PDCT-10. FEASIBILITY OF LEUKAPHERESIS FOR HARVESTING MONOCYTES AND GENERATING AUTOLOGOUS DENDRITIC CELL VACCINES IN CHILDREN WITH MALIGNANT BRAIN TUMORS

Abstract

Abstract BACKGROUND Recurrent medulloblastoma and malignant glioma are virtually incurable. In children, these tumors are often disseminated or occur in deep midline structures that preclude surgery and are not amenable to highly inflammatory treatments. Active immunization is an attractive immunotherapeutic approach. We are conducting a phase I trial evaluating autologous CMV pp65 RNA-pulsed dendritic cell (DC) vaccines in children with recurrent malignant glioma or medulloblastoma. A primary objective is establishing the feasibility of using leukapheresis to harvest sufficient monocytes in order to generate at least 3 autologous DC vaccines. METHODS For children unable to receive two 16-guage IVs, a temporary pheresis catheter is placed in the jugular vein under anesthesia. Leukapheresis is performed with the goal of processing 3 total blood volumes. Circulating monocytes are collected and cultured for 7 days in media supplemented with GM-CSF and IL-4, then matured into dendritic cells and loaded with antigen. The target dose for a single vaccine is 2 x 107 dendritic cells. RESULTS To date, five patients (ages 9, 13, 16, 17, 30) have undergone leukapheresis. All patients tolerated leukapheresis without complications, with run times between 3 to 6 hours depending on achievable pheresis flow rate. Patients generated 2, 3, 7, 8, 8, and 8 vaccines. The medulloblastoma patient who generated 2 vaccines underwent a second leukapheresis that generated 8 vaccines. In this patient, although the initial leukapheresis collected a high number of monocytes, the conversion rate to mature DCs was low. Thusfar, there has not been a strong correlation between the number of monocytes collected and the eventual number of mature dendritic cells. CONCLUSIONS Leukapheresis is tolerable for younger children and appears to be a viable strategy for harvesting sufficient monocytes for creating DC vaccines. Conversion rates between harvested monocytes and the final number of mature dendritic cells vary.