An investigation of DNA mismatch repair capacity under normal culture conditions and under conditions of supra-physiological challenge in human CD4+T cell clones from donors of different ages

T cells undergo rapid clonal expansion upon antigenic stimulation to produce an effective immune response. Any defect in the DNA mismatch repair (MMR) system may have a detrimental effect on T cell proliferation. This study employed an in vitro model of human CD4+T cell ageing to investigate MMR capacity at various stages of T cell lifespan. A novel modification of the alkaline comet assay, which utilised T4 endonuclease VII to detect single base DNA mismatches, was used to assess DNA mismatch frequency. No clear pattern in DNA mismatch frequency with increasing culture age was observed. However, the ability to repair induced DNA mismatches (following treatment with acridine mutagen ICR-191) revealed an age-related decline in the efficiency of the MMR system in clones derived from a 26 and a 45-year-old donor, but not from an 80-year-old very healthy SENIEUR donor. This study suggests that unchallenged, dividing human T cell clones have variable levels of DNA mismatches throughout their lifespan, not affecting proliferation. However, when challenged with supra-physiological levels of DNA mismatches, deficiencies were found in ageing T cell clones in MMR capacity, with the exception of T cell clones from a SENIEUR donor previously shown to maintain effective DNA excision repair.