Analysis of Ig/TCR rearrangements reflects the evolution of the clonal compartment in xenografts. The Ig/TCR rearrangement pattern of diagnostic samples and matched xenografts was determined in 5 VHR- and in 5 SR-ALL samples by PCR using standardized sets of primers that are validated for MRD analysis. (A) Representative examples for a VHR-ALL (left panel) and an SR-ALL (right panel) sample, which showed a marked acceleration from primary to secondary passage. All positive bands of the correct size were sequenced once for verification. Stable rearrangements are framed with an orange line; and bands framed in red represent markers that disappeared in xenografts. In this SR sample, one new Ig/TCR rearrangement appeared (framed in green). (B) Overview of Ig/TCR rearrangements detected. Detected Ig/TCR rearrangements are highlighted in blue. Loss of such a marker in a given xenograft is highlighted in red. Newly detected markers in xenografts are highlighted in green.