Cited by 193Single-cell and spatial transcriptomicsGene expression and cancer classificationBioinformatics and Genomic Networks

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Transformer for one stop interpretable cell type annotation

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Abstract

Consistent annotation transfer from reference dataset to query dataset is fundamental to the development and reproducibility of single-cell research. Compared with traditional annotation methods, deep learning based methods are faster and more automated. A series of useful single cell analysis tools based on autoencoder architecture have been developed but these struggle to strike a balance between depth and interpretability. Here, we present TOSICA, a multi-head self-attention deep learning model based on Transformer that enables interpretable cell type annotation using biologically understandable entities, such as pathways or regulons. We show that TOSICA achieves fast and accurate one-stop annotation and batch-insensitive integration while providing biologically interpretable insights for understanding cellular behavior during development and disease progressions. We demonstrate TOSICA’s advantages by applying it to scRNA-seq data of tumor-infiltrating immune cells, and CD14+ monocytes in COVID-19 to reveal rare cell types, heterogeneity and dynamic trajectories associated with disease progression and severity.

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Overview

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TL;DR

TOSICA is a Transformer-based, multi-head self-attention model for interpretable cell type annotation that uses biologically meaningful tokens such as pathways or regulons. It transfers labels from reference to query scRNA-seq datasets with high accuracy, batch-insensitive integration, and attention-based interpretability across development, cancer, COVID-19, and SLE case studies.

Key findings

  • Across six benchmark datasets and 19 methods, TOSICA had the highest mean accuracy at 86.69%, ranked top 6 on every dataset, and reached 81.06% on the largest dataset mAtlas versus 79.57% for the second-best method ACTINN.
  • On datasets with uneven cell-type distributions between reference and query, TOSICA achieved 76.47% mean accuracy on five unbalanced cell types, compared with 63.23% for SingleR and 68.18% for SciBet; Kullback–Leibler divergence had the strongest negative correlation with accuracy (PCC = −0.9).
  • TOSICA discovered unseen or rare cell types: after deleting alpha cells from the hPancreas reference, 76% of query alpha cells were labeled “Unknown,” while other methods mislabeled them as PP, delta, or beta.
  • In integration benchmarks, scIB ranked TOSICA second of 11 applicable methods on pan-cancer myeloid cells and first of 13 methods on a COVID-19 dataset; on the T cell dataset, TOSICA’s runtime was shortest, while scGen took nearly five days.

Methods

  • TOSICA uses a multi-head self-attention Transformer with a Cell Embedding layer, Multi-head Self-attention layer, and Cell-Type Classifier. Gene expression is transformed into tokens using a mask matrix based on prior knowledge, such as GSEA Reactome or C3 gene sets, so tokens represent pathways or regulons; a CLS token is used for cell-type prediction.
  • The model is trained supervised on reference scRNA-seq data with cell-type labels, with 30% of the training set used as validation, cross-entropy loss, SGD, cosine learning rate decay, and convergence typically within 20 epochs. Attention scores between CLS and pathway tokens serve as interpretable cell embeddings for downstream UMAP, clustering, and trajectory analyses.
  • Benchmarks used six datasets—hArtery, hBone, hPancreas, mBrain, mPancreas, and mAtlas—compared against 18 other annotators, with accuracy defined as the fraction of correctly predicted cells. Integration was assessed with scIB metrics including batch ASW, NMI, ARI, graph connectivity, kBET, and isolated label F1.

Limitations

  • The paper states that no statistical method was used to predetermine sample size, experiments were not randomized, and investigators were not blinded to allocation during experiments and outcome assessment.
  • Evident from the text: benchmark accuracy depends on “ground truth” labels from original publications, and some comparison methods were not applicable to large or highly batched datasets, which may affect relative rankings.
  • Evident from the text: random masks sometimes converged to lower accuracy and required more epochs than knowledge-based masks, though TOSICA was generally robust to mask choice.

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Crossref · 10.1038/s41467-023-35923-4

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Figures

Fig. 1 Algorithmic framework of TOSICA. a The model is trained on single-cell RNA sequencing data and cell type label for each cell. Based on databases or expert knowledge, masked learnable embeddings are used to convert the reference input data (n genes) to k input tokens representing each gene set (GS), to which class token (CLS) is added. In the attention function, query (Q), key (K), and value (V) matrix are linearly projected from these GSs and CLS combined tokens and the weights (attention, A) is computed by a compatibility function of the Q with the corresponding K, then assigned to each V for computing output (O). In each Multi-head Self-attention layer, the attention function is performed H times in parallel. The CLS of O, considered as latent space of each cell, is used as input of the whole conjunction neural network cell type classifier. Meanwhile, the attention of class (CLS) token to gene set (GS) tokens is referred as attention score and used for cell embedding. b hArtery and hBone datasets use healthy samples as training data and predict disease samples. hPancreas and mBrain datasets are split by data source. Training and test data in mPancreas and mAtlas come from different timepoints.
Fig. 1 Algorithmic framework of TOSICA. a The model is trained on single-cell RNA sequencing data and cell type label for each cell. Based on databases or expert knowledge, masked learnable embeddings are used to convert the reference input data (n genes) to k input tokens representing each gene set (GS), to which class token (CLS) is added. In the attention function, query (Q), key (K), and value (V) matrix are linearly projected from these GSs and CLS combined tokens and the weights (attention, A) is computed by a compatibility function of the Q with the corresponding K, then assigned to each V for computing output (O). In each Multi-head Self-attention layer, the attention function is performed H times in parallel. The CLS of O, considered as latent space of each cell, is used as input of the whole conjunction neural network cell type classifier. Meanwhile, the attention of class (CLS) token to gene set (GS) tokens is referred as attention score and used for cell embedding. b hArtery and hBone datasets use healthy samples as training data and predict disease samples. hPancreas and mBrain datasets are split by data source. Training and test data in mPancreas and mAtlas come from different timepoints.CC BY · PubMed Central
Fig. 2 Universality of TOSICA on different datasets. a TOSICA ranks first on mean accuracy compared to 18 other cell type annotators on different datasets. Columns are sorted by the mean accuracy of each method on all datasets (top). The number of cell types (Types), number of cells (Log size), Shannon-entropy (Entropy) in reference, and Kullback-Leibler divergence (DKL) between reference and query are labeled on the right. Gray means this dataset is too large for this method to deal with. b TOSICA succeeds in matching cells in query (mouse age ≠ 18 months) to reference (mouse age = 18 months) on mAtlas as shown by TOSICA attention embedded UMAP. The UMAP is done on the whole mAtlas dataset, including both reference and query. Cells in the reference (left panel) or query (right panel) are colored by cell types while cells in the query (left panel) or reference (right panel) are colored gray. The same types of cells from reference and query are located in the same cluster. Circled cells are rare in reference but clustered correctly in the query by TOSICA. c Runtime of TOSICA (marked by *) is relatively stable with increasing data size, and the fourth shortest on mAtlas. hPanc and mPanc stand for hPancreas and mPancreas. d DKL has the most negative impact on accuracy. Heatmap shows the correlation between accuracy (ACC) and number of cells (Size), number of cell types (Types), Shannon-entropy (Entropy), and Kullback-Leibler divergence (DKL). e TOSICA performs better than two other top-ranked methods on five cell types unbalanced between reference and query (red labels). Heatmap shows the proportion of cells in each row with cell type O (original label, shown on the right) is predicted as cell type P (prediction, shown on the top). Cell types are ordered by ratios of their proportions in reference to query. Data are normalized within each row (origin label). Only values >0.5 are labeled. Source data are provided as a Source data file.
Fig. 2 Universality of TOSICA on different datasets. a TOSICA ranks first on mean accuracy compared to 18 other cell type annotators on different datasets. Columns are sorted by the mean accuracy of each method on all datasets (top). The number of cell types (Types), number of cells (Log size), Shannon-entropy (Entropy) in reference, and Kullback-Leibler divergence (DKL) between reference and query are labeled on the right. Gray means this dataset is too large for this method to deal with. b TOSICA succeeds in matching cells in query (mouse age ≠ 18 months) to reference (mouse age = 18 months) on mAtlas as shown by TOSICA attention embedded UMAP. The UMAP is done on the whole mAtlas dataset, including both reference and query. Cells in the reference (left panel) or query (right panel) are colored by cell types while cells in the query (left panel) or reference (right panel) are colored gray. The same types of cells from reference and query are located in the same cluster. Circled cells are rare in reference but clustered correctly in the query by TOSICA. c Runtime of TOSICA (marked by *) is relatively stable with increasing data size, and the fourth shortest on mAtlas. hPanc and mPanc stand for hPancreas and mPancreas. d DKL has the most negative impact on accuracy. Heatmap shows the correlation between accuracy (ACC) and number of cells (Size), number of cell types (Types), Shannon-entropy (Entropy), and Kullback-Leibler divergence (DKL). e TOSICA performs better than two other top-ranked methods on five cell types unbalanced between reference and query (red labels). Heatmap shows the proportion of cells in each row with cell type O (original label, shown on the right) is predicted as cell type P (prediction, shown on the top). Cell types are ordered by ratios of their proportions in reference to query. Data are normalized within each row (origin label). Only values >0.5 are labeled. Source data are provided as a Source data file.CC BY · PubMed Central
Fig. 3 One stop interpretable de novo, high resolution, dynamic, and hierarchical annotation for biological insights by TOSICA. a TOSICA successfully isolates and labels the masked alpha cells as ‘Unknown’ cell type. UMAP is based on attention of hPancreas test set. Red circled and marked by red arrows are manually deleted alpha cells and blue circled and marked by blue arrows are MHC class II cells, originally not present in training set. These two kinds of cells are learned as isolated ‘Unknown’ cell types, and are separated by TOSICA attention scores’ UMAP. b TOSICA labels most of alpha cell and little other cell types as unknown. Heatmap shows proportion of cells in each row with original label O (original label, shown on the right) predicted as cell type P (prediction, shown on the top). See Supplementary Fig. 9 for comparison to other methods. c Some originally labeled mature Acinar (Mat., top) are predicted by TOSICA as proliferative Acinar (Prlf., bottom), red circled. UMAP is based on attention of mPancreas test set. The inset illustrates naming of MM, MP, PM, and PP, originally (O) labeled versus TOSICA (T) labeled. d Two pathways’ attention score separate the MM and MP. e Hierarchical clustering of DEGs between the originally labeled Mat. Acinar and Prlf. Acinar also groups MM and PM together, and MP and PP together. f The proportion changes of 3 cell types in the human bone (red circled) during the transition from healthy to osteoarthritis (OA), shown by diffusion map of hBone, colored by originally labeled cell type (left), pseudotime (middle) and sample status (healthy versus OA (right). Embedding is based on TOSICA attention. g High level of NF1 tracks the trajectory from HomC to HTC and preHTC (red circled) shown by diffusion map of hBone, colored by attention score of NF1 pathways (left), and by scatter plot (right), where lower CEBP attention score in preHTC versus HTC associates with OA (middle and right). Source data are provided as a Source data file.
Fig. 3 One stop interpretable de novo, high resolution, dynamic, and hierarchical annotation for biological insights by TOSICA. a TOSICA successfully isolates and labels the masked alpha cells as ‘Unknown’ cell type. UMAP is based on attention of hPancreas test set. Red circled and marked by red arrows are manually deleted alpha cells and blue circled and marked by blue arrows are MHC class II cells, originally not present in training set. These two kinds of cells are learned as isolated ‘Unknown’ cell types, and are separated by TOSICA attention scores’ UMAP. b TOSICA labels most of alpha cell and little other cell types as unknown. Heatmap shows proportion of cells in each row with original label O (original label, shown on the right) predicted as cell type P (prediction, shown on the top). See Supplementary Fig. 9 for comparison to other methods. c Some originally labeled mature Acinar (Mat., top) are predicted by TOSICA as proliferative Acinar (Prlf., bottom), red circled. UMAP is based on attention of mPancreas test set. The inset illustrates naming of MM, MP, PM, and PP, originally (O) labeled versus TOSICA (T) labeled. d Two pathways’ attention score separate the MM and MP. e Hierarchical clustering of DEGs between the originally labeled Mat. Acinar and Prlf. Acinar also groups MM and PM together, and MP and PP together. f The proportion changes of 3 cell types in the human bone (red circled) during the transition from healthy to osteoarthritis (OA), shown by diffusion map of hBone, colored by originally labeled cell type (left), pseudotime (middle) and sample status (healthy versus OA (right). Embedding is based on TOSICA attention. g High level of NF1 tracks the trajectory from HomC to HTC and preHTC (red circled) shown by diffusion map of hBone, colored by attention score of NF1 pathways (left), and by scatter plot (right), where lower CEBP attention score in preHTC versus HTC associates with OA (middle and right). Source data are provided as a Source data file.CC BY · PubMed Central
Fig. 4 TOSICA resolves pan-cancer tumor infiltrating myeloid cell heterogeneity. a, b TOSICA predicts cell types reliably across different cell types even when the reference and query contain no overlapping cancer types as shown by TOSICA attention embedded UMAP. UMAP is colored by the cancer types in the reference (3, left panel in a), in query (6, right panel in a), and by cell types in the query as originally labeled (left panel in b) and predicted by TOSICA (right panel in b). c cDC2_FCN1, cDC2_IL1B, and cDC3_LAMP3 distinguish from other cell types in attention scores of 2 REACTOME pathways. Each dot represents one cell and is colored by cell types. d Three developmental trajectories from cDC2_CXCL9 and cDC1_CLEC9A to cDC3_LAMP3 and cDC2 to cDC2_FCN1, cDC2_IL1B delineated by TOSICA attention embedded diffusion map (left) and partition-based graph abstraction (PAGA) (right). Edge weights in PAGA represent confidence for the connections between cell types, colored by pseudotime. e Macro_LYVE1 of ESCA distinguish from that of other cancers in attention scores of 2 REACTOME pathways. f Attention score of SIGNALING_BY_FGFR increases with advanced stage of ESCA. Statistical test is two-sided. g INNATE_IMMUNE_SYSTEM is downregulated and INTERFERON_SIGNALING is upregulated during aging in Mono_CD14. Dots are colored by age. h Attention score based UMAP identifies 4 subtypes of monocytes. i The distribution of the 4 monocyte subtypes changes with tumor (T) versus matching normal (N) tissues or peripheral blood (P) in different cancer types. Source data are provided as a Source data file.
Fig. 4 TOSICA resolves pan-cancer tumor infiltrating myeloid cell heterogeneity. a, b TOSICA predicts cell types reliably across different cell types even when the reference and query contain no overlapping cancer types as shown by TOSICA attention embedded UMAP. UMAP is colored by the cancer types in the reference (3, left panel in a), in query (6, right panel in a), and by cell types in the query as originally labeled (left panel in b) and predicted by TOSICA (right panel in b). c cDC2_FCN1, cDC2_IL1B, and cDC3_LAMP3 distinguish from other cell types in attention scores of 2 REACTOME pathways. Each dot represents one cell and is colored by cell types. d Three developmental trajectories from cDC2_CXCL9 and cDC1_CLEC9A to cDC3_LAMP3 and cDC2 to cDC2_FCN1, cDC2_IL1B delineated by TOSICA attention embedded diffusion map (left) and partition-based graph abstraction (PAGA) (right). Edge weights in PAGA represent confidence for the connections between cell types, colored by pseudotime. e Macro_LYVE1 of ESCA distinguish from that of other cancers in attention scores of 2 REACTOME pathways. f Attention score of SIGNALING_BY_FGFR increases with advanced stage of ESCA. Statistical test is two-sided. g INNATE_IMMUNE_SYSTEM is downregulated and INTERFERON_SIGNALING is upregulated during aging in Mono_CD14. Dots are colored by age. h Attention score based UMAP identifies 4 subtypes of monocytes. i The distribution of the 4 monocyte subtypes changes with tumor (T) versus matching normal (N) tissues or peripheral blood (P) in different cancer types. Source data are provided as a Source data file.CC BY · PubMed Central
Fig. 5 TOSICA reveals change in transcription factor activity during moderate and severe COVID-19. a TOSICA predicts cell types reliably across different cell types even when using healthy individuals as reference (left) and COVID19 patients as query (right). Colors denote 29 origin labels. Red circled cell types are unique in query. b Comparison of integration accuracy on query data places TOSICA first among 13 methods. Each score is minimum–maximum scaled between 0 and 1. Overall scores are computed using a 40:60-weighted mean of batch correction and bio-conservation scores. c, d TOSICA attention score based UMAP predicts 3 known (c) and 6 novel (d) monocyte types. e, f Subtype 3 monocytes increases (e) and subtype 4 decreases (f) in abundance from healthy (N = 25), to moderate (N = 79), and to severe (N = 91) COVID-19. Statistical test is two-sided. * RCC p < 0.05; ***p < 0.001. g TOSICA attention score of 6 transcription factors distinguishes subtype 3 and 4 monocytes across different states of COVID19. h The expression levels of major targets of the 6 TFs (g) generally show consistent trends with TFs attention score. Source data are provided as a Source data file.
Fig. 5 TOSICA reveals change in transcription factor activity during moderate and severe COVID-19. a TOSICA predicts cell types reliably across different cell types even when using healthy individuals as reference (left) and COVID19 patients as query (right). Colors denote 29 origin labels. Red circled cell types are unique in query. b Comparison of integration accuracy on query data places TOSICA first among 13 methods. Each score is minimum–maximum scaled between 0 and 1. Overall scores are computed using a 40:60-weighted mean of batch correction and bio-conservation scores. c, d TOSICA attention score based UMAP predicts 3 known (c) and 6 novel (d) monocyte types. e, f Subtype 3 monocytes increases (e) and subtype 4 decreases (f) in abundance from healthy (N = 25), to moderate (N = 79), and to severe (N = 91) COVID-19. Statistical test is two-sided. * RCC p < 0.05; ***p < 0.001. g TOSICA attention score of 6 transcription factors distinguishes subtype 3 and 4 monocytes across different states of COVID19. h The expression levels of major targets of the 6 TFs (g) generally show consistent trends with TFs attention score. Source data are provided as a Source data file.CC BY · PubMed Central

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  • The paper relies on this without support.

    Consistent annotation transfer from reference dataset to query dataset is fundamental to the development and reproducibility of single-cell research.

    “Consistent annotation transfer from reference dataset to query dataset is fundamental to the development and reproducibility of single-cell research.”
  • The paper relies on this without support.

    Deep learning based methods are faster and more automated than traditional annotation methods.

    “Compared with traditional annotation methods, deep learning based methods are faster and more automated.”
  • The paper relies on this without support.

    Traditional annotation methods often consist of preprocessing, dimensionality reduction, clustering, differential analysis, and manual annotation based on prior knowledge.

    “These traditional methods often consist of preprocessing, dimensionality reduction, clustering, differential analysis, and manual annotation based on prior knowledge.”
  • The paper relies on this without support.

    When subtypes are annotated manually based on a small set of marker genes, the same subtype can sometimes be given a new name in another research due to a slight difference.

    “When subtypes are annotated manually based on a small set of marker genes, the same subtype can sometimes be given a new name in another research due to a slight difference.”
  • The paper relies on this without support.

    Transferring cell type annotation from a reference dataset to newly generated query datasets with consistency and reproducibility is increasingly important and necessary.

    “Thus, transferring cell type annotation from a reference dataset to newly generated query datasets with consistency and reproducibility is increasingly important and necessary.”
  • The paper relies on this without support.

    Specificity of marker genes is determined by comparing with the other cell types in the same dataset.

    “However, specificity of marker genes is determined by comparing with the other cell types in the same dataset.”
  • The paper relies on this without support.

    All previous cell type annotators are gene-based, thus reveal little on the biological insight behind the cell type marker genes, many more subsequent analyses are needed to infer the potential enriched pathways and regulators behind the marker genes.

    “All previous cell type annotators are gene-based, thus reveal little on the biological insight behind the cell type marker genes, many more subsequent analyses are needed to infer the potential enriched pathways and regulators behind the marker genes.”
  • The paper relies on this without support.

    One of the most common demands in single-cell analysis is the transfer of identified cell population from an original reference to newly generated data, which may come from different batch and biological state.

    “One of the most common demands in single-cell analysis is the transfer of identified cell population from an original reference to newly generated data, which may come from different batch and biological state (e.g., disease).”
  • The paper relies on this without support.

    Query and reference datasets are generated in different laboratories with different experimental protocols and thus contain batch effects.

    “Generally, query and reference datasets are generated in different laboratories with different experimental protocols and thus contain batch effects.”
  • The paper relies on this without support.

    Batch information is necessary for conventional data-integration method to try to overcome these batch effects.

    “Batch information is necessary for conventional data-integration method to try to overcome these batch effects, which are difficult to completely remove and mixed up with biological differences.”
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Metadata

Authors
Chen, J., Xu, H., Tao, W., Chen, Z., Zhao, Y., & Han, J.-D. J.
Affiliations
Peking University (CN)
Corresponding author
Han, Jing-Dong J.
Venue
Nature Communications
Published
2023-01-14
Volume
14
Issue
1
Pages
223-223
ISSN
2041-1723 (ISSN-L)
OpenAlex
W4316096017
Cited by
189
References
59
Citations by year
2026: 36 · 2025: 69 · 2024: 70 · 2023: 12
FWCI
16.66
Type
journal article
Language
en
Open access
Locations
  • Nature Communications (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Natural Science Foundation of China (92049302, 32088101)
  • Ministry of Science and Technology of the People’s Republic of China (2020YFA0804000)
  • Science and Technology Commission of Shanghai Municipality (2017SHZDZX01)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Single-cell and spatial transcriptomics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Gene expression and cancer classification
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Bioinformatics and Genomic Networks
Keywords
cell type annotation, single-cell transcriptomics, transformer models, self-attention, interpretability, annotation transfer, multi-head attention, regulon, tumor-infiltrating immune cells, CD14+ monocytes, COVID-19 pandemic, rare cell types, cellular heterogeneity, disease progression
MeSH terms
Exome Sequencing, COVID-19, Humans, Reproducibility of Results, Sequence Analysis, RNA, Disease Progression, Single-Cell Analysis

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