Personalized Neoantigen Vaccine Targets Hard-to-Treat Solid Tumors
A Phase 1/2 trial tests a custom cancer vaccine paired with checkpoint inhibitors in patients with advanced solid tumors.
Summary
Researchers at Gritstone bio tested a personalized neoantigen cancer vaccine — GRT-C901 and GRT-R902 — combined with the checkpoint inhibitors nivolumab and ipilimumab in patients with difficult-to-treat solid tumors. Neoantigens are unique mutant proteins found on a patient's own tumor cells, making them ideal targets for training the immune system to attack cancer specifically. The trial enrolled 29 patients across four cancer types: non-small cell lung cancer, microsatellite stable colorectal cancer, gastroesophageal adenocarcinoma, and metastatic urothelial cancer. The study assessed how safe the vaccine was, what dose worked best, whether it triggered a measurable immune response, and whether it showed early signs of fighting cancer. Completed in late 2022, this trial represents a significant step in making personalized cancer immunotherapy a clinical reality.
Detailed Summary
Personalized cancer vaccines represent one of the most exciting frontiers in oncology. Unlike conventional treatments, these vaccines are designed for each individual patient, targeting unique mutations — called neoantigens — present only on their tumor cells. This approach aims to harness the immune system with precision, minimizing collateral damage to healthy tissue.
This Phase 1/2 trial, sponsored by Gritstone bio, tested GRT-C901 (a viral vector-based vaccine) and GRT-R902 (an mRNA-based booster) in combination with the checkpoint inhibitors nivolumab and ipilimumab. The combination strategy is significant: checkpoint inhibitors remove the immune system's brakes, while the neoantigen vaccine provides the specific targets for immune cells to attack. Together, they may produce a more potent and durable anti-tumor response than either approach alone.
The study enrolled 29 patients with metastatic non-small cell lung cancer, microsatellite stable colorectal cancer, gastroesophageal adenocarcinoma, or metastatic urothelial cancer — all tumor types with historically poor prognoses and limited immunotherapy responses, particularly microsatellite stable colorectal cancer, which typically resists checkpoint blockade.
Primary objectives included evaluating safety and tolerability, identifying optimal dosing, measuring immunogenicity (whether the vaccine successfully activated tumor-specific T cells), and assessing early clinical activity such as tumor shrinkage or disease stabilization. The trial ran from February 2019 through November 2022 and was completed as planned.
If the vaccine demonstrated meaningful immune activation in these resistant tumor types, it could justify larger trials and potentially reshape treatment paradigms for cancers that currently lack effective immunotherapy options. The enrollment of only 29 patients limits statistical conclusions, and full results have not been published in a peer-reviewed journal based on available information. Nonetheless, this trial marks an important proof-of-concept moment for AI-driven personalized neoantigen vaccine platforms.
Key Findings
- Personalized neoantigen vaccine GRT-C901/GRT-R902 was tested alongside nivolumab and ipilimumab in advanced solid tumors.
- Trial targeted four cancer types with historically poor immunotherapy responses, including MSS colorectal cancer.
- Phase 1/2 design assessed safety, dosing, immunogenicity, and early anti-tumor activity across 29 patients.
- Combining a neoantigen vaccine with checkpoint inhibitors may overcome immune resistance in cold tumors.
- Trial completed successfully in 2022, supporting further development of personalized cancer vaccine platforms.
Methodology
This was an open-label Phase 1/2 study enrolling 29 patients with metastatic solid tumors across four indications. The trial evaluated the personalized neoantigen vaccine GRT-C901 and GRT-R902 in combination with nivolumab and ipilimumab, assessing safety, optimal dosing, immunogenicity, and preliminary clinical efficacy. The study ran from February 2019 to November 2022.
Study Limitations
With only 29 patients enrolled, this early-phase trial is underpowered to draw definitive conclusions about clinical efficacy. Full results including immune response rates and survival outcomes have not been published in a peer-reviewed journal based on available information. This summary is based on the clinical trial registry abstract only and does not include final study results.
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