The immunotargeting approach to adjuvant-independent immunization with influenza haemagglutinin

By conjugating the bromelain fragment of the influenza virus haemagglutinin (BHA) to a mouse monoclonal antibody specific for a species-crossreactive, framework determinant on class II major histocompatibility complex molecules, the adjuvant-independent immunotargeting approach could be compared with more conventional immunizations involving Freund's complete adjuvant (FCA) and alum, in different species. Both rabbits and ferrets made significant virus-blocking IgG responses to the immunotargeted BHA in the absence of adjuvant, and no adverse reactions were observed with the conjugate immunizations. As measured by enzyme-linked immunosorbent assay, these responses were equal to those observed with alum, and were approximately one-quarter of the level seen with FCA. In terms of influenza virus haemagglutination inhibition, immunotargeting appeared to be more effective than alum, but less effective than FCA. Collectively, the results indicate that immunotargeting may provide a safe and effective alternative to the use of adjuvants in the development of defined subunit vaccines.