By harnessing the metabolic power of a molecule more commonly recognized for its function in immune regulation, scientists from Fudan University Shanghai have discovered a new method to enhance chimeric antigen receptor (CAR)-T cells. The Cell Metabolism study demonstrated that expressing the transcription factor Foxp3 and a CAR construct fortifies T cells against the harsh, nutrient-starved tumor microenvironment (TME) and preserves their killing power without tipping the immune system into suppression. The result is a durable and resilient cancer-fighting cell, resistant to exhaustion and poised to deliver long-term antitumor effects.
Foxp3 makes CAR-Ts durable and resilient
CAR-T cell therapy has achieved remarkable success against blood cancers, but its effectiveness in solid tumors remains a significant hurdle. TMEs exhaust CAR-T cells and impair their metabolism due to low oxygen, scarce nutrients, and constant antigen stimulation. The challenges have hampered their long-term efficacy in solid malignancies.
By harnessing the metabolic resilience of the transcription factor Foxp3, traditionally associated with regulatory T cells (Tregs), Congyi Niu and colleagues reprogrammed CAR-T cells to endure the harsh TME without losing their antitumor potency. Unlike conventional CAR-T cells, which rely heavily on glycolysis and oxidative phosphorylation (OXPHOS) and succumb to TME-induced metabolic stress, the new Foxp3-expressing CAR-T cells demonstrated a shift toward lipid metabolism.
High-throughput chromatin accessibility analyses, such as ATAC-seq, revealed that the chromatin landscape of Foxp3-expressing CAR-T cells significantly differs from that of Tregs, aligning more closely with control CAR-T cells. For instance, Foxp3-expressing CAR-T cells exhibited lower enrichment of inhibitory transcription factor motifs found in Tregs. Moreover, these cells secreted lower levels of suppressive cytokines and lacked significant inhibitory effects on naive T-cell proliferation, underscoring their distinct functional profile.
Foxp3-mediated metabolic reprogramming in CAR-T cells enhanced cytotoxic capabilities while mitigating exhaustion. Foxp3-expressing CAR-T cells exhibit reduced levels of exhaustion-associated inhibitory molecules and maintain high expression of activation markers. Their cytotoxicity remains robust, comparable to control CAR-T cells, even after repeated tumor antigen stimulation.
The approach was then tested in an in vivo animal model where tumor-bearing mice were treated with Foxp3-expressing CAR-T cells. These mice displayed slower tumor growth, reduced exhaustion markers, and prolonged persistence compared to the control CAR-T cells. RNA sequencing and gene set enrichment analyses revealed lower exhaustion states and enhanced mitochondrial metabolic pathways in Foxp3-expressing CAR-T cells. Even in humanized immunodeficient mouse models, Foxp3-expressing CAR-T cells demonstrated superior antitumor activity without inducing immune suppression, maintaining a balanced cytokine profile, and avoiding a cytokine storm.
A metabolic blueprint for CAR-Ts?
The metabolic engineering approach pioneered here opens new avenues for immunotherapy, suggesting that selectively tailoring metabolic pathways can revolutionize CAR-T cell functionality. As researchers continue exploring the intricate relationship between metabolism and immune regulation, Foxp3 serves as a compelling blueprint for engineering CAR-T cells capable of conquering solid tumors’ metabolic and immunological challenges.
While the Foxp3-expressing CAR-T cell platform appears robust in durable antitumor immunity, at least preclinically, translating these findings into clinical applications will require comprehensive trials to evaluate their persistence, functional stability, and safety in humans. Understanding how Foxp3 influences the interplay between CAR-T cells and the broader immune milieu will also be critical for optimizing long-term outcomes.
