Multiclonal Profiling of FLT3-ITD in AML Using MinION Sequencing: A Tailored Clustering Approach to Enhance Subclonal Detection.

Background: Internal tandem duplications (FLT3-ITDs) in the FLT3 gene constitute a key driver mutation in acute myeloid leukemia (AML), strongly associated with poor prognosis and therapeutic resistance. Although general-purpose structural variant callers such as Sniffles have been used to detect FLT3-ITDs, their limitations in resolving clonal diversity and low-frequency variants can lead to underrepresentation of minor clones. These shortcomings highlight the need for a dedicated bioinformatics pipeline.

Materials and methods: We developed a custom clustering-based pipeline to overcome the constraints of generic SV callers, leveraging Oxford Nanopore's MinION for sequencing. Our method focuses on FLT3-ITDs by grouping near-identical insertions into biologically meaningful subclones, thereby allowing accurate variant detection of even low-frequency events. The pipeline was benchmarked against capillary electrophoresis (CE) and Sniffles at various thresholds (including 10%, 20%, and 50% allele-frequency cutoffs), with results validated via IGV inspection and cross-mapping.

Results: The pipeline successfully detected FLT3-ITDs across all tested samples, including low-frequency variants and diverse subclones that Sniffles overlooked. Analyses uncovered complex multiclonal architectures composed of dominant clones (~20-25% of reads) plus multiple minor subclones differing in length, sequence, and breakpoint. Crucially, our approach identified duplications as short as 15 bp-events often dismissed by conventional SV callers. Comparative analyses showed that Sniffles failed to call several biologically validated ITDs detected by our custom pipeline.

Conclusion: Third-generation sequencing combined with a tailored clustering strategy enhances the detection of FLT3-ITDs and clonal diversity in AML compared to generic variant callers. This method provides critical insights into subclonal populations driving relapse and therapeutic resistance-particularly in relapsed/refractory AML-underscoring the importance of specialized pipelines for precision medicine in leukemia.