Immunization of macaques with formalin-inactivated human metapneumovirus induces hypersensitivity to hMPV infection

Area of Science:

• Virology
• Immunology
• Vaccinology

Background:

• Human metapneumovirus (hMPV) is a significant cause of acute respiratory illness.
• Past research with inactivated respiratory syncytial virus (RSV) and measles virus (MV) vaccines showed they could enhance disease upon natural infection.
• Paramyxoviridae family viruses share similarities that may lead to comparable vaccine-induced immune responses.

Purpose of the Study:

• To investigate the immunogenicity and safety of a formalin-inactivated hMPV (FI-hMPV) vaccine candidate.
• To determine if FI-hMPV induces a hypersensitivity response, similar to other inactivated paramyxovirus vaccines.

Main Methods:

• A formalin-inactivated hMPV preparation (FI-hMPV) was produced.
• Young cynomolgus macaques were immunized with the FI-hMPV preparation.
• Vaccinated macaques were challenged with live hMPV and monitored for disease development.

Main Results:

• FI-hMPV-immunized macaques developed eosinophilic bronchitis and bronchiolitis six days post-challenge.
• These pathological findings are indicative of a significant hypersensitivity immune response.
• The observed immune-mediated disease mirrors the enhanced disease seen with inactivated RSV and MV vaccines.

Conclusions:

• Formalin-inactivated hMPV vaccines carry a risk of predisposing recipients to immune-mediated disease.
• This suggests a common mechanism of vaccine-enhanced pathology across inactivated paramyxovirus vaccines.
• Caution is warranted in the development of inactivated hMPV vaccines due to potential safety concerns.