DRAG in situ barcoding reveals an increased number of HSPCs contributing to myelopoiesis with age.

Ageing is associated with changes in the cellular composition of the immune system. During ageing, hematopoietic stem and progenitor cells (HSPCs) that produce immune cells are thought to decline in their regenerative capacity. However, HSPC function has been mostly assessed using transplantation assays, and it remains unclear how HSPCs age in the native bone marrow niche.

Replicative history marks transcriptional and functional disparity in the CD8 T cell memory pool.

Clonal expansion is a core aspect of T cell immunity. However, little is known with respect to the relationship between replicative history and the formation of distinct CD8 memory T cell subgroups. To address this issue, we developed a genetic-tracing approach, termed the DivisionRecorder, that reports the extent of past proliferation of cell pools in vivo.

The precursors of CD8 tissue resident memory T cells: from lymphoid organs to infected tissues.

CD8 tissue resident memory T cells (T cells) are essential for immune defence against pathogens and malignancies, and the molecular processes that lead to T cell formation are therefore of substantial biomedical interest. Prior work has demonstrated that signals present in the inflamed tissue micro-environment can promote the differentiation of memory precursor cells into mature T cells, and it was therefore long assumed that T cell formation adheres to a 'local divergence' model, in which T cell lineage decisions are exclusively made within the tissue. However, a growing body of work provides evidence for a 'systemic divergence' model, in which circulating T cells already become preconditioned to preferentially give rise to the T cell lineage, resulting in the generation of a pool of T cell-poised T cells within the lymphoid compartment.

Formation of Tissue-Resident CD8 T-Cell Memory.

Resident memory CD8 T (Trm) cells permanently reside in nonlymphoid tissues where they act as a first line of defense against recurrent pathogens. How and when antigen-inexperienced CD8 T cells differentiate into Trm has been a topic of major interest, as knowledge on how to steer this process may be exploited in the development of vaccines and anticancer therapies. Here, we first review the current understanding of the early signals that CD8 T cells receive before they have entered the tissue and that govern their capacity to develop into tissue-resident memory T cells.

A committed tissue-resident memory T cell precursor within the circulating CD8+ effector T cell pool.

An increasing body of evidence emphasizes the role of tissue-resident memory T cells (TRM) in the defense against recurring pathogens and malignant neoplasms. However, little is known with regard to the origin of these cells and their kinship to other CD8+ T cell compartments. To address this issue, we followed the antigen-specific progeny of individual naive CD8+ T cells to the T effector (TEFF), T circulating memory (TCIRCM), and TRM pools by lineage-tracing and single-cell transcriptome analysis.

The Branching Point in Erythro-Myeloid Differentiation.

Development of mature blood cell progenies from hematopoietic stem cells involves the transition through lineage-restricted progenitors. The first branching point along this developmental process is thought to separate the erythro-myeloid and lymphoid lineage fate by yielding two intermediate progenitors, the common myeloid and the common lymphoid progenitors (CMPs and CLPs). Here, we use single-cell lineage tracing to demonstrate that so-called CMPs are highly heterogeneous with respect to cellular output, with most individual CMPs yielding either only erythrocytes or only myeloid cells after transplantation.

T Cell factor 1 represses CD8+ effector T cell formation and function.

The Wnt-responsive transcription factor T cell factor 1 (Tcf1) is well known for its role in thymic T cell development and the formation of memory CD8(+) T cells. However, its role in the initial phases of CD8(+) T effector cell formation has remained unexplored. We report that high levels of Wnt signaling and Tcf1 are operational in naive and memory CD8(+) T cells, whereas Wnt signaling and Tcf1 were low in effector CD8(+) T cells.

Single cell behavior in T cell differentiation.

Upon primary infection, naïve T cells that recognize their cognate antigen become activated, proliferate, and simultaneously differentiate into various subsets. A long-standing question in the field has been how this cellular diversification is achieved. Conceptually, diverse cellular output may either arise from every single cell or only from populations of naïve cells.