Investigating Dendritic Cell Migration: Insights From Tuning the Mechanical Properties of Collagen via Click Chemistry

Abstract

Dendritic cells (DCs) are the primary antigen presenting cell capable of activating T cells, a group of immune cells widely used in cancer immunotherapy due to their ability to kill self-cells. However, outcomes have been varied, with one determinant factor emerging as the mechanical environment of the extracellular matrix (ECM). The increase in collagen crosslinking and ECM stiffness has been correlated with worse outcomes in many solid tumors, but the impact on the migration of DCs has not been extensively studied in 3D culture. This thesis created a highly tunable, well-characterized gel system by conjugating click chemistry groups (either norbornene or tetrazine) to collagen type I. Functionalized collagens were mixed together at differing ratios, thus varying the amount of crosslinking in each gel. The storage modulus, loss modulus, stress relaxation, and pore size of gels was quantified using rheometry and confocal microscopy. Human monocyte-derived DCs (moDCs) were embedded in the gels and their average speed and mean squared distance (MSD) analyzed using TrackMate following time-lapse confocal imaging. Crosslinking increases gel storage modulus (G’) and decreases loss modulus (G”), creating stiffer gels. Crosslinking also increases stress relaxation time, indicating less viscoelastic behavior, and decreases pore size. When embedded in 2 mg/mL gels, moDCs move significantly faster in uncrosslinked conditions. The maximum MSD of cells is also decreased in crosslinked 2 mg/mL gels, indicating increased cell confinement. The moDCs move significantly slower and are more confined in 4 mg/mL gels. These results suggest that collagen deposition and crosslinking occurring in the tumor ECM may negatively affect DC migration.