Single domain antibodies (SDAb) represent an alternative immunotherapeutic platform for veterinary use. Several SDAb targeting canine PD-1 were previously identified with potential for canine cancer immunotherapy. A lead SDAb, clone STX-1B5, with nanomolar binding to canine PD-1 was selected for evaluation of tolerability in dogs. The anti-PD-1 SDAb was expressed in wild-type Komagataella phaffii (Pichia pastoris) at a 100 mg scale, purified by tangential flow filtration, and quality confirmed controlled for host-cell protein, host-cell DNA, and endotoxin. Single 1.0 mL subcutaneous (SQ) injections of 0.15 to 1.12 mg/kg were administered to three adult Beagle dogs (1 male and 2 female) one per week to allow observations from each dose level prior to dose escalation. The dogs were monitored by a veterinarian on the day of dosing and daily for three days. Administering 1.0 ml of STX-1B5 subcutaneously at 0.146, 0.383 or 1.154 mg/kg in young adult male or female Beagle dogs was well tolerated and did not result in adverse test article-related clinical observations.
Dan V. Mourich*1, Carl E. Ruby1, Shay Bracha2, Christopher K. Cebra1, Laura Crowell Orella3, Patrick Iversen4 (Sat,) studied this question.