Cancer Therapy: Preclinical Systemic Inhibition of Transforming Growth Factor-β in Glioma-Bearing Mice Improves the Therapeutic Efficacy of Glioma-Associated Antigen Peptide Vaccines

Purpose: A variety of cancers, including malignant gliomas, overexpress transforming growth factor-β (TGF-β), which helps tumors evade effective immune surveillance through a variety of mechanisms, including inhibition of CD8 CTLs and enhancing the generation of regulatory T (Treg) cells. We hypothesized that inhibition of TGF-β would improve the efficacy of vaccines targeting glioma-associated antigen (GAA)–derived CTL epitopes by reversal of immunosuppression. Experimental Design: Mice bearing orthotopic GL261 gliomas were treated systemically with a TGF-β–neutralizing monoclonal antibody, 1D11, with or without s.c. vaccinations of synthetic peptides for GAA-derived CTL epitopes, GARC-1 (77-85) and EphA2 (671-679), emulsified in incomplete Freund's adjuvant. Results: Mice receiving the combination regimen exhibited significantly prolonged survival compared with mice receiving either 1D11 alone, GAA vaccines alone, or mock treatments alone. TGF-β neutralization enhanced the systemic induction of antigenspecific CTLs in glioma-bearing mice. Flow cytometric analyses of brain-infiltrating lymphocytes revealed that 1D11 treatment suppressed phosphorylation of Smad2, increased GAA-reactive/IFN-γ–producing CD8 T cells, and reduced CD4/FoxP3 Treg cells in the glioma microenvironment. Neutralization of TGF-β also upregulated plasma levels of interleukin-12, macrophage inflammatory protein-1α, and IFN-inducible protein-10, suggesting a systemic promotion of type-1 cytokine/chemokine production. Furthermore, 1D11 treatment upregulated plasma interleukin-15 levels and promoted the persistence of GAA-reactive CD8 T cells in glioma-bearing mice. Conclusions: These data suggest that systemic inhibition of TGF-β by 1D11 can reverse the suppressive immunologic environment of orthotopic tumor-bearing mice both systemically and locally, thereby enhancing the therapeutic efficacy of GAA vaccines. (Clin Cancer Res 2009;15(21):6551–9) Malignant gliomas represent the most common primary central nervous system tumors and exhibit a dismal prognosis despite recent advances made in surgical, radiological, and chemotherapeutic approaches (1). Development of novel, multimodal therapeutic approaches is thus critical to improve the outcome of these deadly tumors (2). Among these approaches, immunotherapy can be promising for glioma treatment if we are able to induce potent immune responses directed against glioma-associated antigens (GAA; refs. 3–5). Indeed, several immunologic strategies have been evaluated in early phase clinical trials; however, modest clinical benefit in glioma immunotherapy trials calls for further improvement of these strategies (6). Transforming growth factor-β (TGF-β) is a highly pleiotropic cytokine that plays key regulatory roles in many aspects of immunity (7). It directly inhibits cytolytic activity of natural killer cells, macrophages, and CD8 cytotoxic T cells (8, 9). It can also inhibit instruction, activation, and expansion of tumor-specific helper and cytotoxic T-cell populations (10) and enhance the generation of immunosuppressive regulatory T (Treg) cells Authors' Affiliations: Departments of Neurological Surgery, Surgery, Dermatology, and Immunology, University of Pittsburgh School of Medicine, Brain Tumor Program, University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania; and Cancer and Immunotherapy Research, Genzyme Corporation, Framingham, Massachusetts Received 4/27/09; revised 8/1/09; accepted 8/10/09; published OnlineFirst