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Genetically engineered RSV vaccine shows early promise
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A live-attenuated respiratory syncytial virus vaccine candidate lacking a specific protein may decrease viral replication while inducing a protective immune response in humans, according to preliminary clinical trial results.
“Efforts to develop live-attenuated [respiratory syncytial virus (RSV)] vaccines have been under way since the 1970s,” researchers wrote in Science Translational Medicine. “In the past, achieving a balance between attenuation and immunogenicity has proved difficult: some live-attenuated RSV vaccine candidates have been insufficiently attenuated, whereas others were highly attenuated but insufficiently immunogenic. In addition, some candidate vaccines have exhibited genetic instability, with a partial loss of attenuating mutations.”
Improving upon previous RSV vaccine candidates, researchers deleted the M2-2 protein from the virus, which resulted in decreased viral RNA replication without sacrificing immunogenicity. The modified virus also appears to be stable, according to the researchers.
Ruth A. Karron
“An RSV vaccine with this M2-2 deletion could tip the balance toward a better immune response, which is what we predicted based on earlier laboratory studies,” Ruth A. Karron, MD, director of the Center for Immunization Research at Johns Hopkins Bloomberg School of Public Health, said in a press release. “From what we have seen in this small preliminary study in young children, this experimental vaccine is working as we hoped it would.”
Developed by the National Institute of Allergy and Infectious Diseases, the MEDI ΔM2-2 vaccine was tested sequentially in 15 adults, 15 RSV-seropositive children aged 15 to 59 months and 30 RSV-negative infants and children aged 6 to 24 months. The vaccine was administered intranasally, and participants were followed for 28 to 56 days.
According to the researchers, one RSV-seropositive child and no adults showed evidence of infection with vaccine virus, which is consistent with attenuation.
When results from RSV-seronegative children were compared with those from children who received a previously leading live-attenuated RSV candidate vaccine, Karron and colleagues found that viral shedding was significantly more restricted with MEDI ΔM2-2 while achieving a greater neutralizing serum antibody responses to RSV (geometric mean titer = 1:97).
Additionally, surveillance data showed that several MEDI ΔM2-2 recipients had “substantial” antibody responses during the subsequent RSV season but without reported illness.
“These early clinical data are exciting, and make us think differently about the development of live vaccines for RSV,” Karron said in the release. “If this research is borne out in future studies, we could be less than a decade away from a safe and effective live-attenuated vaccine for RSV.” – by John Schoen
Disclosure: Karron reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
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