Posttransplant Lymphoproliferative Disorders (PTLD) After Renal Transplantation: Focus on HLA Antigens

PTLD is a lymphoid proliferation that develops as a consequence of immunosuppression. It represents monoclonal B-cell, or rarely T-cell, proliferations, occurring in a setting of decreased T-cell immune surveillance. It has been shown that HLA-B mismatching is associated with increased risk of skin cancer in recipients of renal transplants. An association between skin cancer related to human papillomavirus and HLA-A11 has also been established in this group of patients. Bakker et al has shown that HLA-B mismatching is a risk marker of PTLD. More specifically, Subklewe et al found that HLA-B18 and HLA-B21 were associated with increased risk of PTLD, whereas mismatch at HLA-A03 and HLA-DR7 level reduced the risk of PTLD. We therefore hypothesized that mismatch of certain HLA alleles may be risk predictors of PTLD after renal transplantation.

According to the national renal transplantation database of the Danish Society of Nephrology, 872 renal transplantations in 793 patients were performed at Aarhus University Hospital between 1990 and 2005. A total of 11 cases of PTLD were retrospectively identified through the National Danish Pathology database and individually reviewed by an experienced hematopathologist (KB). PTLD patients were investigated according to transplantation procedure, clinicopathological patient characteristics, type of lymphoma, outcome and HLA haplotype of both donor and recipient.

Univariate Cox regression analysis showed no positive correlation between risk of PTLD and number of HLA-B mismatches, or with HLA-A or HLA-DR mismatches. Conversely, we found a decreased risk with one/two HLA-B mismatches compared to no mismatches (p<0.01). With regard to specific alleles, HLA-B37 showed a trend towards an association with PTLD (OR = 8.62; 95% CI 1.70–43.6; P<0.04), whereas the same association was significantly stronger for HLA-DR6 (OR= 30.7; 95% CI 4.97–189.8; p<0.005). Unlike earlier reports, no association with HLA-B18 and HLA-B21 mismatches was observed.

Our data suggest not only that the risk of developing PTLD is unaffected by an increasing number of HLA-B mismatches, but that a low number of such mismatches may even protect against PTLD developement. In our analysis, we found a moderate correlation between PTLD and HLA-B37, and a stronger one with HLA-DR6. The latter observation has never been previously reported. Further analyses with larger cohorts of renal transplant patients are needed to clarify the role of HLA antigens as risk markers for PTLD in order to establish whether a pre-emptive PTLD monitoring of renal transplant patients expressing certain haplotypes/haplotype mismatches is justified.

No relevant conflicts of interest to declare.