Threshold levels of gene expression of the melanoma antigen gp100 correlate with tumor cell recognition by cytotoxic T lymphocytes

The level of expression of melanoma antigens (MA) may modulate the host imm unologic response. Thus, the accurate measurement of MA expression may allo w proper patient selection for antigen-specific therapies and yield importa nt information for the evaluation of clinical results. in this study, we me asured the absolute levels of MA messenger ribonucleic acid (mRNA) in tumor cell lines utilizing realtime quantitative reverse transcriptase-polymeras e chain reaction (qRT-PCR). mRNA levers of MART-1, gp100, tyrosinase, TRP-1 and TRP-2, melanoma differentiation antigens and MAGE-1, MAGE-3 and ESO-1 cancer testis (CT) antigens were compared in 24 early-passage (<5 passages in culture) and 12 archival melanoma cell lines. MA mRNA expression was ext remely variable among cell lines, occasionally reaching levels comparable t o ribosomal RNA (rRNA). gp100 and MART-I mRNA levels correlated with protei n expression measurement obtained by FAGS analysis. More significantly, a t hreshold of gp 100 mRNA expression required for T-cell stimulation and targ et-cell killing was identified. This threshold level corresponded to approx imately 500 mRNA copies per 10(8) copies of rRNA. Our results suggest that the measurements of MA mRNA levels may yield useful information relevant to the interpretation of clinical outcome during antigen-specific treatments. Published 2000 Wiley-Liss, Inc.