Visualizations for Single-Cell Objects

clonalOverlay

Using the dimensional reduction graphs as a reference, we can also generate an overlay of the position of clonally-expanded cells using clonalOverlay().

reduction

The dimensional reduction for the visualization, (default = “pca”)

cut.category

Use of “clonalFrequency” or “clonalProportion” to filter the overlay

cutpoint

lowest clonal frequency or proportion to generate the contour plot

bins

the number of contours to draw

clonalOverlay() can be used to look across all cells or faceted by a meta data variable using facet.by. The overall dimensional reduction will be maintained as we facet, while the contour plots will adjust based on the facet.by variable. The coloring of the dot plot is based on the active identity of the single-cell object.

This visualization was authored by Dr. Francesco Mazziotta and inspired by Drs. Carmona and Andreatta and their work with ProjectTIL, which is a great pipeline to annotated T cell subtypes.

clonalOverlay(scRep_example, 
              reduction = "umap", 
              cutpoint = 1, 
              bins = 10, 
              facet.by = "Patient") + 
              guides(color = "none")

clonalNetwork

Similar to clonalOverlay(), we can look at the network interaction of clones shared between clusters along the single-cell dimensional reduction using clonalNetwork(). This function shows the relative proportion of clones from the starting node, with the ending node indicated by the arrow.

Filtering for clones can be accomplished using 3 methods:

filter.clones

Select a number to isolate the clones comprising the top n number of cells (e.g., filter.clones = 2000)
Select “min” to make sure all groups are scaled to the size of the minimum group

filter.identity

For the identity chosen to visualize, show the to and from network connections for a single group

filter.proportion

Remove clones that comprise less than a certain proportion of clones in groups.

filter.graph

Remove the reciprocal edges from the half of the graph, allowing for cleaner visualization.

#ggraph needs to be loaded due to issues with ggplot
library(ggraph)

#No Identity filter
clonalNetwork(scRep_example, 
              reduction = "umap", 
              group.by = "seurat_clusters",
              filter.clones = NULL,
              filter.identity = NULL,
              cloneCall = "aa")

We can look at the clonal relationships relative to a single cluster using the filter.identity parameter.

#Examining Cluster 3 only
clonalNetwork(scRep_example, 
              reduction = "umap", 
              group.by = "seurat_clusters",
              filter.identity = 3,
              cloneCall = "aa")

We can also use exportClones parameter to quickly get clones that are shared across multiple identity groups, along with the total number of clones in the data set.

shared.clones <- clonalNetwork(scRep_example, 
                               reduction = "umap", 
                               group.by = "seurat_clusters",
                               cloneCall = "aa", 
                               exportClones = TRUE)
head(shared.clones)

## # A tibble: 6 × 2
##   clone                                sum
##   <chr>                              <int>
## 1 CVVSDNTGGFKTIF_CASSVRRERANTGELFF     906
## 2 CAERGSGGSYIPTF_CASSDPSGRQGPRWDTQYF   140
## 3 CAVTFHYNTDKLIF_CASSQDRTGLDYEQYF      122
## 4 CAVRDDGNTGFQKLVF_CASSQDFNDGGLNIQYF   119
## 5 CARKVRDSSYKLIF_CASSDSGYNEQFF         106
## 6 CAVGAQQGGKLIF_CASSLSLSDGRHGYTF       101

highlightClones

We can also look at the clones by calling specific sequences in the highlightclones() below. In order to highlight the clones, we first need to use the cloneCall, the type of sequence we will be using, and then the specific sequences themselves using sequence. Below, we can see the steps to highlight the most prominent sequences CAERGSGGSYIPTF_CASSDPSGRQGPRWDTQYF, and CARKVRDSSYKLIF_CASSDSGYNEQFF.

scRep_example <- highlightClones(scRep_example, 
                    cloneCall= "aa", 
                    sequence = c("CAERGSGGSYIPTF_CASSDPSGRQGPRWDTQYF", 
                                 "CARKVRDSSYKLIF_CASSDSGYNEQFF"))

Seurat::DimPlot(scRep_example, group.by = "highlight") + 
  ggplot2::theme(plot.title = element_blank())

clonalOccupy

We can also look at the count of cells by cluster assigned into specific frequency ranges by using the clonalOccupy() function and selecting the x.axis to display cluster or other variables in the meta data of the single cell object.

proportion

can be used to look at relative level groupings

label

will still return the absolute number of clones

clonalOccupy(scRep_example, 
              x.axis = "seurat_clusters")

clonalOccupy(scRep_example, 
             x.axis = "ident", 
             proportion = TRUE, 
             label = FALSE)

alluvialClones

After the metadata has been modified, we can look at clones across multiple categories using the alluvialClones() function. We are able to use the plots to examine the interchange of categorical variables. Because this function will produce a graph with each clone arranged by called stratification, this will take some time depending on the size of the repertoire.

To understand the basic concepts of this graphing method and the ggalluvial R package, we recommend reading this post.

alluvialClones(scRep_example, 
               cloneCall = "aa", 
               y.axes = c("Patient", "ident", "Type"), 
               color = c("CVVSDNTGGFKTIF_CASSVRRERANTGELFF", "NA_CASSVRRERANTGELFF")) + 
    scale_fill_manual(values = c("grey", colorblind_vector[3]))

alluvialClones(scRep_example, 
                   cloneCall = "gene", 
                   y.axes = c("Patient", "ident", "Type"), 
                   color = "ident")

getCirclize

Like alluvial graphs, we can also visualize the interconnection of clusters using the chord diagrams from the circlize R package.

The first step is getting the data frame output to feed into the chordDiagram() function in circlize, which can be done using getCirclize().

This will calculate the relative number of clones shared based on the group.by variable using the product of combineExpression(). It is important to note getCirclize() will create a matrix the size of the group.by variable and then simplify into instructions to be read by the circlize R package. The output is the total number of unique and shared clones by the group.by variable.

library(circlize)
library(scales)

circles <- getCirclize(scRep_example, 
                       group.by = "seurat_clusters")

#Just assigning the normal colors to each cluster
grid.cols <- hue_pal()(length(unique(scRep_example$seurat_clusters)))
names(grid.cols) <- unique(scRep_example$seurat_clusters)

#Graphing the chord diagram
chordDiagram(circles, self.link = 1, grid.col = grid.cols)

This can also be used if we want to explore just the lung-specific T cells by just subsetting the single-cell object. For the sake of this vignette, we can also look at setting proportion = TRUE to get a scaled output.