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Flow PRA to detect clinically relevant HLA antibodies
Flow PRA to Detect Clinically Relevant HLA Antibodies H.M. Gebel, R.A. Bray, J.A. Ruth, G.B. Zibari, J.C. McDonald, B.D. Kahan, and R.H. Kerman
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ECENT studies have suggested that nonsensitized renal allograft patients could be safely transplanted independent of a pretransplant crossmatch.1,2 In those studies, patients were defined as nonsensitized based on 0% panel reactive antibody (PRA) activity assessed by antihuman globulin augmented complement-dependent cytotoxicity (AHG-CDC). Separate studies3 have revealed that 20% to 30% of 0% AHG-CDC PRA sera contained true HLA antibodies when assessed using solid-phase, HLA antigen specific assays such as ELISA and FlowPRA. However, the FlowPRA approach also identified HLA antibodies in nearly 10% of sera with 0% PRA by ELISA, indicating that the FlowPRA assay is the most sensitive technique currently available to detect HLA antibodies.3 In the present study, we evaluated whether renal allograft recipients with pretransplant HLA antibodies detected exclusively by the FlowPRA assay were at greater risk for graft rejection than patients without such antibodies. Specifically, pretransplant sera from 47 cyclosporine–prednisone treated “nonsensitized” primary renal allograft recipients (0% PRA by AHG and ELISA; AHG-donor crossmatch negative) were assessed by FlowPRA. Sera from 23% (11/47) of the patients had FlowPRA-detectable antibodies. Although none of the FlowPRA antibody-positive patients experienced hyperacute or accelerated rejection, episodes of graft rejection requiring therapeutic intervention were more likely to occur among FlowPRA antibody-positive patients (36%, 4/11) than in patients with no pretransplant antibody (8%, 3/36; P ⬍ .02). Furthermore, the mean time to a first rejection episode was 100 versus 250 days for patients with FlowPRA antibody compared to patients without antibody. Specificity analysis of the pretransplant HLA antibodies revealed that these HLA antibodies were associated with rejection even when donor reactivity was absent. Why and how nondonor
© 2001 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
directed HLA antibodies correlate with rejection is an enigma. It is known that when a specific HLA antibody is generated in response to humoral epitopes during a stimulation event (eg, blood transfusion, previous transplant), there is simultaneous stimulation of T cells responding to cellular epitopes on the same HLA molecule. We speculate that cellular epitopes can be shared among HLA molecules that are serologically distinct. In this model, the increased incidence of rejection in patients with nondonor-directed HLA antibodies would occur due to restimulation of memory T cells by indirect presentation of donor-derived HLA peptides shared with the original sensitizing antigen.4,5 The nondonor HLA antibodies would not contribute directly to the rejection episode but would be surrogate markers of T-cell sensitization.6 Collectively, our data suggest that pretransplant HLA antibodies detected exclusively by FlowPRA are risk factors for posttransplant rejection in renal allograft recipients. REFERENCES 1. Kerman RH, Susskind B, Ruth J, et al: Transplantation 66:1833, 1998 2. Matas AJ, Sutherland DE: Transplantation 66:1835, 1998 3. Gebel HM, Bray RA: Transplantation 69:1370, 2000 4. Gould DS, Auchincloss H Jr: Immunol Today 20:77, 1999 5. Gebel HM, Tambur A: J Heart Lung Transplant 14:1031, 1995 6. Tambur AR, Bray RA, Takemoto SK, et al: Transplantation (in press)
From LSUMC, Shreveport, Louisiana; Emory School of Medicine, Atlanta, Georgia and UT Medical School, Houston, Texas. Address reprint requests to H.M. Gebel, Department of Surgery, 1501 Kings Highway, Shreveport, LA 71130.
0041-1345/01/$–see front matter PII S0041-1345(00)02100-X 477
Transplantation Proceedings, 33, 477 (2001)
R
ECENT studies have suggested that nonsensitized renal allograft patients could be safely transplanted independent of a pretransplant crossmatch.1,2 In those studies, patients were defined as nonsensitized based on 0% panel reactive antibody (PRA) activity assessed by antihuman globulin augmented complement-dependent cytotoxicity (AHG-CDC). Separate studies3 have revealed that 20% to 30% of 0% AHG-CDC PRA sera contained true HLA antibodies when assessed using solid-phase, HLA antigen specific assays such as ELISA and FlowPRA. However, the FlowPRA approach also identified HLA antibodies in nearly 10% of sera with 0% PRA by ELISA, indicating that the FlowPRA assay is the most sensitive technique currently available to detect HLA antibodies.3 In the present study, we evaluated whether renal allograft recipients with pretransplant HLA antibodies detected exclusively by the FlowPRA assay were at greater risk for graft rejection than patients without such antibodies. Specifically, pretransplant sera from 47 cyclosporine–prednisone treated “nonsensitized” primary renal allograft recipients (0% PRA by AHG and ELISA; AHG-donor crossmatch negative) were assessed by FlowPRA. Sera from 23% (11/47) of the patients had FlowPRA-detectable antibodies. Although none of the FlowPRA antibody-positive patients experienced hyperacute or accelerated rejection, episodes of graft rejection requiring therapeutic intervention were more likely to occur among FlowPRA antibody-positive patients (36%, 4/11) than in patients with no pretransplant antibody (8%, 3/36; P ⬍ .02). Furthermore, the mean time to a first rejection episode was 100 versus 250 days for patients with FlowPRA antibody compared to patients without antibody. Specificity analysis of the pretransplant HLA antibodies revealed that these HLA antibodies were associated with rejection even when donor reactivity was absent. Why and how nondonor
© 2001 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
directed HLA antibodies correlate with rejection is an enigma. It is known that when a specific HLA antibody is generated in response to humoral epitopes during a stimulation event (eg, blood transfusion, previous transplant), there is simultaneous stimulation of T cells responding to cellular epitopes on the same HLA molecule. We speculate that cellular epitopes can be shared among HLA molecules that are serologically distinct. In this model, the increased incidence of rejection in patients with nondonor-directed HLA antibodies would occur due to restimulation of memory T cells by indirect presentation of donor-derived HLA peptides shared with the original sensitizing antigen.4,5 The nondonor HLA antibodies would not contribute directly to the rejection episode but would be surrogate markers of T-cell sensitization.6 Collectively, our data suggest that pretransplant HLA antibodies detected exclusively by FlowPRA are risk factors for posttransplant rejection in renal allograft recipients. REFERENCES 1. Kerman RH, Susskind B, Ruth J, et al: Transplantation 66:1833, 1998 2. Matas AJ, Sutherland DE: Transplantation 66:1835, 1998 3. Gebel HM, Bray RA: Transplantation 69:1370, 2000 4. Gould DS, Auchincloss H Jr: Immunol Today 20:77, 1999 5. Gebel HM, Tambur A: J Heart Lung Transplant 14:1031, 1995 6. Tambur AR, Bray RA, Takemoto SK, et al: Transplantation (in press)
From LSUMC, Shreveport, Louisiana; Emory School of Medicine, Atlanta, Georgia and UT Medical School, Houston, Texas. Address reprint requests to H.M. Gebel, Department of Surgery, 1501 Kings Highway, Shreveport, LA 71130.
0041-1345/01/$–see front matter PII S0041-1345(00)02100-X 477
Transplantation Proceedings, 33, 477 (2001)