T Cell receptor rearrangements in various S49 lymphoma sublines

The S49 cell lines are a unique series of tumor sublines isolated from a single BALB/c thymoma. Several different sublines were previously isolated from non-mutagenized cells using pharmacologie agents that would select for different stages of thymic development. In this report we show that all seven of the sublines studied express TL class I Ag confirming their derivation from immature thymocytes. This uniform TL expression is in contrast to the previously characterized locus-specific shut off of K^d,D^d, and/or L^dAg by various S49 sublines. Furthermore, S49 sublines were found to display disparate CD4/CD8 expression. Whereas the unselected subline is a CD4⁺/CD8⁺ double positive, each of the selected sublines is singly positive for either CD4 or CD8. All seven sublines were found to be CD3⁺ and express αβ TCR heterodimers. To establish whether the S49 sublines have a monoclonal or polyclonal origin, their TCR rearrangements were compared. Based on the detection of identical but unusual TCR γ rearrangements and similarity of the a and β rearrangements, we propose that the S49 sublines probably had a monoclonal origin. However, significant differences between the TCR a and β gene rearrangement were observed, suggesting that these sublines have undergone further differentiation at TCR loci in addition to CD4/CD8 and MHC loci. Evidence is presented that much of this phenotypic diversity preceded their in vitro selection.