Effect of mitochondrial oxidative stress on regulatory T cell manufacturing for clinical application in transplantation: Results from a pilot study

The manufacturing process of regulatory T (Treg) cells for clinical application begins with the positive selection of CD25⁺ cells using superparamagnetic iron oxide nanoparticle (SPION)-conjugated anti-CD25 antibodies (spCD25) and immunomagnetic cell separation technology. Our findings revealed that the interaction of spCD25 with its cell target induced the internalization of the complex spCD25–interleukin-2 receptor. Accumulation of intracellular spCD25 triggered oxidative stress, causing delayed Treg expansion and temporary reduction in suppressor activity. This activation delay hindered the efficient generation of clinically competent cells. During this early phase, Treg cells exhibited elevated mitochondrial superoxide and lipid peroxidation levels, with a concomitant decrease in mitochondrial respiration rates. The results uncovered the increased mitochondrial unfolded protein response. This protective, redox-sensitive activity is inherent in Tregs when contrasted with homologous, spCD25-treated, conventional T cells. Although the temporary effects of spCD25 on clinically competent cells did not impede their use in a safety/feasibility pilot study with kidney transplant recipients, it is reasonable to anticipate a potential reduction in their therapeutic efficacy. The mechanistic understanding of the adverse effects triggered by spCD25 is crucial for improving the manufacturing process of clinically competent Treg cells, a pivotal step in the successful implementation of immune cell therapy in transplantation.