Personalized neoantigen vaccines: a glimmer of hope for glioblastoma

INTRODUCTION

Glioblastoma multiforme (GBM) is the most prevalent primary brain tumor. In spite of the rigorous multimodal treatment involving surgery and radiochemotherapy, GBM has a dismal prognosis and rapid relapsing potential. Hence, search for novel therapeutic agents still continues. Neoantigens are the tumor-specific antigens which arise due to somatic mutations in the tumor genome. In recent years, personalized vaccine approach targeting neoantigens has been explored widely in cancer immunotherapy and several efforts have also been made to revolutionize the immunotherapy of cold tumors such as GBM using neoantigen targeted vaccines.

AREAS COVERED

In this review, we discuss the clinical application of personalized neoantigen targeted vaccine strategy in GBM immunotherapy. While discussing this strategy, we brief about the current challenges faced in GBM treatment by the novel immunotherapeutics.

EXPERT OPINION

To date, very few vaccines developed for GBM have reached till phase III clinical development. Early-phase clinical trials of GBM neoantigen vaccines have shown promising clinical outcomes and therefore, its rapid clinical development is warranted. Advent of newer and faster techniques such as next-generation sequencing will drive the faster clinical development of multiplex neoantigen vaccines and hence, increase in the clinical trials is expected.

Tumor Vaccines for Malignant Gliomas

Despite continued research efforts, glioblastoma multiforme (GBM) remains the deadliest brain tumor. Immunotherapy offers a novel way to treat this disease, the genetic signature of which is not completely elucidated. Additionally, these tumors are known to induce immunosuppression in the surrounding tumor microenvironment via an array of mechanisms, making effective treatment all the more difficult. The immunotherapeutic strategy of using tumor vaccines offers a way to harness the activity of the host immune system to potentially control tumor progression. GBM vaccines can react to a variety of tumor-specific antigens, which can be harvested from the patient's unique pathological condition using selected immunotherapy techniques. This article reviews the rationale behind and development of GBM vaccines, the relevant clinical trials, and the challenges involved in this treatment strategy.

An Update on the Role of Immunotherapy and Vaccine Strategies for Primary Brain Tumors

Existing therapies for glioblastoma (GBM), the most common malignant primary brain tumor in adults, have fallen short of improving the dismal patient outcomes, with an average 14-16-month median overall survival. The biological complexity and adaptability of GBM, redundancy of dysregulated signaling pathways, and poor penetration of therapies through the blood-brain barrier contribute to poor therapeutic progress. The current standard of care for newly diagnosed GBM consists of maximal safe resection, followed by fractionated radiotherapy combined with concurrent temozolomide (TMZ) and 6-12 cycles of adjuvant TMZ. At progression, bevacizumab with or without additional chemotherapy is an option for salvage therapy. The recent FDA approval of sipuleucel-T for prostate cancer and ipilumimab, nivolumab, and pembrolizumab for select solid tumors and the ongoing trials showing clinical efficacy and response durability herald a new era of cancer treatment with the potential to change standard-of-care treatment across multiple cancers. The evaluation of various immunotherapeutics is advancing for GBM, putting into question the dogma of the CNS as an immuno-privileged site. While the field is yet young, both active immunotherapy involving vaccine strategies and cellular therapy as well as reversal of GBM-induced global immune-suppression through immune checkpoint blockade are showing promising results and revealing essential immunological insights regarding kinetics of the immune response, immune evasion, and correlative biomarkers. The future holds exciting promise in establishing new treatment options for GBM that harness the patients' own immune system by activating it with immune checkpoint inhibitors, providing specificity using vaccine therapy, and allowing for modulation and enhancement by combinatorial approaches.

Improving vaccine efficacy against malignant glioma

The effective treatment of adult and pediatric malignant glioma is a significant clinical challenge. In adults, glioblastoma (GBM) accounts for the majority of malignant glioma diagnoses with a median survival of 14.6 mo. In children, malignant glioma accounts for 20% of primary CNS tumors with a median survival of less than 1 y. Here, we discuss vaccine treatment for children diagnosed with malignant glioma, through targeting EphA2, IL-13Rα2 and/or histone H3 K27M, while in adults, treatments with RINTEGA, Prophage Series G-100 and dendritic cells are explored. We conclude by proposing new strategies that are built on current vaccine technologies and improved upon with novel combinatorial approaches.

Rindopepimut: anti-EGFRvIII peptide vaccine, oncolytic

Glioblastoma, the most common primary malignant brain tumor, is among the most difficult cancers to treat. Despite the aggressive standard of care, including surgical removal followed by radiotherapy with concomitant and adjuvant chemotherapy, the often sudden onset, diffuse infiltrating nature and highly malignant features of the lesion result in a median overall survival of < 15 months. Currently employed standard- of-care therapy for glioblastoma is nonspecific, leading to premature withdrawal of treatment due to off-target toxicity. Rindopepimut is a peptide-based vaccine that elicits a potent humoral and cellular immune response specifically against cells expressing EGFRvIII, a rearranged, cell-surface tyrosine kinase receptor present exclusively in glioblastoma and other common neoplasms. Several phase I and phase II clinical trials have demonstrated that vaccination with rindopepimut is safe, well tolerated and produces a highly potent immune response that effectively eradicates EGFRvIII-expressing tumor cells, leading to a 73% increase in survival among patients with newly diagnosed glioblastoma. Furthermore, temozolomide-induced lymphopenia enhances the rindopepimut-induced immune response against EGFRvIII, allowing for enhanced vaccination responses in the context of standard-of-care chemotherapy. Rindopepimut is currently undergoing evaluation in a phase III international trial for newly diagnosed glioblastoma and is under clinical investigation for recurrent glioblastoma and pediatric brain stem gliomas.