Lessons from Apoptotic Mimicry: Induction of Tolerance in Dendritic Cells from Adult and Paediatric Patients with Type 1 Diabetes by Liposomes

Background: The reeducation of the immune system is crucial to tackle autoimmunity in type 1 diabetes (T1D). Since self–tolerance is induced by apoptotic cell clearance (a process known as efferocytosis), a nanotherapy consisting of liposomes rich in phosphatidylserine (PS) encapsulating beta–cell autoantigens was designed to mimic apoptotic beta–cells. This strategy halted autoimmunity and prevented experimental T1D in the non–obese diabetic (NOD) model through the generation of tolerogenic dendritic cells (DCs). To move forward, this study aimed to validate the effect of PS–liposomes in human DCs. Methods: PS–liposomes loaded with human insulin peptides as autoantigens were generated with optimum size and composition for DCs phagocytosis. Human DCs were derived in vitro from peripheral blood monocytes from adult and paediatric patients with T1D. Phagocytosis kinetics of PS–liposomes as well as the changes induced in DCs’ phenotype, function and transcriptome were determined. Results: Human DCs displayed optimal phagocytosis kinetics of PS–liposomes, and their rapid engulfment was dependent on the presence of PS. Remarkably, DCs from paediatric patients at T1D onset captured liposomes more efficiently than DCs from paediatric patients 1–3 years after diagnosis. DCs’ viability was unaffected by PS–liposomes engulfment, although the phenotypic profile was modulated, as evidenced by a decreased expression of efferocytosis receptors and preserved low levels of antigen-presenting, activation and costimulatory molecules. After PS–liposomes uptake, DCs showed anti–inflammatory cytokine secretion and impaired ability to stimulate autologous T lymphocyte proliferation. Furthermore, transcriptomic analysis revealed differential expression of immunoregulatory genes in DCs after PS–liposomes engulfment, indicating tolerance induction. Conclusion: Phagocytosis of apoptotic–mimicking PS–liposomes induced similar effects in DCs from adult and paediatric patients with T1D, thus validating the tolerogenic effect prompted in NOD mice. As PS–liposomes call for apoptotic cell clearance, a physiological and memory–inducing approach, these results reinforce the potential of this biomimicry–based antigen–specific immunotherapy to restablish tolerance to self.