The clinical importance of choosing the right assay for detection of HLA-specific donor-reactive antibodies

Humoral immune response after kidney transplantation is enhanced by acute rejection and urological obstruction and is down-regulated by mycophenolate mofetil treatment

The anti-allograft immune response may have a cellular and a humoral component. Lymphocytotoxic antibodies (Ab) and anti-human leucocyte antigen (HLA) Ab present before kidney transplantation carry an enhanced risk of acute rejection. Current immunosuppressive drugs act predominantly upon the cellular immune pathway which may leave unopposed the humoral mechanisms of anti-allograft response. We studied the production of lymphocytotoxic Ab and anti-HLA Ab after kidney transplantation under different drug therapies. Two hundred and sixty-four consecutive kidney transplant recipients treated with different immunosuppressive drugs, either stable and or with previous acute rejection or acute urologic obstruction, entered this study. Lymphocytotoxic Ab and anti-HLA Ab were evaluated by complement-dependent cytotoxicity and by ELISA. Ab donor-specificity was determined by flow cytometry. Both lymphocytotoxic Ab and anti-HLA Ab were significantly increased in acute rejection whatever the immunosuppressive regimen and almost significantly in urologic obstruction treated with azathioprine (AZA) groups. The presence of antidonor-specific Ab was associated with a significantly higher rate of graft loss. Mycophenolate mofetil (MMF) therapy significantly down-regulated Ab synthesis in all patients groups when compared with AZA. The development of humoral antidonor response post-transplantation is associated with a dismal graft prognosis. This is the first report that acute urologic obstruction may be followed by unspecific lymphocytotoxic and anti-HLA Ab synthesis, surmising that a protracted obstruction may promote renal fibrosis through antibody mediation. The significant down-regulation of the humoral response by MMF when compared with AZA may herald a lower risk to mount a chronic rejection process.

Relationship of donor-specific class-I anti-HLA antibodies detected by ELISA after kidney transplantation on the development of acute rejection and graft survival

BACKGROUND

The objective of this study was to evaluate the role of post-transplant donor-specific anti-HLA antibodies (DS-HLA Abs) detected by an ELISA method on long-term graft survival.

METHODS

The serum pre-/post-transplant profile of anti-HLA Abs was analysed in 71 renal transplant patients by ELISA. The HLA specificity of positive sera was analysed by a different ELISA method. According to the results, patients were classified into two different groups: those who either developed DS-HLA Abs or significantly increased their panel-reactive antibody (PRA) (group A) and those who did not (group B).

RESULTS

Thirteen out of 71 patients showed post-transplant DS-HLA Abs and were included in group A, whereas the remaining 58 were placed in group B. The incidence of acute rejection (AR) was significantly higher in group A than in group B (77 vs 10%). In addition, seven out of eight patients from group A had graft loss secondary to AR, whereas one of nine grafts lost in group B was due to AR. When analysing the clinical outcome according to HLA class specificity, only patients with HLA-I Abs lost their grafts due to vascular AR. The remaining patients with HLA-II Abs who lost their grafts also had HLA-I Abs. In four of the eight patients who lost their grafts, DS HLA-I Abs were detected several days before AR.

CONCLUSIONS

The detection of DS HLA-I Abs in the post-transplant period may provide a good marker for AR and graft loss due to immunological origin. Monitorization of these Abs by ELISA may be a useful tool for tailoring immunosuppression after kidney transplantation.

Isolation of precursor endothelial cells from peripheral blood for donor-specific crossmatching before organ transplantation

BACKGROUND

The clinical importance of endothelial-cell (EC) antibodies (Abs) in allo-transplantation (Tx) has been reported. However, lack of a suitable method for isolation of donor-specific ECs has prevented routine detection of these Abs before Tx. We describe a quick and simple method for the direct isolation of ECs from whole blood, for routine crossmatching (XM) to detect anti-EC Abs.

METHODS

ECs were isolated using magnetic beads coated with Abs against the angiopoietin receptor Tie-2 that is expressed on EC precursors. A retrospective analysis of 50 previously well-characterized XM sera taken immediately before transplantation from patients with end-stage kidney disease were tested.

RESULTS

Tie-2+ cells expressed human leukocyte antigen (HLA) class I, class II, and other EC markers. Sera known to contain only EC-specific or EC- and monocyte (EM)-reactive Abs reacted positively with Tie-2+ cells but not with Tie-2- cells from the same individual. In addition, the Tie-2+ cells reacted with sera containing only HLA class I or class II Abs. In all, 3 of 25 sera from patients with stable graft outcome and no rejections reacted with Tie-2+ cells.

CONCLUSIONS

For the first time, with use of a single-target cell population, the detection of clinically relevant donor-specific HLA class I, class II, EM, and EC-specific Abs can be performed routinely before Tx. This method is promising because it is quick, specific, and easy to perform on whole blood samples and can therefore be used to perform routine donor-specific EC crossmatching (ECXM) in the future. Routine use of ECXM will aid in identifying better donor-recipient combinations and thus have a greater impact on transplant survival as compared with lymphocyte crossmatch (LXM).

Identification of the nonclassical HLA molecules, mica, as targets for humoral immunity associated with irreversible rejection of kidney allografts

BACKGROUND

A substantial portion of kidney allografted patients experience early acute rejection episodes and even irreversible rejections in the early posttransplantation period. The presence of HLA alloantibodies before grafting is associated with early immunological complications, but in many patients rejections and graft loss occur even in the absence of such antibodies.

METHODS

In this study, 748 serum samples taken before and at various time points after kidney transplantation from 139 patients were investigated for the presence, frequency, and specificity of kidney microvascular endothelial cell (KMEC)-reactive antibodies using major histocompatability class (MHC) I-related chain A (MICA) transfected cells and flow cytometry, antibody blocking experiments, and Western blotting. The ability of MICA-specific antibodies to fix complement and to induce a prothrombotic phenotype in KMECs was investigated.

RESULTS

A polymorphic, 62 kDa nonclassical HLA class I molecule is identified as a new target molecule for reactivity in sera from patients with irreversible rejections. Specific blocking and transfection experiments verified the target molecule as MICA. A significant correlation was established for pre- or posttransplantation MICA humoral immunity and graft loss (P<0.001). MICA-specific antibody titers increased in the posttransplantation period and were present before any signs of clinical rejection. MICA antibody-containing patient sera induced a prothrombotic phenotype in KMECs.

CONCLUSION

The increasing polymorphism detected at the MIC loci combined with the results of this study suggest that typing for the MIC loci and crossmatching for the detection of anti-MIC antibodies before transplantation should be used routinely. A better recipient-donor selection based on a negative crossmatch for both anti-donor HLA and MICA antibodies will decrease early graft rejections and losses.

Long-term kidney graft survival across a positive historic but negative current sensitized cross-match

BACKGROUND

The sensitive cross-match (XM) techniques that have been introduced for clinical transplantation can detect anti-donor immune reactivity despite a negative standard National Institute of Health (NIH) cross-match. One of them uses anti-kappa human light chain globulins (AHG). But there is some discussion about the clinical consequences of a positive AHG-XM in the historical sera that became negative in the sera collected just before the transplantation (pretransplant sera). This study was intended to assess the risk of kidney graft failure associated with a positive historic but negative pretransplant AHG-XM in allosensitized patients having a negative historic NIH-XM.

METHODS

This retrospective study includes 90 consecutive renal transplants in immunized patients performed at one center between 1985 and 1991. All of the patients had negative historical and pretransplant standard NIH lymphocytotoxic cross-matches and received the same immunosuppressive regimen. The AHG-XMs were done retrospectively using peak historic and sera collected on the day of the transplantation.

RESULTS

The AHG cross-match (AHG-XM) was positive in 17 patients, although the standard NIH cross-match was negative. Fourteen of them had a positive historical but negative pretransplant AHG-XM. The actuarial graft survival in this group of 14 patients was 100% at 1 year and 78% at 9 years compared with 90 and 67%, respectively, in patients with negative historical AHG-XM. In addition, the number of rejection episodes per patient as well as renal function at 1, 2, and 5 years were similar in the two groups. IgG anti-donor HLA class I accounted for the XM positivity in 12 of the 14 patients; most rapidly lost all antibody reactivity by NIH technique in an average time of 8 months before the transplantation. In conclusion, this study suggests that transplant patients having a negative historic NIH-XM but a positive historic AHG-XM may not be at high risk of graft failure especially if there is a well-documented sera history showing a marked decrease in PRA level before transplantation and a negative pretransplant AHG-XM.

HLA-specific alloantibodies and renal graft outcome

HLA-specific humoral immunity, as a result of recipient allosensitization, induces hyperacute rejection of allogenic kidney grafts. Cross-match tests are performed to avoid this complication. However, current techniques do not allow determination of HLA-specificity of donor-reactive antibodies in the acute cadaver-donor situation. New methods are described and discussed in this report as well as the alloantibody specificities that are of clinical importance. Alloantibodies not only mediate hyperacute rejection but may also participate in the acute rejection of organ grafts. Clinical associations between early immunological complications, such as acute rejection, in heart, liver and kidney allografted patients and pre-transplantation humoral alloimmunity emphasize the need for proper determination of donor-specific humoral immunity prior to transplantation.

Characterization of HLA class I specific antibodies by ELISA using solubilized antigen targets: II. Clinical relevance

Until recently, the nature of humoral sensitization to HLA has been characterized by data from lymphocyte-based assays, predominantly cytotoxicity tests. We have examined the characteristics, determined by enzyme-linked immunosorbent assay (ELISA), of sera from 191 subjects known to have produced HLA-specific antibody. We found that ELISA detected higher frequencies compared with cytotoxicity of many (74.5%), but not all, HLA-specific antibodies; in many cases (42.6%) the frequencies of these antibodies were higher than predicted from population frequencies whereas some antibodies (23.4%) occurred with lower than expected frequencies. Some of the increase in frequencies can be accounted for by crossreactivity, i.e., sensitization to epitopes shared among two or more allelic products. The presence of epitopes shared between a recipient's antigen and a mismatched antigen in a donor also tended to narrow the specificity of antibody produced. However the data also indicate differences in immunogenicity among different antigens suggesting that crossreactive group matching would be beneficial in some but not all cases. Finally, we present case studies to illustrate the value of ELISA in predicting humoral rejection episodes and in monitoring the efficacy of rejection therapies.

Human leukocyte antigen matching in renal transplantation: an update

Cadaveric kidney allocation, in most countries, is based on human leukocyte antigen matching of the donor kidney with the recipient. Traditional human leukocyte antigen matching is based on defining human leukocyte antigen specificities by antibodies. Newer techniques have emerged from the tissue typing laboratory, which challenge the accuracy of serological typing and crossmatching. Improvements in renal allograft survival, predominantly as a result of newer immunosuppressive drugs, have led to longer survival times even in poorly matched human leukocyte antigen renal allografts. The scarcity of donor organs has focused attention on organ allocation policies, and the exact role of human leukocyte antigen matching in renal transplantation is under scrutiny. In this review, we examine developments in human leukocyte antigen matching as well as attempts to utilize this information to allocate cadaveric kidneys optimally.