Immunotherapy of malignant ascites with trifunctional antibodies

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Abstract
A new class of intact bispecific antibodies shows unmet effector qualities by activation of not only T cells but also simultaneous activation of Fcγ receptor type I/III+ cells (macrophages, NK-cells and DC). These trifunctional antibodies (trAb) lead to efficient specific killing of targeted tumor cells without any pre- or co-stimulation. This concept was investigated in vivo in patients with malignant ascites in a clinical situation that allowed monitoring of tumor cell elimination and correlation with clinical effects. In a prospective study, 8 patients with malignant ascites due to peritoneal carcinomatosis were treated with intraperitoneal application of trAb, which bound either the EpCAM- or Her2/neu-antigen on tumor cells. Treatment consisted of 4–6 applications within 9–23 days with a total amount of 145–940 μg. Seven of eight patients required no further paracentesis during follow-up or until death with a mean paracentesis-free interval of 38 weeks (median = 21.5, range = 4–136). Tumor cell monitoring showed a complete elimination of tumor cells in ascites already at total doses as low as 40–140 μg. Clinical response with disappearance of ascites accumulation was seen in all patients, which was correlated with elimination of tumor cells (p = 0.0014). Severe adverse events were not observed. Clinically relevant side effects were fever, moderate abdominal pain and skin reactions. Intraperitoneal immunotherapy with trAb showed convincing efficacy in patients with malignant ascites. This treatment offers new therapeutic options for patients with peritoneal carcinomatosis.