IF a triple-combination thymic regeneration protocol—comprising (1) a single intrathymic injection of AAV9-CAG-FOXN1 (estimated dose: 1×10¹¹ vector genomes per lobe, based on intrathymic/perithymic delivery precedents), (2) systemic LHRH agonist (degarelix, 200 µg subcutaneous, monthly) initiated simultaneously, and (3) recombinant IL-7 (rhIL-7, 10 µg/dose intraperitoneal, three times weekly for eight weeks)—is administered concurrently to aged C57BL/6 male mice (20–24 months), commencing four weeks after AAV injection to allow stromal priming,

THEN functional peripheral immune reconstitution—defined as a ≥3-fold increase in circulating naïve CD4⁺CD62L⁺CD44⁻ and CD8⁺CD62L⁺CD44⁻ T cells with documented lymph-node colonization by recent thymic emigrants (RTEs), a broadened TCR Vβ spectratype, and restored de novo antibody response to a neoantigen challenge—will be observed at 16 weeks post-initiation, exceeding the effect of any single agent or dual combination by a statistically significant margin (effect size d > 0.8 for naïve T-cell output vs. vehicle controls),

BECAUSE the three agents act on mechanistically independent and sequentially dependent nodes of thymic involution:

1. FOXN1 restores the structural substrate for thymopoiesis. Age-related thymic involution is driven primarily by progressive downregulation of FOXN1 in thymic epithelial cells (TECs), collapsing cortico-medullary architecture. Direct FOXN1 augmentation via transplanted FOXN1-reprogrammed cells has been shown to drive aged thymus regrowth through intrathymic/perithymic delivery, restoring discrete cortical and medullary zones and increasing thymic cellularity; treated mice showed reduced senescent peripheral T cells and enhanced TCR responsiveness, demonstrating that stromal repair is sufficient for downstream T-cell quality improvement. (FREFs drove aged thymus regrowth and reduced senescent T cells)[https://doi.org/10.1172/jci.insight.140313] AAV9-FOXN1 recapitulates this by delivering FOXN1 directly to resident TECs without requiring cell transplantation, reducing logistical complexity and immunogenic risk. [SPECULATIVE: AAV9 TEC transduction efficiency in 24-month mice has not been directly quantified and may be reduced by the adipose replacement of the aged thymic stroma.]

2. LHRH agonist removes the dominant extrinsic suppressor of TEC proliferation and early thymic progenitor (ETP) seeding. Sex steroid ablation (SSA) via the LHRH agonist degarelix in old mice (≥18 months) produces robust increases in thymic size and cellularity; this structural recovery is mechanistically distinct from FOXN1-mediated epithelial repair, operating instead by lifting androgen/estrogen-mediated suppression of TEC proliferation and ETP bone-marrow egress and homing. (SSA or KGF treatment improves thymic cellularity in aged mice)[https://doi.org/10.1111/acel.12865] By combining SSA with AAV-FOXN1, the stromal compartment is simultaneously rebuilt (FOXN1) and derepressed (SSA), a...

SENS category: RepleniSENS

Key references: • doi.org/10.1172/jci.insight.140313] • doi.org/10.1111/acel.12865] • doi.org/10.1016/j.coi.2013.06.002] • doi.org/10.3389/fimmu.2020.01399] • doi.org/10.1111/acel.12865].