In vitro production of anti-influenza virus antibody after simultaneous administration of H3N2 and H1N1 cold-adapted vaccines in seronegative children

Abstract

Sixteen doubly seronegative (H3N2 and H1N1) young children were recently enrolled in a study of live, attenuated cold-adapted influenza A vaccines. Twelve children received simultaneously H3N2 and H1N1 live, attenuated influenza vaccine intranasally and four received saline as placebo controls. Peripheral blood lymphocytes (PBL) were obtained sequentially from all children and the in vitro production of anti-influenza H3N2 and H1N1 antibody from unstimulated and influenza stimulated cells was measured by ELISA. In vitro antibody studies were performed at 0, 2, 4, and 12 weeks after immunization. PBL from six of 12 children spontaneously produced H3N2 antibody and eleven of 12 produced H1N1 antibody. Influenza stimulation of PBL induced antibody production in 8/12 for H3N2 and 12/12 for H1N1. PBL from all four placebo immunized children failed to produce specific influenza antibody in vitro at any time studied. In vitro antibody produced after immunization was primarily of the IgG isotype with peak production occurring at 4–12 weeks, supporting the primary nature of the response. The correlation between the presence of positive serum HAI and ELISA titres, and the production of in vitro antibody was good for both H3N2 and H1N1 vaccines. In summary, the simultaneous administration of two attenuated influenza A vaccines into the upper respiratory tract of seronegative children resulted in the stimulation of PBL capable of secreting both H3N2 and H1N1 influenza specific antibody in vitro.