Introduction: Renal transplant success is affected by several long-term events; the main cause of graft loss is antibody-mediated rejection. These rejection events will occur more frequently the greater the pre-transplant immunological risk, which depends largely on the presence of anti-HLA antibodies (HLA-Ab) directed at the donor due to previous exposure to sensitizing factors. The impact of natural HLA-Ab (pretransplant HLA-Ab without exposure to sensitizing factors) has not been clarified. A better understanding of the risk groups, would help us to give us guidelines for the management of long-term immunosuppression. The objective of this study was to compare the immunological outcomes and graft survival according to exposure to sensitizing factors and the presence of pre-transplant HLA-Ab in kidney transplant recipients.

Methods: Retrospective study that included transplanted patients between January 2014 and December 2015. Four groups were compared, based on exposure to sensitizing factors and the presence of pre-transplant HLA-Ab. The relevant outcomes to be analyzed between the 4 groups were: generation of post-transplant DSAs, acute rejections, graft loss and deaths.

Results: 135 patients were evaluated, 51% female, with a mean age of 36±13 years. In patients with pre-transplant HLA-Ab, 50% had their persistence, and in patients without pre-transplant antibodies, 33% generated de novo HLA-Ab with a wider difference after the third year. The last control shows us that more than 50% of patients with HLA-Ab before transplantation and with exposure to sensitizing factors. The AMR events were more frequent among the groups with pre-transplant HLA-Ab of 37% and 36% with and without exposure to sensitizing factors, respectively and followed by the group with exposure to sensitizing factors and without HLA-Ab of 24%. As expected, the importance of post-transplant DSA in the incidence of AMR is highlighted.The groups with HLA-Ab before transplant, regardless of exposure to sensitizing factors, show a trend to lower graft survival, although it does not reach statistical significance (p=0.067).

Conclusion: This study shows a negative impact of the presence of HLA-Ab before transplantation including natural HLA-Ab. Therefore, it is essential to carry out compatibility studies and measurement of HLA-Ab before transplantation for adequate stratification of immunological risk, in addition to post-transplant monitoring of antibodies as a useful and effective surveillance tool.