The relationship between flow cytometer crossmatch results and subsequent rejection episodes in cadaver renal allograft recipients

Image cytometry as an alternative to flow cytometry for the transplant histocompatibility crossmatch assay

The lymphocyte crossmatch is currently the only cell-based compatibility assay performed by histocompatibility laboratories for transplant purposes. While in many transplant programs the complement-dependent cytotoxicity crossmatch (CDCXM) remains in use, when available, the flow cytometry crossmatch (FCXM) is the method of choice because of its superior sensitivity and specificity. Unfortunately, the maintenance and cost of a flow cytometer is a considerable limitation for small histocompatibility laboratories. Therefore, in this study, we evaluated the use of the Cellometer Vision CBA image cytometer (Nexcelom Bioscience LLC, Lawrence, Massachusetts) as an alternative instrument to perform the crossmatch assay. The 3-color FCXM protocol was modified into two separate 2-color panel image cytometry crossmatches (IXMs), one for T cells and one for B cells. After initial serum and cell incubation, a cocktail consisting of PE/Cy5-conjugated anti-human CD3 or CD19 and PE-conjugated anti-human IgG F(ab')₂ was added to the T cell and B cell panels, respectively. The final cell preparation was added to a separate counting chamber. Images were captured using the Cellometer Vision CBA, an image cytometer designed for cell counting, size analysis and fluorescence intensity measurement. Thirty-nine IXMs were performed and compared with the FCXM. We obtained a concordance sensitivity of 94.1% and 100% and specificity of 100% and 88.9% for T cells and B cells, respectively. The linearity of the system was verified using dilutions of a sample containing known donor-specific anti-HLA antibodies (DSA) against the target cells. This feasibility study demonstrates that the FCXM test could be easily adapted to the Cellometer Vision CBA image cytometer without compromising specificity and sensitivity. The low instrumentation cost, minimal maintenance, and simple operation allow for efficient implementation or transition from the FCXM to the IXM method.

Clinical cytometry and progress in HLA antibody detection

For most solid organ and selected stem cell transplants, antibodies against mismatched HLA antigens can lead to early and late graft failure. In recognition of the clinical significance of these antibodies, HLA antibody identification is one of the most critical functions of histocompatibility laboratories. Early methods employed cumbersome and insensitive complement-dependent cytotoxicity assays with a visual read-out. A little over 20 years ago flow cytometry entered the realm of antibody detection with the introduction of the flow cytometric crossmatch. Cytometry's increased sensitivity and objectivity quickly earned it popularity as a preferred crossmatch method especially for sensitized recipients. Although a sensitive method, the flow crossmatch was criticized as being "too sensitive" as false positive reactions were a know drawback. In part, the shortcomings of the flow crossmatch were due to the lack of corresponding sensitive and specific HLA antibody screening assays. However, in the mid 1990s, solid phase assays, capable of utilizing standard flow cytometers, were developed. These assays used microparticles coated with purified HLA molecules. Hence, the era of solid-phase, microparticle technology for HLA antibody detection was born permitting the sensitive and specific detection of HLA antibody. It was now possible to provide better correlation between HLA antibody detection and the flow cytometric crossmatch. This flow-based technology was soon followed by adaptation to the Luminex platform permitting a mutltiplexed approach for the identification and characterization of HLA antibodies. It is hoped that these technologies will ultimately lead to the identification of parameters that best correlate with and/or predict transplant outcomes.

Back to the future: application of contemporary technology to long-standing questions about the clinical relevance of human leukocyte antigen-specific alloantibodies in renal transplantation

Luminex technology allows the accurate identification of human leukocyte antigen (HLA) class I and class II-specific antibodies at levels below the threshold detectable by either conventional complement-dependent lymphocytotoxicity or flow cytometry. The technology enables the analysis of complex antibody profiles in sensitized patients and gives improved definition of acceptable and unacceptable HLA specificities to guide donor kidney allocation. This helps to facilitate virtual cross-matching and avoid inappropriate shipping of kidneys for incompatible patients in distant centers. Luminex allows the cause of a positive cross-match test to be determined in a clinically relevant time scale and, when used in conjunction with lymphocytotoxic and flow cytometric cross-matching, it provides an assessment of the level of immunological risk in patients being considered as potential recipients for a particular donor kidney. Information is now emerging to enable the full clinical potential of Luminex to be realized.

Is Positive Flow Cytometric Cross-Match a Risk Factor for Early Cadaveric Kidney Graft Dysfunction?

INTRODUCTION

The final decision about transplantation is based primarily on a negative result of a complement-dependent cytotoxicity cross-match. The significance of a positive flow cytometric cross-match (FCXM) is unclear.

MATERIALS AND METHODS

From July 2002 to October 2004, FCXM was performed prior to cadaveric kidney transplantation in 63 patients aged 1.5 to 26 years (mean 13 +/- 5). Immunosuppression (not adjusted to results of FCXM) was considered standard (prednisone + mycophenolate mofetil or azathioprine + cyclosporine or rapamycin) in 57%, or "enhanced" (+ monoclonal antibodies and/or tacrolimus) in 43% of patients.

RESULTS

Immunoglobulin IgG and/or IgM antibodies against T and/or B cells were found in 14/63 patients (22.2%). The distribution of immunosuppressive regimens was similar for FCXM(+) and FCXM(-) patients. Deteriorated graft function (creatinine > or =1.5 mg/dL) or demand for dialysis was observed in 6/14 (42.9%) FCXM(+) group versus 6/49 (12.2%) in the FCXM(-) group. During the first month after kidney transplantation biopsy-proven rejection episodes occurred more frequently among the FCXM(+) than the FCXM(-) group: 21.4% versus 4.1%, respectively. During the first 3 months after transplantation two of four kidneys in the FCXM(+) group (14.3%) demonstrated histological evidence of rejection plus one case of immunological cause of graft failure later found to be associated with an extremely high panel-reactive antibodies that were absent before transplantation (altogether 21.4%). Only one kidney (2.0%) was lost due to rejection among the FCXM(-) group.

CONCLUSION

A positive flow cytometric cross-match should be considered an important risk factor for early kidney graft dysfunction.

Pancreas transplantation in crossmatch-positive recipients

BACKGROUND

Prolonged cold preservation time can unfavorably affect outcome in pancreas transplantation. To reduce this ischemic time, cadaver pancreas grafts, in selected cases, are sometimes transplanted before crossmatch results are known. We report our experience with pancreas transplants in recipients with either current or historically positive T- or B-cell crossmatches.

METHODS

Crossmatch-positive pancreas transplants were identified using a computerized database. T-cell crossmatches were performed using an antihuman-globulin-augmented complement-dependent cytotoxicity (CDC) test; B-cell crossmatches were performed using an extended incubation CDC test. All patients received anti-T-cell induction therapy and either cyclosporine (1987-1993) or tacrolimus-based (1994-2001) immunosuppression. More recent recipients (2000-2001) also received intravenous gamma globulin and postoperative plasmapheresis.

RESULTS

Between October 1, 1987 and March 31, 2001, of a total of 1076 pancreas transplants performed, 59 (5.48%) were crossmatch-positive. Of these, 8 had a current T-cell-positive crossmatch and 15 had a current B-cell-positive crossmatch. One recipient was both current B- and T-positive, and the rest were past B- and/or T-cell positive. One-year pancreas graft survival for current T- and B-cell crossmatch-positive transplants was 63% and 67%, respectively. T- or B-cell crossmatch-negative transplants had a 1-yr survival of 70%. In the T-cell crossmatch-positive group, four grafts are still functioning (follow-up range, 2-12 yr), one patient died with a functioning graft at 4 months, and four grafts failed (one each from pancreatitis, infection, primary nonfunction, and vascular thrombosis). No grafts were lost to rejection. In the B-cell crossmatch-positive group, six grafts are still functioning (follow-up range, 2-11 yr) and nine have failed (four from chronic rejection, three from vascular thromboses, and two from pancreatitis). Crossmatch-positive cases were significantly more likely to be retransplants (70.8%) than crossmatch-negative cases (14.8%, p < 0.0001). In a multivariate analysis, crossmatch positivity did not affect pancreas graft outcome, whereas retransplants had a significant impact on outcome (relative risk 1.84, p < 0.0001).

CONCLUSIONS

(: i) Pancreas transplants performed in the setting of a positive current crossmatch may have long-term function. (ii) With current immunosuppressive protocols, graft loss from hyperacute and acute rejection may be prevented in current crossmatch-positive pancreas transplants. Chronic rejection was only seen in B-cell crossmatch-positive cases. (iii) High rates of technical graft loss in crossmatch-positive cases may reflect a high frequency of retransplants in this group.

Improved flow cytometric detection of HLA alloantibodies using pronase: potential implications in renal transplantation

BACKGROUND

Flow cytomeric crossmatch (FCXM) has grown in popularity and has become the "standard of practice" in many programs. Although FCXM is the most sensitive method for detecting alloantibody, the B cell FCXM has been problematic. Difficulties with the B cell FCXMs have been centered around high nonspecific fluorescence background owing to Fc-receptors present on the B cells and autoantibodies. To improve the specificity and sensitivity of the B cell FCXM, we utilized the proteolytic enzyme pronase to remove Fc receptors from lymphocytes before their use in FCXM.

METHODS

Lymphocytes isolated from peripheral blood, spleen, or lymph nodes were treated with pronase and then used in a three-color FCXM. A total of 167 T- and B cell FCXMs using pronase-treated and untreated cells were performed. Testing used serial dilutions of HLA allosera (22 class I and 6 class II), with the titer of each antibody at one dilution past the titer at which the complement-mediated cytotoxicity anti-human globulin crossmatch became negative.

RESULTS

After pronase treatment, the actual channel values of the negative control in both T cell and B cell FCXMs declined from 78+/-10 to 57+/-4 (P<0.05) and 107+/-11 to 49+/-3 (P<0.00001), respectively. Pronase treatment resulted in improved sensitivity of the T and B cell FCXM in detecting class I antibody by 20% and 80%, respectively. In no instance was a false-positive reaction observed. In this study, pronase treatment improved the specificity of B cell FCXM for detecting class II antibodies from 75% to 100% (P=0.03). In no instance was a false-negative reaction recorded. Lastly, on the basis of these observations we re-evaluated three primary transplant recipients who lost their allografts because of accelerated rejection. One of the patients was transplanted across negative T and B cell FCXM, whereas the other two patients were transplanted across a positive T cell, but negative B cell, FCXM. After pronase treatment, T and B cell FCXMs of each patient became strongly positive, and donor-specific anti-HLA class I antibody was identi. fied in each case.

CONCLUSION

Utilization of pronase-treated lymphocytes improves both the sensitivity and specificity of the FCXM.

Plasmapheresis and intravenous immune globulin provides effective rescue therapy for refractory humoral rejection and allows kidneys to be successfully transplanted into cross-match-positive recipients

BACKGROUND

Hyperacute rejection (HAR) and acute humoral rejection (AHR) remain recalcitrant conditions without effective treatments, and usually result in graft loss. Plasmapheresis (PP) has been shown to remove HLA- specific antibody (Ab) in many different clinical settings. Intravenous gamma globulin (IVIG) has been used to suppress alloantibody and modulate immune responses. Our hypothesis was that a combination of PP and IVIG could effectively and durably remove donor-specific, anti-HLA antibody (Ab), rescuing patients with established AHR and preemptively desensitizing recipients who had positive crossmatches with a potential live donor.

METHODS

The study patients consisted of seven live donor kidney transplant recipients who experienced AHR and had donor-specific Ab (DSA) for one or more mismatched donor HLA antigens. The patients segregated into two groups: three patients were treated for established AHR (rescue group) and four cross-match-positive patients received therapy before transplantation (preemptive group).

RESULTS

Using PP/IVIG we have successfully reversed established AHR in three patients. Four patients who were cross-match-positive (3 by flow cytometry and 1 by cytotoxic assay) and had DSA before treatment underwent successful renal transplantation utilizing their live donor. The overall mean creatinine for both treatment groups is 1.4+/-0.8 with a mean follow up of 58+/-40 weeks (range 17-116 weeks).

CONCLUSIONS

In this study, we present seven patients for whom the combined therapies of PP/IVIG were successful in reversing AHR mediated by Ab specific for donor HLA antigens. Furthermore, this protocol shows promise for eliminating DSA preemptively among patients with low-titer positive antihuman globulin-enhanced, complement-dependent cytotoxicity (AHG-CDC) cross-matches, allowing the successful transplantation of these patients using a live donor without any cases of HAR.

Sensitization and sensitivity: defining the unsensitized patient

BACKGROUND

Since the landmark studies of Patel and Terasaki in the late 1960s, pretransplant cross-matching has been performed by HLA laboratories on a 24-hr/7-day basis. In fact, regulating agencies such as the American Society for Histocompatibility and Immunogenetics and the United Network for Organ Sharing have mandated prospective crossmatching for selected solid organ transplants. However, two recent publications (Transplantation 1998; 66: 1833; and Transplantation 1998; 66: 1835) have suggested a change to this approach. Specifically, those authors advocate the transplantation of non-sensitized individuals without a final prospective cross-match as a means to reduce cold ischemia time and the incidence of delayed graft function. Such considerations were predicated upon results generated by cytotoxicity-based antibody screening. We and others, however, have reported that a flow cytometric-based assay is a more sensitive method to detect alloantibodies than cytotoxicity. Furthermore, an increasing number of reports document that graft survival is improved among patients whose final flow cytometric crossmatches were negative compared to patients with positive flow cytometric crossmatches. Although we agree that it is reasonable to transplant truly non-sensitized patients without a prospective final crossmatch, our data demonstrate that a large number of patients deemed non-sensitized by cytotoxicity-based antibody assessment are, in fact, sensitized.

METHODS

Panel-reactive antibody (PRA) testing was performed with 703 sera from 527 patients. The patient population consisted of individuals awaiting either renal or cardiac transplantation. PRA evaluations were performed using lymphocyte cytotoxicity (antiglobulin-enhanced, complement-dependent cytotoxicity [AHG-CDC]) or assays (enzyme-linked immunosorbent assay [ELISA]; flow cytometry) in which solubilized HLA molecules were affixed to solid phase matrices.

RESULTS

PRA activity in 264 sera from 88 patients was evaluated by AHG-CDC, ELISA, and flow cytometry. Results among the three methods were concordant for 83% of these sera. Discordant results occurred with 32 samples and demonstrated a distinct hierarchy in the sensitivity of the three techniques to detect alloantibodies. None of the 32 sera were positive by AHG-CDC, 20/32 were positive by ELISA, and 32/32 were positive by flow cytometry. Subsequent studies revealed that, among 527 patients, 302 (57%) exhibited 0% PRA by AHG-CDC. Of these 302 AHG-CDC-negative patients, 76 (25%) had class I or class II antibodies detectable using a flow cytometric approach. Within the AHG-CDC-negative/flow cytometric-positive patients, PRA values exhibited a wide range (6-99%) for both class I and class II antibodies. The average PRA was 27% and 38% for class I and II, respectively. Retrospective flow cytometric crossmatches performed for 30 recipients of cardiac allografts whose AHG-CDC PRA were 0% revealed that 11/30 crossmatches were positive.

CONCLUSIONS

The concept of transplanting non-sensitized patients without a prospective final crossmatch is appealing and, if bona fide, clearly makes sense. However, our data demonstrate that how a patient is deemed non-sensitized is critical. The difference between AHG- and flow cytometric-based PRA testing is significant and can result in transplantation of alloimmunized patients considered to be non-sensitized. Therefore, we recommend that, if a transplant center chooses to forego a prospective final crossmatch, the decision to do so should be based on methods more sensitive than AHG-CDC.

Flow cytometry crossmatching as a predictor of acute rejection in sensitized recipients of cadaveric renal transplants

Flow cytometry crossmatching (FCXM) was developed as a more sensitive assay than the standard complement-dependent cytotoxicity crossmatch (CDCXM) for the detection of anti-donor antibodies, that mediate hyperacute rejection and graft loss in the early post-transplant period in renal transplant recipients. The role of FCXM in predicting long-term clinical outcome in renal allograft recipients is unclear. This study examines the role of FCXM in predicting long-term clinical outcome in highly sensitized recipients of cadaveric renal transplants. All patients (n = 100) with peak panel reactive antibody (PRA) levels > 30%, who received cadaveric renal transplants between 1/1/'90 and 12/31/'95 at our institution, were divided into FCXM + and FCXM - groups. The incidence of acute rejection was determined for each group during the first yr after transplant. Graft survival rates at 1, 2, and 3 yr, and creatinine levels were also compared between groups. FCXM + patients experienced a higher incidence of acute rejection during the first yr after transplant (69 vs. 45%), and a higher percentage of FCXM + patients had more than one episode of acute rejection during the first yr after transplant (34 vs. 8%) when compared to FCXM - patients. There was no statistically significant difference in 1-, 2-, or 3-yr graft survival between FCXM + and FCXM - patients (76 vs. 83, 62 vs. 80, 62 vs. 72%, respectively). These results suggest that sensitized FCXM + cadaveric renal transplant recipients have a higher incidence of acute rejection episodes in the first yr after transplant. Given the association of multiple rejection episodes with poor long-term allograft survival, FCXM may be a useful predictor of long-term clinical outcome in this sub-group of renal transplant recipients.

The application of flow cytometry to histocompatibility testing

Flow cytometry is a powerful technique that enables the sensitive and quantitative detection of both cellular antigens and bound biological moieties. This article reviews how flow cytometry is increasingly being used as histocompatibility laboratories for the analysis of antibody specificity and HLA antigen expression. A basic description of flow cytometry principles and standardisation is given, together with an outline of clinical application in the areas of pre-transplant cross-matching, antibody screening, post-transplant antibody monitoring and HLA-B27 detection. It is concluded that flow cytometry is a useful multi-parametric analytical tool, yielding clinical benefit especially in the identification of patients at risk of early transplant rejection.

Are all successful renal transplants really successful?

We previously described a small group of renal transplant recipients considered to have successful allografts statistically, but who did not benefit clinically. These were patients in whom the grafts survived greater than 6 months but less than 3 years. This expanded study evaluates 179 consecutive renal transplant recipients divided into three groups. Group 1 (n = 18), group 2 (n = 41), and group 3 (n = 120) have patients with graft survival less than 6 months, between 6 months and 3 years, and greater than 3 years, respectively. Mean age, cause of renal failure, HLA match, and immunosuppressive regimen were not statistically different in any group. The number of acute rejection episodes, number of hospitalizations, and number and seriousness of complications were significantly greater in group 2 patients compared with the other groups. Patients in group 2 experienced five times the number of acute rejections (P < 0.0001), three times the number of hospitalizations (P < 0.0001), and two times the number of complications (P < 0.0001) compared with group 3 patients. In conclusion, those transplant recipients whose grafts survived longer than 6 months but less than 3 years were the most unfortunate. They experienced repeated and serious complications and spent many days in the hospital at great expense. A study with more sensitive methods of detecting presensitization might impact on graft performance in the future.

Long-term graft survival is improved in cadaveric renal retransplantation by flow cytometric crossmatching

BACKGROUND

Cadaveric renal retransplantation is associated with a higher risk of early graft failure than primary grafts. A large proportion of those graft losses is likely attributable to donor-directed HLA class I antibodies, detectable by flow cytometry cross-matching but not by conventional crossmatching techniques.

METHODS

Long-term graft survival in a group of 106 recipients of consecutive cadaveric renal regrafts between 1990 and 1997, in whom a negative flow T-cell IgG crossmatch was required for transplantation, was compared with two other groups of cadaveric transplant recipients. The first group consisted of 174 cadaveric regrafts transplanted between 1985 and 1995 using only a negative anti-human globulin (AHG) T-cell IgG crossmatch. The second group was primary cadaveric transplants done concurrently with the flow group (1990 to 1997) using only the AHG T-cell IgG crossmatch.

RESULTS

The long-term (7 year) graft survival rate of flow crossmatch-selected regraft recipients (68%; n= 106) was significantly improved over that of regraft recipients who were selected for transplantation by only the AHG crossmatch technique (45%; n=174; log-rank=0.001; censored for patients dying with a functioning graft). Graft outcome for the flow cross-matched regraft recipients was not significantly different from that of primary cadaveric patients (72%; n=889; log-rank=0.2; censored for patients dying with a functioning graft). Finally, a positive B-cell IgG flow cytometric crossmatch had no influence on long-term regraft outcome.

CONCLUSIONS

The use of the flow T-cell IgG cross-match as the exclusion criterion for cadaveric renal retransplantation yields an improved long-term graft outcome over that obtained when only the AHG cross-match is used and has improved survival of regraft recipients to the level of our primary cadaveric renal transplant population.

Postoperative production of anti-donor antibody and chronic rejection in renal transplantation

To study the relevance of anti-donor antibody (ADA) to chronic rejection in kidney transplantation, we retrospectively examined the long-term kinetics of ADA by flow cytometric analysis. Among 537 recipients who underwent living-donor kidney transplantation between 1986 and 1994, 29 patients with chronic rejection (CR group) and 33 patients with stable graft function (ST group) were randomly selected for analysis. Patient serum taken 1 or 2 days before transplantation, serum taken 1 month after transplantation, and the most current serum were analyzed for the presence of ADA to donor T and B cells. In the CR group, IgG antibody to donor B cells of the most current serum was positive in 25 of 29 patients, whereas it was positive in only 5 patients in the ST group P<0.001. The mean fluorescent intensity of the antibody was also significantly higher in the CR group than that in ST group P<0.01. In contrast, IgG antibody to donor T cells of the most current serum was positive in only five patients in the CR group. No significant difference was observed in the pretransplant and 1-month posttransplant sera between the CR and ST groups. We conclude that the posttransplant production of IgG antibody to donor B cells seemed to be highly relevant to chronic rejection.

Clinical and economic impact of flow cytometry crossmatching in primary cadaveric kidney and simultaneous pancreas-kidney transplant recipients

We retrospectively compared the clinical and financial impact of a final cross-match by T cell flow cytometry (FXM) versus conventional complement-dependent cytotoxicity (CXM) in consecutive primary cadaveric kidney (K) and primary simultaneous cadaveric pancreas-kidney (SPK) transplant recipients. Mean follow-up was 14 months for both the K (range, 5-22 months) and SPK (range, 5-22 months) recipients. There were no instances of a positive CXM result if the FXM result was negative. However, 18 of the 102 (18%) K recipients and 11 of the 66 (17%) SPK recipients were FXM positive, CXM negative, but no grafts lost to hyperacute rejection in this group. In addition, patient survival, graft survival, incidence of acute rejection, and kidney and pancreas function (immediate and late) were not different in the FXM-positive versus the FXM-negative groups. Charges for the CXM and FXM methods were compared over a 6-month period. During that period, the FXM charges averaged $583 less per recipient than the CXM charges (58% reduction in charges), and the time required to perform the FXM method was 50% of that required for the CXM method. These results demonstrate that a clinical pathway for primary transplantation that utilizes the FXM rather than the CXM final cross-match is clinically safe, with no adverse effect on posttransplant outcome, reduces organ preservation time by shortening the waiting period for the final cross-match results, and significantly reduces the tissue typing charges. However, about 9% of all primary K and SPK recipients will be FXM positive, CXM negative on final cross-match and will be unnecessarily denied a transplant. In this study, we describe a method to identify these patients so that they can be tested by traditional CXM to avoid being denied access to donor organs.

No advantage of flow cytometry crossmatch over complement-dependent cytotoxicity in immunologically well-documented renal allograft recipients

The effect of flow cytometry crossmatches on clinical outcome was studied retrospectively in two groups of immunologically well-documented patients who had received transplants with a negative complement-dependent cytotoxicity crossmatch. The first group consisted of 114 consecutive renal allograft recipients, and the second group consisted of 76 immunologically at-risk recipients. Flow cytometry crossmatches were performed with current and historic sera. In group 1, positive flow cytometry (FC) crossmatches were shown in 15/114 (13%) recipients. Rejection occurred in 8/15 (53%) FC-positive versus 41/99 (41%) FC-negative recipients. The 1-year graft survival rate was 80% for FC-positive patients and 87% for FC-negative patients. Sixty-seven patients were nonsensitized patients; 4 of them had a positive FC crossmatch but no rejection episodes, graft loss, or patient loss. Of 47 retransplanted and/or sensitized recipients, 11 had a positive FC crossmatch. Rejection treatment was needed in 8/11 (73%) FC-positive patients compared with 19/36 (53%) FC-negative patients. Their 1-year graft survival rates were 73% and 81%. None of these differences reached statistical significance. Group 2 consisted of 76 at-risk recipients; 37 were retransplant patients and 39 were sensitized first-transplant patients. Twenty-one (28%) patients showed a positive FC crossmatch. Rejection episodes did not differ between the FC-positive (48%) and FC-negative patients (46%). There was no difference in 1-year graft survival rate (76% vs. 80%) or in 1-year patient survival rate (100% vs. 95%). We conclude that FC crossmatches in our patient group are not superior to the classical complement-dependent cytotoxicity crossmatches with regard to clinical outcome. On the contrary, transplantation with a mandatory negative FC crossmatch would have excluded 28% of the recipients from transplantation, who in fact are doing well.

Prevention of hyperacute rejection by removal of antibodies to HLA immediately before renal transplantation

BACKGROUND

Many patients with circulating antibodies to human leucocyte antigens (anti-HLA) are highly sensitised against renal transplantation and are liable to immediate graft loss through hyperacute rejection. Our aim was to find out whether removal of anti-HLA immediately before renal transplantation prevented hyperacute graft rejection.

METHODS

13 highly sensitised patients underwent cadaveric renal transplants immediately after immunoadsorption (IA) treatment to remove anti-HLA. Before IA, 12 patients had a positive crossmatch against donor cells either by cytotoxic or flow-cytometric assay; results for one patient were equivocal.

FINDINGS

Renal biopsy samples were obtained 20 min after removal of the vascular clamps in nine patients. There was no evidence of hyperacute rejection in six of the nine patients; the other three patients showed glomerular thrombosis but no other evidence of hyperacute rejection. Two of these three grafts were functioning at 31 months of follow-up. Six episodes of acute rejection occurred in five patients during the first month after transplantation and overall there were 13 rejection episodes in nine patients. At latest follow-up (median 26 months, range 9-42), 12 of 13 patients were alive and seven of 13 grafts were surviving with a median plasma creatinine concentration of 185 mumol/L (range 106-296) in the functioning grafts. No graft was lost as a result of classic hyperacute rejection.

INTERPRETATION

Immediate pretransplant IA can prevent hyperacute rejection and provide an opportunity for successful transplantation in highly sensitised patients.

Evaluation of the flow cytometric crossmatch. Preliminary results of a multicenter study

The flow cytometric crossmatch is a technique that is increasingly being used by clinical transplant laboratories. In this multicenter study by the British Society for Histocompatibility and Immunogenetics Flow Cytometry Group, a series of crossmatches were carried out to determine whether different centers obtained same results when performing the same crossmatch. There was greater than 80% agreement among participating laboratories on the results of 35/54 tests. There was no clear agreement in the remaining 20 cases. Quantitative analysis, estimating the number of cell-bound fluorescein molecules, demonstrated that differences in the criteria used by each center to define a positive crossmatch were responsible for some discordant results. When applied, definition of positivity based on the molecules of fluorescein increased concordance from 57.5% to 81.4%.l. These results suggest that a criterion for the interpretation of results based on quantitative analysis of bound antibody may be more reliable than methods in current routine use.

The clinical significance of post-transplantation non-HLA antibodies in renal transplantation

This study was undertaken to examine the clinical relevance of antibodies detected in the sera of patients following renal transplantation. The sera from 23 transplant recipients with acute rejection and 10 transplant recipients with diagnosed chronic rejection were tested against various epithelial, monocyte and endothelial cell lines (A549, HTB44, primary renal epithelial, U937 and Ea-hy 926). The test used for detecting binding antibodies was a simple, indirect immunofluorescence flow cytometric technique. The level of IgG antibodies directed against the test cell lines was examined in the sera of patients with mild or severe rejection and compared to those of patients showing no signs of rejection. Patients with chronic rejection were found to have increased levels of antibodies (IgG and IgM) when compared to patients with either end-stage renal failure or patients with stable post-transplant renal function. Antibodies detected by the present technique were directed against antigens found on all cell lines tested, and immunoblotting indicated that they were directed against non-HLA antigens. In conclusion, monitoring for the presence of such antibodies may provide a valuable prognostic indicator of graft rejection in renal transplant patients.

Transplantation and quality of care for end-stage renal disease: 1993

We describe a group of renal transplant recipients whose allografts are in general considered to be successful statistically, but who are not greatly benefitted clinically. Grafts in these recipients survive somewhat longer than 6 months, but generally less than 3 years. Many of these individuals are chronically ill. They have many hospitalizations, experience most of the complications associated with transplantation, and incur more mortality and less benefit. Research initiatives need to be focused on this group of patients. A major study of more sensitive methods of detecting presensitization might be beneficial.

Flow cytometric crossmatching in human organ transplantation

When donor class I directed 'warm' antibodies are detected by the conventional cytotoxic crossmatch preoperatively, there is a negative correlation with outcome in renal, liver, cardiac and pancreatic transplantation. When the cytotoxic crossmatch assay is negative and IgG antibodies to T donor lymphocytes are shown to be present in the recipient sera by flow cytometry then there is an increase in postoperative complications in renal transplants. This includes primary nonfunction and treatable rejection which in some cases results in graft failure. Since its introduction into clinical practice for recipient selection in Newcastle, the complication rate of rejection episodes, primary nonfunction and graft failure has been reduced. When applied to other organs there seems to be a definite detrimental association between a positive flow cytometric crossmatch preoperatively and rejection in cardiac transplantation, in some cases leading to death. The role in liver and pancreas transplants to date has not been determined. In the postoperative period there appears to be a limited role for the flow cytometric crossmatch in the detection of antibody prior to the first clinical episode of rejection. This has been applied to renal transplants but to no other organ.

A new method for determining anti-B cell antibodies and their specificity using flow cytometry

We describe a new flow cytometric B cell crossmatch method with improved sensitivity and specificity. It is based on the coating of B cell surface immunoglobulins with an unconjugated polyvalent anti-human immunoglobulin antibody. The method also provides a means for determining the specificity of anti-B cell antibodies and, potentially, for anti-HLA class II antibody specificity differentiation (DR, DQ or DP) in a binding inhibition test using mouse monoclonal antibodies directed against human HLA class II antigens.

Flow cytometric crossmatch and early pregnancy loss in women with a history of recurrent spontaneous abortions who underwent paternal leukocyte immunotherapy

OBJECTIVE

The purpose of our study was to evaluate the clinical significance of flow cytometric crossmatch in managing women with unexplained recurrent spontaneous abortions who have been immunized with paternal leukocytes.

STUDY DESIGN

Two-color flow cytometric crossmatch was performed after immunotherapy in 69 women with recurrent spontaneous abortions to detect maternal immunoglobulin G antibodies against paternal T lymphocytes. A positive flow cytometric crossmatch was determined by a > or = 20 channel increases (256 channel linear scale-log amplification) in the fluorescence intensity of the T-cell peak. We analyzed the clinical correlation between flow cytometric crossmatch results and subsequent pregnancy outcome in those patients using the Fisher exact test.

RESULTS

In 46 subsequent pregnancies among 69 immunized women the incidence of early subsequent pregnancy wastage was only 6 (17.1%) of 35 in flow cytometric crossmatch-positive patients and 7 (63.6%) of 11 in flow cytometric crossmatch-negative patients (p < 0.01).

CONCLUSIONS

These data indicate that a two-color T cell flow cytometric crossmatch predicts subsequent pregnancy outcome in patients undergoing immunotherapy for recurrent spontaneous abortion.

Kidney transplant monitoring by anti donor specific antibodies

Donor-specific anti-HLA antibodies were studied by cytotoxicity crossmatching (CTXM) and flow cytometry crossmatching (FCXM) in 117 kidney transplant candidates; the same study was carried out in 33 cadaver-donor kidney recipients, during the first 3 post-transplant months, for which donor cells were available. Pre-transport evaluation showed that 82.9% of subjects were CTXM negative/FCXM negative, 6.8% of patients were positive in both tests, and 10.3% were CTXM negative/FCCM positive. Post-transplant monitoring for donor-specific antibodies (Abs-DS) showed that nine recipients (27.3%) were FCXM positive; six of them were IgG+ and three IgM+. In comparing these results with the clinical course, a significant association between FCXM IgG+ and rejection episodes was observed (P < 0.01).

Lack of correlation between IgG T-lymphocyte flow cytometric crossmatches with primary renal allograft outcome

The flow cytometric crossmatch (FCXM) has been reported to be more sensitive and capable of detecting very low levels of antibodies than the normally used complement dependent cytotoxicity test. We studied both the two colour IgG T cell FCXM and CDC-XM in 146 renal allograft recipients, 111 primary and 35 regrafts, of which 26% (29/111) of 1st and 20% (7/35) of regrafts had a positive FCXM. There was no overall correlation between the FCXM results and early graft outcome in primary renal allografts. The FCXM did not appear to have any advantage over the CDC-XM in predicting graft outcome in unsensitized first grafts. In the small number of regrafts studied, a positive FCXM was associated with a higher degree of graft failure. FCXM can exhibit false negative results if sera are used solely neat although these prozone phenomena do not influence subsequent graft outcome.

Clinical applicability of the immunomagnetic beads technique for serological crossmatching in renal transplantation

The aim of the present prospective study was to investigate the clinical applicability of the immunomagnetic (IM) beads technique for serological crossmatching (XM) in renal transplantation. The IM XM were read after various periods of incubation, and the results were compared with those obtained by the conventional Kissmeyer-Nielsen (KN) technique. A total of 132 sera from 96 potential recipients were tested against cells from 62 donors. Eight-nine KN T-cell XM-negative renal allograft transplantations were performed, and the IM XM results were related to clinical 3-month follow-up data (incidence of primary non-function, never functioning grafts, graft losses and rejection episodes). The IM technique was clearly more sensitive than KN, and sensitivity increased markedly with increasing duration of incubation. KN-, IM+ reactions were predominantly found among sera from patients with panel-reactive antibodies (PRA, 2p less than 0.01), and thus probably caused by HLA antibodies. However, positive IM XM, appearing after more than 35 min of incubation, did not influence the overall clinical outcome in the observation period. With reading after exactly 35 min of incubation, XM results obtained by IM and KN techniques correlated well. Thus, we believe, that the IM XM technique will be as safe and effective in avoidance of hyperacute rejections as the conventional assay. In the present material, the incidence of primary nonfunction was significantly (2p = 0.0023) higher among PRA+ recipients compared to PRA- patients. To conclude, we recommended the IM technique with reading after exactly 35 min of incubation for easy, fast (70 min) and reliable XM, that is always possible to perform using peripheral blood.

The relevance of more sensitive ancillary crossmatch techniques in predicting early cadaver renal graft outcome

The predictive value of varying levels of antibody activity, its class and antigen specificity in sera of 81 recipients of cadaver renal allografts was evaluated. Recipients for transplantation were selected on the basis of a negative dye uptake T-cell crossmatch, after which the more sensitive 51Cr release technique was employed in a blind study using unseparated donor target cells. Recipient sera with peak panel reactivity and current samples were evaluated before and after reduction with dithiothreitol to destroy the IgM subclass. Double absorption with pooled platelets allowed antibodies against HLA class I antigens to be distinguished from those against HLA class II/non-HLA antigens. Optimal levels of cytotoxicity were established, giving a sensitivity of 73%. Data were assessed in terms of positive predictive value, and showed that conventional T-cell crossmatching is adequate for the primary transplant group, but more sensitive ancillary tests are indicated for regrafts. In this category of patients, IgG antibodies, whether against HLA class I antigens or HLA class II/non-HLA antigens, were highly predictive of early graft loss (positive predictive value 50%-100%). Using this protocol for patient selection, 1-month graft survival would have improved from 73% to 96%.