Chemical modification of Thalassiosira weissflogii with calcium precursor: A biomimetic platform for artificial antigen presenting cells in adaptive immunotherapy

Artificial antigen-presenting cells (aAPCs) offer a precise system for modulating immune cells, effectively addressing major challenges in immunotherapy, such as unintended effects. Diatoms have attracted considerable interest as natural templates for biomaterials owing to their surface characteristics, which can replicate those found in cellular structures. The diatom's frustule, characterised by its rugged and porous exterior, exhibits a remarkable biomimetic morphology attributable to its highly ordered pores, extensive surface area, and unique architecture. Despite these advantages, the toxicity and non-biodegradable nature of silica-based organisms pose a significant challenge when attempting to utilize these organisms as nanotopographically functionalised microparticles in the realm of biomedicine. This study addressed this limitation by modulating the chemical composition of diatom microparticles by modulating the active silica metabolic uptake mechanism while maintaining their intricate three-dimensional architecture through calcium incorporation into living diatoms. In the phase I of the study, the diatom Thalassiosira weissflogii was chemically modified to replace its silica composition with a biodegradable calcium template, while simultaneously preserving the unique three-dimensional (3D) frustule structure with hierarchical patterns of pores and nanoscale architectural features, which was evident with the deposition of calcium as calcium carbonate. Calcium hydroxide (Ca(OH)₂) was incorporated into the exoskeleton through the active mechanism of calcium uptake via a carbon-concentrating mechanism, without altering the microstructure. These findings suggest that calcium-modified diatoms hold potential as a nature-inspired delivery system for immunotherapy through antibody-specific binding. To this extent, phase II study involved the creation of Ca(OH)₂-modified diatoms that act as artificial antigen-presenting cells (aAPCs). This innovative strategy aimed to enhance immunological interactions and emulate the functions of natural antigen-presenting cells. The findings in this study indicate that amine polymerisation on Ca(OH)₂-modified diatoms improved the attachment of immunomodulatory proteins (anti-CD28 and anti-CD3) to the diatom surface, thereby promoting specific antibody-antigen interactions with Jurkat cells, as evidenced by the robust interaction of Jurkat cells and diatom-based aAPCs and formation of immunological synapses, which initiated targeted immune responses, thus informing the proof-of-concept of functional diatom-based aAPCs for Jurkat cell activation. In phase III, this study aimed to translate the functional diatom-based aAPCs for cell activation in the primary human CD4+ T cells isolated from peripheral blood peripheral blood mononuclear cells. Through co-stimulatory signalling, diatom-based aAPCs exhibited robust expression of T cell activation markers, not only during early activation (CD69) but also sustained at a later time point (CD25), indicating activation of T cells. These was also evidence of higher intracellular calcium signalling and immunological synapse as structural a confirmation for activation of T cells. Subsequently, an increase of proliferation was observed in activated T cells. Metabolically, diatom-based aAPCs promoted glycolysis over mitochondrial oxidative respiration to meet the elevated energy demand for immune activation and metabolic homeostasis. Overall, these findings highlight the potential of a structurally preserved calcium-modified diatom as a biomimetic delivery platform for immunotherapy. Immunofunctionalisation of calcium-modified diatoms offers a promising strategy for the development of bioinspired, functional aAPC, which are adaptive immunomodulatory systems, and hold future potential as immunotherapeutic platforms for diseases such as cancer and autoimmunity.

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University of Galway

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CC BY-NC-ND

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University of Galway Theses (PhD Theses)