Preclinical Pharmacology and Toxicology of Humanized Anti-B-Cell Antibodies (Anti-CD22 and Anti-CD20) in Cynomolgus Monkeys (CM).

hLL2 (epratuzumab) and hA20 are humanized IgG1 monoclonal antibodies (MAbs) recognizing B-cell antigens, CD22 and CD20, respectively. CD22 and CD20 are expressed at all stages of B-cell development, except progenitor stem cells and plasma cells. Both hLL2 and hA20 have shown promising clinical activity in patients with non-Hodgkin’s lymphomas (NHL). Further, hLL2 has demonstrated clinical efficacy in patients with autoimmune diseases, such as systemic lupus erythematosus and Sjögren’s syndrome. Here, we discuss preclinical toxicology studies and compare the pharmacodynamics (PD) and pharmacokinetics (PK) of hA20 and hLL2 in CD20/CD22-crossrecative CM. For hLL2, we performed two toxicology studies. In the first 14-Day tolerability study, CM received hLL2 as two intravenous (IV) infusions at 0 (vehicle), 10, 60 and 160 mg/kg given one week apart, followed by necropsy on Day 14. In a second 6-month PK/PD study, hLL2 was administered in 2 cycles of 4-weekly infusions, with a 1-month treatment-free period between cycles followed by necropsy at the end of the second cycle. For hA20, CM received 4-weekly infusions of hA20 at 0 (vehicle), 8, 24, 80, and 240 mg/kg-doses and were either sacrificed 1 week after the last infusion or followed for recovery. Both hA20 and hLL2 were well tolerated. There were no drug-related clinical signs or changes in body weight, food intake, ophthalmic condition, EKG, blood pressure, and standard hematology, serum chemistry, coagulation or urinalysis parameters. Also, there were no changes in organ weights, gross necropsy, or histopathology findings. For hLL2, PD indicated a mean reduction from baseline for all B-lymphocytes (CD20+B-cells, or activated CD20+HLA-DR+ and CD20+CD27+ B-cells) of approximately 30–50%, starting on Day 3 in both studies, with no apparent dose-response. In the cyclical regimen study, this effect continued through Day 113 (day after the end of 2nd cycle). In contrast, for hA20, almost 85–95% B cell depletion was observed in all treatment groups on Day 6 and there was a trend towards dose-related depletion. Both hLL2 and hA20 had little discernable effect on T cell subsets, monocytes, or plasma cells. hLL2 and hA20 had a t1/2 of 3–5 days after the first infusion, and hLL2 had a t1/2 of 6–7 days after the fourth infusion. There was no significant difference between PK of hLL2 after the first and second cycles. With regard to immunogenicity, primate antibodies to either hA20 or hLL2 were not detected. In conclusion, hA20 demonstrates significantly higher B-cell depletion, similar to Rituximab, compared to hLL2 in CM. Clinical results obtained with hLL2 as well as studies of in vitro mechanism of action suggest that partial B-cell modulation by hLL2 in autoimmune diseases may provide benefit, and may function by different mechanisms than B-cell depletion related to hA20. In NHL, combined therapy of CD20 and CD22 may be more effective than single-MAb treatment, as has been suggested clinically.