Problems and pitfalls in assessing human T-lymphocyte mutant frequencies.

Area of Science:

• Human molecular toxicology
• Somatic cell mutation assays
• Immunogenetics

Background:

• The hypoxanthine-guanine phosphoribosyltransferase (HPRT) assay in T-lymphocytes is a tool for quantifying in vivo mutation frequencies.
• Existing data reveal substantial variability in HPRT mutant frequencies among healthy individuals.

Purpose of the Study:

• To assess the reliability of different scoring methods for the HPRT assay.
• To evaluate the statistical precision and biological representativeness of the assay for in vivo human mutagenesis.
• To determine the assay's suitability as a screen for mutagen exposure.

Main Methods:

• Investigated reliability using five scoring methods: visual, [3H]thymidine uptake (cutoff and statistical), cell count, and cytogenetic analysis.
• Analyzed T-lymphocyte subpopulations using cell surface monoclonal antibodies.
• Examined statistical precision under experimental limitations.

Main Results:

• None of the five scoring methods proved viable for reliable assay scoring.
• Significant inherent error was identified in the estimation of mutant frequencies.
• Observed mutant frequencies may not accurately reflect true in vivo frequencies due to T-lymphocyte subpopulation heterogeneity.

Conclusions:

• The current HPRT T-lymphocyte assay methodology requires comprehensive reevaluation and a deeper understanding of its underlying biology.
• The assay's utility for qualitative human mutagenesis research is confirmed, but its quantitative application for mutagen exposure screening is questionable without significant improvements.