Moderna and Pfizer may be considered the front-runners in the effort to develop mRNA vaccines against COVID-19, but they’re not the only contenders in that race. Sanofi and its partner Translate Bio have also been working on a vaccine that uses mRNA to prompt an immune response—and now they have animal data that they believe provide strong backing for the phase 1/2 trial expected to start this quarter.

The vaccine candidate, MRT5500, was tested in mice and macaques in a two-dose regimen, and their immune responses were measured. The animals developed neutralizing antibodies against the spike protein on SARS-CoV-2, the virus that causes COVID-19, as well as a T-cell response, according to the study, which was published (PDF) on the journal preprint site bioRxiv.

The researchers measured a specific immune reaction called the “Th1-biased T cell response.” That’s because previous studies have suggested that mild cases of COVID-19 are associated with a rapid acceleration of Th1 cell responses while “TH2-biased responses have been associated with enhancement of lung disease” in mouse models of COVID-19 infection, the researchers explained in the study.

They found that both the mice and macaques had strong Th1-biased T-cell responses to MRT5500. They did not see evidence of inflammatory cytokines that have been linked to severe lung symptoms, suggesting a “lack of TH2 response” following vaccination, they wrote.

Sanofi and Translate teamed up in 2018 to develop mRNA vaccines in a deal worth $45 million upfront. In March, the two penned a second partnership to develop a COVID-19 vaccine, and, in June, Sanofi upped the ante on its original deal with Translate. Now that partnership is worth $300 million upfront, $125 million in equity and $1.9 billion in potential milestone payments.

And MRT5500 is not Sanofi’s sole attempt at a COVID-19 vaccine. Sanofi is also working with GlaxoSmithKline on a vaccine candidate that’s based on an adjuvant recombinant technology. That vaccine was selected for Operation Warp Speed, the U.S. government’s broad attempt to accelerate COVID-19 vaccine development. Sanofi and GSK won $2.1 billion in Warp Speed funding in July to speed up that effort. A phase 1/2 trial started in September.

Many of the companies working on mRNA vaccines have released data from preclinical studies. Last month, Pfizer and its partner BioNTech said their vaccine candidate, BNT162b2, elicited neutralizing antibodies against SARS-CoV-2, as well as antigen-specific CD4+ and CD8+ T cells, in nonhuman primates and mice. CureVac and Moderna also released animal data that they argued supported the advance of their mRNA candidates into clinical trials.

Unlike some of the other preclinical studies on mRNA vaccine candidates, Sanofi’s and Translate’s new trial was not a “challenge” study, meaning the animals were not infected with COVID-19. A challenge study is ongoing, and the companies plan to release full data in the future, a Sanofi spokesperson said in response to a query from Fierce Biotech.

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