Intermittent Senolytic Plus Low-Dose JAK Inhibition Preserves Immune Memory While Clearing Senescent Cells in Aged Mice

Hypothesis

Intermittent dosing of dasatinib + quercetin (D+Q) combined with low‑dose JAK inhibition will reduce senescent cell burden and SASP‑driven inflammation without compromising vaccine‑induced immune memory, whereas D+Q alone impairs memory B and T cell responses.

Rationale

Senolytics clear senescent cells but also harm healthy lymphocytes, decreasing viability and cytokine production [2]. This off‑target effect may stem from transient JAK‑STAT activation triggered by SASP factors released during senolysis, which can promote apoptosis of memory lymphocytes via STAT3‑dependent pathways [4]. Low‑dose JAK inhibitors (e.g., tofacitinib) suppress STAT3 phosphorylation in lymphocytes, protecting them from SASP‑induced death while having minimal impact on senescent cell apoptosis, which relies more on p53‑p21 and BCL‑2 family pathways [7]. Thus, a hit‑and‑run senolytic pulse followed by a short window of JAK blockade could decouple beneficial SASP reduction from detrimental lymphotoxicity.

Experimental Design

• Animals: 20‑month‑old C57BL/6 mice (n=10 per group).
• Groups: (1) Vehicle control; (2) Intermittent D+Q (5 mg/kg dasatinib + 50 mg/kg quercetin, i.p., once weekly for 3 weeks); (3) Low‑dose tofacitinib (10 mg/kg diet, continuous); (4) Intermittent D+Q + low‑dose tofacitinib (same schedule as group 2, with tofacitinib administered only during the 48 h after each D+Q dose).
• Intervention duration: 6 weeks.
• Readouts (collected 1 week after final dose):
  • Senescent cell burden (p16^Ink4a^‑positive cells) in adipose, spleen, and bone via flow cytometry and immunohistochemistry [1].
  • Serum SASP cytokines (IL‑6, TNF‑α, TGF‑β) by ELISA.
  • Vaccine response: subcutaneous immunization with OVA‑alum at week 4; measure anti‑OVA IgG titers and OVA‑specific IFN‑γ^+^ CD8^+^ T cells by ELISPOT.
  • Lymphocyte viability and proliferation ex vivo (CFSE dilution, Annexin V/7‑AAD).
  • Functional assessment: grip strength and treadmill endurance.

Predicted Outcomes

• Groups receiving D+Q alone will show reduced p16^Ink4a^+ cells and lower SASP levels but a significant decline in anti‑OVA IgG titers and IFN‑γ^+^ T cells compared with control.
• The combination group will retain senolytic benefits (comparable senescent cell clearance and SASP suppression to D+Q alone) while maintaining vaccine‑induced antibody titers and T cell responses at levels not statistically different from vehicle.
• Low‑dose tofacitinib alone will not reduce senescent burden but may modestly lower serum IL‑6 due to STAT3 blockade in non‑senescent immune cells.

Potential Pitfalls and Alternatives

If JAK inhibition interferes with senolytic‑induced apoptosis of senescent cells, we would observe diminished senescent cell clearance in the combination group. In that case, adjusting the timing—administering JAK inhibitor 24 h after D+Q rather than concurrently—could preserve senolysis while still shielding lymphocytes. Alternative senomorphics (e.g., rapamycin) could be tested similarly to determine whether mTOR inhibition offers a safer window for immune preservation.

This hypothesis is testable with standard immunological and senescence biomarkers, and its falsifiability hinges on whether the combination fails to protect memory immunity despite achieving senescent cell reduction.