Activation of cross-reactive mucosal T and B cell responses in human nasopharynx-associated lymphoid tissue in vitro by Modified Vaccinia Ankara-vectored influenza vaccines

Highlights

• MVA-vectored influenza vaccines are highly efficient in infecting human NALT.

• Tonsillar B cells are efficient in expressing the encoded vaccine antigen.

• MVA vaccine expressing highly conserved nucleoprotein (NP) elicits T cell response.

• MVA expressing pdmH1N1 HA can induce cross-reactive anti-HA antibodies.

• MVA vaccines may have the potential to be used as intranasal vaccines against influenza.

Abstract

Recent efforts have been focused on the development of vaccines that could induce broad immunity against influenza virus, either through T cell responses to conserved internal antigens or B cell response to cross-reactive haemagglutinin (HA). We studied the capacity of Modified Vaccinia Ankara (MVA)-vectored influenza vaccines to induce cross-reactive immunity to influenza virus in human nasopharynx-associated lymphoid tissue (NALT) in vitro. Adenotonsillar cells were isolated and stimulated with MVA vaccines expressing either conserved nucleoprotein (NP) and matrix protein 1 (M1) (MVA-NP-M1) or pandemic H1N1 HA (MVA-pdmH1HA). The MVA vaccine uptake and expression, and T and B cell responses were analyzed. MVA-vectored vaccines were highly efficient infecting NALT and vaccine antigens were highly expressed by B cells. MVA-NP-M1 elicited T cell response with greater numbers of IFNγ-producing CD4+ T cells and tissue-resident memory T cells than controls. MVA-pdmH1HA induced cross-reactive anti-HA antibodies to a number of influenza subtypes, in an age-dependent manner. The cross-reactive antibodies include anti-avian H5N1 and mainly target HA2 domain. Conclusion: MVA vaccines are efficient in infecting NALT and the vaccine antigen is highly expressed by B cells. MVA vaccines expressing conserved influenza antigens induce cross-reactive T and B cell responses in human NALT in vitro, suggesting the potential as mucosal vaccines for broader immunity against influenza.

Introduction

Influenza continues to cause widespread morbidity and mortality, resulting in major challenges for healthcare systems [1], [2]. 2009 pandemic H1N1 (pdmH1N1) influenza and the potential of pandemics by H5N1 or other avian influenza viruses highlight the need to find more effective preventative measures against these threats.

The most cost-effective public health intervention is vaccination. Current influenza vaccines principally induce humoral immunity against haemagglutinin (HA), which varies between virus strains, so the composition has to be reformulated each year. Recent studies suggest 2009 pdmH1N1 elicited cross-reactive memory B cell responses that produce antibodies against multiple influenza subtypes [3], [4], [5], [6], [7]. Current efforts focus on developing vaccines that induce broad immunity against influenza, either through T cell responses to conserved internal antigens or B cell response to cross-reactive HA. These include the novel influenza vaccine MVA-NP+ M1, using a replication-deficient viral vector (Modified Vaccinia Ankara, MVA) expressing the highly conserved internal proteins nucleoprotein (NP) and matrix protein 1 (M1) to boost memory T-cell responses [8]; and the use of a viral vector expressing pdmH1N1 HA to induce protective antibody response [9].

As influenza virus causes disease by infecting nasopharynx mucosa, intranasal immunization provides an effective vaccination strategy. Live attenuated influenza vaccines (LAIV) have been used as intranasal immunization effectively in children, and has been shown to elicit lasting T and B-cell immunity (>1 year) [10]. The induction of local mucosal immunity by intranasal immunization critically relies on local immune organs–nasopharynx-associated lymphoid tissue (NALT). Adenoids and tonsils are major components of NALT and are known to be important induction sites for immunity against respiratory pathogens including influenza [11], [12], [13], [14].

Recombinant replication-deficient viral vectors are capable of priming and boosting T cell responses against antigens they encode. Intranasal delivery of an adenovirus vectored vaccine expressing NP and M1 was shown in animal studies to induce stronger immune responses and greater protection than via intramuscular immunization [15]. MVA is one of the most studied viral vectors and has an excellent safety profile. MVA is highly attenuated and has been used to boost T-cell responses against HIV, tuberculosis and malaria in addition to influenza [16], [17], [18]. Recent studies in animal models showed MVA encoding influenza antigens could induce cross-reactive immunity [19], [20]. Experimental use of MVA constructs via mucosal routes has been demonstrated to be efficient in generating protective immune responses to influenza and respiratory syncytial virus in mice [21], [22].

Although animal models are frequently used to assess the immunogenicity of influenza vaccines, these are of limited utility since the animals used are naïve to influenza virus, and are not a good model for humans who have been exposed to influenza virus many times during lifetime, and have accumulated both B and T cell immunity to influenza as a result [23].

We previously studied the naturally acquired immunity including memory responses to influenza virus and Streptococcus pneumoniae protein antigens in human NALT tissue [7], [24], [25], [26]. In this study, we have investigated the capacity of MVA-vectored influenza vaccines expressing either NP or HA to induce mucosal T and B cell immune response in vitro against influenza viruses in human NALT. We show that MVA vectored vaccines are very efficient in infecting the NALT in vitro and highly expressed in B cells and are able to induce cross-reactive T and B cell immunity to influenza viruses.