A personalized DNA vaccine targeting up to 40 patient-specific neoantigens generated robust immune responses and encouraging survival outcomes in patients with MGMT-unmethylated glioblastoma in a small Phase I clinical trial, according to new findings published in Nature Cancer.
The study evaluated GNOS-PV01, a personalized therapeutic cancer vaccine developed by Geneos Therapeutics in collaboration with researchers at Washington University School of Medicine in St. Louis. Investigators reported that the vaccine was safe, feasible to administer, and capable of stimulating circulating and tumor-infiltrating T-cell responses in a cancer type long considered highly resistant to immunotherapy.
Glioblastoma remains one of the deadliest cancers, with median survival typically ranging from 12 to 18 months. Patients with MGMT-unmethylated disease face especially poor outcomes because they derive limited benefit from temozolomide, a standard chemotherapy agent commonly used after surgery and radiation.
“Nothing really works in this MGMT-negative or unmethylated glioblastoma patient population,” said Niranjan Sardesai, Geneos’ CEO. “Median survival is around a year, and effective treatments are very much needed.”
The open-label, single-arm GT-20 study enrolled nine patients with newly diagnosed MGMT-unmethylated glioblastoma following surgical resection and radiation therapy. Each patient received a fully individualized vaccine constructed from neoantigens identified through sequencing of their own tumors. Vaccines encoded between 17 and 40 neoantigens per patient.
According to the paper, the vaccine caused no serious adverse events, unexpected toxicities, or dose-limiting toxicities. Eight of the nine evaluable patients developed measurable immune responses. The lone nonresponder had been treated with dexamethasone, an immunosuppressive corticosteroid frequently used in glioblastoma management.
Sardesai emphasized that the immunogenicity findings were particularly notable because glioblastoma is considered an “immune-excluded” tumor with low tumor mutational burden, characteristics that have historically limited the effectiveness of checkpoint inhibitors such as anti–PD-1 therapies.
“Checkpoint-based immunotherapy has not worked in GBM,” he said. “This is a cold tumor.”
The investigators also observed signals of clinical activity. Six-month progression-free survival and 12-month overall survival were each achieved in 66.7% of patients. Median progression-free survival was 8.5 months, while median overall survival reached 16.3 months. Survival at 24 months was 33%, including one patient who remains alive four years after surgery.
“What was very striking was that three of nine patients, or one-third of the patients, had lived more than two years,” Sardesai said. “The two-year survival rate is about 10% to 15%” with standard treatment approaches in this population.
The study also identified an association between stronger CD8-positive T-cell responses and longer survival. Investigators reported that patients generating higher levels of vaccine-induced cytotoxic T cells tended to experience improved overall survival.
One of the most compelling findings involved a long-term survivor who has remained progression-free for nearly five years. Researchers analyzed a brain biopsy obtained approximately three years after treatment initiation and identified vaccine-induced T-cell clones within the tumor tissue that matched T-cell populations detected in the patient’s blood.
“For the first time, we are able to match vaccine-driven immune responses,” Sardesai said. “We are able to see T-cell clones in the blood, and these T-cell clones have infiltrated and are found in her brain.”
The vaccine platform differs from earlier glioblastoma vaccine strategies in several ways. Rather than targeting a small number of antigens, the DNA-based approach allows investigators to incorporate a much larger neoantigen repertoire into each personalized product.
“These patients received as many as 40 different antigens that were identified from their own tumor,” Sardesai said. “Prior treatments had typically been looking at 20 or fewer in GBM.”
He argued that broader antigen targeting may be especially important in glioblastoma because of the disease’s pronounced intratumoral heterogeneity.
“When it comes to targeting cancer, more is better,” he said. “You want to take more shots on goal.”
Another distinguishing feature of the platform is its apparent ability to stimulate CD8-positive killer T cells, which are considered critical for direct tumor cell elimination. Sardesai noted that generating robust CD8 responses has historically been difficult for many cancer vaccine technologies.
Importantly, each vaccine is uniquely manufactured for a single patient.
“These are exquisitely personalized vaccines,” Sardesai said. “Every patient gets their own vaccine.”
The authors cautioned that the findings remain preliminary because of the trial’s small sample size and lack of a control arm. Still, they believe the results justify larger randomized studies.
“We are very encouraged by the data,” Sardesai said. “But this is still only nine patients. We have to replicate these findings in larger, well-controlled studies.”
The company has previously reported results using the same platform in hepatocellular carcinoma, suggesting the strategy could potentially extend across multiple tumor types characterized by immune exclusion and low tumor mutational burden.
“All cancers carry neoantigens,” Sardesai said. “These personalized cancer vaccines provide a very convenient way” to target those tumor-specific alterations across different cancers.
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