Iron and Ferroptosis: A Hidden Barrier to CAR T-Cell Function

CAR T-cell therapy has been used to treat several blood cancers, however, sustaining CAR T-cell activity has been difficult. A 2026 study published in Nature Cancer discovered that iron-induced ferroptosis could be responsible for CAR T-cell dysfunction and reduced antitumor activity (Kong et al. 2026).

The study found that after CAR T cells expand following their administration, they enter a decline phase associated with elevated serum iron concentration and an iron-dependent mechanism of cell death known as ferroptosis. The research revealed that increased iron concentration induced reactive oxygen species (ROS) production in mitochondria and lipid peroxidation in CAR T cells, which led to ferroptosis.

This blog discusses how iron affects CAR T cells, why ferroptosis may contribute to CAR T-cell dysfunction, and what this could mean for improving cancer immunotherapy.

Why CAR T Cells Are So Important

CAR T cells are genetically engineered T cells that recognize certain proteins on the surface of cancer cells. Once activated, CAR T cells can expand and eliminate tumor cells. For effective CAR T-cell treatment, the cells need to survive and stay functional after being introduced into the body.

Unfortunately, CAR T cells can gradually become dysfunctional due to various reasons, such as T cell exhaustion, metabolic stress, and the immunosuppressive tumor microenvironment. Kong and colleagues found that iron may be another factor contributing to this decline. Analysis of patient samples showed ferroptosis-related changes during the period when CAR T-cells began to decrease.

What Is Ferroptosis?

Ferroptosis is a form of programmed cell death involving the use of iron and the degradation of lipids via lipid peroxidation. Iron is required for a number of cell activities; however, too much of it can promote oxidative stress in cells. This causes the formation of ROS and damage to cell components.

Lipids in cell membranes are prone to oxidation. Cells have built-in antioxidant defense mechanisms to guard against this kind of oxidative damage, but in situations where lipid oxidation exceeds normal levels, ferroptosis may happen. This makes iron and lipid metabolism important areas to consider when studying CAR T-cell survival.

How Iron Affects CAR T Cells

The research team showed that excess intracellular iron caused an increase in mitochondrial ROS production and lipid peroxidation in CAR T cells. This was linked to reduced efficacy of CAR T cells and the induction of ferroptosis.

Upon deeper inspection, the scientists uncovered acyl-CoA synthetase long-chain family member 4 (ACSL4) as a key mediator of this effect. ACSL4 plays an essential role in lipid metabolism by regulating the composition of cellular membrane lipids, enriching for those that are more susceptible to oxidation. In doing so, ACSL4 essentially primes cells for ferroptosis.

Thus, increased iron levels cause a change in lipid metabolism, which makes CAR T-cells prone to ferroptosis.

The researchers found that removing ACSL4 reduced the harmful effects of iron and improved CAR T-cell activity. These findings were also supported in models of blood cancers and solid tumors. This suggests that lipid metabolism is not simply a consequence of CAR T-cell dysfunction. It may actively contribute to whether these cells survive and remain effective.

Why Mitochondria Matter

Mitochondria not only serve as the source of energy required for proper T-cell activation and function, but they are also a prominent source of ROS. In the current study, the researchers demonstrated that iron buildup was correlated with mitochondrial ROS generation in CAR T cells.

Increased oxidative stress can damage lipids and other cellular components, making it more difficult for CAR T cells to maintain normal function. This is particularly important because CAR T cells undergo major metabolic changes as they activate and expand. Their ability to control oxidative stress may therefore influence how long they remain functional.

Implications for Cancer Immunotherapy

The study adds another factor to the expanding body of knowledge about the dysfunction of CAR T cells. CAR T cells are affected not only by immune signals but also by their metabolic environment. Within tumors, CAR T cells encounter oxidative stress, limited nutrients, altered lipid metabolism, and other conditions that can affect their survival. Changes in iron metabolism may add to this stress and increase their susceptibility to ferroptosis.

This raises important questions for future research. Could CAR T cells be modified to better control intracellular iron? Could changes in lipid metabolism protect them from oxidative damage? Could targeting ACSL4 improve CAR T-cell persistence?

What Researchers Should Take Away

CAR T cells are an active metabolic cell type that has to survive under harsh conditions. In addition to assessing T-cell activation and exhaustion, investigators studying CAR T cells should assess iron content, mitochondrial ROS generation, lipid peroxidation, ACSL4, oxidative stress pathways, and CAR T-cell persistence.

However, while this is an encouraging perspective, most of the mechanistic data is based on experimental models, and more research is needed to determine how important iron-driven ferroptosis is across different cancers and CAR T products and whether this pathway can be safely targeted in patients.