Table 1. B-ALL patient sample information.

Patient ID	Fusion gene and other genetic abnormality	BCR sequence pattern in diagnostic sample	BCR sequence pattern in relapse or MRD sample	Disease status	BCR sequencing template
527a	E2A-PBX1	Monoclonal expansion	Original clone (low level)	No relapse	RNA
859a	ETV6-RUNX1	Biclonal expansionb (with secondary rearrangements)	Original clone (low level)	No relapse	RNA
1592a	E2A-PBX1	Monoclonal expansion	Non-clonal	No relapse	RNA
1611a	E2A-PBX1	Monoclonal expansion	Non-clonal	No relapse	RNAc
1703a	ETV6-RUNX1	Monoclonal expansionb	Monoclonal expansion (novel clone)	CNS relapse (+ low-level BM)	RNAc
3243a	BCR-ABL	Monoclonal expansion	Non-clonal	No relapse	RNA
Patient Ad	ETV6-RUNX1	Monoclonal expansion	Monoclonal expansion (diagnostic clone)	BM relapse	DNA
Patient Bd	Additional RUNX1	Biclonal expansion	Monoclonal expansion (of one of diagnostic clones)	BM relapse	DNA
Patient Cd	ETV6-RUNX1	Biclonal expansione	Biclonal expansion (two diagnostic clones)e	BM relapse	DNA
Patient Dd	TCF3 rearrangement	Monoclonal expansion	Monoclonal expansion (diagnostic clone)	BM relapse	DNA
Patient Ed	ETV6-RUNX1	Biclonal expansion	Monoclonal expansion (diagnostic clone)	BM relapse	DNA
Patient Fd	ETV6-RUNX1	Monoclonal expansion	Biclonal expansion (with diagnostic clones)	Combined relapse	DNA
Patient Gd	ETV6-RUNX1; -X; abn. Chr 3,4,7,12,15	Biclonal expansion	Monoclonal expansion (novel clone)	Combined relapse	DNA
Patient Hd	ETV6-RUNX1, loss of one CDKN2A and one MLL signal	Polyclonal expansion	Non-clonal	CNS only relapse	DNA
Patient Id	Bi-allelic CDKN2A deletion	Polyclonal expansion	Monoclonal expansion (of one of diagnostic clones)	BM relapse (+low-level CNS)	DNA

Abbreviations: B-ALL, B-cell acute lymphoblastic leukemia; BCR, B-cell receptor; BM, bone marrow; CNS, central nervous system; MRD, minimal residual disease.

^aTreated under the UKALL XI protocol.⁵⁵

^bThe 'diagnostic' samples from patients 859 and 1703 were taken after treatment had commenced.

^cDNA samples were also available from these samples (see Supplementary Figure S2).

^dTreated under the UKALL2003 protocol.⁵⁵

^eLikely to represent bi-allelic VDJ rearrangements in the transformed B cell.