In recent decades, non-caloric sweeteners like sucralose have become a common component of modern diets. Marketed as safe alternatives to sugar, they’ve been widely adopted by people looking to reduce calories, control blood sugar, or simply consume “light” products. However, a recent study published in Cancer Discovery suggests that this seemingly harmless ingredient may be significantly undermining the effectiveness of immunotherapy in cancer treatment.

Immunotherapy—especially immune checkpoint inhibitors (ICIs)—has revolutionized cancer care. By blocking proteins such as PD-1 or CTLA-4, these treatments allow T cells of the immune system to better recognize and attack tumors. Yet, not all patients respond equally, and one of the key modulators of this response is the gut microbiome. Numerous studies have shown that certain microbial profiles are associated with better immunotherapy outcomes. High-fiber diets or the use of probiotics can enhance this interaction, while antibiotics or microbial imbalances may impair it. What hadn’t been fully understood was how common dietary elements like artificial sweeteners might influence this dynamic.

The study, led by Abigail Overacre-Delgoffe and Diwakar Davar, revealed that consumption of sucralose—even within FDA-approved safety limits—significantly disrupts the gut microbiota and reduces the efficacy of immunotherapy in cancers such as melanoma and non-small cell lung cancer (NSCLC). In both preclinical models and patient data, those with higher sucralose intake had lower objective response rates and shorter progression-free survival. Mice consuming sucralose developed larger tumors, had fewer CD8+ T cell infiltrates, and showed elevated expression of exhaustion markers like PD-1, TOX, and CTLA-4.

Through transcriptomic analysis of tumor and lymph node cells, the researchers found that sucralose directly impaired T cell function and metabolism. T cells exhibited reduced proliferation, lower mitochondrial mass, metabolic dysfunction, and a phenotype characteristic of exhaustion. While some of these effects may stem from direct exposure to sucralose, the data point strongly to the microbiome as the central mediator.

The immunosuppressive effect of sucralose was especially evident in mice with a susceptible microbiome. Changes in bacterial composition—such as increases in Firmicutes and Proteobacteria, and in particular, Clostridiaceae and Lachnospiraceae—were associated with reduced microbial diversity and increased resistance to immunotherapy. Strikingly, mice that did not consume sucralose but received fecal transplants from sucralose-fed mice developed resistance to immunotherapy. Conversely, restoring a healthy microbiome through fecal transplants from ICI-responsive mice rescued the treatment response, even in the presence of sucralose.

One of the study’s most critical findings was that sucralose consumption led to a significant reduction in available arginine in the gut, bloodstream, and tumor microenvironment. This was attributed to increased microbial activity degrading arginine. Since this amino acid is essential for the function of cytotoxic T cells, its deficiency directly contributed to immune dysfunction. The researchers tested a simple solution: supplementing the diet with arginine or citrulline (a precursor of arginine). This restored arginine levels and reversed T cell dysfunction, thereby improving immunotherapy response in animal models.

The findings are clear: sucralose is not metabolically inert. It can substantially alter gut microbial ecology, interfere with amino acid metabolism, and ultimately reduce the effectiveness of advanced immunological cancer therapies. This is especially relevant for patients undergoing immunotherapy, where the interplay between microbiota, metabolism, and immune function is critical.

Figure 1. Sucralose intake alters the gut microbiota, increasing arginine-degrading bacteria and reducing arginine availability. This impairs T cell metabolism, promotes exhaustion, and reduces the efficacy of immunotherapy.

The results show that higher pre-treatment intake of sucralose is associated with shorter progression-free survival in melanoma and lung cancer patients treated with anti-PD-1 therapy, and with lower relapse-free survival in resectable melanoma patients treated with anti-PD-1 plus a TLR9 agonist. Although some direct effects on T cell activation were observed in vitro, the main mechanism appears to be gut microbiota disruption, which triggers a cascade of metabolic and immune dysfunctions.

This study serves as a significant wake-up call regarding the role of diet in cancer immunotherapy. What might seem like a minor detail—a diet soda sweetened with sucralose—could be the difference between a successful or failed treatment. Beyond sucralose, the core message is clear: the metabolic and microbial environment we shape through what we eat matters—a lot.

Main Reference: 

Morder, K. M., Nguyen, M., Wilfahrt, D. N., Dahmani, Z. L., Burr, A. B., Xie, B., Morikone, M., Nieves-Rosado, H., Gunn, W. G., Hurd, D. E., Wang, H., Mullett, S. J., Bossong, K., Gelhaus, S. L., Rajasundaram, D., Kane, L. P., Delgoffe, G. M., Das, J., Davar, D., & Overacre-Delgoffe, A. E. (2025). Sucralose consumption ablates cancer immunotherapy response through microbiome disruption. Cancer discovery, 10.1158/2159-8290.CD-25-0247. Advance online publication. https://doi.org/10.1158/2159-8290.CD-25-0247 

Other References: 

Aggarwal, V., Workman, C. J., & Vignali, D. A. A. (2023). LAG-3 as the third checkpoint inhibitor. Nature immunology, 24(9), 1415–1422. https://doi.org/10.1038/s41590-023-01569-z 

Olivares-Hernández, A., González Del Portillo, E., Tamayo-Velasco, Á., Figuero-Pérez, L., Zhilina-Zhilina, S., Fonseca-Sánchez, E., & Miramontes-González, J. P. (2023). Immune checkpoint inhibitors in non-small cell lung cancer: from current perspectives to future treatments-a systematic review. Annals of translational medicine, 11(10), 354. https://doi.org/10.21037/atm-22-4218 

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