Assaying Potency of Novel Vaccines
Scientific Questions For Discussion
- Does vector replication (titer) and in vitro expression correlate sufficiently with immunogenicity to use these two surrogates for vector vaccine potency, or the latter for plasmid vaccine potency?
- How should potency of vaccines that will only be used in combination (i.e., heterologous prime-boost) be measured, since neither vaccine alone can result in protective efficacy? (Releasing a lot of vaccine predicated on another lot of a different vaccine would be problematic)
- For vaccines that are proposed to protect because they induce humoral immunity, what type of assay should be used (neutralization?) and against what targets (e.g., a panel of HIV viruses, the vaccine immunogen)? If neutralization potency must be demonstrated against a panel of viruses/malaria immunogens, how will specifications be set (must similar quantitative values be obtained with each lot for each member of the panel?)
- For vaccines that are proposed to protect because they induce cellular immunity, which assay should be used? Against what targets/antigens (e.g., multiple malaria proteins; multiple clades of HIV; HIV, TB, and malaria antigens for multi-valent products)? How quantitative are these assays ("suitably" as defined by the International Conference on Harmonisation in their Q5C and Q6B documents)?
- Can in vitro assays rather than bioassays be developed?
- What species should be used for the bioassays? (Does this depend on the assay - i.e., for cellular vs. humoral?)