Cross-subtype Immunity against Avian Influenza in Persons Recently Vaccinated for Influenza

Gioia, Cristiana; Castilletti, Concetta; Tempestilli, Massimo; Piacentini, Paola; Bordi, Licia; Chiappini, Roberta; Agrati, Chiara; Squarcione, Salvatore; Ippolito, Giuseppe; Puro, Vincenzo; Capobianchi, Maria R.; Poccia, Fabrizio

Avian influenza virus (H5N1) can be transmitted to humans, resulting in a severe or fatal disease. The aim of this study was to evaluate the immune cross-reactivity between human and avian influenza (H5N1) strains in healthy donors vaccinated for seasonal influenza A (H1N1)/(H3N2). A small frequency of CD4 T cells specific for subtype H5N1 was detected in several persons at baseline, and seasonal vaccine administration enhanced the frequency of such reactive CD4 T cells. We also observed that seasonal vaccination is able to raise neutralizing immunity against influenza (H5N1) in a large number of donors. No correlation between influenza-specific CD4 T cells and humoral responses was observed. N1 may possibly be a target for both cellular and humoral cross-type immunity, but additional experiments are needed to clarify this point. These findings highlight the possibility of boosting cross-type cellular and humoral immunity against highly pathogenic avian influenza A virus subtype H5N1 by seasonal influenza vaccination.