Greater Impact of Living Donation Than HLA Mismatching in Short-Term Renal Allograft Survival

Introduction: Living donor kidney transplantation (LDKT) is accepted as first-line treatment for patients with end-stage kidney disease with advantages over deceased donor kidney transplantation (DDKT). Still, how the known detrimental effect of HLA mismatch (MM) may hamper these advantages remains unsettled. We sought to determine the effect of the degree of HLA MM, separately in deceased and living donor renal allograft outcomes. Methods: We evaluated all adults submitted to LDKT and DDKT at our center between 2006 and 2018. Their HLA MM was classified according to the British Society of Transplantation system in low mismatch (LM) (level 1-2) and high mismatch (HM) (level 3-4). Acute rejection (AR) and global or censored graft survival were the outcomes of interest. Recipients were followed up from transplant until death, graft failure or the end of 2020. Results: One thousand sixty-eight kidney transplant recipients were analyzed, 815 (76%) received a DDKT whereas 253 (24%) received an LDKT. From those submitted to DDKT, 95 (12%) had an LM and 720 (88%) had an HM, whereas in LDKT 32 (13%) had an LM and 221 (87%) had an HM. The AR at one year was 9% in the full cohort. Significant risk factors for AR were HM DDKT (OR:2.3, P=0.047) or HM LDKT (OR:5.6, P=0.003) (LM DDKT as reference), calculated panel-reactive antibody (cPRA) ≥5% (OR:1.9, P=0.040) and delayed graft function (DGF), (OR:3.2, P<0.001). Censored graft survival (CGS) at five years was 96% in the full cohort. Independent predictors for censored graft failure (CGF) were HM LDKT (HR:0.2, P=0.046) (LM DDKT as reference), AR (HR:2.7, P=0.008) and DGF (HR:2.2, P=0.017). Global graft survival (GGS) at five years was 91% in the full cohort. Independent predictors for global graft failure (GGF) were HM LDKT (HR:0.2, P=0.042) (LM DDKT as reference), recipient age (HR:1.8, P<0.001) and DGF (HR:1.8, P=0.006). No AR, CGF or GGF episodes were observed in the LM LDKT group. Conclusions: In our cohort, the level of HLA MM increased the risk of AR independently of donor type. Considering short graft survival, our results support the advantage of living donor vs deceased donor even with an increased HLA MM. However, its effect on long-term graft survival remains to be settled, emphasizing the need for further studies on this matter.