Interpreting next-generation immunosequencing results in children and young adults with acute lymphoblastic leukemia

Determination of measurable residual disease (MRD) in pediatric acute lymphoblastic leukemia (ALL) using next-generation immunosequencing (clonoSEQ; Adaptive Biotechnologies) has emerged as an essential and sensitive tool. The clonoSEQ assay identifies and tracks all the B-cell and T-cell receptor rearrangements present in a sample. With widening clinical use of immunosequencing for MRD monitoring (next-generation sequencing [NGS]-MRD), clinicians are increasingly encountering cases with results that are considered to be inconclusive, where immunosequencing yields detectable clonotypic sequences, yet it is unclear whether they indicate ALL, normal background, or an independent etiology. There is a need for guidance in the clinical interpretation of immunosequencing results. In this article, we describe various features of immunosequencing reporting and their clinical implications through a series of illustrative clinical cases. Each case presents a distinct scenario encountered in the clinical setting where NGS-MRD had varying clinical implications. Through aggregate evaluation of the various components of the results, such as the sequence locus, sequence abundance, clonal tracking, and levels of detection and blank, we formulate systematic interpretative tools that can be leveraged to inform clinical decision-making. The goal of this article is to serve as a useful guide for clinicians as they interpret immunosequencing results for pediatric ALL.