Imlifidase Desensitization in Crossmatch-positive, Highly Sensitized Kidney Transplant Recipients: Results of an International Phase 2 Trial (Highdes)

BACKGROUND:Highly-HLA sensitized patients have limited access to life-saving kidney transplantation due to a paucity of immunologically suitable donors. Imlifidase is a cysteine protease that cleaves IgG leading to a rapid decrease in antibody level and inhibition of IgG-mediated injury. This study investigates the efficacy and safety of imlifidase in converting a positive crossmatch test to negative, allowing highly sensitized patients to be transplanted with a living or deceased donor kidney. METHODS:This open-label, single arm, phase 2 trial conducted at five transplant centers, evaluated the ability of imlifidase to create a negative crossmatch test within 24 hours. Secondary endpoints included post-imlifidase DSA levels compared to pre-dose levels, renal function, and pharmacokinetic/pharmacodynamic profiles. Safety endpoints included adverse events and immunogenicity profile. RESULTS:89.5% of the transplanted patients demonstrated conversion of baseline positive crossmatch to negative within 24 hours after imlifidase treatment. DSA most often rebounded 3-14 days post-imlifidase dose, with substantial interpatient variability. Patient survival was 100% with graft survival of 88.9% at 6 months. 38.9% had early biopsy proven antibody mediated rejection with onset 2-19 days post-transplantation. Serum IgG levels began to normalize after ~3-7 days post-transplantation. Anti-drug antibody levels were consistent with previous studies. Seven adverse events in six patients were classified as possibly or probably related to treatment and were mild-moderate in severity. CONCLUSIONS:Imlifidase was well tolerated, converted positive crossmatches to negative, and enabled patients with a median cPRA of 99.83% to undergo kidney transplantation resulting in good kidney function and graft survival at 6 months.