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Development of a HIV-1 vaccine is a major global priority. The yellow fever virus (YFV) attenuated vaccine 17D is among the most effective of currently used vaccines. However, the stability of the YFV17D vector when carrying non-flavivirus genes has been problematic. We have constructed and expressed HIV-1 Env in YFV17D with either single transmembrane (STM) or double transmembrane (DTM) YFV E protein domains for the development of anti-HIV antibodies. Here we describe modifications of the YFV17D vector such that HIV-1 Env gp120 is expressed in up to 5 passages in Vero cells. Immunization with recombinant YFV17D vector prime followed by HIV-1 CH505 TF gp120 protein boosts were able to induce neutralizing antibodies for a HIV-1 tier 1 isolate in mice. This modified YFV vector may be a starting point for constructing HIV-1 vaccine candidate priming vectors.

Despite the wide availability of antiretroviral drugs, more than 250,000 infants are vertically infected with HIV-1 annually, emphasizing the need for additional interventions to eliminate pediatric HIV-1 infections. Here, we aimed to define humoral immune correlates of risk of mother-to-child transmission (MTCT) of HIV-1, including responses associated with protection in the RV144 vaccine trial. Eighty-three untreated, HIV-1–transmitting mothers and 165 propensity score–matched nontransmitting mothers were selected from the Women and Infants Transmission Study (WITS) of US nonbreastfeeding, HIV-1–infected mothers. In a multivariable logistic regression model, the magnitude of the maternal IgG responses specific for the third variable loop (V3) of the HIV-1 envelope was predictive of a reduced risk of MTCT. Neutralizing Ab responses against easy-to-neutralize (tier 1) HIV-1 strains also predicted a reduced risk of peripartum transmission in secondary analyses. Moreover, recombinant maternal V3–specific IgG mAbs mediated neutralization of autologous HIV-1 isolates. Thus, common V3-specific Ab responses in maternal plasma predicted a reduced risk of MTCT and mediated autologous virus neutralization, suggesting that boosting these maternal Ab responses may further reduce HIV-1 MTCT.

SummaryInduction of HIV-1 broad neutralizing antibodies (bnAbs) is a goal of HIV-1 vaccine development but has remained challenging partially due to unusual traits of bnAbs, including high somatic hypermutation (SHM) frequencies and in-frame insertions and deletions (indels). Here we examined the propensity and functional requirement for indels within HIV-1 bnAbs. High-throughput sequencing of the immunoglobulin (Ig) VHDJH genes in HIV-1 infected and uninfected individuals revealed that the indel frequency was elevated among HIV-1-infected subjects, with no unique properties attributable to bnAb-producing individuals. This increased indel occurrence depended only on the frequency of SHM point mutations. Indel-encoded regions were generally proximal to antigen binding sites. Additionally, reconstruction of a HIV-1 CD4-binding site bnAb clonal lineage revealed that a large compound VHDJH indel was required for bnAb activity. Thus, vaccine development should focus on designing regimens targeted at sustained activation of bnAb lineages to achieve the required SHM and indel events.

The ALVAC prime/ALVAC + AIDSVAX B/E boost RV144 vaccine trial induced an estimated 31% efficacy in a low-risk cohort where HIV‑1 exposures were likely at mucosal surfaces. An immune correlates study demonstrated that antibodies targeting the V2 region and in a secondary analysis antibody-dependent cellular cytotoxicity (ADCC), in the presence of low envelope-specific (Env-specific) IgA, correlated with decreased risk of infection. Thus, understanding the B cell repertoires induced by this vaccine in systemic and mucosal compartments are key to understanding the potential protective mechanisms of this vaccine regimen. We immunized rhesus macaques with the ALVAC/AIDSVAX B/E gp120 vaccine regimen given in RV144, and then gave a boost 6 months later, after which the animals were necropsied. We isolated systemic and intestinal vaccine Env-specific memory B cells. Whereas Env-specific B cell clonal lineages were shared between spleen, draining inguinal, anterior pelvic, posterior pelvic, and periaortic lymph nodes, members of Env‑specific B cell clonal lineages were absent in the terminal ileum. Env‑specific antibodies were detectable in rectal fluids, suggesting that IgG antibodies present at mucosal sites were likely systemically produced and transported to intestinal mucosal sites.