Hypothesis

Engineering iPSC-derived neural progenitors to constitutively express HLA‑G and to load secreted exosomes with miR‑124 will produce a synergistic graft that survives longer, integrates better, and attenuates microglial‑mediated neuroinflammation in Alzheimer’s disease, thereby improving cognitive outcomes relative to unmodified progenitors or either modification alone.

Mechanistic Rationale

• HLA‑G is a non‑classical MHC class I molecule that inhibits NK cell cytotoxicity and modulates T‑cell responses, reducing allo‑immune clearance of transplanted cells HLA‑G immune checkpoint.
• miR‑124 is a neuron‑specific microRNA that drives microglia toward an anti‑inflammatory (M2) phenotype and suppresses NF‑κB signaling miR‑124 microglia.
• Exosomes are natural carriers; loading them with miR‑124 enables paracrine delivery to host microglia and astrocytes, amplifying the immunosuppressive niche without requiring cell‑cell contact Exosome miRNA loading.
• Combining cell‑intrinsic immune evasion (HLA‑G) with extrinsic immunomodulation (exosomal miR‑124) addresses both the immediate graft‑host immune barrier and the chronic neuroinflammatory milieu that limits engraftment in AD models iPSC trials overview.

Experimental Design

1. Cell lines – Generate three iPSC‑derived neural progenitor (NPC) lines from a healthy donor: (a) WT control, (b) HLA‑G overexpressing (HLA‑G+), (c) HLA‑G+ NPCs engineered to overexpress miR‑124 in exosomes (HLA‑G+/exo‑miR124). Use lentiviral vectors with constitutive promoters; verify HLA‑G surface flow cytometry and exosome miR‑124 by qRT‑PCR.
2. Transplantation – Stereotactically inject 1×10^5 cells into the hippocampus of 6‑month‑old APP/PS1 mice (n=10 per group). Include a sham‑injected vehicle control.
3. Readouts (at 4 and 12 weeks post‑transplant)
   • Graft survival: human Nuclei immunostaining + stereology.
   • Integration: co‑localization of human MAP2 with host synapses (Synaptophysin) and electrophysiological LTP in hippocampal slices.
   • Microglial phenotype: Iba1 staining; flow cytometry for CD86 (M1) vs CD206 (M2); cytokine profiling (IL‑1β, TNF‑α, IL‑10, TGF‑β).
   • Exosome biodistribution: PKH26‑labeled exosomes harvested from graft area; confocal microscopy.
   • Behavior: Morris water maze and novel object recognition.
4. Controls – Additional groups receiving WT NPCs + exogenous exosomes purified from HLA‑G+/exo‑miR124 NPCs to test paracrine sufficiency.

Expected Outcomes

• HLA‑G+ NPCs will show ~2‑fold increase in survival vs WT (reduced NK‑mediated clearance).
• HLA‑G+/exo‑miR124 NPCs will exhibit the highest survival (~3‑fold), greatest synaptic integration, and a shifted microglial ratio (M2/M1 >2) accompanied by reduced hippocampal IL‑1β and TNF‑α.
• Behavioral improvement: escape latency reduced by ~30% and discrimination index increased by ~25% vs WT grafts; sham and vehicle groups remain impaired.
• Paracrine exosome alone will improve microglial phenotype but not graft survival, confirming the need for both mechanisms.

Potential Pitfalls & Alternatives

• Over‑immunosuppression risk – Persistent HLA‑G could impede pathogen surveillance; mitigate by incorporating an inducible HLA‑G cassette responsive to doxycycline.
• Exosome loading variability – Optimize miR‑124 loading via exosomal sorting signals (e.g., UBAP1‑LAMP2b fusion) and confirm via nanoparticle tracking.
• Species mismatch – Human HLA‑G may engage mouse inhibitory receptors weakly; consider co‑expressing human HLA‑E or using humanized NSG mice for validation.

If the combination fails to outperform single modifications, the hypothesis would be falsified, indicating that immune evasion and microglial re‑programming act independently or that additional barriers (e.g., extracellular matrix, aberrant amyloid‑β oligomers) dominate engraftment failure in AD.