Caracterización antigénica e inmunogénica de la proteína F del metapneumovirus humano y de proteínas quiméricas con la proteína homóloga del virus respiratorio sincitial humano

Abstract

Human metapneumovirus (hMPV) and human respiratory syncytial virus (hRSV) are members of the new Pneumoviridae family of viruses, recently detached from the Paramyxoviridae family. Both viruses, but particularly hRSV, account for the majority of bronchiolitis and severe lower respiratory tract infections worldwide in infants and very young children, and they are also a frequent cause of morbidity and mortality in the elderly and immunocompromised adults. hMPV and hRSV are similar in genomic organization, viral structure, antigenicity and clinical symptoms. There are no licensed hMPV or hRSV vaccines currently available. Efforts to control these pathogens are now focused on the prophylactic use of neutralizing antibodies against the fusion protein (F) and the development of efficacious and safety vaccines based on the F glycoprotein, which is the primary target of neutralizing antibodies and is thus a critical vaccine antigen. The F protein promotes fusion of the virus and the cell membranes during virus entry. While the fusion membrane occurs, the F protein transits from a metastable pre-fusion conformation to a highly stable post-fusion conformation. The recently determined atomic structures of hRSV F and hMPV F in the postfusion conformation have revealed a high degree of structural similarity, including known antigenic sites such as antigenic sites II and IV. However, no cross-neutralization is observed in polyclonal antibody responses raised after immunization with purified viral F proteins, despite sporadic reports of cross-neutralizing monoclonal antibodies (mAbs). In this Thesis we first describe the generation and characterization of a panel of mAbs based on their postfusion conformational specificity, or their neutralization activity. Some of these antibodies could be mapped onto hMPV F antigenic sites II and IV. The main objective of this Thesis was to design chimeric F proteins in which certain antigenic sites of one virus were replaced by the equivalent antigenic site of the other virus. The antigenic changes were monitored with virus-specific mAbs to confirm that the resulting chimeric proteins gained site-specific epitopes of the heterologous virus. Moreover, mice immunization with these chimeras induced polyclonal cross-reactive and cross-neutralizing antibody responses and mice were even protected against a challenge with the virus used for grafting of the Resumen en inglés heterologous antigenic site. These results set the path for the generation of “universal vaccines” that could protect against infections by the Pneumoviridae.