HIV Vaccine Development
A successful HIV vaccine remains a light at the end of the tunnel, but that light may be growing brighter. Among the best examples of this renewed hope can be found in the research conducted by the HIV Vaccines Trial Network (HVTN), which has made incremental but important developments with some of its latest HIV vaccine candidates.
In a presentation at the AIDS Vaccine 2012 Conference, Nicole Frahm, Ph.D., highlighted the latest research developments by comparing the immunogenicity -- the ability to induce immune responses -- of some of these HVTN vaccine candidates.
Two of the DNA vaccines seemed to elicit better T-cell responses when combined with an adjuvant (a substance that enhances immune-stimulating properties) and electroporation (a process that creates temporary holes in cell membranes for better permeability), Frahm said. This suggests a synergistic effect in which the sum is better than each separate approach.
Poxvector vaccines elicited a better T-cell response when heterologous regimens were given -- i.e., when different vaccine candidates were administered to the same volunteer in succession, the first as a "prime" and the second as a "booster." Prime-boosting is a common method used in vaccine research to induce different immune reactions and enhance overall response.
Compared to heterologous vaccine regimens, higher antibody response rates were seen when homologous regimens (just one vaccine candidate as both prime and booster) were given. Again, these results support the contention that it will be crucial to find the combination that has the best synergistic effect.
Frahm also discussed two of the most promising vaccine candidates, NYVAC and MRKAd5 (or simply "Ad5"), each of which uses a weakened pathogen as a vector. The NYVAC vaccine candidate (a weakened poxvirus) works better as a booster, rather than a prime, when combined with Ad5 (a weakened cold virus), Frahm said, suggesting that the order in which vaccine doses are given play a role in immune response.
Ad5 remains the most potent vaccine candidate, in terms of eliciting T-cell and antibody responses. Out of all the candidates, it is the farthest along: It is currently in a phase 2b trial, with results expected next year.