# Project 1. Optimization and in vivo evaluation of HIV-1 Env trimer sortase A-conjugated nanoparticles

> **NIH NIH U19** · DUKE UNIVERSITY · 2024 · $826,400

## Abstract

ABSTRACT-PROJECT 1
Previous vaccines have been unable to elicit HIV-1 broadly neutralizing antibodies (bnAbs) in humans. Two of
the reasons for this failure are that bnAb precursor B cells are often rare and that the B cell receptors on those
rare B cells require extensive somatic mutation to evolve into high-affinity bnAbs. A subset of these somatic
mutations—termed improbable mutations—have a low probability of being made by the somatic mutation
machinery due to codon bias and positioning of somatic mutation recognition motifs. Our central hypothesis
for eliciting bnAbs is that immunogens must have a higher affinity for Abs with the required improbable
mutations than for Abs lacking these key mutations. Moreover, we hypothesize that mutation-guided vaccine
design will need to engage low-affinity rare bnAb precursors and, then, through immunization with sequential
immunogens, select for Abs acquiring the somatic changes requisite for a broad neutralization phenotype. We
and others have observed that multimerizing HIV-1 envelope (Env) immunogens on nanoparticles (NPs) can
increase Ab titers and affinity maturation of HIV-1 bnAb lineages. However, Env is unstable and can adopt
non-native conformations on the surface of NPs, leading to undesired Ab responses. Additionally, NPs bearing
HIV-1 envelope can be of low protein yield. To overcome these pitfalls, we have developed an innovative,
rapid platform that uses the enzyme sortase A to covalently link well-folded, cleaved Env trimers to self-
assembling ferritin protein NPs. These sortase A-conjugated NPs (scNPs) maintain near-native Env trimer
conformation, allowing avid selection of improbable mutations in evolving bnAb lineages. In humanized mice,
we used a scNP displaying an engineered Env trimer called CH505.M5 G458Y to select for a key improbable
mutation required for maturation of the 8ANC131/CH235 class of CD4 binding site (CD4bs) bnAbs. The same
scNP elicited CD4bs monoclonal neutralizing Abs and serum neutralizing Abs in nonhuman primates (NHPs).
To further guide these Abs to develop neutralization breadth, we have generated a boosting Env trimer scNP
immunogen called CH505.TF scNP and have a third boosting Env under development. In CH505.M5 G458Y
scNP-primed NHPs, CH505 TF scNP immunization boosts neutralizing Ab titers against multiple CH505
viruses. This IPCAVD will generate a CH505 TF scNP boosting immunogen and a second sequential Env
trimer scNP boosting immunogen for a Phase I trial. In Specific Aim 1, Project 1 will determine an optimal NP
boosting regimen to broaden the neutralization capacity of current CD4bs B cell lineages in humanized mice.
In Specific Aim 2, we will compare conjugation efficiency and immunogenicity of scNPs assembled from
research-grade or development-run ferritin and sortase A components from Project 2. Lastly, Specific Aim 3
will demonstrate the induction of CD4bs lineages in NHPs using the prime-boost strategy and cGMP scNPs
proposed for the Phase I trial...

## Key facts

- **NIH application ID:** 10738740
- **Project number:** 5U19AI160546-03
- **Recipient organization:** DUKE UNIVERSITY
- **Principal Investigator:** KEVIN O SAUNDERS
- **Activity code:** U19 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $826,400
- **Award type:** 5
- **Project period:** 2021-12-17 → 2026-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10738740

## Citation

> US National Institutes of Health, RePORTER application 10738740, Project 1. Optimization and in vivo evaluation of HIV-1 Env trimer sortase A-conjugated nanoparticles (5U19AI160546-03). Retrieved via AI Analytics 2026-05-28 from https://api.ai-analytics.org/grant/nih/10738740. Licensed CC0.

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