DL4-µbeads induce T cell lineage differentiation from stem cells in a stromal cell-free system.

T cells are pivotal effectors of the immune system and can be harnessed as therapeutics for regenerative medicine and cancer immunotherapy. An unmet challenge in the field is the development of a clinically relevant system that is readily scalable to generate large numbers of T-lineage cells from hematopoietic stem/progenitor cells (HSPCs). Here, we report a stromal cell-free, microbead-based approach that supports the efficient in vitro development of both human progenitor T (proT) cells and T-lineage cells from CD34+cells sourced from cord blood, GCSF-mobilized peripheral blood, and pluripotent stem cells (PSCs). DL4-µbeads, along with lymphopoietic cytokines, induce an ordered sequence of differentiation from CD34+ cells to CD34+CD7+CD5+ proT cells to CD3+αß T cells. Single-cell RNA sequencing of human PSC-derived proT cells reveals a transcriptional profile similar to the earliest thymocytes found in the embryonic and fetal thymus. Furthermore, the adoptive transfer of CD34+CD7+ proT cells into immunodeficient mice demonstrates efficient thymic engraftment and functional maturation of peripheral T cells. DL4-µbeads provide a simple and robust platform to both study human T cell development and facilitate the development of engineered T cell therapies from renewable sources.

Close Quarters Can Be a Good Fit for Stem Cells to Become T Cells.

Human pluripotent stem cells (PSCs) could potentially provide a potentially unlimited supply of T cells. In this issue of Cell Stem Cell, Montel-Hagen et al. (2019) take advantage of a three-dimensional mouse stromal cell-based system that combines mesoderm specification with organoid-induced hematopoietic differentiation to enable commitment, selection, and maturation of conventional human T cells.

A key role for IL-7R in the generation of microenvironments required for thymic dendritic cells.

Interleukin-7 receptor (IL-7R) signaling is critical for multiple stages of T-cell development, but a role in the establishment of the mature thymic architecture needed for T-cell development and thymocyte selection has not been established. Crosstalk signals between developing thymocytes and thymic epithelial cell (TEC) precursors are critical for their differentiation into cortical TECs (cTECs) and medullary TECs (mTECs). In addition, mTEC-derived factors have been implicated in the recruitment of thymic dendritic cells (DCs) and intrathymic DC development. We therefore examined corticomedullary structure and DC populations in the thymus of Il7r-/- mice. Analysis of TEC phenotype and spatial organization revealed a striking shift in the mTEC to cTEC ratio, accompanied by disorganized corticomedullary structure. Several of the thymic subsets known to have DC potential were nearly absent, accompanied by reductions in DC cell numbers. We also examined chemokine expression in the Il7r-/- thymus, and found a significant decrease in mTEC-derived CCR7 ligand expression, and high levels of cTEC-derived chemokines, including CCL25 and CXCL12. Although splenic DCs were similarly affected, bone marrow (BM) precursors capable of giving rise to DCs were unperturbed. Finally, BM chimeras showed that there was no intrinsic need for IL-7R signaling in the development or recruitment of thymic DCs, but that the provision of wild-type progenitors enhanced reconstitution of thymic DCs from Il7r-/- progenitors. Our results are therefore supportive of a model in which Il7r-dependent cells are required to set up the microenvironments that allow accumulation of thymic DCs.