3962 BALANCING THE RISK OF ALLOIMMUNITY WHILE MINIMIZING IMMUNOSUPPRESSIVE THERAPY: A RETROSPECTIVE STUDY OF PAEDIATRIC KIDNEY TRANSPLANT RECIPIENTS

Abstract Background and Aims Kidney transplantation is the best treatment for end-stage kidney disease, but life with a kidney allograft comes with significant challenges. Many paediatric kidney transplant recipients (KTRs) experience side effects from immunosuppressive medication. Reducing the medication is often necessary, but the reduction comes with a risk of inducing alloimmunity. We aimed to describe the alteration in immunosuppressive medication after kidney transplantation, the reasons for the reductions, and the possible impact on alloimmunity. Method 49 paediatric KTRs aged 1-16 years, receiving a kidney allograft from 2009 to 2020 in a Danish single centre were retrospectively studied. The standard protocol for immunologically low risk KTRs was steroid-free immunosuppression with basiliximab as induction, tacrolimus and mycophenolate mofetil (MMF) as maintenance therapy. KTRs were screened for anti-HLA antibodies with mixed and single bead antigen kits. We defined reduced immunosuppression as a KTR receiving one; OR two immunosuppressive medications AND MMF below 600 mg/m2. Results 49 KTRs received a kidney allograft, two were ABO incompatible transplantations and six KTRs had pretransplant donor specific antibodies. The median age of the KTRs was 11 years (IQR 8), with a median follow-up time of 5 years (IQR 5). In total, 78% KTRs received standard immunosuppressive therapy (steroid free). 5-year death censored (one KTR died) graft survival was 88%, and the cumulative incidence of rejection was 4% (95% CI: -1.5; 5.5) within the first year. None of the six graft losses were related to alloimmunity. 11.4% developed de novo donor specific antibodies (dnDSA) within a median of 3.91 years (IQR 2.28; range: 2.22-9.20) from transplantation. At transplantation, 6% received reduced immunosuppressive medication increasing to 74% at year one. Immunosuppression (primarily MMF) remained reduced in most of the KTRs during follow-up (Figure 1). Side effects predominantly to MMF led to the reduction. Leukopenia caused a reduction in 77%, gastrointestinal side effects in 34%, EBV in 19% (two KTRs developed PTLD), CMV in 15%, and BK polyomavirus in 15%. The reduction was significantly more pronounced in KTRs under 11 years (87% vs. 61%, p-0.044). Tacrolimus seemed well tolerated and was sufficiently regulated according to a target through of five microg/L two months after transplantation (Figure 2). Figure 1: Mycophenolate mofetil dose (mg) per body surface area