Hypothesis: In aging CD4+ T cells, declining TET2 activity reduces 5‑hydroxymethylcytosine (5hmC) at enhancer regions of core autophagy regulators (ATG7, ULK1, TFEB, BECN1). This epigenetic erosion decouples the cell’s ability to scale autophagy output to the severity of metabolic stress, converting a proportional ‘rationing’ response into either an insufficient or excessive autophagic flux. Consequently, T cells fail to optimally recycle intracellular components during nutrient limitation, leading to accumulated damage, aberrant cytokine production, and accelerated immunosenescence.

Mechanistic rationale: TET2 preferentially oxidizes 5mC to 5hmC at lineage‑specific enhancers, correlating with enhancer activity and transcription factor binding. Autophagy genes are regulated by stress‑responsive enhancers that integrate AMPK/mTOR signaling inputs. Loss of 5hmC at these sites is predicted to diminish enhancer accessibility, blunting stress‑induced transcriptional upregulation of autophagy machinery. Conversely, in contexts where basal autophagy is already elevated (e.g., chronic low‑grade inflammation), the same enhancer loss may impede feedback inhibition, resulting in runaway autophagy. Both extremes deviate from the optimal ‘siege‑rationing’ set‑point, impairing T cell fitness.

Testable predictions:

1. Young vs. aged murine CD4+ T cells will show a significant reduction in 5hmC enrichment at ATG7, ULK1, TFEB, and BECN1 enhancers, measured by oxidative bisulfite sequencing or 5hmC‑CUT&Tag.
2. Under defined metabolic stress (e.g., EBSS starvation or rapamycin treatment), aged T cells will exhibit a flattened autophagy flux curve (LC3‑II turnover measured by bafilomycin A1 chase) relative to stress intensity, whereas young cells display a steep, proportional increase.
3. Restoring TET2 activity via lentiviral overexpression or supplementing with α‑ketoglutarate (a TET cofactor) in aged T cells will rescue 5hmC levels at autophagy enhancers, restore stress‑proportional autophagy flux, and improve functional readouts (IFN‑γ production, proliferative capacity) after stress.
4. Pharmacological inhibition of TET activity in young T cells (using DMOG or Bobcat339) will phenocopy the aged autophagy‑stress uncoupling, confirming causality.

Falsification: If 5hmC levels at autophagy gene enhancers do not decline with age, or if manipulating 5hmC at these sites fails to alter the stress‑dependent autophagy flux curve, the hypothesis would be refuted. Likewise, if rescuing 5hmC does not normalize autophagy proportionality or T cell function despite confirmed epigenetic restoration, alternative mechanisms must be considered.

This hypothesis directly links the ‘autophagy as rationing’ concept to a measurable epigenetic lesion, offering a precise mechanistic bridge between TET‑mediated 5hmC erosion, metabolic stress sensing, and the autophagy dysregulation that underlies T‑cell immunosenescence.