Engineered Lactococcus lactis bacteria secreting KRAS oncopeptides via a novel signal peptide successfully triggered mucosal IgA immune responses against colorectal cancer antigens in mice, though secretion efficiency depended on signal peptide choice.
Positive IgA immune response against KRAS cancer antigensOral administration of engineered L. lactis secreting KRAS oncopeptides successfully triggered intestinal IgA antibodies in mice — the first step toward an oral cancer vaccine for colorectal cancer
What the researchers found
L. lactis NZ9000 engineered with signal peptide SPK1 secreted KRAS oncopeptides (mutant 68V-DT and wild-type KRAS) more efficiently than the mutant signal peptide SPKM19, producing approximately 1.3-fold higher yields. This was unexpected, as SPKM19 had previously outperformed SPK1 with a different reporter protein.
In BALB/c mice, oral immunization with SPK1-mediated KRAS secretion produced a superior IgA immune response compared to SPKM19. However, even the SPKM19 construct triggered a positive IgA response in intestinal washes. The discrepancy between signal peptide performance with different cargo proteins was attributed to differences in size and secondary conformation of the mature proteins.
Why it matters
Colorectal cancer is the third most common cancer worldwide, and KRAS mutations are present in approximately 40% of cases. Current immunotherapies (checkpoint inhibitors) have limited effectiveness in most colorectal cancers. An oral vaccine that trains the gut immune system to recognize KRAS-mutant cancer cells could provide a non-invasive, targeted immunotherapy approach. Using food-grade bacteria as the delivery vehicle makes this potentially safer and more scalable than traditional vaccine platforms.
How the study worked
Two signal peptides (SPK1 and SPKM19) were used to express and secrete KRAS oncopeptides from L. lactis NZ9000. Expression and secretion efficiency were compared in vitro. BALB/c mice were orally immunized, and mucosal immune responses were assessed by measuring KRAS-specific IgA antibodies in intestinal washes.
What this study cannot tell us
The study demonstrated immune response (IgA production) but did not assess whether this response actually prevents or treats colorectal tumors in an animal cancer model. IgA alone may be insufficient for anti-tumor immunity — T cell responses were not measured. The mouse immune system differs from humans. L. lactis does not colonize the gut, so repeated dosing would likely be required. The secretion yields and resulting antigen levels at the mucosal surface were not quantified in sufficient detail to predict human immunogenicity.
How to read the evidence
This is a preclinical proof-of-concept study demonstrating that engineered bacteria can secrete cancer peptides and trigger mucosal immune responses in mice. While the immune response was confirmed, anti-tumor efficacy was not tested, placing this at an early stage of vaccine development.
When this study was published
Published in 2023, this is a recent study reflecting current approaches to engineered bacterial vaccine delivery and KRAS-targeted cancer immunotherapy.
The bigger picture
KRAS-targeted vaccines are one of the most active areas in cancer immunotherapy, with several peptide vaccines in clinical trials. Most use traditional injection-based delivery, but oral mucosal vaccines could be particularly advantageous for gastrointestinal cancers where the immune response needs to be primed at the site of disease. L. lactis-based vaccine delivery is a growing field — these bacteria are safe, can be produced cheaply, and naturally interact with the gut immune system. The finding that signal peptide performance is cargo-dependent is an important engineering lesson for this platform.
Questions still open
- Does the mucosal IgA response generated by this oral vaccine actually prevent or slow KRAS-mutant colorectal tumor growth in a cancer mouse model?
- Can T cell responses (critical for tumor killing) be generated in addition to the IgA antibody response demonstrated here?
- Could this L. lactis platform be combined with checkpoint inhibitors to enhance immunotherapy effectiveness in KRAS-mutant colorectal cancer?
Common questions
What is KRAS and why is it important in colorectal cancer?
Why use yogurt bacteria to deliver a cancer vaccine?
Read the original research
Effect of Secretion Efficiency of Mutant KRAS Neoantigen by Lactococcus lactis on the Immune Response of a Mucosal Vaccine Delivery Vehicle Targeting Colorectal Cancer.
International journal of molecular sciences, 24(10)
Citation
Alias, Nur Aqlili Riana; Hoo, Winfrey Pui Yee; Siak, Pui Yan; Othman, Siti Sarah; Mohammed Alitheen, Noorjahan Banu; In, Lionel Lian Aun; Abdul Rahim, Raha; Song, Adelene Ai-Lian. (2023). Effect of Secretion Efficiency of Mutant KRAS Neoantigen by Lactococcus lactis on the Immune Response of a Mucosal Vaccine Delivery Vehicle Targeting Colorectal Cancer.. International journal of molecular sciences, 24(10). https://doi.org/10.3390/ijms24108928