Hierarchy of immune responses to antigen in the normal brain

Insight into lipid-based nanoplatform-mediated drug and gene delivery in neuro-oncology and their clinical prospects

Tumors of the Central nervous System (CNS) are a spectrum of neoplasms that range from benign lesions to highly malignant and aggressive lesions. Despite aggressive multimodal treatment approaches, the morbidity and mortality are high with dismal survival outcomes in these malignant tumors. Moreover, the non-specificity of conventional treatments substantiates the rationale for precise therapeutic strategies that selectively target infiltrating tumor cells within the brain, and minimize systemic and collateral damage. With the recent advancement of nanoplatforms for biomaterials applications, lipid-based nanoparticulate systems present an attractive and breakthrough impact on CNS tumor management. Lipid nanoparticles centered immunotherapeutic agents treating malignant CNS tumors could convene the clear need for precise treatment strategies. Immunotherapeutic agents can selectively induce specific immune responses by active or innate immune responses at the local site within the brain. In this review, we discuss the therapeutic applications of lipid-based nanoplatforms for CNS tumors with an emphasis on revolutionary approaches in brain targeting, imaging, and drug and gene delivery with immunotherapy. Lipid-based nanoparticle platforms represent one of the most promising colloidal carriers for chemotherapeutic, and immunotherapeutic drugs. Their current application in oncology especially in brain tumors has brought about a paradigm shift in cancer treatment by improving the antitumor activity of several agents that could be used to selectively target brain tumors. Subsequently, the lab-to-clinic transformation and challenges towards translational feasibility of lipid-based nanoplatforms for drug and gene/immunotherapy delivery in the context of CNS tumor management is addressed.

Tumor-associated macrophages in glioma: friend or foe?

Tumor-associated macrophages (TAMs) contribute substantially to the tumor mass of gliomas and have been shown to play a major role in the creation of a tumor microenvironment that promotes tumor progression. Shortcomings of attempts at antiglioma immunotherapy may result from a failure to adequately address these effects. Emerging evidence supports an independent categorization of glioma TAMs as alternatively activated M2-type macrophages, in contrast to classically activated proinflammatory M1-type macrophages. These M2-type macrophages exert glioma-supportive effects through reduced anti-tumor functions, increased expression of immunosuppressive mediators, and nonimmune tumor promotion through expression of trophic and invasion-facilitating substances. Much of our work has demonstrated these features of glioma TAMs, and together with the supporting literature will be reviewed here. Additionally, the dynamics of glioma cell-TAM interaction over the course of tumor development remain poorly understood; our efforts to elucidate glioma cell-TAM dynamics are summarized. Finally, the molecular pathways which underlie M2-type TAM polarization and gene expression similarly require further investigation, and may present the most potent targets for immunotherapeutic intervention. Highlighting recent evidence implicating the transcription factor STAT3 in immunosuppressive tumorigenic glioma TAMs, we advocate for gene array-based approaches to identify yet unappreciated expression regulators and effector molecules important to M2-type glioma TAMs polarization and function within the glioma tumor microenvironment.

Challenges in immunotherapy presented by the glioblastoma multiforme microenvironment

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. Despite intensive treatment, the prognosis for patients with GBM remains grim with a median survival of only 14.6 months. Immunotherapy has emerged as a promising approach for treating many cancers and affords the advantages of cellular-level specificity and the potential to generate durable immune surveillance. The complexity of the tumor microenvironment poses a significant challenge to the development of immunotherapy for GBM, as multiple signaling pathways, cytokines, and cell types are intricately coordinated to generate an immunosuppressive milieu. The development of new immunotherapy approaches frequently uncovers new mechanisms of tumor-mediated immunosuppression. In this review, we discuss many of the current approaches to immunotherapy and focus on the challenges presented by the tumor microenvironment.

Immunotherapy coming of age: what will it take to make it standard of care for glioblastoma?

With the recent approval by the FDA of an immunotherapy for prostate cancer and another positive immunotherapy trial in melanoma, immunotherapy may finally be coming of age. So what will it take for it to become part of the standard treatment for glioblastoma? To put this question into perspective, we summarize critical background information in neuro-immunology, address immunotherapy clinical trial design, and discuss a number of extrinsic factors that will impact the development of immunotherapy in neuro-oncology.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Cerebrospinal fluid is an efficient route for establishing brain infection with feline immunodeficiency virus and transfering infectious virus to the periphery

Like human immunodeficiency virus (HIV), feline immunodeficiency virus (FIV) invades and infects the central nervous system (CNS) soon after peripheral infection. The appearance of viral RNA is particularly prominent in the cerebrospinal fluid (CSF), suggesting an efficient route of virus transfer across the blood-CSF barrier. This raises the concern whether this route can establish a stable viral reservoir and also be a source of virus capable of reseeding peripheral systems. To examine this possibility, 200 mul of cell-free NCSU1 FIV or FIV-infected choroid plexus macrophages (ChP-Mac) was directly injected into the right lateral ventricle of the brain. Negative controls were sham inoculated with uninfected ChP-Mac or virus-free culture supernatant and positive controls were infected systemically by intraperitoneal (i.p.) injection. Intracerebroventricular (i.c.v.) inoculation with cell-free FIV resulted in high levels of plasma FIV RNA detected as early as 1 to 2 weeks post inoculation in all cats. In each case, the plasma viremia preceded the detection of CSF viral RNA. Compared to i.p. cats, i.c.v. cats had 32-fold higher CSF viral loads, 8-fold higher ratios of CSF to plasma viral load, and a 23-fold greater content of FIV proviral DNA in the brain. No FIV RNA was detected in plasma or CSF from the cats inoculated with FIV-infected ChP-Mac but an acute inflammatory response and a slight suppression of the CD4+:CD8+ ratio were observed. These results indicate that free FIV circulating in the CSF promotes infection of the CNS and provides a highly efficient pathway for the transfer of infectious virus to the periphery.