Siegel, Ruby J.

ABSTRACT HLA‐C*07:1268 differs from HLA‐C*07:02:01:01 by one nucleotide substitution in exon 3.

ABSTRACT HLA‐B*08:345Q differs from HLA‐B*08:238 by one nucleotide substitution, introducing a premature stop codon in exon 5.

ABSTRACT HLA‐A*32:202 differs from HLA‐A*32:01:01:01 by two nucleotide substitutions in exons 1 and 2.

ABSTRACT HLA‐DQB1*06:144N differs from HLA‐DQB1*06:03:01:01 by one nucleotide substitution, introducing a premature stop codon in exon 2.

ABSTRACT HLA‐B*57:205 differs from HLA‐B*57:01:01:01 by one nucleotide substitution in Exon 1.

ABSTRACT HLA‐A*24:675 differs from HLA‐A*24:02:01:01 by one nucleotide substitution in exon 3.

ABSTRACT HLA‐DQB1*06:549 differs from HLA‐DQB1*06:02:01:01 by one nucleotide substitution in exon 2.

ABSTRACT HLA‐C*03:737 differs from HLA‐C*03:05:01:01 by one nucleotide substitution in exon 3.

Significance Statement There is no standardized desensitization regimen for kidney transplant candidates. CD38, expressed by plasma cells, could be targeted for desensitization to deplete plasma cells producing alloantibodies and donor-specific antibodies. Few studies and case reports are available regarding the use of CD38 antibodies for desensitization in patients awaiting kidney transplant. This study shows that isatuximab, a CD38-targeting therapy, was well tolerated in kidney transplant candidates, with a durable decrease in anti-HLA antibodies and partial desensitization activity. The short treatment period and long follow-up of this study allowed for the understanding of the mechanism and timing for any antibody rebound. Isatuximab could be further investigated as an option for adjunct therapy to existing desensitization for patients on the kidney transplant waitlist. Background Patients with calculated panel reactive antibody (cPRA) ≥80.00%, particularly those with cPRA ≥99.90%, are considered highly sensitized and underserved by the Kidney Allocation System. Desensitization removes circulating reactive antibodies and/or suppresses antibody production to increase the chances of a negative crossmatch. CD38 is expressed highly on plasma cells, thus is a potential target for desensitization. Methods This was an open-label single-arm phase 1/2 study investigating the safety, pharmacokinetics, and preliminary efficacy of isatuximab in patients awaiting kidney transplantation. There were two cohorts, cohorts A and B, which enrolled cPRA ≥99.90% and 80.00% to <99.90%, respectively. Results Twenty-three patients (12 cohort A, 11 cohort B) received isatuximab 10 mg/kg weekly for 4 weeks then every 2 weeks for 8 weeks. Isatuximab was well tolerated with pharmacokinetic and pharmacodynamic profiles that indicated similar exposure to multiple myeloma trials. It resulted in decreases in CD38 + plasmablasts, plasma cells, and NK cells and significant reductions in HLA-specific IgG-producing memory B cells. Overall response rate, on the basis of a predefined composite desensitization end point, was 83.3% and 81.8% in cohorts A and B. Most responders had decreases in anti-HLA antibodies that were maintained for 26 weeks after the last dose. Overall, cPRA values were minimally affected, however, with only 9/23 patients (39%) having cPRA decreases to target levels. By study cutoff (median follow-up of 68 weeks), six patients received transplant offers, of which four were accepted. Conclusions In this open-label trial, isatuximab was well tolerated and resulted in a durable decrease in anti-HLA antibodies with partial desensitization activity. Clinical Trial registration number NCT04294459.