Modified Peptides Train the Immune System to Attack Cancers With RAS Mutations | Research

The takeaway

Anchor-modified peptides derived from mutant RAS protein generated strong cancer-killing T cell responses in lab and mouse studies, demonstrating that the 'undruggable' RAS mutation can be targeted through peptide immunotherapy.

~20% of cancers targeted
RAS mutations occur in approximately one-fifth of all cancers, and these optimized peptides generated specific killer T cells against six common variants

What the researchers found

The researchers identified immunogenic peptides from six common codon 12 RAS mutations (G12A, G12C, G12D, G12R, G12S, and G12V) that bind to HLA-A*02:01 and HLA-A*03:01, the two most common HLA types. These peptides elicited strong CD8+ T cell responses.

Modifying the anchor residues of these peptides enhanced their binding affinity to HLA-A*02:01, and the resulting T cells responded to both the modified and original peptide forms. Crucially, cytotoxic T cells generated against these peptides specifically lysed tumor cells expressing mutant RAS. In humanized HLA-A2/DR1 mice, vaccination with a long peptide containing an anchor-modified G12V epitope generated CD8+ T cells that recognized both the original peptide and a human cancer cell line harboring the G12V mutation.

Why it matters

RAS is the most commonly mutated oncogene in human cancer, but targeting it with conventional drugs has been extremely difficult — earning it the label 'undruggable.' This peptide immunotherapy approach sidesteps the problem entirely by training the patient's own immune system to seek out and destroy RAS-mutant cancer cells. If it works in clinical trials, it could benefit the ~20% of cancer patients whose tumors carry RAS mutations.

How the study worked

The team identified candidate peptides from six RAS codon 12 mutations and tested their binding to common HLA molecules. They then modified anchor residues to improve binding affinity. T cell responses were evaluated in vitro using human blood cells and in vivo using transgenic mice expressing human HLA-A2/DR1. Tumor cell killing was assessed using cytotoxicity assays against RAS-mutant cancer cell lines.

What this study cannot tell us

The in vivo results come from humanized transgenic mice, which approximate but don't fully replicate the human immune system. The study focused on codon 12 mutations and two HLA types, covering a significant but not complete portion of RAS mutations and patient populations. The modified peptides improve T cell activation but the clinical efficacy — whether enough T cells can be generated and sustained to control tumors in patients — remains unproven. No human clinical trial data is available.

How to read the evidence

This is a preclinical study combining in vitro human cell experiments and in vivo humanized mouse models. The evidence is strong for proof of concept — demonstrating that the immune system can be trained to target RAS mutations via peptides — but clinical efficacy in humans remains to be tested.

When this study was published

Published in 2022, this study is recent and reflects the accelerating development of neoantigen-based cancer immunotherapies.

The bigger picture

This research is part of a broader movement toward neoantigen-based cancer vaccines — therapies that use peptides derived from tumor-specific mutations to activate the immune system. While recent approvals of KRAS G12C inhibitors (like sotorasib) have partially cracked the 'undruggable' label, peptide immunotherapy could address multiple RAS mutations simultaneously and may work where small molecule inhibitors fail. Combined with checkpoint inhibitors, these vaccines could significantly expand treatment options for RAS-mutant cancers.

Questions still open

Will these anchor-modified RAS peptide vaccines generate sufficient anti-tumor immune responses in human patients?
Could combining these peptide vaccines with immune checkpoint inhibitors enhance their effectiveness?
Can this approach be extended to RAS mutations at other codons (13, 61) or to other 'undruggable' oncogenes?

Common questions

Why has RAS been called 'undruggable' and how do peptides change that?

RAS proteins have a smooth, featureless surface that makes it extremely difficult for traditional drugs to latch onto. Instead of trying to block RAS with a drug, this approach uses peptide fragments from the mutant protein as a vaccine to train the immune system's killer T cells to recognize and destroy cancer cells carrying the mutation — essentially using the body's own defenses as the 'drug.'

What are 'anchor modifications' and why do they help?

For the immune system to recognize a cancer peptide, it must be displayed on the cell surface by HLA molecules. Anchor residues are the parts of the peptide that hold it in place on the HLA molecule. By modifying these anchor points, the researchers made the peptides bind more tightly, which produces a stronger immune response — while the resulting T cells can still recognize the original, unmodified cancer peptide.

Read the original research

Optimized Anchor-Modified Peptides Targeting Mutated RAS Are Promising Candidates for Immunotherapy.

Frontiers in immunology, 13, 902709

View on PubMed ↗Publisher’s paper ↗

Citation

Baleeiro, Renato B; Dunmall, Louisa S Chard; Liu, Peng; Lu, Shuangshuang; Lone, Yuchun; Lemoine, Nicholas R; Wang, Yaohe. (2022). Optimized Anchor-Modified Peptides Targeting Mutated RAS Are Promising Candidates for Immunotherapy.. Frontiers in immunology, 13, 902709. https://doi.org/10.3389/fimmu.2022.902709