Immunogenicity of rVSVΔG-ZEBOV-GP Ebola vaccine (ERVEBO®) in African clinical trial participants by age, sex, and baseline GP-ELISA titer: A post hoc analysis of three Phase 2/3 trials.

Background: ERVEBO®, a live recombinant vesicular stomatitis virus (VSV) vaccine containing the Zaire ebolavirus glycoprotein (GP) in place of the VSV GP (rVSVΔG-ZEBOV-GP), was advanced through clinical development by Merck & Co., Inc., Rahway, NJ, USA in collaboration with multiple partners to prevent Ebola virus disease (EVD) and has been approved for human use in several countries.

Accelerating model-informed decisions for COVID-19 vaccine candidates using a model-based meta-analysis approach.

Background: The COVID-19 pandemic has increased the need for innovative quantitative decision tools to support rapid development of safe and efficacious vaccines against SARS-CoV-2. To meet that need, we developed and applied a model-based meta-analysis (MBMA) approach integrating non-clinical and clinical immunogenicity and protection data.

Methods: A systematic literature review identified studies of vaccines against SARS-CoV-2 in rhesus macaques (RM) and humans.

Lessons Learned from the Development and Roll-Out of the rVSVΔG-ZEBOV-GP Vaccine to Inform Marburg Virus and Vaccines.

This review describes key aspects of the development of the rVSVΔG-ZEBOV-GP Ebola vaccine and key activities which are continuing to further expand our knowledge of the product. Extensive partnerships and innovative approaches were used to address the various challenges encountered during this process. The rVSVΔG-ZEBOV-GP Ebola vaccine was initially approved by the European Medicines Agency and prequalified by the World Health Organization in November 2019.

Estimation of the correlates of protection of the rVSVΔG-ZEBOV-GP Zaire ebolavirus vaccine: a post-hoc analysis of data from phase 2/3 clinical trials.

Background: Establishment of immune correlates of protection can provide a measurable criterion for assessing protection against infection or disease. For some vaccines, such as the measles vaccine, antibodies serve as the correlate of protection, but for others, such as human papillomavirus, the correlate of protection remains unknown. Merck & Co, Kenilworth, NJ, USA, in collaboration with multiple partners, developed a live recombinant vesicular stomatitis virus vaccine (rVSVΔG-ZEBOV-GP [ERVEBO]) containing the Zaire ebolavirus glycoprotein (GP) in place of the recombinant vesicular stomatitis virus GP to prevent Ebola virus disease.

Environmental Risk Assessment for rVSVΔG-ZEBOV-GP, a Genetically Modified Live Vaccine for Ebola Virus Disease.

rVSVΔG-ZEBOV-GP is a live, attenuated, recombinant vesicular stomatitis virus (rVSV)-based vaccine for the prevention of Ebola virus disease caused by . As a replication-competent genetically modified organism, rVSVΔG-ZEBOV-GP underwent various environmental evaluations prior to approval, the most in-depth being the environmental risk assessment (ERA) required by the European Medicines Agency. This ERA, as well as the underlying methodology used to arrive at a sound conclusion about the environmental risks of rVSVΔG-ZEBOV-GP, are described in this review.

Accelerating Vaccine Development During the 2013-2016 West African Ebola Virus Disease Outbreak.

The Ebola virus disease outbreak that began in Western Africa in December 2013 was unprecedented in both scope and spread, and the global response was slower and less coherent than was optimal given the scale and pace of the epidemic. Past experience with limited localized outbreaks, lack of licensed medical countermeasures, reluctance by first responders to direct scarce resources to clinical research, community resistance to outside interventions, and lack of local infrastructure were among the factors delaying clinical research during the outbreak. Despite these hurdles, the global health community succeeded in accelerating Ebola virus vaccine development, in a 5-month interval initiating phase I trials in humans in September 2014 and initiating phase II/III trails in February 2015.

A Single-Dose Recombinant Parainfluenza Virus 5-Vectored Vaccine Expressing Respiratory Syncytial Virus (RSV) F or G Protein Protected Cotton Rats and African Green Monkeys from RSV Challenge.

Human respiratory syncytial virus (RSV) is a common cause of severe respiratory disease among infants, immunocompromised individuals, and the elderly. No licensed vaccine is currently available. In this study, we evaluated two parainfluenza virus 5 (PIV5)-vectored vaccines expressing RSV F (PIV5/F) or G (PIV5/G) protein in the cotton rat and African green monkey models for their replication, immunogenicity, and efficacy of protection against RSV challenge.

A replication-defective human cytomegalovirus vaccine for prevention of congenital infection.

Congenital human cytomegalovirus (HCMV) infection occurs in ~0.64% of infants born each year in the United States and is the leading nongenetic cause of childhood neurodevelopmental disabilities. No licensed HCMV vaccine is currently available.

Effector and Central Memory Poly-Functional CD4(+) and CD8(+) T Cells are Boosted upon ZOSTAVAX(®) Vaccination.

ZOSTAVAX(®) is a live attenuated varicella-zoster virus (VZV) vaccine that is licensed for the protection of individuals ≥50 years against shingles and its most common complication, postherpetic neuralgia. While IFNγ responses increase upon vaccination, the quality of the T cell response has not been elucidated. By using polychromatic flow cytometry, we characterized the breadth, magnitude, and quality of ex vivo CD4(+) and CD8(+) T cell responses induced 3-4 weeks after ZOSTAVAX vaccination of healthy adults.

A novel lipid nanoparticle adjuvant significantly enhances B cell and T cell responses to sub-unit vaccine antigens.

Sub-unit vaccines are primarily designed to include antigens required to elicit protective immune responses and to be safer than whole-inactivated or live-attenuated vaccines. But their purity and inability to self-adjuvant often result in weaker immunogenicity. Emerging evidence suggests that bio-engineered nanoparticles can be used as immunomodulatory adjuvants.

Rapid isolation of dengue-neutralizing antibodies from single cell-sorted human antigen-specific memory B-cell cultures.

Monitoring antigen-specific memory B cells and the antibodies they encode is important for understanding the specificity, breadth and duration of immune response to an infection or vaccination. The antibodies isolated could further help design vaccine antigens for raising relevant protective immune responses. However, developing assays to measure and isolate antigen-specific memory B cells is technically challenging due to the low frequencies of these cells that exist in the circulating blood.

Preclinical and clinical development of a dengue recombinant subunit vaccine.

This review focuses on a dengue virus (DENV) vaccine candidate based on a recombinant subunit approach which targets the DENV envelope glycoprotein (E). Truncated versions of E consisting of the N-terminal portion of E (DEN-80E) have been expressed recombinantly in the Drosophila S2 expression system and shown to have native-like conformation. Preclinical studies demonstrate that formulations containing tetravalent DEN-80E adjuvanted with ISCOMATRIX™ adjuvant induce high titer virus neutralizing antibodies and IFN-γ producing T cells in flavivirus-naïve non-human primates.

Mapping HIV-1 vaccine induced T-cell responses: bias towards less-conserved regions and potential impact on vaccine efficacy in the Step study.

Unlabelled: T cell directed HIV vaccines are based upon the induction of CD8+ T cell memory responses that would be effective in inhibiting infection and subsequent replication of an infecting HIV-1 strain, a process that requires a match or near-match between the epitope induced by vaccination and the infecting viral strain. We compared the frequency and specificity of the CTL epitope responses elicited by the replication-defective Ad5 gag/pol/nef vaccine used in the Step trial with the likelihood of encountering those epitopes among recently sequenced Clade B isolates of HIV-1. Among vaccinees with detectable 15-mer peptide pool ELISpot responses, there was a median of four (one Gag, one Nef and two Pol) CD8 epitopes per vaccinee detected by 9-mer peptide ELISpot assay.

Synthesis and immunological activities of novel Toll-like receptor 7 and 8 agonists.

Single-stranded oligoribonucleotides (ORNs) stimulate innate immune responses through TLR7 and TLR8. Specific linkages and chemical modifications incorporated into synthetic ORN can greatly enhance nuclease stability, selectivity, and potency. In the present study, we have synthesized 15 ORN containing different sequence compositions and chemical modifications and studied their TLR7- and TLR8-mediated immune response profiles in HEK293 cells expressing human TLR7 or TLR8, human PBMCs, mDCs and pDCs, non-human primate (NHP) PBMCs, and in vivo in mice and NHPs.

Vaccination with Ad5 vectors expands Ad5-specific CD8 T cells without altering memory phenotype or functionality.

Background: Adenoviral (Ad) vaccine vectors represent both a vehicle to present a novel antigen to the immune system as well as restimulation of immune responses against the Ad vector itself. To what degree Ad-specific CD8(+) T cells are restimulated by Ad vector vaccination is unclear, although such knowledge would be important as vector-specific CD8(+) T cell expansion could potentially further limit Ad vaccine efficacy beyond Ad-specific neutralizing antibody alone.

Methodology/principal Findings: Here we addressed this issue by measuring human Adenovirus serotype 5 (Ad5)-specific CD8(+) T cells in recipients of the Merck Ad5 HIV-1 vaccine vector before, during, and after vaccination by multicolor flow cytometry.

Comparison of T cell immune responses induced by vectored HIV vaccines in non-human primates and humans.

Following the disappointing outcome of the phase IIb test-of-concept step study in which Merck's adenovirus type 5 (Ad5) HIV-1 clade B gag/pol/nef vaccine failed to demonstrate efficacy in HIV high-risk individuals, an extensive review of the trial and preclinical studies which supported the trial is ongoing. One point of interest is how well preclinical nonhuman primate immunogenicity studies predicted what was observed in humans. Here we compare the HIV-1-specific cellular immune responses elicited in nonhuman primates and human clinical trial subjects to several HIV-1 vaccine candidates.

Synthesis and immunological activities of novel agonists of toll-like receptor 9.

Novel agonists of TLR9 with two 5'-ends and synthetic immune stimulatory motifs, referred to as immune modulatory oligonucleotides (IMOs) are potent agonists of TLR9. In the present study, we have designed and synthesized 15 novel IMOs by incorporating specific chemical modifications and studied their immune response profiles both in vitro and in vivo. Analysis of the immunostimulatory profiles of these IMOs in human and NHP cell-based assays suggest that changes in the number of synthetic immunostimulatory motifs gave only a subtle change in immune stimulation of pDCs as indicated by IFN-alpha production and pDC maturation while the addition of self-complementary sequences produced more dramatic changes in both pDC and B cell stimulation.

Comparative cell-mediated immunogenicity of DNA/DNA, DNA/adenovirus type 5 (Ad5), or Ad5/Ad5 HIV-1 clade B gag vaccine prime-boost regimens.

Background: We report composite results from the Merck phase I program of near-consensus clade B human immunodeficiency virus (HIV) type 1 gag vaccines.

Methods: Healthy HIV-uninfected adults were enrolled in 6 blinded placebo-controlled studies evaluating the immunogenicity of (1) a 4-dose regimen of a DNA vaccine, (2) a 3-dose priming regimen of the DNA vaccine with a booster dose of an adenovirus type 5 (Ad5)-vectored vaccine, or (3) a 3-dose regimen of the Ad5 vaccine. The DNA plasmid was provided with or without an aluminum phosphate or CRL1005 adjuvant.

Baseline Ad5 serostatus does not predict Ad5 HIV vaccine-induced expansion of adenovirus-specific CD4+ T cells.

The mechanisms underlying possible increased HIV-1 acquisition in adenovirus 5 (Ad5)-seropositive subjects vaccinated with Ad5-HIV-1 vectors in the Merck STEP trial remain unclear. We find that Ad5 serostatus does not predict Ad5-specific CD4(+) T cell frequency, and we did not observe durable significant differences in Ad5-specific CD4(+) T cells between Ad5-seropositive and Ad5-seronegative subjects after vaccination. These findings indicate no causative role for Ad5-specific CD4(+) T cells in increasing HIV-1 susceptibility in the STEP trial.

Adenovirus-specific immunity after immunization with an Ad5 HIV-1 vaccine candidate in humans.

The immunologic basis for the potential enhanced HIV-1 acquisition in adenovirus serotype 5 (Ad5)-seropositive individuals who received the Merck recombinant Ad5 HIV-1 vaccine in the STEP study remains unclear. Here we show that baseline Ad5-specific neutralizing antibodies are not correlated with Ad5-specific T lymphocyte responses and that Ad5-seropositive subjects do not develop higher vector-specific cellular immune responses as compared with Ad5-seronegative subjects after vaccination. These findings challenge the hypothesis that activated Ad5-specific T lymphocytes were the cause of the potential enhanced HIV-1 susceptibility in the STEP study.

Safety and immunogenicity of adenovirus-vectored near-consensus HIV type 1 clade B gag vaccines in healthy adults.

Vaccines inducing pathogen-specific cell-mediated immunity are being developed using attenuated adenoviral (Ad) vectors. We report the results of two independent Phase I trials of similar replication-deficient Ad5 vaccines containing a near-consensus HIV-1 clade B gag transgene. Healthy HIV-uninfected adults were enrolled in two separate, multicenter, dose-escalating, blinded, placebo-controlled studies to assess the safety and immunogenicity of a three-dose homologous regimen of Ad5 and MRKAd5 HIV-1 gag vaccines given on day 1, week 4, and week 26.

DNA gag/adenovirus type 5 (Ad5) gag and Ad5 gag/Ad5 gag vaccines induce distinct T-cell response profiles.

Results from Merck's phase II adenovirus type 5 (Ad5) gag/pol/nef test-of-concept trial showed that the vaccine lacked efficacy against human immunodeficiency virus (HIV) infection in a high-risk population. Among the many questions to be explored following this outcome are whether (i) the Ad5 vaccine induced the quality of T-cell responses necessary for efficacy and (ii) the lack of efficacy in the Ad5 vaccine can be generalized to other vector approaches intended to induce HIV type 1 (HIV-1)-specific T-cell responses. Here we present a comprehensive evaluation of the T-cell response profiles from cohorts of clinical trial subjects who received the HIV CAM-1 gag insert delivered by either a regimen with DNA priming followed by Ad5 boosting (n = 50) or a homologous Ad5/Ad5 prime-boost regimen (n = 70).

Safety and immunogenicity of a replication-incompetent adenovirus type 5 HIV-1 clade B gag/pol/nef vaccine in healthy adults.

Background: The safety and immunogenicity of the MRK adenovirus type 5 human immunodeficiency virus type 1 clade B gag/pol/nef vaccine, a replication-incompetent adenovirus type 5-vectored vaccine designed to elicit cell-mediated immunity against conserved human immunodeficiency virus proteins, was assessed in a phase 1 trial.

Methods: Healthy adults not infected with human immunodeficiency virus were enrolled in a multicenter, dose-escalating, blind, placebo-controlled study to evaluate a 3-dose homologous prime-boost regimen of the trivalent MRK adenovirus type 5 human immunodeficiency virus type 1 vaccine containing from 3 x 10(6) to 1 x 10(11) viral particles per 1-mL dose administered on day 1, during week 4 and during week 26. Adverse events were recorded for 29 days after each intradeltoid injection.

Evaluation of cellular immune responses in subjects chronically infected with HIV type 1.

The importance of host cellular immune responses, particularly CD8(+) cytotoxic T-lymphocyte (CTL) responses, in control of human immunodeficiency virus type 1 (HIV-1) infection has been demonstrated in many clinical studies. These studies, along with vaccination challenge studies in rhesus macaques, indicate the importance of cellular immune responses against HIV-1. Toward this end, we evaluated anti-HIV-1 cellular immune responses in a cohort of 54 subjects who were chronically infected with HIV-1.

A comparison of standard immunogenicity assays for monitoring HIV type 1 gag-specific T cell responses in Ad5 HIV Type 1 gag vaccinated human subjects.

Currently, there are numerous candidate HIV vaccines aimed at inducing T-cell mediated immune responses against HIV. To assess the immunogenicity of such vaccines, a reliable T cell assay must be utilized and typically one of the following assays is chosen for this purpose: bulk culture CTL, MHC I tetramer staining, IFN-gamma ELISPOT, or IFN-gamma intracellular cytokine staining. In this paper we report a comparison of the T cell responses detected by each assay in a large cohort of healthy normal volunteers vaccinated with adenovirus serotype 5 expressing HIV gag.