Early Exposure of Kidney Transplant Recipients with Chronic Antibody-Mediated Rejection to Tocilizumab—A Preliminary Study

Tocilizumab prevents clinical worsening of chronic antibody-mediated rejection (CAMR) of kidney transplant recipients. Optimization of this treatment is necessary. We identified the determinants of early tocilizumab exposure (within the first three months) and investigated the relationship between early plasma tocilizumab exposure and graft function. Patients with CAMR who started treatment with tocilizumab were retrospectively included. Demographic, clinical, and biological determinants of the tocilizumab trough concentration (C(min)) were studied using a linear mixed effect model, and the association between early exposure to tocilizumab (expressed as the sum of C(min) over the three first months (M) of treatment (ΣC(min))) and the urinary albumin-to-creatinine ratio (ACR) determined at M3 and M6 were investigated. Urinary tocilizumab was also measured in seven additional patients. Seventeen patients with 51 tocilizumab C(min) determinations were included. In the multivariate analysis, the ACR and time after tocilizumab initiation were independently associated with the tocilizumab C(min). The ΣC(min) was significantly lower (p = 0.014) for patients with an ACR > 30 mg/mmol at M3 and M6 than for patients with an ACR < 30 mg/mmol. Tocilizumab was detected in urine in only 1/7 patients. This study is the first to suggest that early exposure to tocilizumab may be associated with macroalbuminuria within the first six months in CAMR patients.