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ChromFound: Towards A Universal Foundation Model for Single-Cell Chromatin Accessibiltiy Data
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Introduces ChromFound, a hybrid Mamba + window-attention foundation model pretrained on 1.97M scATAC-seq cells with genome-coordinate OCR tokenization, evaluated zero-shot on clustering and transferred to batch correction, cell annotation, and cross-omics prediction.
Problem
Single-cell ATAC-seq data are high-dimensional, sparse, and lack a standardized feature space, so there is no foundation model that supports zero-shot cell identification and multi-omics analysis.
Approach
Treat each open chromatin region as a token encoded by chromosome embedding, sinusoidal start/end genomic coordinate embeddings, and continuous accessibility value, and process the long genome-wide sequence with a hybrid of window-partitioned self-attention and Mamba blocks, pretrained with masked MSE reconstruction.
Key results
- Zero-shot cell clustering on PBMC169K (VIB_10xv1_1) reaches ARI 0.6953 vs best baseline PoissonVI 0.6314; average ARI gain reported as 17.02% across 8 datasets.
- Cross-omics prediction on Zhu11K cell lines reaches PCC 0.9449 vs best baseline 0.9196 (BABEL).
- Enhancer-gene link prediction for K562 achieves AUC 0.77 for COPZ1 and 0.61 for HNRNPA1.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use ChromFound instead of the strongest baseline | Zero-shot cell clustering · Eight scATAC-seq datasets across cortex, heart, retina, and PBMC | ARI: average ARI improvement of 17.02% | Helped |
| remove genome-aware tokenization (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.6452±0.0149 | Hurt |
| remove WPSA (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.5897±0.0086 | Hurt |
| remove Mamba block (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.3075±0.0019 | Hurt |
| reduce pretraining data size to 0.2 million cells (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.6539±0.0057 | Hurt |
| reduce pretraining data size to 0.02 million cells (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.6142±0.0053 | Hurt |
| reduce input length to 220000 OCRs per cell (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.4012±0.0047 | Hurt |
| reduce input length to 110000 OCRs per cell (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953±0.0035 -> 0.3276±0.0051 | Hurt |
| use pretrained checkpoint rather than training from scratch (ablation) | ChromFound cross-omics prediction · Five paired datasets | PCC: 0.7864 -> 0.8316; 0.7887 -> 0.8304; 0.4213 -> 0.4249; 0.9279 -> 0.9293; 0.8992 -> 0.9449 | Mixed |
| set positional embedding temperature to 1000 (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953 -> 0.6535 | Hurt |
| set Mamba projection dimension to 16 (ablation) | ChromFound · PBMC169K batch VIB_10xv1_1 | ARI: 0.6953 -> 0.6158 | Hurt |
Surprising findings
- Dropping the Mamba block or the WPSA attention leaves the other intact, but using only WPSA drops ARI to 0.3075, and Geneformer/scGPT Transformer-only variants reach ARI only 0.05 and 0.39 at 4k-32k peaks.
- Baseline VAE methods trained on cPeaks-aligned fixed-vocabulary data lose substantial performance on unseen tissues, while ChromFound performs well even on reference-aligned data.
Limitations
- Some baselines (BABEL, CMAE) are evaluated after filtering to top 10,000 highly variable OCRs, which the authors note makes comparison on enhancer perturbation unfair.
- Cell-type annotation and cross-omics results depend on fine-tuning or supervised MLP heads, not purely zero-shot.
- Reported ARI variance is high on some datasets (e.g., ±0.0387 and ±0.0500), and the 17.02% average gain is relative to a mix of baselines.
Experimental setup
Datasets: HumanAtlas FetalAtlas PBMCBenchmark Cortex130K Zhu45K Kuppe139K Liang154K To326K Morabito130K Zhu11K Fulco4K
Benchmarks: Morabito130K Kuppe139K Liang154K PBMC169K To326K Zhu45K Zhu11K Fulco4K
Metrics: ARI FMI NMI AMI AvgBIO AvgBATCH accuracy macro F1 PCC CCC
Baselines: PeakVI PoissonVI SnapATAC2 Signac SCALE SCALEX CASTLE scBasset Cellcano EpiAnno SANGO BABEL
Builds on: Mamba xTrimoGene scBasset
Closest papers by meaning
- A versatile informative diffusion model for single-cell ATAC-seq data generation and analysis (NeurIPS 2024 · similarity 0.87)
- scPilot: Large Language Model Reasoning Toward Automated Single-Cell Analysis and Discovery (NeurIPS 2025 · similarity 0.85)
- Cell ontology guided transcriptome foundation model (NeurIPS 2024 · similarity 0.85)
- Semi-supervised Knowledge Transfer Across Multi-omic Single-cell Data (NeurIPS 2024 · similarity 0.84)
- PertEval-scFM: Benchmarking Single-Cell Foundation Models for Perturbation Effect Prediction (ICML 2025 · similarity 0.83)
- A Simple and Comprehensive Benchmark for Single-Cell Transcriptomics (AAAI 2025 · similarity 0.82)
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