287. Improved Outcomes Following Drug-Resistant Immunotherapy in a Human Xenograft Model of Temozolomide-Resistant Glioblastoma Multiforme

Abstract

INTRODUCTION: Conventional treatment strategies for Temozolomide (TMZ)-resistant high-grade gliomas have been uniformly dismal. We have shown that TMZ-resistant tumors up-regulate stress-associated NKG2D ligands (NKG2DL) during the first hours after exposure to TMZ, thereby creating an opportunity for NKG2DL-directed cell therapies. We report improved survival using a combination of TMZ chemotherapy and gene modified TMZ-resistant γΔ T cells which we term Drug Resistant Immunotherapy (DRI). TMZ resistance is conferred by lentivector transfer of methylguanine methyltransferase (MGMT) enabling cytotoxic lymphocyte function during high-dose chemotherapy.METHODS: Tumor NKG2DL expression and DRI cytotoxicity were assessed by flow cytometry. Intracranial (IC) glioma xenografts were established on Day 0 with either unmodified (P) or a TMZ resistant clone (T) of human primary GBM-X12 passaged exclusively in immunodeficient mice. Tumor-bearing mice were treated with intraperitoneal TMZ 60mg/kg on days 6, 8,13, and 15 followed by IC injection of 1.5 × 106 DRI 4h after each TMZ dose × 2 weeks. Control mice received non-modified cells, TMZ, or no therapy. Survival was assessed using Kaplan-Meier analysis.RESULTS: Both GBM-X12P and X12T express NKG2DL MIC-A, MIC-B, and ULBP-4. DRI cells killed both tumors in vitro at approximately 80% at an effector: target ratio of 20:1 with no toxicity against cultured human astrocytes. Cell therapy alone did not improve survival beyond that of untreated mice. For the parent tumor X12P (Figure 1), TMZ therapy significantly improved median survival over untreated controls (29 vs. 59 days, p < 0.0001), and addition of DRI increased median survival to 120 days with 80% long term survivors. For the TMZ-resistant X12T (Figure 2), TMZ alone did not improve survival over untreated controls (22 vs. 27 days p = 0.4827). Addition of DRI significantly increased median survival from 22 days to 38 days (p = 0.0004) with 10% of animals surviving to day +119. View Large Image | Download PowerPoint Slide View Large Image | Download PowerPoint SlideCONCLUSIONS: This is the first report of combined TMZ chemotherapy and drug-resistance modified γΔ T cell therapy resulting in a significant increase in time to progression and improvement in median and overall survival in immunodeficient mice bearing otherwise impervious human primary xenograft tumors using a strategy is readily adaptable to the clinical setting