Degree of Labeling Impacts ADTs for Single-Cell Multi-Omics
Key takeaways
- Degree of labeling is the number of oligos per antibody. Testing 1 to 6 oligos showed moderate labeling gives the best signal-to-noise ratio in the antibody-derived tag (ADT) counts, while over-labeling adds background and reduces specificity.
- Each antibody clone responds differently to activation and conjugation, so activation and labeling conditions should be optimized per clone rather than applied as one recipe across the panel.
- In CITE-seq, fine-tuning oligo labeling lifts low-expressing proteins into the detectable range, balances amplification across ADTs, and lowers sequencing costs by not wasting reads on over-represented targets.
- The conjugation method uses copper-free SPAAC click chemistry, and finding the right balance keeps single-cell multi-omics experiments cost-effective and reproducible.
Single-cell RNA sequencing (scRNA-seq) measures the transcriptome but not protein. Oligonucleotide-labeled antibodies add the protein layer: each antibody carries a short oligo that is sequenced and counted alongside the transcriptome. In CITE-seq these tags are called antibody-derived tags, or ADTs. The hard part is building a large antibody panel in which every conjugate performs well at once.
A 2021 study by Kleino et al. describes an adjustable antibody-oligo conjugation method and tests how the number of oligos per antibody affects protein detection in single-cell multi-omics. The main findings are below.
How many oligos per antibody
The team conjugated oligos to antibodies using strain-promoted azide-alkyne cycloaddition (SPAAC), a copper-free click chemistry technique, and varied the degree of labeling, the number of oligos per antibody, to see how it changed the signal.
- 1 to 6 oligos per antibody were tested.
- Moderate labeling gave the best ADT signal-to-noise ratio.
- Over-labeling reduced antibody performance, adding background and lowering specificity.
More oligos per antibody is not better past a point. Beyond the moderate range, the extra oligos cost specificity without adding usable signal.
Optimize each clone
Antibody clones did not respond to conjugation the same way, so the conjugation conditions have to be set per clone.
- High activation reduced binding efficiency for some antibodies.
- Low to moderate activation preserved antigen recognition while improving signal.
- Testing each clone separately gave the best result for each antibody in the panel.
The practical consequence is that activation and labeling should be tuned per clone rather than run as a single recipe across the whole panel. That is what holds specificity and keeps background low.
CITE-seq: detecting low-expression proteins
A common CITE-seq problem is detecting proteins present at low levels. Kleino et al. found that tuning the degree of labeling brings those weak ADT signals into the detectable range.
In practice this gives:
- Better detection of low-expressing proteins
- More balanced amplification across ADTs
- Lower sequencing costs, because fewer reads are spent on over-represented targets
What this means for your panel
For a CITE-seq panel, the degree of labeling is a parameter worth optimizing rather than leaving at a default. A moderate level of labeling, tuned per clone, keeps single-cell experiments sensitive, cost-effective, and reproducible.