A recombinant herpesvirus-based vector comprising a nucleic acid sequence encoding a heterologous antigen and a promoter for controlling the expression of the antigen, in which the promoter is expressed at a time selected to provide a required immune response in a subject.

Compositions, methods, and systems for modifying sterol metabolism in a subject is disclosed. In some embodiments, the subjects may be administered one or more mammalian cells modified to express at least one sterol degrading enzyme derived from a bacterium. In many embodiments, the cell is a macrophage or monocyte stably expressing three or more enzymes that aid in opening the ring of cholesterol. The disclosed compositions and methods may be useful in lowering cholesterol levels in a subject in need thereof. In some embodiments, the subject may have a genetic predisposition to atherosclerosis.