RENAL TRANSPLANTATION OF HIGHLY IMMUNIZED PATIENTS ON THE BASIS OF ACCEPTABLE HLA-A, -B MISMATCHES(1).
           Doxiadis* I.I.N.,  P. de Lange*, J. De Meester#, G.G. Persijn#, and F.H.J. Claas*, *Immunohaematology and Blood Bank,  Leiden University Medical Center and  #Eurotransplant, Leiden, The Netherlands.
          Highly immunized (HI) patients (85% or more panel reactive antibodies; PRA) are accumulating on renal transplant waiting lists, because they formed HLA alloantibodies towards a large variety of non-self HLA antigens, which often lead to positive crossmatches. In 1985 Eurotransplant (ET) has introduced the Acceptable Mismatch (AM) Program for HI patients having in two different occasions allo-PRA values of 85%. Both current and historical sensitization were considered to be relevant. AM were those HLA-A,-B antigens towards which these patients never formed alloantibodies. The AM were defined at the recipient center and checked at the ET Reference Laboratory. Once a donor becomes available, who is compatible to a patient's HLA-A,B,DR antigens in combination with the AM the organ is offered. Most of the transplants (82%) were transplanted to HLA-DR compatible recipients. Final crossmatches with current and historical sera must be negative. Until December 1997, 263 transplants have been performed (230 directly via the AM program). From the patients on the AM waiting list 153 were transplanted within 12 months with the first offer. The number of transplants performed yearly ranged between 11 and 36 (mean = 21). The PRA value at the day of transplantation was 0% in 13.5% of the patients, <60% in 32.5%, and >85% in 54 % of the patients. The graft survival rates of AM transplants match those of all transplants done in the participating centers in the same period: 75.6%, 66.2%, and 54.5% at 1, 3, and 5 years. No effect of blood group matching, age of patients or donors, gender, current immunization or consecutive transplantation number was observed. In order to increase the chance for the patients to receive an offer both epitope and CREG matching will be further analyzed. To date we can conclude that the AM program increases the chance of HI patients to receive an organ, especially in the first 12 months after entering the program.