The Thy-1loB220+population in the primary thymomas had not rearranged TCRγ, TCRβ, or Igκ genes, butcontained subpopulations that assembled Ig DJH or VDJH genes and were therefore similar totransformed pro- and pre-B cells obtained from A-MuLV infected fetal liver and adult bonemarrow, respectively. The gene discussed is TRGC1; the disease is thymoma.