Single-cell analysis of RHAMM isoform expression patterns in MM plasma cells. (A) Electropherogram analysis of sorted, single, clonotypic MM (Patient 8) plasma cell (PC) expressing (clockwise from top left) RHAMM^FL alone, neither RHAMM^FL nor RHAMM^-exon4, both RHAMM^FL and RHAMM^-exon4, and RHAMM^-exon4 alone. All samples were RT-PCR positive, by ethidium bromide detection, for β₂-microglobulin and clonotypic message. RT-PCR products were EtOH precipitated prior to GeneScan analysis. To maximize the sensitivity of the single-cell assay, large amounts of RT-PCR product were analyzed, as seen by the large product peaks. (B) Electropherogram analysis of RHAMM-specific RT-PCR amplification of cDNA from 1000 sorted MM (patient 8) plasma cells. For ratio determination, product peaks were kept below 3500 relative fluorescent units (RFU), and size standards were within the manufacturer's suggested levels (ie, 150-600 RFU). (C) Plot of RHAMM ratio (1000 cells) versus the fraction of RHAMM^-exon4 single cells. A Pearson R² correlation coefficient of 0.667 indicates a significant linear relationship (P < .02) between the 2 parameters. Error bars indicate ± 2 standard deviations.