Beschreibung: Purpose: Study objectives included evaluating the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity of VX15/2503 in advanced solid tumor patients. Experimental Design: Weekly i.v. doses were administered on a 28-day cycle. Safety, immunogenicity, PK, efficacy, T-cell membrane–associated SEMA4D (cSEMA4D) expression and saturation, soluble SEMA4D (sSEMA4D) serum levels, and serum biomarker levels were evaluated. Results: Forty-two patients were enrolled into seven sequential cohorts and an expansion cohort (20 mg/kg). VX15/2503 was well tolerated. Treatment-related adverse events were primarily grade 1 or 2 and included nausea (14.3%) and fatigue (11.9%); arthralgia, decreased appetite, infusion-related reaction, and pyrexia were each 7.3%. One pancreatic cancer patient (15 mg/kg) experienced a Grade 3 dose-limiting toxicity; elevated -glutamyl transferase. Complete cSEMA4D saturation was generally observed at serum antibody concentrations ≥0.3 μg/mL, resulting in decreased cSEMA4D expression. Soluble SEMA4D levels increased with dose and infusion number. Neutralizing anti-VX15/2503 antibodies led to treatment discontinuation for 1 patient. VX15/2503 C max and AUC generally increased with dose and dose number. One patient (20 mg/kg) experienced a partial response, 19 patients (45.2%) exhibited SD for ≥8 weeks, and 8 (19%) had SD for ≥16 weeks. Subjects with elevated B/T lymphocytes exhibited longer progression-free survival. Conclusions: VX15/2503 was well tolerated and produced expected PD effects. The correlation between immune cell levels at baseline and progression-free survival is consistent with an immune-mediated mechanism of action. Future investigations will be in combination with immunomodulatory agents. Clin Cancer Res; 22(4); 827–36. ©2015 AACR .