FLT3 Ligand, CD40 Agonist Antibody, and Stereotactic Radiotherapy

This is a randomized, open-label phase I/II study. Subjects will be randomized in a 1:1 ratio to receive FLT3 ligand (CDX-301), anti-CD40 antibody (CDX-1140) and SBRT (Arm 1) versus standard care (Arm 2). Subjects on either study arm with limited disease will receive SBRT to all evident sites of active disease. Subjects on Arm 1 with extensive disease will initially receive SBRT to a single site of disease but may receive additional "cycles" of FLT3 ligand (CDX-301) anti-CD40 antibody (CDX-1140), and SBRT at later time points. Subjects on Arm 2 with extensive disease are expected to receive some form of standard systemic therapy (e.g., docetaxel). Subjects on Arm 2 with limited disease may also receive standard systemic therapy following completion of SBRT to all sites of evident disease, at the discretion of the treating physicians. All subjects will be followed closely for treatment-related toxicities. Whole-body PET/CT and CT imaging will be performed prior to study entry, and restaging CT will be performed every 8 weeks thereafter. In the phase I component of this study, subjects will be randomized between study arms until 6 subjects have been randomized to Arm 1. Study accrual will then be halted until 8 weeks after the last study subject begins treatment. If the pre-specified safety criteria are achieved in the Phase I portion of this study, the study will proceed to phase II. The total sample size (Phase I and Phase II) will be 46 subjects. All 46 subjects will be included in efficacy analyses. If the pre-specified safety criteria are not achieved in the Phase I portion of this study, the investigators and Celldex will review safety data from this trial as well as other trials using CDX-301 and CDX-1140 and determine if the experimental treatment regimen should be altered (e.g., by reducing the CDX-1140 dose). The study protocol would be amended accordingly, and Phase I component with the new treatment regimen would be added.