Co-administration of viral vector-based vaccines suppresses antigen-specific effector CD8 T cells

Safety and immunogenicity of an adjuvanted chikungunya virus virus-like particle (CHIKV VLP) vaccine in previous recipients of other alphavirus vaccines versus alphavirus vaccine-naive controls: an open-label, parallel-group, age-matched, sex-matched, phase 2 randomised controlled study

BACKGROUND

Immune responses to alphavirus vaccines might be impaired when heterologous alphavirus vaccines are administered sequentially. We aimed to compare immunogenicity and safety of a chikungunya virus virus-like particle (CHIKV VLP) vaccine in previous recipients of heterologous alphavirus vaccines with alphavirus-naive controls in the USA.

METHODS

In this open-label, parallel-group, age-matched, sex-matched, phase 2 randomised controlled trial, which was conducted at two clinical study sites in the USA, adults (aged 18-65 years) who had previously received an investigational Venezuelan equine encephalitis virus vaccine (previous alphavirus vaccine recipients; n=30) and sex-matched and age-matched alphavirus vaccine-naive controls (n=30) were intramuscularly administered one 40 μg dose of CHIKV VLP vaccine on day 1. Immunogenicity was based on serum neutralising antibodies assessed by an in-vitro luciferase-based anti-CHIKV NT80 neutralisation assay. The primary immunogenicity endpoint, which was assessed in the immunogenicity evaluable population (CHIKV VLP-vaccinated participants who had no important protocol deviations, had not received a prohibited medication, and provided evaluable serum sample results for baseline and on day 22), was to compare the proportion of previous alphavirus vaccine recipients with the proportion of alphavirus vaccine-naive controls who reached seroconversion 21 days after vaccination (ie, study day 22) with a single dose of CHIKV VLP vaccine, based on a four-fold increase of CHIKV neutralising antibodies compared with baseline. The significance of the comparison of the two groups was assessed using Fisher's exact test. The proportion with seroconversion in each group is presented with 95% CIs calculated using the Wilson method. The difference and 95% CIs for this difference was calculated based on Newcombe hybrid score method. An ANOVA model was fit with log10-transformed titre as the dependent variable, and study arm, age, and sex as predictors. Least squares means, difference, and 95% CIs were back-transformed and reported as geometric mean titres (GMTs). This trial is registered with ClinicalTrials.gov, NCT03992872.

FINDINGS

Between Nov 20, 2019, and Jan 19, 2021, 60 participants (20 [33%] female and 40 [67%] male; 40 (67%) White; median age 47·0 years [IQR 13·5]), 30 previous alphavirus vaccine recipients and 30 alphavirus vaccine-naive controls, were enrolled, vaccinated with CHIKV VLP, and completed the trial. The anti-CHIKV neutralising antibody seroconversion rate at day 22 was 100% (95% CI 88·6-100) in both groups. GMTs peaked in previous alphavirus vaccine recipients and alphavirus vaccine-naive controls at day 22 (2032·5 [95% CI 1413·0-2923·6] and 2299·2 [1598·1-3307·8], respectively) and were similar between the groups on day 22 and all subsequent visits. A higher proportion of previous alphavirus vaccine recipients (93·3% [95% CI 78·7-98·2]) had a four-fold neutralising antibody increase at day 8 than did alphavirus vaccine-naive controls (66·7% [48·8-80·8]; p=0·021). There was no statistically significant difference in the incidence of solicited adverse events between the previous alphavirus vaccine recipients and alphavirus vaccine-naive controls (53·3% vs 40·0%, respectively), although the relatively small sample size of the trial limited the power to detect a significant difference, and there were no reported vaccine-related serious adverse events.

INTERPRETATION

CHIKV VLP vaccine was well tolerated and similarly immunogenic in both alphavirus vaccine-naive participants and previous recipients of a heterologous alphavirus vaccine. There were no significant differences in adverse events between the groups. The results of this study support the use of CHIKV VLP vaccine in individuals with previous alphavirus vaccine exposure.

FUNDING

Defense Health Program, Emergent Travel Health, and Bavarian Nordic A/S.

Early Post-Vaccination Gene Signatures Correlate With the Magnitude and Function of Vaccine-Induced HIV Envelope-Specific Plasma Antibodies in Infant Rhesus Macaques

A better understanding of the impact of early innate immune responses after vaccine priming on vaccine-elicited adaptive immune responses could inform rational design for effective HIV vaccines. The current study compared the whole blood molecular immune signatures of a 3M-052-SE adjuvanted HIV Env protein vaccine to a regimen combining the adjuvanted Env protein with simultaneous administration of a modified Vaccinia Ankara vector expressing HIV Env in infant rhesus macaques at days 0, 1, and 3 post vaccine prime. Both vaccines induced a rapid innate response, evident by elevated inflammatory plasma cytokines and altered gene expression. We identified 25 differentially-expressed genes (DEG) on day 1 compared to day 0 in the HIV protein vaccine group. In contrast, in the group that received both the Env protein and the MVA-Env vaccine only two DEG were identified, implying that the MVA-Env modified the innate response to the adjuvanted protein vaccine. By day 3, only three DEG maintained altered expression, indicative of the transient nature of the innate response. The DEG represented immune pathways associated with complement activation, type I interferon and interleukin signaling, pathogen sensing, and induction of adaptive immunity. DEG expression on day 1 was correlated to Env-specific antibody responses, in particular antibody-dependent cytotoxicity responses at week 34, and Env-specific follicular T helper cells. Results from network analysis supported the interaction of DEG and their proteins in B cell activation. These results emphasize that vaccine-induced HIV-specific antibody responses can be optimized through the modulation of the innate response to the vaccine prime.

A Novel Vaccine Strategy Employing Serologically Different Chimpanzee Adenoviral Vectors for the Prevention of HIV-1 and HCV Coinfection

Background: Nearly 3 million people worldwide are coinfected with HIV and HCV. Affordable strategies for prevention are needed. We developed a novel vaccination regimen involving replication-defective and serologically distinct chimpanzee adenovirus (ChAd3, ChAd63) vector priming followed by modified vaccinia Ankara (MVA) boosts, for simultaneous delivery of HCV non-structural (NSmut) and HIV-1 conserved (HIVconsv) region immunogens.

Methods: We conducted a phase I trial in which 33 healthy volunteers were sequentially enrolled and vaccinated via the intramuscular route as follows: 9 received ChAd3-NSmut [2.5 × 10¹⁰ vp] and MVA-NSmut [2 × 10⁸ pfu] at weeks 0 and 8, respectively; 8 received ChAdV63.HIVconsv [5 × 10¹⁰ vp] and MVA.HIVconsv [2 × 10⁸ pfu] at the same interval; 16 were co-primed with ChAd3-NSmut [2.5 × 10¹⁰ vp] and ChAdV63.HIVconsv [5 × 10¹⁰ vp] followed at week 8 by MVA-NSmut and MVA.HIVconsv [both 1 × 10⁸ pfu]. Immunogenicity was assessed using peptide pools in ex vivo ELISpot and intracellular cytokine assays. Vaccine-induced whole blood transcriptome changes were assessed by microarray analysis.

Results: All vaccines were well tolerated and no vaccine-related serious adverse events occurred. Co-administration of the prime-boost vaccine regimens induced high magnitude and broad T cell responses that were similar to those observed following immunization with either regimen alone. Median (interquartile range, IQR) peak responses to NSmut were 3,480 (2,728–4,464) and 3,405 (2,307–7,804) spot-forming cells (SFC)/10⁶ PBMC for single and combined HCV vaccinations, respectively (p = 0.8). Median (IQR) peak responses to HIVconsv were 1,305 (1,095–4,967) and 1,005 (169–2,482) SFC/10⁶ PBMC for single and combined HIV-1 vaccinations, respectively (p = 0.5). Responses were maintained above baseline to 34 weeks post-vaccination. Intracellular cytokine analysis indicated that the responding populations comprised polyfunctional CD4⁺ and CD8⁺ T cells. Canonical pathway analysis showed that in the single and combined vaccination groups, pathways associated with antiviral and innate immune responses were enriched for upregulated interferon-stimulated genes 24 h after priming and boosting vaccinations.

Conclusions: Serologically distinct adenoviral vectors encoding HCV and HIV-1 immunogens can be safely co-administered without reducing the immunogenicity of either vaccine. This provides a novel strategy for targeting these viruses simultaneously and for other pathogens that affect the same populations.

Clinical trial registration:https://clinicaltrials.gov, identifier: NCT02362217

Overcoming tumor resistance by heterologous adeno-poxvirus combination therapy

Successful cancer control relies on overcoming resistance to cell death and on activation of host antitumor immunity. Oncolytic viruses are particularly attractive in this regard, as they lyse infected tumor cells and trigger robust immune responses during the infection. However, repeated injections of the same virus promote antiviral rather than antitumor immunity and tumors may mount innate antiviral defenses to restrict oncolytic virus replication. In this article, we have explored if alternating the therapy virus could circumvent these problems. We demonstrate in two virus-resistant animal models a substantial delay in antiviral immune- and innate cellular response induction by alternating injections of two immunologically distinct oncolytic viruses, adenovirus, and vaccinia virus. Our results are in support of clinical development of heterologous adeno-/vaccinia virus therapy of cancer.

Developments in Viral Vector-Based Vaccines

Viral vectors are promising tools for gene therapy and vaccines. Viral vector-based vaccines can enhance immunogenicity without an adjuvant and induce a robust cytotoxic T lymphocyte (CTL) response to eliminate virus-infected cells. During the last several decades, many types of viruses have been developed as vaccine vectors. Each has unique features and parental virus-related risks. In addition, genetically altered vectors have been developed to improve efficacy and safety, reduce administration dose, and enable large-scale manufacturing. To date, both successful and unsuccessful results have been reported in clinical trials. These trials provide important information on factors such as toxicity, administration dose tolerated, and optimized vaccination strategy. This review highlights major viral vectors that are the best candidates for clinical use.

Immune interference in the setting of same-day administration of two similar inactivated alphavirus vaccines: eastern equine and western equine encephalitis

We compared the effect on primary vaccination plaque-reduction neutralization 80% titers (PRNT80) responses of same-day administration (at different injection sites) of two similar investigational inactivated alphavirus vaccines, eastern equine encephalitis (EEE) vaccine (TSI-GSD 104) and western equine encephalitis (WEE) vaccine (TSI-GSD 210) to separate administration. Overall, primary response rate for EEE vaccine was 524/796 (66%) and overall primary response rate for WEE vaccine was 291/695 (42%). EEE vaccine same-day administration yielded a 59% response rate and a responder geometric mean titer (GMT)=89 while separate administration yielded a response rate of 69% and a responder GMT=119. WEE vaccine same-day administration yielded a 30% response rate and a responder GMT=53 while separate administration yielded a response rate of 54% and a responder GMT=79. EEE response rates for same-day administration (group A) vs. non-same-day administration (group B) were significantly affected by gender. A logistic regression model predicting response to EEE comparing group B to group A for females yielded an OR=4.10 (95% CL 1.97-8.55; p=.0002) and for males yielded an OR=1.25 (95% CL 0.76-2.07; p=.3768). WEE response rates for same-day administration vs. non-same-day administration were independent of gender. A logistic regression model predicting response to WEE comparing group B to group A yielded an OR=2.14 (95% CL 1.22-3.73; p=.0077). We report immune interference occurring with same-day administration of two completely separate formalin inactivated viral vaccines in humans. These findings combined with the findings of others regarding immune interference would argue for a renewed emphasis on studying the immunological mechanisms of induction of inactivated viral vaccine protection.

Mixed vector immunization with recombinant adenovirus and MVA can improve vaccine efficacy while decreasing antivector immunity

Substantial protection can be provided against the pre-erythrocytic stages of malaria by vaccination first with an adenoviral and then with an modified vaccinia virus Ankara (MVA) poxviral vector encoding the same ME.TRAP transgene. We investigated whether the two vaccine components adenovirus (Ad) and MVA could be coinjected as a mixture to enhance protection against malaria. A single-shot mixture at specific ratios of Ad and MVA (Ad+MVA) enhanced CD8⁺ T cell-dependant protection of mice against challenge with Plasmodium berghei. Moreover, the degree of protection could be enhanced after homologous boosting with the same Ad+MVA mixture to levels comparable with classic heterologous Ad prime-MVA boost regimes. The mixture increased transgene-specific responses while decreasing the CD8⁺ T cell antivector immunity compared to each vector used alone, particularly against the MVA backbone. Mixed vector immunization led to increased early circulating interferon-γ (IFN-γ) response levels and altered transcriptional microarray profiles. Furthermore, we found that sequential immunizations with the Ad+MVA mixture led to consistent boosting of the transgene-specific CD8⁺ response for up to three mixture immunizations, whereas each vector used alone elicited progressively lower responses. Our findings offer the possibility of simplifying the deployment of viral vectors as a single mixture product rather than in heterologous prime-boost regimens.