T-cell development: Is Notch a key player in lineage decisions?

AbstractAt two consecutive ‘checkpoints’ in their development, T cells have to be rescued from programmed cell death and to choose between distinct lineage fates; recent results show that the Notch transmembrane receptor can significantly influence T-cell development at both of these points

Targeting the CD4 Binding Site of HIV

The immunologic obstacles to develop a broadly neutralizing antibody (bNAb) against HIV by vaccine mandate for methodical testing in order to understand and direct the immune response. A mouse model with the predicted human heavy chain variable domain of a bNAb precursor or mature version introduced into the mouse heavy chain immunoglobulin locus proved to be very useful. The immunoglobulin heavy-chain of the predicted germline (GLVH) or mature mutated (MuVH) version of 3BNC60 was knocked into the JH4 locus in mice. 3BNC60 is a bNAb that targets the CD4 binding site (CD4bs) of HIV-11,2 and belongs to the IgHV1-2 class of broadly neutralizing CD4bs antibodies3. In the first part of my thesis I will describe the evolution of the HIV-1 antibody response in GLVH and MuVH mice upon immunization. We immunized the mice with antigens designed to bind to the predicted unmutated precursor of 3BNC60 or with BG505 SOSIP trimers that resemble the native HIV-1 Env. Immunogens specifically designed to activate B cells bearing germline antibodies initiate immune responses, but they do not elicit bNAbs. In contrast, native-like Env trimers fail to activate B cells expressing germline antibodies but elicit bNAbs by selecting for a restricted group of light chains bearing specific somatic mutations that enhance neutralizing activity. The data suggest that vaccination to elicit broad anti-HIV-1 antibodies will require immunization with a succession of related immunogens. Although CD4bs bNAbs are attractive candidates for immunogen design, their features, such as a high degree of somatic hypermutation and a short CDRL3 in combination with our data in 3BNC60 knock-in mice suggest that they might be difficult to elicit through vaccination. In the second part I will describe IOMA, a new class of CD4-mimetic bNAb derived from the VH1-2 germline but with a normal-length CDRL3 and fewer somatic hypermutations than other bNAbs of its class. We defined IOMA’s complete epitope, by using crystal structures of a natively glycosylated Env trimer. Analysis of the native glycan shield on HIV-1 Env allowed us to provide what is, to our knowledge, the first full description of the interplay between heterogeneous untrimmed high-mannose and complex-type N-glycans within the CD4bs and of a natively glycosylated trimer

Oral tolerance: is it all retinoic acid?

Oral tolerance has been argued to depend on “special” presentation of antigen in the gut. New studies support this idea by showing that the catalysis of vitamin A into retinoic acid (RA) in gut-associated dendritic cells (DCs) enhances the transforming growth factor (TGF)-β–dependent conversion of naive T cells into regulatory T (T reg) cells and also directs T reg cell homing to the gut. These results reveal new tolerance mechanisms that will aid the use of T reg cells in the clinic

Identification of a T Lineage-Committed Progenitor in Adult Blood

SummaryWith help of a hCD25 reporter controlled by pre-T cell receptor α (Ptcra) regulatory elements, T cell precursors were identified in peripheral blood. Sca-1+IL-7Rα+Flt3− precursors that were c-kitloThy-1hi generated T lineage cells when cultured on OP9-DL1 stromal cells and upon transfer into Rag2−/−Il2rg−/− mice. No B cells were generated in vivo and only few in vitro. These cells, which we call circulating T cell progenitors (CTP), were found at the same frequency in Foxn1nu/nu thymus-deficient mice and wild-type mice, indicating that they were pre- rather than postthymic. Inhibition of Notch-dependent transcription in vivo reduced the frequency of intrathymic early T cell progenitors (ETP), but not CTP, indicating that the latter are less Notch dependent. Thus, CTP represent T lineage-committed T cell precursors linking extrathymic with intrathymic lymphopoiesis in adult mice

Notch Signaling in T-Cell Development and T-ALL

The Notch signaling pathway is an evolutionarily conserved cell signaling system present in most multicellular organisms, as it controls cell fate specification by regulating cell proliferation, differentiation, apoptosis, and survival. Regulation of the Notch signaling pathway can be achieved at multiple levels. Notch proteins are involved in lineage fate decisions in a variety of tissues in various species. Notch is essential for T lineage cell differentiation including T versus B and αβ versus γδ lineage specification. In this paper, we discuss Notch signaling in normal T-cell maturation and differentiation as well as in T-cell acute lymphoblastic lymphoma/leukemia

PLZF Controls the Expression of a Limited Number of Genes Essential for NKT Cell Function

Natural killer (NKT) T cells exhibit tissue distribution, surface phenotype, and functional responses that are strikingly different from those of conventional T cells. The transcription factor PLZF is responsible for most of these properties, as its ectopic expression in conventional T cells is sufficient to confer to them an NKT-like phenotype. The molecular program downstream of PLZF, however, is largely unexplored. Here we report that PLZF regulates the expression of a surprisingly small set of genes, many with known immune functions. This includes several established components of the NKT cell developmental program. Expression of the transcriptional regulators Id2, previously shown to be required for iNKT cell survival in the liver and c-Maf, which shapes the NKT cytokine profile, was compromised in PLZF-deficient cells. Ectopic expression of c-Maf complemented the cells’ defect in producing IL-4 and IL-10. PLZF also induced a program of cell surface receptors which shape the NKT cell’s response to external stimuli, including the costimulatory receptor ICOS and the cytokine receptors IL12rb1 and IL18r1. As an ensemble, the known functions of the molecules whose expression is affected by PLZF explain many defects observed in $PLZF^{−/−}$ NKT cells