Abstract-Human

Resident memory T (Trm) cells stably occupy tissues and cannot be sampled in superficial venous blood. Trm cells are heterogeneous but collectively constitute the most abundant memory T cell subset. Trm cells form an integral part of the immune sensing network, monitor for local perturbations in homeostasis throughout the body, participate in protection from infection and cancer, and likely promote autoimmunity, allergy, and inflammatory diseases and impede successful transplantation. Thus Trm cells are major candidates for therapeutic manipulation. Here we review CD8+ and CD4+ Trm ontogeny, maintenance, function, and distribution within lymphoid and nonlymphoid tissues and strategies for their study. We briefly discuss other resident leukocyte populations, including innate lymphoid cells, macrophages, natural killer and natural killer T cells, nonclassical T cells, and memory B cells. Lastly, we highlight major gaps in knowledge and propose ways in which a deeper understanding could result in new methods to prevent or treat diverse human diseases.

Rationale Cardiomyocytes differentiated from human pluripotent stem cells (PSCs) are increasingly being used for cardiovascular research including disease modeling and hold promise for clinical applications. Current cardiac differentiation protocols exhibit variable success across different PSC lines and are primarily based on the application of growth factors. However, extracellular matrix (ECM) is also fundamentally involved in cardiac development from the earliest morphogenetic events such as gastrulation. Objective We sought to develop a more effective protocol for cardiac differentiation of human PSCs by using ECM in combination with growth factors known to promote cardiogenesis. Methods and Results PSCs were cultured as monolayers on Matrigel, an ECM preparation, and subsequently overlayed with Matrigel. The matrix sandwich promoted an epithelial-to-mesenchymal transition as in gastrulation with the generation of N-cadherin+ mesenchymal cells. Combining the matrix sandwich with sequential application of growth factors (Activin A, BMP4, and bFGF) generated cardiomyocytes with high purity (up to 98%) and yield (up to 11 cardiomyocytes/input PSC) from multiple PSC lines. The resulting cardiomyocytes progressively mature over 30 days in culture based on myofilament expression pattern and mitotic activity. Action potentials typical of embryonic nodal, atrial and ventricular cardiomyocytes were observed, and monolayers of electrically coupled cardiomyocytes modeled cardiac tissue and basic arrhythmia mechanisms. Conclusions Dynamic ECM application promoted EMT of human PSCs and complemented growth factor signaling to enable robust cardiac differentiation.