Stem Cell-Derived T Cells Offer New Human Model for Genotoxicity Testing

Japanese researchers have built a micronucleus test around T lymphocytes grown from human induced pluripotent stem cells, creating what they describe as a promising proof-of-principle alternative to the immortalized cell lines and fresh blood lymphocytes that dominate current in vitro genotoxicity screening.

The micronucleus test is one of the standard tools for detecting chromosomal damage. In vitro versions of the assay are widely used alongside chromosomal aberration tests and comet assays to flag substances that might damage genomes before they reach animal or human studies.

The problem the Kyoto University-led team set out to address lies in the cells those tests typically use. Mammalian immortalized lines such as the Chinese hamster lung fibroblast lines CHL/IU and V79 and the Chinese hamster ovary line CHO are easy to handle and highly sensitive, but they are prone to false positive results. The authors point to dysfunction of the tumor-suppressor gene p53 and chromosomal abnormalities as likely contributors. Even the human lymphoblastoid line TK6, which retains normal p53 function, carries several chromosomal aberrations, including trisomy of chromosome 13 and multiple reciprocal translocations, and one report has suggested that factors beyond p53 status also drive false positives in immortalized cells.

The human alternative, lymphocytes taken from fresh blood, brings its own difficulties. Because these cells have limited proliferative capacity, fresh blood must be collected for every test, and donors must satisfy criteria covering age, medical history, and smoking status. Results can vary from donor to donor, the cellular profile depends on the donor’s physiological condition at collection, and the number of cells obtained is limited. The result is a test system that is difficult to supply stably and in a timely manner.

Induced pluripotent stem cells offer a way around both sets of constraints. The researchers established hiPSCs from cryopreserved human peripheral blood mononuclear cells and differentiated them into T lymphocytes at the Center for iPS Cell Research and Application, Kyoto University, following a protocol previously shown to yield functionally competent T cells with high proliferative capacity and elongated telomeres. Frozen stocks of the resulting lymphocytes were prepared for each experiment, meaning the cells can be frozen, thawed after expansion culture, and supplied in a stable and homogeneous form.

Before running the assay, the team screened five hiPSC clones for spontaneous micronucleus frequency and found statistically significant variation among them. They selected a clone with a low spontaneous frequency, confirmed by Giemsa-banding that it had normal diploidy with 46 chromosomes, and verified that its p53 gene sequence showed no abnormalities. After differentiation, 92.0 percent of the cells expressed TCRαβ and CD3, the characteristic surface markers of T lymphocytes, and the cells grew well when stimulated through an anti-CD3 antibody-coated culture plate.

The genotoxicity panel covered the main mechanistic classes. Clastogens that do not require metabolic activation, namely mitomycin C, cytosine arabinoside, N-ethyl-N-nitrosourea, methyl methanesulfonate, N-methyl-N-nitro-N-nitrosoguanidine, 4-nitroquinoline 1-oxide, and etoposide, were tested under long-term treatment without S9 liver fraction. The aneugens colchicine and vinblastine sulfate, which disrupt chromosome segregation, and the negative controls mannitol and sodium chloride were tested under the same conditions. The clastogens cyclophosphamide and benzo[a]pyrene, which need metabolic activation, were evaluated in a short-term treatment with phenobarbital and 5,6-benzoflavone-induced rat liver S9. Cytochalasin B was used to block cytokinesis so that micronuclei could be scored in binucleate cells, with at least 1,000 binucleate cells scored per slide in a blinded analysis and replication index calculated according to OECD Test Guideline 487.

The results followed the expected pattern. For the clastogens and aneugens, the team observed dose-dependent and statistically significant increases in micronucleated binucleate cells compared with the concurrent solvent control, using Fisher’s exact test at a significance level of 0.05. For both negative substances, no statistically significant increase appeared at any dose up to the maximum of 10 mM. Concentrations causing excessive toxicity, defined as a replication index below 40 percent, were excluded from analysis. Solvent controls showed no cytotoxicity, with cytokinesis-block proliferation index values between 1.5 and 1.8, confirming that cells divided during the culture period. Overall, the positive and negative responses for all thirteen substances matched previously published reports.

The authors frame the work as proof of principle rather than a finished, validated test. They note that OECD Test Guideline 487 selects cells on the basis of growth in culture, karyotype stability, spontaneous micronucleus frequency, and observable micronucleus induction, criteria their cells appear to satisfy. They also highlight a further potential application: because hiPSC-derived T lymphocytes can be generated stably and homogeneously from almost any donor, the system could support more accurate investigation of inter-individual differences in susceptibility to genotoxic substances, an area where fresh blood lymphocytes are hampered by lifestyle-related variation in spontaneous micronucleus frequency and by the very low baseline frequencies that make small experimental fluctuations consequential.

Wider adoption will require more work. The researchers state that the testing system is expected to be authorized through additional verification, including formal validation compliant with OECD Test Guideline 487 in multiple laboratories, using more reference substances spanning different types of aneugens and a wide range of negative controls. Until such multi-laboratory validation is complete, the assay remains a promising experimental platform rather than a regulatory alternative, but it demonstrates that pluripotent stem cell technology can extend beyond regenerative medicine and adoptive immunotherapy into the routine machinery of chemical safety assessment.

Subject of Research: An in vitro micronucleus genotoxicity test developed with human induced pluripotent stem cell-derived T lymphocytes

Article Title: Development of a novel in vitro micronucleus test using human induced pluripotent stem cell-derived T lymphocytes

Article References: Kobayashi, R., Sasaki, K., Matsuyama, R., Saito, K., Kumagai, A., Kitayama, S., Kawai, Y., & Kaneko, S. (2025). Development of a novel in vitro micronucleus test using human induced pluripotent stem cell-derived T lymphocytes. Genes and Environment, 47(1), Article 24. https://doi.org/10.1186/s41021-025-00345-9

Image Credits: AI Generated

DOI: 10.1186/s41021-025-00345-9

Keywords: micronucleus test, genotoxicity, induced pluripotent stem cells, T lymphocytes, OECD TG 487, chromosomal aberration, clastogens, aneugens, p53, karyotype, in vitro testing, toxicology