Cancer Research Lab

The highly attenuated modified vaccinia virus Ankara (MVA) induces an antibody response as robust as that induced by the conventional smallpox vaccine Dryvax, scientists report in the January Journal of Virology.

Because it has been attenuated through passage in chicken embryo fibroblasts, MVA replicates poorly in nonavian cells. Its safety profile indicates that it may be a useful alternative to Dryvax for immunocompromised individuals, individuals with atopic dermatitis, children, and pregnant women, for whom Dryvax is contraindicated. It is also being considered for immunization prior to Dryvax administration to reduce Dryvax reactogenicity.

However, there have been concerns that the genetic mutations and deletions in MVA may have affected its immunogenicity, lead author Dr. D. Huw Davies at the University of California, Irvine, and associates note. They theorize that “since the structural genes appear to be intact in MVA…critical targets for antibody neutralization have been retained.”

To compare the humoral responses elicited by MVA and Dryvax vaccines, the researchers applied blood serum from vaccinated humans and macaques to microarray chips containing vaccinia virus proteins.

“The MVA and Dryvax antibody profiles were broadly similar, with antibodies against membrane and core proteins being the best conserved,” the authors report.

Moreover, human and macaque immune profiles were very similar, verifying the macaque as “a close model for human antibody response.”

Dr. Davies’ team also tested a regimen involving a first vaccination with MVA followed by a Dryvax “boost,” to see if preexisting immunity to MVA would block Dryvax infectivity.

“We found that immunization of macaques with MVA followed by Dryvax engendered a profile indistinguishable from that achieved with Dryvax alone,” the team reports, indicating that “the MVA prime-boost regimen does not diminish the immunogenicity engendered by Dryvax.”