What Is The Difference Of Treatment Protocol In ABO Incompatible Transplant Recipients Compared To ABO Compatible
The primary difference in treatment protocols is that ABO-incompatible (ABOi) recipients require an intensive preoperative “desensitization” phase to remove circulating anti-A/B antibodies and suppress their production, whereas ABO-compatible (ABOc) recipients generally proceed directly to surgery with standard induction.
The specific differences in treatment protocols are detailed below:
- Preoperative Desensitization (ABOi Only)
The cornerstone of ABOi protocols is the reduction of circulating isoagglutinins before surgery to prevent hyper-acute rejection.
- Physical Antibody Removal: ABOi recipients undergo multiple sessions of plasmapheresis (PE), double filtration plasmapheresis (DFPP), or antigen-specific immunoadsorption (IA). The goal is typically to reach a preoperative target titer of <1:8.
- Early Initiation of Immunosuppression: ABOi patients begin triple maintenance therapy (tacrolimus, mycophenolate mofetil, and prednisone) roughly two weeks before transplantation. In contrast, ABOc recipients usually start these medications at the time of surgery.
- Induction Therapy
While both groups receive induction therapy, the agents used for ABOi are significantly more potent to manage the higher immunological risk.
- B-Cell Depletion: Modern ABOi protocols use Rituximab (an anti-CD20 monoclonal antibody) to deplete B-cells and prevent antibody rebound, making the historical practice of splenectomy obsolete.
- Combined T- and B-Cell Targeting: Recent studies show that ABOi outcomes are improved when Rituximab is combined with T-cell directed agents like Anti Thymocyte Globulin.
- Postoperative Management
- Antibody Monitoring and Rebound: ABOi protocols require frequent monitoring of anti-A/B titers postoperatively to check for “rebound.”
- “On-Demand” Antibody Removal: While routine postoperative antibody removal is increasingly withheld to reduce bleeding risks, it is still performed “on-demand” in ABOi recipients if titers rise above specific thresholds (e.g., >1:16 or >1:32).
- Maintenance: Once established, maintenance immunosuppression for both groups typically involves tacrolimus, MMF, and steroids, though some ABOi protocols allow for steroid withdrawal after three months.
- Specialized Subgroups (A2 Donors)
A unique protocol exists for A2 subgroup donors; if the recipient has low baseline anti-A IgG titers (≤1:8 to 1:16), transplantation can sometimes be performed without any preoperative antibody removal or Rituximab, using conventional immunosuppression alone.
