CTIM-31. IMMUNOLOGIC MONITORING AFTER ADOPTIVE CELL THERAPY IN PEDIATRIC PATIENTS WITH RECURRENT MEDULLOBLASTOMA USING IMMUNOGENOMICS APPROACH

Abstract

Abstract BACKGROUND Adoptive cellular therapy (ACT) using transfer of tumor-specific lymphocytes has emerged as a potent strategy for treatment of advanced and refractory malignancies. We have employed the use of total tumor RNA (TTRNA)-pulsed DCs in the ex vivo expansion of tumor-specific lymphocytes for use in adoptive cellular therapy targeting pediatric malignant brain tumors. METHODS Total RNA was isolated from patient PBMC samples collected prior to adoptive cellular therapy and after 2-weeks and 4-weeks following immunotherapy treatment from 18 patients (Re-MATCH protocol, FDA IND BB-14058). We applied bulk RNA-Seq and high-throughput T cell receptor sequencing to monitor changes in blood draws after ACT. RESULTS We observed an increase of expression level of genes responsible for T cell activation in PBMC after adoptive cell therapy. We found that these genes were involved in T cell signaling pathways, proliferative signals, and cytokine production. The data revealed that certain T-cells were clonally expanded after ACT, with an increasing number of “hyper-expanded” TCR clones (comprising > 1% of all TCR beta or alpha sequences) after adoptive cellular therapy. These TCR clones established a new balance in the peripheral blood that was stable over the month following the completion of cellular immunotherapy. Hyper-expanded TCR clones and increased TCR diversity following ACT was associated with radiographic response to ACT and prolonged progression-free and overall survival. Limited TCR expansion and diversity following ACT was observed in patients with short overall and progression-free survival. CONCLUSIONS These results emphasize the importance of gene expression profiling to achieve higher resolution in monitoring immune responses in patients receiving immunotherapeutic treatment. Also, these findings support further study of the use of TCR sequencing to monitor responses to adoptive cellular therapy and suggest that TCR clonal expansion and increasing TCR diversity following treatment may be associated with positive clinical responses.