Cellular-based immunotherapies for patients with glioblastoma multiforme

Abstract

Treatment of patients with glioblastoma multiforme (GBM) remains to be a challenge with a median survival of 14.6 months following diagnosis. Standard treatment options include surgery, radiation therapy, and systemic chemotherapy with temozolomide. Despite the fact that the brain constitutes an immunoprivileged site, recent observations after immunotherapies with lysate from autologous tumor cells pulsed on dendritic cells (DCs), peptides, protein, messenger RNA, and cytokines suggest an immunological and even clinical response from immunotherapies. Given this plethora of immunomodulatory therapies, this paper gives a structure overview of the state-of-the art in the field. Particular emphasis was also put on immunogenic antigens as potential targets for a more specific stimulation of the immune system against GBM.

Figure 1

DC-based active immunotherapy for GBM. DCs display a unique capacity to induce and to maintain T-cell responses. Mature DCs are generated from PBMC in vitro in the presence of IL-4, GM-CSF, TNF-alpha, IL-1beta, PGE2, IFN-gamma, and other cytokines, in addition to TLR agonists. Subsequently, they are loaded with GBM or glioblastoma stem cell lysates, GBM-associated antigen-derived peptides, protein, or RNA. Due to their high surface expression of HLA-peptide-complexes and costimulatory molecules, DCs could efficiently activate and expand CD8⁺ CTLs and CD4⁺ Th cells. CD8⁺ CTLs are able to recognize and eliminate tumor cells, especially the GBM stem cells (CD133). CD4⁺ Th cells enhance the capacity of DCs to induce CTLs by the interaction between CD40 on DCs and CD40 ligand on activated CD4⁺ T cells. In addition, CD4⁺ T cells help in the maintenance and expansion of CTLs by secreting IL-2. CTLs: cytotoxic T cells; imDC: immature dendritic cells; GZMB: granzyme B; GSCs: glioblastoma stem cells, HLA: human leukocyte antigen; IL: interleukin; IFN: interferon; mDC: mature dendritic cells; PBMC: peripheral blood mononuclear cells; TCR: T-cell receptor; Th: T helper cell; TLR: toll-like receptor.

Figure 2

Adoptive immunotherapy for GBM patients with CMV or GAA peptides. CMV and GAAs are highly expressed in GBM, but neither in healthy brain tissue, nor in nonmalignant brain tumors. Therefore, GAAs constitute good targets for immunotherapy of GBM patients. The streptamer technology offers the advantage of selecting CMV- or GAA-specific CD8⁺ CTLs at the good manufacturing practice (GMP) level in vitro. PBMCs from healthy donors are collected and isolated by streptamer beads. Noninduced antigen-specific T cells are purified and accumulated through a magnetic field and released by D-biotin from the streptamer complex. Subsequently, these cells are administered to the GBM patient. CMV/GAA-specific cytotoxic T cells can recognize the target antigens which are presented on the surface of GBM cells or GSCs. Cytotoxicity is exerted directly through the Fas or perforin pathway and/or indirectly by the release of cytokines. CMV: cytomegalovirus; GAA: glioblastoma associated antigen; GBM: glioblastoma multiforme; GSCs: glioblastoma stem cells; HD: healthy donor; PBMC: peripheral blood mononuclear cells; Pt: patient.