Background

Xenotransplantation using gene-edited pigs has emerged as a major alternative to address the chronic shortage of organ donations. With the development of transgenic pigs that remove major xenoantigens, such as alpha-gal, and introduce human complement regulatory genes, the devastating hyperacute rejection that occurred immediately after transplantation has entered a clinically manageable domain.

However, as organs enter the long-term survival stage, another barrier has appeared. This is due to the continuous observation of subtle immune-mediated damage that persists despite standard immunosuppressive therapy in organs that have survived hyperacute rejection. It is difficult to capture early signs of micro-immune rejection in response to xenoantigens using conventional blood tests and invasive biopsies based on allotransplantation standards. By the time damage is visible to the naked eye in routine histological examinations, extensive vascular injury and fibrosis have often progressed to a point where recovery is impossible. This necessitated a precision diagnostic system reflecting the unique characteristics of interspecies immune responses.

Key Findings

The researchers proposed a multimodal precision diagnostic framework to comprehensively track potential graft injury observed following the prevention of hyperacute rejection. This approach moves beyond existing single-biomarker-centric testing by integrating genomic, transcriptomic, and molecular pathological data in a three-dimensional manner.

The new system combines non-invasive testing with high-resolution molecular analysis. It utilizes donor-derived cell-free DNA (dd-cfDNA) analysis in the recipient's blood to monitor minute fractional changes in donor pig-derived DNA in real-time. This method detects pig genomic signals released due to the destruction of vascular endothelial cells before long-term damage becomes fully established. This integrates single-cell RNA sequencing (scRNA-seq) technology with spatial transcriptomics analysis. Based on this, the interaction between infiltrating human immune cells and pig parenchymal cells was mapped at the molecular level to accurately classify the processes of graft vasculitis and microthrombosis formation.

This framework subdivides rejection types to quantitatively determine the contribution of each immune pathway. It is designed to measure not only antibody-mediated rejection and T-cell-mediated rejection but also innate immune-mediated damage caused by xenoantigen-specific macrophages and natural killer (NK) cells as independent axes.

Significance and Outlook

The establishment of this diagnostic system is evaluated as a turning point that will fundamentally change the approach to clinical entry for xenotransplantation. Previously, reliance was placed on reactive measures, such as administering high-dose immunosuppressants after signs of rejection appeared; however, in the future, early identification of subtle signs of damage will allow for the activation of personalized targeted immunosuppression protocols. This opens the way to extending the lifespan of transplanted organs while reducing the risk of infection caused by unnecessary excessive immunosuppression.

Furthermore, this diagnostic data provides a direct blueprint for the design of next-generation transgenic pigs. By back-tracing the molecular damage pathways captured in the diagnostic framework, precise genome editing targets can be derived, determining which pig genes should be additionally knocked out or which human immune regulatory genes should be additionally inserted.

However, significant challenges remain before full integration into clinical practice. There is a need to reduce the high testing costs and analysis time associated with high-resolution molecular analysis and multimodal data integration. Follow-up work to firmly verify the clinical validity and reproducibility of non-invasive indicators through multi-center clinical trials must also be conducted.