PGE2 Is Crucial for the Generation of FAST Whole- Tumor-Antigens Loaded Dendritic Cells Suitable for Immunotherapy in Glioblastoma

In vivo targeting of a tumor-antigen encoded DNA vaccine to dendritic cells in combination with tumor-selective chemotherapy eradicates established mouse melanoma

Despite remarkable progress during the past decade, eradication of established tumors by targeted cancer therapy and cancer immunotherapy remains an uphill task. Herein, we report on a combination approach for eradicating established mouse melanoma. Our approach employs the use of tumor selective chemotherapy in combination with in vivo dendritic cell (DC) targeted DNA vaccination. Liposomes of a newly synthesized lipopeptide containing a previously reported tumor-targeting CGKRK-ligand covalently grafted in its polar head-group region were used for tumor selective delivery of cancer therapeutics. Liposomally co-loaded STAT3siRNA and WP1066 (a commercially available inhibitor of the JAK2/STAT3 pathway) were used as cancer therapeutics. In vivo targeting of a melanoma antigen (MART-1) encoded DNA vaccine (p-CMV-MART1) to dendritic cells was accomplished by complexing it with a previously reported mannose-receptor selective in vivo DC-targeting liposome. Liposomes of the CGKRK-lipopeptide containing encapsulated FITC-labeled siRNA, upon intravenous administration in B16F10 melanoma bearing mice, showed remarkably higher accumulation in tumors 24 h post i.v. treatment, compared to their degree of accumulation in other body tissues including the lungs, liver, kidneys, spleen and heart. Importantly, the findings in tumor growth inhibition studies revealed that only in vivo DC-targeted genetic immunization or only tumor-selective chemotherapy using the presently described systems failed to eradicate the established mouse melanoma. The presently described combination approach is expected to find future applications in combating various malignancies (with well-defined surface antigens).

Dendritic Cells and Cancer Immunotherapy: The Adjuvant Effect

Dendritic cells (DCs) are immune specialized cells playing a critical role in promoting immune response against antigens, and may represent important targets for therapeutic interventions in cancer. DCs can be stimulated ex vivo with pro-inflammatory molecules and loaded with tumor-specific antigen(s). Protocols describing the specific details of DCs vaccination manufacturing vary widely, but regardless of the employed protocol, the DCs vaccination safety and its ability to induce antitumor responses is clearly established. Many years of studies have focused on the ability of DCs to provide overall survival benefits at least for a selection of cancer patients. Lessons learned from early trials lead to the hypothesis that, to improve the efficacy of DCs-based immunotherapy, this should be combined with other treatments. Thus, the vaccine’s ultimate role may lie in the combinatorial approaches of DCs-based immunotherapy with chemotherapy and radiotherapy, more than in monotherapy. In this review, we address some key questions regarding the integration of DCs vaccination with multimodality therapy approaches for cancer treatment paradigms.

Extrinsic factors associated with the response to immunotherapy in glioblastoma

Glioblastoma (GBM) is a heterogeneous and lethal brain tumor. Despite the success of immune checkpoint inhibitors against various malignancies, GBM remains largely refractory to treatment. The immune microenvironment of GBM is highly immunosuppressive, which poses a major hurdle for the success of immunotherapy. Obviously, except for the GBM cells itself, there are also extrinsic reasons for the lack of efficacy of immunotherapy. Accumulated evidence indicates that factors other than GBM cells determine the efficacy of immunotherapy. In this review, we first described the unique immune microenvironment of the brain, which must be considered when using immunotherapy in patients with GBM. Second, we also described the mechanisms by which different immune and non-immune cells in the GBM microenvironment affect the efficacy of immunotherapy. Furthermore, the impact of standard therapies on the response to immunotherapy was delineated. Finally, we briefly discussed strategies for resolving these problems and improving the efficacy of immunotherapy.