PROJECT SUMMARY
Developing a preventative HIV vaccine remains a global health priority and to be effective will most likely
need to elicit broadly neutralizing antibodies (bnAbs). HIV bnAbs are derived from rare, unmutated common
ancestor (UCA) B-cell precursors in elite HIV+ human repertoires. To reproducibly activate such UCA+ B-cells
to affinity mature and acquire bnAb function, `Germline Targeting' (GT) vaccine protocols are being developed
typically for a single bnAb lineage, and only induce sporadic and/or weak serum bnAb responses using
protracted boosting schemes that are clinically impractical. Clearly, more efficient GT regimens are needed
that can elicit multiple bnAb specificities, and appropriate animal models to track and follow up on promising
lead neutralization signals in the serum. We recently equipped a new membrane (m)Env liposome (MEL)
platform with a GT mutation in mEnv that reproducibly induces tier 2 serum neutralization using semi-
polyclonal CH103 UCA knockin (KI) mice after only two boosts. This represents the first GT regimen to elicit a
`CDRH3 dominated' nAb response to the CD4-binding site (CD4bs) in which UCA B-cells are also under
anergy control. The overall objective of this proposal is to build on this novel GT platform, to both improve
HCDR3-dominated specific responses, and to adapt it to target the relatively better-studied VH restricted-
targeted CD4BS cluster and HIV's Fusion Peptide (FP) domain. We hypothesize that GT MEL sequential
priming modalities (and mRNA-LNPs) tested in strategically selected CD4BS bnAb UCA knock in models
(while manipulating frequencies and tracking development of multiple UCA lineages), will help us identify a
vaccine regimen that will elicit HIV serum neutralization in “higher bar”, fully polyclonal human Ig pre-clinical
animal models. Specifically, in Aim 1, we will optimize the existing MEL-based GT regimen, as above, in the
lead CH103 UCA KI model. Then, in Aim 2, we will test the ability of mEnv modalities first to drive physiological
numbers of `VRC01-class' CH31 UCA precursors towards breadth in WTàCH31 KI chimeric mice, and then
evaluate CH31/CH103 UCA multi-GT mEnv regimens promoting elicitation of both CD4BS bnAb lineages (in
CH31àCH103 chimeras). Finally, in Aim 3, we will test the ability of FP nanoparticle (FP-NP) prime-mEnv
boosting regimens to elicit serum nAb responses in WT and UCAàWT chimeric mice, and ultimately test the
best FP and CD4BS regimens combined in Omni Mice and Omni Rats, which express fully polyclonal,
unrearranged human V (D)J repertoires. These studies, even if partially successful, will reveal the serum HIV
nAb breadth that can be elicited by next-generation mEnv vaccine platforms against multiple overlapping
targets on the CD4BS and FP, and may be advantageous in overcoming Ig repertoire holes across individuals,
preventing viral escape, and requiring less overall boosting.
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