Studies on the immunogenicity of an endogenously processed protein antigen in mice

We have examined the general immunogenicity of a non-replicating antigen which was introduced artificially into the endogenous pathway of antigen processing. EG7.OVA cells transfected with the OVA gene are efficient presenters of endogenously processed OVA and induced high levels of class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) in vivo. In addition, mice immunised with EG7.OVA cells developed immune responses more characteristic of class II MHC-restricted T cells, including IgG antibody production, systemic delayed type hypersensitivity (DTH) and a proliferative response to OVA in vitro. However, most of these responses were small, and EG7.OVA cells did not prime mice for secondary antibody or DTH responses. Thus endogenously synthesised, non-replicating antigens are poor stimulators of T cells which exploit the exogenous processing pathway. If vaccine vectors containing purified epitopes are to stimulate all T cells effectively, they will need to utilise strategies which enable direct entry to both antigen processing pathways.