Sunday, September 15, 2013

NIAID-DVI: Sanofi CYD dengue vaccine--Where do we go from here? Jean Lang and Bruno Guy

Blog Series: NIAID-DVI

Sanofi Pasteur CYD dengue vaccine programme update
Jean Lang
Sanofi Pasteur

Immunological characterization of the Sanofi Pasteur dengue vaccine candidate: hypotheses and investigations to explain results of the Phase IIb proof of concept efficacy trial in Ratchaburi
Bruno Guy
Sanofi Pasteur

So by way of quick review:
  • the CYD-TDV vaccine is a yellow fever backbone with the prM and E genes replaced by each of the dengue serotypes.
  • There was good response in efficacy trials to dengue 1, 3 and 4 however the vaccine failed in illiciting a response to dengue 2 (response was about 30%) DESPITE having satsifactory PRNT titers...see previous blog post.
  • In 2012 there was a Phase IIb efficacy trial in Ratchaburi, Thailand
    • It showed the vaccine was safe.
    • It showed that it was possible to make an efficacious vaccine against dengue
    • It raised questions on the reference PRNT assay
    • It challenged some of the dengue vaccine development hypotheses
    • It reminds us how complex the disease is

  • Follow up analyses ongoing:
    • Sequencing clinical isolated from the Phase IIb study
      • These clinical isolates were different from the vaccine however they did cross neutralize in Vero cell-based in vitro assays.
      • Mel's Thought: That's a lot of unknowns in my head with respect to this is as 'out of nature' as we come...vero cells and in vitro assays. So how much we can extrapolate out to what's actually going on in nature I think will be limited.
    • Continued characterization of vaccine-induced cellular response
      • A trial conducted in Singapore confirmed the previous data showing the induction of broad serotype-specific Th1 responses dominated by IFN-gamma
      • Cellular responses persist for at least one year after vaccination
    • Assessment of safety
      • As of January 2013: more than 28,900  have received 1 or more vaccinations with CYD-TDV with no safety signals.
      • A safety analysis of 9 completed clinical trials  (5,300 vaccinees) confirmed good reactogenicity and safety profile (includes Phase IIb trial) with 2 years of active follow up.
  • The Phase III efficacy trials:
    • Vaccinations complete, active surveillance ongoing
    • Drop rate after 20 mos is <5% which is a big kudos to those involved in site preparation efforts, local teams and investigational team commitment.
    • Results expected in 2014.
and with that update from Jean...lets jump into Bruno's talk

So I really liked Bruno's abstract so I'm just going to quote it below rather than paraphrase and bullet like I do with most of the abstracts; I'll highlight some parts of it:
"The Sanofi Pasteur CYD tetravalent dengue vaccine candidate has been extensively characterized at the microbiological and immunological levels, both in preclinical models and in clinical trials. The results form these investigations showed that the vaccine induces broad and significant immune response. However, the proof-of-concept efficacy trial of this vaccine--a Phase IIb trial conducted in Thailand between 2009-2012 ( NCT00842530)--showed that this does not necessarily translate into protection against disease caused by all viruses of all 4 serotypes. Indeed, despite high PRNT50 titers against DENV2, protection was not observed against the circulating DENV2 viruses. The research program initiated to understand this unexpected result was built assuming that the underlying explanation involved one or more of four key factors influencing vaccine-induced immunity: the circulating viruses, the vaccine, the mosquito vector, and host immunity. Ongoing investigations, in partnership with academic laboratories, are exploring the contribution of : interference between vaccine serotypes, host immunity prior to vaccination, quantitative and qualitative immune responses (e.g. heterotypic and homotypic response; enhancing and neutralizing responses), and cell mediated immunity."
 The presentation and discussion around Bruno's information and update was quite lively as evidenced by my rapid fire note taking...

So there are many many things to consider with respect to why a dengue vaccine might fail for one or more's a translation of my rapid fire notes, much of which is mentioned in his abstract as well:
  • Vaccine/serotype interference
  • Pre-immunity/antigenic sin
  • Understanding the qualitative responses to the vaccine
  • Cell mediated immunity: recovery and before/after immune profiles
  • Interestingly, there seems to be a dominant serotype response. For monkeys it's dengue 1, for humans it's dengue 4...we need to look at ways to mitigate interference and dominance (mentioned in the first bullet above as well).
  • A multi-dose regime can be explored
  • "Protective immune response" has to be better or more explicitly defined.
  • Vaccine factors: structure, sequence, infectivity
  • Host factors: intrinsic and extrinsic need to be considered (e.g. immune status, environment/exposure, age, prior exposures to other viruses...)
  • Vector factors: competence, force of infection
  • Viral factors: structure, sequence, infectivity, virulence and I'm going to add...population complexity I'll get up on my quasi-soap box in a later blog.
If you interrogate my notes further (in above picture) you'll notice I write cells down...though I know nothing of specific cell types of what their potential affects would be, I do know, typically speaking, primary cells might give us a better idea of how 'wildtype' virus may act versus transformed cells which might be more stable in laboratory yet might make viral population diversity different than what you might see 'in the wild''s what I wrote:
  • Use of non-transformed primary cells...would that help?
  • CVI cells?
  • Fc-gamma-R+ cells? (more physiological cell line?)
  • NK cells
  • THP1 cells?
One final thought I had during all these conversations was...I was under the impression that the prM and E genes swapped into the yellow fever backbone originated from American version viruses--viruses 'originating' from the Americas. I wonder...given the replacement of American lineages with Asian lineages for dengue 2 (refs 1,2) if perhaps these 'inserts' might not be effective against an Asian circulating diversity? Lineage replacement is nothing new to dengue virus after all (refs 3-7).

For those who aren't familiar with the importance of clade/lineage replacement in dengue see refs 3-7 and if you are interested in the overall analysis of dengue virus evolution via phylogenetics Scott Weaver and Nikos Vasilakis have a nice article in Infection, Genetics and Evolution that should bring you up to speed: Molecular evolution of dengue viruses: Contributions of phylogenetics to understanding the history and epidemiology of the preeminent arboviral disease.


  1. Ty Hang VT, et al. (2010) Emergence of the Asian 1 Genotype of Dengue Virus Serotype 2 in Viet Nam: In Vivo Fitness Advantage and Lineage Replacement in South-East Asia. PLoS Negl Trop Dis 4(7): e757
  2. Rico-Hesse, et al., 1997. Origins of dengue type 2 viruses associated with increased pathogenicity in the Americas. Virology. 230: 244
  3. Zhang et al., 2005. Clade replacements in dengue virus serotypes 1 and 3 are associated with changing serotype prevalence. Journal of Virology. 79: 15123.
  4. Carrillo-Valenzo, E et al., 2010. Evolution of dengue virus in Mexico is characterized by frequent lineage replacement. Archives in Virology. 155: 1401.
  5. Philip M. Armstrong and Rebeca Rico-Hesse. Differential Susceptibility of Aedes aegypti to Infection by the American and Southeast Asian Genotypes of Dengue Type 2 Virus Vector-Borne and Zoonotic Diseases. June 2001, 1(2): 159-168
  6. Kukreti et al., 2008. Emergence of an independent lineage of dengue virus type 1 (DENV-1) and its co-circulation with predominant DENV-3 during the 2006 dengue fever outbreak in Delhi. Int'l Journal of Infectious Disease 12: 542
  7. Bennett et al., 2006. Molecular evolution of dengue 2 virus in Puerto Rico: positive selection in the viral envelope accompanies clade reintroduction. Journal of General Virology 87: 885