mKRAS-VAX Peptide Vaccine with Dual Checkpoint Blockade Safely Boosts T-Cell Immunity in Metastatic Colorectal Cancer
Background
Patients with mismatch repair proficient or microsatellite stable (MMRp/MSS) colorectal cancer (CRC) often exhibit limited response to immune checkpoint inhibitors (ICIs). This represents a significant unmet need in advanced CRC treatment. KRAS mutations, present in approximately 40% of these cancers, are known to generate neoantigens. These neoantigens can serve as specific targets for therapeutic vaccines, offering a potential strategy to overcome ICI resistance by stimulating a targeted anti-tumor immune response.
Study Design
This single-arm, phase I study (NCT04117087) evaluated mKRAS-VAX, a pooled mutant KRAS peptide vaccine, in 13 patients with pretreated metastatic MMRp/MSS CRC. The vaccine targeted six common KRAS mutations and was administered in combination with nivolumab and ipilimumab. Primary endpoints were safety and immunogenicity, assessed within 17 weeks post-vaccination. Secondary endpoints included treatment efficacy, defined by RECIST v1.1 criteria. Immunogenicity was measured by direct ex vivo IFNγ ELISpot and following in vitro expansion of T-cells.
Results
Both primary endpoints of safety and immunogenicity were successfully met. All adverse events attributed to mKRAS-VAX were mild, classified as grade 1 or 2. Crucially, the addition of mKRAS-VAX did not increase the frequency of severe immune-related adverse events beyond the expected profile observed with dual ICIs alone. This indicates a favorable safety profile for the vaccine component. The vaccine demonstrated robust immunogenicity: > mKRAS-VAX elicited a significant increase in tumor-specific mKRAS-reactive T-cells in 8/12 biomarker-evaluable patients (75%) when measured by direct ex vivo IFNγ ELISpot. Following in vitro expansion, an even stronger response was observed, with 12 patients (100%) showing an increase in mKRAS-reactive T-cells. These findings strongly support the vaccine's ability to stimulate a targeted immune response.
Key Findings
- mKRAS-VAX peptide vaccine was safe, with all attributed adverse events being grade 1 or 2.
- The vaccine did not increase severe immune-related adverse events beyond dual ICIs alone.
- mKRAS-VAX boosted tumor-specific mKRAS-reactive T-cells in 8/12 (75%) patients by ex vivo
IFNγ ELISpot. - Following
in vitro expansion, 12/12 (100%) patients showed increased mKRAS-reactive T-cells.
Why It Matters
This study provides compelling evidence that a mutant KRAS peptide vaccine can safely enhance anti-tumor immunity in MMRp/MSS colorectal cancer when combined with dual immune checkpoint blockade. For patients with MMRp/MSS CRC, who typically respond poorly to ICIs, this combination offers a novel and promising therapeutic avenue. The ability to generate specific T-cell responses against KRAS neoantigens suggests a path toward personalized immunotherapy. While a phase I study, these results lay the groundwork for larger trials to evaluate clinical efficacy, potentially leading to a new protocol for advanced CRC that leverages both vaccination and checkpoint inhibition.
kras-vaccine
colorectal-cancer
immune-checkpoint-inhibitor
nivolumab
ipilimumab
neoantigen