Induction of broad, durable immune responses is a challenge in HIV vaccine development. HVTN 100 Part A administered subtype C-containing ALVAC-HIV at months 0 and 1, and ALVAC-HIV with bivalent subtype C gp120/MF59 at months 3, 6 and 12. As IgG binding antibody and T-cell responses were similar or greater at month 12.5 vs. month 6.5, but waned by month 18, we investigated vaccine-elicited immune responses after a month 30 boost in this study, HVTN 100 Part B. From 13 September 2017 to 7 August 2018, a subgroup of vaccinees was randomized to receive intramuscular injections of ALVAC+gp120/MF59 (n = 32) or gp120/MF59 alone (n = 31) and a subgroup of placebo recipients was administered placebo (n = 7) at month 30. Primary outcomes were safety, IgG binding antibodies (bAbs) to vaccine-specific and V1V2 Env proteins and vaccine-specific CD4+ T cells at month 30.5. Secondary outcomes included neutralizing and antibody dependent cellular cytotoxicity functions and durability at months 30 and 36. Both vaccine groups had an acceptable safety profile. There were no statistically significant differences in the occurrence or level of IgG bAbs between the vaccine boost groups for any vaccine-specific or V1V2 antigens. IgG responses were higher to vaccine-matched gp120 than to V1V2. The booster vaccination restored the magnitude-breadth IgG bAb response to V1V2 antigens at month 30.5. However, it rapidly waned by month 36. CD4+ T-cell response rates to the 3 vaccine-matched Env antigens for the combined vaccine groups ranged from 37% at month 30, boosted to as high as 91% at month 30.5, and waned by month 36 to as low as 44%, with no significant differences between the vaccine boost groups. Because these responses waned after 6 months, additional strategies may be needed to maintain the durability of prime-boost vaccine regimens and to generate these or other immune responses that confer protection. Trial registration: South African National Clinical Trials Register (SANCTR number: DOH—27-0215-4796) and ClinicalTrials.gov (NCT02404311).

Vaccine R&D is typically a lengthy process taking >10 years. However, vaccines still fail in clinical development because of unreliable animal models or absent immunological correlates of protection. Without a correlate of protection, phase-1 and -2 studies of safety and immunogenicity can fail to predict phase-3 efficacy. Indeed, the history of vaccine development is replete with promising phase-1 and -2 results and failed phase-3 efficacy trials. To avoid this misfortune, we present Reverse Vaccine Development for vaccines against antimicrobial-resistant (AMR) pathogens. In this approach, instead of evaluating efficacy in phase 3, proof-of-principle efficacy is evaluated as early as possible in a population with a high incidence of disease, which may differ from the population intended for registration, and can be a controlled human infection population. To identify a correlate of protection in these populations, the vaccine-elicited immune response is compared between protected and unprotected subjects. If a correlate is identified, it can help to refine the vaccine dosage, schedule, and formulation, and facilitate the assessment of vaccine efficacy in other populations with different attack rates, subject characteristics, and disease manifestations. This may be the only way to provide life-saving vaccines to populations affected by AMR-pathogen diseases at incidences that are typically low and unsuited to phase-3 efficacy trials. The availability of a correlate of protection early in clinical development can potentially prevent failures of large phase-3 trials and unnecessary exposures of populations to inefficacious vaccines that have resulted in disinvestment in the development of vaccines against AMR pathogens.

Carbohydrates are abundantly expressed on the surface of both eukaryotic and prokaryotic cells, often as post translational modifications of proteins. Glycoproteins are recognized by the immune system and can trigger both innate and humoral responses. This feature has been harnessed to generate vaccines against polysaccharide-encapsulated bacteria such as Streptococcus pneumoniae, Hemophilus influenzae type b and Neisseria meningitidis. In cancer, glycosylation plays a pivotal role in malignancy development and progression. Since glycans are specifically expressed on the surface of tumor cells, they have been targeted for the discovery of anticancer preventive and therapeutic treatments, such as vaccines and monoclonal antibodies. Despite the various efforts made over the last years, resulting in a series of clinical studies, attempts of vaccination with carbohydrate-based candidates have proven unsuccessful, primarily due to the immune tolerance often associated with these glycans. New strategies are thus deployed to enhance carbohydrate-based cancer vaccines. Moreover, lessons learned from glycan immunobiology paved the way to the development of new monoclonal antibodies specifically designed to recognize cancer-bound carbohydrates and induce tumor cell killing. Herein we provide an overview of the immunological principles behind the immune response towards glycans and glycoconjugates and the approaches exploited at both preclinical and clinical level to target cancer-associated glycans for the development of vaccines and therapeutic monoclonal antibodies. We also discuss gaps and opportunities to successfully advance glycan-directed cancer therapies, which could provide patients with innovative and effective treatments.

The COVID-19 pandemic is a shocking reminder of how our world would look in the absence of vaccination. Fortunately, new technologies, the pace of understanding new and existing pathogens, and the increased knowledge of the immune system allow us today to develop vaccines at an unprecedented speed. Some of the vaccine technologies that are fast-tracked by the urgency of COVID-19 may also be the answer for other health priorities, such as antimicrobial resistance, chronic infections, and cancer, that the post-COVID-19 world will urgently need to face. This perspective analyzes the way COVID-19 is transforming vaccinology and the opportunities for vaccines to have an increasingly important role in health and well-being.

Staphylococcus aureus is one of the most important human pathogens worldwide. Its high antibiotic resistance profile reinforces the need for new interventions like vaccines in addition to new antibiotics. Vaccine development efforts against S. aureus have failed so far however, the findings from these human clinical and non-clinical studies provide potential insight for such failures. Currently, research is focusing on identifying novel vaccine formulations able to elicit potent humoral and cellular immune responses. Translational science studies are attempting to discover correlates of protection using animal models as well as in vitro and ex vivo models assessing efficacy of vaccine candidates. Several new vaccine candidates are being tested in human clinical trials in a variety of target populations. In addition to vaccines, bacteriophages, monoclonal antibodies, centyrins and new classes of antibiotics are being developed. Some of these have been tested in humans with encouraging results. The complexity of the diseases and the range of the target populations affected by this pathogen will require a multipronged approach using different interventions, which will be discussed in this review.

BACKGROUND:A safe, effective vaccine is essential to eradicating human immunodeficiency virus (HIV) infection. A canarypox-protein HIV vaccine regimen (ALVAC-HIV plus AIDSVAX B/E) showed modest efficacy in reducing infection in Thailand. An analogous regimen using HIV-1 subtype C virus showed potent humoral and cellular responses in a phase 1-2a trial in South Africa. Efficacy data and additional safety data were needed for this regimen in a larger population in South Africa. METHODS:In this phase 2b-3 trial, we randomly assigned 5404 adults without HIV-1 infection to receive the vaccine (2704 participants) or placebo (2700 participants). The vaccine regimen consisted of injections of ALVAC-HIV at months 0 and 1, followed by four booster injections of ALVAC-HIV plus bivalent subtype C gp120-MF59 adjuvant at months 3, 6, 12, and 18. The primary efficacy outcome was the occurrence of HIV-1 infection from randomization to 24 months. RESULTS:In January 2020, prespecified criteria for nonefficacy were met at an interim analysis; further vaccinations were subsequently halted. The median age of the trial participants was 24 years; 70% of the participants were women. The incidence of adverse events was similar in the vaccine and placebo groups. During the 24-month follow-up, HIV-1 infection was diagnosed in 138 participants in the vaccine group and in 133 in the placebo group (hazard ratio, 1.02; 95% confidence interval, 0.81 to 1.30; P = 0.84). CONCLUSIONS:The ALVAC-gp120 regimen did not prevent HIV-1 infection among participants in South Africa despite previous evidence of immunogenicity. (HVTN 702 ClinicalTrials.gov number, NCT02968849.).

BACKGROUND:The RV144 phase 3 vaccine trial in Thailand demonstrated that ALVAC-HIV (vCP1521) and AIDSVAX B/E administration over 6 months resulted in a 31% efficacy in preventing HIV acquisition. In this trial, we assessed the immunological effect of an additional vaccine boost to the RV144 regimen at varying intervals between the priming vaccine series and the boost. METHODS:RV306 is a double-blind, placebo-controlled, randomised clinical trial done at three clinical sites in Thailand. Eligible volunteers were HIV-uninfected individuals aged 20-40 years who were at low risk for HIV infection and in good health. A randomisation schedule was centrally generated with fixed sized strata for Research Institute for Health Sciences Chiang Mai and combined Bangkok clinics. Participants were randomly assigned to one of five groups and then further randomly assigned to either vaccine or placebo. All participants received the primary RV144 vaccine series at months 0, 1, 3, and 6. Group 1 received no additional boost, group 2 received additional AIDSVAX B/E and ALVAC-HIV (vCP1521) or placebo at month 12, group 3 received AIDSVAX B/E alone or placebo at month 12, group 4a received AIDSVAX B/E and ALVAC-HIV or placebo at month 15, and group 4b received AIDSVAX B/E and ALVAC-HIV or placebo at month 18. Primary outcomes were safety and tolerability of these vaccination regimens and cellular and humoral immune responses compared between the RV144 series alone and regimens with late boosts at different timepoints. Safety and tolerability outcomes were assessed by evaluating local and systemic reactogenicity and adverse events in all participants. This trial is registered at ClinicalTrials.gov (NCT01931358); clinical follow-up is now complete. FINDINGS:Between Oct 28, 2013, and April 29, 2014, 367 participants were enrolled, of whom 27 were assigned active vaccination in group 1, 102 in group 2, 101 in group 3, 52 in group 4a, 51 in group 4b, and 34 combined placebo across all the groups. No vaccine-related serious adverse events were recorded. Occurrence and severity of local and systemic reactogenicity were similar across active groups. Groups with late boosts (groups 2, 3, 4a, and 4b) had increased peak plasma IgG-binding antibody levels against gp70 V1V2 relative to group 1 vaccine recipients with no late boost (gp70 V1V2 92TH023 adjusted p<0·02 for each; gp70 V1V2 CaseA2 adjusted p<0·0001 for each). Boosting at month 12 (groups 2 and 3) did not increase gp120 responses compared with the peak responses after the RV144 priming regimen at month 6; however, boosting at month 15 (group 4a) improved responses to gp120 A244gD- D11 (p=0·0003), and boosting at month 18 (group 4b) improved responses to both gp120 A244gD- D11 (p<0·0001) and gp120 MNgD- D11 (p=0·0016). Plasma IgG responses were significantly lower among vaccine recipients boosted at month 12 (pooled groups 2 + 3) than at month 15 (group 4a; adjusted p<0·0001 for each, except for gp70 V1V2 CaseA2, p=0·0142) and at month 18 (group 4b; all adjusted p<0·001). Boosting at month 18 versus month 15 resulted in a significantly higher plasma IgG response to gp120 antigens (all adjusted p<0·01) but not gp70 V1V2 antigens. CD4 functionality and polyfunctionality scores after stimulation with HIV-1 Env peptides (92TH023) increased with delayed boosting. Groups with late boosts had increased functionality and polyfunctionality scores relative to vaccine recipients with no late boost (all adjusted p<0·05, except for the polyfunctionality score in group 1 vs group 4b, p<0·01). INTERPRETATION:Taken together, these results suggest that additional boosting of the RV144 regimen with longer intervals between the primary vaccination series and late boost improved immune responses and might improve the efficacy of preventing HIV acquisition. FUNDING:US National Institute of Allergy and Infectious Diseases and US Department of the Army.

In the RV144 HIV-1 phase III trial, vaccine efficacy directly correlated with the magnitude of the variable region 2-specific (V2-specific) IgG antibody response, and in the presence of low plasma IgA levels, with the magnitude of plasma antibody-dependent cellular cytotoxicity. Reenrollment of RV144 vaccinees in the RV305 trial offered the opportunity to define the function, maturation, and persistence of vaccine-induced V2-specific and other mAb responses after boosting. We show that the RV144 vaccine regimen induced persistent V2 and other HIV-1 envelope-specific memory B cell clonal lineages that could be identified throughout the approximately 11-year vaccination period. Subsequent boosts increased somatic hypermutation, a critical requirement for antibody affinity maturation. Characterization of 22 vaccine-induced V2-specific mAbs with epitope specificities distinct from previously characterized RV144 V2-specific mAbs CH58 and CH59 found increased in vitro antibody-mediated effector functions. Thus, when inducing non-neutralizing antibodies, one method by which to improve HIV-1 vaccine efficacy may be through late boosting to diversify the V2-specific response to increase the breadth of antibody-mediated anti-HIV-1 effector functions.

BACKGROUND:HVTN 100 evaluated the safety and immunogenicity of an HIV subtype C pox-protein vaccine regimen, investigating a 12-month booster to extend vaccine-induced immune responses. METHODS AND FINDINGS:A phase 1-2 randomized double-blind placebo-controlled trial enrolled 252 participants (210 vaccine/42 placebo; median age 23 years; 43% female) between 9 February 2015 and 26 May 2015. Vaccine recipients received ALVAC-HIV (vCP2438) alone at months 0 and 1 and with bivalent subtype C gp120/MF59 at months 3, 6, and 12. Antibody (IgG, IgG3 binding, and neutralizing) and CD4+ T-cell (expressing interferon-gamma, interleukin-2, and CD40 ligand) responses were evaluated at month 6.5 for all participants and at months 12, 12.5, and 18 for a randomly selected subset. The primary analysis compared IgG binding antibody (bAb) responses and CD4+ T-cell responses to 3 vaccine-matched antigens at peak (month 6.5 versus 12.5) and durability (month 12 versus 18) timepoints; IgG responses to CaseA2_gp70_V1V2.B, a primary correlate of risk in RV144, were also compared at these same timepoints. Secondary and exploratory analyses compared IgG3 bAb responses, IgG bAb breadth scores, neutralizing antibody (nAb) responses, antibody-dependent cellular phagocytosis, CD4+ polyfunctionality responses, and CD4+ memory sub-population responses at the same timepoints. Vaccines were generally safe and well tolerated. During the study, there were 2 deaths (both in the vaccine group and both unrelated to study products). Ten participants became HIV-infected during the trial, 7% (3/42) of placebo recipients and 3% (7/210) of vaccine recipients. All 8 serious adverse events were unrelated to study products. Less waning of immune responses was seen after the fifth vaccination than after the fourth, with higher antibody and cellular response rates at month 18 than at month 12: IgG bAb response rates to 1086.C V1V2, 21.0% versus 9.7% (difference = 11.3%, 95% CI = 0.6%-22.0%, P = 0.039), and ZM96.C V1V2, 21.0% versus 6.5% (difference = 14.5%, 95% CI = 4.1%-24.9%, P = 0.004). IgG bAb response rates to all 4 primary V1V2 antigens were higher 2 weeks after the fifth vaccination than 2 weeks after the fourth vaccination: 87.7% versus 75.4% (difference = 12.3%, 95% CI = 1.7%-22.9%, P = 0.022) for 1086.C V1V2, 86.0% versus 63.2% (difference = 22.8%, 95% CI = 9.1%-36.5%, P = 0.001) for TV1c8.2.C V1V2, 67.7% versus 44.6% (difference = 23.1%, 95% CI = 10.4%-35.7%, P < 0.001) for ZM96.C V1V2, and 81.5% versus 60.0% (difference = 21.5%, 95% CI = 7.6%-35.5%, P = 0.002) for CaseA2_gp70_V1V2.B. IgG bAb response rates to the 3 primary vaccine-matched gp120 antigens were all above 90% at both peak timepoints, with no significant differences seen, except a higher response rate to ZM96.C gp120 at month 18 versus month 12: 64.5% versus 1.6% (difference = 62.9%, 95% CI = 49.3%-76.5%, P < 0.001). CD4+ T-cell response rates were higher at month 18 than month 12 for all 3 primary vaccine-matched antigens: 47.3% versus 29.1% (difference = 18.2%, 95% CI = 2.9%-33.4%, P = 0.021) for 1086.C, 61.8% versus 38.2% (difference = 23.6%, 95% CI = 9.5%-37.8%, P = 0.001) for TV1.C, and 63.6% versus 41.8% (difference = 21.8%, 95% CI = 5.1%-38.5%, P = 0.007) for ZM96.C, with no significant differences seen at the peak timepoints. Limitations were that higher doses of gp120 were not evaluated, this study was not designed to investigate HIV prevention efficacy, and the clinical significance of the observed immunological effects is uncertain. CONCLUSIONS:In this study, a 12-month booster of subtype C pox-protein vaccines restored immune responses, and slowed response decay compared to the 6-month vaccination. TRIAL REGISTRATION:ClinicalTrials.gov NCT02404311. South African National Clinical Trials Registry (SANCTR number: DOH--27-0215-4796).

Over one million people become infected with HIV-1 each year, making the development of an efficacious HIV-1 vaccine an important unmet medical need. The RV144 human HIV-1 vaccine regimen is the only HIV-1 clinical trial to date to demonstrate vaccine efficacy. An area of focus has been on identifying ways by which to improve upon RV144 vaccine efficacy. The RV305 HIV-1 vaccine regimen was a follow-up boost of RV144 vaccine recipients that occurred 6 to 8 years after the conclusion of RV144. Our study focused on the effect of delayed boosting in humans on the vaccine-induced Env constant region 1 and 2 (C1C2)-specific antibody repertoire. It was found that boosting with an HIV-1 Env vaccine increased C1C2-specific antibody-dependent cellular cytotoxicity potency and breadth.

In the RV144 trial, vaccine-induced V1V2 IgG correlated with decreased HIV-1 risk. We investigated circulating antibody specificities in two phase 1 poxvirus prime-protein boost clinical trials conducted in South Africa: HVTN 097 (subtype B/E) and HVTN 100 (subtype C). With cross-subtype peptide microarrays and multiplex binding assays, we probed the magnitude and breadth of circulating antibody responses to linear variable loop 2 (V2) and conformational V1V2 specificities. Antibodies targeting the linear V2 epitope, a correlate of decreased HIV-1 risk in RV144, were elicited up to 100% and 61% in HVTN 097 and HVTN 100, respectively. Despite higher magnitude of envelope-specific responses in HVTN 100 compared to HVTN 097 (p’s < 0.001), the magnitude and positivity for V2 linear epitope and V1V2 proteins were significantly lower in HVTN 100 compared to HVTN 097. Meanwhile, responses to other major linear epitopes including the variable 3 (V3) and constant 5 (C5) epitopes were higher in HVTN 100 compared to HVTN 097. Our data reveal substantial differences in the circulating antibody specificities induced by vaccination in these two canarypox prime-protein boost trials. Our findings suggest that the choice of viral sequences in prime-boost vaccine regimens, and potentially adjuvants and immunogen dose, influence the elicitation of V2-specific antibodies.

Complete Dataset for Schifanella Manuscript

The use of heterologous immunization regimens and improved vector systems has led to increases in immunogenicity of HIV-1 vaccine candidates in nonhuman primates. In order to resolve interrelations between different delivery modalities, three different poxvirus boost regimens were compared. Three groups of rhesus macaques were each primed with the same DNA vaccine encoding Gag, Pol, Nef, and gp140. The groups were then boosted with either the vaccinia virus strain NYVAC or a variant with improved replication competence in human cells, termed NYVAC-KC. The latter was administered either by scarification or intramuscularly. Finally, macaques were boosted with adjuvanted gp120 protein to enhance humoral responses. The regimen elicited very potent CD4+ and CD8+ T cell responses in a well-balanced manner, peaking 2 weeks after the boost. T cells were broadly reactive and polyfunctional. All animals exhibited antigen-specific humoral responses already after the poxvirus boost, which further increased following protein administration. Polyclonal reactivity of IgG antibodies was highest against HIV-1 clade C Env proteins, with considerable cross-reactivity to other clades. Substantial effector functional activities (antibody-dependent cell-mediated cytotoxicity and antibody-dependent cell-mediated virus inhibition) were observed in serum obtained after the last protein boost. Notably, major differences between the groups were absent, indicating that the potent priming induced by the DNA vaccine initially framed the immune responses in such a way that the subsequent boosts with NYVAC and protein led only to an increase in the response magnitudes without skewing the quality. This study highlights the importance of selecting the best combination of vector systems in heterologous prime-boost vaccination regimens.IMPORTANCE The evaluation of HIV vaccine efficacy trials indicates that protection would most likely correlate with a polyfunctional immune response involving several effector functions from all arms of the immune system. Heterologous prime-boost regimens have been shown to elicit vigorous T cell and antibody responses in nonhuman primates that, however, qualitatively and quantitatively differ depending on the respective vector systems used. The present study evaluated a DNA prime and poxvirus and protein boost regimen and compared how two poxvirus vectors with various degrees of replication capacity and two different delivery modalities-conventional intramuscular delivery and percutaneous delivery by scarification-impact several immune effectors. It was found that despite the different poxvirus boosts, the overall immune responses in the three groups were similar, suggesting the potent DNA priming as the major determining factor of immune responses. These findings emphasize the importance of selecting optimal priming agents in heterologous prime-boost vaccination settings.

One of the most successful HIV vaccines to date, the RV144 vaccine tested in Thailand, demonstrated correlates of protection including cross-clade V1V2 immunoglobulin G (IgG) breadth, Env-specific CD4+ T cell polyfunctionality, and antibody-dependent cellular cytotoxicity (ADCC) in vaccinees with low IgA binding. The HIV Vaccine Trials Network (HVTN) 097 trial evaluated this vaccine regimen in South Africa, where clade C HIV-1 predominates. We compared cellular and humoral responses at peak and durability immunogenicity time points in HVTN 097 and RV144 vaccinee samples, and evaluated vaccine-matched and cross-clade immune responses. At peak immunogenicity, HVTN 097 vaccinees exhibited significantly higher cellular and humoral immune responses than RV144 vaccinees. CD4+ T cell responses were more frequent in HVTN 097 irrespective of age and sex, and CD4+ T cell Env-specific functionality scores were higher in HVTN 097. Env-specific CD40L+ CD4+ T cells were more common in HVTN 097, with individuals having this pattern of expression demonstrating higher median antibody responses to HIV-1 Env. IgG and IgG3 binding antibody rates and response magnitude to gp120 vaccine- and V1V2 vaccine-matched antigens were higher or comparable in HVTN 097 than in RV144 ADCC, and ADCP functional antibody responses were elicited in HVTN 097. Env-specific IgG and CD4+ Env responses declined significantly over time in both trials. Overall, cross-clade immune responses associated with protection were better than expected in South Africa, suggesting wider applicability of this regimen.

Induction of protective antibodies is a critical goal of HIV-1 vaccine development. One strategy is to induce non-neutralizing antibodies that kill virus-infected cells as these antibody specificities have been implicated in slowing HIV-1 disease progression and in protection. HIV-1 Env constant region 1 and 2 (C1C2) antibodies frequently contain potent antibody dependent cellular cytotoxicity (ADCC) making them a vaccine target. Here we explore the effect of delayed and repetitive boosting of RV144 vaccinee recipients with ALVAC/AIDSVAX B/E on the C1C2-specific antibody repertoire. It was found that boosting increased clonal lineage specific ADCC breadth and potency. A ligand crystal structure of a vaccine-induced broad and potent ADCC-mediating C1C2-specific antibody showed that it bound a highly conserved Env gp120 epitope. Thus, rationally designed boosting strategies to affinity mature these type of IgG C1C2-specific antibody responses may be one method by which to make an improved HIV vaccine with higher efficacy than seen in the RV144 trial. Significance Over one million people become infected with HIV-1 each year making the development of an efficacious HIV-1 vaccine an important unmet medical need. The RV144 human HIV-1 vaccine-regimen is the only HIV-1 clinical trial to date to demonstrate vaccine-efficacy. An area of focus has been on identifying ways by which to improve upon RV144 vaccine-efficacy. The RV305 HIV-1 vaccine-regimen was a follow-up boost of RV144 vaccine-recipients that occurred 6-8 years after the conclusion of RV144. Our studies focused on the effect of delayed boosting in humans on the vaccine-induced antibody repertoire. It was found that boosting with a HIV-1 Env vaccine increased antibody-mediated effector function potency and breadth.

[This corrects the article DOI: 10.1371/journal.ppat.1008121.].

Author(s): Kibler, Karen V; Asbach, Benedikt; Perdiguero, Beatriz; Garcia-Arriaza, Juan; Yates, Nicole L; Parks, Robert; Stanfield-Oakley, Sherry; Ferrari, Guido; Montefiori, David C; Tomaras, Georgia D; Roederer, Mario; Foulds, Kathryn E; Forthal, Donald N; Seaman, Michael S; Self, Steve; Gottardo, Raphael; Phogat, Sanjay; Tartaglia, James; Barnett, Susan; Cristillo, Anthony D; Weiss, Deborah; Galmin, Lindsey; Ding, Song; Heeney, Jonathan L; Esteban, Mariano; Wagner, Ralf; Pantaleo, Giuseppe; Jacobs, Bertram L | Abstract: Volume 93, no. 3, e01513-18, 2019, https://doi.org/10.1128/JVI.01513-18. The article was originally published on 17 January 2019 with a standard copyright line (“© 2019 American Society for Microbiology. All Rights Reserved.”). We elected to pay for open access for the article after publication, necessitating replacement of the original copyright line with “© 2019 Kibler et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.” This change was made to the online version of the article on 21 August 2019.

As part of the continuing effort to develop an effective HIV vaccine, we generated a poxviral vaccine vector (previously described) designed to improve on the results of the RV144 phase III clinical trial. The construct, NYVAC-KC, is a replication-competent, attenuated recombinant of the vaccinia virus strain NYVAC. NYVAC is a vector that has been used in many previous clinical studies but is replication deficient. Here, we report a side-by-side comparison of replication-restricted NYVAC and replication-competent NYVAC-KC in a nonhuman primate study, which utilized a prime-boost regimen similar to that of RV144. NYVAC-C and NYVAC-C-KC express the HIV-1 antigens gp140, and Gag/Gag-Pol-Nef-derived virus-like particles (VLPs) from clade C and were used as the prime, with recombinant virus plus envelope protein used as the boost. In nearly every T and B cell immune assay against HIV-1, including neutralization and antibody binding, NYVAC-C-KC induced a greater immune response than NYVAC-C, indicating that replication competence in a poxvirus may improve upon the modestly successful regimen used in the RV144 clinical trial.IMPORTANCE Though the RV144 phase III clinical trial showed promise that an effective vaccine against HIV-1 is possible, a successful vaccine will require improvement over the vaccine candidate (ALVAC) used in the RV144 study. With that goal in mind, we have tested in nonhuman primates an attenuated but replication-competent vector, NYVAC-KC, in direct comparison to its parental vector, NYVAC, which is replication restricted in human cells, similar to the ALVAC vector used in RV144. We have utilized a prime-boost regimen for administration of the vaccine candidate that is similar to the one used in the RV144 study. The results of this study indicate that a replication-competent poxvirus vector may improve upon the effectiveness of the RV144 clinical trial vaccine candidate.

Background: The RV144 phase 3 vaccine trial in Thailand demonstrated that ALVAC-HIV (vCP1521) and AIDSVAX® B/E administration over six months resulted in a 31% efficacy in preventing HIV acquisition. Subsequent boosting of RV144 vaccine recipients 6 to 8 years later improved the magnitude and quality of immune responses, expanding subdominant memory B cells.Methods: RV306 is a double-blind, placebo-controlled, randomized clinical trial of the primary RV144 vaccine series with additional AIDSVAX® B/E with or without ALVAC-HIV boosting at months 12, 15, or 18 in healthy volunteers.Findings: Late boosting was safe, and improved antigen-specific plasma IgG responses to HIV-1 envelope and the first and second variable loops (V1V2), an inverse correlate of HIV risk in RV144, without increasing HIV-specific plasma IgA, a direct correlate of risk. Late boosting improved Tier 1 neutralization and HIV-1 envelope-specific CD4+ T cell polyfunctionality, an independent correlate contributing to RV144 vaccine efficacy. Late boosting was also required to maintain antigen-specific CD4+ T cell proliferation. Interestingly, increasing the interval between priming and boosting improved several humoral and cellular immune responses.Interpretation: Taken together, these results suggest that additional boosting of the RV144 regimen with longer intervals between the primary vaccination series and late boost improved immune responses and may improve the efficacy of preventing HIV acquisition.Funding Statement: Cooperative Agreement # W81XWH-18-2-0040 in collaboration with the US Army and DAIDS/NIAID/NIH.Declaration of Interests: J. T., and C. D. are employees of Sanofi Pasteur. S.P. was an employee of Sanofi Pasteur during the conduct of this study and analysis. F. S. is an employee of Global Solutions for Infectious Diseases. All other authors report no potential conflicts. The opinions expressed herein are those of the authors and do not represent the official position of the US Army or the Department of Defense. Trade names are used for identification purposes only and do not imply endorsement.Ethics Approval Statement: The study was approved by ethical review boards at the Walter Reed Army Institute of Research, Thai Ministry of Public Health, Royal Thai Army Medical Department, Faculty of Tropical Medicine, Mahidol University, Chiang Mai University, and Chulalongkorn University Faculty of Medicine. This study was conducted in accordance with Good Participatory Practice principles.

Multiple approaches utilizing viral and DNA vectors have shown promise in the development of an effective vaccine against HIV. In this study, an alternative replication-defective flavivirus vector, RepliVax (RV), was evaluated for the delivery of HIV-1 immunogens. Recombinant RV-HIV viruses were engineered to stably express clade C virus Gag and Env (gp120TM) proteins and propagated in Vero helper cells. RV-based vectors enabled efficient expression and correct maturation of Gag and gp120TM proteins, were apathogenic in a sensitive suckling mouse neurovirulence test, and were similar in immunogenicity to recombinant poxvirus NYVAC-HIV vectors in homologous or heterologous prime-boost combinations in mice. In a pilot NHP study, immunogenicity of RV-HIV viruses used as a prime or boost for DNA or NYVAC candidates was compared to a DNA prime/NYVAC boost benchmark scheme when administered together with adjuvanted gp120 protein. Similar neutralizing antibody titers, binding IgG titers measured against a broad panel of Env and Gag antigens, and ADCC responses were observed in the groups throughout the course of the study, and T cell responses were elicited. The entire data demonstrate that RV vectors have the potential as novel HIV-1 vaccine components for use in combination with other promising candidates to develop new effective vaccination strategies.