The primary objective of this project is to determine if a surrogate selection approach utilizing mutation at a reporter gene (hypoxanthine- guanine phosphoribosyltransferase (hprt]) as a probe for in vivo cell division can be used as a diagnostic tool for detection of sub-clinical clonal T-cell expansion in human T lymphotropic HTLV-1 carriers. Such a test would be to allow preventive therapy (initially in the setting of HTLV-1-mediated adult T-cell leukemia) to be initiated before the expanding clone has progressed to a more aggressive and untreatable state. The objective will be achieved by testing blood samples from HTLV-1-infected individuals with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Wild type and hprt mutant T-cell clones will be isolated, and clonal identity determined by multiplex PCR and DNA sequencing of T-cell receptor (TCR) variable region beta chain and third complimentarity determining regions. In vivo- expanded clones will be identified, and representatives of the amplified clones will be tested for monoclonal HTLV integration as compared to that observed in the peripheral blood sample. These studies may provide new insights into the precise mechanism of HTLV-1 leukemogensis, and direct the development of more effective therapies. PROPOSED COMMERCIAL APPLICATIONS: Development of an automated test for clonal T-cell expansion would aid in the diagnosis and treatment of virally-mediated pathologies. The test would also have diagnostic/therametric applications in disease conditions where therapeutic agents are used that target the puring salvage pathway.