The next step was to dissect the immune D b NPN3A + CD8 + CTL repertoire to determine how TCR diversity relates to the size of the immune D b NPN3A + CD8 + T cell response. The D b NPN3Aspecific CD8 + T cells were first analysed for Vb usage by staining with a panel of anti-TCRVb mAbs and the D b NPN3A tetramer. After infection with the NPN3A viruses, the strong Vb8.3 bias characteristic of responding D b NP 366 + CD8 + T cells [34, 35] was prominent for the D b NPN3A + CD8 + sets in only 50% of the immune mice (n = 10). The mutant D b NPN3A + CD8 + T cells utilized a variable spectrum of TCRVb elements, with overrepresentation of Vb 7, 8.1/8.2, 9, 11, and 12 after primary ( Fig  S2A) or Vb6, 7 and 9 following secondary ( Fig S2B) NPN3A virus challenge.