Induction of Broadly Cross-Reactive Stalk-Specific Antibody Responses to Influenza Group 1 and Group 2 Hemagglutinins by Natural H7N9 Virus Infection in Humans.

Background: The outbreak of novel avian H7N9 influenza virus infections in China in 2013 has demonstrated the continuing threat posed by zoonotic pathogens. Deciphering the immune response during natural infection will guide future vaccine development. Methods: We assessed the induction of heterosubtypic cross-reactive antibodies induced by H7N9 infection against a large panel of recombinant hemagglutinins and neuraminidases by quantitative enzyme-linked immunosorbent assay, and novel chimeric hemagglutinin constructs were used to dissect the anti-stalk or -head humoral immune response. Results: H7N9 infection induced strong antibody responses against divergent H7 hemagglutinins. Interestingly, we also found induction of antibodies against heterosubtypic hemagglutinins from both group 1 and group 2 and a boost in heterosubtypic neutralizing activity in the absence of hemagglutination inhibitory activity. Kinetic monitoring revealed that heterosubtypic binding/neutralizing antibody responses typically appeared and peaked earlier than intrasubtypic responses, likely mediated by memory recall responses. Conclusions: Our results indicate that cross-group binding and neutralizing antibody responses primarily targeting the stalk region can be elicited after natural influenza virus infection. These data support our understanding of the breadth of the postinfection immune response that could inform the design of future, broadly protective influenza virus vaccines.

A Systemic Prime-Intrarectal Pull Strategy Raises Rectum-Resident CD8+ T Cells for Effective Protection in a Murine Model of LM-OVA Infection.

As the entry sites of many pathogens such as human immunodeficiency virus (HIV), mucosal sites are defended by rapidly reacting resident memory T cells (TRM). TRMs represent a special subpopulation of memory T cells that persist long term in non-lymphoid sites without entering the circulation and provide the "sensing and alarming" role in the first-line defense against infection. The rectum and vagina are the two primary mucosal portals for HIV entry. However, compared to vaginal TRM, rectal TRM is poorly understood. Herein, we investigated the optimal vaccination strategy to induce rectal TRM. We identified an intranasal prime-intrarectal boost (pull) strategy that is effective in engaging rectal TRM alongside circulating memory T cells and demonstrated its protective efficacy in mice against infection of Listeria monocytogenes. On the contrary, the same vaccine delivered via either intranasal or intrarectal route failed to raise rectal TRM, setting it apart from vaginal TRM, which can be induced by both intranasal and intrarectal immunizations. Moreover, intramuscular prime was also effective in inducing rectal TRM in combination with intrarectal pull, highlighting the need of a primed systemic T cell response. A comparison of different pull modalities led to the identification that raising rectal TRM is mainly driven by local antigen presence. We further demonstrated the interval between prime and boost steps to be critical for the induction of rectal TRM, revealing circulating recently activated CD8+ T cells as the likely primary pullable precursor of rectal TRM. Altogether, our studies lay a new framework for harnessing rectal TRM in vaccine development.

Influenza Vaccine With Consensus Internal Antigens as Immunogens Provides Cross-Group Protection Against Influenza A Viruses.

Given that continuing antigenic shift and drift of influenza A viruses result in the escape from previous vaccine-induced immune protection, a universal influenza vaccine has been actively sought. However, there were very few vaccines capable of eliciting cross-group ant-influenza immunity. Here, we designed two novel composite immunogens containing highly conserved T-cell epitopes of six influenza A virus internal antigens, and expressed them in DNA, recombinant adenovirus-based (AdC68) and recombinant vaccinia vectors, respectively, to formulate three vaccine forms. The introduction of the two immunogens via a DNA priming and viral vectored vaccine boosting modality afforded cross-group protection from both PR8 and H7N9 influenza virus challenges in mice. Both respiratory residential and systemic T cells contributed to the protective efficacy. Intranasal but not intramuscular administration of AdC68 based vaccine was capable of raising both T cell subpopulations to confer a full protection from lethal PR8 and H7N9 challenges, and blocking the lymphatic egress of T cells during challenges attenuated the protection. Thus, by targeting highly conserved internal viral epitopes to efficiently generate both respiratory and systemic memory T cells, the sequential vaccination strategy reported here represented a new promising candidate for the development of T-cell based universal influenza vaccines.