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This review synthesizes evidence and provides author-actionable feedback on a preprint investigating a single-gene (SB000) approach to rejuvenate human cells while preserving somatic identity.

Summary

Question. Can a single defined factor (SB000) reverse multi-omic aging signatures in human cells without activating pluripotency or eroding somatic function?

Design. The study used primary aged human dermal fibroblasts (HDF; n=6 donors), lung fibroblasts (HLF; n=4), and epidermal keratinocytes (NHEK; n=2). Cells were transduced by lentivirus to overexpress SB000, with comparators including Yamanaka factors (OSK, OSKM, and individual O/S/K) plus eGFP and no-virus controls. Key readouts were single-cell RNA-seq analyzed with the AC3 aging clock at ~2 weeks and EPICv2 DNA methylation profiling with multiple clocks at ~6 weeks. Additional assays quantified senescence signatures, somatic identity (e.g., scTab and fibroblast scores), pluripotent colony formation, and collagen I secretion. Analyses were donor-matched; randomization and blinding were not reported.

Key results. 

1. AC3 accuracy: single-cell r=0.913 vs PCSkinAndBlood; sample-median r=0.946 (Fig.1A).

2. Transcriptomic age: SB000 −4.52 years (SD 2.98; p=0.0036) across fibroblasts; OSKM −5.46 (SD 1.65; p=0.029) (Fig.2D).

3. Senescence (SenMayo): SB000 −0.281 (SD 0.078; p=1.89×10⁻⁵); OSK −0.285; OSKM −0.158 (p=0.103) (Fig.2E, S1).

4. Global DNAm: SB000 +3.00% (SD 2.8; p=0.047) vs eGFP; OSK −2.21% (SD 1.71; p=0.082) (Fig.2H–I).

5. DNAm clocks (HDFs): SB000 Δage—PCSkinAndBlood −5.29 y; PCHorvath2013 −7.42 y; GrimAge2 −4.12 y; DunedinPACE −0.132 (vs OSK −1.47 y, −3.36 y, −4.38 y, −0.168) (Fig.2J–M).

6. Identity/safety: fibroblast identity score change SB000 −0.594 vs OSK −2.13; scTab “fibroblast” probability SB000 70.5% vs eGFP 75.0% (ns), OSK 41.8% (Fig.3A–C); SB000 0 colonies; O/S/K and OSKM formed colonies (Fig.3H–I); SB000 increased collagen I secretion; OSK ~control; iPSC ≈0 (Fig.3K).

7. Generalization (NHEKs): global DNAm +~4%; PCHorvath2013 −13.6 y (≈ −9.7 y/month); significant decreases across multiple clocks (Fig.4B–G, S7).

Implication. SB000 reproducibly reverses transcriptomic and epigenetic aging markers while preserving somatic identity in vitro, supporting the claim that rejuvenation can be decoupled from pluripotency.

List of major concerns and feedback

1. Causality and on-target specificity not shown (overexpression only). Because the current evidence is based only on overexpression, demonstrate on-target causality by performing rapid loss-of-function rescue: rapid knockdown of the transgene with 2 independent siRNAs targeting SB000 coding sequence in SB000⁺ HDFs (≥2 donors); confirm ≥70% mRNA reduction by RT-qPCR; readouts at 48-72h: Quantify SenMayo markers (CDKN2A/p16^INK4a and CDKN1A/p21^CIP1), COL1A1/2 by qPCR, and EdU incorporation, with the a priori expectation of partial reversal toward control levels; include a non-targeting siRNA control and OSK⁺ cells as comparators.

2. Potential confounding by viral dose/VCN and proliferation selection. To rule out artifacts from vector load or growth advantages, quantify vector copy number (VCN) by qPCR for SB000, OSK, and eGFP with at least three technical replicates per sample; report MOI and the percentage of GFP-positive cells by FACS; normalize all molecular and phenotypic endpoints to VCN; and add 24-hour EdU/7-AAD cell-cycle profiling plus Annexin V/PI viability assays to demonstrate the absence of proliferative selection bias.

3. Safety readouts lack DNA-damage and pluripotency-marker negatives. To strengthen safety claims, immunostain SB000⁺, eGFP, and OSKM plates for γH2AX and 53BP1 foci (score ≥200 cells per condition) and quantify NANOG, TRA-1-60, and POU5F1 by immunofluorescence or RT-qPCR, including an iPSC positive control, to document the absence of pluripotency signaling beyond colony morphology.

List of minor concerns and feedback

1. AC3 external validity. To demonstrate that AC3’s findings generalize, run at least one published external single-cell transcriptomic aging clock (e.g., Buckley 2023 or Tyshkovskiy 2024) on the same scRNA-seq data and report concordance with AC3 (Pearson’s r and regression slope) as well as parallel effect sizes for each intervention.

2. Pluripotency colony identity. To verify that counted colonies are truly pluripotent, immunostain them for TRA-1-60/SSEA4 and alkaline phosphatase, and report colony counts normalized to the number of GFP⁺ cells to control for transduction efficiency.

Conclusions and limitations discussed

Current data support that SB000 reverses transcriptomic and DNAm aging signatures and preserves fibroblast identity with no detectable pluripotency by colony assay, generalizing to keratinocytes. They do not yet establish on-target causality, rule out vector/VCN-driven artifacts, or provide durability/safety beyond in vitro. The single biggest threat to validity is the non-disclosure of SB000’s identity, which blocks independent replication and mechanistic checks. Minimal added evidence to move from “plausible” to “compelling”: disclose SB000, show on-target reversal by acute transgene knockdown with per-donor mixed-effects statistics, and control for VCN/proliferation.

Concluding remarks

Promising, potentially important advance—if the effect is on-target and independent of vector/proliferation confounds.

The fastest path: (1) disclose SB000 and deposit the construct, (2) do 48 h siRNA knockdown-of-transgene with SenMayo/EdU/collagen readouts and mixed-effects stats, (3) provide VCN-normalized analyses with bootstrap CIs and FDR across clocks. Expect modest attenuation of SB000’s effect sizes after VCN/proliferation control if the mechanism is clean.

Competing interests

No competing interests declared by the reviewer.

Competing interests

The author declares that they have no competing interests.