The Human T-Cell Cloning Assay: Identifying Genotypes Susceptible to Drug Toxicity and Somatic Mutation

Abstract

Humans exhibit marked genetic polymorphisms in drug metabolism that contribute to high incidence of adverse effects in susceptible individuals due to altered balance between metabolic activation and detoxification. The T-cell cloning assay, which detects mutations in the gene for hypoxanthine-guanine phosphoribosyl transferase (HPRT), is the most well-developed reporter system for studying specific locus mutation in human somatic cells. The assay is based on a mitogen- and growth factor-dependent clonal expansion of peripheral T-lymphocytes in which the 6-thioguanine-resistant HPRT mutants can be selected, enumerated, and collected for molecular analysis of the mutational nature. The assay provides a unique tool for studying in vivo and in vitro mutagenesis, for investigating the functional impact of common polymorphism in metabolism and repair genes, and for identifying risk genotypes for drug-induced toxicity and mutagenicity. This chapter presents a simple and reliable method for the enumeration of HPRT mutant frequency induced in vitro without using any source of recombinant interleukin-2. The other main feature is that only truly induced and unique mutants are collected for further analysis.