Blood transfusions (BT) are administered prior to kidney transplantation, as an immunomodulating treatment to extend graft survival. Several variables are known to influence the final clinical effect of pretransplantation BT, including the number of transfused leukocytes and the degree of HLA matching between blood donor and recipient. Presumably, tolerization takes place because alloreactive recipient cells are anergized or deleted, in the presence of donor-derived cells or antigens. However, the kinetics of this process require further study. The persistence of allogeneic (blood donor type) DNA following blood transfusion might be a predictive parameter for the effect of BT on kidney graft survival. In this study, the duration of microchimerism was analyzed in relation to HLA matching between blood donor and recipient, as well as in relation to the method of leukocyte depletion used for the transfusate preparation.
Thirty-eight patients on the waiting list for kidney transplantation were transfused with, packed red cells, buffy-coat-depleted, prepared by the Amsterdam Blood Bank.
Prior to 1995, buffy coats were manually separated from packed cells. Since 1995 an automated blood separation system has been in use (Compomat ®, NPBI, Amstelveen, The Netherlands). Numbers of leukocytes were estimated as follows: for the period before 1995, values were taken from the annual quality control report for 1991 of the Amsterdam Blood Bank; for the current period, transfusate samples were analyzed in our own laboratory. HLA-matched blood transfusions were defined as having at least one HLA-B and one HLA-DR antigen shared between donor and recipient, while transfusions with no HLA-B and one HLA-DR shared were termed "mismatched". Serial blood samples were drawn from the recipient before and at several time points after blood transfusion. Microchimerism was determined by means of a nested PCR on genomic DNA, in which a donor-type (mismatched) HLA gene was amplified. PCR's were developed for the detection of microchimerism of several common antigens, namely HLA-DR3, HLA-DR7, HLA-DR15, and HLA-A24. All BT recipients in this study were shown to be negative for the discordant antigen prior to BT. Each PCR test included standard controls for sensitivity and contamination, as well as a positive control derived from the BT donor.
HLA-matched BT led to longer persistence of microchimerism than unmatched BT, regardless of how the packed cells were prepared. In patients treated before 1995, the difference between matched and unmatched BT was most pronounced one week after BT (p<0.05, Fisher's exact test), and this trend continued till at least 4 weeks after BT. Transfusates prepared after 1995, using automated blood separation, gave rise to fewer cases of microchimerism, and shorter duration of microchimerism, than transfusates prepared by the manual method. This difference is probably due to the lower number of leukocytes in the packed red cells produced by the Compomat® as compared to manually prepared packed cells (mean ± SD respectively 5.0 ± 2.6 x 100 milion and 7.7 ± 3.5 x 100 million, two-tailed P value <0.0001 by unpaired t-test with Welch correction). Variation in the production method of packed cells might also influence the effectiveness of BT on kidney transplant survival. |
