Briquilimab

For successful engraftment of donor hematopoietic stem cells (HSC), conditioning with chemotherapy and/or radiation prior to hematopoietic cell transplantation (HCT) has been required to open marrow niche space and minimize the risk of immune rejection. Briquilimab, a humanized IgG1 monoclonal antibody that blocks the interaction between the c-Kit receptor and stem cell factor on various C-Kit expressing tissues including HSC, is a potential nonmyeloablative conditioning agent in clinical development for patients with severe combined immunodeficiency (SCID), myelodysplastic syndromes (MDS), and acute myeloid leukemia (AML). This study aimed to characterize pharmacokinetics (PK) and develop a population PK model of briquilimab after single intravenous infusions of 4 different doses in patients with SCID, MDS, or AML receiving HCT. The PK data was collected from 2 different studies: JAS-BMT-CP-001 and JSP-CP-003. JAS-BMT-CP-001 is a phase 1/2 open-label study of briquilimab as a conditioning agent prior to allogenic HCT in SCID patients. The participants received single intravenous infusions of 0.1, 0.3, 0.6, or 1.0 mg/kg. JSP-CP-003 was a phase 1a/b open-label study of briquilimab in combination with a standard conditioning regimen of low dose total body irradiation and fludarabine in MDS or AML subjects undergoing HCT. The participants received a single intravenous dose of 0.6 mg/kg briquilimab. In both studies, briquilimab PK samples were obtained at pre-treatment, 5 minutes post-end of infusion, 4- and 24-hours post-start of infusion, any time between 2 days and 30 days postinfusion, and on the day of HCT prior to donor cell infusion.The population PK model was developed using the PK data from these 2 clinical studies, and the effect of participants' baseline characteristics on the briquilimab PK was evaluated. PK simulations were performed using the developed PK model to calculate the time to reach target concentrations for HCT. A total of 49 participants (21 SCID adult and pediatric participants with a median age of 12 yr and 28 MDS/AML adult participants with a median age of 70 yr) were included in the PK analysis. A 2-compartment model with combined linear and non-linear elimination best described the PK of briquilimab. Body weight was determined as the sole covariate of the PK parameters among the explored covariates. For a typical subject with a body weight 70 kg, the estimated parameters for clearance, maximum metabolic rate of Michaelis Menten elimination, Michaelis Menten constant, central volume, peripheral volume, and intercompartmental clearance were 17.6 mL/h, 51,434.8 ng/h, 71.5 ng/mL, 3444.0 mL, 1613.3 mL, and 21.2 mL/h, respectively. The median time to reach target concentrations of 500, 1000, and 2000 ng/mL after a single dose of 0.6 mg/kg was calculated as 12.3, 10.4, and 7.7 days, respectively. The PK of intravenous briquilimab was characterized in subjects with SCID, MDS, or AML receiving HCT, and a population PK model was developed to estimate briquilimab clearance to use as a guide to the timing of donor cell infusion post-briquilimab. Body weight was identified as a significant covariate on elimination and volume of distribution of briquilimab.

Intravenous immunoglobulin (IVIG) (2000 mg/kg) increased the clearance of the mouse monoclonal antibody 7E3, directed against platelet integrin IIb/IIIa (alpha IIb beta 3, CD41/CD61) in rodents. We wanted to investigate the effect of IVIG on clearance of monoclonal antibodies in humans as there is extremely limited data regarding this interaction in the literature. Using the tyrosine protein kinase KIT anti‐cluster of differentiation 117 (c‐Kit) humanized monoclonal antibody (JSP191) as a case study, we used physiologically‐based pharmacokinetic (PBPK) modeling to evaluate the pharmacokinetic interaction between monoclonal antibodies and IVIG at doses (300–600 mg/kg) administered to patients with primary human immunodeficiency (PI). We first characterized the interaction between monoclonal antibodies and IVIG in PK‐Sim®/MoBi® using published literature data, including the following: IVIG plus 7E3 in mice and rats and IVIG plus the human anti‐C5 monoclonal antibody tesidolumab in adults with end‐stage renal disease. We next developed a PBPK model using digitized data for JSPI91 alone in older adults with myelodysplastic syndrome and acute myeloid leukemia and in pediatric patients with severe combined immunodeficiency (SCID). Finally, we simulated the impact of IVIG (300–2000 mg/kg) coadministration with JSP191 on the area under the curve of JSP191 in patients with SCID. Model predictions were within 1.5‐fold of observed values for 7E3 plus IVIG and tesidolumab plus IVIG as well as for JSP191 administered alone. Based on our simulations, IVIG doses ≥500 mg exceeded the 80%–125% no‐effect boundaries. IVIG treatment with monoclonal antibodies in patients with PI may result in a clinically significant interaction depending on the IVIG dose administered and the exposure–response relationship for the specific monoclonal antibody.