Hypothesis

Engineered iPSC lines lacking HLA class I/II and expressing PD‑L1 generate cardiomyocytes that engraft in aged myocardial tissue, survive long term, and improve function without requiring chronic immunosuppression.

Mechanistic Rationale

Aged hearts exhibit heightened innate immune surveillance and reduced regenerative capacity, which contributes to poor outcomes after cell therapyiPSC dominance. HLA molecules on graft cells trigger recipient T‑cell activation, while PD‑L1 engagement delivers inhibitory signals that dampen effector responses. Removing HLA eliminates direct antigen presentation, and overexpressing PD‑L1 reinforces peripheral tolerance. In aged tissue, senescent cells secrete SASP factors that can upregulate PD‑1 on infiltrating lymphocytes, making PD‑L1 blockade a relevant checkpointiPSC immunoevasion. Combining HLA knockout with PD‑L1 overexpression should therefore create a double shield: loss of antigenic visibility plus active inhibition of residual immune activity.

Testable Predictions

1. iPSC‑derived cardiomyocytes with HLA‑KO/PD‑L1 will show <5 % T‑cell mediated lysis in vitro compared with wild‑type iPSC‑cardiomyocytes when co‑cultured with aged human peripheral blood mononuclear cells.
2. In immunodeficient mice reconstituted with aged human immune cells, grafts of HLA‑KO/PD‑L1 cardiomyocytes will retain >70 % engraftment at 8 weeks, whereas wild‑type grafts will drop below 30 %.
3. Functional improvement (ejection fraction increase ≥10 %) will be observed in aged murine myocardial infarction models receiving HLA‑KO/PD‑L1 cardiomyocytes without any postoperative immunosuppressants.
4. Adding a PD‑1 blocking antibody to the circulation will abolish the survival advantage of HLA‑KO/PD‑L1 grafts, confirming PD‑L1 dependence.

Experimental Design

• Cell preparation: Generate iPSCs from a healthy donor, edit with CRISPR‑Cas9 to knockout HLA‑A, HLA‑B, HLA‑C, HLA‑DR, HLA‑DQ, and HLA‑DP loci, then insert a constitutive PD‑L1 cassette. Differentiate to cardiomyocytes using established protocols (80‑90 % efficiency)iPSC differentiation. Validate HLA surface loss by flow cytometry and PD‑L1 overexpression by western blot.
• In vitro assay: Co‑culture 1 × 10⁴ cardiomyocytes with 5 × 10⁴ PBMCs from donors >65 years old for 48 h. Measure lactate dehydrogenase release and Annexin V/PI staining.
• In vivo model: Induce myocardial infarction in 12‑month‑old NSG mice, then reconstitute with irradiated aged human PBMCs (1 × 10⁶ cells via tail vein). Inject 1 × 10⁶ cardiomyocytes into the infarct border zone. Groups: (1) HLA‑KO/PD‑L1, (2) wild‑type iPSC‑cardiomyocytes, (3) vehicle. No cyclosporine or tacrolimus administered.
• Readouts: Bioluminescence imaging for graft survival weekly, MRI for ejection fraction at 4 and 8 weeks, histology for CD45⁺ infiltration and caspase‑3 apoptosis at endpoint.
• Checkpoint test: In a subset of HLA‑KO/PD‑L1 recipients, administer anti‑PD‑1 (200 µg i.p. twice weekly) starting day 0.

Potential Outcomes and Falsifiability

If the data confirm predictions 1‑3 and show that prediction 4 abolishes graft benefit, the hypothesis is supported: HLA knockout plus PD‑L1 overexpression creates an immunoprivileged iPSC‑derived graft suitable for aged hosts without chronic drugs. Conversely, if HLA‑KO/PD‑L1 cardiomyocytes exhibit lysis rates comparable to wild‑type, fail to engraft beyond 30 %, or show no functional improvement despite lack of immunosuppression, the hypothesis is falsified. Likewise, if PD‑1 blockade does not reduce graft survival, the claimed mechanism would be incorrect, prompting re‑evaluation of other immune pathways.

This framework directly tests whether engineering universal iPSC lines can overcome the age‑related immune barrier that has limited ESC and unedited iPSC therapies, offering a clear, falsifiable path toward clinical translation.