Possible explanations for the poor immunogenicity include instability of the S protein expressed by the vector, differences in antigen presentation between protein secreted by the vector and protein displayed on the virus surface, and differences in post-translational modification (i.e., glycosylation) between protein expressed via virus infection of eukaryotic cells and protein expressed by an intracellular prokaryotic vector. The gene discussed is PROS1; the disease is viral infectious disease.