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Incidence of HLA class I antibodies following Islet cell transplant and the effect of HLA matching in graft function
Abstracts
S79
6.6 #85
INCIDENCE OF HLA CLASS I ANTIBODIES FOLLOWING ISLET CELL TRANSPLANT AND THE EFFECT OF HLA MATCHING IN GRAFT FUNCTION Anne M. Halpin,1 James Shapiro,2 Edmond Ryan,2 Breay Paty,2 Jonathan Lakey,2 Paticia M. Campbell.1 1Laboratory Medicine, Histocompatibility Laboratory, University of Alberta Hospital, Edmonton, AB, Canada; 2Clinical Islet Transplant Program, University of Alberta Hospital, Edmonton, AB, Canada Islet cell transplantation has been demonstrated to be a successful therapy for Type I Diabeties. Between March, 1999 and April, 2002, 34 patients received Islet cell transplants; 25 have completed transplant. Pre– transplant, Class I antibodies (Ab) were not detected in any recipients and all were C peptide negative. Currently, fifteen patients are greater than 1 year post tranplant. Most patients required 2 allografts. Post transplant sera (n ⫽ 124) were screened for HLA Class I Ab by GTI QuikScreen威 and/or CDC–AHG PRA by One Lambda LCT–1W60威 trays. The number of HLA mismatched (MM) A, B and DR antigens was calculated for each recipient, except one for which no DR typing as available. Correlation between HLA MM and the following patient groups was measured: Group A: C peptide pos, insulin independent (n ⫽ 17) Group B: C peptide pos, insulin dependent (n ⫽ 5) Group C: C peptide neg, insulin dependent (n ⫽ 3) Two of the patients in Group C are no longer on any immunosuppressive therapy. No patients in Group A or B have developed Class I Ab. One patient in Group C has developed a PRA of 67% with donor specific Ab, detected 5 months after removal of immunosuppression; PRA is currently being followed. The other such patient has not yet been screened since the cessation of immunosuppression. The average number of HLA MM antigens per recipient is 10.1; average number of repeat MM is 1.3. There is no correlation between the number of HLA MM antigens or repeat MM and Groups A, B, or C. Despite exposure to multiple MM antigens, no HLA Class I Ab were detected in any patients currently immunosuppressed. However, when immunosuppression is discontinued, there is a risk of developing donor specific Class I Ab and the PRA should be monitored. HLA matching does not appear to play a role in early graft survival under Sirolimus/Tacrolimus combined immunosuppression. More long–term monitoring of PRA and correlation between HLA matching and allograft function with a larger patient population needs to be done. Studies are currently underway to screen for HLA Ab by flow cytometry.
6.6 #86
USE OF HIGH DEFINITION BEADS FOR PREDICTING CROSSMATCH IN HIGH PRA PATIENTS Deborah O. Crowe,1 Angie Turner.1 1Transplant Immunology, DCI Laboratory, Nashville, TN The highly sensitized patient (PRA ⬎ 80%) presents a challenge for the HLA laboratory in determining antibody specificity and unacceptable antigens. Our laboratory put considerable effort into identifying unacceptable antigens and predicting negative crossmatches for our highly sensitized patients. Our initial attempt was to make a list of possible acceptable antigens based on self antigens and the CREG families of self antigens as well as cell types found to be negative on the HLA antibody screens. Unacceptable antigens were identified, if possible, from antibody screening and from CREGs of the known unacceptable antigens. Flow crossmatches were negative with only 49% of the predicted negative cells. The antibody specificities were then further fine–tuned using the flow reactions with the cells tested to identify additional CREG and HLA antibody specificites. After the unacceptable antigens were updated, additional flow crossmatches were done on cells predicted to be negative. The ability to correctly predict the Flow crossmatch improved to 62% (28/45). Recipient cells were not available for auto– crossmatches, which may explain some of the positive crossmatches. This approach to predicting negative crossmatches proved to be very time– consuming and expensive and not practical on a routine basis. With the development of high definition Flow PRA beads, we wished to determine if the beads could be used to more accurately predict unacceptable antigens. We tested 12 of the patients from this study in which there was previously a failure to correctly predict the crossmatch. Thirty– nine crossmatches were initially performed with these patients and only 12 were correctly predicted as negative (31%). Using the specificities obtained from the Flow Beads, only 8 cells were incorrectly predicted as Negative (80% correct prediction). Comparison of HLA specificity obtained using the High Definition Beads with CDC and Flow PRA illustrates that many specificities (especially against HLA–A) are often masked by when CREG specificities are present. The High Definition HLA antibody test is a great tool for identifying specificity in highly sensitized patients and should be used when determining unacceptable antigens for these patients.
S79
6.6 #85
INCIDENCE OF HLA CLASS I ANTIBODIES FOLLOWING ISLET CELL TRANSPLANT AND THE EFFECT OF HLA MATCHING IN GRAFT FUNCTION Anne M. Halpin,1 James Shapiro,2 Edmond Ryan,2 Breay Paty,2 Jonathan Lakey,2 Paticia M. Campbell.1 1Laboratory Medicine, Histocompatibility Laboratory, University of Alberta Hospital, Edmonton, AB, Canada; 2Clinical Islet Transplant Program, University of Alberta Hospital, Edmonton, AB, Canada Islet cell transplantation has been demonstrated to be a successful therapy for Type I Diabeties. Between March, 1999 and April, 2002, 34 patients received Islet cell transplants; 25 have completed transplant. Pre– transplant, Class I antibodies (Ab) were not detected in any recipients and all were C peptide negative. Currently, fifteen patients are greater than 1 year post tranplant. Most patients required 2 allografts. Post transplant sera (n ⫽ 124) were screened for HLA Class I Ab by GTI QuikScreen威 and/or CDC–AHG PRA by One Lambda LCT–1W60威 trays. The number of HLA mismatched (MM) A, B and DR antigens was calculated for each recipient, except one for which no DR typing as available. Correlation between HLA MM and the following patient groups was measured: Group A: C peptide pos, insulin independent (n ⫽ 17) Group B: C peptide pos, insulin dependent (n ⫽ 5) Group C: C peptide neg, insulin dependent (n ⫽ 3) Two of the patients in Group C are no longer on any immunosuppressive therapy. No patients in Group A or B have developed Class I Ab. One patient in Group C has developed a PRA of 67% with donor specific Ab, detected 5 months after removal of immunosuppression; PRA is currently being followed. The other such patient has not yet been screened since the cessation of immunosuppression. The average number of HLA MM antigens per recipient is 10.1; average number of repeat MM is 1.3. There is no correlation between the number of HLA MM antigens or repeat MM and Groups A, B, or C. Despite exposure to multiple MM antigens, no HLA Class I Ab were detected in any patients currently immunosuppressed. However, when immunosuppression is discontinued, there is a risk of developing donor specific Class I Ab and the PRA should be monitored. HLA matching does not appear to play a role in early graft survival under Sirolimus/Tacrolimus combined immunosuppression. More long–term monitoring of PRA and correlation between HLA matching and allograft function with a larger patient population needs to be done. Studies are currently underway to screen for HLA Ab by flow cytometry.
6.6 #86
USE OF HIGH DEFINITION BEADS FOR PREDICTING CROSSMATCH IN HIGH PRA PATIENTS Deborah O. Crowe,1 Angie Turner.1 1Transplant Immunology, DCI Laboratory, Nashville, TN The highly sensitized patient (PRA ⬎ 80%) presents a challenge for the HLA laboratory in determining antibody specificity and unacceptable antigens. Our laboratory put considerable effort into identifying unacceptable antigens and predicting negative crossmatches for our highly sensitized patients. Our initial attempt was to make a list of possible acceptable antigens based on self antigens and the CREG families of self antigens as well as cell types found to be negative on the HLA antibody screens. Unacceptable antigens were identified, if possible, from antibody screening and from CREGs of the known unacceptable antigens. Flow crossmatches were negative with only 49% of the predicted negative cells. The antibody specificities were then further fine–tuned using the flow reactions with the cells tested to identify additional CREG and HLA antibody specificites. After the unacceptable antigens were updated, additional flow crossmatches were done on cells predicted to be negative. The ability to correctly predict the Flow crossmatch improved to 62% (28/45). Recipient cells were not available for auto– crossmatches, which may explain some of the positive crossmatches. This approach to predicting negative crossmatches proved to be very time– consuming and expensive and not practical on a routine basis. With the development of high definition Flow PRA beads, we wished to determine if the beads could be used to more accurately predict unacceptable antigens. We tested 12 of the patients from this study in which there was previously a failure to correctly predict the crossmatch. Thirty– nine crossmatches were initially performed with these patients and only 12 were correctly predicted as negative (31%). Using the specificities obtained from the Flow Beads, only 8 cells were incorrectly predicted as Negative (80% correct prediction). Comparison of HLA specificity obtained using the High Definition Beads with CDC and Flow PRA illustrates that many specificities (especially against HLA–A) are often masked by when CREG specificities are present. The High Definition HLA antibody test is a great tool for identifying specificity in highly sensitized patients and should be used when determining unacceptable antigens for these patients.