Enhanced immunotherapy by combining a vaccine with a novel murine GITR ligand fusion protein

Y Maurice Morillon,Nicholas M Durham,Jeffrey Schlom,Scott A Hammond,John W Greiner

doi:10.18632/oncotarget.20703

Abstract

Immunotherapy was significantly enhanced in a murine tumor model by combining a vaccine with a fusion protein designed to target the glucocorticoid-induced tumor necrosis factor (TNF) receptor related gene (GITR) on the surface of T cells. The recombinant poxvirus-based vaccine platform included Modified Vaccinia virus Ankara (rMVA) and fowlpox (rF) vectors as the driver immunogens both engineered to express the human carcinoembryonic antigen (CEA) and three murine costimulatory molecules B7.1, ICAM-1, LFA-3 (designated TRICOM). In previous studies, mice expressing human CEA as a transgene (CEA.Tg mice) vaccinated with rMVA/rF-CEA-TRICOM overcame CEA immune tolerance by inducing anti-CEA‒specific immunity and regression of CEA-expressing tumors. The murine GITR ligand fusion protein (mGITRL-FP) consisted of a mouse IgG2a Fc region, a yeast-derived coiled GCN4 pII and the extracellular GITR-binding domain of murine GITR ligand. The design maximized valency and the potential to agonize the GITR receptor. Combined treatment of the vaccine and mGITRL-FP mediated a more robust tumor regression, leading to sustained improvement in overall survival. The enhanced immunotherapeutic effect was linked to the generation of a strong CD8+ T cell antitumor immune response. A treatment schedule with mGITRL-FP administered prior to the priming rMVA-CEA-TRICOM vaccination was of paramount importance. The mechanism of action for the enhanced antitumor effects resided in the depletion of immune cells, particularly FoxP3+ regulatory T cells, that express high GITR levels following activation. The results provide evidence that targeting GITR with mGITRL-FP in concert with a cancer vaccine represents a potential novel approach to more effective immunotherapy.

Highlights

IntroductionCross-linking of glucocorticoid-induced tumor necrosis factor receptor (GITR) reduces T cell receptor (TCR)-induced apoptosis [7] and improves T cell survival by maintaining responsiveness through www.impactjournals.com/oncotarget signaling of multiple protein kinases (i.e., MAPK, ERKs, JNKs, etc.) and nuclear factor kB (NF-kB) pathways [810]
Glucocorticoid-induced tumor necrosis factor (TNF) receptor related gene or “glucocorticoid-induced tumor necrosis factor receptor (GITR),” known as TNF receptor superfamily member 18 (TNFRSF18), was listed by the National Cancer Institute as among the most promising immunotherapy agents for cancer [1]
MGITRL-FP was co-administered, at doses ranging from 0.01-10 mg/kg, in combination with the vaccine

Summary

Introduction

Cross-linking of GITR reduces TCR-induced apoptosis [7] and improves T cell survival by maintaining responsiveness through www.impactjournals.com/oncotarget signaling of multiple protein kinases (i.e., MAPK, ERKs, JNKs, etc.) and nuclear factor kB (NF-kB) pathways [810]. Multiple mechanisms seem to work in concert that manifest the antitumor effects of targeting GITR. They include: (a) impairment of intratumoral Treg expression of FoxP3, resulting in a loss of Treg cell lineage stability and abrogation of intratumoral Treg suppressive function [15], (b) downregulation of exhaustion markers for CD8+ intratumoral T cells increasing their CTL function [16] and (c) generation of high-avidity CTL responses to tumor-associated antigens [17]. In more recent studies, targeting GITR, on Tregs, using the anti-GITR monoclonal antibody, clone DTA-1, has led to Treg depletion, which is linked to FcγR function [18, 19]

Methods

Results

Conclusion