Hypothesis

Intermittent, low‑dose expression of OSKM factors restricted to hematopoietic stem and progenitor cells (HSPCs) will rejuvenate senescent immune cells, suppress their SASP, and thereby slow systemic aging without triggering dedifferentiation or tumorigenesis.

Rationale

• Partial, transient reprogramming resets epigenetic age while preserving somatic identity, with rejuvenation peaking before loss of identity (1, 3).
• Senescent hematopoietic immune cells export SASP that drives aging in distant tissues; transplant experiments prove causality (4, 5).
• Cyclic OSKM regimens extend lifespan in progeroid mice without tumor formation, demonstrating a therapeutic window where rejuvenation is uncoupled from pluripotency (2).

Novel Mechanistic Insight

We propose that senescent immune cells maintain a self‑reinforcing loop: SASP‑rich exosomes deliver miR‑146a and miR‑155 to neighboring leukocytes, locking them into a pro‑inflammatory, epigenetically aged state. It's notable that transient OSKM pulses in HSPCs reset the epigenetic landscape of these exosomes by increasing SIRT6‑mediated deacetylation of H3K9 at SASP gene promoters, which diminishes NF‑κB binding and reduces miRNA loading. Consequently, the exosomal cargo shifts toward anti‑inflammatory miRNAs (e.g., miR‑124), breaking the paracrine senescence cascade.

Testable Predictions

1. Mice expressing a doxycycline‑inducible OSKM cassette under the Vav1 promoter (hematopoietic‑specific) subjected to 2‑day pulses every two weeks will show:
   • ↓ epigenetic age of CD8⁺ T cells measured by Horvath clock (>15 % reduction) after 3 months.
   • ↓ plasma SASP factors (IL‑6, TNF‑α, CCL2) relative to controls.
   • Improved grip strength, treadmill endurance, and delayed onset of age‑related pathology.
2. The same regimen won't increase teratoma incidence, nor alter lineage‑specific surface markers (CD34, Sca‑1, c‑Kit) beyond physiological variation.
3. Administering exosomes isolated from OSKM‑pulsed HSPCs to aged wild‑type mice will recapitulate the SASP‑suppressive phenotype, confirming the exosome‑mediated mechanism.
4. Blocking SIRT6 in HSPCs during OSKM pulses will abolish the exosome miRNA shift and prevent systemic benefits, linking the epigenetic enzyme to the observed outcome.

Falsifiability

If intermittent hematopoietic OSKM fails to reduce immune cell epigenetic age or SASP levels, or if lifespan extension does not occur despite confirmed molecular changes, the hypothesis is refuted. Likewise, observation of teratoma formation or loss of hematopoietic identity would indicate that the proposed uncoupling does not hold in this context.