Comparison of Minimal Residual Disease Detection Using High-Throughput Sequencing and Allele-Specific Oligonucleotide PCR Methods in Pediatric B-Lineage Acute Lymphoblastic Leukemia.
Authors: Harris Marian , Faham Malek , Fang Lei , Moorhead Martin , Zheng Jianbiao , Neuberg Donna S. , Sallan Stephen E. , Silverman Lewis B. , Stevenson Kristen E. 
Published: October 2019

Abstract
Abstract 2532

Background:
The clinical management of patients with pediatric B-lineage acute lymphoblastic leukemia (B-ALL) relies on combinations of multiagent anticancer drugs and risk-stratified treatment. The prognostic significance of minimal residual detection (MRD) in pediatric B-ALL has been demonstrated in multiple cohorts. Allele-specific oligonucleotide PCR (ASO-PCR) amplification of immunoglobulin or T-cell receptor rearrangements, a method for MRD detection, requires the development of patient-specific reagents and cannot detect clonal evolution. ASO-PCR also has limited coverage, with clonal rearrangements being detected in only 90% of patients. We developed the sequencing-based LymphoSIGHT platform to address these limitations. Here we report the results of a pilot study of MRD detection using both the sequencing assay and ASO-PCR in paired diagnostic and end-of-induction samples from 7 B-ALL patients. Analysis of 82 additional patients is ongoing.

Methods:
Using universal primer sets, we amplified immunoglobulin heavy chain (IgH@) variable (V), diversity, and joining gene segments from genomic DNA in diagnostic and follow-up bone marrow samples. Amplified products were sequenced to obtain >1 million reads (20× coverage per B-cell), and were analyzed using standardized algorithms for clonotype determination. Tumor-specific clonotypes were identified in the diagnostic sample of each patient based on high-frequency within the B-cell repertoire. The presence of the tumor-specific clonotype was then assessed in the end-of-induction sample. A quantitative and standardized measure of MRD level among all leukocytes in the sample was determined using internal reference DNA. Following identification of IgH clonal rearrangements and MRD assessment using the sequencing assay, we examined the MRD results obtained at Boston Children's Hospital using ASO-PCR. Among the 7 patients analyzed to date, 6 patients were in complete remission at the time of the second sample; 1 patient had persistent evidence of disease. Sequencing was performed blinded to all clinical and ASO-PCR information on these patients.

Results:
With the sequencing platform, we detected a high-frequency IgH clonal rearrangement in all 7 diagnostic ALL samples. The leukemic clonotype that was identified at diagnosis was detected in the end-of-induction sample in each of the 7 patients. The quantitative range of the leukemic sequence in MRD samples ranged over 5 orders of magnitude. MRD results were concordant between sequencing and ASO-PCR in 5 of 7 patients. The detected MRD level differed by > 10 fold in 2 patients. In patient 1, sequencing detected high MRD, while low MRD was detected by ASO-PCR; this patient relapsed 1 year later while still on therapy. In patient 6, sequencing detected low MRD, while ASO-PCR detected high MRD. This patient remains in complete remission after 7 years. In patient 7, sequencing and ASO-PCR concordantly detected low MRD; this patient relapsed after completion of therapy.

Conclusions:
Results from the application of a high-throughput sequencing method for MRD detection in childhood B-ALL are shown. The sequencing assay does not require development of patient-specific reagents, which will reduce cost and laboratory turnaround time. This data, along with the laboratory workflow improvements, support the use of the sequencing assay as a next-generation MRD test for B-ALL. Analysis of samples from 82 patients is ongoing.

Disclosures:
Faham: Sequenta, Inc.: Employment, Equity Ownership, Research Funding. Fang:Sequenta, Inc.: Employment, Equity Ownership, Research Funding. Moorhead:Sequenta, Inc.: Employment, Equity Ownership, Research Funding. Zheng:Sequenta, Inc.: Employment, Equity Ownership, Research Funding.