Introduction to scAnnotatR

Vy Nguyen

2026-11-12

Introduction

scAnnotatR is an R package for cell type prediction on single cell RNA-sequencing data. Currently, this package supports data in the forms of a Seurat object or a SingleCellExperiment object.

More information about Seurat object can be found here: https://satijalab.org/seurat/ More information about SingleCellExperiment object can be found here: https://osca.bioconductor.org/

scAnnotatR provides 2 main features:

Installation

The scAnnotatR package can be directly installed from Bioconductor:

if (!requireNamespace("BiocManager", quietly = TRUE))
    install.packages("BiocManager")

if (!require(scAnnotatR))
  BiocManager::install("scAnnotatR")

For more information, see https://bioconductor.org/install/.

Included models

The scAnnotatR package comes with several pre-trained models to classify cell types.

# load scAnnotatR into working space
library(scAnnotatR)
#> Loading required package: Seurat
#> Loading required package: SeuratObject
#> Loading required package: sp
#> 'SeuratObject' was built with package 'Matrix' 1.7.5 but the current
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#> Loading required package: SingleCellExperiment
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The models are stored in the default_models object:

default_models <- load_models("default")
#> loading from cache
names(default_models)
#>  [1] "B cells"           "Plasma cells"      "NK"               
#>  [4] "CD16 NK"           "CD56 NK"           "T cells"          
#>  [7] "CD4 T cells"       "CD8 T cells"       "Treg"             
#> [10] "NKT"               "ILC"               "Monocytes"        
#> [13] "CD14 Mono"         "CD16 Mono"         "DC"               
#> [16] "pDC"               "Endothelial cells" "LEC"              
#> [19] "VEC"               "Platelets"         "RBC"              
#> [22] "Melanocyte"        "Schwann cells"     "Pericytes"        
#> [25] "Mast cells"        "Keratinocytes"     "alpha"            
#> [28] "beta"              "delta"             "gamma"            
#> [31] "acinar"            "ductal"            "Fibroblasts"

The default_models object is named a list of classifiers. Each classifier is an instance of the scAnnotatR S4 class. For example:

default_models[['B cells']]
#> An object of class scAnnotatR for B cells 
#> * 31 marker genes applied: CD38, CD79B, CD74, CD84, RASGRP2, TCF3, SP140, MEF2C, DERL3, CD37, CD79A, POU2AF1, MVK, CD83, BACH2, LY86, CD86, SDC1, CR2, LRMP, VPREB3, IL2RA, BLK, IRF8, FLI1, MS4A1, CD14, MZB1, PTEN, CD19, MME 
#> * Predicting probability threshold: 0.5 
#> * No parent model

Basic pipeline to identify cell types in a scRNA-seq dataset using scAnnotatR

Preparing the data

To identify cell types available in a dataset, we need to load the dataset as Seurat or SingleCellExperiment object.

For this vignette, we use a small sample datasets that is available as a Seurat object as part of the package.

# load the example dataset
data("tirosh_mel80_example")
tirosh_mel80_example
#> An object of class Seurat 
#> 91 features across 480 samples within 1 assay 
#> Active assay: RNA (91 features, 0 variable features)
#>  2 layers present: counts, data
#>  1 dimensional reduction calculated: umap

The example dataset already contains the clustering results as part of the metadata. This is not necessary for the classification process.

head(tirosh_mel80_example[[]])
#>                               orig.ident nCount_RNA nFeature_RNA percent.mt
#> Cy80_II_CD45_B07_S883_comb SeuratProject   42.46011            8          0
#> Cy80_II_CD45_C09_S897_comb SeuratProject   74.35907           14          0
#> Cy80_II_CD45_H07_S955_comb SeuratProject   42.45392            8          0
#> Cy80_II_CD45_H09_S957_comb SeuratProject   63.47043           12          0
#> Cy80_II_CD45_B11_S887_comb SeuratProject   47.26798            9          0
#> Cy80_II_CD45_D11_S911_comb SeuratProject   69.12167           13          0
#>                            RNA_snn_res.0.8 seurat_clusters RNA_snn_res.0.5
#> Cy80_II_CD45_B07_S883_comb               4               4               2
#> Cy80_II_CD45_C09_S897_comb               4               4               2
#> Cy80_II_CD45_H07_S955_comb               4               4               2
#> Cy80_II_CD45_H09_S957_comb               4               4               2
#> Cy80_II_CD45_B11_S887_comb               4               4               2
#> Cy80_II_CD45_D11_S911_comb               1               1               1

Cell classification

To launch cell type identification, we simply call the classify_cells function. A detailed description of all parameters can be found through the function’s help page ?classify_cells.

Here we use only 3 classifiers for B cells, T cells and NK cells to reduce computational cost of this vignette. If users want to use all pretrained classifiers on their dataset, cell_types = 'all' can be used.

seurat.obj <- classify_cells(classify_obj = tirosh_mel80_example, 
                             assay = 'RNA', layer = 'counts',
                             cell_types = c('B cells', 'NK', 'T cells'), 
                             path_to_models = 'default')
#> loading from cache

Parameters

  • The option cell_types = ‘all’ tells the function to use all available cell classification models. Alternatively, we can limit the identifiable cell types:
    • by specifying: cell_types = c('B cells', 'T cells')
    • or by indicating the applicable classifier using the classifiers option: classifiers = c(default_models[['B cells']], default_models[['T cells']])
  • The option path_to_models = ‘default’ is to automatically use the package-integrated pretrained models (without loading the models into the current working space). This option can be used to load a local database instead. For more details see the vignettes on training your own classifiers.

Result interpretation

The classify_cells function returns the input object but with additional columns in the metadata table.

# display the additional metadata fields
seurat.obj[[]][c(50:60), c(8:ncol(seurat.obj[[]]))]
#>                                            B_cells_p B_cells_class      NK_p
#> cy80.Cd45.pos.PD1.pos.B09.S45.comb       0.007754246            no 0.4881285
#> cy80.Cd45.pos.Pd1.neg.S366.H06.S366.comb 0.999385770           yes 0.4440553
#> cy80.Cd45.pos.Pd1.neg.S202.A10.S202.comb 0.998317662           yes 0.4416114
#> cy80.Cd45.pos.Pd1.neg.S201.A09.S201.comb 0.997774856           yes 0.4398997
#> cy80.Cd45.pos.Pd1.neg.S221.B05.S221.comb 0.998874031           yes 0.4541005
#> cy80.Cd45.pos.PD1.pos.A03.S15.comb       0.999944282           yes 0.4511450
#> cy80.Cd45.pos.PD1.pos.B11.S47.comb       0.015978230            no 0.4841041
#> cy80.Cd45.pos.PD1.pos.S189.H09.S189.comb 0.099311534            no 0.4858084
#> cy80.Cd45.pos.PD1.pos.A05.S17.comb       0.055754074            no 0.4924746
#> cy80.Cd45.pos.PD1.pos.C02.S62.comb       0.048558881            no 0.5002238
#> cy80.Cd45.pos.PD1.pos.D12.S96.comb       0.996979702           yes 0.4994867
#>                                          NK_class  T_cells_p T_cells_class
#> cy80.Cd45.pos.PD1.pos.B09.S45.comb             no 0.94205232           yes
#> cy80.Cd45.pos.Pd1.neg.S366.H06.S366.comb       no 0.11269306            no
#> cy80.Cd45.pos.Pd1.neg.S202.A10.S202.comb       no 0.09834696            no
#> cy80.Cd45.pos.Pd1.neg.S201.A09.S201.comb       no 0.22256938            no
#> cy80.Cd45.pos.Pd1.neg.S221.B05.S221.comb       no 0.12903487            no
#> cy80.Cd45.pos.PD1.pos.A03.S15.comb             no 0.27242536            no
#> cy80.Cd45.pos.PD1.pos.B11.S47.comb             no 0.94929624           yes
#> cy80.Cd45.pos.PD1.pos.S189.H09.S189.comb       no 0.93390248           yes
#> cy80.Cd45.pos.PD1.pos.A05.S17.comb             no 0.98161289           yes
#> cy80.Cd45.pos.PD1.pos.C02.S62.comb            yes 0.96436674           yes
#> cy80.Cd45.pos.PD1.pos.D12.S96.comb             no 0.94848597           yes
#>                                          predicted_cell_type
#> cy80.Cd45.pos.PD1.pos.B09.S45.comb                   T cells
#> cy80.Cd45.pos.Pd1.neg.S366.H06.S366.comb             B cells
#> cy80.Cd45.pos.Pd1.neg.S202.A10.S202.comb             B cells
#> cy80.Cd45.pos.Pd1.neg.S201.A09.S201.comb             B cells
#> cy80.Cd45.pos.Pd1.neg.S221.B05.S221.comb             B cells
#> cy80.Cd45.pos.PD1.pos.A03.S15.comb                   B cells
#> cy80.Cd45.pos.PD1.pos.B11.S47.comb                   T cells
#> cy80.Cd45.pos.PD1.pos.S189.H09.S189.comb             T cells
#> cy80.Cd45.pos.PD1.pos.A05.S17.comb                   T cells
#> cy80.Cd45.pos.PD1.pos.C02.S62.comb                NK/T cells
#> cy80.Cd45.pos.PD1.pos.D12.S96.comb           B cells/T cells
#>                                          most_probable_cell_type
#> cy80.Cd45.pos.PD1.pos.B09.S45.comb                       T cells
#> cy80.Cd45.pos.Pd1.neg.S366.H06.S366.comb                 B cells
#> cy80.Cd45.pos.Pd1.neg.S202.A10.S202.comb                 B cells
#> cy80.Cd45.pos.Pd1.neg.S201.A09.S201.comb                 B cells
#> cy80.Cd45.pos.Pd1.neg.S221.B05.S221.comb                 B cells
#> cy80.Cd45.pos.PD1.pos.A03.S15.comb                       B cells
#> cy80.Cd45.pos.PD1.pos.B11.S47.comb                       T cells
#> cy80.Cd45.pos.PD1.pos.S189.H09.S189.comb                 T cells
#> cy80.Cd45.pos.PD1.pos.A05.S17.comb                       T cells
#> cy80.Cd45.pos.PD1.pos.C02.S62.comb                       T cells
#> cy80.Cd45.pos.PD1.pos.D12.S96.comb                       B cells

New columns are:

Result visualization

The predicted cell types can now simply be visualized using the matching plotting functions. In this example, we use Seurat’s DimPlot function:

# Visualize the cell types
Seurat::DimPlot(seurat.obj, group.by = "most_probable_cell_type")

With the current number of cell classifiers, we identify cells belonging to 2 cell types (B cells and T cells) and to 2 subtypes of T cells (CD4+ T cells and CD8+ T cells). The other cells (red points) are not among the cell types that can be classified by the predefined classifiers. Hence, they have an empty label.

For a certain cell type, users can also view the prediction probability. Here we show an example of B cell prediction probability:

# Visualize the cell types
Seurat::FeaturePlot(seurat.obj, features = "B_cells_p")

Cells predicted to be B cells with higher probability have darker color, while the lighter color shows lower or even zero probability of a cell to be B cells. For B cell classifier, the threshold for prediction probability is currently at 0.5, which means cells having prediction probability at 0.5 or above will be predicted as B cells.

The automatic cell identification by scAnnotatR matches the traditional cell assignment, ie. the approach based on cell canonical marker expression. Taking a simple example, we use CD19 and CD20 (MS4A1) to identify B cells:

# Visualize the cell types
Seurat::FeaturePlot(seurat.obj, features = c("CD19", "MS4A1"), ncol = 2)

We see that the marker expression of B cells exactly overlaps the B cell prediction made by scAnnotatR.

Session Info

sessionInfo()
#> R version 4.6.1 (2026-06-24)
#> Platform: x86_64-pc-linux-gnu
#> Running under: Ubuntu 24.04.5 LTS
#> 
#> Matrix products: default
#> BLAS:   /home/biocbuild/bbs-3.24-bioc/R/lib/libRblas.so 
#> LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.12.0  LAPACK version 3.12.0
#> 
#> locale:
#>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
#>  [3] LC_TIME=en_GB              LC_COLLATE=C              
#>  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
#>  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
#>  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
#> 
#> time zone: America/New_York
#> tzcode source: system (glibc)
#> 
#> attached base packages:
#> [1] stats4    stats     graphics  grDevices utils     datasets  methods  
#> [8] base     
#> 
#> other attached packages:
#>  [1] scAnnotatR_1.19.1           SingleCellExperiment_1.35.2
#>  [3] SummarizedExperiment_1.43.0 Biobase_2.73.2             
#>  [5] GenomicRanges_1.65.4        Seqinfo_1.3.2              
#>  [7] IRanges_2.47.5              S4Vectors_0.51.10          
#>  [9] BiocGenerics_0.59.13        generics_0.1.4             
#> [11] MatrixGenerics_1.25.0       matrixStats_1.5.0          
#> [13] Seurat_6.0.0                SeuratObject_5.4.0         
#> [15] sp_2.2-4                   
#> 
#> loaded via a namespace (and not attached):
#>   [1] RColorBrewer_1.1-3   jsonlite_2.0.0       magrittr_2.0.5      
#>   [4] farver_2.1.2         rmarkdown_2.32       vctrs_0.7.3         
#>   [7] ROCR_1.0-12          memoise_2.0.1        htmltools_0.5.9     
#>  [10] S4Arrays_1.13.2      BiocBaseUtils_1.15.1 AnnotationHub_4.3.3 
#>  [13] curl_8.1.0           pROC_1.19.1          SparseArray_1.13.4  
#>  [16] caret_7.0-1          sass_0.4.10          sctransform_0.4.3   
#>  [19] parallelly_1.50.0    KernSmooth_2.23-27   bslib_0.12.0        
#>  [22] ica_1.0-3            plyr_1.8.9           httr2_1.3.0         
#>  [25] lubridate_1.9.5      cachem_1.1.0         igraph_2.3.4        
#>  [28] lifecycle_1.0.5      iterators_1.0.14     pkgconfig_2.0.3     
#>  [31] Matrix_1.7-6         R6_2.6.1             fastmap_1.2.0       
#>  [34] future_1.82.0        digest_0.6.39        patchwork_1.3.2     
#>  [37] AnnotationDbi_1.75.2 RSpectra_0.16-2      irlba_2.4.1         
#>  [40] RSQLite_3.53.3       labeling_0.4.3       filelock_1.0.3      
#>  [43] progressr_1.1.0      timechange_0.4.0     httr_1.4.9          
#>  [46] abind_1.4-8          compiler_4.6.1       proxy_0.4-29        
#>  [49] withr_3.0.3          bit64_4.8.6          S7_0.2.2            
#>  [52] DBI_1.3.0            fastDummies_1.7.6    lava_1.11           
#>  [55] MASS_7.3-66          rappdirs_0.3.4       DelayedArray_0.39.8 
#>  [58] ModelMetrics_1.2.2.2 tools_4.6.1          otel_0.3.0          
#>  [61] ape_5.8-1            future.apply_1.21.0  nnet_7.3-21         
#>  [64] glue_1.8.1           nlme_3.1-172         grid_4.6.1          
#>  [67] Rtsne_0.17           cluster_2.1.8.3      reshape2_1.4.5      
#>  [70] recipes_1.4.0        gtable_0.3.6         class_7.3-24        
#>  [73] data.table_1.18.6.1  XVector_0.53.0       RcppAnnoy_0.0.23    
#>  [76] ggrepel_0.9.8        RANN_2.6.3           BiocVersion_3.24.0  
#>  [79] foreach_1.5.2        pillar_1.11.1        stringr_1.6.0       
#>  [82] spam_2.11-4          RcppHNSW_0.7.0       splines_4.6.1       
#>  [85] dplyr_1.2.1          BiocFileCache_3.3.3  lattice_0.23-1      
#>  [88] survival_3.8-12      bit_4.6.0            tidyselect_1.2.1    
#>  [91] Biostrings_2.81.9    pbapply_1.7-5        knitr_1.52          
#>  [94] gridExtra_2.3.1      scattermore_1.2      xfun_0.62           
#>  [97] pls_2.9-0            hardhat_1.4.3        timeDate_4052.112   
#> [100] stringi_1.8.9        yaml_2.3.12          evaluate_1.0.5      
#> [103] codetools_0.2-20     kernlab_0.9-33       data.tree_1.2.0     
#> [106] tibble_3.3.1         BiocManager_1.30.27  cli_3.6.6           
#> [109] rpart_4.1.27         uwot_0.2.5           jquerylib_0.1.4     
#> [112] dichromat_2.0-1      Rcpp_1.1.2           globals_0.20.0      
#> [115] dbplyr_2.6.0         png_0.1-9            parallel_4.6.1      
#> [118] gower_1.0.2          ggplot2_4.0.3        blob_1.3.0          
#> [121] dotCall64_1.2        listenv_1.1.0        ipred_0.9-16        
#> [124] e1071_1.7-17         prodlim_2026.03.11   scales_1.4.0        
#> [127] ggridges_0.5.7       purrr_1.2.2          crayon_1.5.3        
#> [130] rlang_1.3.0          cowplot_1.2.0        KEGGREST_1.53.6