Fiona Hudson

Since its inception in the early 1960s, the serologically based complement-dependent cytotoxicity (CDC) assay has been the cornerstone technique for the detection of human leucocyte antigen (HLA) antibodies, not only in pre-transplant renal patients, but also in other forms of organ transplantation. Recently, solid phase assays have been developed and introduced for this purpose, and in particular the Flow-based bead assays such as the Luminex system. This latter assay has proved to be far more sensitive than the CDC assay and has revealed pre-sensitization in potential transplant recipients not detected by other methods of HLA antibody detection. However, the clinical implications of this increased sensitivity have not been convincingly demonstrated until recently. This technology for HLA antibody detection permits the evaluation of the clinical importance of antibodies directed at, for example, HLA-DPB1 and HLA-DQA1, which has not been possible to date. There are Luminex issues, however, requiring resolution such as the ability to distinguish between complement fixing and non-complement fixing antibodies and determination of their relative clinical significance. Luminex technology will permit a re-evaluation of the role of HLA antibodies in both early and late antibody-mediated rejection.

Rituximab may improve graft survival in renal acute antibody-mediated rejection (AMR), but data confirming efficacy and optimal dosing is lacking. High-dose regimens may be associated with significant rates of infective complications. We therefore conducted a pilot study of a single low-fixed dose (500 mg) of rituximab in seven consecutive patients with AMR resistant to standard therapy. After a mean follow-up of 21 months (range, 9.5-33 months), graft and patient survival were 100% with serum creatinine levels significantly lower than peak rejection levels (171+/-73 micromol/L vs. 559+/-358 micromol/L, P=0.028). B cells were undetectable in all patients for more than or equal to 6 months and in six of seven patients for more than or equal to 12 months after rituximab. Three patients encountered a significant infective complication including cytomegalovirus reactivation, viral pneumonia, and polyoma viral nephropathy. All have since resolved. A single low-fixed dose of rituximab may help improve graft survival in AMR and offers the potential advantage of reduced infective complications.

BACKGROUND AND AIM OF THE STUDY: As the cause of allograft heart valve degeneration is poorly understood, the study aim was to investigate the host antibody response to allograft valve implantation. METHODS: Sera were obtained from 92 recipients of allograft heart valves (61 pulmonary, 31 aortic). Sera were tested for anti-HLA class I antibodies by ELISA and complement-dependent cytotoxicity (CDC) methods, and anti-HLA class II antibodies by ELISA. Specificities of recipient anti-HLA class I antibodies were defined by standard CDC testing against a panel of T lymphocytes from 80 blood donors. Donor valve HLA typing was performed on stored donor DNA samples using molecular methods. The presence of donor-specific anti-HLA class I antibodies was hence defined in recipient sera. The presence of anti-HLA antibodies and donor-specific anti-HLA class I antibodies were correlated with function of allograft valves at the most recent echocardiographic follow up. RESULTS: At a mean of 3.0 years (range: 0.3-5.4 years) after allograft implantation, 96% (87/92) and 82% (75/92) of patients were positive for anti-HLA class I and II antibodies, respectively, by ELISA testing. Some 68% (61/90) of patients were positive for anti-HLA class I antibody (PRA > 5%) by CDC testing. PRA levels decreased with greater postoperative interval (r = -0.31, p = 0.003). In 68 recipients where donor HLA type was defined, 54% (37/68) of patients had antibodies specific to at least one donor HLA class I antigen. In 87 patients with a recent echocardiographic examination available for analysis (at a mean of 3.5 +/- 1.6 years postoperatively), there was no association between valve dysfunction and antibody status. CONCLUSION: Anti-HLA class I and II antibodies were detected by ELISA methods in most patients after allograft implantation extending to 5.4 years. The clinical significance of these findings is unclear, as no correlation was found between the prevalence of anti-HLA antibody and echocardiographic parameters of valve dysfunction at a mean of 3.5 years follow up.

Tissue typing is the process by which an individual's human leukocyte antigens (HLA) are determined. In transplantation, this vital process allows the immunologic or rejection risk of a donor-recipient pairing to be assessed through reviewing their HLA matching and whether any anti-HLA antibodies present in recipient serum are donor specific. Tissue typing has increased in sophistication over time which has allowed a deeper appreciation of the antigenically important parts of HLA and increased the complexity of determining immunologic risk.