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Alexion Pharmaceuticals reports interim results from phase 1 trial on samalizumab antibody

September 14, 2015

Samalizumab appeared to be well tolerated. Adverse events to date were mostly mild or moderate, and were considered manageable. The most common adverse events included fatigue (50%), headache (20%), fever (20%), and rash (20%). Grade 3 to 5 events deemed possibly, probably, or definitely related to study drug included anemia (8%), neutropenia (8%), thrombocytopenia (4%), reduced visual acuity (4%), respiratory syncytial virus infection (4%), muscular weakness (4%), and rash (4%). Samalizumab dosing was associated with no severe or dose-limiting adverse cytokine reactions. The maximum tolerated dose was not reached in this trial.

In patients with sufficient peripheral immune cells to evaluate biological activity, 95% (19/20) showed 81% to 98% reductions in peripheral CD200+ CD4+ T cells. In addition, 67% (14/21) of patients demonstrated 64% to 75% CD200 loss on B-CLL cells following the first dose of samalizumab, which may represent CD200 down-modulation or CD200+ cell loss. These findings are consistent with the predicted immunomodulatory mechanism of action for samalizumab, which is designed to inhibit CD200-dependent immune suppression, enabling a more efficient immune response against CD200+ tumor cells.

Overall, 36% (8/22) of evaluable patients experienced at least a 10% reduction in bulky disease. Notably, one patient, who received 13 cycles of samalizumab (400mg/m^2), achieved a confirmed partial response as defined in the protocol, with a maximum 71% reduction in bulky disease by CAT scan together with >50% reduction in absolute lymphocyte count while maintaining neutrophil count ?? 1.5 x 10^9/L.

Source: Alexion Pharmaceuticals, Inc.