Blood transfusions in organ transplant patients: mechanisms of sensitization and implications for prevention

Sensitization by previous pregnancies or transplants is considered unavoidable, but it is transfusions given to these patients that leads most often to broad sensitization. Both leukocytes and red cells carry a significant HLA antigen load, and residual leukocytes and/or red cell HLA may explain why leukocyte-reduced units are unable to prevent sensitization to any significant degree. Prevention of sensitization will require a more active effort to avoid blood transfusions, whenever possible. When transfusions are required, there is evidence that the use of HLA-matched blood or immunosuppression in selected situations may reduce sensitization, even in patients previously exposed to alloantigens. These additional measures are not logistically straightforward or devoid of risks and need to be confirmed by rigorous studies. However, remaining as passive observers when patients become broadly sensitized should no longer be considered an acceptable alternative for potential transplant recipients.

Value of posttransplant antibody tests in the evaluation of patients with renal graft dysfunction

Posttransplant HLA antibodies correlate with C4d positive rejection and decreased graft survival. However, the diagnostic value of various antibody tests in the management of patients presenting with graft dysfunction is uncertain. Whether all or some patients should be tested, how often, what antibodies to test for and how to interpret results in presensitized or transfused patients, are issues still unresolved. We tested for HLA and non-HLA antibodies by flow cytometry assays in 103 consecutive patients with graft dysfunction. The results show that: (1) C4d positive rejection was diagnosed in 75% of patients who developed posttransplant HLA antibodies, but only in 2% in antibody negative patients. (2) The correlation existed for donor specific IgG antibodies but not for IgM or nondonor specific IgG antibodies. (3) Weak antibody reactivity required confirmation by alternative testing as there were false positive results. (4) Posttransplant transfusions did not induce de novo HLA antibodies. (5) Negative antibody results were unlikely to turn positive after several months of follow-up. (6) Antibodies to the angiotensin II type 1 receptor, HLA-DP and MICA did not correlate with C4d+ rejection. We conclude that testing for posttransplant HLA antibodies is critical in narrowing the diagnostic alternatives in patients with graft dysfunction.

Susceptibility of liver allografts to high or low concentrations of preformed antibodies as measured by flow cytometry

Liver grafts are more resistant to damage by HLA antibodies than other organ allografts, but it is not clear if the antibodies are associated with graft rejection or graft loss, or if different antibody concentrations have different effects. To explore potential associations between antibody concentrations and outcome, preformed IgG antibodies against donor cells were quantified by flow cytometry in 465 consecutive liver transplant recipients. Antibody-positive patients were classified according to whether they had high or low antibody concentrations and analyzed for possible correlation with graft rejection or graft loss. The results showed that the incidence of rejection was not significantly different between antibody-positive and negative patients. However, patients with high antibody concentrations had a higher incidence of steroid-resistant rejections (31% at 1 year) than patients with low antibody (4%) or no antibody (8%, p < 0.0004). These effects were mainly due to T-cell (HLA class 1) antibodies. The overall incidence of rejection at 1 year was 69% for high antibody patients, 51% for patients with low antibodies and 53% for patients with no antibodies (p not significant). In an apparent paradox, antibody-positive patients underwent fewer early graft losses. Thus, the associations of preformed antibodies and outcome depend, on the one hand, on antibody concentrations, and on the other hand on whether the outcome measured is steroid-sensitive rejection, steroid-resistant rejection or graft survival. These complex interactions may explain the controversial results observed in previous studies.

Analysis of early deaths after isolated lung transplantation

STUDY OBJECTIVES

To determine the causes of death in patients dying within 30 days after lung transplantation at the University of Florida, to assess the importance of several diagnostic modalities for determining the causes of their decline, and to construct an algorithm for the evaluation of patients with severe respiratory compromise occurring early after lung transplantation.

DESIGN

Retrospective review of medical records and pathology slides from all patients dying within 30 days after lung transplantation, and biopsy specimen diagnoses from all lung allograft recipients at the University of Florida.

PATIENTS

Nine deaths occurred during the first 30 days after transplantation among 117 patients undergoing 123 isolated lung transplantation operations.

RESULTS

Infections accounted for the greatest number of deaths (bacterial pneumonia, four patients; catheter-related bacteremia, one patient). Persistent pneumonia confirmed by biopsy specimen was usually accompanied by histologic manifestations of acute cellular rejection and was associated with poor patient outcome (ie, death or subsequent development of bronchiolitis obliterans syndrome). In two patients, antibody-mediated rejection either was the immediate cause of death (hyperacute rejection, one patient) or preceded a fatal case of pneumonia (accelerated antibody-mediated rejection, one patient). Other causes of death included hypoxic-ischemic encephalopathy secondary to an intraoperative cardiac arrest (one patient), pulmonary venous thrombosis with bacterial colonization of the thrombotic material (one patient), and ischemic reperfusion injury (one patient). In most patients, more than one type of diagnostic technique was needed to ascertain the cause of the catastrophic decline.

CONCLUSIONS

The causes of early posttransplant death in our patient group included infections, antibody-mediated rejection, hypoxic-ischemic encephalopathy secondary to cardiac arrest, pulmonary venous thrombosis, and ischemic reperfusion injury. Because these processes often demonstrate overlapping clinical and morphologic features requiring multiple diagnostic techniques for resolution, a systematic multimodality approach to diagnosis is advantageous for determining the causes of decline in individual patients and for estimating the incidences of the different causes of early graft and patient loss in the lung transplant population.

What happens to renal transplant recipients who lose their grafts?

Little attention has been given to the fate of patients who lose their grafts. We reviewed outcomes of 438 recipients of first renal allografts who underwent transplantation at our institution between January 1, 1988, and December 31, 1997, and lost their grafts or died with a functioning transplant. Of the 438 patients, 168 patients died with a functioning transplant. The most common causes of death were cardiac disease, infection, and cancer. Patients who died with a functioning graft were older (>49 years, 64.3%) than patients who died after returning to dialysis therapy or who are still alive (>49 years, 25.9%). Eighty-six patients (39%) who returned to dialysis therapy were again placed on a cadaveric waiting list. Only 44 patients received a second transplant, of which 30 transplants (68.2%) are still functioning. Our study shows that relatively few patients who lose kidney transplants are returned to the cadaveric waiting list and even fewer undergo retransplantation.

OUTCOME OF KIDNEY TRANSPLANTS IN PATIENTS KNOWN TO BE FLOW CYTOMETRY CROSSMATCH POSITIVE1

BACKGROUND

The clinical significance of the flow cytometry crossmatch has been addressed in several retrospective studies, but the results have been controversial. There are no prospective studies in which patients known to be antibody positive underwent transplantation.

METHODS

The flow cytometry crossmatch was performed prospectively in 1130 renal transplant recipients. A decision to perform transplantation was based on whether the positive results were on T or B cells, in the current or peak specimen, and taking into account the presence or absence of other immunological risk factors. One hundred antibody-positive patients received a transplant. Graft survival and rejection episodes were analyzed in this group and compared with 100 crossmatch-negative patients matched for age, sex, race, and time of transplantation.

RESULTS

The incidence of rejection at 1 month was higher in antibody-positive patients (26%) than in antibody-negative patients (12%, P<0.01). Early rejection seemed to be more frequent in antibody-positive patients regardless of whether the antibodies were current or historic, or against T or B cells. There were more steroid-resistant rejections in antibody-positive than in antibody-negative patients. However, biopsy specimens showed that vascular lesions that can be associated with humoral rejection were not more frequent in the antibody-positive patients than in the controls. There were no differences in graft survival between the two groups.

CONCLUSIONS

Low-level preformed alloantibodies detected by flow cytometry represent a risk of rejection even for patients purposely selected for having no additional immunological risk factors. The risk seems to be due to donor-specific memory rather than to a direct effect of the antibodies. The results indicate that flow cytometry provides useful information to assess donor-recipient compatibility.

Infusion of donor spleen cells and rejection in liver transplant recipients

Intact or inactivated donor lymphoid cells have been found to downregulate the alloimmune response in a number of experimental models. We conducted a randomized, prospective, double blind, and placebo-controlled trial to determine whether heat-treated donor spleen cells would affect early rejection after liver transplantation. Donor spleen was obtained during organ procurement for 40 patients undergoing liver transplantation. All patients were treated with cyclosporine, azathioprine and steroids. The patients were randomized after surgery to receive either heat-treated (45 degrees C for 1 h) spleen cells or placebo. Patients underwent protocol biopsies at 1 wk, 4 and 12 months, or as needed. Biopsies were reviewed in a blind fashion and scored according to the Banff consensus criteria. Randomization resulted in 19 patients in the spleen cell group and 21 in the placebo group. One-yr graft survival was 94 and 100%, respectively. Early rejection was more frequent in the spleen cell group (61 vs. 35%, p, not significant). The histopathological rejection activity index at 7 d was also higher for the patients in the spleen cell group: 39% of spleen cell treated patients had a score of 4 or higher as opposed to 5% in the placebo group (p < 0.01). The mean score was 2.9 +/- 2.8 for the spleen cell group versus 1.3 + 1.7 for the placebo group (p = 0.034). It is concluded that heat-treated donor spleen cells given within 24 h after liver transplantation were not clinically beneficial and increased the intensity of rejection in 7-d protocol liver biopsies.

Susceptibility of lung transplants to preformed donor-specific HLA antibodies as detected by flow cytometry

BACKGROUND

Preformed anti-HLA antibodies are known to have the potential to induce early graft damage in organ transplant recipients. However, in lung transplant recipients, little information exists about the significance of preformed antibodies directed to either class I or class II HLA antigens.

METHODS

A two-color flow cytometry cross-match was performed in 92 consecutive lung transplant recipients using serum obtained immediately before transplantation. The presence of preformed antibodies was correlated with the incidence of severe graft dysfunction manifested as pulmonary infiltrates and severe hypoxemia with onset in the first few hours after transplantation.

RESULTS

Six patients (6.5%) had low-level anti-donor IgG antibodies detected by flow cytometry, four against T and two against B lymphocytes. Three patients (50%) developed severe graft dysfunction with pulmonary infiltrates and hypoxemia. Two patients responded to treatment, but the third, who had an antibody highly specific for HLA-DR11, died at 48 hr after transplant. Results of histopathologic studies in this patient are consistent with hyperacute rejection and support a pathogenic role of these antibodies. In contrast, of 86 (93.5%) cases with a negative flow cytometry cross-match, only 4 (5%) had severe but reversible early graft dysfunction with pulmonary infiltrates and hypoxemia, attributed to ischemia-reperfusion injury (P<0.005).

CONCLUSIONS

Class II, and perhaps class I HLA antibodies at relatively low concentrations represent a risk factor for severe early pulmonary graft dysfunction, with the potential to progress to hyperacute rejection and death.

Poststreptococcal reactive arthritis: clinical characteristics and association with HLA-DR alleles

OBJECTIVE

To assess the relationship of poststreptococcal reactive arthritis (ReA) to other forms of ReA and rheumatic fever by comparing the frequency of HLA-B27 and DRB1 alleles in these diseases.

METHODS

The diagnosis of poststreptococcal ReA was established in 25 children seen in a pediatric rheumatology clinic. HLA-B27 and DRB1 genotyping was performed in 18 of the white American patients. The DRB1 genotyping results were compared with those in 33 patients with rheumatic fever and 190 normal individuals.

RESULTS

HLA-B27 was positive in 3 of the 18 poststreptococcal ReA patients, a frequency not different from that found in normal individuals. Compared with normal controls, the frequency of the DRB1*01 allele was higher in poststreptococcal ReA patients (odds ratio [OR] 2.7, P=0.044), while DRB1*16 was increased in patients with rheumatic fever (OR 4.3, P=0.028).

CONCLUSION

The association of poststreptococcal ReA with HLA-DRB1*01, but not with HLA-B27, suggests that its pathogenesis may be more similar to that of rheumatic fever than to that of ReA associated with enteric pathogens.

Multicenter evaluation of the flow cytometry T-cell crossmatch: results from the American Society of Histocompatibility and Immunogenetics-College of American Pathologists proficiency testing program

BACKGROUND

The performance characteristics and interlaboratory comparisons of the T-cell flow cytometry crossmatch remain largely unknown.

METHODS

This study was performed using data from the ASHI-CAP proficiency testing program. Four unknown sera and two unknown cells were sent to participating laboratories twice a year for 4 years.

RESULTS

In one survey in which different crossmatch techniques were compared, flow cytometry was slightly more sensitive than the antiglobulin method and considerably more sensitive than direct cytotoxicity. However, the proportion of participants in any given survey detecting antibodies in all sera expected to be positive was 50-60% and has not changed over the years. Failure to detect antibodies correlated with low antibody concentration, diluting the unknown serum by the testing laboratory, and with the instrument used. False positive results with normal sera were infrequent. Fluorescence intensity values were not standardized and were highly variable, but when fluorescence units reported by individual laboratories were divided by their own positive-negative cutoff values, results from different centers were more comparable. In general, fluorescence-to-cutoff ratios >5 correlated with complement binding activity, whereas values <5 denoted concentrations below those required to fix complement.

CONCLUSIONS

Flow cytometry, as used by most centers, is highly sensitive and allows relative antibody quantitation. Furthermore, the data define objective parameters that may help to standardize the test and improve its predictive value in clinical transplantation.

Antibody screening by enzyme-linked immunosorbent assay using pooled soluble HLA in renal transplant candidates

The enzyme-linked immunosorbent assay (ELISA) using HLA class I molecules purified from pooled platelets has the potential to detect HLA antibodies with increased efficiency without sacrificing sensitivity or specificity. This test, which was originally developed in our institution, has been independently validated by recent studies and is now commercially available. We now present evidence of its usefulness as a routine HLA antibody screening test for renal transplant patients. A total of 515 patients were tested monthly by ELISA (13.9 tests/patient) and by antiglobulin-enhanced panel reactivity (6.3 tests/patient). In patients found to be unsensitized, the incidence of false-positive results was less for ELISA than for the panel studies. In patients who were highly sensitized, both tests performed equally well, whereas discordant results were registered mainly in cases of mild sensitization. Because 66% of our patients were not sensitized, the ELISA was effective in reducing the number of more involved tests aimed at characterizing the antibodies. These results provide a foundation to use the pooled platelet HLA ELISA on a routine basis for HLA antibody screening.

Significance of preformed anti-donor antibodies in liver transplantation

The significance of a positive cross-match in liver transplantation remains controversial, as documented by a number of recent conflicting reports. In this study, we evaluated 195 consecutive orthotopic liver transplant recipients in whom the cross-match was either negative or positive for T or B cells. Special emphasis was placed on the outcome of patients with high levels of preformed IgG antibodies directed against donor T cells. IgG anti-donor antibodies were confirmed by flow cytometry in all cases. Of 10 patients with strong T-cell antibodies, there was one early death due to nonimmunological causes. Transplantation was successful in 9/10 patients followed for 3 months to 3 years. Graft survival, incidence of acute rejection, and number of liver biopsies in patients with a positive cross-match (strong T, weak T, or B cell) were not significantly different from those of patients with a negative cross-match. In the strong T cell antibody group, one patient had early graft dysfunction, with extensive hepatic necrosis and histological signs of antibody-induced damage. Two other patients also showed some evidence of possible antibody-mediated events, such as neutrophil infiltration and hepatocyte swelling. These lesions were reversible, and the patients had uneventful recoveries. Thus, in our experience, preformed antibodies did not preclude good graft survival.

Immune responsiveness and renal transplantation

Children and young adults produce lymphocytotoxic antibodies in response to blood transfusions more frequently than older patients. Young transplant recipients also have a higher incidence of rejection episodes, which lends support to the concept that young age is associated with a state of heightened immune responsiveness to alloantigens. Heightened immune responsiveness, however, does not explain the lower graft survival reported for Black transplant recipients. Black recipients have an increased rate of DGF, whose origin remains to be elucidated.

Detection of alloantibodies by flow cytometry: relevance to clinical transplantation

Before an organ transplant is performed, donor-recipient compatibility must be established by a crossmatch in much the same way as it is done for blood transfusions. The target antigens in organ transplantation, however, are HLA rather than blood group molecules, and the target cells are lymphocytes instead of red cells. If antidonor antibodies are detected, it is important to know whether they are IgG or IgM, whether they recognize T and/or B cells, and whether the antibody reactivity is weak or strong. These test requirements are better met by flow cytometry than by the standard cytotoxicity technique. A growing body of evidence now indicates that flow cytometry can provide more sensitive and timely crossmatch information than cytotoxicity assays to decide whether or not a transplant should be done. Flow cytometry crossmatch (FCXM) is a new and evolving technique that has already been found to be extremely useful in the clinical transplantation setting, even though significant questions yet remain about the precision and reliability of using flow cytometry to quantify alloantibodies and about the limits of normal reactivity in the assay. This article reviews important technical details of the FCXM and its interpretation and clinical application in transplantation medicine.

Increased antibody responsiveness to blood transfusions in pediatric patients

Heightened immune responsiveness has been proposed as one of the reasons underlying suboptimal renal transplant results in very young children or African American recipients. Because multiple factors influence graft outcome, it has been difficult to provide experimental evidence to confirm or refute this suggestion. In the present study we measured IgG antibodies with confirmed HLA specificity produced in response to blood transfusions. The patients evaluated were renal transplant candidates who had not had previous pregnancies or transplants. The overall incidence of HLA sensitization was 12%. Age was the most influential factor in sensitization: patients < 20 years old were 4-5 times as likely to produce anti-HLA antibodies than patients > 20 (P = 0.0018). Female patients were also high responders. However, this was explained by the higher proportion of children among nulliparous female patients rather than by differences in gender. In contrast, the antibody response of black and white recipients was similar. The antibody levels in most patients were low and decreased significantly with time. We conclude that the immunoregulatory influences in patients < 20 years old favor the production of anti-HLA antibodies in response to blood transfusions, a fact that may explain some clinical observations in pediatric transplant recipients.

Increased incidence of rejection in patients with delayed graft function

Because of the difficulties in diagnosing rejection in patients with delayed graft function, such patients were routinely biopsied 7-10 days after kidney transplantation. We found histologic evidence of rejection in 48% of the cases during the lst month posttransplant, a proportion that was significantly higher than in patients with immediate graft function. Furthermore, the 2-year graft survival in patients with delayed graft function and rejection, but not in those without rejection, was significantly lower than in patients with immediate function. The results suggest that there is an association between delayed graft function and rejection and that rejection is the component responsible for the decreased graft survival previously reported for patients with delayed graft function.

The crossmatch in renal transplantation. Evaluation of flow cytometry as a replacement for standard cytotoxicity

Flow cytometry (FC) is increasingly being used as a crossmatch procedure in addition to the standard complement-dependent cytotoxicity (CDC) test. In fact, FC offers a number of advantages over CDC and has the potential to become the primary crossmatch technique for cadaveric donor renal transplantation. We evaluated this possibility in 230 patients crossmatched by both CDC and FC. The results showed that when the T cell crossmatch was negative by FC it was always negative by CDC, and that when the T cell results were positive by CDC (IgM antibodies excluded) they were also positive by FC. As expected, a number of tests were T cell-positive by FC but negative by CDC. A T cell CDC crossmatch was more likely to be positive when FC was positive for both T and B cells and when FC results were quantitatively higher. However, FC was unable to consistently predict a positive, dithiothreitol-resistant B cell CDC crossmatch. A policy to transplant patients with negative FC results (70% of the patients evaluated) and not to transplant sensitized patients with FC+ T cell results (10%) would allow us to make a final decision with only FC in 80% of the cases. Actual graft survival was similar for nonsensitized first-transplant candidates with positive (83%) or all patients with negative (86%) FC results. We conclude that FC is sufficient to make a final decision in most cases. Wider utilization will require improvements in the ability of FC to measure B cell antibodies and to quantitate antibodies to T cells.

Hepatitis C virus infection in kidney transplant recipients

To determine the prevalence and significance of hepatitis C virus infection in kidney transplant recipients, paired serum samples collected from 100 renal allograft recipients on admission for kidney transplantation and 1 yr after transplantation were tested for antibody to hepatitis C virus with second-generation enzyme immunoassay and recombinant immunoblot assay and for hepatitis C virus RNA with reverse transcription-polymerase chain reaction. Before kidney transplantation, hepatitis C virus antibody was detected with second-generation enzyme immunoassay in 18 patients (12 second-generation recombinant immunoblot assay-positive, 6 second-generation recombinant immunoblot assay-indeterminate). Nine of 12 second-generation recombinant immunoblot assay-positive and 2 of 6 second-generation recombinant immunoblot assay-indeterminate samples were hepatitis C virus RNA positive. In addition, 7 of 82 patients who had no detectable antibody on second-generation enzyme immunoassay or second-generation recombinant immunoblot assay were hepatitis C virus RNA positive. After kidney transplantation, hepatitis C virus antibody was detected in 19 patients (12 second-generation recombinant immunoblot assay-positive, 7 second-generation recombinant immunoblot assay-indeterminate, 14 seropositive for hepatitis C virus antibody). Eleven of 12 patients with second-generation recombinant immunoblot assay-positive results and 4 of 7 with second-generation recombinant immunoblot assay-indeterminate results were positive for hepatitis C virus RNA. Hepatitis C virus RNA was present in 28 patients 1 yr after kidney transplantation. Six patients appeared to have acquired active hepatitis C virus infection 1 yr after kidney transplantation (seroconverted to hepatitis C virus RNA positivity).(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme-linked immunoassay for anti-HLA antibodies--an alternative to panel studies by lymphocytotoxicity

In order to provide a simple and specific assay for the detection and quantitation of IgG and IgM anti-HLA antibodies in sera, HLA antigens purified from a pool of 240 random donor platelets were used to develop a solid-phase enzyme-linked immunoassay (EIA). The reference values for identifying the presence of IgG or IgM anti-HLA antibodies were determined by assaying sera from 39 healthy individuals without prior HLA alloimmunization. The assay was evaluated by studying sera from 122 patients who had been characterized previously for panel reactive antibodies by the lymphocytotoxicity assay (LCA). A significant linear correlation between two assays was noted (r = 0.8, P = 0.0001). Further analyses of the data demonstrated that the newly developed EIA has 100% specificity and 95.3% sensitivity as compared with the LCA. Additional studies revealed that patients whose PRA increased or decreased over time were in parallel with antibody levels measured by EIA. When the EIA was used to measure anti-HLA antibody titers, it was more sensitive than the LCA. Since the EIA is sensitive, specific, and technically less demanding, it should provide an useful alternative to reduce the number of the more laborious panel studies for monitoring anti-HLA antibody status in candidates for organ transplantation and recipients of blood transfusions.

Hyperacute and acute kidney graft rejection due to antibodies against B cells

Because of the perception of its uncertain clinical significance, the B cell crossmatch is not universally performed before renal transplantation. Even though sporadic cases of hyperacute rejection associated with B cell antibodies have been reported, doubts remain in light of other studies suggesting no effect on graft survival. This report describes 4 cases of graft rejection (3 hyperacute and 1 acute) that occurred in patients with anti-B-cell antibodies specific against donor HLA-DR or DQ antigens. Absence of anti-donor class I antibodies was confirmed in all cases by 2-color flow cytometry. Strong evidence for an antibody-mediated mechanism was found in one patient with anti-class I and anti-class II antibodies in serum transplanted with a class II mismatched kidney. In this case, only anti-class II antibodies were recovered in the eluate of the nephrectomy specimen. These four cases were compiled from three different institutions over a four-year period, which confirms the infrequent occurrence of these events. While anti-class II antibodies may not always be detrimental for graft survival, these results also confirm that they have the potential to cause hyperacute or acute graft loss. We conclude that the information provided by the B cell crossmatch should be available at the time that a decision to proceed with a renal transplant is made.

HLA epitope matching. Contribution of matched residues to epitopes recognized by alloantibodies

Applying absorption-elution techniques with homozygous typing cells and flow cytometry, a number of alloantibodies that recognized HLA-B62 but not B46 were identified. B62 and B46 are identical except in amino acids 66-76, which are probably recognized by the B62-specific antibodies. The patients who made these antibodies, however, had HLA antigens sharing amino acids 66-76 with B62, indicating that residues that are identical to the patient's own contribute to the antigenic determinants of foreign HLA molecules. Fine specificity analysis of most of these antibodies revealed that they recognized residues in the 66-76 segment in addition to other residues which were located in close proximity to this segment. We conclude that mismatched amino acid residues located in one part of the HLA molecule can interact with residues that are not different from those in the patient's own HLA molecules to form epitopes recognizable by alloantibodies. These findings should be helpful in improving our understanding of how to use current knowledge at the molecular level for the purpose of matching transplant donors and recipients.

Intramolecular specificity of anti-HLA alloantibodies

Recent descriptions of epitopes within HLA class I antigens recognized by mouse monoclonal antibodies are providing an antigenic map of such molecules. However, for transplantation purposes, it is crucial to understand the epitope specificity of alloantibodies. To investigate this issue, we performed sequential absorption/elution studies with serum from a broadly sensitized patient and homozygous typing cells (HTCs) which shared one HLA-A,B antigen with the patient. Antibody reactivity in the different eluates was measured by flow cytometry in a panel of 20 HTCs. These studies revealed two major findings: (a) There were multiple antibodies recognizing one HLA antigen. For example, there were 8 anti-B62 antibodies, 8 anti-B51, 5 anti-B57, 5 anti-B46, and 4 anti-B35. (b) The reactivity of most antibodies correlated highly with the presence of specific amino acids at a given position in the target HLA molecule. Such residues were absent in most HLA antigens not recognized by the antibody. Most of the target residues were located in the accessible alpha helices or connecting loops, but at least one antibody reactivity appeared to be influenced by residues located in the beta sheets. The HLA antigens evaluated in this study were those of the B5, B15, B17 cross-reactive group which have multiple epitopic sites. However, further studies are necessary to determine if alloantibodies directed to other HLA molecules will have a similar or more restricted degree of complexity.

Induction of erythrocyte HLA expression during interferon treatment and HIV infection

Although HLA antigens are present on the surface membrane of most cells, erythrocytes express little or no HLA. Occasionally red cells from normal individuals or patients with certain diseases express elevated levels of these molecules. The reasons for such variations are currently not understood. We report here that the expression of very high levels of HLA on erythrocytes occurs in response to interferon alpha given as a therapeutic agent for viral hepatitis. Increased expression became apparent after the second or third week of treatment, peaked at 3-4 months, and decreased at the end of the treatment period. This chronology suggests that elevated HLA expression is originated during erythropoiesis and persists throughout the lifetime of the erythrocyte. Furthermore, erythrocyte HLA expression did not correlate with changes of plasma HLA or beta 2-microglobulin concentrations and was not affected by in vitro chloroquine treatment, ruling out the possibility that HLA was adsorbed from plasma. Increased expression of HLA on erythrocytes was also demonstrated in patients infected with the human immunodeficiency virus, a disease in which increased production of endogenous interferon has been previously documented. We conclude that high HLA expression in red cells occurs in response to persistent interferon stimulation. Further studies will determine if this effect can also be produced by interferon tau or other factors.

Evaluation of individual specificities of class I HLA on platelets by a newly developed monoclonal antibody

In order to quantify each specific HLA-A or -B antigen on platelets, a monoclonal antibody against HLA heavy chains was developed and designated as 2F2 monoclonal antibody. This monoclonal antibody reacted on Western blot with platelet HLA from each of 10 individuals with different HLA phenotypes and precipitated all 35S-methionine-labeled HLA-A and -B antigens from three different Epstein-Barr Virus--transformed lymphoblastoid cell lines. The results indicate that the 2F2 monoclonal antibody recognizes an epitope shared by different HLA-A and -B antigens. The quantitative variation of specific HLA antigens on platelets was then studied in nine different donors by isoelectric-focusing gel electrophoresis and immunoblot using the 2F2 monoclonal antibody. The results of our studies showed that the shared HLA antigens such as A2, B35, and B62, varied three- to fivefold among different individuals and individual HLA-A or -B antigen was not equally expressed on a person's platelets. The relative quantities of specific HLA-A and -B antigens on lymphocytes were also noted to be the same as those on platelets. The finding suggests that differential expression of HLA specificities may not be restricted to platelets but is a more general phenomenon including other nucleated cells.

Renal transplantation: a 20-year experience at the University of Florida

Substantial gains have been made in both patient and graft survival during 20 years of transplanting kidneys at the University of Florida. The number of transplant recipients yearly has increased from six in 1966 to more than 100 in 1986. The use of immunosuppression reflects our evolving understanding of transplant immunology, with current morbidity and mortality rates considerably improved over those of the early years. This paper summarizes our transplantation experience over the past two decades.

Accurate quantitation of the low number of white cells in white cell-depleted blood components

A simple method of accurate quantification of low concentrations of white cells (WBCs) in WBC-depleted blood components was developed by using propidium iodide (PI) to stain the nuclei of WBCs. The method was validated by correlating the PI-determined WBC concentrations with those determined with Coulter S-plus IV counter in units of packed red cells (PRBCs) or random-donor platelets (RDPs). The correlations were linear and had coefficients of 0.99. The sensitivity of PI staining permitted the detection of concentrations of WBCs as low as 1 cell per microL of RDPs or 11 cells per microL of PRBCs. Therefore, PI staining will be useful in investigating the role of transfused WBC-depleted blood components in the prevention of primary alloimmunization to HLA antigens, as well in evaluating various new procedures with high efficiency in depleting WBCs from blood components.

Prevention of transfusion-induced broad sensitization in renal transplant candidates

Blood transfusions can induce broadly reactive anti-HLA cytotoxic antibodies, particularly in patients who have had previous transplants or pregnancies. To evaluate if HLA-matched transfusions were less immunogenic, renal transplant candidates at high risk of becoming sensitized were transfused with blood from partially or totally HLA-matched donors. The study was performed in multiparous patients who in addition had low level antilymphocyte antibodies detected by flow cytometry. Only 1/24 patients (4.2%) developed cytotoxic antibodies. Crossover studies were possible in 3 patients. In 2 patients the HLA-matched transfusions did not elicit a response, but the patients produced cytotoxic antibodies of broad reactivity when they were subsequently transfused with random donor blood. The third patient developed cytotoxic antibodies after transfusions mismatched for only one HLA-A,B antigen. Subsequent transfusions mismatched for a different antigen did not, in contrast, result in sensitization. These results demonstrate that HLA-matched transfusions, unlike regular and leukocyte-free transfusions evaluated in previous studies, can prevent sensitization in patients with a high probability of becoming untransplantable if transfused with random donor blood.

Posttransplant antidonor antibodies and graft rejection. Evaluation by two-color flow cytometry

The posttransplant production of antibodies against cryopreserved donor cells was studied in 50 consecutive cadaveric kidney graft recipients and in 23 additional patients selected for acute rejection. Serum was obtained twice weekly during the first 3 weeks posttransplant and then monthly for 6 months. IgM and IgG anti-T cell Abs were measured by 2-color flow cytometry. Results were analyzed in conjunction with the patients' demographics, previous sensitization, HLA-matching, posttransplant blood transfusions, incidence of delayed function, rejection episodes, and biopsy results. Antidonor antibodies, predominantly IgG, were detected in 19/48 (40%) of the patients proximate to the time of rejection. In contrast, antibodies were seen in only 2/22 (9%) of nonrejecting patients, and these antibodies were exclusively IgM. Younger patients were more likely to have antibody-mediated rejections. Cytotoxic antibody reactivity against panel cells developed or increased posttransplant in some patients, but it did not correlate with rejection. Previous sensitization and posttransplant transfusions favored the development of posttransplant panel reactivity but not of antidonor antibodies. Most rejections, including those associated with antidonor antibodies, were reversed by antirejection therapy. We conclude that antidonor antibodies are involved in a significant proportion of rejection episodes and that the damage induced does not necessarily culminate with loss of the graft.

Incidental and purposeful random donor blood transfusion. Sensitization and transplantation

We conducted a prospective study to gauge the frequency and degree of sensitization by transfusion and/or pregnancy in 797 candidates for first renal transplants. Sensitization was proportional to the number of blood transfusions. Multiple transfusions or a history of pregnancy without transfusions had similar effects on sensitization. The combination of transfusion and prior pregnancy resulted in sensitization of 1/3 of the candidates. Patients who were not sensitized and were accepted for 1-haplotype living-related donor grafts or first-cadaver donor grafts were transfused to receive a total of 5 units of packed red blood cells. Parous patients had an undue rate of antibody formation and alternate means of selecting and managing parous women are described. Nonparous candidates had a low rate of sensitization (8%) that did not prove an impediment to obtaining a transplant. Only 2% of prospective LRD graft recipients developed antibody against their intended donor. Transplant patients were generally managed with azathioprine and prednisone. One-haplotype LRD graft survival of protocol patients was 93.7% one year posttransplant, and 82.1% at 5 years. One-year CD graft survival was 77%. There was no reduction in graft survival when the interval between transfusion and transplantation exceeded one year. Random donor transfusion is effective in improving renal graft survival. Some recent multiinstitutional reports indicate a reduction or absence of the transfusion effect with current immunosuppression. Discarding blood transfusion as a preparation for transplantation may be ill-advised pending a prospective study.

Association between HLA phenotype and HLA concentration in plasma or platelets

To understand the relationship between HLA phenotype and plasma or platelet HLA better, concentrations of plasma and platelet HLA were measured in 215 individuals of known HLA phenotypes. Precise quantitation of HLA antigens was achieved by means of an enzyme-linked immunoassay using the W6/32 monoclonal antibody and purified HLA molecules. The mean plasma and platelet HLA concentrations were 2.04 +/- 1.67 micrograms/ml (+/- SD, n = 215) and 11.28 +/- 4.65 fg/cell (+/- SD, n = 213), respectively. Statistical analysis of associations between HLA phenotypes and plasma HLA revealed that the mean plasma HLA concentration of individuals with HLA-A23 or HLA-A24 was 1.4 (p less than 0.002) or 1.9 (p less than 0.001) times higher than those without these two HLA antigens. Furthermore, the mean plasma HLA concentration of individuals who have HLA-A26 was 25% less than those without HLA-A26 (p less than 0.05). In contrast, the only association between HLA phenotypes and HLA concentrations of platelets was observed in HLA-B7-positive individuals. The mean platelet HLA concentration of HLA-B7 individuals was 27% higher than those without HLA-B7 (p less than 0.005). This finding is in accordance with previous observations made on red blood cells. The results indicate that the HLA concentrations in plasma are regulated, at least in part, by genetic factors that are different from those regulating platelet HLA.

Late results of renal transplantation

A total of 315 (64%) of 491 primary cadaver and living-related donor transplants performed from 1975 through 1984 were still functioning at 24 months. These selected patients were examined further to assess the impact of several risk factors on late graft and patient survival. Black recipients, patients with underlying diabetes mellitus or hypertension, patients with poor renal function at 24 months, and recipients of cadaver grafts had significantly poorer long-term graft survival. Age greater than or equal to 40, diabetes or hypertension, poor 24-month function, and cadaver donor transplantation were associated with poorer long-term patient survival. Considerable improvement in graft survival at 24 months was seen in 1980-1984 compared with the earlier period, coincident with our adoption of routine pretransplant random donor blood transfusion. In contrast, long-term graft survival in patients with functioning graft at two years did not improve significantly over the same period. Although living-related donor transplants showed greater graft and patient survival than cadaver donor grafts by univariate analysis, no such advantage was demonstrated by multivariate analysis.

Evaluation of antibody synthesis in broadly sensitized patients

This study was conducted to evaluate the rate of lymphocyte antibody synthesis in broadly sensitized patients. Antibody synthesis was estimated utilizing two approaches. In one, the time required by the antibodies to reach half their original values was determined by quantitating their levels by flow cytometry over periods of several months. In the other approach we measured the rate at which antibodies rose after inducing an artificial reduction by means of plasma exchanges. Patients not previously transplanted and not transfused during the study period showed low antibody synthesis and decreasing panel reactivity. In most previously transplanted patients panel reactivity did not change during the observation period. However, some patients displayed low antibody synthesis activity whereas others produced antibodies at a high rate. Extensive studies in one patient demonstrated active antibody synthesis even though he had not been transfused for more than two years. The results suggest that while frequent plasma exchanges can reduce antibody concentrations, concomitant use of immunosuppression may be needed only in patients shown to be actively producing antibodies.

Class I HLA molecules on human erythrocytes. Quantitation and transfusion effects

HLA class I molecules were quantitated on erythrocytes from individuals expressing either high or low levels of such antigens. Quantitative determinations were accomplished using 125I-labeled Fab fragments of the anti-HLA monoclonal antibody W6/32 in a competitive binding assay. The experimental conditions of the test system were established using red cells from an individual found to express high levels of red cell HLA when examined by flow cytometry. The competitive binding assay met the requirements of ligand specificity and specific binding saturability. Scatchard analysis revealed that there were 1684 +/- 39 (mean +/- SD) HLA molecules/red cell. In two other donors in whom erythrocyte HLA was undetectable by flow cytometry specific binding of the 125I-W6/32 Fab fragments was clearly demonstrated, indicating the presence of HLA on red cells of these donors as well. The number of HLA molecules/red cell was estimated to be between 100 and 200 for these individuals. Thus, in a blood transfusion unit, the number of HLA molecules contributed by the red cells is comparable to that of the leukocytes. Blood highly depleted of leukocytes and platelets and selected from donors with low amounts of red cell HLA was not beneficial (when transfused to selected patients) in that their sensitizing effects were not significantly different from regular blood transfusions. These results show that the amount of HLA antigens on red cells, while low if compared with other cell types, is significant in terms of the absolute antigenic content of blood transfusions. They also show that transfusion of blood units containing HLA antigens in concentrations as low as can be achieved with current technology were not useful in preventing HLA sensitization in patients at risk.

HLA-A2 epitopes recognized by alloantibodies from broadly sensitized patients

Alloantibodies in broadly sensitized patients are difficult to characterize because they comprise mixtures with different specificities. By studying the ability of patients' sera to inhibit or enhance the binding of two anti-HLA-A2 monoclonal antibodies, BB7.2 and MA2.1, reactivity with A2 epitopes could be operationally defined. One group of patients had antibodies that inhibited the binding of both monoclonal antibodies. The inhibitory activity was removed by absorption with A2 positive cells but not with A28 or B17 positive cells. These alloantibodies apparently recognized the A2-Bw69 epitope also defined by the BB7.2 monoclonal antibody. In other patients, the inhibitory activity was removed by A2 and B17 positive cells, suggesting the involvement of the same epitope recognized by the MA2.1 monoclonal antibody. A third type of reactivity was detected in other patients. These alloantibodies enhanced the binding of BB7.2, inhibited MA2.1, and were absorbed by A2 and B17 positive cells indicating that the A2-B17 epitope was involved in these cases too. These studies underscore the potential value of monoclonal antibodies in dissecting the specificities of complex alloantibody mixtures.