Cracking KRAS: How TCR-T and TCR-Mimic Antibodies Are Changing KRAS Mutant Cancers

Introduction

Kirsten rat sarcoma viral oncogene homolog (KRAS) is the most frequently mutated oncogenes in human cancer​ [1]. Mutations in KRAS occur in a significant fraction of lung, colorectal, and pancreatic cancers – roughly 20–35% of lung cancers, 35–50% of colorectal cancers, and up to 90% of pancreatic cancers [2]. These KRAS mutations make tumors aggressive and therapy-resistant. 

Historically, KRAS earned a reputation as an “undruggable” target: its protein surface is smooth with no obvious pockets, thwarting efforts to bind it with small molecules​ [3]. However, new drug modalities  like T cell receptor (TCR)-engineered T cell therapies and TCR mimic antibodies, are emerging as innovative strategies to target KRAS-driven cancers by recognizing mutant KRAS peptides presented on tumor cells. Could these immune-based approaches be the next frontier in attacking KRAS-mutant tumors? In this article, we explore the landscape of KRAS mutations and how TCR-T cell therapies and TCR-mimic antibodies are poised to complement traditional inhibitors and revolutionize treatment of KRAS-positive cancers.

KRAS Mutations in Cancer: A High-Value Target

KRAS sits at the top of the list of oncogenic targets due to its prevalence and importance. Overall, KRAS mutations are found in about 30% of all human tumors​ [4], making it one of the most common driver alterations in cancer. The hotspot mutations tend to occur at codon 12 of the KRAS protein, where glycine 12 is substituted by other amino acids. The key KRAS mutants include G12C, G12D, G12V, G12A, G12S, and G12R, each notation indicating a different amino-acid replacement at position 12. These six variants represent the majority of KRAS-driven cancers. Notably, their distribution varies by tumor type: for instance, KRAS G12C is frequently observed in lung cancer (~13% of lung tumors) but rare in pancreatic cancer, which instead is enriched for G12D, G12V, and G12R mutations​ [4]. Regardless of type, one KRAS mutation confers a potent growth advantage to the tumor, making it a high-value target for therapy.

Figure 1. Distribution of KRAS mutations in selected types of cancer: Lung Adenocarcinoma (LUAD), Colorectal Cancer (CRC), Pancreatic Ductal Adenocarcinoma (PDAC) [5].

T Cell Therapies Targeting KRAS Mutants

Recent research has focused on T cell receptor-engineered T cell therapy (TCR-T) to target KRAS tumor-associated antigens (TAAs). In TCR-T, patients’ T cells are engineered to express a custom TCR that recognizes one KRAS mutant peptide presented on the tumor’s HLA (human leukocyte antigen) molecules. Unlike conventional antibodies that only target cell surface proteins, TCR-T cells can recognize intracellular proteins like KRAS because tumor cells process KRAS proteins into peptides, which are presented on the cell surface by major histocompatibility complex (MHC) molecules.

Clinically, Leidner et al. infused engineered T cells expressing HLA-C*08:02-specific TCRs targeting mutant KRAS G12D in a patient with pancreatic cancer. They found a regression of metastases with an overall 72% partial response [6]. In preclinical research, Wang et al. immunized HLA-A*11:01 transgenic mice with mutant KRAS peptides and isolated TCRs highly reactive to KRAS G12D and KRAS G12V​. When human T cells were engineered with KRAS G12D-specific TCRs and transferred into mice bearing KRAS-mutant tumors, the T cells significantly slowed the tumor growth​ rate [7]. 

A critical consideration in TCR-T therapies is the specificity and safety. Since KRAS mutations differ from its wild-type form by only a single amino acid, a therapeutic TCR must distinguish the mutant peptide from the normal peptide. Encouragingly, studies have found that it’s possible to achieve such high specificity. Poole et al. in a study published in Nature Communications, demonstrated that a TCR isolated for the KRAS G12D peptide (10-mer) restricted to HLA-A*11:01 recognized the mutant sequence but did not respond to the wild-type KRAS peptide [8]. Such high-affinity and high-specificity TCRs may be better at recognizing tumor cells that present only a few copies of the KRAS neoantigen.

Figure 2. A redirected T cell killing assay where engineered T cells target HLA-A*11 KRAS G12D mutant cancer cells (CL40) and HLA-A*11 KRAS WT normal colon epithelial cells. Significant cytolysis of KRAS G12D mutant cancer cells (red) is observed in a dose-dependent manner. Minimal cytolysis of normal colon epithelial cells (black), indicating specificity of engineered T cells [8].

Of course, challenges still remain before KRAS-targeted T cell therapy becomes widely applied. Since each TCR is HLA-restricted, it is necessary to either focus on prevalent HLA alleles or develop a collection of TCRs to cover multiple alleles. Moreover, manufacturing clinical-grade TCR-T cells and ensuring persistence and function in patients are non-trivial tasks being addressed in ongoing trials. Despite these hurdles, the early success stories and rapid progress in TCR discovery have put KRAS on the map as a viable target for T cell therapy. 

TCR Mimic Antibodies: Expanding Targetability

Another novel immunotherapeutic approach to KRAS-mutant cancers is the use of TCR mimic (TCRm) antibodies. These are engineered antibodies that recognize the same MHC-peptide complexes that T cells do​ [9]. A TCRm antibody binds to a specific mutant peptide in an HLA molecule on the cell surface, thereby “mimicking” the way a TCR would recognize an intracellular antigen. This innovation expands the targetable landscape for antibodies. Traditional monoclonal antibodies can only target proteins on the cell surface (or secreted factors), which represent a small portion of tumor-specific antigens. TCRm antibodies, by contrast, can target intracellular oncoproteins like KRAS, p53, etc via peptide presented on MHC molecules​ [10].

Several studies have already demonstrated the potential of TCRm antibodies against KRAS. In one report, researchers generated two TCRm antibody-drug conjugates (ADC) targeting KRAS G12V with antitumor activity and low toxicity [11]/. Recently, the fully human TCR-mimic antibodies have been raised against KRAS G12D and KRAS G12V mutants presented by common HLA alleles with impressive drug potential. These antibodies exhibit high affinities for their target MHC-peptide and showed potent tumor cell lysis in vitro when configured as CD3-engaging bispecifics – all with minimal off-target binding observed​ [12]. These results underscore that KRAS mutant peptides can be distinguished enough from their wild-type counterparts to be targeted safely by the immune system. 

Figure 3. Graphical representation of TCRm-ADC causing tumor cell death in KRAS G12V mutant cells.  

TCRm antibody can be a more advantageous drug modality over  T cell therapy because it is more easily manufactured and administered off-the-shelf without requiring patient-specific cell harvesting. Additionally, TCRm antibodies can be engineered into various formats. For example,  The concept of TCRm antibody can be incorporated into bispecific T cell engager modality, such as a BiTE, where one arm of the antibody binds the mutant KRAS peptide–MHC on a cancer cell and the other arm binds CD3 on T cells, forcefully bridging T cells to the cancer cell to induce killing. TCRm antibodies can also be conjugated with small molecules to make antibody–drug conjugates (ADCs) that deliver a lethal payload specifically to KRAS-expressing tumor cells. 

KACTUS: Your Partner in KRAS Immunotherapy Research

KACTUS is proud to support T cell-based therapy researchers by providing a comprehensive catalog of MHC-peptide complexes, including KRAS mutant MHC-peptide complexes. Our MHC proteins are expressed using single-chain trimer expression, yielding properly folded complexes with secure peptides and mimicking native MHC presentation. Our mammalian expression system ensures correct folding and post-translational modifications. 

MHC Catalog Highlights

• Monomers & Tetramers 

• Biotinylated Monomers

• Fluorescent Tetramers

• Verified Bioactivity using ELISA and SPR

• High Purity & Low Endotoxin

Product Performance Data

Biotinylated Human HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Monomer Protein (MHC-HM418B)

Figure 4. Biotinylated Human HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Monomer, His Tag captured on CM5 Chip via anti-his antibody can bind Anti-HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Antibody with an affinity constant of 0.14 uM as determined in SPR assay (Biacore T200).

Human HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Tetramer Protein (MHC-HM418T)

Figure 5. Anti-HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Antibody captured on CM5 Chip via Protein A can bind Human HLA-A*03:01&B2M&KRAS G12V (VVVGAVGVGK) Tetramer, His Tag with an affinity constant of 42.3 nM as determined in SPR assay (Biacore T200).

PE-Labeled Human HLA-A*11:01&B2M&KRAS G12D (VVVGADGVGK) Tetramer Protein (MHC-HM420TP)

Figure 6. Immobilized HLA-A*11:01&B2M&KRAS G12D (VVVGADGVGK) TCR at 1ug/ml (100ul/well) on the plate. Dose response curve for PE-Labeled Human HLA-A*11:01&B2M&KRAS G12D (VVVGADGVGK) Tetramer, His Tag with the EC50 of 96.7ng/ml determined by ELISA.

Biotinylated Human HLA-A*11:01&B2M&KRAS G12D (VVVGADGVGK) Monomer Protein (MHC-HM454B)

Figure 7. Immobilized HLA-A*11:01&B2M&KRAS G12D TCR at 2ug/ml (100ul/well) on the plate. Dose response curve for Biotinylated HLA-A*11:01&B2M&KRAS G12D (VVVGADGVGK) Monomer, His Tag with the EC50 of 0.1ug/ml determined by ELISA.

KRAS Wild-Type and Mutant MHC-Peptide Products

• KRAS G12A: VVVGAAGVGK

• KRAS G12C: VVVGACGVGK

• KRAS G12D: GADGVGKSAL (10-mer), VVGADGVGK, VVVGADGVGK

• KRAS G12R: VVVGARGVGK

• KRAS G12S: VVVGASGVGK

• KRAS G12V: VVGAVGVGK, VVVGAVGVGK

• KRAS Wild-type (G12): VVVGAGGVGK (for reference and specificity controls)

Additional MHC Solutions by KACTUS

Peptide-Ready MHCs

Our Peptide-Ready MHCs are stabilized, peptide-free MHC molecules that can be loaded with a custom peptide in-house using a quick and simple protocol. These off-the-shelf catalog products are bioactivity-verified and simplify your loading procedure as they don’t require UV or peptide exchange technology. 

Custom MHC Expression Services

Our expert team also offers specialized MHC solutions, including MHC alleles or peptides not in our catalog or large-scale production. We have expertise in both HEK293 expression and E. coli refolding for MHC molecules. Our team can produce quality, stable MHC molecules with quality control for purity and activity. 

References

1. Zhu, C., Guan, X., Zhang, X. et al. Targeting KRAS mutant cancers: from druggable therapy to drug resistance. Mol Cancer 21, 159 (2022). https://doi.org/10.1186/s12943-022-01629-2 

2. Duan, Z., & Ho, M. (2021). T-Cell Receptor Mimic Antibodies for Cancer Immunotherapy. Molecular cancer therapeutics, 20(9), 1533–1541. https://doi.org/10.1158/1535-7163.MCT-21-0115 

3. BioSpace. (n.d.). Rise of KRAS inhibitors in cancer treatment. BioSpace. Retrieved March 18, 2025, from https://www.biospace.com/rise-of-kras-inhibitors-in-cancer-treatment#:~:text=For%20many%20years%2C%20targeting%20KRAS,preventing%20cancer%20cells%20from%20proliferating 

4. Merz, V., Gaule, M., Zecchetto, C., Cavaliere, A., Casalino, S., Pesoni, C., Contarelli, S., Sabbadini, F., Bertolini, M., Mangiameli, D., Milella, M., Fedele, V., & Melisi, D. (2021). Targeting KRAS: The Elephant in the Room of Epithelial Cancers. Frontiers in Oncology, 11, 638360. https://doi.org/10.3389/fonc.2021.638360

5. Zhu, C., Guan, X., Zhang, X. et al. Targeting KRAS mutant cancers: from druggable therapy to drug resistance. Mol Cancer 21, 159 (2022). https://doi.org/10.1186/s12943-022-01629-2 

6. Leidner, R., Sanjuan Silva, N., Huang, H., Sprott, D., Zheng, C., Shih, Y.-P., Leung, A., Payne, R., Sutcliffe, K., Cramer, J., Rosenberg, S. A., Fox, B. A., Urba, W. J., & Tran, E. (2022). Neoantigen T-cell receptor gene therapy in pancreatic cancer. The New England Journal of Medicine, 386(22), 2112–2119. https://doi.org/10.1056/NEJMoa2119662 

7. Wang, Q. J., Yu, Z., Griffith, K., Hanada, K., Restifo, N. P., & Yang, J. C. (2016). Identification of T-cell Receptors Targeting KRAS-Mutated Human Tumors. Cancer immunology research, 4(3), 204–214. https://doi.org/10.1158/2326-6066.CIR-15-0188 

8. Poole, A., Karuppiah, V., Hartt, A. et al. Therapeutic high affinity T cell receptor targeting a KRASG12D cancer neoantigen. Nat Commun 13, 5333 (2022). https://doi.org/10.1038/s41467-022-32811-1 

9. Duan, Z., & Ho, M. (2021). T-Cell Receptor Mimic Antibodies for Cancer Immunotherapy. Molecular cancer therapeutics, 20(9), 1533–1541. https://doi.org/10.1158/1535-7163.MCT-21-0115 

10. Shen, Y., Wei, X., Jin, S., Wu, Y., Zhao, W., Xu, Y., Pan, L., Zhou, Z., & Chen, S. (2020). TCR-mimic antibody-drug conjugates targeting intracellular tumor-specific mutant antigen KRAS G12V mutation. Asian journal of pharmaceutical sciences, 15(6), 777–785. https://doi.org/10.1016/j.ajps.2020.01.002 

11. Shen, Y., Wei, X., Jin, S., Wu, Y., Zhao, W., Xu, Y., Pan, L., Zhou, Z., & Chen, S. (2020). TCR-mimic antibody-drug conjugates targeting intracellular tumor-specific mutant antigen KRAS G12V mutation. Asian journal of pharmaceutical sciences, 15(6), 777–785. https://doi.org/10.1016/j.ajps.2020.01.002 

12. Biocytogen. (2024). Targeting mutant KRAS proteins with novel TCR-mimic fully human antibodies. Poster presented at the American Association for Cancer Research Annual Meeting 2024. Retrieved from https://biocytogen.com/posters/targeting-mutant-kras-proteins-with-novel-tcr-mimic-fully-human-antibodies/