Canine platelet alloimmunization: the role of donor selection

Five different platelet transfusion programmes were evaluated in a canine model to determine the most effective method of providing long-term platelet support. When a weekly transfusion from a single unrelated donor was used, alloimmune platelet refractoriness developed in 95% of recipients after an average of 3.1 +/- 0.7 transfusions, and donor platelets circulated for a total of 8.2 +/- 2.3 d. When multiple unrelated donors were used, the percentage of refractory recipients was similar (60% versus 77%) whether platelets came from six single donors given sequentially or from a pool of the same six donors given repeatedly. There was, however, a significant difference in the number of transfusions given prior to immunization (14 +/- 5 transfusions lasting 32 +/- 12 d for sequential single donors as compared to 5.5 +/- 1.0 transfusions lasting 13 +/- 2 d for the pooled donors). When littermates were used as platelet donors, the frequency of refractory recipients, the number of transfusions required to immunize, and the circulation time of donor platelets before refractoriness was not better than when multiple unrelated single donors were used. Furthermore, there was no significant difference in effectiveness between DLA-identical and DLA-nonidentical littermate platelet donors. In recipients previously immunized by a pool of six unrelated donors, the same percentage of recipients was refractory to DLA-identical littermate donors as had been observed following only DLA-identical platelet transfusions. This suggests that non-DLA immunizing platelet antigens, not shared between approximately 30% of DLA-identical littermates, are well represented in a random canine population. However, prior random transfusions did not compromise long-term platelet support from 'truly' platelet compatible DLA-identical littermate donors. These studies indicate that single donor transfusions either from littermates or sequential unrelated donors are the most effective method of providing long-term platelet support. However, the use of pooled unrelated donor transfusions, followed by DLA-identical donors in immunized recipients is an equally acceptable alternative.