IMMU-15. HIGH-RESOLUTION ANALYSIS OF THE T-CELL RECEPTOR REPERTOIRE AFTER ADOPTIVE CELLULAR THERAPY IN PEDIATRIC PATIENTS WITH CENTRAL PNETs (Re-MATCH TRIAL)

Abstract

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 deep TCR repertoire sequencing approach to explore dynamics of T-cell immunity in the nine patients with recurrent medulloblastoma and PNETs undergoing adoptive cellular therapy (Re-MATCH protocol, FDA IND BB-14058). Total RNA was isolated from patient PBMC samples collected prior to adoptive cellular therapy and weekly for one month and then monthly following immunotherapy treatment. cDNA was generated with addition of a common adapter at 5' end of cDNA using RACE technology. Raw sequencing data were preprocessed using MiXCR software. Further TCR repertoire analysis was performed using tcR R-package and VDJtools software. We observed remarkable dynamic changes in the TCR repertoire in peripheral blood following ACT in all patients. The blood samples collected after adoptive cellular therapy 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). 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. 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.