Tetanus toxoid and CCL3 improve DC vaccines in mice and glioblastoma patients

Upon stimulation, dendritic cells (DCs) mature and migrate to draining lymph nodes to induce immune responses(1). As such, autologous DCs generated ex vivo have been pulsed with tumor antigens and injected back into patients as immunotherapy. While DC vaccines have shown limited promise in the treatment of patients with advanced cancers(2–4) including glioblastoma (GBM),(5–7) the factors dictating DC vaccine efficacy remain poorly understood. Here we demonstrate that pre-conditioning the vaccine site with a potent recall antigen such as tetanus/diphtheria (Td) toxoid can significantly improve the lymph node homing and efficacy of tumor antigen-specific DCs. To assess the impact of vaccine site pre-conditioning in humans, we randomized patients with GBM to pre-conditioning with mature DCs(8) or Td unilaterally before bilateral vaccination with Cytomegalovirus pp65 RNA-pulsed DCs. We and other laboratories have shown that pp65 is expressed in > 90% of GBM specimens but not surrounding normal brain(9–12), providing an unparalleled opportunity to subvert this viral protein as a tumor-specific target. Patients given Td had enhanced DC migration bilaterally and significantly improved survival. In mice, Td pre-conditioning also enhanced bilateral DC migration and suppressed tumor growth in a manner dependent on the chemokine CCL3. Our clinical studies and corroborating investigations in mice suggest that pre-conditioning with a potent recall antigen may represent a viable strategy to improve antitumor immunotherapy.