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Can single-cell RNA clocks tell how old your immune system is?

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sc-ImmuAging clocks trained on 1,081 healthy adults’ PBMCs showed monocyte age acceleration in COVID-19 that eased with recovery, and CD8+ T-cell rejuvenation after BCG mainly in people with high baseline interferon genes.

Source

Single-cell immune aging clocks reveal inter-individual heterogeneity during infection and vaccination

Li W, Zhang Z, Kumar S, et al. · Nature aging · 2025

doi.org/10.1038/s43587-025-00819-zRead the full paper ↗43 citationscc by

Study at a glance

Design
Computational / modelling — Cell-type-specific scRNA-seq aging clocks (sc-ImmuAging) trained on 1,081 healthy adults then applied to COVID-19 and BCG vaccination transcriptomes
N
N=1081 · 1,081 healthy European adults (18–97 years); 864 train / 217 internal validation plus external tests and disease/vaccine applications
Population
Healthy adult PBMC scRNA-seq donors, with separate COVID-19 patient and BCG vaccinee applications
Outcome
Predicted immune biological age vs chronological age (R, RMSE, MAE) and age acceleration in monocytes and CD8+ T cells

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What they did

Built cell-type-specific transcriptomic clocks for circulating myeloid and lymphoid cells from 1,081 European healthy adults (18–97). Split 80/20 (864/217) for training/internal validation, then applied clocks to COVID-19 and BCG vaccination datasets.

What they found

Internal and external validation favored the constructed models. COVID-19 patients showed monocyte age acceleration that decreased during recovery. Vaccination effects were heterogeneous: elevated baseline interferon response genes marked CD8+ T-cell age rejuvenation after BCG.

The limits

What it doesn't show

Clock residuals are not a proven clinical diagnostic, and observational COVID/vaccine applications cannot prove that changing interferon genes would reverse immune aging.

Key terms

sc-ImmuAging
Cell-type-specific single-cell RNA aging clocks for circulating immune cells.
Biological immune age
Clock-predicted age versus chronological age (R, RMSE, MAE).
Age acceleration
Predicted age older than chronological age; seen in monocytes during COVID-19.
Inflammaging
Age-related inappropriate systemic inflammation plus reduced immune responsiveness.
BCG
Bacillus Calmette–Guérin vaccine; associated with heterogeneous CD8+ rejuvenation.
PBMC
Peripheral blood mononuclear cells used for scRNA-seq clocks.

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Clocks were trained on about:

Common questions

How many healthy people trained the clocks?

1,081 adults aged 18–97 (864/217 train/test split).

What happened in COVID-19 monocytes?

Age acceleration that decreased during recovery.

Who showed CD8+ rejuvenation after BCG?

People with elevated baseline interferon response genes.

What data type?

Single-cell RNA-seq of PBMCs.

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