Page 90 - Haematologica-April 2018

Correspondence:
christine.harrison@newcastle.ac.uk
Received: May 15, 2017. Accepted: February 8, 2018. Pre-published: February 15, 2018.
doi:10.3324/haematol.2017.172304
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Haematologica 2018 Volume 103(4):634-644
2311 Peter Carey, Christina Halsey, Olaf Heidenreich, Anthony V. Moorman and
634
Ferrata Storti Foundation
Acute Lymphoblastic Leukemia
Dynamic clonal progression in xenografts of acute lymphoblastic leukemia with intrachromosomal amplification
of chromosome 21
Paul. B. Sinclair,1 Helen H. Blair,1 Sarra L. Ryan,1 Lars Buechler,1 Joanna
Cheng,1 Jake Clayton,1 Rebecca Hanna,1 Shaun Hollern,1 Zoe Hawking,1
Matthew Bashton,1 Claire J. Schwab,1 Lisa Jones,1 Lisa J. Russell,1 Helen Marr,1
Christine J. Harrison
1
1Wolfson Childhood Cancer Research Centre, Northern Institute for Cancer Research, Newcastle University, Newcastle-upon-Tyne; 2Department of Clinical Haematology, Royal Victoria Infirmary, Newcastle-upon-Tyne and 3Wolfson Wohl Cancer Research Centre, Institute of Cancer Sciences, University of Glasgow, UK
ABSTRACT
Intrachromosomal amplification of chromosome 21 is a heterogeneous chromosomal rearrangement occurring in 2% of cases of childhood precursor B-cell acute lymphoblastic leukemia. These abnormalities are too complex to engineer faithfully in animal models and are unrepre- sented in leukemia cell lines. As a resource for future functional and pre- clinical studies, we have created xenografts from the leukemic blasts of patients with intrachromosomal amplification of chromosome 21 and characterized them by in-vivo and ex-vivo luminescent imaging, flow immunophenotyping, and histological and ultrastructural analyses of bone marrow and the central nervous system. Investigation of up to three generations of xenografts revealed phenotypic evolution, branching genomic architecture and, compared with other B-cell acute lymphoblas- tic leukemia genetic subtypes, greater clonal diversity of leukemia-initiat- ing cells. In support of intrachromosomal amplification of chromosome 21 as a primary genetic abnormality, it was always retained through gen- erations of xenografts, although we also observed the first example of structural evolution of this rearrangement. Clonal segregation in xenografts revealed convergent evolution of different secondary genomic abnormalities implicating several known tumor suppressor genes and a region, containing the B-cell adaptor, PIK3AP1, and nuclear receptor co- repressor, LCOR, in the progression of B-cell acute lymphoblastic leukemia. Tracking of mutations in patients and derived xenografts pro- vided evidence for co-operation between abnormalities activating the RAS pathway in B-cell acute lymphoblastic leukemia and for their aggres- sive clonal expansion in the xeno-environment. Bi-allelic loss of the CDKN2A/B locus was recurrently maintained or emergent in xenografts and also strongly selected as RNA sequencing demonstrated a complete absence of reads for genes associated with the deletions.
Introduction
Xenograft models of leukemia have been used to address a number of important fundamental and translational research questions relating to: the nature of leukemia stem cells, clonal evolution and experimental therapies.1-8 Limiting dilution studies have demonstrated that leukemia-initiating cells are common, while fluorescence in situ hybridization (FISH), genomic arrays, analysis of immunoglobulin/T-cell recep- tor rearrangements, immunophenotype and drug response have suggested that the
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