Usage

The Scaden deconvolution workflow consists of three mandatory steps:

  • scaden process
  • scaden train
  • scaden predict

In the process step, Scaden performs pre-processing on your training data, making sure it has the same genes as your prediction (bulk) data and performing some data transformations to make the data suitable for machine learning

In the train step, training of the Scaden ensemble model is performed.

Finally, the predictions are generated in the predict step, for which the trained model is used.

This assumes that you already have a training dataset. If not, Scaden contains functionality to create a dataset from one or several scRNA-seq datasets. For this, you can use the scaden simulate command after preparing some data. Have a look at the scaden simulate section for instructions on how to use this command.

Note that we already provide datasets for certain tissues. All available datasets are listed in the Datasets section. We will update this section when new datasets are added.

Webtool (beta)

If you don't want to install Scaden on your local machine, we now provide a webtool for you:

https://scaden.ims.bio

It contains pre-generated training datasets for several tissues, and all you need to do is to upload your expression data. Please note that this is still in preview.

scaden process

The first step is to pre-process your training data. For this you need your training data and the dataset you want to perform deconvolution on. In this step, Scaden will create a new file for training which only contains the intersection of genes between the training and the prediction data. Furthermore, the training data will be log2-transformed and scaled to the range [0,1]. Use the following command for pre-processing:

scaden process <training data> <prediction data>

By the default, the output file will be called "processed.h5ad". Have a look at scaden process --help for further options.

scaden train

Now that your data is set-up, you can start training a Scaden ensemble model. Scaden consists of three deep neural network models. By default, each of them will be trained for 5,000 steps, which is the recommended number of training steps. You can train longer if you want, although we got good results with this number for datasets of around 30,000 samples. Use the following command to just train a model:

scaden train <processed data>

This will save the model parameters in your working directory. We recommend to explicitly specify a model directory like so:

scaden train <processed data> --model_dir <model dir> 

For more options, have a look at

scaden train --help

scaden predict

Finally, after your model is trained, you can perform the prediction. If you haven't specified any model directory and just trained a model in your current directory, you can use the following command to perform the deconvolution:

scaden predict <prediction file>

Scaden will then generate a file called 'scaden_predictions.txt' in your current directory. If the models were saved elsewhere, you have to tell Scaden where to look for them:

scaden predict <prediction file> --model_dir <model dir>

You can also change the path and name of the output predictions file using the outname flag:

--outname <path/to/output.txt

scaden simulate

To generate training data for Scaden, you will first have to process the scRNA-seq dataset(s) you want to use for training. Once you have done this, you can use Scaden's command scaden simulate to generate the actual training data. I will explain this process in the following.

scRNA-seq data processing

The first step is to process your scRNA-seq dataset(s) that you want to use for training. I used Scanpy for this, and would therefore recommend to do the same, but you can of course use other software for this purpose. I've uploaded the scripts I used to preprocess the data used for the Scaden paper here.

You will have to normalize your count data to library size and create a file containing cell type labels. The file for the cell type labels should be of size (n x 1), where n is the number of cells you have in your data. The single column in this file has to be labeled 'Celltype'. You can have extra columns if you like, as long as you have a 'Celltype' column which specifies the cell type labels in the correct order. The count data should be of size (n x g), where g is the number of genes and n is the number of samples. The order must be the same as for the cell type labels. You can create an example dataset of the correct format using

scaden example

Which will generate the files "example_counts.txt", "example_celltypes.txt" and "example_bulk_data.txt". If you want to try out Scaden, you can directly use those files for simulation, processing, training and prediction.

Bulk simulation

Once the data is processed, you can use the command scaden simulate to generate your artificial bulk samples for training. To allow Scaden to find your datasets and use them for simulation, they should be stored in the same directory and must be formatted like this:

_.txt for the count data

_celltypes.txt for the cell type labels

Here, the pattern should be same among all the different datasets (unless you only want to use a specific dataset).

As example, you can generate 1000 artificial bulk samples from 100 cells per samples with the following command:

scaden simulate --cells 100 --n_samples 1000 --data <data_directory> --pattern <your_pattern>

An example for a pattern would be *_counts.txt. This pattern would find the following dataset: * dataset_counts.txt * dataset_celltypes.txt

Make sure to include an * in your pattern!

This command will create the artificial samples in the current working directory. You can also specificy an output directory using the --out parameter. Scaden will also directly create a .h5ad file in this directory, which is the file you will need for training. By default, this file will be called data.h5ad, however you can change the prefix using the --prefix flag.

File Formats

For Scaden to work properly, your input files have to be correctly formatted. As long as you use Scadens inbuilt functionality to generate the training data, you should have no problem with formatting there. The prediction file, however, you have to format yourself. This should be a file of shape m X n, where m are your features (genes) and n your samples. So each row corresponds to a gene, and each column to a sample. Leave the column name for the genes empy (just put a \t there). This is a rather standard format to store gene expression tables, so you should have not much work assuring that the format fits.

Your data can either be raw counts or normalized, just make sure that they are not in logarithmic space already. When loading a prediction file, Scaden applies its scaling procedure to it, which involves taking the logarithm of your counts. So as long as they are not already in logarithmic space, Scaden will be able to handle both raw and normalized counts / expression values.

When in doubt, just use the scaden example command which will generate random example data of correct format, and have a look at that.

If you get any errors with the above process, pleas don't hesitate to open an issue on GitHub.