[PMC free article] [PubMed] [Google Scholar] 11. be explored further. Poxviruses have unique characteristics which make them appealing as vectors for cancer gene therapy (4, 25). They have been investigated as vectors for delivery of tumor-associated antigens, cytokines, and costimulatory molecules in CP-673451 cancer patients, for the development of an antitumor immune response (5, 17, 22, 32). Recently, laboratory experiments have supported the utility of vaccinia virus (VV) as a vector for tumor-directed delivery of genes for enzyme-prodrug therapy and sensitization to systemic treatment with tumor necrosis factor (13, 15, 30). A replicating virus has distinct advantages over nonreplicating vectors for these tumor-directed applications, as it leads to an increase in the percentage of cells within a tumor that express the therapeutic gene over time (23, 35). VV is an efficient, replicating virus that leads to high levels of transgene expression, selectively in tumor tissue when delivered systemically, and this can lead to a significant antitumor response. Selective mutations CP-673451 of CP-673451 the virus may enhance tumor specificity (29) (J. A. McCart, Y. K. Hu, H. R. Alexander, S. K. Libutti, B. Moss, D. L. Bartlett, Abstr. Am. Soc. Gene Ther., abstr. 633, 1999). Clinical trials with intravascular delivery of mutant VV will likely be hampered by the high percentage of cancer patients with preformed immunity against the virus as a result of vaccination against smallpox. High levels of circulating antibody titers and cytotoxic T CP-673451 cells recognizing VV can be detected many years after vaccination, and it is likely that this preformed immune reactivity will prevent adequate infection and spread of VV throughout a tumor when used as a vector for tumor-directed gene therapy. An alternative replicating poxvirus vector may mediate the selective, high transgene expression within tumors, without immune cross-reactivity. In general, the host range for poxviruses that do not cross-react with orthopoxviruses is quite limited, and although members of the avipoxvirus genus and entomopoxvirus subfamily will infect and express genes in human cells, they will not replicate in human cells (21, 34). Members of the yatapoxvirus genus, on the other hand, have been responsible for zoonotic infections, forming cutaneous nodules in caretakers handling infected monkeys, and replicating virus has been recovered from these lesions (16). GREM1 These viruses have not been previously explored as expression vectors, nor has their host range been adequately defined. In this study we explore the Yaba-like disease (YLD) virus as an expression vector. This CP-673451 virus was first recognized in monkey caretakers in 1965 and 1966, in primate centers in the United States, and was traced to a single source (12). YLD infection in caretakers produced a brief fever and the development of a few firm, elevated, round, necrotic maculopapular nodules, followed by complete resolution of the infection. Compared to Tanapox virus and Yaba monkey tumor virus, YLD virus is the least characterized of the yatapoxvirus genus. We demonstrate here that the YLD virus does not cross-react with VV antibodies. It replicates efficiently in human cells and can be grown under normal conditions in CV-1 cells and purified in high titer. We demonstrate that the YLD virus RNA polymerase can express genes regulated by a synthetic promoter designed for use in orthopoxviruses and that a recombinant virus can be made by homologous recombination into the YLD virus thymidine kinase (TK) gene. Finally, we compare the in vitro gene transfer efficiency of YLD virus and VV and explore the in vivo efficiency of gene delivery in a murine model of ovarian cancer. MATERIALS AND METHODS Cell lines. CV-1 (monkey kidney; ATCC CCL 70), RK-13 (rabbit kidney; ATCC CCL 37), CHO (Chinese hamster ovary; ATCC CCL 61), WIDR (human colon cancer; ATCC CCL 218), HT-29 (human colon cancer; ATCC HTB 38), 205 (human colon.