Sym001, the First Recombinant Polyclonal Rhesus-D Specific Antibody Product, Was Safe and Well-Tolerated in a Placebo-Controlled Randomized Phase I Trial.

Sym001 is the first compound in a new class of biopharmaceuticals in clinical development for the treatment of Immune Thrombocytopenic Purpura (ITP), and the prevention of hemolytic disease of the newborn by anti-D prophylaxis (ADP). Sym001 is a recombinant polyclonal antibody product consisting of 25 different anti-Rhesus D specific (RhD) antibodies. The primary objective of this clinical study was to assess the safety of Sym001 following a single intravenous (iv) dose in RhD⁺ and RhD⁻ healthy male volunteers. Secondary objectives were to assess the potential immunogenicity and pharmacokinetic (PK) profile of Sym001. Fifty-nine RhD⁺ subjects and 18 RhD⁻ subjects were randomized to receive up to 12.5 μg/kg or 75 μg/kg, respectively, in seven dose cohorts as shown below:

Treatment with Sym001 was well tolerated and there were no serious adverse events (SAEs), no AEs of severe intensity and no AEs that resulted in discontinuation of the study in either the RhD⁺ or RhD⁻ population. The frequencies of treatment-emergent AEs (TEAE), i.e. AEs occurring after drug administration, were similar among Sym001 and placebo treated subjects and there was no dose-dependent pattern of TEAEs. No significant decrease in mean hemoglobin level compared to baseline was observed at any dose level during the study, and no decrease in hemoglobin > 2 g/dL in any subject was seen. No other laboratory findings were suggestive of clinically significant hemolysis. In addition, no clinically significant changes in vital signs or electrocardiograms (ECGs) were observed, and there were no significant changes in clinical chemistry variables that did translate into SAEs or were assessed as being related to study medication. No immunogenicity to Sym001 was detected and analysis of PK is in progress. In conclusion, Sym001 was found to be safe and well-tolerated in healthy volunteers in doses up to 75 μg/ kg. Sym001 is now being evaluated in a red blood cell (RBC) challenge trial for the ADP indication and in a Phase II trial for treatment of patients with ITP.