IF a dual pharmacological regimen consisting of (1) ex vivo pretreatment of aged donor hematopoietic stem cells (HSCs) with low-dose esomeprazole (1–10 μM, 16 hours, suspension culture) to achieve lysosomal pH correction via off-target vacuolar H⁺-ATPase (v-ATPase) modulation, combined with (2) oral esomeprazole administration to aged C57BL/6J recipient mice (20 mg/kg/day × 14 days pre-transplant) to suppress STING-driven bone marrow niche inflammaging,

is administered in a competitive transplantation model using aged (22–24 month) male C57BL/6J donors into aged syngeneic recipients conditioned with anti-CD117 antibody-drug conjugate (briquilimab analog, non-myeloablative),

THEN the following measurable outcomes will be observed at 16 weeks post-transplant:

• Lysosomal pH in treated donor HSCs normalized to within 0.25 units of young (3-month) controls (measured by LysoSensor Yellow/Blue DND-160 ratiometric flow cytometry)
• ≥50% reduction in phospho-STING (Ser365) and downstream phospho-IRF3 in treated HSCs (quantitative Western blot and intracellular flow cytometry)
• ≥5-fold improvement in peripheral blood donor chimerism (CD45.2⁺) relative to aged vehicle-treated controls
• Secondary: reduction in bone marrow niche macrophage IL-6 and CXCL10 secretion (ELISA), consistent with reduced niche inflammaging

BECAUSE the following causal chain operates:

1. Aged HSCs exhibit progressive lysosomal de-acidification (elevated pH) caused by transcriptional downregulation of Carbonic Anhydrase II (CAII), which reduces cytosolic H⁺ availability for v-ATPase-driven proton import into the lysosomal lumen (Lysosomal acidification controls HSC fate)[https://doi.org/10.1084/jem.20192283].

2. Enlarged, alkalinized lysosomes in aged HSCs fail to contain and degrade mitochondrial DNA (mtDNA) fragments and damaged chromatin; these nucleic acid species escape into the cytosol and activate the cGAS-STING innate immune axis, producing constitutive type I interferon (IFN-I) and NF-κB-driven gene expression that impairs quiescence, self-renewal, and engraftment capacity (Lysosomal dysfunction → cGAS-STING → HSC aging)[https://doi.org/10.1084/jem.20192283].

3. Esomeprazole, a benzimidazole-class PPI, covalently inactivates H⁺/K⁺-ATPase as its primary target, but is well-documented in osteoclast and tumor biology to accumulate preferentially in acidic lysosomal compartments and to exert measurable inhibitory effects on v-ATPase subunit V0a3 and V1 assembly in a concentration-dependent manner. [SPECULATIVE] At sub-pharmacological concentrations (1–10 μM) in a de-acidified lysosomal environment (as exists in aged HSCs), the accumulation-driven acidification kinetics may paradoxically restore partial v-ATPase proton pumping efficiency by reducing counter-ion back-leak, a mechanism distinct from the osteoclast hyperacidification context where higher doses are used to inhibit net acidification.

4. Ex vivo esomeprazole pretreatment of donor HSCs (16h, 5 μM) is predic...

SENS category: LysoSENS

Key references: • doi.org/10.1084/jem.20192283].