Neo-adjuvant Evaluation of Glioma Lysate Vaccines in WHO Grade II Glioma

Low-grade gliomas (LGG), the most common of which are pilocytic astrocytomas, diffuse astrocytomas, oligodendrogliomas, and mixed oligo-astrocytomas are a diverse family of central nervous system (CNS) neoplasms that occur in children and adults. Based on data from the American Cancer Society and Central Brain Tumor Registry of the United States (CBRTUS), approximately 1800 LGG were diagnosed in 2006, thus representing approximately 10% of newly diagnosed primary brain tumors in the United States. Pilocytic astrocytomas (WHO grade I) are the most common brain tumor in children 5 to 19 years of age3. Diffuse astrocytomas, oligodendrogliomas, and oligoastrocytomas are all considered WHO grade II low grade gliomas (LGG) and are more common in adults. Pilocytic astrocytomas are generally well circumscribed histologically and radiographically and amenable to cure with gross total resection. In contrast, the diffuse astrocytomas, oligodendrogliomas, and oligoastrocytomas are more infiltrative and less amenable to complete resection. From a molecular genetics standpoint, the most common alterations in LGG are Isocitrate dehydrogenase 1 (IDH1) mutations and mutations in the tumor suppressor gene TP53, located on chromosome 17, the gene product of which is a multifunctional protein involved in the regulation of cell growth, cell death (apoptosis), and transcription. Additionally, several molecular factors are of favorable prognostic significance, particularly the presence of 1p/19q co-deletion and IDH1 mutations.

WHO grade II LGGs are at extremely high risk to undergo malignant transformation into more aggressive and lethal WHO grade III or IV high-grade glioma (HGG). Even with a combination of available therapeutic modalities (i.e., surgery, radiation therapy [RT], chemotherapy), the invasive growth and resistance to therapy exhibited by these tumors results in recurrence and death in most patients. Although postoperative RT in LGG significantly improves 5-year progression-free survival (PFS), it does not prolong overall survival (OS) compared with delayed RT given at the time of progression. Early results from a randomized trial of radiation therapy plus procarbazine, lomustine, and vincristine (PCV) chemotherapy for supratentorial adult LGG (RTOG 9802) demonstrated improved PFS in patients receiving PCV plus RT compared RT alone. Nonetheless, PCV is considerably toxic and currently not widely used for management of glioma patients. Although chemotherapy with temozolomide (TMZ) is currently being investigated in LGG patients, it is unknown whether it confers improves OS in these patients. Further, our recent study has indicated that 6 of 10 LGG cases treated with TMZ progressed to HGG with markedly increased exome mutations and, more worrisome, driver mutations in the RB and protein kinase B (AKT)-mechanistic target of rapamycin (mTOR) pathways, with predominant C>T/G>A transitions at CpC and CpT dinucleotides, strongly suggesting a signature of TMZ-induced mutagenesis; this study also showed that in 43% of cases, at least half of the mutations in the initial tumor were undetected at recurrence. These data suggests the possibility that treatment of LGG patients with TMZ may enhance oncogenic mutations and genetic elusiveness of LGG, therefore calling for development of safer and effective therapeutic modalities such as vaccines.

Taken together, LGG are considered a premalignant condition for HGG, such that novel interventions to prevent malignant transformation need to be evaluated in patients with LGG. Immunotherapeutic modalities, such as vaccines, may offer a safe and effective option for these patients due to the slower growth rate of LGG (in contrast with HGG), which should allow sufficient time for multiple immunizations and hence high levels of anti-glioma immunity. Because patients with LGGs are generally not as immuno-compromised as patients with HGG, they may also exhibit greater immunological response to and benefit from the vaccines. Further, the generally mild toxicity of vaccines may improve quality of life compared with chemotherapy or RT.