Acute lymphoblastic leukemia (ALL) and multiple myeloma (MM) are characterized by a monoclonal expansion of B- and/or T-cell lymphocyte progenitor/plasma cells, respectively. These diseases can be monitored by the detection of clonally rearranged immunoglobulin and/ or T-cell receptor genes, which are tumor specific and allow the detection of small numbers of malignant cells, so-called measurable residual disease (MRD). Detection of MRD to guide therapy has been a standard practice in treatment of (childhood) ALL for decades. In MM, a clear correlation is found between absence of MRD and longer survival. Quantitative allele-specific oligonucleotide (qASO)-PCR is the current gold standard molecular method for MRD detection in these hematologic malignant tumors and has been standardized and performed in EuroMRD-approved laboratories all over Europe and beyond. However, this technique has some drawbacks: it is a labor-intensive technique that follows only two immunoglobulin and/or T-cell receptor gene rearrangements over time; clonal evolution can interfere with detection, possibly leading to false-negative results; false-positive results after stem cell transplantation have been reported; and the applicability of qASO-PCR in MM is limited to 50% to 70% of patients due to somatic hypermutation. However, these drawbacks can be overcome by next-generation sequencing (NGS). In this study, NGS is validated as an alternative method to qASO-PCR for MRD detection in both ALL and MM. The use of calibrators was a prerequisite for this comparison. These calibrators are composed of three different synthetic junctional regions per immunoglobulin and/or T-cell receptor locus and are added to the reaction mixture at a known amount. MRD results obtained by NGS and qASO-PCR were compared in 59 and 39 bone marrow samples of 33 and 14 patients with ALL and MM, respectively. Our results indicate that the use of gBlocks as calibrators makes the NGS approach a powerful tool to quantify MRD. With an input of 400 ng of DNA (corresponding to approximately 7E+04 cells), a limit of detection of 0.01% was achieved. The specificity of the NGS-MRD technique was 100%, and a correlation with qASO-PCR for quantifiable MRD results of 0.93/0.91 was found in ALL/MM, respectively. Especially for MM, the higher applicability (100%) of the NGS-MRD protocol, compared with qASO-PCR (57%), was clearly demonstrated. These results indicate that NGS-MRD is a reliable MRD detection method for more patients than the current gold standard qASO-PCR.

Dr.Jona Van der Straeten graduated as Master in Biomedical Sciences in 2005 at the Vrije Universiteit Brussel (VUB). From 2005-2008 she worked in the research lab CYTO at the Department for Cell Biology and Histology at VUB. The focus of this research group is to gain better insights in the mechanisms of liver regeneration and the pathogenesis of liver fibrosis. Since 2008, she started working at the Molecular Hematology laboratory (Universitair Ziekenhuis Brussel) as scientific collaborator. This lab is the reference lab for MRD assessment in Belgium and is involved in many clinical studies like ALLTogether, Interfant, EsPhall, IntreALL for childhood ALL, and HOVON for adult ALL.