Frequently Asked Questions

Welcome to our library of frequently asked questions!

The FAQs are grouped into categories of related topics for your convenience:

  • Explore different category titles to see number of questions and answers under each category
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Company overview

What is Pixelgen Technologies?

Pixelgen Technologies is a life science tools company founded in 2020 by serial entrepreneurs behind multiple innovative products and companies in the life sciences and located in Stockholm, Sweden.

Ordering & Shipment

How much does a Pixelgen Kit cost?

The Pixelgen Single Cell Spatial Proteomics Kit price can be found in our webshop (link).

How can I order a Pixelgen Single Cell Spatial Proteomics Kit?

You can place an order directly on our website (https://shop.pixelgen.com/) or email hello@pixelgen.com and we will contact you.

Product

What is Molecular Pixelation and what does it do?

The name of our technology is Molecular Pixelation (MPX™) and it is currently applied to deeply phenotype immune cells by building spatial 3D maps of the cell surface proteins in a highly multiplexed and low resolution manner.

What is the name of your product?

The name of our product is Pixelgen Single Cell Spatial Proteomics Kit, Immunology Panel 1, Human (Pixelgen SCSP Kit).

What makes Molecular Pixelation unique compared to other technologies?

Other technologies that detect protein expression on a single cell will not offer multiplex spatial relationships between the proteins on the cell surface, for up to 1000 cells in parallel per sample. MPX is unique by offering relative abundance data, co-localization data of protein pairs and polarity data of each protein, for every single cell. Up to 1000 cells per reaction can be assessed, generating up to 3 million data points per sample.

What does the kit consist of?

There are three boxes that come with the kit, one box for +4C storage and two boxes for -20C storage.

What is the shelf life-time for a Pixelgen SCSP Kit?

The kits have a 6 months shelf-life from production date.
Please store the different components at their recommended temperatures, as specified in the kit documentation.

How many reactions are in the kit?

The kit is enough for running 8 reactions in parallel, with 300 – 1000 cells output per reaction.

Protocol

What automatic cell counters can you recommend?

The Countess™ II Automated Cell Counter (ThermoFisher) has been used during validation and optimization of MPX™.

What manual cell counters can you recommend?

Hemocytometers and single-use counting hemocytometers have been used during validation and optimization of MPX™.

Are there stopping points in the protocol?

Yes, the protocol contains many stopping points to offer flexibility, as noted in the protocol.

How long does it take to run the protocol?

If you intend to run the protocol consecutively from live cells to sequence-ready library, we recommend planning for 3 days.

If you intend to fix live cells and then freeze for -80C storage for up to 3 months, we recommend 2 hours for fixing and freezing, and then 2 days for running the remainder of the protocol, including thawing of fixed cells.

Can you recommend a workflow timeline to me?

A suggested workflow would be to perform fixation and AOC binding day 1, perform pixelation steps on day 2 and finally quality control and NGS on day 3.

Can I use other PCR primers than supplied with the kit?

If there is a need to use other PCR primers than the ones supplied with the kit, please contact support for guidance.

Can I run MPX on frozen live PBMCs as starting material?

Yes – The workflow has been validated on frozen fixed cells as well as on frozen live cells.

How many cells are needed as input?

MPX requires 500 000 – 1 000 000 live cells as input.

What type of internal controls are included in the kit?

There are two types of controls in the AOC panel. The first part consists of mouse isotype control antibodies (mIgG1, mIgG2a, mIgG2b) that can be  used to set non-specific binding levels. The other part contains an intracellular marker to validate that the cell membrane is intact and not permeabilized.

What type of external controls do you recommend?

It is always recommended to include a control sample in the experimental design. The kind of control sample depends on the experiment but each sample condition should have a control for comparison and differential analysis.

What sample type can you run MPX on?

We recommend PBMCs or isolated immune cells. The panel contains targets for T-cells, B-cells, NK cells and monocytes.

Can I use another fixation protocol than the one in the User Manual?

No, this is not recommended. The antibodies have been validated with the fixation protocol that is in the MPX User Manual and other fixation protocols might impact the antibody binding negatively and should therefore not be used.

What does AOC stand for?

Antibody Oligonucleotide Conjugate

Panel design

What type of antibodies do you use in your panel?

The AOC panel in MPX consists of monoclonal antibodies.

Can I include personal targets in the panel?

The panel included in the kit is fixed with targets that have been extensively validated.

We do have a target wish list where we are more than happy to receive your feedback, please fill in the form here

Can you provide full custom panels?

The product we offer at this time contains a fixed panel, The Immunology Panel I, Human.

We are open to discussing your interest in different targets for potential future panels, Please fill in the form in the link and we will add your suggestions to our wish list.

Can I suggest targets for coming panels?

We have a target wish list where we are more than happy to receive your feedback, please fill in the form link.

What targets are included in your panel?

Please find the complete list of targets here.

How was the panel designed?

The Pixelgen® Single Cell Spatial Proteomics panel is focused on immunology, targeting 80 validated and exploratory surface protein assays that have been carefully selected in collaboration with leading experts in the field. The panel was designed to cover a variety of immune cell types including targets for cell activation, cell adhesion, cell-cell communication, etc.

How do you validate your Antibodies?

The specificity of each antibody was first validated prior to conjugation using flow cytometry on PFA-fixed cells, and the specificity of each AOC was validated using MPX.

Applications

What sample type can you run on?

We recommend PBMCs or isolated immune cells. The panel contains targets for T-cells, B-cells, NK cells and monocytes.

Can you run on tissue (FFPE or FF)?

No, our antibodies have been validated for use with PFA fixed cells in suspension only.

Technology

What is the difference between DNA barcode and UMI on the antibody?

The DNA barcode is unique to the antibody type, whereas the UMI is unique for each conjugate oligonucleotide molecule. For example, 5 different anti-CD3 antibodies will all have the CD3 barcode, but unique UMIs.

What are UMI and UPI?

The UMI stands for Unique Molecular Identifier and is used to identify the oligonucleotide conjugated to the antibody. The UPI stands for Unique Pixel Identifier and is used to identify the pixel.  

What is the difference between UPI-A and UPI-B?

There is a pool of different A pixels, where each A pixel has a Unique Pixel Identifier A (UPI-A). Each A pixel is a rolling circle amplification product and will have several repeats of its UPI-A, but UPI-As between A pixels differ. The same stands for B pixels and UPI-Bs.

What kind of single cell partitioning is needed?

As this is performed in a standard PCR tube format in bulk, partitioning is performed by the unique properties of the Molecular Pixelation assay itself.

How many antibodies can each pixel bind to?

Each pixel will typically bind 5 – 10 antibody molecules, which will all incorporate the same UPI.

How many pixel zones do you get per cell?

Each cell will typically be divided into 500 – 1500 pixels or spatial zones for unstimulated PBMCs. This may vary depending on sample type, condition and cell size.

How many cells do you get pixelation data for?

The Pixelator software is compatible with 300 – 1000 cells output per reaction.

What is the resolution and how big are the pixels?

The DNA-pixels are <100 nm in size, as measured by scanning electron microscopy.

Can Molecular Pixelation measure abundance?

Yes relative abundance, within the same run and same target. The abundance capabilities are on par with flow cytometry.

What is the sensitivity (Limit of Detection) of the technology?

It is dependent on the antibody clone and equivalent to flow cytometry for PFA fixed cells.

What is the specificity of the technology?

Specificity is equivalent to flow cytometry for PFA fixed cells.

Instrument and Sequencing

What instruments do I need to run Pixelgen Single Cell Spatial Proteomics Kit, Immunology Panel 1, Human (Pixelgen SCSP Kit)?

There is no need for additional instruments other than available in a standard cell/molecular lab. For complete lists of required equipment and consumables for Pixelgen SCSP Kit, please contact Pixelgen Scientific Application Support.

How much sequencing is needed?

We recommend 120 000 reads per cell (which includes reads for PhiX).

How much PhiX is needed?

Since there are regions of low diversity in the reads, 15% PhiX is required.

What is the read configuration for sequencing?

Any pair format can be used as long as read1 is >= 28 cycles and read2 >= 66 cycles. Single end sequencing needs to be >132 bp (e.g. 150 SE).

What sequencing instrument has been used during validation of MPX?

NextSeq2000 and NovaSeq6000 sequencing

Data Analysis

How many cells do you get MPX data for?

The Pixelator software is compatible with 300 – 1000 cells output per reaction

What hardware requirements are needed for Pixelator?

How does the analysis work?

The NGS FASTQ files are imported to Pixelgen’s open source software Pixelator, undergoing several steps of quality control and analysis. The read sequences from the Unique Molecular Identifier (UMI), the antibody barcode on the AOC, and the Unique Pixel Identifier A (UPI-A) and Unique Pixel Identifier B (UPI-B) of the amplicon, are used to produce a graph, ultimately generating a network of protein connections. Each graph is a reconstruction of the surface of a cell. https://software.pixelgen.com/common/what-is-mpx.

Do I need to have bioinformatic knowledge to run Pixelator?

To run Pixelator you need to be familiar with working on the command line.

Do I need to have bioinformatic knowledge to analyze the data?

You need to be familiar with a programming language for data analysis such as Python or R. A basic understanding of analyzing single-cell data can be helpful but not mandatory.

What kind of results do you get from the MPX data analysis?

Pixelator will generate absolute and centered log-ratio (CLR) abundance data for each marker in the panel for every single cell, a polarity score for each marker in the panel for every single cell as well as colocalization score for each marker pair in the panel for every single cell. You will therefore get both abundance data as well as spatial metrics.

What is the output?

Pixelator returns two main outputs: a Web Report with quality control summaries and plots, and a .pxl file for downstream data analysis. https://software.pixelgen.com/pixelator/outputs/.

What is the .pxl file?

The .pxl file contains a number of elements that can be used for downstream analysis

  • Adata: AnnData file containing the cell by cell count data, similarly to other single cell omics techniques
  • Polarization – a table containing the spatial protein polarity scores per each detected cell.
  • Colocalization – a table containing the spatial protein-protein colocalization scores per each detected cell.
  • Edgelist – A table containing the edgelist; a list of edges in the graph components which each correspond to a cell. This file is used to visualize individual cells, and has been used to calculate spatial statistics like polarization scores and colocalization scores.
  • Metadata is a file with information about the Pixelator run

For more information, check our software page about the .pxl file (https://software.pixelgen.com/pixelator/outputs/pxl-file/)

What does polarity score mean?

The polarity score of a marker will tell you if the spatial distribution of that marker is non-random, as well as how non-random it is. The more polarized a marker is in a cell, the higher the polarity score. For more details, please see link.

What does co-localization score mean?

The co-localization score of two markers will tell you if the two markers appear at the same locations more often than expected by random chance, as well as how co-localized they are. The more co-localized two markers are in a cell, the higher the co-localization score. For more details, please see link.

Can I visualize my cells?

One of the tutorials is aimed for 2D cell visualization, see link.

Example code for 3D visualization can be found in Advanced Topics, see link.

Do you have software documentation?

Yes. Please see link.

Do you offer tutorials?

Yes. Please see link.

Do you have any example datasets?

Yes. Please see link.

How do I install Pixelator?

We recommend that you run Pixelator through our nf-core/pixelator. For more information, please visit link.

What programming languages do tutorials support?

We have tutorials based on both R and Python.

If I use Python, what Python version is needed?

It is compatible with Python versions from 3.8 to 3.10.

If I use R for downstream analysis, what R version is needed?

R version v4.3.1+.

What does component mean?

A component is a reconstruction of a cell, in a graph format consisting of nodes and edges.

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