Background:
Recent studies have indicated that HIV-1 infected infants and children more frequently develop broadly neutralizing antibodies (bnAbs) and do so faster than adults. However, the cellular and molecular mechanisms of infant bnAb development are not fully understood. We sought to develop a neonatal model to reproducibly study bnAb induction.
Methods:
Thirteen therapy-naïve infant rhesus macaques (RMs) were infected soon after birth with a pathogenic Simian-HIV (SHIV) designed to elicit V2-apex and V3-glycan bnAbs. Viral load was monitored by quantification of plasma SIV RNA. Envelope (Env) evolution was evaluated by single genome sequencing of circulating viral envs, and plasma Abs were functionally characterized. We performed flow-cytometry phenotyping of lymph node (LN)-derived germinal center (GC) cells, and single-cell transcriptomics of peripheral blood cells (PBMCs) to interrogate neonatal host immunity associated with bnAb induction.
Results:
All infant RMs were successfully infected; 8 RMs had viral loads ranging from 103-107 RNA copies/ml for 12-24 months of infection, but 5 RMs developed partial or full control of viremia. In 11 RMs studied, we observed rapid onset of mutations at glycan hole sites D133, T138, H289, and P291. By month 6 post-infection, a fraction of circulating viruses in 8/11 RMs studied carried env mutations in and around the C-strand of the V2-apex (residues 166-172), and by 18-24 months post-infection, the majority of sequences from 7/8 RMs contained mutations at residue 169 that is a key contact residue of V2-apex bnAbs. Additionally, mutations D325N and I326T in V3 324GDIR327-motif also emerged in two RMs, indicative of possible development of GDIR-targeted and polyclonal b/NAbs in these two RMs. Of 13 RMs, all of them generated plasma Abs that neutralized tier 2 or difficult-to-neutralize autologous SHIV, while 8/13 (62%) RMs also generated Abs that potently neutralized 1-4 heterologous tier 2 HIV-1 isolates. RMs that developed heterologous NAbs had increased frequency of GC Env-reactive B cells and total follicular-helper CD4 T cells overtime, as well as increased expression of genes in PBMCs associated with activated immune cells and inflammation.
Conclusions:
Thus, SHIV infection of neonatal RMs elicited plasma nascent bnAbs that may affinity mature overtime to develop neutralization breadth. Moreover, we define a neonatal model of nascent bnAb induction that may provide insights for pediatric HIV-1 vaccine designs.