HIV Vaccine Boost Induces Significant Antibody Response

An additional dose of HIV vaccine MVA-B four years after the last immunization induces significant immune responses in healthy volunteers, researchers from Spain report.

In an earlier trial involving healthy volunteers, three doses of HIV-modified vaccinia virus Ankara vector-expressing HIV-1 antigens from clade B (MVA-B) was safe, well-tolerated, and elicited moderate and durable HIV-specific T-cell responses in 75% of recipients and antibody responses in 95% of recipients.

Dr. Montserrat Plana from the University of Barcelona, in Spain, and colleagues in the RISVAC02boost study administered a fourth MVA-B boost four years after the last immunization in 13 of the original 24 vaccinated volunteers and analyzed the effect of this single-dose on the HIV- and vector-specific T- and B-cell immune responses.

Two and four weeks after the late MVA-B boost, about 45% of the volunteers had detectable HIV-specific CD4 and CD8 T cells, compared with only 12.5% immediately before the boost, according to the October 24 PLoS ONE online report.

 At four weeks, 80% had vaccine vector-specific CD8 T-cell responses, compared with 12.5% immediately before the boost. This responder rate declined to 50% at week 12.

HIV antibody responses peaked two weeks after the boost (with mean titers rising from 96.5 before the boost to 11,460) and subsequently declined to mean titers of 5,353 at week 4 and 1,946 at week 12.

Serum neutralizing activity against HIV-1 was negative in all volunteers immediately before the boost, but 10 of 13 volunteers (77%) were able to neutralize HIV-1 two weeks after the boost. Neutralizing-activity titers decreased until the end of follow-up at week 12.

All participants had at least one adverse event related to vaccination, but most events (96%) were grade 1 and only two (4%) were grade 2.

 “Our results show that one boost of MVA-B four years after receiving 3 doses of the same vaccine against HIV was safe, with more reactogenicity than previous immunizations,” the researchers conclude. “The late MVA-B boost induced moderate increases in the HIV-specific T-cell responses but significantly boosted the antibody responses to HIV-1 Env protein as well as the generation of HIV-1 neutralizing antibodies. Hence, MVA-based vaccines have the potential to be further explored as a suitable component of an optimal HIV vaccine regimen.”

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