Lumos: Long-Read Somatic Variant Calling

This Nextflow (v25.10.0) workflow implements a full long-read somatic variant analysis pipeline.
It supports tumor–normal and tumor-only configurations, running on Biowulf (Slurm scheduler).

Currently, the pipeline includes the following steps:

• Alignment with minimap2
• Small variant calling with Clair3
• Phasing with longphase
• Somatic SV calling with Severus
• Copy-number analysis (CNA) with Wakhan
• Somatic SNV calling with DeepSomatic
• Methylation analysis with modkit

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🚀 Quickstart

Tumor–Normal Run

module load nextflow/25.10.0
nextflow run tumorNormalONT.nf   --tumor_reads tumor.bam   --normal_reads normal.bam   --reference hg38.fasta   --vntr vntr.bed   --clair3_model clair3_models/ont --cpgs cpgs.bed

Tumor-Only Run

module load nextflow/25.10.0
nextflow run tumorOnlyONT.nf   --reads tumor.bam   --reference hg38.fasta   --vntr vntr.bed   --sv_pon PoN_1000G_hg38.tsv.gz   --clair3_model clair3_models/ont --cpgs cpgs.bed

Tip: Always run inside an interactive session or with sbatch — not on the Biowulf head node.

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📥 Required Inputs

Tumor–Normal Only

--normal_reads  Path to normal BAM file (must be indexed)
--tumor_reads   Path to tumor BAM file (must be indexed)

Tumor-Only Only

--reads         Path to tumor BAM file (must be indexed)
--sv_pon        Panel of Normals file (e.g. ./annot/PoN_1000G_hg38_extended.tsv.gz)

For both modes

--reference     Reference FASTA  
--vntr          BED file of tandem repeats (must be ordered)(e.g. ./annot/human_GRCh38_no_alt_analysis_set.trf.bed)
--clair3_model  Path to Clair3 model  
--cpgs          CpG island BED file required in sv_cna_dmr and all modes (e.g. ./annot/hg38_cpg_cleaned.bed)

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⚙️ Optional Parameters

--mode       sv_cna       Run only SV and CNA calling  
             sv_cna_dmr   Run SV, CNA, and DMR calling  
             all          Run SV, CNA, DMR, and somatic SNV calling (default)
--cosmic        Path to COSMIC genes in tsv format for Wakhan visualization

Pre-existing bam alignment, use:

--alignment false --bam BAM --bai BAI

instead of --reads

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⚠️ Notes & Caveats

• Input reads: Must be in unmapped BAM format.
  • Multiple files can be passed as a space-separated string wrapped in single quotes:
    --reads_tumor 'BAM1 BAM2'
  • Wildcards are supported:
    --reads_tumor 'BAM_DIR/*bam'
• Multiple runs: Each Nextflow run must be launched from a unique working directory.
  Nextflow creates a work/ folder and .nextflow.log inside the run directory.
• Resuming after failure: Use the -resume flag (note single dash).
  The workflow will attempt to reuse existing results.
  Resume must be launched from the same working directory.
• Output directory change By default, final outputs will be available in lumos_out directory. You can change it by adding -output-dir XXX argument (note single dash)
• Nexflow version Note that the workflow has been tested with Nextflow v25.10.0, and may not run with other versions due to recent synthax changes.

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🛠️ Debugging & Development Tips

• To run locally, comment out

  process.executor = 'slurm'

  in nextflow.config.
• Job status looks like:

  [11/4852c3] tumorOnlyOntWorkflow:alignMinimap2 (1) [ 0%] 0 of 1
  

  Outputs are in the corresponding working directory under work/11/4852c3....
• Useful files inside a job’s work directory:
  • .command.sh → exact command executed
  • .command.out → stdout
  • .command.err → stderr
• Each process runs inside a Singularity/Docker container.
  Custom container build scripts are available in the docker/ folder.

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📚 Learning Resources

• New to Nextflow? Start with the excellent tutorial:
  👉 https://training.nextflow.io/

Notes

• Tumor-only: omit --reads_normal; provide --sv_pon for Severus.
• Modes:
  • --mode sv_cna runs Severus + Wakhan.
  • --mode sv_cna_dmr adds DMR from modkit.
  • --mode all runs all modules including DeepSomatic.
• Consistency: tumor and normal BAMs are haplotagged by the same method to ensure consistent phasing.