Dendritic cells (DCs) are the most potent inducers of immune reactions. Genetically modified DCs, which express tumor-associated antigens (TAA), can efficiently induce antitumor immunity and thus have a high potential as tools in cancer therapy. The gene delivery is most efficiently achieved by viral vectors. Here, we explored the capacity of influenza virus vectors to transduce TAA genes. These viruses abortively infect DCs without interfering with their antigen-presenting capacity. In contrast to other viruses used for DC transduction, influenza viruses can be efficiently controlled by antiviral pharmaceuticals, lack the ability to integrate into host chromosomes, and fail to establish persistent infections. Genes encoding a melanoma-derived TAA (MAGE-3), or the green fluorescence protein (GFP), were introduced into a high-expression avian influenza virus vector. Monocyte-derived mature DCs infected by these recombinants efficiently produced GFP or MAGE-3. More than 90% of the infected DCs can express a transduced gene. Importantly, these transduced DCs retained their characteristic phenotype and their potent allogeneic T cell stimulatory capacity, and were able to stimulate MAGE-3-specific CD8(+) cytotoxic T cells. Thus influenza virus vectors provide a highly efficient gene delivery system in order to transduce human DCs with TAA, which consequently stimulate TAA-specific T cells.

Adoptive transfer of in vitro generated antigen-specific T cells has been successfully used to treat viral infections in immunodeficient patients. Therefore, methods for the rapid in vitro expansion of antigen-specific T cells are needed. Influenza virus efficiently infects dendritic cells, and peptides derived from viral proteins are processed and presented to CD8 + cytotoxic T cells. However, both, CD4 + and CD8 + T cells are necessary for the efficient control of viral infections, and it is becoming increasingly clear that a T helper cell response is very important for the maintenance and strength of the immune response. Here we show that recombinant influenza virus efficiently infects a wide range of professional antigenpresenting cells and does not interfere with antigen presentation pathways. Using T cell clones for three different MHC class II-restricted antigens we demonstrate that peptides derived from these antigens are efficiently presented on MHC class II molecules. Importantly, it was possible to generate and expand antigen-specific CD4 + T cells following in vitro infection of professional antigen-presenting cells with recombinant influenza virus. These findings support the notion that recombinant influenza virus is a valuable tool for the expansion of antigen-specific CD4 + T cells in vitro.

Catalytic RNAs are a genetic property not only of some particular viroids or viruses, but also are more common naturally among eukaryotes and even prokaryotes than earlier expected. However, the major interest in ribozymes results from their potential for development of "tailor-made" cDNA constructions designed to be transcribed into catalytic RNAs that will recognize by hybridization and destroy by specific cleavage their cellular or viral RNA targets. The efficiency of an antiviral ribozyme is determined by both the accessibility and sequence conservation of the target region, as well as the design of the ribozyme: its type, size, and composition of flanking sequences; expression rates; and cellular compartment localization. Until now the most frequently selected viral target is the human immunodeficiency virus, where an up to a 10(4)-fold inhibition in its progeny production has been achieved. Although the first generation ribozymes focused on improvements in basic design and expression rates, more recently the efficiency of antiviral catalytic activity has been increased by employing polyribozymes and/or multitarget ribozymes, as well as special constructions to enhance the cellular co-compartmentation of the ribozyme with its viral RNA target.

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