TCR diversity as determined by TCR vector β spectratyping in mobilized FV vector–treated dogs. Rearrangement of the TCR β chain was assessed by PCR amplification of complementary DNA using 17 different primer pairs (annotated on top) at various time points posttreatment in a normal littermate control H866 (A) and in treated SCID-X1 dogs H864 and H867 (B).