The OECD Test Guideline 490 describes the in vitro mammalian cell gene mutation tests that use the thymidine kinase (TK) gene to detect gene mutations induced by test chemicals. The guideline covers two cell systems: the L5178Y TK+/− mouse lymphoma cell line which is used in the Mouse Lymphoma Assay (MLA), and the TK6 human lymphoblastoid cell line.

In the Mouse Lymphoma Assay, forward mutations at the endogenous thymidine kinase locus are measured in L5178Y cells. Loss of thymidine kinase function can result from a range of genetic events, including point mutations, frameshift mutations, small and large deletions, chromosomal rearrangements, and mitotic recombination.

The mutant cells are identified based on their ability to form colonies under selective conditions. Both large and small colony mutants are evaluated to get additional information on the nature of the genetic damage induced by the test chemical.

Vipragen Biosciences offers Mouse Lymphoma Assay testing in accordance with OECD TG 490 as part of its in vitro genetic toxicology testing services.