Magnetic Resonance Spectroscopy Metabolites as Biomarkers of Disease Status in Pediatric Diffuse Intrinsic Pontine Gliomas (DIPG) Treated with Glioma-Associated Antigen Peptide Vaccines.

PURPOSE: Diffuse intrinsic pontine gliomas (DIPG) are highly aggressive tumors with no currently available curative therapy. This study evaluated whether measurements of in vivo cell metabolites using magnetic resonance spectroscopy (MRS) may serve as biomarkers of response to therapy, including progression. METHODS: Single-voxel MR spectra were serially acquired in two cohorts of patients with DIPG treated with radiation therapy (RT) with or without concurrent chemotherapy and prior to progression: 14 participants were enrolled in a clinical trial of adjuvant glioma-associated antigen peptide vaccines and 32 patients were enrolled who did not receive adjuvant vaccine therapy. Spearman correlations measured overall survival associations with absolute metabolite concentrations of myo-inositol (mI), creatine (Cr), and n-acetyl-aspartate (NAA) and their ratios relative to choline (Cho) during three specified time periods following completion of RT. Linear mixed-effects regression models evaluated the longitudinal associations between metabolite ratios and time from death (terminal decline). RESULTS: Overall survival was not associated with metabolite ratios obtained shortly after RT (1.9-3.8 months post-diagnosis) in either cohort. In the vaccine cohort, an elevated mI/Cho ratio after 2-3 doses (3.9-5.2 months post-diagnosis) was associated with longer survival (rho = 0.92, 95% CI 0.67-0.98). Scans performed up to 6 months before death showed a terminal decline in the mI/Cho ratio, with an average of 0.37 ratio/month in vaccine patients (95% CI 0.11-0.63) and 0.26 (0.04-0.48) in the non-vaccine cohort. CONCLUSION: Higher mI/Cho ratios following RT, consistent with less proliferate tumors and decreased cell turnover, were associated with longer survival, suggesting that this ratio can serve as a biomarker of prognosis following RT. This finding was seen in both cohorts, although the association with OS was detected earlier in the vaccine cohort. Increased mI/Cho (possibly reflecting immune-effector cell influx into the tumor as a mechanism of tumor response) requires further study.

The evolution of alternative splicing in glioblastoma under therapy.

BACKGROUND: Alternative splicing is a rich source of tumor-specific neoantigen targets for immunotherapy. This holds promise for glioblastomas (GBMs), the most common primary tumors of the adult brain, which are resistant to standard-of-care therapy. Although most clinical trials enroll patients at recurrence, most preclinical studies have been done with specimens from primary disease. There are limited expression data from GBMs at recurrence and surprisingly little is known about the evolution of splicing patterns under therapy. RESULT: We profile 37 primary-recurrent paired human GBM specimens via RNA sequencing. We describe the landscape of alternative splicing in GBM at recurrence and contrast that to primary and non-malignant brain-tissue specimens. By screening single-cell atlases, we identify cell-type-specific splicing patterns and novel splicing events in cell-surface proteins that are suitable targets for engineered T cell therapies. We identify recurrent-specific isoforms of mitogen-activated kinase pathway genes that enhance invasiveness and are preferentially expressed by stem-like cells. CONCLUSION: These studies shed light on gene expression in recurrent GBM and identify novel targets for therapeutic development.

Tumor antigens in glioma.

Immunotherapy applications to glioblastoma represent a new treatment frontier. Antigen-targeted immunotherapy approaches hold enormous potential to elicit antigen-specific anti-tumor effects in central nervous system tumors. Still, the paucity of effective antigen targets remains a significant obstacle in safely and effectively treating glioblastoma and other malignant gliomas with relatively low mutation loads. In this review, we highlight the current understanding of and development of immunotherapy to target 1) shared non-mutant antigens 2) shared mutant antigens (neoantigens) derived from cancer-specific mutations 3) personalized neoantigens derived from tumor-specific genetic alterations containing de novo peptide sequences and 4) virus-derived antigens. We also discuss strategies to enhance tumor immunogenicity and neoantigen prediction. Spatial heterogeneity remains a formidable challenge for immunotherapy of glioma; recent advances in targeting multiple antigens and refining the antigen selection pipeline hold great promise to turn the tide against glioma.

Novel and shared neoantigen derived from histone 3 variant H3.3K27M mutation for glioma T cell therapy.

The median overall survival for children with diffuse intrinsic pontine glioma (DIPG) is less than one year. The majority of diffuse midline gliomas, including more than 70% of DIPGs, harbor an amino acid substitution from lysine (K) to methionine (M) at position 27 of histone 3 variant 3 (H3.3). From a CD8+ T cell clone established by stimulation of HLA-A2+ CD8+ T cells with synthetic peptide encompassing the H3.3K27M mutation, complementary DNA for T cell receptor (TCR) α- and ß-chains were cloned into a retroviral vector. TCR-transduced HLA-A2+ T cells efficiently killed HLA-A2+H3.3K27M+ glioma cells in an antigen- and HLA-specific manner. Adoptive transfer of TCR-transduced T cells significantly suppressed the progression of glioma xenografts in mice. Alanine-scanning assays suggested the absence of known human proteins sharing the key amino acid residues required for recognition by the TCR, suggesting that the TCR could be safely used in patients. These data provide us with a strong basis for developing T cell-based therapy targeting this shared neoepitope.

The role of emerging therapy in the management of patients with diffuse low grade glioma.

QUESTION: What is the role of immunotherapy/tumor vaccines in the treatment of low grade gliomas? TARGET POPULATION: Adult patients with newly diagnosed WHO grade 2 astrocytoma, oligo-astroctyoma, or oligodendroglioma. RECOMMENDATIONS: There is no evidence to support a recommendation in regards to the efficacy of immunotherapy or tumor vaccines for the treatment of low grade gliomas. It is recommended that patients be enrolled in properly designed clinical trials to assess immunotherapies and tumor vaccines for low grade gliomas. QUESTION: What is the role of nutrition in the treatment of low grade gliomas? TARGET POPULATION: Adult patients with newly diagnosed WHO grade 2 astrocytoma, oligo-astroctyoma, or oligodendroglioma. RECOMMENDATIONS: There was no evidence to support a recommendation in regard to the efficacy of nutritional therapy for the treatment of low grade gliomas. It is recommended that patients be enrolled in properly designed clinical trials to assess the efficacy of nutrition for this target population. QUESTION: Is there a role for alternative or targeted therapies in the treatment of low grade gliomas? TARGET POPULATION: Adult patients with newly diagnosed WHO grade 2 astrocytoma, oligo-astroctyoma, or oligodendroglioma. RECOMMENDATION: There was no evidence to support a recommendation in regard to the efficacy of targeted or alternative agents for the treatment of low grade gliomas. It is recommended that patients be enrolled in properly designed clinical trials to assess alternative and targeted therapies for this target population.

Biologic therapy for brain cancers--based on cellular and immunobiology.

The overall goal of our research projects is to develop effective immunotherapeutic regimens, particularly combining vaccine and gene therapy/ cell therapy strategies. For the development of clinically effective immunotherapy for brain cancers, the following issues are considered to be particularly important: 1) Induction of effective immune responses against tumors (afferent arm of the immune response), 2) Delivery of immune effector cells to the target tumor sites and maintaining the activity of the effector cells (efferent arm), 3) For specific and safe immunotherapy, specific brain tumor rejection antigens have to be identified, 4) Feasibility, safety and efficacy need to be tested in a series of clinical trials. The following presentation summarizes my research projects and demonstrates how each plan will fit in the whole schema of designing successful immunotherapeutic strategies for brain cancers. In this presentation, I would like to focus on our clinical and basic studies related to the vaccine strategies for patients with glioma, and modulation of tumor-microenvironment using bone-marrow derived stroma cells as vehicles for cytokine- gene delivery.