Reproducing SIVΔnef vaccine correlates of protection: trimeric gp41 antibody concentrated at mucosal front lines

Molecular insights into antibody-mediated protection against the prototypic simian immunodeficiency virus

SIVmac239 infection of macaques is a favored model of human HIV infection. However, the SIVmac239 envelope (Env) trimer structure, glycan occupancy, and the targets and ability of neutralizing antibodies (nAbs) to protect against SIVmac239 remain unknown. Here, we report the isolation of SIVmac239 nAbs that recognize a glycan hole and the V1/V4 loop. A high-resolution structure of a SIVmac239 Env trimer-nAb complex shows many similarities to HIV and SIVcpz Envs, but with distinct V4 features and an extended V1 loop. Moreover, SIVmac239 Env has a higher glycan shield density than HIV Env that may contribute to poor or delayed nAb responses in SIVmac239-infected macaques. Passive transfer of a nAb protects macaques from repeated intravenous SIVmac239 challenge at serum titers comparable to those described for protection of humans against HIV infection. Our results provide structural insights for vaccine design and shed light on antibody-mediated protection in the SIV model.

Neutralizing monoclonal antibodies for COVID-19 treatment and prevention

The SARS-CoV-2 pandemic has caused unprecedented global health and economic crises. Several vaccine approaches and repurposed drugs are currently under evaluation for safety and efficacy. However, none of them have been approved for COVID-19 yet. Meanwhile, several nMAbs targeting SARS-CoV-2 spike glycoprotein are in different stages of development and clinical testing. Preclinical studies have shown that cocktails of potent nMAbs targeting the receptor binding site of SARS-CoV-2, as well as broad-nMAbs targeting conserved regions within the virus spike, might be effective for the treatment and prophylaxis of COVID-19. Currently, several clinical trials have started to test safety, tolerability, PKs and efficacy of these nMAbs. One paramount limitation for the use of nMAbs in clinical settings is the production of large amounts of MAbs and the high costs related to it. Cooperation among public and private institutions coupled with speed of development, rapid safety evaluation and efficacy, and early planning for scale-up and manufacture will be critical for the control of COVID-19 pandemic.

Use of broadly neutralizing antibodies for HIV-1 prevention

Antibodies have a long history in antiviral therapy, but until recently, they have not been actively pursued for HIV-1 due to modest potency and breadth of early human monoclonal antibodies (MAbs) and perceived insurmountable technical, financial, and logistical hurdles. Recent advances in the identification and characterization of MAbs with the ability to potently neutralize diverse HIV-1 isolates have reinvigorated discussion and testing of these products in humans, since new broadly neutralizing MAbs (bnMAbs) are more likely to be effective against worldwide strains of HIV-1. In animal models, there is abundant evidence that bnMAbs can block infection in a dose-dependent manner, and the more potent bnMAbs will allow clinical testing at infusion doses that are practically achievable. Moreover, recent advances in antibody engineering are providing further improvements in MAb potency, breadth, and half-life. This review summarizes the current state of the field of bnMAb protection in animal models as well as a review of variables that are critical for antiviral activity. Several bnMAbs are currently in clinical testing, and we offer perspectives on their use as pre-exposure prophylaxis (PrEP), potential benefits beyond sterilizing immunity, and a discussion of future approaches to engineer novel molecules.

A multiplex assay for detection of SHIV plasma and mucosal IgG and IgA

Evaluating antibody maturation provides valuable data to characterize immune responses to HIV infection and can provide insight into biomedical intervention efficacy. It is important to develop assays that evaluate antibody maturation in both plasma and mucosal compartments. The nonhuman primate model provides a controlled system to collect temporal data that are integral to assessing intervention strategies. We report the development of a novel multiplex assay, based on the Bio-Plex platform, to evaluate plasma and mucosal IgG and IgA avidity and maturation against simian/human immunodeficiency virus (SHIV) in this controlled system. Vaginal mucosa and plasma samples were collected from a prior study evaluating the efficacy of a tenofovir disoproxil fumarate (TDF) intravaginal ring (IVR) against SHIVSF162P3 challenge in female pigtailed macaques. For validation of the multiplex assay, specimens from six SHIV-infected placebo animals and one TDF breakthrough animal were evaluated. For SHIV and HIV envelope analytes, antibody levels and avidity in both compartments continued to mature post-infection. Maturation of IgG and IgA levels was similar in each compartment, however, mucosal antibody levels tended to be more variable. This SHIV assay elucidates IgG/IgA antibody kinetics in the plasma and vaginal mucosa and will be a valuable tool in vaccine and other biomedical intervention studies in the nonhuman primate model.

Immunogenicity of a novel Clade B HIV-1 vaccine combination: Results of phase 1 randomized placebo controlled trial of an HIV-1 GM-CSF-expressing DNA prime with a modified vaccinia Ankara vaccine boost in healthy HIV-1 uninfected adults

Background

A phase 1 trial of a clade B HIV vaccine in HIV-uninfected adults evaluated the safety and immunogenicity of a DNA prime co-expressing GM-CSF (Dg) followed by different numbers and intervals of modified vaccinia Ankara Boosts (M). Both vaccines produce virus-like particles presenting membrane-bound Env.

Methods

Four US sites randomized 48 participants to receiving 1/10^th the DNA dose as DgDgMMM given at 0, 2, 4, 6 and 8 months, or full dose DgDgM_M or DgDgMM_M regimens, given at 0, 2, 4, and 8 months, and 0, 2, 4, 6, and 10 months, respectively. Peak immunogenicity was measured 2 weeks post-last vaccination.

Results

All regimens were well tolerated and safe. Full dose DgDgM_M and DgDgMM_M regimens generated Env-specific IgG to HIV-1 Env in >90%, IgG3 in >80%, and IgA in <20% of participants. Responses to gp140 and gp41 targets were more common and of higher magnitude than to gp120 and V1V2. The gp41 antibody included reactivity to the conserved immunodominant region with specificities known to mediate virus capture and phagocytosis and did not cross-react with a panel of intestinal flora antigens. The 3^rd dose of MVA increased the avidity of elicited antibody (7.5% to 39%), the ADCC response to Bal gp120 (14% to 64%), and the one-year durability of the IgG3 responses to gp41 by 4-fold (13% vs. 3.5% retention of peak response). The co-expressed GM-CSF did not enhance responses over those in trials testing this vaccine without GM-CSF.

Conclusion

This DNA/MVA prime-boost regimen induced durable, functional humoral responses that included ADCC, high antibody avidity, and Env IgG1 and IgG3 binding responses to the immunodominant region of gp41. The third, spaced MVA boost improved the overall quality of the antibody response. These products without co-expressed GM-CSF but combined with protein boosts will be considered for efficacy evaluation.

Trial registration

ClinicalTrials.gov NCT01571960

A recombinant multi-epitope protein MEP1 elicits efficient long-term immune responses against HIV-1 infection

The effective protective HIV vaccine should elicit either protective antibodies or effective T cell response, or both. To improve the efficacy of HIV-1 vaccines, HLA polymorphism and HIV-1 diversity are 2 key factors to be considered for vaccine development. In this study, we expressed a recombinant multi-epitope protein MEP1 which has the same amino acid sequence as a DNA vaccine for Chinese population in our previous report. We found that MEP1 alone could elicit moderate levels of humoral and cellular immune responses, but these responses could not provide protection from challenge with a recombinant virus rTTV-lucgag, which expresses Gag of HIV-1 CRF_07BC. Nevertheless, when MEP1 was immunized with aluminum adjuvant, both humoral and cellular immune responses were significantly increased, and they were protective against virus infection; meanwhile, MEP1 with aluminum not only elicited early (10 d post immunization) but also a long-term (at least 44 weeks post immunization) immune responses in BALB/c mice. These results suggested that MEP1 has the potential to be developed as an effective vaccine candidate, and that suitable adjuvant is necessary for this protein to generate protective immune responses.