KRAS Peptide Vaccines: Targeting Cancer's Top Mutation

Personalized Cancer Vaccines

25% of all cancers

KRAS is the most frequently mutated oncogene in human cancer, found in roughly 25% of all tumors. Peptide vaccines targeting these mutations are advancing through clinical trials.

Wang et al., Cancer Gene Therapy, 2024

Wang et al., Cancer Gene Therapy, 2024

View as image

KRAS mutations appear in roughly 90% of pancreatic cancers, 40% of colorectal cancers, and 30% of non-small cell lung cancers. For decades, KRAS was considered "undruggable" because the protein's smooth surface offered no obvious binding pocket for small molecules. The peptide approach is different: instead of blocking the mutant protein directly, KRAS peptide vaccines train the immune system to recognize and destroy cells displaying mutant KRAS fragments on their surface. As the pillar article on neoantigen peptide vaccines explains, this strategy targets what makes each cancer unique. KRAS mutations are among the most promising targets because the same handful of mutations appear across millions of patients.

Why KRAS Is an Ideal Vaccine Target

Most tumor neoantigens are patient-specific. A mutation unique to one person's tumor cannot be used for an off-the-shelf vaccine. KRAS is different. The six most common KRAS mutations (G12D, G12V, G12C, G12R, G12A, G13D) account for the vast majority of KRAS-mutant cancers. G12D alone drives approximately 40% of KRAS-mutant pancreatic cancers. G12C predominates in lung cancer. G12V is common across all three major KRAS-driven cancer types.

This recurrence means a single peptide vaccine formulation can target millions of patients. The mKRAS-VAX vaccine, currently in clinical trials, contains synthetic long peptides covering all six hotspot mutations. A patient's tumor is sequenced to identify which KRAS mutation is present, then the matching peptide component activates mutation-specific T cells.

The mutant KRAS peptide must be processed by the proteasome, loaded onto MHC class I molecules, and presented on the tumor cell surface for T cells to recognize it. This is the same peptide-MHC presentation process used by all peptide vaccines. The challenge is that KRAS-derived peptides do not always bind MHC molecules with high affinity, limiting how many patients can develop an immune response to any single formulation.

The Spliced Epitope Discovery

Mishto et al. (2019) identified a solution to the MHC binding problem^[2]. Using an in silico-in vitro pipeline, they discovered that the proteasome can generate spliced epitopes from KRAS G12V. In proteasomal splicing, the proteasome cuts the KRAS protein at two separate sites and ligates the fragments together, creating a hybrid peptide that does not exist in the original protein sequence.

One of these spliced epitopes bound HLA-A02:01 (the most common HLA class I allele) and activated CD8+ T cell responses. This finding is significant because the conventional (non-spliced) KRAS G12V peptide has poor binding affinity for HLA-A02:01. Proteasomal splicing creates new peptide sequences that may be better MHC binders, expanding the pool of patients who can mount immune responses against their KRAS-mutant tumors.

The implication for vaccine design is that peptide sequences included in KRAS vaccines should account for proteasomal splicing products, not just linear fragments of the mutant protein. Including spliced epitopes in multi-peptide formulations could substantially increase the fraction of patients who generate immune responses, because the spliced peptides access HLA alleles that linear KRAS peptides cannot bind.

This also raises a surveillance question. If the immune system can generate T cell responses against spliced KRAS epitopes, why does this not happen naturally? The answer likely involves immune tolerance and the tumor microenvironment: cancer cells suppress antigen presentation and T cell function through multiple mechanisms, preventing what would otherwise be a detectable immune target from triggering a response.

Intranasal Delivery: Meeting the Tumor Where It Lives

Wang et al. (2024) tested a novel approach: intranasal delivery of a KRAS peptide vaccine for NSCLC^[1]. Lung cancers grow on mucosal surfaces, and the mucosal immune system is largely separate from the systemic immune compartment. Systemically injected vaccines may generate circulating T cells that fail to infiltrate the lung epithelium efficiently.

The intranasal KRAS vaccine generated mucosal immune responses directly at the tumor site. In mouse models of KRAS-mutant NSCLC, intranasal vaccination inhibited tumor growth more effectively than subcutaneous delivery. The local mucosal T cell response provided direct tumor access without requiring immune cells to cross from the bloodstream into the lung tissue.

This route-of-delivery question applies broadly to all lung cancer peptide vaccines. A subcutaneous injection might generate a blood-borne immune response that never reaches adequate concentrations in the lung microenvironment. Intranasal delivery solves this by activating lung-resident immune cells directly.

Clinical Trial Landscape (2024-2026)

Several KRAS peptide vaccine trials are producing early results:

mKRAS-VAX + checkpoint inhibitors: A Phase I trial combined a pooled synthetic long peptide vaccine targeting six KRAS mutations with ipilimumab and nivolumab in patients with MMR-proficient/microsatellite stable colorectal cancer. These are cancers that typically do not respond to checkpoint immunotherapy alone. 75% of patients (8 of 12) developed KRAS mutation-specific T cell responses, measured by IFN-gamma ELISpot, with a median 9-fold increase from baseline. The vaccine created new immune responses that checkpoint inhibitors alone could not generate.

ELI-002 2P (AMPLIFY-201): This Phase 1 trial tested lymph node-targeting amphiphile KRAS peptide antigens (G12D, G12R) with CpG adjuvant in 25 patients (20 pancreatic, 5 colorectal cancer). At a median follow-up of 19.7 months, patients with strong mKRAS-specific T cell responses had not reached median relapse-free survival, compared to 3.02 months for weak responders. The correlation between immune response strength and clinical outcome was clear.

Combination with mRNA platforms: Multiple trials are testing mRNA-encoded KRAS neoantigens alongside peptide approaches. The ABO2102 trial (started September 2024) evaluates mRNA KRAS vaccine with PD-1 inhibition in advanced KRAS-mutant pancreatic and solid tumors.

The convergence of peptide, mRNA, and combination strategies reflects a broad recognition that mutant KRAS is one of the most actionable shared neoantigens in oncology. The synthetic long peptide approach offers manufacturing simplicity and stability advantages over mRNA, while mRNA platforms may generate stronger CD8+ T cell responses due to their ability to express full-length antigens intracellularly. Head-to-head comparisons between these platforms for KRAS-specific immunization have not been published.

Beyond Vaccines: Peptide-Based KRAS Inhibitors

Peptide approaches to KRAS extend beyond vaccination. Cyclic peptides can directly bind and inhibit the mutant KRAS protein inside cells, functioning as targeted drugs rather than immune stimulators.

Kage et al. (2024) reported structure-activity relationships for middle-size cyclic peptides derived from mRNA display screening that directly inhibit KRAS^[3]. The clinical candidate LUNA18 was developed from this approach. Unlike small molecule KRAS inhibitors (sotorasib, adagrasib) that target only G12C, cyclic peptides can potentially target other KRAS mutations that lack small molecule inhibitors.

Zhang et al. (2026) discovered a dual-targeting peptide inhibitor that simultaneously blocks KRAS G12D signaling and HDAC activity in pancreatic cancer cells^[5]. This bifunctional peptide exploits KRAS and HDAC's roles in the same signaling pathway, attacking both the oncogenic driver and its downstream effector.

Mondal et al. (2025) took a different approach entirely: peptide nucleic acid oligomers attached to cell-penetrating peptides that selectively target KRAS G12D mRNA for degradation^[6]. This peptide-nucleic acid hybrid silences KRAS at the RNA level before the mutant protein is even produced.

TCR-T Cells: Peptide Specificity Meets Cell Therapy

Liang et al. (2026) developed avidity-optimized T cell receptor T cells (TCR-T cells) that specifically recognize KRAS neoantigens presented on MHC molecules^[4]. These engineered T cells achieved complete tumor clearance in preclinical models and generated tumor-specific immunological memory.

The connection to peptide vaccines is direct: TCR-T cells recognize the same peptide-MHC complexes that a peptide vaccine would generate immune responses against. The peptide vaccine approach trains the patient's own T cells to recognize these complexes. The TCR-T approach engineers T cells externally and infuses them. Both depend on the same peptide epitope biology.

Alias et al. (2023) explored a different delivery platform: using Lactococcus lactis bacteria engineered to secrete mutant KRAS neoantigens in the gut^[7]. The efficiency of KRAS peptide secretion by the bacteria directly correlated with the strength of the immune response in mice, suggesting that oral delivery of KRAS antigens through engineered probiotics could become a practical vaccination strategy.

Limitations and Open Questions

KRAS peptide vaccines face several unresolved challenges. HLA restriction limits which patients can respond: a peptide that binds HLA-A*02:01 is irrelevant for patients with different HLA types. Multi-peptide formulations and spliced epitope inclusion can partially address this, but complete HLA coverage requires complex cocktails.

Tumor immune evasion remains a problem. Cancers can downregulate MHC class I expression, becoming invisible to T cells regardless of how strong the vaccine-induced response is. Combining peptide vaccines with checkpoint inhibitors (as in the mKRAS-VAX trials) partially addresses this by removing T cell exhaustion, but MHC loss is a separate mechanism that checkpoint inhibitors do not fix.

Duration of response is unknown. The longest follow-up in published KRAS peptide vaccine trials is approximately 20 months. Whether vaccine-induced T cell responses persist long enough to prevent recurrence is an open question. The correlation between immune response strength and relapse-free survival in the AMPLIFY-201 trial is encouraging but preliminary. Booster vaccination strategies and optimal scheduling relative to surgery, chemotherapy, and checkpoint inhibitor dosing are all under active investigation. The adjuvant setting (post-surgical, minimal residual disease) may be where KRAS vaccines prove most effective, as the immune system faces a smaller tumor burden and has the best chance of achieving complete elimination.

Cross-cluster context: the challenges of immune escape from peptide vaccines and the strategies for combining peptide vaccines with checkpoint inhibitors are covered in dedicated articles within the personalized cancer vaccines cluster. The gp100 and HER2 peptide vaccine histories provide instructive parallels for how KRAS peptide vaccine development may unfold.

The Bottom Line

KRAS mutations are the most common oncogenic driver in human cancer, appearing in roughly 25% of all tumors with concentration in pancreatic, colorectal, and lung cancers. The recurrence of the same six hotspot mutations across millions of patients makes KRAS an ideal target for off-the-shelf peptide vaccines. Clinical trials of synthetic long peptide vaccines combined with checkpoint inhibitors have generated KRAS-specific T cell responses in 75% of treated patients, and early survival data shows correlation between immune response strength and clinical outcomes. Parallel peptide approaches include cyclic KRAS inhibitors, peptide nucleic acid conjugates, and engineered TCR-T cells. HLA restriction, immune evasion, and durability of response remain open challenges.

Frequently Asked Questions

What is a KRAS peptide vaccine?

A KRAS peptide vaccine contains synthetic peptide fragments corresponding to common KRAS mutations (G12D, G12V, G12C, and others). When injected, these peptides are taken up by antigen-presenting cells and displayed on MHC molecules to train T cells to recognize and kill cancer cells carrying the same KRAS mutation. Unlike personalized neoantigen vaccines, KRAS peptide vaccines can be manufactured as off-the-shelf products because the same mutations recur across patients.

How effective are KRAS cancer vaccines?

In early clinical trials, KRAS peptide vaccines combined with checkpoint inhibitors have generated mutation-specific T cell responses in 75% of colorectal cancer patients (mKRAS-VAX trial). The AMPLIFY-201 trial showed that strong immune responders had significantly longer relapse-free survival than weak responders. These are Phase I results with small patient numbers and limited follow-up. No KRAS peptide vaccine has received FDA approval.

Which cancers have KRAS mutations?

KRAS mutations occur in approximately 90% of pancreatic cancers, 40% of colorectal cancers, and 30% of non-small cell lung cancers. The six most common mutations are G12D, G12V, G12C, G12R, G12A, and G13D. G12D is the dominant mutation in pancreatic and colorectal cancer, while G12C predominates in lung cancer. KRAS mutations also appear at lower frequencies in endometrial, ovarian, and other cancers.

What is the difference between KRAS vaccines and KRAS inhibitors?

KRAS peptide vaccines train the immune system to destroy cells carrying mutant KRAS by presenting mutant peptide fragments to T cells. KRAS inhibitors (like sotorasib and adagrasib) are small molecules or cyclic peptides that directly bind and block the mutant KRAS protein inside cancer cells. Vaccines generate lasting immune memory; inhibitors require continuous dosing. Current small molecule inhibitors only target G12C, while peptide vaccines can target all six common mutations.

Can KRAS vaccines be given intranasally?

Wang et al. (2024) tested intranasal KRAS peptide vaccination in mouse models of KRAS-mutant lung cancer and found it inhibited tumor growth more effectively than subcutaneous delivery. Intranasal administration activates mucosal immune cells directly in the lungs, where the tumor resides. This approach has not been tested in human clinical trials but addresses the challenge of getting vaccine-induced immune cells to infiltrate the lung tumor microenvironment.

Do KRAS vaccines work with immunotherapy?

Yes, and this combination is central to the clinical strategy. KRAS peptide vaccines are designed to generate new anti-tumor T cell responses, while checkpoint inhibitors (ipilimumab, nivolumab, pembrolizumab) remove the brakes that prevent those T cells from attacking tumors. In the mKRAS-VAX trial, the combination produced KRAS-specific immune responses in MMR-proficient colorectal cancers, a cancer type that normally does not respond to checkpoint immunotherapy alone.