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Short answer
CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by sequencing) is a single-cell multi-omics method that simultaneously measures cell-surface protein abundance and whole-transcriptome mRNA expression within individual cells. By converting antibody binding into sequenceable DNA barcodes, CITE-seq overcomes flow cytometry spectral limits and bridges the gap between gene expression and surface phenotype.
Definition and scope
The acronym CITE-seq stands for Cellular Indexing of Transcriptomes and Epitopes by sequencing. Developed in 2017 by Marlon Stoeckius and colleagues at the New York Genome Center, the technique addresses a fundamental biological challenge: the discordance between messenger RNA abundance and surface protein expression.
In single-cell biology, mRNA levels provide an unbiased survey of gene expression but correlate imperfectly with functional protein levels due to post-transcriptional regulation, variable translation rates, and technical dropouts. Conversely, cytometric tools like flow cytometry and mass cytometry (CyTOF) profile proteins with high sensitivity, but cannot measure unbiased whole transcriptomes. CITE-seq overcomes this divide by converting surface protein detection into a sequencing readout, pairing single-cell genomics and proteomics on standard droplet microfluidic platforms.
How it works or how it is used in practice
A CITE-seq experiment integrates antibody-oligonucleotide labeling with droplet microfluidics and dual-library sequencing across four stages:
1. Conjugate Architecture
Monoclonal antibodies targeting specific surface epitopes are covalently conjugated to synthetic single-stranded DNA oligonucleotides containing three elements:
- PCR amplification handle: A 5′ priming site for library construction.
- Antibody barcode: An internal 8 to 15 nucleotide sequence identifying the target marker (such as CD4, CD8, or CD19).
- Capture sequence: A 3′ sequence that anneals to capture primers on microfluidic gel beads.
2. Staining and Droplet Encapsulation
Single-cell suspensions are incubated with Fc receptor blockers (such as TruStain FcX) to prevent non-specific binding to Fcγ receptors on monocytes, macrophages, and B cells. Cells are then stained with titrated DNA-barcoded antibodies at 4°C for 30 minutes; cold incubation prevents antibody-induced internalization and shedding. After staining, cells are washed three times with cold buffer (PBS with 0.5% BSA) to eliminate unbound conjugates before encapsulation into Gel Beads-in-Emulsion (GEMs) on microfluidic controllers.
3. Co-Lysis, Barcoding, and Library Separation
Inside each droplet, cell lysis releases cellular mRNA and antibody-derived tags (ADTs). Both molecules hybridize to primers on the shared gel bead and incorporate identical cell barcodes during reverse transcription. Following emulsion reversal, SPRI magnetic beads separate larger cDNA fragments (~1 to 2 kb) from smaller ADT products (~180 bp), enabling independent library construction via multiplexed PCR.
4. Sequencing and Computational Analysis
Both libraries are pooled and sequenced on Illumina next-generation sequencing systems. Pipelines like Cell Ranger demultiplex the data, generating paired RNA and protein matrices. Downstream tools like Seurat apply Weighted Nearest Neighbor (WNN) algorithms (Hao et al., Cell 2021) to calculate cell-specific modality weights, creating joint clusters without allowing transcriptomic noise to obscure distinct surface phenotypes.
Types or related concepts
CITE-seq belongs to the single-cell multi-omics field. The table below compares CITE-seq with related single-cell and cytometric technologies based on published literature and manufacturer documentation.
| Platform | Readout Modality | Multiplex Capacity | Transcriptome Capture | Measurement Basis | Key Primary Source |
|---|---|---|---|---|---|
| CITE-seq | Surface protein + mRNA | 10 to >250 proteins | Yes (whole transcriptome) | Sequencing counts of antibody-derived tags | Stoeckius et al., Nat Methods 2017 |
| scRNA-seq | mRNA only | None (0 proteins) | Yes (whole transcriptome) | Sequencing counts of cDNA reads | Macosko et al., Cell 2015 |
| Flow Cytometry | Protein only | 15 to 30 fluorophores | No | Mean Fluorescence Intensity (MFI) | Stoeckius et al., Nat Methods 2017 |
| Mass Cytometry (CyTOF) | Protein only | 40 to 60 metal isotopes | No | Time-of-flight ion counts | Bandura et al., Anal Chem 2009 |
| Cell Hashing | Sample tag + mRNA | Ubiquitous markers (CD298/β2M) | Yes (whole transcriptome) | Sequencing counts of hashtag oligos | Stoeckius et al., Genome Biol 2018 |
Commercial TotalSeq conjugate series are engineered for specific chemistries: TotalSeq-A uses a poly(A) tail for Drop-seq and poly(dT) capture; TotalSeq-B pairs with 10x Chromium 3′ v3/v3.1 Feature Barcoding; TotalSeq-C integrates with 10x Chromium 5′ Immune Profiling and V(D)J assays; and TotalSeq-D targets single-cell DNA and protein multi-omics on Mission Bio Tapestri. In epigenomics, ArchR for single-cell ATAC-seq provides complementary chromatin accessibility mapping.
Where it matters for labs, clinics or supply decisions
Successful CITE-seq implementation requires strict protocol controls and read budget planning:
- Antibody Titration: Reagent cocktails must be titrated on control cells before single-cell encapsulation. Excess antibody elevates unbound ambient background, while insufficient antibody leads to false-negative surface calls.
- Cell Viability (>95%): Dead cells release ambient nucleic acids and non-specifically bind antibody-oligo conjugates. BioLegend and 10x Genomics guidelines require viability exceeding 95% to preserve low background.
- Fc Receptor Blocking: Pre-incubation with Fc blocking reagents (such as TruStain FcX) for 5 to 10 minutes prevents non-specific binding of IgG constant domains to Fcγ receptors on myeloid and B-cell subsets.
- Staining Temperature and Wash Cycles: Incubation must remain at 4°C for 30 minutes to prevent receptor internalization and shedding. Three consecutive wash cycles with cold PBS containing 0.5% BSA at 300 to 400 × g are mandatory to remove free conjugates.
- Sequencing Depth Economics: Feature Barcode (ADT) libraries reach count saturation at 2,000 to 5,000 read pairs per cell, whereas whole-transcriptome cDNA libraries require 20,000 to 50,000 read pairs per cell. Sequencing ADT libraries at higher depths wastes flow cell capacity.
- Ambient Background Denoising: Raw ADT counts include ambient oligos trapped during droplet formation. Downstream pipelines must apply Centered Log-Ratio (CLR) normalization or empty-droplet background correction (such as DSB) rather than raw read counts.
Common misunderstandings
- Misunderstanding: Surface protein expression matches mRNA transcript levels.
Reality: Stoeckius et al. demonstrated marked discordance between mRNA and surface proteins. In cord blood, natural killer cells showed undetectable CD56 mRNA due to dropouts, yet CD56 ADT reads cleanly resolved CD56bright and CD56dim subsets matching flow cytometry. - Misunderstanding: Protein libraries require the same sequencing depth as RNA libraries.
Reality: Because ADT panels target a discrete set of known markers, 2,000 to 5,000 reads per cell achieve saturation, compared to 20,000 to 50,000 reads per cell for unbiased transcriptomes. - Misunderstanding: Standard CITE-seq profiles intracellular epitopes.
Reality: Standard CITE-seq labels surface proteins on intact live cells. Intracellular staining requires permeabilization and fixation, which degrades cellular mRNA and inhibits droplet enzyme activity unless specialized fixed-cell chemistries are used. - Misunderstanding: Free antibodies are separated inside the microfluidic droplet.
Reality: Droplets capture whatever enters the microfluidic channel. Any free antibody-oligo conjugate remaining in the cell suspension becomes barcoded, elevating global background. Thorough pre-encapsulation washing is required.
Frequently asked questions
What does CITE-seq stand for?
CITE-seq stands for Cellular Indexing of Transcriptomes and Epitopes by sequencing, a multimodal method pairing single-cell transcriptomics with antibody-based surface protein quantification.
What is the difference between TotalSeq-A, TotalSeq-B, and TotalSeq-C?
TotalSeq-A utilizes a poly(A) tail for poly(dT) capture workflows like Drop-seq. TotalSeq-B uses Capture Sequence 1 for 10x Chromium 3′ v3/v3.1 Feature Barcoding. TotalSeq-C uses Capture Sequence 2 for 10x Chromium 5′ Immune Profiling.
How many surface proteins can CITE-seq measure at once?
Because CITE-seq uses sequenceable DNA barcodes rather than fluorophores, it avoids spectral overlap. Commercial pre-titrated panels routinely measure 100 to over 250 surface proteins simultaneously.
Why is Fc blocking required prior to staining?
Immune cells express Fcγ receptors that non-specifically bind antibody constant regions. Pre-blocking ensures that conjugates bind exclusively through target-specific Fab antigen-binding domains.
Sources
- Stoeckius, M., et al. (2017). Simultaneous epitope and transcriptome measurement in single cells. Nature Methods, 14(9), 865–868. DOI: 10.1038/nmeth.4380. URL: PMC5669064 (read 2026-11-09).
- BioLegend. TotalSeq™ Antibody-Oligonucleotide Conjugates User Manual. San Diego, CA. URL: https://www.biolegend.com/totalseq (read 2026-11-09).
- 10x Genomics. Chromium Feature Barcode Technology: Cell Surface Protein Protocol. Pleasanton, CA. URL: https://www.10xgenomics.com (read 2026-11-09).
- Hao, Y., et al. (2021). Integrated analysis of multimodal single-cell data. Cell, 184(13), 3573–3587. DOI: 10.1016/j.cell.2021.04.048. URL: PMC8238499 (read 2026-11-09).
