Title: Electrospun antibody-functionalized poly(dimethyl siloxane)-based meshes for improved T cell expansion
Description: Adoptive cell transfer (ACT) has garnered significant interest in recent years within the medical field due to its potential in providing an effective form of personalized medicine for patients suffering from a wide range of chronic illnesses, including but not limited to cancer. By leveraging the patient’s own cells as the therapeutic agent, concerns over patient compatibility and adverse reactions are significantly reduced. Central to this therapy is the ability to optimize cell quantity and cell activation in order to produce a more robust infusion to the patient. This thesis focuses on two main aspects. The first is the materials synthesis and development of a novel platform for the ex vivo expansion of human T cells for ACT, while the second aims to elucidate the underlying structural mechanics of this platform. This platform, which consists of an electrospun mesh of micron and sub-micron diameter poly (dimethyl siloxane)-based fibers, aims to maintain the high surface-area to volume ratio characteristic of the current clinical gold standard.

This also simultaneously allows for effective leveraging of T cell mechanosensing, a phenomenon previously discovered by our lab that is the ability of a human T cell to respond differently to surface mechanical cues. By modulating the concentration of poly (ε-caprolactone) in these fibers, a biocompatible polymer, the mesh mechanical rigidity was varied: this effectively allowed for the leverage of T cell mechanosensing by maintaining a low and tunable Young’s modulus throughout. Additionally, safety concerns involving transfusion of the expansion platform into the patient were addressed by having a single continuous substrate instead of an array of disjoint ferromagnetic beads. Our results thus far indicate that this soft mesh platform can produce upwards of 5.6-12.5 times more T cells in healthy patients than the clinical gold standard while maintaining comparable levels of cellular activation and phenotypic distributions as measured through IFNγ secretion and expression of surface proteins CD107b, CD45RO, and CCR7, respectively.

Additionally, this platform demonstrates the ability to produce improved expansion of exhausted (PD-1high) T cells from CLL patients compared to the clinical gold standard across all analyzed Rai stages. Finally, experiments have shown our platform to be scalable to produce clinically relevant levels of cells (> 50 million) from a given starting population, thus indicating its potential in adaptation in larger scale in vitro systems. The currently demonstrated capabilities of our mesh platform thus hold significant promise in the clinical development and adoption of ACT, as well as the development of larger scale in vitro systems. In order to elucidate the underlying structural mechanics of our platform, quantitative AFM studies have indicated a force-dependency in rigidity measurement, thus indicating that standard Hertzian contact models and their derivatives (DMT, Sneddon, etc.), may not be ideal in calculating the rigidity of this material. In order to better model the effective Young’s modulus (E_eff) of the mesh and account for cantilever beam-bending type mechanical deformation, a modification of Euler-Bernoulli theory was established.

This mathematical model was subsequently used to correlate fiber geometry parameters to bending stiffness, thus allowing for us to estimate E_eff for a range of meshes. Subsequent T cell expansions and comparison of data to previous expansions on planar surfaces provided verification of our model.