 Subjects will be enrolled sequentially into 5 planned dose cohorts according to a standard, dose escalation study design. A disease assessment will be performed at study week 5 - 3 days by the investigator. The assessment will be based both on changes in clinical symptoms, and radiographic images. Subjects without evidence of disease progression may receive AGS-16M18 extended therapy at the dose and schedule of their assigned cohort until disease progression or intolerability of AGS-16M18. Disease assessments will be performed every 8 weeks during the extended period. A safety follow-up visit will occur 4 weeks after the last infusion of AGS-16M18. 