Immunometabolism and functional fitness in cell therapies: cutting-edge perspectives for the optimisation of CAR-T cells

CAR-T cell therapy and other adoptive immunotherapy strategies have revolutionised the treatment of refractory haematological malignancies and certain solid tumours. However, the efficacy of these therapies remains limited in a significant proportion of patients due to factors that go beyond the design of the chimeric receptor or the selection of tumour antigens.

Among the critical factors determining the success of these therapies are the metabolic state of T cells and their functional fitness, aspects that have gained prominence in immunometabolism research. Understanding these phenomena allows not only for the optimisation of cell product manufacturing, but also for the design of strategies to improve the persistence, proliferative capacity and cytotoxic activity of therapeutic cells.

Immunometabolism in T cells: fundamentals and clinical relevance

Immunometabolism is defined as the set of metabolic processes that regulate the function, activation and survival of immune cells. In T cells, these processes determine their ability to respond to prolonged antigenic stimuli, hypoxic conditions or oxidative stress within the tumour microenvironment.

Metabolism and effector function

Activated T cells require rapid availability of energy and metabolites to maintain their cytotoxic function. In general terms:

• Aerobic glycolysis: promotes the rapid production of ATP and substrates for macromolecule synthesis during clonal expansion.
• Mitochondrial oxidative phosphorylation (OXPHOS): essential for maintaining long-term resilience and the persistence of memory cells.
• Nucleotide and lipid biosynthesis: necessary to support proliferation and effector differentiation.

Metabolic imbalance, induced by excessive antigenic stimulation or by adverse ex vivo conditions, can lead to metabolic exhaustion, characterised by decreased mitochondrial activity, accumulation of reactive oxygen species and progressive loss of functional capacity.

Functional fitness: advanced definition and determinants

The concept of functional fitness refers to the combination of cellular attributes that enable T cells to maintain an optimal functional state, withstand metabolic stress and preserve epigenetic and transcriptomic plasticity. For cell therapies, this implies that cells are capable of:

1. Persisting in vivo following infusion.
2. Expand clonally in a sustained manner in response to the antigen.
3. Perform effector functions such as cytotoxicity and cytokine secretion without premature loss of functionality.

Determinants of functional fitness

• Early memory phenotype (TSCM and TCM): cells with high proliferative capacity, lower propensity for exhaustion and greater epigenetic plasticity.
• Epigenetic and transcriptomic status: regulators such as TOX, NR4A, BATF and EOMES determine functional programming and susceptibility to exhaustion.
• Energy and mitochondrial metabolism: the integrity of mitochondrial function and the balance between OXPHOS and glycolysis are critical for expansion and sustained function.

The interplay between metabolism, epigenetics and cell phenotype determines whether a batch of CAR-T cells achieves optimal clinical performance.

Advanced strategies for optimising functional fitness

In experimental and clinical practice, various strategies aim to modulate immunometabolism to maximise therapeutic efficacy:

1. Selection of optimal T-cell subpopulations: Prioritising stem memory or central memory T cells to improve persistence and clonal expansion capacity.
2. Optimisation of ex vivo expansion: Adjusting the intensity of antigenic stimulation, cytokine composition (IL-7, IL-15, IL-21) and nutrient availability to preserve functional fitness.
3. Pharmacological or genetic metabolic modulation:Interventions that enhance mitochondrial biogenesis, antioxidant capacity or the glycolysis/OXPHOS balance may prolong CAR-T cell functionality.
4. Multiparametric monitoring:Combined assessment of phenotypic, transcriptomic, epigenetic and metabolic markers allows the persistence and efficacy of the cell product to be predicted prior to infusion.

These advanced strategies not only improve cytotoxicity but also reduce the likelihood of states of dysfunction or premature exhaustion.

Clinical applications and the future of the immunometabolic approach

The approach based on immunometabolism and functional fitness has concrete clinical applications:

• Improved persistence of CAR-T cells in adverse tumour microenvironments.
• Production of more robust and consistent cell therapies, with lower functional variability between batches.
• Personalisation of therapies, adjusting the manufacturing strategy according to the patient’s metabolic profile or specific tumour characteristics.

The combination of single-cell RNA-seq, ATAC-seq, metabolomics and machine learning technologies will, in the near future, enable the identification of predictive signatures of clinical response and the precise optimisation of cell therapy manufacturing.

Conclusion

The study of immunometabolism and the preservation of functional fitness are establishing themselves as strategic pillars for next-generation cell therapies. Understanding the relationship between metabolism, epigenetics, and cellular phenotype enables the development of more persistent therapeutic products. These products are also more effective and adaptable to the patient.

Investing in strategies that maintain metabolic resilience, epigenetic plasticity, and effector functionality will be essential. These approaches will help unlock the full potential of CAR-T therapies. They will also support the development of other adoptive immunotherapies.