IMST-33. ENHANCED T CELL ACTIVATION USING DENDRITIC CELLS PULSED WITH CHIMERIC RNAs ENCODING FULL-LENGTH LAMP-1 FUSION CONSTRUCTS

Abstract

BACKGROUND: Human CMV antigens have been proposed as novel targets for immunotherapy in glioblastoma (GBM). We previously demonstrated in a pilot randomized and blinded clinical trial, that vaccination of patients with newly-diagnosed GBM with autologous dendritic cells (DC) pulsed with RNA encoding the CMV antigen pp65 led to the expansion of pp65-specific T cell responses and was associated with prolonged survival (Mitchell, Batich et al., Nature 2015). A short targeting peptide from the lysosomal associated membrane protein 1 (LAMP-1) was expressed as a fusion construct with pp65 to enhance antigen-processing and presentation in RNA-pulsed DCs. In this study, we compared the use of a full-length LAMP fusion RNA construct (flLAMP-pp65, provided by Immunomic Technologies, Inc.) with the used short peptide chimeric antigen (shLAMPpp65). METHODS: DCs from HLA-A2+ or B7+, CMV seropositive (n=7) were pulsed with flLAMP-pp65 or shLAMP-pp65 RNA and used to stimulate autologous lymphocytes in vitro. Activation of CMV-specific T cells was evaluated by tetramer expansion, cytokine secretion, flow cytometric phenotyping, and recognition of HLA-matched GBM tumor cells expressing CMV pp65. RESULTS: DCs pulsed with full-length LAMP-1-pp65 chimeric RNAs demonstrated enhanced CMV-specific T cells as assessed by tetramer expansion in 7 out of 7 evaluated subjects, comparable induction of effector memory and central memory T cells, and increased IFNgamma secretion in recognition of pp65-expressing GBM tumor cells. CONCLUSIONS: Our results demonstrated potential superiority in the expansion of CMV-specific T cells and recognition of CMV pp65-expressing GBM tumor cells in vitro with use of the full-length LAMP-1 pp65 chimeric RNA pulsed DCs. A multi-institutional, blinded, randomized, and placebo-controlled phase 2 clinical trial is underway at our center utilizing flLAMP-pp65 RNA pulsed DCs, shLAMP-pp65 RNA pulsed DCs, and unpulsed PBMCs as a control vaccine.