Introduction: Given the complexities of HIV infection and the HIV genetic heterogeneity, a successful HIV vaccine should elicit broad adaptive and innate immune responses. Vaccine prime-boost platforms may achieve this goal. Several factors including selection of antigen, type of vector, delivery route, dose, adjuvant, boosting regimen, order of vector injection, and intervals between vaccinations influence the outcome. Areas covered: We reviewed the literature on the latest findings of the various prime-boost HIV vaccine clinical trials, with particular emphasis on the most advanced and promising strategies. Expert opinion: Data suggest that heterologous may be better than homologous prime-boost regimens for protection. The most advanced strategies to have reached efficacy trials use either canarypox vector (ALVAC) boosted by adjuvanted gp120 protein or adenovirus (Ad26) vector expressing mosaic antigens boosted by gp140 protein. DNA prime and vectors and/or protein boost regimens are at less advanced development stage. These regimens, while imperfect (efficacy ≥50%), could contribute substantially to the control of HIV epidemics as a part of a comprehensive HIV prevention program. To ensure prompt vaccine access in populations with the greatest need, attention should be given to post-efficacy activities necessary to achieve appropriate uptake and implementation of effective vaccines.
Keywords: ALVAC; Ad26; HIV vaccine; efficacy; envelope protein; immune correlates of risk; mosaic; prime-boost; viral vector.