CHAPTER 10: Micronucleus Assays with Human Lymphocytes for in Vitro Genetic Toxicology Testing

The toxicological relevance of the micronucleus (MN) assay is well defined: it is a multi-target genotoxicity endpoint, assessing both clastogenic and aneugenic events, it is simple to score, accurate, applicable in different cell types, predictive for cancer and amenable for automation. Using human lymphocytes for the in vitro MN (IVMN) assay has the advantage to provide a primary cell system with a normal mitotic machinery. In this chapter, we discuss the prerequisites for an acceptable MN assay, including the cell as a unit of observation, the importance of cell membranes, necessary assessment of cell division in the presence of the test substance and selection of an adequate top concentration. The advantages and disadvantages of using lymphocytes as a primary cell model system are discussed. The importance of adequate design of protocols is highlighted and references to the relevant OECD (Organisation for Economic Co-operation and Development) and HUMN (HUman MicroNucleus project) guidelines are provided. The main achievements over the last decades with regards to the lymphocyte IVMN assay and its application using the cytokinesis-block technique are summarized. Adaptation of the IVMN assays to assess the genotoxic potential of new materials, in particular nanomaterials, including the scoring of nucleoplasmic bridges and understanding their modes of action will strength the predictivity of the assay for hazard and risk assessment.