What Are the Future Perspectives of ABO-Incompatible Kidney Transplantation?
Future perspectives for ABO-incompatible (ABOi) kidney transplantation focus on reducing the biological “antigenic footprint” of the graft, refining pharmacological protocols to minimize side effects, and expanding donor allocation policies.
- Enzymatic Conversion and Graft Engineering
A revolutionary area of research involves enzymatically converting donor kidneys into “universal” blood group O organs.
- Antigen “Stripping”: Researchers are using specific enzymes, such as FpGalNAc deacetylase and FpGalactosaminidase, to remove A or B antigens from the renal vasculature.
- Model Success: In ex vivo models, treated kidneys demonstrated an 80% loss of A antigens within hours and did not bind circulating anti-A antibodies or activate the complement pathway.
- Clinical Implications: This donor-centric strategy could eventually allow incompatible kidneys to be transplanted without aggressive preoperative desensitization.
- Novel Pharmacological Agents
New drugs are being evaluated to replace broad B-cell depletion with more targeted action:
- Imlifidase: This IgG-degrading enzyme can rapidly clear IgG from blood and tissue within hours. However, its future in ABOi is debated because it does not cleave IgM, which appears to be a highly relevant factor in preventing early antibody-mediated rejection (ABMR).
- Eculizumab: This C5 complement inhibitor is being explored as an adjunctive or rescue therapy. Case studies show it can prevent ABMR in high-risk ABOi recipients even without traditional antibody removal or splenectomy.
- Refined Induction and Personalized Protocols
There is a shifting focus toward optimizing the intensity of immunosuppression to balance rejection and infection risks:
- Combined Induction: Future standards are moving away from rituximab monotherapy toward combined T- and B-cell targeted induction (e.g., rituximab with basiliximab or alemtuzumab), which has shown a trend toward better graft survival and significantly lower rejection rates.
- Simplified Post-Transplant Care: Protocols are increasingly abandoning routine postoperative antibody removal in favor of “on-demand” treatment to avoid excess bleeding and infectious complications.
- Expanding Allocation Policies (A2 to B Donation)
Policy shifts aim to utilize low-antigen expressers more effectively:
- A2/A2B to B Transplantation: In the United States and UK, deceased donor A2 kidneys are increasingly allocated to blood group B recipients with low anti-A titers (≤1:4), yielding outcomes similar to compatible transplants.
- Eurotransplant Rules: While successful in the US and UK, this practice is not yet standard under Eurotransplant rules, representing a potential area for future regulatory expansion.
- Standardizing Metrics
A critical goal for the future is the standardization of antibody titer measurement methods.
Because current semi-quantitative tests vary significantly between laboratories, establishing a uniform assay is essential for conducting the large-scale randomized controlled trials needed to confirm the safety of newer, simplified protocols.
Gender: Women have been found to be overrepresented in major bleeding events, though the exact reason remains unclear.
