Protection in macaques immunized with HIV-1 candidate vaccines can be predicted using the kinetics of their neutralizing antibodies

Potent immune responses in rhesus macaques induced by nonviral delivery of a self-amplifying RNA vaccine expressing HIV type 1 envelope with a cationic nanoemulsion

Self-amplifying messenger RNA (mRNA) of positive-strand RNA viruses are effective vectors for in situ expression of vaccine antigens and have potential as a new vaccine technology platform well suited for global health applications. The SAM vaccine platform is based on a synthetic, self-amplifying mRNA delivered by a nonviral delivery system. The safety and immunogenicity of an HIV SAM vaccine encoding a clade C envelope glycoprotein formulated with a cationic nanoemulsion (CNE) delivery system was evaluated in rhesus macaques. The HIV SAM vaccine induced potent cellular immune responses that were greater in magnitude than those induced by self-amplifying mRNA packaged in a viral replicon particle (VRP) or by a recombinant HIV envelope protein formulated with MF59 adjuvant, anti-envelope binding (including anti-V1V2), and neutralizing antibody responses that exceeded those induced by the VRP vaccine. These studies provide the first evidence in nonhuman primates that HIV vaccination with a relatively low dose (50 µg) of formulated self-amplifying mRNA is safe and immunogenic.

In vitro neutralization of low dose inocula at physiological concentrations of a monoclonal antibody which protects macaques against SHIV challenge

BACKGROUND

Passive transfer of antibodies can be protective in the simian human immunodeficiency virus (SHIV)--rhesus macaque challenge model. The human monoclonal antibody IgG1 b12 neutralizes human immunodeficiency type 1 (HIV-1) in vitro and protects against challenge by SHIV. Our hypothesis is that neutralizing antibodies can only completely inactivate a relatively small number of infectious virus.

METHODS AND FINDINGS

We have used GHOST cell assays to quantify individual infectious events with HIV-1SF162 and its SHIV derivatives: the relatively neutralization sensitive SHIV(SF162P4) isolate and the more resistant SHIV(SF162P3). A plot of the number of fluorescent GHOST cells with increasing HIV-1SF162 dose is not linear. It is likely that with high-dose inocula, infection with multiple virus produces additive fluorescence in individual cells. In studies of the neutralization kinetics of IgG1 b12 against these isolates, events during the absorption phase of the assay, as well as the incubation phase, determine the level of neutralization. It is possible that complete inactivation of a virus is limited to the time it is exposed on the cell surface. Assays can be modified so that neutralization of these very low doses of virus can be quantified. A higher concentration of antibody is required to neutralize the same dose of resistant SHIV(SF162P3) than the sensitive SHIV(SF162P4). In the absence of selection during passage, the density of the CCR5 co-receptor on the GHOST cell surface is reduced. Changes in the CD4 : CCR5 density ratio influence neutralization.

CONCLUSIONS

Low concentrations of IgG1 b12 completely inactivate small doses of the neutralization resistant SHIV(SF162P3). Assays need to be modified to quantify this effect. Results from modified assays may predict protection following repeated low-dose shiv challenges in rhesus macaques. It should be possible to induce this level of antibody by vaccination so that modified assays could predict the outcome of human trials.

Genetic imprint of vaccination on simian/human immunodeficiency virus type 1 transmitted viral genomes in rhesus macaques

Understanding the genetic, antigenic and structural changes that occur during HIV-1 infection in response to pre-existing immunity will facilitate current efforts to develop an HIV-1 vaccine. Much is known about HIV-1 variation at the population level but little with regard to specific changes occurring in the envelope glycoprotein within a host in response to immune pressure elicited by antibodies. The aim of this study was to track and map specific early genetic changes occurring in the viral envelope gene following vaccination using a highly controlled viral challenge setting in the SHIV macaque model. We generated 449 full-length env sequences from vaccinees, and 63 from the virus inoculum. Analysis revealed a different pattern in the distribution and frequency of mutations in the regions of the envelope gene targeted by the vaccine as well as different patterns of diversification between animals in the naïve control group and vaccinees. Given the high stringency of the model it is remarkable that we were able to identify genetic changes associated with the vaccination. This work provides insight into the characterization of breakthrough viral populations in less than fully efficacious vaccines and illustrates the value of HIV-1 Env SHIV challenge model in macaques to unravel the mechanisms driving HIV-1 envelope genetic diversity in the presence of vaccine induced-responses.