Functional modeling of MRD-positive ALL. (A) Schematic of the disease course and treatment from initial diagnosis of UPN 25. BM cells from the +7.8-month MRD-positive (pos) sample: 3.65 × 10−2 were transplanted into 3 individual recipient mice (8 × 10−4 nucleated cells/mouse). (B) Phenotypic characterization of BM from the single MRD engrafted recipient mouse shows CD34− xenografted leukemia; CD34+ disease was characterized at diagnosis. (C) (a) MGG staining of BM shows infiltration by monomorphic lymphoid blasts in the MRD engrafted recipient, ×60. (b) Hematoxylin and eosin–stained histological section of the liver parenchyma, ×20, and (c) human CD10 immunostaining of liver, ×20 in the MRD engrafted recipient mouse. Images were taken using Nikon Eclipse E600 microscope and Nikon DS-Fi1 camera. Black arrows indicate focal areas of leukemic infiltration. (D) FISH analysis (×100), showing presence of the original IgH@CRLF2 chromosomal rearrangement in cells harvested from BM as separated red (red arrow) and green signals (green arrow); the normal copy of the IgH gene is seen as a red-green fused signal in the same cell (yellow arrow). IgH rearrangement was detected in 97% of BM cells. (E) (Upper) Heteroduplex assessment of the original diagnostic sample from patient UPN 25 and (lower) murine BM that had engrafted with the patients MRD-ALL. MRD-ALL reproduced the identical Ig/TCR clonal rearrangements of the diagnostic sample as confirmed by sequence analysis.
