sequencing data (454) kept conflicting and the overall site quality was low. So just surprising is all that after 53 passages this virus is mostly unchanged.
• Following on this vein of thought and given my lack of background in cell passaging, vaccine development and how to attenuate something I sought out  my Post Doc mentor MAJ/Dr. Richard Jarman who usually welcomes to chance to take a break from military or admin stuff to talk research and augment my understanding on all things infectious. Some good points he brought up:
1. We have no idea what the passage history on the virus, New Guinea C, is (which I just cleaned up following NGS sequencing).
2. The reason the PDK53 might not have as many mutations, aside from the fact its inherently different than New Guinea C, probably has to do with its passage history.
3. Full passage histories are a necessity when interpreting the changes in different viruses especially vaccine attenuated ones.
4. Passage history matters...youve got different cell types that will exert different forces of nature onto your virus hence promoting or extinguishing its ability to genetically adapt.
5. Cell type examples where passaging can be done: Vero cells, HeLa, Primary Dog Kidney Cells (PDK), MDCK (also of canine origin), hey did you know theres a cell line for zebrafish? Not applicable to viral passsaging of dengue, but interesting nonetheless. Ive seen work with dengue virus passaging in C6/36 cells mimicking the mosquito and dendritic (DC) cells mimicking the human. There have also been forays into macrophages...

A moment to digress: I am not going to elaborate on macrophages because my background is limited but I must say everytime I hear macrophages I think cell that eats things (ie. phagocyte) and then I get transported back to the first SciFi film my parents ever let me watch...from 1966 Fantastic Voyage. In that movie a guy gets eaten by a macrophage...