Ongoing projects

Thus far it has not been possible to associate the ubiquitous TT viruses to a specific disease. Our investigations to address this problem include:

• Serum samples and biopsies from healthy individuals, as well as patients with multiple sclerosis, rheumatoid arthritis, colon carcinoma, leukemia and lymphoma were analyzed for the presence of TT virus DNA. Although TT virus DNA was present in the majority of these samples, we demonstrated the existence of additional intragenomic rearranged viral molecules, a phenomenon uncommon for animal viruses. Two groups of these subviral molecules were isolated and characterized: comprising replication-defective and replication-competent episomes. The latter consisted of as little as 10% of the originating full-length TT virus genome and was termed TTV. More than 100 full-length TT viral genomes were also isolated and characterized.
• We developed an in vitro replication system for these viruses in which we confirmed the formation and existence of TTV molecules, and replication of full-length genomes.
• Intragenomic rearranged TT molecules, as well as in vitro transcripts revealed new open reading frames of which the putative proteins shared similarities to signature motifs present in cellular proteins involved in autoimmune diseases.
• The highly conserved region (71bp) of TT viruses harboring the origin of replication was demonstrated in diverse cell lines. Long distance PCR-amplification based on this region led to the identification of circular chimeric molecules comprising TT virus sequences combined with cellular sequences. These often involved sequences originating from genes known to be involved in the pathogenesis of specific tumors or autoimmune disease.