Pharmacokinetics of Basiliximab for the Prevention of Graft-versus-Host Disease in Patients Undergoing Hematopoietic Cell Transplantation with Minimal-Intensity Cyclophosphamide and Fludarabine.

STUDY OBJECTIVE: Basiliximab is an immunosuppressive monoclonal antibody used for rejection prevention following solid organ transplantation; the pharmacokinetics (PK) of basiliximab in this setting are known. Basiliximab may also be used for prophylaxis and treatment of graft-versus-host disease (GVHD) in patients undergoing allogeneic hematopoietic cell transplantation (HCT); however, the PK of basiliximab in this setting are not known. Clinical transplant providers expect variation in the volume of distribution and clearance after nonmyeloablative allogeneic transplantation (NMAT) compared with solid organ transplantation. Blood loss, organ site-specific antibody accumulation, and differences in blood product use during the two transplantation approaches may generate differences in basiliximab PK. Therefore, the objective of this study was to describe the PK of basiliximab after its addition to a minimally intense NMAT regimen, in conjunction with cyclosporine, for GVHD prophylaxis in patients with hematologic malignancies. DESIGN: Population PK analysis of a single-center, single-arm, phase II clinical trial. SETTING: Academic cancer research center. PATIENTS: Fourteen adults with hematologic malignancies (acute myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, myelodysplastic syndrome, non-Hodgkin's lymphoma, Hodgkin's lymphoma, myelofibrosis, or severe aplastic anemia) and undergoing NMAT with a fully HLA-matched (10 of 10 antigen matched) related or unrelated donor. MEASUREMENTS AND MAIN RESULTS: Basiliximab was used in conjunction with cyclosporine to deplete activated T cells in vivo as GVHD prophylaxis. We developed a novel competitive enzyme-linked immunosorbent assay (ELISA) method using recombinant interleukin-2 receptor alpha-chain (IL-2Ra) and a commercially available soluble sIL-2R ELISA kit to permit the quantification of serum basiliximab concentrations and characterization of the PK properties of the drug in this patient population. Using a nonlinear mixed effects model with NONMEM software, a one-compartment model with first-order elimination best described the PK, as covariate analysis using stepwise covariate modeling did not improve the base model. CONCLUSION: We suggest a one-compartment population model with first-order elimination to capture the PK profile for basiliximab for this patient population.

"Simulect" as a model compound for assessing placental transfer of monoclonal antibodies in minipigs.

The aim of this study was to directly test and measure in vivo, if placental transfer of monoclonal antibodies takes place in pregnant Göttingen Minipigs to assess their suitability for reproductive assessment of therapeutic monoclonal antibodies. Simulect®, an approved anti CD25 (anti IL-2 receptor alpha) chimeric monoclonal IgG1 antibody, was used as a model monoclonal antibody. Maternal systemic exposure and potential placental transfer of Simulect® to fetuses were investigated following 4 weekly bolus intravenous administration of 5.0 mg/kg from gestation day (GD) 79 or 80 (e.g GD 79, 86, 93 and 100) and with terminal Caesarean section on GD 108 or GD 109 respectively. Results clearly showed exposure in maternal animals, detectable compound in the amniotic fluid from one out of 9 maternal animals, but no exposure in fetuses confirming absence of placental transfer of the selected model antibody Simulect® in minipigs. The absence of Simulect® in the fetuses further supports that the presence of Simulect® in the amniotic fluid in one maternal animal was likely due to contamination with maternal blood during sampling. The demonstrated absence of fetal exposure clearly indicates that, the minipig is not a suitable species for conduct of reproductive toxicity studies with monoclonal antibodies.