Immunotherapy represents an appealing option to specifically target CNS tumors using the immune system. In this report, we tested whether adjunctive treatment with the TLR-7 agonist imiquimod could augment antitumor immune responsiveness in CNS tumor-bearing mice treated with human gp100 + tyrosine-related protein-2 melanoma-associated Ag peptide-pulsed dendritic cell (DC) vaccination. Treatment of mice with 5% imiquimod resulted in synergistic reduction in CNS tumor growth compared with melanoma-associated Ag-pulsed DC vaccination alone. Continuous imiquimod administration in CNS tumor-bearing mice, however, was associated with the appearance of robust innate immune cell infiltration and hemorrhage into the brain and the tumor. To understand the immunological mechanisms by which imiquimod augmented antitumor immunity, we tested whether imiquimod treatment enhanced DC function or the priming of tumor-specific CD8+ T cells in vivo. With bioluminescent, in vivo imaging, we determined that imiquimod dramatically enhanced both the persistence and trafficking of DCs into the draining lymph nodes after vaccination. We additionally demonstrated that imiquimod administration significantly increased the accumulation of tumor-specific CD8+ T cells in the spleen and draining lymph nodes after DC vaccination. The results suggest that imiquimod positively influences DC trafficking and the priming of tumor-specific CD8+ T cells. However, inflammatory responses induced in the brain by TLR signaling must also take into account the local microenvironment in the context of antitumor immunity to induce clinical benefit. Nevertheless, immunotherapeutic targeting of malignant CNS tumors may be enhanced by the administration of the innate immune response modifier imiquimod.

The purpose of this study was to evaluate the use of adipose-derived stem cells (ADSCs) as a source for full-thickness cartilage repair in an animal model. Autologous ADSCs were isolated and induced with growth medium and placed in a fibrin glue scaffold and into 3-mm x 4-mm full-thickness chondral defects in rabbits with negative controls. Specimens were evaluated for early healing using immunostaining, Western blotting, reverse transcriptase polymerase chain reaction, transfection with the Lac Z gene, and quantitative assessment. Twelve of 12 (100%) articular surface defects containing tissue-engineered stem cell constructs healed with hyaline-like cartilage, versus 1 of 12 (8%) in the control group (p < .001). There was complete healing to subchondral bone in 12 of 12 experimental defects (100%), and 10 of 12 (83%) had seamless annealing to the native cartilage. Aggrecan, superficial zone protein, collagen type II messenger ribonucleic acid, and Lac-Z gene products were identified in 12 of 12 experimental specimens, which exhibited a collagen type II:I protein ratio similar to that of normal rabbit cartilage. Quantitative histologic analysis revealed an average score of 18.2 of 21 in the experimental group, compared with 10.0 in the controls (p = .001). Induced ADSCs supported in a fibrin glue matrix are a promising cell source for cartilage tissue engineering.

It is commonly believed that T cells have difficulty reaching tumors located in the brain due to the presumed "immune privilege" of the central nervous system (CNS). Therefore, we studied the biodistribution and antitumor activity of adoptively transferred T cells specific for an endogenous tumor-associated antigen (TAA), gp100, expressed by tumors implanted in the brain. Mice with preestablished intracranial (i.c.) tumors underwent total body irradiation (TBI) to induce transient lymphopenia, followed by the adoptive transfer of gp100 25-33 -specific CD8 + T cells (Pmel-1). Pmel-1 cells were transduced to express the bioluminescent imaging (BLI) gene luciferase. After adoptive transfer, recipient mice were vaccinated with hgp100 25-33 peptidepulsed dendritic cells (hgp100 25-33 /DC) and systemic interleukin 2 (IL-2). This treatment regimen resulted in significant reduction in tumor size and extended survival. Imaging of T cell trafficking demonstrated early accumulation of transduced T cells in lymph nodes draining the hgp100 25-33 /DC vaccination sites, the spleen and the cervical lymph nodes draining the CNS tumor. Subsequently, transduced T cells accumulated in the bone marrow and brain tumor. BLI could also detect significant differences in NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript the expansion of gp100-specific CD8 + T cells in the treatment group compared with mice that did not receive either DC vaccination or IL-2. These differences in BLI correlated with the differences seen both in survival and tumor infiltrating lymphocytes (TIL). These studies demonstrate that peripheral tolerance to endogenous TAA can be overcome to treat tumors in the brain and suggest a novel trafficking paradigm for the homing of tumor-specific T cells that target CNS tumors.

NK cells represent a potent immune effector cell type that have the ability to recognize and lyse tumors. However, the existence and function of NK cells in the traditionally “immune-privileged” CNS is controversial. Furthermore, the cellular interactions involved in NK cell anti-CNS tumor immunity are even less well understood. We administered non-Ag-loaded, immature dendritic cells (DC) to CD8α knockout (KO) mice and studied their anti-CNS tumor immune responses. DC administration induced dramatic antitumor immune protection in CD8α KO mice that were challenged with B16 melanoma both s.c. and in the brain. The CNS antitumor immunity was dependent on both CD4+ T cells and NK cells. Administration of non-Ag-loaded, immature DC resulted in significant CD4+ T cell and NK cell expansion in the draining lymph nodes at 6 days postvaccination, which persisted for 2 wk. Finally, DC administration in CD8α KO mice was associated with robust infiltration of CD4+ T cells and NK cells into the brain tumor parenchyma. These results represent the first demonstration of a potent innate antitumor immune response against CNS tumors in the absence of toxicity. Thus, non-Ag-loaded, immature DC administration, in the setting of CD8 genetically deficient mice, can induce dramatic antitumor immune responses within the CNS that surpass the effects observed in wild-type mice. Our results suggest that a better understanding of the cross-talk between DC and innate immune cells may provide improved methods to vaccinate patients with tumors located both systemically and within the CNS.

Malignant gliomas are the most common type of primary brain tumor and are in great need of novel therapeutic approaches. Advances in treatment have been very modest, significant improvement in survival has been lacking for many decades and prognosis remains dismal. Despite 'gross total' surgical resections and currently available radio-chemotherapy, malignant gliomas inevitably recur due to reservoirs of notoriously invasive tumor cells that infiltrate adjacent and nonadjacent areas of normal brain parenchyma. In principle, the immune system is uniquely qualified to recognize and target these infiltrative pockets of tumor cells, which have generally eluded conventional treatment approaches. In the span of the last 10 years, our understanding of the cancer-immune system relationship has increased exponentially, and yet, we are only beginning to tease apart the intricacies of the CNS and immune cell interactions. This article reviews the complex associations of the immune system with brain tumors. We provide an overview of currently available treatment options for malignant gliomas, existing gaps in our knowledge of brain tumor immunology, and molecular techniques and targets that might be exploited for improved patient stratification and design of 'custom immunotherapeutics'. We will also examine major new immunotherapy approaches that are being actively investigated to treat patients with malignant glioma, and identify some current and future research priorities in this area.