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We report an optical molecular imaging technique that exploits local administration of fluorophore-conjugated antibodies and confocal fluorescence microscopy to achieve high-contrast imaging of host cell populations in normal and tumor tissue in living mice. The method achieves micron-scale spatial resolution to depths greater than 100 μm. We illustrate the capabilities of this approach by imaging two dendritic cell populations in the skin and normal and tumor vasculature in vivo. [ABSTRACT FROM AUTHOR]

There is great interest in developing new immunization vectors. Helper virus-free herpes amplicons, plasmidbased vectors that encode no viral gene products and have an extremely large coding capacity, are attractive viral vaccine candidates for expressing recombinant proteins in vivofor immunization. Earlier studies in mice, using amplicons encoding the gp120 protein of human immunodeficiency virus (HIV), resulted in strikingly robust cellular immune responses as measured by cytotoxicity and interferon γ enzyme-linked immunospot assays. To begin to understand how such vectors function in vivoto generate an immune response, we used amplicons encoding reporter constructs including green fluorescent protein (GFP) and luciferase to examine the duration of expression after administration to mice. Luciferase expression, measured with the IVIS system from XenogenCaliper Life Sciences (Hopkinton, MA) and by enzymatic assays of tissue extracts, revealed that expression after injection of the HSVluc amplicons peaked earlier than 24 hr after injection into mice. HSVegfp injection resulted in peak accumulation of GFP 24 hr after administration in vivo. Thus, both reporter genes revealed a rather rapid and robust expression pattern of short duration. The short period of expression appears in part to be due to gene silencing. Examination of the cells transduced by amplicons encoding GFP and human B7.1 suggested that the amplicons transduce a variety of cells, including professional antigen-presenting cells. From this and previous work, we conclude that amplicons may engender a potent immune response by directly transducing dendritic cells as well as by cross-priming of antigen produced by other transduced host cells. [ABSTRACT FROM AUTHOR]