Immunization of rabbits with highly purified, soluble, trimeric human immunodeficiency virus type 1 envelope glycoprotein induces a vigorous B cell response and broadly cross-reactive neutralization

GALT CD4+PD-1hi T follicular helper (Tfh) cells repopulate after anti-retroviral therapy

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections are characterized by dramatic alterations in the mucosal CD4 T cell compartment. Though viremia is effectively suppressed, and peripheral CD4 T cell numbers recover to near healthy levels after highly active anti-retroviral therapy (HAART), some of the dysfunctional consequences of HIV infection continue to persist during therapy. We hypothesized that CD4 T follicular helper (Tfh) cell deficiencies may play a role in this process. Using the macaque model we show that SIV infection was associated with a significant loss of Tfh cells in the GALT that drain the mesentery lining the gastrointestinal tract (GIT). Loss of Tfh cells significantly correlated with the depletion of the overall memory CD4 T cell compartment; most Tfh cells in the GALT expressed a CD95+CD28+ memory phenotype suggesting that infection of the memory compartment likely drives the loss of GALT Tfh cells during infection. Continuous anti-retroviral therapy (cART) was accompanied by a significant repopulation of Tfh cells in the GALT to levels similar to those of uninfected animals. Repopulating Tfh cells displayed significantly higher capacity to produce IL-21 as compared to SIV infected animals suggesting that cART fully restores Tfh cells that are functionally capable of supporting GC reactions in the GALT.

Microbial Dysbiosis During Simian Immunodeficiency Virus Infection is Partially Reverted with Combination Anti-retroviral Therapy

Human immunodeficiency virus (HIV) infection is characterized by a massive loss of CD4 T cells in the gastrointestinal tract (GIT) that is accompanied by changes in the gut microbiome and microbial translocation that contribute to inflammation and chronic immune activation. Though highly active antiretroviral therapy (HAART) has led to better long-term outcomes in HIV infected patients, it has not been as effective at reverting pathogenesis in the GIT. Using the simian immunodeficiency virus (SIV) infection model, we show that combination antiretroviral therapy (c-ART) partially reverted microbial dysbiosis observed during SIV infection. Though the relative abundance of bacteria, their richness or diversity did not significantly differ between infected and treated animals, microbial dysbiosis was evident via multiple beta diversity metrics: Jaccard similarity coefficient, Bray-Curtis similarity coefficient, and Yue & Clayton theta similarity coefficient. Principal coordinates analysis (PCoA) clustered SIV-infected untreated animals away from healthy and treated animals that were clustered closely, indicating that c-ART partially reversed the gut dysbiosis associated with SIV infection. Metastats analysis identified specific operational taxonomic units (OTUs) falling within the Streptococcus, Prevotella, Acinetobacter, Treponema, and Lactobacillus genera that were differentially represented across the three groups. Our results suggest that complete viral suppression with c-ART could potentially revert microbial dysbiosis observed during SIV and HIV infections.

A Prime-Boost Immunization Strategy with Vaccinia Virus Expressing Novel gp120 Envelope Glycoprotein from a CRF02_AG Isolate Elicits Cross-Clade Tier 2 HIV-1 Neutralizing Antibodies

Development of new immunogens eliciting broadly neutralizing antibodies (bNAbs) is a main priority for the HIV-1 vaccine field. Envelope glycoproteins from non-B-non-C HIV-1clades have not been fully explored as components of a vaccine. We produced Vaccinia viruses expressing a truncated version of gp120 (gp120t) from HIV-1 clades CRF02_AG, H, J, B, and C and examined their immunogenicity in mice and rabbits. Mice primed with the recombinant Vaccinia viruses and boosted with the homologous gp120t or C2V3C3 polypeptides developed antibodies that bind potently to homologous and heterologous envelope glycoproteins. Notably, a subset of mice immunized with the CRF02_AG-based envelope immunogens developed a cross-reactive neutralizing response against tier 2 HIV-1 Env-pseudoviruses and primary isolates. Rabbits vaccinated with the CRF02_AG-based envelope immunogens also generated potent binding antibodies, and one animal elicited antibodies that neutralized almost all (13 of 16, 81.3%) tier 2 HIV-1 isolates tested. Overall, the results suggest that the novel CRF02_AG-based envelope immunogens and prime-boost immunization strategy elicit the type of immune responses required for a preventive HIV-1 vaccine.

Exploiting Natural Cross-reactivity between Human Immunodeficiency Virus (HIV)-1 p17 Protein and Anti-gp41 2F5 Antibody to Induce HIV-1 Neutralizing Responses In Vivo

Anti-p17 antibodies are able to neutralize human immunodeficiency virus (HIV) entry in a mouse model. In this study, we identified a region of sequence similarity between the epitopes of anti-p17 neutralizing antibodies and anti-gp41 neutralizing 2F5 antibody and verified cross-reactivity between p17 and 2F5 in vitro. The p17 sequence was modified to increase sequence identity between the p17 and 2F5 epitopes, which resulted in enhanced cross-reactivity in vitro. Immunogenicity of wild-type and modified p17 was characterized in a rabbit model. Both wild-type and mutated p17 induced anti-gp41 responses in rabbits; sera from these animals reacted with gp41 from different HIV clades. Moreover, introduction of the 2F5 sequence in p17 resulted in induction of antibodies with partially neutralizing activity. Based upon these data, we suggest that the natural cross-reactivity between HIV-1 p17 protein and 2F5 antibody can be exploited to induce antibodies with neutralizing activity in an animal model.

Comparable Antigenicity and Immunogenicity of Oligomeric Forms of a Novel, Acute HIV-1 Subtype C gp145 Envelope for Use in Preclinical and Clinical Vaccine Research

Eliciting broadly reactive functional antibodies remains a challenge in human immunodeficiency virus type 1 (HIV-1) vaccine development that is complicated by variations in envelope (Env) subtype and structure. The majority of new global HIV-1 infections are subtype C, and novel antigenic properties have been described for subtype C Env proteins. Thus, an HIV-1 subtype C Env protein (CO6980v0c22) from an infected person in the acute phase (Fiebig stage I/II) was developed as a research reagent and candidate immunogen. The gp145 envelope is a novel immunogen with a fully intact membrane-proximal external region (MPER), extended by a polylysine tail. Soluble gp145 was enriched for trimers that yielded the expected "fan blade" motifs when visualized by cryoelectron microscopy. CO6980v0c22 gp145 reacts with the 4E10, PG9, PG16, and VRC01 HIV-1 neutralizing monoclonal antibodies (MAbs), as well as the V1/V2-specific PGT121, 697, 2158, and 2297 MAbs. Different gp145 oligomers were tested for immunogenicity in rabbits, and purified dimers, trimers, and larger multimers elicited similar levels of cross-subtype binding and neutralizing antibodies to tier 1 and some tier 2 viruses. Immunized rabbit sera did not neutralize the highly resistant CO6980v0c22 pseudovirus but did inhibit the homologous infectious molecular clone in a peripheral blood mononuclear cell (PBMC) assay. This Env is currently in good manufacturing practice (GMP) production to be made available for use as a clinical research tool and further evaluation as a candidate vaccine.

IMPORTANCE

At present, the product pipeline for HIV vaccines is insufficient and is limited by inadequate capacity to produce large quantities of vaccine to standards required for human clinical trials. Such products are required to evaluate critical questions of vaccine formulation, route, dosing, and schedule, as well as to establish vaccine efficacy. The gp145 Env protein presented in this study forms physical trimers, binds to many of the well-characterized broad neutralizing MAbs that target conserved Env epitopes, and induce cross-subtype neutralizing antibodies as measured in both cell line and primary cell assays. This subtype C Env gp145 protein is currently undergoing good manufacturing practice production for use as a reagent for preclinical studies and for human clinical research. This product will serve as a reagent for comparative studies and may represent a next-generation candidate HIV immunogen.