B-cell reduction and inhibited splenocyte proliferation in normal mice and monkeys; no disease model
“The in vivo studies in mice as well as in monkeys demonstrated that belimumab inhibits splenocyte proliferation and decreased the number of B-cells in spleen, lymph node and circulating B cells.”
10-fold lower affinity for mouse BLyS and strong ADA with anaphylactoid deaths on repeat dosing in mice
“Although belimumab binds mouse BLyS, it does so with a 10-fold lower affinity for murine BLyS compared with belimumab binding to human or cynomolgus monkey BLyS. Moreover, multiple injections of belimumab in mice led to a strong anti-drug antibody response that altered the PK and in some cases led to death by an anaphylactoid–like response.”
CHMP: expected reduction of peripheral and lymphoid B cells in monkeys without associated toxicological findings
“Intravenous and subcutaneous administration to monkeys resulted in the expected reduction in the number of peripheral and lymphoid tissue B cell counts with no associated toxicological findings.”