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Respiratory Syncytial Virus (RSV) remains a leading cause of severe respiratory disease for which no licensed vaccine is available. We have previously described the derivation of an RSV Fusion protein (F) stabilized in its prefusion conformation (preF) as vaccine immunogen and demonstrated superior immunogenicity in naive mice of preF versus wild type RSV F protein, both as protein and when expressed from an Ad26 vaccine vector. Here we address the question if there are qualitative differences between the two vaccine platforms for induction of protective immunity. In naïve mice, both Ad26.RSV.preF and preF protein induced humoral responses, whereas cellular responses were only elicited by Ad26.RSV.preF. In RSV pre-exposed mice, a single dose of either vaccine induced cellular responses and strong humoral responses. Ad26-induced RSV-specific cellular immune responses were detected systemically and locally in the lungs. Both vaccines showed protective efficacy in the cotton rat model, but Ad26.RSV.preF conferred protection at lower virus neutralizing titers in comparison to RSV preF protein. Factors that may contribute to the protective capacity of Ad26.RSV.preF elicited immunity are the induced IgG2a antibodies that are able to engage Fcγ receptors mediating Antibody Dependent Cellular Cytotoxicity (ADCC), and the induction of systemic and lung resident RSV specific CD8 + T cells. These data demonstrate qualitative improvement of immune responses elicited by an adenoviral vector based vaccine encoding the RSV preF antigen compared to the subunit vaccine in small animal models which may inform RSV vaccine development.

Background: The Ebola epidemics in west Africa and the Democratic Republic of the Congo highlight an urgent need for safe and effective vaccines to prevent Ebola virus disease. We aimed to assess the safety and long-term immunogenicity of a two-dose heterologous vaccine regimen, comprising the adenovirus type 26 vector-based vaccine encoding the Ebola virus glycoprotein (Ad26.ZEBOV) and the modified vaccinia Ankara vector-based vaccine, encoding glycoproteins from Ebola virus, Sudan virus, and Marburg virus, and the nucleoprotein from the Tai Forest virus (MVA-BN-Filo), in Sierra Leone, a country previously affected by Ebola. Methods: The trial comprised two stages: an open-label, non-randomised stage 1, and a randomised, double-blind, controlled stage 2. The study was done at three clinics in Kambia district, Sierra Leone. In stage 1, healthy adults (aged ≥18 years) residing in or near Kambia district, received an intramuscular injection of Ad26.ZEBOV (5 × 1010 viral particles) on day 1 (first dose) followed by an intramuscular injection of MVA-BN-Filo (1 × 108 infectious units) on day 57 (second dose). An Ad26.ZEBOV booster vaccination was offered at 2 years after the first dose to stage 1 participants. The eligibility criteria for adult participants in stage 2 were consistent with stage 1 eligibility criteria. Stage 2 participants were randomly assigned (3:1), by computer-generated block randomisation (block size of eight) via an interactive web-response system, to receive either the Ebola vaccine regimen (Ad26.ZEBOV followed by MVA-BN-Filo) or an intramuscular injection of a single dose of meningococcal quadrivalent (serogroups A, C, W135, and Y) conjugate vaccine (MenACWY; first dose) followed by placebo on day 57 (second dose; control group). Study team personnel, except those with primary responsibility for study vaccine preparation, and participants were masked to study vaccine allocation. The primary outcome was the safety of the Ad26.ZEBOV and MVA-BN-Filo vaccine regimen, which was assessed in all participants who had received at least one dose of study vaccine. Safety was assessed as solicited local and systemic adverse events occurring in the first 7 days after each vaccination, unsolicited adverse events occurring in the first 28 days after each vaccination, and serious adverse events or immediate reportable events occurring up to each participant's last study visit. Secondary outcomes were to assess Ebola virus glycoprotein-specific binding antibody responses at 21 days after the second vaccine in a per-protocol set of participants (ie, those who had received both vaccinations within the protocol-defined time window, had at least one evaluable post-vaccination sample, and had no major protocol deviations that could have influenced the immune response) and to assess the safety and tolerability of the Ad26.ZEBOV booster vaccination in stage 1 participants who had received the booster dose. This study is registered at ClinicalTrials.gov, NCT02509494. Findings: Between Sept 30, 2015, and Oct 19, 2016, 443 participants (43 in stage 1 and 400 in stage 2) were enrolled; 341 participants assigned to receive the Ad26.ZEBOV and MVA-BN-Filo regimen and 102 participants assigned to receive the MenACWY and placebo regimen received at least one dose of study vaccine. Both regimens were well tolerated with no safety concerns. In stage 1, solicited local adverse events (mostly mild or moderate injection-site pain) were reported in 12 (28%) of 43 participants after Ad26.ZEBOV vaccination and in six (14%) participants after MVA-BN-Filo vaccination. In stage 2, solicited local adverse events were reported in 51 (17%) of 298 participants after Ad26.ZEBOV vaccination, in 58 (24%) of 246 after MVA-BN-Filo vaccination, in 17 (17%) of 102 after MenACWY vaccination, and in eight (9%) of 86 after placebo injection. In stage 1, solicited systemic adverse events were reported in 18 (42%) of 43 participants after Ad26.ZEBOV vaccination and in 17 (40%) after MVA-BN-Filo vaccination. In stage 2, solicited systemic adverse events were reported in 161 (54%) of 298 participants after Ad26.ZEBOV vaccination, in 107 (43%) of 246 after MVA-BN-Filo vaccination, in 51 (50%) of 102 after MenACWY vaccination, and in 39 (45%) of 86 after placebo injection. Solicited systemic adverse events in both stage 1 and 2 participants included mostly mild or moderate headache, myalgia, fatigue, and arthralgia. The most frequent unsolicited adverse event after the first dose was headache in stage 1 and malaria in stage 2. Malaria was the most frequent unsolicited adverse event after the second dose in both stage 1 and 2. No serious adverse event was considered related to the study vaccine, and no immediate reportable events were observed. In stage 1, the safety profile after the booster vaccination was not notably different to that observed after the first dose. Vaccine-induced humoral immune responses were observed in 41 (98%) of 42 stage 1 participants (geometric mean binding antibody concentration 4784 ELISA units [EU]/mL [95% CI 3736–6125]) and in 176 (98%) of 179 stage 2 participants (3810 EU/mL [3312–4383]) at 21 days after the second vaccination. Interpretation: The Ad26.ZEBOV and MVA-BN-Filo vaccine regimen was well tolerated and immunogenic, with persistent humoral immune responses. These data support the use of this vaccine regimen for Ebola virus disease prophylaxis in adults. Funding: Innovative Medicines Initiative 2 Joint Undertaking and Janssen Vaccines & Prevention BV.

Summary Background Children account for a substantial proportion of cases and deaths from Ebola virus disease. We aimed to assess the safety and immunogenicity of a two-dose heterologous vaccine regimen, comprising the adenovirus type 26 vector-based vaccine encoding the Ebola virus glycoprotein (Ad26.ZEBOV) and the modified vaccinia Ankara vector-based vaccine, encoding glycoproteins from the Ebola virus, Sudan virus, and Marburg virus, and the nucleoprotein from the Tai Forest virus (MVA-BN-Filo), in a paediatric population in Sierra Leone. Methods This randomised, double-blind, controlled trial was done at three clinics in Kambia district, Sierra Leone. Healthy children and adolescents aged 1–17 years were enrolled in three age cohorts (12–17 years, 4–11 years, and 1–3 years) and randomly assigned (3:1), via computer-generated block randomisation (block size of eight), to receive an intramuscular injection of either Ad26.ZEBOV (5 × 1010 viral particles; first dose) followed by MVA-BN-Filo (1 × 108 infectious units; second dose) on day 57 (Ebola vaccine group), or a single dose of meningococcal quadrivalent (serogroups A, C, W135, and Y) conjugate vaccine (MenACWY; first dose) followed by placebo (second dose) on day 57 (control group). Study team personnel (except for those with primary responsibility for study vaccine preparation), participants, and their parents or guardians were masked to study vaccine allocation. The primary outcome was safety, measured as the occurrence of solicited local and systemic adverse symptoms during 7 days after each vaccination, unsolicited systemic adverse events during 28 days after each vaccination, abnormal laboratory results during the study period, and serious adverse events or immediate reportable events throughout the study period. The secondary outcome was immunogenicity (humoral immune response), measured as the concentration of Ebola virus glycoprotein-specific binding antibodies at 21 days after the second dose. The primary outcome was assessed in all participants who had received at least one dose of study vaccine and had available reactogenicity data, and immunogenicity was assessed in all participants who had received both vaccinations within the protocol-defined time window, had at least one evaluable post-vaccination sample, and had no major protocol deviations that could have influenced the immune response. This study is registered at ClinicalTrials.gov , NCT02509494 . Findings From April 4, 2017, to July 5, 2018, 576 eligible children or adolescents (192 in each of the three age cohorts) were enrolled and randomly assigned. The most common solicited local adverse event during the 7 days after the first and second dose was injection-site pain in all age groups, with frequencies ranging from 0% (none of 48) of children aged 1–3 years after placebo injection to 21% (30 of 144) of children aged 4–11 years after Ad26.ZEBOV vaccination. The most frequently observed solicited systemic adverse event during the 7 days was headache in the 12–17 years and 4–11 years age cohorts after the first and second dose, and pyrexia in the 1–3 years age cohort after the first and second dose. The most frequent unsolicited adverse event after the first and second dose vaccinations was malaria in all age cohorts, irrespective of the vaccine types. Following vaccination with MenACWY, severe thrombocytopaenia was observed in one participant aged 3 years. No other clinically significant laboratory abnormalities were observed in other study participants, and no serious adverse events related to the Ebola vaccine regimen were reported. There were no treatment-related deaths. Ebola virus glycoprotein-specific binding antibody responses at 21 days after the second dose of the Ebola virus vaccine regimen were observed in 131 (98%) of 134 children aged 12–17 years (9929 ELISA units [EU]/mL [95% CI 8172–12 064]), in 119 (99%) of 120 aged 4–11 years (10 212 EU/mL [8419–12 388]), and in 118 (98%) of 121 aged 1–3 years (22 568 EU/mL [18 426–27 642]). Interpretation The Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen was well tolerated with no safety concerns in children aged 1–17 years, and induced robust humoral immune responses, suggesting suitability of this regimen for Ebola virus disease prophylaxis in children. Funding Innovative Medicines Initiative 2 Joint Undertaking and Janssen Vaccines & Prevention BV.

Background Respiratory syncytial virus (RSV) can cause serious lower respiratory tract disease (LRTD) among older adults. There is no licensed RSV vaccine. In CYPRESS (a randomized, double-blind, placebo-controlled, phase 2b proof-of concept trial; NCT03982199), an Ad26.RSV.preF/RSV preF protein vaccine demonstrated 80.0% efficacy for prevention of RSV LRTD and 69.8% efficacy for prevention of any RSV acute respiratory infection in adults aged ≥65 years through the first RSV season. This study evaluated the durability of immune responses elicited by Ad26.RSV.preF/RSV preF protein after two RSV seasons (up to 1.5 years post-vaccination) in the overall study population and in groups of participants stratified by age and risk level for severe RSV LRTD. Methods Participants (N=5782) were randomized 1:1 to receive vaccine or placebo before the RSV season. The primary endpoint was first occurrence of RSV LRTD. RSV A2 virus neutralizing antibodies (VNAs; through Day 365), RSV preF binding antibodies (through Day 533), and RSV-F–specific IFN-γ enzyme-linked immune absorbent spot (ELISpot; through Day 533), were evaluated in an immunogenicity subset (n=195; ages 65–74 years: n=141; 75–84 years: n=47; ≥85 years: n=6; increased risk [chronic heart or lung disease]: n=48; non-increased risk: n=147). Results In the vaccine group of the immunogenicity subset, RSV A2 VNAs peaked at Day 15 and were maintained at 2.8-fold over baseline at 1 year. Similarly, RSV preF-specific binding antibodies peaked at Day 15 and were maintained at 2.1-fold above baseline at 1.5 years. Median RSV-F–specific IFN-γ T-cell frequency increased from 34 spot-forming cells (SFC)/106 peripheral blood mononuclear cells (PBMCs) at baseline to 143 SFC/106 PBMCs at 1.5 years. Comparable immune responses were observed in age/risk subgroups. No relevant changes were observed in the placebo group at any time point. Pre-existing Ad26 VNAs did not appear to impact RSV-specific immune response durability. Conclusion Ad26.RSV.preF/RSV preF protein vaccine was efficacious and elicited robust, durable (to at least 1.5 years) humoral and cellular immune responses in adults aged ≥65 years, older participants (≥75 years), and in participants with increased risk for severe RSV LRTD. Disclosures Christy A. Comeaux, MD, PhD, Janssen Vaccines & Prevention B.V.: Employee Ann R. Falsey, MD, BioFire Diagnostics: Grant/Research Support|Janssen: Grant/Research Support|Merck Sharp & Dohme: Grant/Research Support|Novavax: Advisor/Consultant|Pfizer: Grant/Research Support Kristi Williams, PhD, Janssen Research and Development: Employee John E. Ervin, MD, The Alliance for Multispecialty Research – KCM: Contractual agreement for conduct of study protocol Arangassery R. Bastian, PhD, Janssen Vaccines & Prevention BV: Employee Joris Menten, PhD, Janssen Infectious Diseases: Employee Els De Paepe, MSc, Janssen Infectious Diseases: employee Sjouke Vandenberghe, PhD, Janssen Infectious Diseases: Employee Eric K. H. Chan, PhD, Janssen Global Services, LLC: Employee Jerald Sadoff, MD, Janssen Vaccines & Prevention BV: Employee Macaya Douoguih, MD, MPH, Janssen Vaccines & Prevention B.V.: Employee Benoit Callendret, PhD, Janssen Vaccines & Prevention B.V.: Employee Esther Heijnen, MD, PhD, Janssen Vaccines & Prevention B.V.: Employee.

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory disease for which no licensed vaccine is available. We have previously shown that a prefusion (preF) conformation– stabilized RSV F protein antigen and an adenoviral vector encoding RSV preF protein (Ad26.RSV.preF) are immunogenic and protective in animals when administered as single components. Here, we evaluated a combination of the 2 components. Strong induction of both humoral and cellular responses was shown in RSV-naïve and pre-exposed mice and pre-exposed African green monkeys (AGMs). Both components of the combination vaccine contributed to humoral immune responses, while the Ad26.RSV.preF component was the main contributor to cellular immune responses in both mice and AGMs. Immunization with the combination elicited superior protection against RSV A2 challenge in cotton rats. These results demonstrate the advantage of a combination vaccine and support further clinical development.

Background Respiratory syncytial virus (RSV) remains a leading cause of pediatric morbidity, with no approved vaccine. We assessed the safety and immunogenicity of the Ad26.RSV.preF vaccine candidate in adults and children. Methods In this randomized, double-blind, phase 1/2a, placebo-controlled study, 12 adults (18–50 years) and 36 RSV-seropositive children (12–24 months) were randomized 2:1 to Ad26.RSV.preF (1 × 1011 viral particles [vp] for adults, 5 × 1010 vp for children) or placebo, at day 1 and 29, with 6-month immunogenicity and 1-year safety follow-up. Respiratory syncytial virus infection was an exploratory outcome in children. Results In adults, solicited adverse events (AEs) were generally mild to moderate, with no serious AEs. In children, no vaccination-related serious AEs were reported; fever was reported in 14 (58.3%) Ad26.RSV.preF recipients. Baseline pediatric geometric mean titers for RSV A2 neutralization increased from 121 (95% confidence interval [CI], 76–191) to 1608 (95% CI, 730–3544) at day 29, and 2235 (95% CI, 1586–3150) at day 57, remaining elevated over 7 months. Respiratory syncytial virus infection was confirmed in fewer children receiving Ad26.RSV.preF (1, 4.2%) than placebo (5, 41.7%). Conclusions Ad26.RSV.preF demonstrated immunogenicity in healthy adults and toddlers, with no safety concerns raised. Evaluations in RSV-seronegative children are underway.

Background Though clinically similar, Ebola virus disease and Marburg virus disease are caused by different viruses. Of the 30 documented outbreaks of these diseases in sub-Saharan Africa, eight were major outbreaks (≥200 cases; five caused by Zaire ebolavirus [EBOV], two by Sudan ebolavirus [SUDV], and one by Marburg virus [MARV]). Our purpose is to develop a multivalent vaccine regimen protecting against each of these filoviruses. This first-in-human study assessed the safety and immunogenicity of several multivalent two-dose vaccine regimens that contain Ad26.Filo and MVA-BN-Filo. Methods Ad26.Filo combines three vaccines encoding the glycoprotein (GP) of EBOV, SUDV, and MARV. MVA-BN-Filo is a multivalent vector encoding EBOV, SUDV, and MARV GPs, and Taï Forest nucleoprotein. This Phase 1, randomized, double-blind, placebo-controlled study enrolled healthy adults (18–50 years) into four groups, randomized 5:1 (active:placebo), to assess different Ad26.Filo and MVA-BN-Filo vaccine directionality and administration intervals. The primary endpoint was safety; immune responses against EBOV, SUDV, and MARV GPs were also assessed. Results Seventy-two participants were randomized, and 60 (83.3%) completed the study. All regimens were well tolerated with no deaths or vaccine-related serious adverse events (AEs). The most frequently reported solicited local AE was injection site pain/tenderness. Solicited systemic AEs most frequently reported were headache, fatigue, chills, and myalgia; most solicited AEs were Grade 1–2. Solicited/unsolicited AE profiles were similar between regimens. Twenty-one days post-dose 2, 100% of participants on active regimen responded to vaccination and exhibited binding antibodies against EBOV, SUDV, and MARV GPs; neutralizing antibody responses were robust against EBOV (85.7–100%), but lower against SUDV (35.7–100%) and MARV (0–57.1%) GPs. An Ad26.Filo booster induced a rapid further increase in humoral responses. Conclusion This study demonstrates that heterologous two-dose vaccine regimens with Ad26.Filo and MVA-BN-Filo are well tolerated and immunogenic in healthy adults. ClinicalTrials.gov NCT02860650.

Respiratory syncytial virus (RSV) infection is a major cause of severe lower respiratory tract infection and death in young infants and the elderly. With no effective prophylactic treatment available, current vaccine candidates aim to elicit neutralizing antibodies. However, binding and neutralization have poorly predicted protection in the past, and accumulating data across epidemiologic cohorts and animal models collectively point to a role for additional antibody Fc-effector functions. To begin to define the humoral correlates of immunity against RSV, here we profiled an adenovirus 26 RSV-preF vaccine-induced humoral immune response in a group of healthy adults that were ultimately challenged with RSV. Protection from infection was linked to opsonophagocytic functions, driven by IgA and differentially glycosylated RSV-specific IgG profiles, marking a functional humoral immune signature of protection against RSV. Furthermore, Fc-modified monoclonal antibodies able to selectively recruit effector functions demonstrated significant antiviral control in a murine model of RSV.

It has been proven challenging to conduct traditional efficacy trials for Ebola virus (EBOV) vaccines. In the absence of efficacy data, immunobridging is an approach to infer the likelihood of a vaccine protective effect, by translating vaccine immunogenicity in humans to a protective effect, using the relationship between vaccine immunogenicity and the desired outcome in a suitable animal model. We here propose to infer the protective effect of the Ad26.ZEBOV, MVA-BN-Filo vaccine regimen with an 8-week interval in humans by immunobridging. Immunogenicity and protective efficacy data were obtained for Ad26.ZEBOV and MVA-BN-Filo vaccine regimens using a fully lethal EBOV Kikwit challenge model in cynomolgus monkeys (nonhuman primates [NHP]). The association between EBOV neutralizing antibodies, glycoprotein (GP)-binding antibodies, and GP-reactive T cells and survival in NHP was assessed by logistic regression analysis. Binding antibodies against the EBOV surface GP were identified as the immune parameter with the strongest correlation to survival post EBOV challenge, and used to infer the predicted protective effect of the vaccine in humans using published data from phase I studies. The human vaccine-elicited EBOV GP-binding antibody levels are in a range associated with significant protection against mortality in NHP. Based on this immunobridging analysis, the EBOV GP-specific-binding antibody levels elicited by the Ad26.ZEBOV, MVA-BN-Filo vaccine regimen in humans will likely provide protection against EBOV disease.

Summary Background To address the unmet medical need for an effective prophylactic vaccine against Ebola virus we assessed the safety and immunogenicity of three different two-dose heterologous vaccination regimens with a replication-deficient adenovirus type 26 vector-based vaccine (Ad26.ZEBOV), expressing Zaire Ebola virus glycoprotein, and a non-replicating, recombinant, modified vaccinia Ankara (MVA) vector-based vaccine, encoding glycoproteins from Zaire Ebola virus, Sudan virus, and Marburg virus, and nucleoprotein from the Tai Forest virus. Methods This randomised, observer-blind, placebo-controlled, phase 2 trial was done at seven hospitals in France and two research centres in the UK. Healthy adults (aged 18–65 years) with no history of Ebola vaccination were enrolled into four cohorts. Participants in cohorts I–III were randomly assigned (1:1:1) using computer-generated randomisation codes into three parallel groups (randomisation for cohorts II and III was stratified by country and age), in which participants were to receive an intramuscular injection of Ad26.ZEBOV on day 1, followed by intramuscular injection of MVA-BN-Filo at either 28 days (28-day interval group), 56 days (56-day interval group), or 84 days (84-day interval group) after the first vaccine. Within these three groups, participants in cohort II (14:1) and cohort III (10:3) were further randomly assigned to receive either Ad26.ZEBOV or placebo on day 1, followed by either MVA-BN-Filo or placebo on days 28, 56, or 84. Participants in cohort IV were randomly assigned (5:1) to receive one dose of either Ad26.ZEBOV or placebo on day 1 for vector shedding assessments. For cohorts II and III, study site personnel, sponsor personnel, and participants were masked to vaccine allocation until all participants in these cohorts had completed the post-MVA-BN-Filo vaccination visit at 6 months or had discontinued the trial, whereas cohort I was open-label. For cohort IV, study site personnel and participants were masked to vaccine allocation until all participants in this cohort had completed the post-vaccination visit at 28 days or had discontinued the trial. The primary outcome, analysed in all participants who had received at least one dose of vaccine or placebo (full analysis set), was the safety and tolerability of the three vaccination regimens, as assessed by participant-reported solicited local and systemic adverse events within 7 days of receiving both vaccines, unsolicited adverse events within 42 days of receiving the MVA-BN-Filo vaccine, and serious adverse events over 365 days of follow-up. The secondary outcome was humoral immunogenicity, as measured by the concentration of Ebola virus glycoprotein-binding antibodies at 21 days after receiving the MVA-BN-Filo vaccine. The secondary outcome was assessed in the per-protocol analysis set. This study is registered at ClinicalTrials.gov , NCT02416453 , and EudraCT, 2015-000596-27. Findings Between June 23, 2015, and April 27, 2016, 423 participants were enrolled: 408 in cohorts I–III were randomly assigned to the 28-day interval group (123 to receive Ad26.ZEBOV and MVA-BN-Filo, and 13 to receive placebo), the 56-day interval group (124 to receive Ad26.ZEBOV and MVA-BN-Filo, and 13 to receive placebo), and the 84-day interval group (117 to receive Ad26.ZEBOV and MVA-BN-Filo, and 18 to receive placebo), and 15 participants in cohort IV were assigned to receive Ad26.ZEBOV and MVA-BN-Filo (n=13) or to receive placebo (n=2). 421 (99·5%) participants received at least one dose of vaccine or placebo. The trial was temporarily suspended after two serious neurological adverse events were reported, one of which was considered as possibly related to vaccination, and per-protocol vaccination was disrupted for some participants. Vaccinations were generally well tolerated. Mild or moderate local adverse events (mostly pain) were reported after 206 (62%) of 332 Ad26.ZEBOV vaccinations, 136 (58%) of 236 MVA-BN-Filo vaccinations, and 11 (15%) of 72 placebo injections. Systemic adverse events were reported after 255 (77%) Ad26.ZEBOV vaccinations, 116 (49%) MVA-BN-Filo vaccinations, and 33 (46%) placebo injections, and included mostly mild or moderate fatigue, headache, or myalgia. Unsolicited adverse events occurred after 115 (35%) of 332 Ad26.ZEBOV vaccinations, 81 (34%) of 236 MVA-BN-Filo vaccinations, and 24 (33%) of 72 placebo injections. At 21 days after receiving the MVA-BN-Filo vaccine, geometric mean concentrations of Ebola virus glycoprotein-binding antibodies were 4627 ELISA units (EU)/mL (95% CI 3649–5867) in the 28-day interval group, 10 131 EU/mL (8554–11 999) in the 56-day interval group, and 11 312 mL (9072–14106) in the 84-day interval group, with antibody concentrations persisting at 1149–1205 EU/mL up to day 365. Interpretation The two-dose heterologous regimen with Ad26.ZEBOV and MVA-BN-Filo was safe, well tolerated, and immunogenic, with humoral and cellular immune responses persisting for 1 year after vaccination. Taken together, these data support the intended prophylactic indication for the vaccine regimen. Funding Innovative Medicines Initiative and Janssen Vaccines & Prevention BV. Translation For the French translation of the abstract see Supplementary Materials section.

Background Respiratory syncytial virus (RSV) is a significant cause of severe lower respiratory tract disease in children and older adults, but has no approved vaccine. This study assessed the potential of Ad26.RSV.preF to protect against RSV infection and disease in an RSV human challenge model. Methods In this double-blind, placebo-controlled study, healthy adults aged 18–50 years were randomized 1:1 to receive 1 × 1011 vp Ad26.RSV.preF or placebo intramuscularly. Twenty-eight days postimmunization, volunteers were challenged intranasally with RSV-A (Memphis 37b). Assessments included viral load (VL), RSV infections, clinical symptom score (CSS), safety, and immunogenicity. Results Postchallenge, VL, RSV infections, and disease severity were lower in Ad26.RSV.preF (n = 27) vs placebo (n = 26) recipients: median VL area under the curve (AUC) quantitative real-time polymerase chain reaction: 0.0 vs 236.0 (P = .012; predefined primary endpoint); median VL-AUC quantitative culture: 0.0 vs 109; RSV infections 11 (40.7%) vs 17 (65.4%); median RSV AUC-CSS 35 vs 167, respectively. From baseline to 28 days postimmunization, geometric mean fold increases in RSV A2 neutralizing antibody titers of 5.8 and 0.9 were observed in Ad26.RSV.preF and placebo, respectively. Ad26.RSV.preF was well tolerated. Conclusions Ad26.RSV.preF demonstrated protection from RSV infection through immunization in a human challenge model, and therefore could potentially protect against natural RSV infection and disease. Clinical Trials Registration NCT03334695; CR108398, 2017-003194-33 (EudraCT); VAC18193RSV2002.

Background This phase 1 placebo-controlled study assessed the safety and immunogenicity of 2-dose regimens of Ad26.ZEBOV (adenovirus serotype 26 [Ad26]) and MVA-BN-Filo (modified vaccinia Ankara [MVA]) vaccines with booster vaccination at day 360. Methods Healthy US adults (N = 164) randomized into 10 groups received saline placebo or standard or high doses of Ad26 or MVA in 2-dose regimens at 7-, 14-, 28-, or 56-day intervals; 8 groups received booster Ad26 or MVA vaccinations on day 360. Participants reported solicited and unsolicited reactogenicity; we measured immunoglobulin G binding, neutralizing antibodies and cellular immune responses to Ebola virus glycoprotein. Results All regimens were well tolerated with no serious vaccine-related adverse events. Heterologous (Ad26,MVA [dose 1, dose 2] or MVA,Ad26) and homologous (Ad26,Ad26) regimens induced humoral and cellular immune responses 21 days after dose 2; responses were higher after heterologous regimens. Booster vaccination elicited anamnestic responses in all participants. Conclusions Both heterologous and homologous Ad26,MVA Ebola vaccine regimens are well tolerated in healthy adults, regardless of interval or dose level. Heterologous 2-dose Ad26,MVA regimens containing an Ebola virus insert induce strong, durable humoral and cellular immune responses. Immunological memory was rapidly recalled by booster vaccination, suggesting that Ad26 booster doses could be considered for individuals at risk of Ebola infection, who previously received the 2-dose regimen.

Ebola epidemics constitute serious public health emergencies. Multiple vaccines are under development to prevent these epidemics and avoid the associated morbidity and mortality. Assessing the potential impact of these vaccines on morbidity and mortality of Ebola is essential for devising prevention strategies. A mean-field compartmental stochastic model was developed for this purpose and validated by simulating the 2014 Sierra Leone epidemic. We assessed the impacts of prophylactic vaccination of healthcare workers (HCW) both alone and in combination with the vaccination of the general population (entire susceptible population other than HCW). The model simulated 8,706 (95% confidence intervals [CI]: 478-21,942) cases and 3,575 (95%CI: 179-9,031) deaths in Sierra Leone, in line with WHO-reported statistics for the 2014 epidemic (8,704 cases and 3,587 deaths). Relative to this base case, the model then estimated that prophylactic vaccination of only 10% of HCW will avert 12% (95% CI: 6%-14%) of overall cases and deaths, while vaccination of 30% of HCW will avert 34% of overall cases (95% CI: 30%-64%) and deaths (95% CI: 30%-65%). Prophylactic vaccination of 1% and 5% of the general population in addition to vaccinating 30% of HCW was estimated to result in reduction in cases by 44% (95% CI: 39%-61%) and 72% (95% CI: 68%-84%) respectively, and deaths by 45% (95% CI: 40%-61%) and 74% (95% CI: 70%-85%) respectively. Prophylactic vaccination of even small proportions of HCW is estimated to significantly reduce incidence of Ebola and associated mortality. The effect is greatly enhanced by the additional vaccination even of small percentages of the general population. These findings could be used to inform the planning of prevention strategies.

Background Respiratory syncytial virus (RSV) and influenza cause significant disease burden in older adults. Overlapping RSV and influenza seasonality presents the opportunity to coadminister vaccines for both infections. This study assessed coadministration of the investigational vaccine, Ad26.RSV.preF, an adenovirus serotype 26 (Ad26) vector encoding RSV F protein stabilized in its prefusion conformation (pre-F), with a seasonal influenza vaccine in older adults. Methods In this phase 2a, double-blind, placebo-controlled study, 180 adults aged ≥60 years received Ad26.RSV.preF plus Fluarix on day 1 and placebo on day 29, or placebo plus Fluarix on day 1 and Ad26.RSV.preF on day 29 (control). Results The coadministration regimen had an acceptable tolerability profile. Reactogenicity was generally higher after Ad26.RSV.preF versus Fluarix, but symptoms were generally transient and mild or moderate. At 28 days after the first vaccination, the upper confidence intervals of the hemagglutination inhibition antibody geometric mean ratio (control/coadministration) for all influenza strains were Conclusions Coadministration of Fluarix with Ad26.RSV.preF vaccine had an acceptable safety profile and showed no evidence of interference in immune response. The results are compatible with simultaneous seasonal vaccination with both vaccines. Clinical Trials Registration NCT03339713.

Background Despite the high disease burden of respiratory syncytial virus (RSV) in older adults, there is no approved vaccine. We evaluated the experimental RSV vaccine, Ad26.RSV.preF, a replication-incompetent adenovirus 26 vector encoding the F protein stabilized in prefusion conformation. Methods This phase 1 clinical trial was performed in healthy adults aged ≥60 years. Seventy-two participants received 1 or 2 intramuscular injections of low-dose (LD; 5 × 1010 vector particles) or high-dose (HD; 1 × 1011 vector particles) Ad26.RSV.preF vaccine or placebo, with approximately 12 months between doses and 2-year follow-up for safety and immunogenicity outcomes. Results Solicited adverse events were reported by 44% of vaccine recipients and were transient and mild or moderate in intensity. No serious adverse events were related to vaccination. After the first vaccination, geometric mean titers for RSV-A2 neutralization increased from baseline (432 for LD and 512 for HD vaccine) to day 29 (1031 for LD and 1617 for HD). Pre-F–specific antibody geometric mean titers and median frequencies of F-specific interferon γ–secreting T cells also increased substantially from baseline. These immune responses were still maintained above baseline levels 2 years after immunization and could be boosted with a second immunization at 1 year. Conclusions Ad26.RSV.preF (LD and HD) had an acceptable safety profile and elicited sustained humoral and cellular immune responses after a single immunization in older adults.

Background Respiratory syncytial virus (RSV) can cause serious lower respiratory tract disease (LRTD) in older adults. Despite a high burden of disease, there is currently no licensed vaccine for RSV. Here, we report the primary efficacy and immunogenicity results from a Phase 2b proof-of-concept trial of an Ad26.RSV.preF-based vaccine for the prevention of RSV-mediated LRTD in adults aged ≥65 years. Methods CYPRESS (NCT03982199) is a randomized, double-blind, placebo-controlled Phase 2b trial. Adults ≥65 years of age were randomized 1:1 prior to the RSV season to receive an Ad26.RSV.preF-based vaccine or placebo. Symptoms of acute respiratory infection (ARI) were collected through an RSV-specific patient-reported Respiratory Infection Intensity and Impact Questionnaire (RiiQ) and/or by a clinician assessment until the end of the RSV season. The primary endpoint was the first occurrence of RT-PCR-confirmed RSV-mediated LRTD according to any of 3 case definitions: (1) ≥3 symptoms of lower respiratory tract infection (LRTI), (2) ≥2 symptoms of LRTI, or (3) ≥2 symptoms of LRTI or ≥1 symptom of LRTI with ≥1 systemic symptom. The secondary endpoint was the first occurrence of any RT-PCR-confirmed RSV-mediated ARI. Immunogenicity assessments were performed in a subset of approximately 200 participants. Results A total of 5782 participants (2891 in each study arm) received study treatment (92.5% white, 57.7% female, median age 71 years). Vaccine efficacy was 80% (94.2% CI, 52.2–92.9%), 75% (50.1–88.5%), and 69.8% (43.7–84.7%) for case definition 1, 2, and 3, respectively (all P values < 0.001). Efficacy for any RSV-mediated ARI was 69.8% (95% CI, 42.7–85.1%). In the vaccine arm of the immunogenicity subset, geometric mean fold increase in antibody titers 14 days after vaccination was 13.5 for RSV neutralizing antibodies and 8.6 for RSV prefusion F-specific binding antibodies. Median frequency of RSV-F-specific INFγ T-cells increased from 34 to 444 SFC/106 PBMC 14 days after vaccination in the vaccine arm; no relevant changes were observed in the placebo arm. Conclusion In CYPRESS, the Ad26.RSV.preF-based vaccine was highly effective against RSV-mediated LRTD through the first RSV season and elicited robust humoral and cellular immune responses in adults aged ≥65 years. Disclosures Ann R. Falsey, MD, AstraZeneca (Individual(s) Involved: Self): Grant/Research Support; BioFire Diagnostics (Individual(s) Involved: Self): Grant/Research Support; Janssen (Individual(s) Involved: Self): Grant/Research Support; Merck, Sharpe and Dohme (Individual(s) Involved: Self): Grant/Research Support; Novavax (Individual(s) Involved: Self): Other Financial or Material Support, Paid DSMB member; Pfizer (Individual(s) Involved: Self): Grant/Research Support Kristi Williams, PhD, Janssen R&D US (Employee) Efi Gymnopoulou, MSc, Janssen Infectious Diseases BV (Employee) Arangassery Rosemary Bastian, PhD, Janssen Vaccines & Prevention BV (Employee) Joris Menten, n/a, Janssen Infectious Diseases BV (Employee) Els De Paepe, MSc, Janssen Infectious Diseases BV (Employee) Hilde de Boer, MSc, Janssen-Cilag (Employee) Sjoukje Vandenberghe, n/a, Janssen Infectious Diseases BV (Employee) Eric Chan, PhD, Janssen Global Services, LLC (Employee) Jerald Sadoff, MD, Johnson & Johnson (Employee, Shareholder) Macaya Douoguih, MD, MPH, Janssen (Employee) Benoit Callendret, PhD, Janssen Vaccines & Prevention BV (Employee) Christy Comeaux, MD, Janssen Vaccines & Prevention BV (Employee) Esther Heijnen, MD, Janssen Vaccines & Prevention BV (Employee)

Background Despite the high disease burden of RSV in older adults and children, there is currently no approved vaccine. Ad26.RSV.preF, an experimental RSV vaccine, has demonstrated immunogenicity and tolerability in first-in-human clinical studies. The aim of this study was to assess the potential of the Ad26.RSV.preF vaccine to protect against RSV infection and disease in an established RSV human challenge model, used for the first time to evaluate a vaccine. Methods We conducted a randomized, double-blind, placebo-controlled, human challenge study (NCT03334695). Healthy adults received 1 × 1011 vp Ad26.RSV.preF vaccine (active) or placebo (pbo) intramuscularly. After 28 days, volunteers were challenged intranasally with a low-passage clinical strain of RSV-A (0.8 mL of Memphis 37b) and then quarantined for 12 days. Nasal washes were collected twice daily throughout quarantine, starting 2 days post-challenge (viral load [VL] by qRT-PCR and quantitative cultures). Disease severity was recorded thrice daily using symptom diary cards. Results Fifty-three volunteers (active, n = 27; pbo, n = 26) were challenged with RSV-A. Quantitative viral assessments were consistently lower in active than pbo. The primary endpoint of the study was met: the area under the curve (AUC) for RSV VL over time (via qRT-PCR) was significantly lower in active pbo (P = 0.012). Median peak VL was lower for active (0 log10 copies/mL) than pbo (5.4 log10 copies/mL). Median AUC for RSV VL over time (quantitative culture) was lower for active than pbo (0 vs. 109, P = 0.002). Disease severity was lower for active than pbo, with a median AUC total symptom score of 35 (active) vs. 167 (pbo) (P = 0.002). Overall, RSV infection (defined by qRT-PCR alone or combined with symptoms) and disease severity over time were lower in active vs. pbo. Conclusion RSV infections, VL, and RSV disease severity were consistently lower in healthy adults receiving Ad26.RSV.preF vs. placebo, demonstrating promising protection from RSV infection and disease. This was the first time that antiviral prevention was observed against RSV after active immunization. Ad26.RSV.preF warrants further evaluation in field trials for efficacy against natural RSV infections in populations considered at risk of severe RSV disease. Disclosures All Authors: No reported Disclosures.

Exhaustion of antiviral CD8(+) T cells contributes to persistence of hepatitis C viral (HCV) infection. This immune response has proved difficult to restore by therapeutic vaccination, even when HCV replication is suppressed using antiviral regimens containing type I interferon. Because immunomodulatory effects of type I interferon may be a factor in poor T-cell priming, we undertook therapeutic vaccination in two chronically infected chimpanzees during treatment with a direct-acting antiviral (DAA) targeting the HCV NS5b polymerase protein. Immunization with genetic vaccines encoding the HCV NS3-NS5b nonstructural proteins during DAA treatment resulted in a multifunctional CD8(+) T-cell response. However, these antiviral CD8(+) T cells did not prevent persistent replication of DAA-resistant HCV variants that emerged during treatment. Most vaccine-induced CD8(+) T cells targeted class I epitopes that were not conserved in the circulating virus. Exhausted intrahepatic CD8(+) T-cell targeting-conserved epitopes did not expand after vaccination, with a notable exception. A sustained, multifunctional CD8(+) T-cell response against at least one intact class I epitope was detected in blood after vaccination. Persistence of HCV was not due to mutational escape of this epitope. Instead, failure to control HCV replication was likely caused by localized exhaustion in the liver, where CD8(+) T-cell expression of the inhibitory receptor programmed cell death 1 increased 25-fold compared with those in circulation. CONCLUSION: Treatment with a DAA during therapeutic vaccination provided transient control of HCV replication and a multifunctional T-cell response, primarily against nonconserved class I epitopes; exhaustion of liver-infiltrating CD8(+) T cells that target conserved epitopes may not be averted when DAA therapy fails prematurely due to emergence of resistant HCV variants.

Background Influenza and RSV can cause respiratory tract infections leading to severe illness, hospitalization and mortality in at-risk populations, particularly the elderly. The seasonality of influenza and RSV present the potential to co-administer vaccines. This study aimed to demonstrate the non-inferiority of co-administration of the experimental RSV vaccine Ad26.RSV.preF with an influenza vaccine (Fluarix) vs. Fluarix alone in terms of immunogenicity against influenza. Methods This was a single-center, randomized, double-blind, placebo-controlled Phase 2a study (NCT03339713) in healthy adults ≥60 years old. Volunteers were randomized 1:1 to receive Fluarix + 1 × 1011 vp Ad26.RSV.preF on Day 1 and placebo on Day 29 (Group 1), or Fluarix + placebo on Day 1 and 1 × 1011 vp Ad26.RSV.preF on Day 29 (Group 2). Blood samples were taken prior to each vaccination and at Day 57. The primary endpoints were geometric mean titers (GMTs) of hemagglutination inhibition (HI) antibody titers against Fluarix strains (A/Michigan, A/Hong Kong, B/Brisbane and B/Phuket) and the safety and tolerability of Ad26.RSV.preF administered with or without Fluarix. A key secondary endpoint was neutralizing antibody titers to RSV A2. Results Volunteers (N = 180) were included in Group 1 (n = 90) or Group 2 (n = 90). Most volunteers were white (89%) and female (63%), with a median age of 65 years. Both groups exhibited an increase from baseline in HI antibody response on Day 29. The 95% one-sided upper confidence limit of all GMT ratios were below the non-inferiority margin of 2. The frequency of solicited adverse events (AE) after Ad26.RSV.preF vaccination was similar with and without influenza co-administration. Solicited AEs were mainly of Grade 1 and 2 and of transient duration. Most unsolicited AEs were considered unrelated to the study vaccination and were Grade 1 or 2. There were no serious AEs related to the study vaccine and there were no discontinuations due to AEs. RSV neutralizing antibody titers 29 days post- Ad26.RSV.preF immunization were similar in both groups (1404, Group 1; 1690, Group 2). Conclusion Co-administration of Ad26.RSV.preF with Fluarix was non-inferior to Fluarix alone in terms of immunogenicity against influenza and had an acceptable tolerability profile. Disclosures All authors: No reported disclosures.

The search for a universal filovirus vaccine that provides protection against multiple filovirus species has been prompted by sporadic but highly lethal outbreaks of Ebolavirus and Marburgvirus infections. A good prophylactic vaccine should be able to provide protection to all known filovirus species and as an upside potentially protect from newly emerging virus strains. We investigated the immunogenicity and protection elicited by multivalent vaccines expressing glycoproteins (GP) from Ebola virus (EBOV), Sudan virus (SUDV), Tai Forest virus (TAFV) and Marburg virus (MARV). Immune responses against filovirus GP have been associated with protection from disease. The GP antigens were expressed by adenovirus serotypes 26 and 35 (Ad26 and Ad35) and modified Vaccinia virus Ankara (MVA) vectors, all selected for their strong immunogenicity and good safety profile. Using fully lethal NHP intramuscular challenge models, we assessed different vaccination regimens for immunogenicity and protection from filovirus disease. Heterologous multivalent Ad26-Ad35 prime-boost vaccination regimens could give full protection against MARV (range 75%-100% protection) and EBOV (range 50% to 100%) challenge, and partial protection (75%) against SUDV challenge. Heterologous multivalent Ad26-MVA prime-boost immunization gave full protection against EBOV challenge in a small cohort study. The use of such multivalent vaccines did not show overt immune interference in comparison with monovalent vaccines. Multivalent vaccines induced GP-specific antibody responses and cellular IFNγ responses to each GP expressed by the vaccine, and cross-reactivity to TAFV GP was detected in a trivalent vaccine expressing GP from EBOV, SUDV and MARV. In the EBOV challenge studies, higher humoral EBOV GP-specific immune responses (p = 0.0004) were associated with survival from EBOV challenge and less so for cellular immune responses (p = 0.0320). These results demonstrate that it is feasible to generate a multivalent filovirus vaccine that can protect against lethal infection by multiple members of the filovirus family.

The consequences of the 2013–16 Ebola Zaire virus disease epidemic in West Africa were grave. The economies, healthcare systems and communities of Guinea, Sierra Leone and Liberia were devastated by over 18 months of active Ebola virus transmission, followed by sporadic resurgences potentially related to sexual transmission by survivors with viral persistence in body fluids following recovery. The need to develop and implement strategies to prevent and mitigate future outbreaks is now beyond dispute. The potential for unpredictable outbreaks of indeterminate duration, and control challenges posed by the possibility of sporadic re-emergence, mean that implementation of an effective vaccination program for outbreak containment necessitates a vaccine providing durable immunity. Heterologous prime-boost vaccine regimens deliver the same or similar antigens through different vaccine types, the first to prime and the second to boost the immune system. Ad26.ZEBOV/MVA-BN-Filo is an investigational Ebola Zaire vaccine regimen that uses this heterologous prime-boost approach. Preliminary Phase 1 data suggest that Ad26.ZEBOV/MVA-BN-Filo confers durable immunity for at least 240 d and is well-tolerated with a good safety profile. This regimen may therefore be suitable for prophylactic use in a regional or targeted population vaccination strategy, and could potentially aid prevention and control of future Ebola outbreaks.

Spontaneous resolution of acute primary hepatitis C virus (HCV) infection in chimpanzees and humans generates long-lived T cell memory(1, 2). These memory CD4+ and CD8+ T cells appear to be important for rapid control of secondary HCV infections(2) and a 4–5 fold reduction in the risk of a persistent outcome when compared with primary infections in HCV naive human subjects(3, 4). Chronic HCV infection results in functional exhaustion of CD8+ T cells and mutational escape of some class I epitopes encoded by the virus(1, 2). CD8+ T cell exhaustion is characterized by low expression of CD127, the IL-7α receptor important for self-renewal of memory populations, and high expression of co-inhibitory receptors like PD-1, CTLA-4, 2B4, and TIM-3 in blood(5, 6) and liver(7). This phenotype is tempered to some degree by mutational escape of class I HCV epitopes early in the course of infection(8–10). Because exhaustion is caused in part by constant antigenic stimulation of CD8+ T cells(11, 12), cure of chronic infection has the potential for at least partial restoration of the response. The capacity of CD8+ T cells to recover after successful antiviral therapy and respond to a secondary infection has not been widely studied. Circulating CD8+ T cells from patients cured with pegylated type I interferon (pegIFN) and ribavirin failed to produce antiviral cytokines or proliferate after ex vivo stimulation with HCV antigens(13, 14). Control of HCV replication in a cell co-culture model was also impaired, suggesting that damage caused by chronic infection is permanent even after antigen production is terminated by therapy(13–15). Much less is known about the ability of virus-specific CD8+ T cells to control HCV replication upon reinfection, a more stringent test of functionality. Some humans successfully treated with pegIFN and ribavirin do spontaneously resolve secondary infections(16, 17). Expansion of one HCV-specific CD8+ T cell population was described in the blood of a human subject who developed a secondary resolving infection several months after cure of chronic hepatitis C with pegIFN and ribavirin(10). This observation is consistent with the potential for effective CD8+ T cell immunity to secondary infection despite profound impairment of the response during the earlier chronic infection. New small molecules inhibitors of non-structural HCV proteins like NS3, NS5a and NS5b may cure most chronic infections without the need for type I IFN(18–20), a cytokine that is sometimes necessary for CD8+ T cell differentiation(21–23) but under some circumstances also limits effector function or survival(24–29) and contributes to virus persistence in murine models(30, 31). With oral dosing, a shorter duration of therapy, and reduced toxicity of direct acting antivirals (DAA) it is predicted that treatment will become more common. The perceived potential for HCV reinfection is one factor that might be considered in DAA treatment decisions, especially for people who acquired the infection through injection drug use and have an ongoing risk of re-exposure to the virus. Indeed, reinfection has already been documented in a subject after successful treatment with 2 DAA (daclatasvir and sofosbuvir) in the context of a clinical trial(32). Understanding the factors that determine if exhausted T cells recover after antiviral cure and respond to reinfection is therefore of practical importance. It is not yet known if the intrahepatic CD8+ T cell repertoire is stable in the years following cure or whether CD8+ T cells targeting intact or escaped epitopes expand upon reinfection. Whether the pace of CD8+ T cell immunity is accelerated or delayed as in primary HCV infection, and the capacity of the virus to escape the response by mutation, has also not been studied. Here we addressed these questions in a chimpanzee that was cured of chronic hepatitis C after a 28 day course of treatment with small molecule inhibitors of the HCV NS5a and NS5b proteins.

Hepatitis C virus (HCV) persistence is facilitated by exhaustion of CD8+ T cells that express the inhibitory receptor programmed cell death 1 (PD-1). Blockade of PD-1 signaling improves in vitro proliferation of HCV-specific T lymphocytes, but whether antiviral function can be restored in infected individuals is unknown. To address this question, chimpanzees with persistent HCV infection were treated with anti–PD-1 antibodies. A significant reduction in HCV viremia was observed in one of three treated animals without apparent hepatocellular injury. Viremia rebounded in the responder animal when antibody treatment was discontinued. Control of HCV replication was associated with restoration of intrahepatic CD4+ and CD8+ T-cell immunity against multiple HCV proteins. The responder animal had a history of broader T-cell immunity to multiple HCV proteins than the two chimpanzees that did not respond to PD-1 therapy. The results suggest that successful PD-1 blockade likely requires a critical threshold of preexisting virus-specific T cells in liver and warrants consideration of therapeutic vaccination strategies in combination with PD-1 blockade to broaden narrow responses. Anti–PD-1 immunotherapy may also facilitate control of other persistent viruses, notably the hepatitis B virus where options for long-term control of virus replication are limited.

CD4+ T cells play a dominant role in control of acute HAV infection in chimpanzees., Hepatitis A virus (HAV) infection typically resolves within 4–7 wk but symptomatic relapse occurs in up to 20% of cases. Immune mechanisms that terminate acute HAV infection, and prevent a relapse of virus replication and liver disease, are unknown. Here, patterns of T cell immunity, virus replication, and hepatocellular injury were studied in two HAV-infected chimpanzees. HAV-specific CD8+ T cells were either not detected in the blood or failed to display effector function until after viremia and hepatitis began to subside. The function of CD8+ T cells improved slowly as the cells acquired a memory phenotype but was largely restricted to production of IFN-γ. In contrast, CD4+ T cells produced multiple cytokines when viremia first declined. Moreover, only CD4+ T cells responded during a transient resurgence of fecal HAV shedding. This helper response then contracted slowly over several months as HAV genomes were eliminated from liver. The findings indicate a dominant role for CD4+ T cells in the termination of HAV infection and, possibly, surveillance of an intrahepatic reservoir of HAV genomes that decays slowly. Rapid contraction or failure to sustain such a CD4+ T cell response after resolution of symptoms could increase the risk of relapsing hepatitis A.

The discovery of the hepatitis C virus (HCV) more than 20 years ago offered the promise of a vaccine to prevent life-long persistent infection and associated progressive liver diseases. To date, only a few candidate vaccines have been tested in human beings for safety and immunogenicity. None have yet been assessed for prevention of HCV infection or persistence. In the event that current vaccine candidates do not advance to efficacy trials, or fail to provide protection against HCV, the pipeline of alternatives appears to be very small. With a sharp reduction in new HCV infections because of effective screening of the blood supply, and the possibility that acute and chronic infections will be curable because of improving therapy, 1 it is reasonable to ask if the considerable effort to develop a preventive HCV vaccine still is needed. The answer is almost certainly affirmative. Vaccines that protect against hepatitis A and B virus infections were first targeted to health care workers. The value of adding a vaccine to prevent accidental HCV infection in the workplace is clear. A preventive HCV vaccine would have a far greater impact on public health. The need is highlighted by a concerning increase in new infections among adolescents and young adults recently observed in Massachusetts. Between 2002 and 2009, confirmed HCV cases shifted from a unimodal to bimodal age distribution because infection rates increased among those aged 15‐24 years, however, they continued to decline among older adults. 2 The increase in new HCV infections in the younger age group is attributable to needle sharing and probably will be confirmed elsewhere in the United States and in other countries. Without a preventive vaccine it will be difficult to contain a smoldering epidemic of unrecognized HCV infections involving those who are least likely to seek or receive antiviral therapy, no matter how effective. A vaccine also would be highly beneficial in regions of the world with high HCV endemicity, for instance, in countries such as Egypt where it has proved difficult to interrupt several decades of HCV transmission by standard public health measures.3 When considering the need for a vaccine, it is important to remember that symptoms of acute hepatitis are often mild or inapparent, therefore years can elapse before infection is recognized and treated. Serious liver disease can develop during that time and the infection remains transmissible to others by high-risk practices. Perhaps as importantly, only a very small percentage of HCV infections were ever treated with pegylated type I interferon and ribavirin. 4 New direct-acting antivirals will improve this situation, but only with a much greater effort to diagnose the large number of unrecognized infections and provide access to costly treatment that must be managed carefully to prevent emergence of resistant viral variants.

The RNA genome of the hepatitis C virus (HCV) diversifies rapidly during the acute phase of infection, but the selective forces that drive this process remain poorly defined. Here we examined whether Darwinian selection pressure imposed by CD8 + T cells is a dominant force driving early amino acid replacement in HCV viral populations. This question was addressed in two chimpanzees followed for 8 to 10 years after infection with a well-defined inoculum composed of a clonal genotype 1a (isolate H77C) HCV genome. Detailed characterization of CD8 + T cell responses combined with sequencing of recovered virus at frequent intervals revealed that most acute-phase nonsynonymous mutations were clustered in class I epitopes and appeared much earlier than those in the remainder of the HCV genome. Moreover, the ratio of nonsynonymous to synonymous mutations, a measure of positive selection pressure, was increased 50-fold in class I epitopes compared with the rest of the HCV genome. Finally, some mutation of the clonal H77C genome toward a genotype 1a consensus sequence considered most fit for replication was observed during the acute phase of infection, but the majority of these amino acid substitutions occurred slowly over several years of chronic infection. Together these observations indicate that during acute hepatitis C, virus evolution was driven primarily by positive selection pressure exerted by CD8 + T cells. This influence of immune pressure on viral evolution appears to subside as chronic infection is established and genetic drift becomes the dominant evolutionary force.

Public health measures successfully contained outbreaks of the severe acute respiratory syndrome coronavirus (SARS-CoV) infection. However, the precursor of the SARS-CoV remains in its natural bat reservoir, and reemergence of a human-adapted SARS-like coronavirus remains a plausible public health concern. Vaccination is a major strategy for containing resurgence of SARS in humans, and a number of vaccine candidates have been tested in experimental animal models. We previously reported that antibody elicited by a SARS-CoV vaccine candidate based on recombinant full-length Spike-protein trimers potentiated infection of human B cell lines despite eliciting in vivo a neutralizing and protective immune response in rodents. These observations prompted us to investigate the mechanisms underlying antibody-dependent enhancement (ADE) of SARS-CoV infection in vitro. We demonstrate here that anti-Spike immune serum, while inhibiting viral entry in a permissive cell line, potentiated infection of immune cells by SARS-CoV Spike-pseudotyped lentiviral particles, as well as replication-competent SARS coronavirus. Antibody-mediated infection was dependent on Fcγ receptor II but did not use the endosomal/lysosomal pathway utilized by angiotensin I converting enzyme 2 (ACE2), the accepted receptor for SARS-CoV. This suggests that ADE of SARS-CoV utilizes a novel cell entry mechanism into immune cells. Different SARS vaccine candidates elicit sera that differ in their capacity to induce ADE in immune cells despite their comparable potency to neutralize infection in ACE2-bearing cells. Our results suggest a novel mechanism by which SARS-CoV can enter target cells and illustrate the potential pitfalls associated with immunization against it. These findings should prompt further investigations into SARS pathogenesis. © 2011, American Society for Microbiology., link_to_OA_fulltext

Studies of hepatitis C virus (HCV) infection in humans and chimpanzees, the only animal model of natural HCV infection, have documented a critical role of T cell responses in preventing persistent lifelong viremia. In the minority of individuals developing self-limiting infection, control of acute phase virus replication is critically dependent on the expansion of HCV-specific CD4 and CD8 T cells.1–7 In contrast, the establishment of a persistent infection is associated with an impaired virus-specific CD8 T cell response and failure to sustain virus-specific CD4 T cells past the point of apparent control of virus replication.7–11 The failure of CD8 T cell responses directed against HCV epitopes in persistent hepatitis C is likely the result of multiple factors. Functional anergy, including the loss of proliferative capacity, impaired cytokine production, and diminished cytotoxicity, has been shown to be mediated in part by signaling through the inhibitory coreceptors programmed cell death-1 and cytotoxic T lymphocyte antigen-4.12–16 Additionally, due to the low fidelity of the viral polymerase, HCV genomes display a high rate of mutation, and CD8 T cell–mediated immune selection pressure has been demonstrated in both humans and chimpanzees to drive the accumulation of escape mutations, which can subvert the immune response and contribute to viral persistence.6,17–20 These mechanisms are also potentially linked, as demonstrated in a recent study that showed decreased coinhibitory receptor expression on HCV-specific CD8 T cells that recognize mutated versus intact viral epitopes.16 In contrast, much less is known regarding the mechanisms driving virus-specific CD4 T cell failure in chronic HCV infection. Comparisons of HCV-specific CD4 T cell responses in chronic versus resolved HCV infections have shown that an inability to control viral replication is associated with early failure of CD4 T cell help.7–11 Although HCV-specific CD4 T cells have been detected in both the blood and liver during chronic infection, these responses are generally greatly attenuated in breadth, proliferative capacity, and production of T helper 1 cytokines.7,8,10,20,21 Several reports have documented amino acid changes arising in well-characterized major histocompatibility complex (MHC) class II–restricted epitopes of HCV, with some conferring escape from the CD4 T cell response, or skewing it toward a T helper 2 profile of cytokine secretion.7,22–24 These data would suggest the hypothesis that HCV-specific CD4 T cells exert immune selection pressure similar to CD8 T cell responses to HCV, thus driving HCV escape mutations and promoting viral persistence. Nevertheless, no comprehensive analysis has yet been performed to explore how common such CD4 T cell escape mutations are, or to compare their frequency with escape mutations in CD8 T cell epitopes. To determine if HCV immune escape from CD4 T cells was a significant factor in driving the failure of these virus-specific cells, we analyzed the sequences of multiple CD4 and CD8 T cell HCV epitopes for mutations in the circulating virus of four persistently infected chimpanzees. The input genotype 1a HCV strain (HCV-1/910) was used for comparison, and mutational frequencies in MHC class I– and II–restricted epitopes and nonepitope flanking regions were assessed. We report here that HCV CD4 T cell epitopes exhibit far fewer amino acid changes than CD8 T cell epitopes. Although we identified a mutation in a single CD4 T cell epitope in the NS3 protein that impaired activation of a specific CD4 T cell clone, the late emergence of this mutation makes it unlikely to have been a factor in initial establishment of viral persistence. Finally, we confirmed that amino acid changes occur at elevated frequencies in restricted CD8 T cell epitopes during persistent HCV infection, whereas amino acid replacements in restricted CD4 epitopes occur no more frequently than in nonrestricted epitopes or flanking regions, consistent with the hypothesis that CD8 T cells exert significant selection pressure on HCV to drive immune escape, whereas CD4 T cells do not.

Mechanisms by which hepatitis C virus (HCV) evades cellular immunity to establish persistence in chronically infected individuals are not clear. Mutations in human leukocyte antigen (HLA) class I-restricted epitopes targeted by CD8+ T cells are associated with persistence, but the extent to which these mutations affect viral fitness is not fully understood. Previous work showed that the HCV quasispecies in a persistently infected chimpanzee accumulated multiple mutations in numerous class I epitopes over a period of 7 years. During the acute phase of infection, one representative epitope in the C-terminal region of the NS3/4A helicase, NS31629-1637, displayed multiple serial amino acid substitutions in major histocompatibility complex (MHC) anchor and T cell receptor (TCR) contact residues. Only one of these amino acid substitutions at position 9 (P9) of the epitope was stable in the quasispecies. We therefore assessed the effect of each mutation observed during in vivo infection on viral fitness and T cell responses using an HCV subgenomic replicon system and a recently developed in vitro infectious virus cell culture model. Mutation of a position 7 (P7) TCR-contact residue, I1635T, expectedly ablated the T cell response without affecting viral RNA replication or virion production. In contrast, two mutations at the P9 MHC-anchor residue abrogated antigen-specific T cell responses, but additionally decreased viral RNA replication and virion production. The first escape mutation, L1637P, detected in vivo only transiently at 3 mo after infection, decreased viral production, and reverted to the parental sequence in vitro. The second P9 variant, L1637S, which was stable in vivo through 7 years of follow-up, evaded the antigen-specific T cell response and did not revert in vitro despite being less optimal in virion production compared to the parental virus. These studies suggest that HCV escape mutants emerging early in infection are not necessarily stable, but are eventually replaced with variants that achieve a balance between immune evasion and fitness for replication., Author Summary Hepatitis C virus (HCV)-associated liver disease is a leading indication for liver transplantation in the United States. With more than 170 million people infected with HCV worldwide and more than 70% of those infected unable to clear the virus, it is of paramount importance to elucidate the factors leading to viral persistence. A well-characterized experimental chimpanzee chronically infected with HCV was found to develop multiple viral sequence variations over the course of 7 years. Serial mutations in an HCV epitope that was originally immunogenic in the host were observed during the course of infection, and we sought to better understand how each mutation affected viral persistence. We recreated the viral variants detected in the chimpanzee and assessed the ability of each variant to replicate, produce progeny virus, and evade the host immune system. We found that certain HCV variants present long after initial infection are able to avoid recognition by host immune cells, but have reduced replication fitness. Importantly, in the absence of immune pressure, these viruses mutate back to variants better able to replicate and produce new viral progeny. Our experiments suggest that rapidly mutating viruses like HCV seek a balance between replication efficiency and the ability to evade the host immune system.

Finding mechanisms of viral resistance and new ways to tackle chronic hepatitis will help find a cure for this disease. In 'Bench to Bedside', Christopher Walker and Benoit Callendret highlight studies showing that overcoming immune exhaustion during chronic infection by blocking several inhibitory pathways of T cells may restore an adequate immune response. In 'Bedside to Bench', Lawrence Corey, Joshua Schiffer and John Scott discuss recent advances in antiviral therapy with protease inhibitors and the findings of a mathematical model that predicts possible single and double mutations prior to antiviral therapy.

Hepatitis C virus (HCV)-specific CD8+ T cells persist in the chronically infected liver but provide no apparent control of virus replication. Epitopes targeted by some of these T cells contain escape mutations while others remain intact. Studies in acutely infected humans suggest that circulating CD8+ T cells targeting the intact epitopes express more PD-1, a molecule associated with loss of effector function. Whether this is true in the persistently infected liver is unknown. CD8+ T cells targeting intact or mutated epitopes were visualized using tetramers in the liver of chronically infected chimpanzees. Unexpectedly, there was no obvious relationship between expression of PD-1 on the HCV-specific CD8+ T cells and the nature of the targeted epitope. More importantly all HCV-specific CD8+ T cells we examined displayed functional incapacity regardless of the nature of the targeted epitope and anergy could not be reversed by blockade of the PD-1/PD-L1 pathway. We conclude that decreased PD-1 expression previously observed on acute phase CD8+ T cells after escape of the targeted epitope is not necessarily maintained in the liver during chronic hepatitis C. Rather, our data suggest that mechanisms other than continuous TCR triggering might be responsible for PD-1 upregulation and exhaustion of CD8+ T cells, or that escaped epitopes are still able to induce TCR engagement without T cell activation resulting in exhaustion of viral specific CD8+ T cells.