Analysis of switch circle transcripts in HCL expressing multiple sIg isotypes. Circle transcripts are a hallmark of active class switching deletional recombination, and these were analyzed in our series of HCL cases by an RT-PCR method as described previously.¹⁵  All HCL cases were found negative for both Iα-Cμ and Iγ-Cμ circle transcripts as shown. Template cDNA input was compared by using identical amounts of cDNA for amplification of V_H as a reference gene (V). Assay conditions were validated by identifying CTs, confirmed by sequence analysis, in comparable amounts of cDNA from 3 control cases of CLL displaying unmutated V_H genes (C1, C2, C3), which exhibit ongoing switching deletional events as reported.¹⁵  For CLL, β-actin was used as a loading marker gene (labeled B).