b SCRs of HI antibodies to the homologous A/Vietnam/1194/2004 NIBRG-14 vaccine strain after the first and second vaccine dose with 95% confidence intervals To determine whether the impact of the adjuvant around the magnitude and persistence of the antibody responses would be paralleled by enhanced B-cell responses, we measured the frequencies of memory B cells specific for A/Vietnam H5N1 split antigen (further referred to as split antigen) at the different time points in the groups vaccinated with the 3

b SCRs of HI antibodies to the homologous A/Vietnam/1194/2004 NIBRG-14 vaccine strain after the first and second vaccine dose with 95% confidence intervals To determine whether the impact of the adjuvant around the magnitude and persistence of the antibody responses would be paralleled by enhanced B-cell responses, we measured the frequencies of memory B cells specific for A/Vietnam H5N1 split antigen (further referred to as split antigen) at the different time points in the groups vaccinated with the 3.75?g HA dose with or without adjuvant. the H5N1 vaccine with AS03A enhances antibody persistence and induces stronger T- and B-cell responses. The cross-clade T-cell immunity indicates that this adjuvanted vaccine primes individuals to respond to either contamination and/or subsequent vaccination with strains drifted from the primary vaccine strain. Keywords: CD4 T cells, pandemic influenza, AS03A, H5N1, vaccine Introduction Novel influenza viruses arising as a result of antigenic shift can potentially lead to an influenza pandemic in humans due to the lack of immunity in the general population. The 2009 2009 pandemic outbreak was due to the emergence Merck SIP Agonist of the influenza A H1N1/2009 virus [1]. The highly pathogenic avian influenza A H5N1 virus, which has been circulating among poultry and birds in several countries during the last decade, remains as a pandemic threat however due to its potential to evolve into a strain with efficient human-to-human transmission [2]. Concern about the H5N1 virus focused attention around the development of pandemic vaccines [3C6]. The experience gained using H5N1 as a model antigen in vaccines can be applied to H1N1/2009 or other pandemic strains. The principal strategy to develop H5N1 vaccines was based on the use of reverse genetics to generate attenuated strains which express H5 surface antigens [7, 8]. The formulation of H5N1 vaccines with oil-in-water adjuvants has been found to substantially enhance Merck SIP Agonist vaccine immunogenicity [9C15], thereby minimizing the amount of antigen required and alleviating pressure on the limited global influenza antigen manufacturing capacity. We Merck SIP Agonist conducted a doseCresponse study with four antigen doses (3.75, 7.5, 15, or 30?g hemagglutinin antigenHA) of recombinant H5N1 (A/Vietnam/1194/2004 NIBRG-14, clade 1) split-virion vaccine adjuvanted with AS03A, an oil-in-water emulsion-based Adjuvant System containing -tocopherol, squalene, and polysorbate-80 [11]. The vaccine was administered as a two-dose schedule to volunteers aged 18C60?years and the study included matched control groups where the same antigen doses were administered without adjuvant [11]. We exhibited that adjuvantation with AS03A conferred significant antigen H3/l sparing so that the hemagglutinationCinhibition (HI) antibody response with the lowest antigen dose of 3.75?g HA met all US and European immunological licensure criteria [11]. Large safety studies [16, 17] with the adjuvanted vaccine indicated a clinically acceptable safety profile and the vaccine has now Merck SIP Agonist been licensed in Europe [18]. Another important observation was the ability of AS03A-adjuvanted H5N1 vaccine to induce cross-reactive seroprotective immune responses against heterologous recombinant H5N1 strains. Thus, adjuvantation of the A/Vietnam/1194/2004 H5N1 strain, which belongs to clade 1, induced cross-reactive neutralizing responses against three other H5N1 strains associated with human disease belonging to clade 2 [11, 12]. The same vaccine was also shown to induce protection against heterologous lethal H5N1 challenge in ferrets [19]. An influenza vaccine with cross-immunogenic potential could play a key role in pandemic mitigation by promoting a rapid immune response to contamination and/or subsequent vaccination with strains drifted from the primary vaccine strain. Although an effective vaccination against influenza is usually routinely measured in terms of the humoral response, it is also important to monitor the induction of antigen-specific T and B cells which are crucial components of the immune response, particularly with respect to long-term memory. In addition to the provision of CD4 T-cell help for B-cell differentiation, both CD4 effector and memory T cells appear to have multifaceted roles in the protective responses to influenza contamination [20, 21]. Here, we determine the effect of AS03A adjuvantation on B- and T-cell responses following vaccination with the clade 1 H5N1 A/Vietnam/1194/2004 in the doseCresponse study. We found that AS03A adjuvantation enhanced antibody Merck SIP Agonist persistence, promoted stronger B-cell and CD4 T-cell responses and induced polyfunctional cross-clade T-cell responses to two heterologous clade 2 H5N1 isolates A/Indonesia/5/2005 (subclade 2.1) and A/Anhui/1/2005 (subclade 2.3). Materials and Methods Study Design and Participants This was a single-centre, randomized, and observer-blind phase I clinical trial to assess the safety and immunogenicity of the candidate H5N1 vaccine. The Ethics Committee of the Ghent University Hospital, Ghent, Belgium, approved the protocol and other relevant study documentation and the trial was registered with the ClinicalTrials.gov registry (number “type”:”clinical-trial”,”attrs”:”text”:”NCT00309634″,”term_id”:”NCT00309634″NCT00309634). The study was conducted according to the Declaration of Helsinki, with written.