Differentiation Of pre-T Cells Research Articles

Germline RUNX1 Variation and Predisposition to T-Cell Acute Lymphoblastic Leukemia in Children

Previous studies by us and others have linked germline genetic variants to the familial predisposition to childhood B-cell acute lymphoblastic leukemia (B-ALL), with pathogenic variants discovered in TP53, PAX5, ETV6, and IKZF1 (J. Clin. Oncol 2018, Nature Genet 2014, Lancet Oncol 2015, Cancer Cell 2018). However, genetic predisposition to T-ALL is much less understood. Rare care reports of T-ALL pedigrees with germline RUNX1 point to its potential role in ALL susceptibility. RUNX1 plays significant roles in definitive hematopoiesis and primarily functions as a transcription factor. RUNX1 germline variants are associated with familial platelet disorder, with a significant proportion of patients also developing myeloid malignancies. To comprehensively examine the pattern and prevalence of RUNX1 germline variation in T-ALL, we performed targeted germline sequencing of 1,231 cases enrolled on the Children's Oncology Group AALL0434 trial. In this largely unbiased T-ALL cohort, we identified 13 germline RUNX1 variants in 16 cases (Figure 1), including six missense (46.2%), two nonsense (15.4%), three frameshift (23.1%), and two indel variants (15.4%). These variants are divided into three groups: Group I, truncating both the DNA-binding RHD domain and the transcriptional activation AD domain (p.K117* and p.S141fs); Group II, truncating the AD domain only (p.Q213fs, p.R232fs, and p.Y287*); and Group III, missense and indel variants. To comprehensively characterize the function of these T-ALL-related RUNX1 variants, we performed a variety of biochemical and cellular assays in different model systems. Using reporter gene assays, we first directly evaluated the transcriptional activity of RUNX1 variants in Hela cells and identified both loss-of-function (e.g., Group I variants) and dominant-negative effects (e.g., p.G365R in Group III variants). Group I variants also showed dramatic subcellular mislocalization in the cytoplasm, with concomitant loss of CBFβ binding, both of which were significantly subtler for Groups II and III variants. Focusing on representative variants in these three groups (p.S141fs, p.R232fs, Y287*, and p.G365R), we next examined their effects on hematopoietic phenotypes in vitro. Ectopic expression of Group II and III variants in human CD34+ cells significantly increased CFU-M/GM colony formation and long-term proliferation, while repressing BFU-E colonies. Variant RUNX1 cells also showed defects in megakaryocyte and pre-T cell differentiation, with decreased apoptosis compared to cells expressing wild-type RUNX1. Expression of Group I variant led to phenotypes similar to that of empty vector, suggesting a complete loss of RUNX1 function. In parallel, we engineered isogenic T-ALL single clones with epitope-tagged RUNX1 variant introduced at the endogenous locus via CRISPR-Cas9 mediated homology recombination. Chromatin immunoprecipitation (ChIP)-seq profiling of these cells suggested a varying degree of changes in RUNX1 binding sites across the genome as a result of the RUNX1 genetic variation. On the other hand, RNA-seq profiling identified down-regulation of genes that were activated by wild-type RUNX1, again confirming the loss-of-function effects of these variants. Finally, we performed whole-genome seq of matched leukemia and germline samples and RNA-seq of leukemia cells in 7 T-ALL cases with RUNX1 predisposition variants. In this analysis, we observed a significant enrichment of JAK3 mutations (5 of 7 cases, 71.4%) compared to a cohort of 264 T-ALL with wild-type RUNX1 in the germline (P=3.39×10-7). By comparison, only 27.3% (3 of 7) of T-ALL with a somatic mutation in RUNX1 had concurrent JAK3 mutations in this cohort. Unsupervised clustering based on RNA-seq derived gene expression profile showed that RUNX1-mutated cases, either germline or somatic, clustered tightly with early T precursor (ETP) and near-ETP immunophenotypes. In conclusion, we comprehensively characterized 13 RUNX1 germline variants in T-ALL, ~40% of which are frameshift or nonsense. These variants result in a loss of function, by disrupting DNA binding or deleting the transcriptional activation domain, and in some cases in a dominant-negative fashion. RUNX1 genetic variation also results in significant defects in hematopoietic cell differentiation and functions in vitro, but additional somatic lesions are most likely required for overt leukemogenesis. Disclosures Gastier Foster: Incyte Corporation: Other: Commercial Research; Bristol Myers Squibb (BMS): Other: Commercial Research. Raetz:Pfizer: Research Funding. Zweidler-McKay:ImmunoGen: Employment. Mullighan:Illumina: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored travel; Pfizer: Honoraria, Other: speaker, sponsored travel, Research Funding; AbbVie: Research Funding; Loxo Oncology: Research Funding; Amgen: Honoraria, Other: speaker, sponsored travel. Hunger:Amgen: Consultancy, Equity Ownership; Bristol Myers Squibb: Consultancy; Novartis: Consultancy; Jazz: Honoraria. Relling:Servier Pharmaceuticals: Research Funding. Loh:Medisix Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees.

Vital roles of mTOR complex 2 in Notch-driven thymocyte differentiation and leukemia

Notch plays critical roles in both cell fate decisions and tumorigenesis. Notch receptor engagement initiates signaling cascades that include a phosphatidylinositol 3-kinase/target of rapamycin (TOR) pathway. Mammalian TOR (mTOR) participates in two distinct biochemical complexes, mTORC1 and mTORC2, and the relationship between mTORC2 and physiological outcomes dependent on Notch signaling is unknown. In this study, we report contributions of mTORC2 to thymic T-cell acute lymphoblastic leukemia (T-ALL) driven by Notch. Conditional deletion of Rictor, an essential component of mTORC2, impaired Notch-driven proliferation and differentiation of pre-T cells. Furthermore, NF-κB activity depended on the integrity of mTORC2 in thymocytes. Active Akt restored NF-κB activation, a normal rate of proliferation, and differentiation of Rictor-deficient pre-T cells. Strikingly, mTORC2 depletion lowered CCR7 expression in thymocytes and leukemic cells, accompanied by decreased tissue invasion and delayed mortality in T-ALL driven by Notch. Collectively, these findings reveal roles for mTORC2 in promoting thymic T cell development and T-ALL and indicate that mTORC2 is crucial for Notch signaling to regulate Akt and NF-κB.

MTOR complex 2 mediates Notch signaling in thymocyte and T-cell leukemia development (64.8)

Abstract Mammalian target of rapamycin (mTOR) is an important component of the PI3-kinase (PI3K) pathway that regulates cell growth and proliferation. PI3K signaling cascades can be initiated by activation of Notch, a critical regulator for T lineage commitment and leukemia development. Here we show that mTOR complex 2 (mTORC2) is functionally vital as a downstream target of Notch in thymocytes and T-cell acute lymphoblastic leukemia (T-ALL). Conditional deletion of rictor, an essential component of mTORC2, results in impaired proliferation and differentiation of pre-T cells driven by Notch ligation. Moreover, mTORC2 is a primary kinase for Akt S473 and enhances Akt activity in thymocytes. Furthermore, mTORC2 regulates NF-κB activity, such that constitutively active Akt can restore nuclear NF-κB levels in the rictor-depleted pre-T cells, as well as normalizing Notch-initiated proliferation and differentiation. Strikingly, interruption of mTORC2 significantly delays T-ALL induced by Notch1 activating mutation and suppresses infiltration of leukemic cells into the non-lymphoid organs. Our study provides evidence of a key role of mTORC2 in relaying Notch signaling in thymocyte development, and reveals that mTORC2 promotes Notch-driven leukemia progression.

Notch-induced T cell development requires phosphoinositide-dependent kinase 1

Phosphoinositide-dependent kinase l (PDK1) phosphorylates and activates multiple AGC serine kinases, including protein kinase B (PKB), p70Ribosomal S6 kinase (S6K) and p90Ribosomal S6 kinase (RSK). PDK1 is required for thymocyte differentiation and proliferation, and herein, we explore the molecular basis for these essential functions of PDK1 in T lymphocyte development. A key finding is that PDK1 is required for the expression of key nutrient receptors in T cell progenitors: CD71 the transferrin receptor and CD98 a subunit of L-amino acid transporters. PDK1 is also essential for Notch-mediated trophic and proliferative responses in thymocytes. A PDK1 mutant PDK1 L155E, which supports activation of PKB but no other AGC kinases, can restore CD71 and CD98 expression in pre-T cells and restore thymocyte differentiation. However, PDK1 L155E is insufficient for thymocyte proliferation. The role of PDK1 in thymus development thus extends beyond its ability to regulate PKB. In addition, PDK1 phosphorylation of AGC kinases such as S6K and RSK is also necessary for thymocyte development.

PKB Rescues Calcineurin/NFAT-Induced Arrest of Rag Expression and Pre-T Cell Differentiation

Protein kinase B (PKB), an Ag receptor activated serine-threonine kinase, controls various cellular processes including proliferation and survival. However, PKB function in thymocyte development is still unclear. We report PKB as an important negative regulator of the calcineurin (CN)-regulated transcription factor NFAT in early T cell differentiation. Expression of a hyperactive version of CN induces a profound block at the CD25+CD44- double-negative (DN) 3 stage of T cell development. We correlate this arrest with up-regulation of Bcl-2, CD2, CD5, and CD27 proteins and constitutive activation of NFAT but a severe impairment of Rag1, Rag2, and intracellular TCR-beta as well as intracellular TCR-gammadelta protein expression. Intriguingly, simultaneous expression of active myristoylated PKB inhibits nuclear NFAT activity, restores Rag activity, and enables DN3 cells to undergo normal differentiation and expansion. A correlation between the loss of NFAT activity and Rag1 and Rag2 expression is also found in myristoylated PKB-induced CD4+ lymphoma cells. Furthermore, ectopic expression of NFAT inhibits Rag2 promoter activity in EL4 cells, and in vivo binding of NFATc1 to the Rag1 and Rag2 promoter and cis-acting transcription regulatory elements is verified by chromatin immunoprecipitation analysis. The regulation of CN/NFAT signaling by PKB may thus control receptor regulated changes in Rag expression and constitute a signaling pathway important for differentiation processes in the thymus and periphery.

Differential Requirement for RhoA GTPase Depending on the Cellular Localization of Protein Kinase D

This study explores the links between the GTPase RhoA and the serine kinase protein kinase D (PKD) during thymocyte development. The rationale is that RhoA and PKD regulate common biological responses during T cell development, but there is nothing known about their interdependence. In fibroblasts, Rho function is required for activation of PKD catalytic activity. However, the data show that activation of Rho is neither sufficient nor essential for PKD activation in T cells. One alternative explanation for the apparent convergence of PKD and Rho signaling in T cells is that PKD responses might be Rho-dependent. To address this latter possibility, we probed the Rho requirements for the actions of constitutively active PKD mutants in pre-T cells of transgenic mice. Active PKD can localize to either the plasma membrane or the cytosol, and we therefore compared the Rho requirements for the actions of membrane- or cytosol-localized PKD. Here we show that membrane-localized PKD regulation of pre-T cell differentiation is Rho-dependent, but the actions of cytosol-localized PKD are not. These studies demonstrate that a Rho requirement for PKD activation is not ubiquitous. Moreover, links between PKD and Rho are determined by the cellular location of PKD.

Interleukin-7 inhibits pre-T-cell differentiation induced by the pre-T-cell receptor signal and the effect is mimicked by hGM-CSF in hGM-CSF receptor transgenic mice.

We have previously reported that human granulocyte-macrophage colony-stimulating factor (hGM-CSF) causes a stage-specific inhibition of T-cell receptor (TCR) alphabeta cell development in the thymus of transgenic mice constitutively expressing the hGM-CSF receptor. Since it has been reported that the addition of interleukin-7 (IL-7) to fetal thymic organ culture (FTOC) has similar effects, we compared the effects of IL-7 and hGM-CSF on TCR(alphabeta) cell development in hGM-CSF receptor transgenic mice. We reconstituted fetal lobes with sorted pre-T, or post pre-T CD4(-)CD8(-) precursor cells. The addition of either IL-7 or hGM-CSF to these cultures suppressed further differentiation of pre-T cells but not post pre-T cells. At the same time, the cell number was increased, suggesting that pre-T-cell proliferation is stimulated by these cytokines. Furthermore, the differentiation of recombination-activating gene-1 (RAG-1)-deficient pre-T cells in response to anti-CD3 antibody stimulation was suppressed by either IL-7 or hGM-CSF, suggesting that these cytokines inhibit the pre-T-cell receptor (pre-TCR) signal. This inhibition is unexpected because the pre-TCR signal and the IL-7 signal have previously been considered to be co-operative. Recent analysis of the downstream events of IL-7 receptor and GM-CSF receptor revealed that they share common signal transduction molecules. Our results show that IL-7 is able to promote pre-T cell proliferation and to suppress differentiation induced by the pre-TCR signal. GM-CSF can mimic these biological activities of IL-7 when the pre-T cells express GM-CSF receptors. Our data suggest that both timing and level of activation of the IL-7 signalling pathway must be precisely regulated to facilitate the differentiation of thymocytes.

Differential developmental regulation and functional effects on pre-TCR surface expression of human pTalpha(a) and pTalpha(b) spliced isoforms.

Functional rearrangement at the TCRbeta locus leads to surface expression on developing pre-T cells of a pre-TCR complex composed of the TCRbeta-chain paired with the invariant pre-TCRalpha (pTalpha) chain and associated with CD3 components. Pre-TCR signaling triggers the expansion and further differentiation of pre-T cells into TCRalphabeta mature T cells, a process known as beta selection. Besides the conventional pTalpha transcript (termed pTalpha(a)), a second, alternative spliced, isoform of the pTalpha gene (pTalpha(b)) has been described, whose developmental relevance remains unknown. In this study, phenotypic, biochemical, and functional evidence is provided that only pTalpha(a) is capable of inducing surface expression of a CD3-associated pre-TCR complex, which seems spontaneously recruited into lipid rafts, while pTalpha(b) pairs with and retains TCRbeta intracellularly. In addition, by using real-time quantitative RT-PCR approaches, we show that expression of pTalpha(a) and pTalpha(b) mRNA spliced products is differentially regulated along human intrathymic development, so that pTalpha(b) transcriptional onset is developmentally delayed, but beta selection results in simultaneous shutdown of both isoforms, with a relative increase of pTalpha(b) transcripts in beta-selected vs nonselected pre-T cells in vivo. Relative increase of pTalpha(b) is also shown to occur upon pre-T cell activation in vitro. Taken together, our data illustrate that transcriptional regulation of pTalpha limits developmental expression of human pre-TCR to intrathymic stages surrounding beta selection, and are compatible with a role for pTalpha(b) in forming an intracellular TCRbeta-pTalpha(b) complex that may be responsible for limiting surface expression of a pTalpha(a)-containing pre-TCR and/or may be competent to signal from a subcellular compartment.

Analysis of thymocyte development reveals that the GTPase RhoA is a positive regulator of T cell receptor responses in vivo.

Loss of function of the guanine nucleotide binding protein RhoA blocks pre-T cell differentiation and survival indicating that this GTPase is a critical signaling molecule during early thymocyte development. Previous work has shown that the Rho family GTPase Rac-1 can initiate changes in actin dynamics necessary and sufficient for pre-T cell development. The present data now show that Rac-1 actions in pre-T cells require Rho function but that RhoA cannot substitute for Rac-1 and induce the actin cytoskeletal changes necessary for pre-T cell development. Activation of Rho is thus not sufficient to induce pre-T cell differentiation or survival in the absence of the pre-T cell receptor (TCR). The failure of RhoA activation to impact on pre-TCR-mediated signaling was in marked contrast to its actions on T cell responses mediated by the mature TCR alpha/beta complex. Cells expressing active RhoA were thus hyperresponsive in the context of TCR-induced proliferation in vitro and in vivo showed augmented positive selection of thymocytes expressing defined TCR complexes. This reveals that RhoA function is not only important for pre-T cells but also plays a role in determining the fate of mature T cells.

Control of pre-T cell proliferation and differentiation by the GTPase Rac-1

The GTPase Rac-I has the potential for pleiotropic functions due to its ability to interact with multiple effectors. Here, activation of Rac-I is shown to potently regulate pre-T cell differentiation and proliferation at the point of T cell antigen receptor (TCR) beta selection. An activated Rac-I effector domain mutant that restricts signaling to particular actions on actin dynamics can drive pre-T cell differentiation. Rac-I activation cannot fully substitute for the pre-TCR complex but can fully correct defects in pre-T cell development in mice lacking the adapter molecule Vav-1. The present study identifies the subset of Rac-I responses that mediate Vav-1 action as critical regulators of TCR beta selection.

Pre-TCR Signaling and Inactivation of p53 Induces Crucial Cell Survival Pathways in Pre-T Cells

Signaling through the pre-TCR is essential for early T cell development and is severely impaired in mice lacking the CD3γ chain of the pre-TCR. We here address the molecular mechanisms underlying this defect. Impaired pre-TCR signaling is shown to be associated with a profound increase in the number of apoptotic CD4 −CD8 − (DN) thymocytes. Introduction of p53 deficiency into CD3γ-deficient mice completely reverses the cell survival defect in CD3γ-deficient DN thymocytes and rescues the block in pre-T cell differentiation. In addition, the CD4 +CD8 + (DP) compartment is expanded to its normal size. These findings suggest that the pre-TCR regulates progression through the DNA-damage checkpoint of the DN to DP transition by inactivating p53.

High Level Expression of the Xlr Nuclear Protein in Immature Thymocytes and Colocalization with the Matrix-Associated Region-Binding SATB1 Protein

The X-linked lymphocyte-regulated (Xlr) protein is a 30,000 Mr nuclear protein bearing homology with meiosis-specific proteins and expressed in late stage B lymphoid cell lines. In the present study we investigated its expression in the T lymphoid lineage. In adults, a high level of expression was detected in CD4-CD8- thymocytes. Most remarkably, the peak of Xlr expression occurred early during thymus cell ontogeny, precisely on days 14-15 of gestation, and was associated with the first wave of pre-T cell differentiation. Its onset preceded the rearrangement of TCR genes, as Xlr expression was conserved in thymus cells from RAG1(0/0) mice. The lower expression of Xlr on day 13 of fetal development, the bright Thy1+ phenotype of Xlr-positive cells, their large size, and their absence from subcapsular areas suggest that Xlr expression must be turned on within the thymus and not in prethymic precursors. From day 16 of gestation, Xlr expression decreased markedly. At birth and later, Xlr(high) cells were mostly large cells scattered throughout the cortical area. As shown by confocal microscopy, expression of Xlr closely overlapped that of SATB1, which binds special AT-rich DNA sequences associated with the nuclear matrix and plays an important regulatory role for many genes. The remarkably regulated expression of Xlr in the lymphoid cell lineage and of its homologue Xmr in the germ cell lineage suggests that they might play an important role in chromatin metabolism at critical stages of differentiation during which the genome undergoes irreversible rearrangements.

Thymocyte proliferation and differentiation in human granulocyte-macrophage colony-stimulating factor receptor transgenic mice

Thymocytes display varying responses to cytokines depending on their stage of differentiation. Whether these responses are due to stage-specific cytokine receptor expression or to downstream signaling mechanisms is unknown. We examined the relationship between receptor expression and thymocyte proliferation or differentiation by using thymocytes from transgenic mice that constitutively expressed the human granulocyte-macrophage colony stimulating factor (hGM-CSF) receptor. Transgenic CD4-CD8-, CD4+CD8-, and CD4-CD8+ thymocyte populations expressing the hGM-CSF receptor proliferated when cultured with hGM-CSF, whereas CD4+CD8+ cells failed to proliferate despite expressing this receptor. We next examined the effect of hGM-CSF receptor signaling on thymocyte differentiation in fetal thymic organ culture supporting a full program of T cell development in vitro. Addition of hGM-CSF to the transgenic fetal thymic organ culture resulted in failure of CD4-CD8- cells to differentiate into CD4+CD8+ cells. To investigate this maturational inhibition more closely, we repopulated wild-type fetal lobes with sorted pro-T, pre-T or post pre-T precursor cells from hGM-CSF receptor transgenic mice. In these cultures hGM-CSF blocked both pro-T and pre-T cell differentiation, whereas the more mature post pre-T cells differentiated normally. These results suggest that hGM-CSF receptor signaling during thymocyte differentiation causes stage-specific inhibition of precursor cell maturation. In addition, repopulation studies of transgenic fetal lobes with sorted wild-type thymocyte precursors indicated that hGM-CSF inhibited proliferation and differentiation of the wild-type precursors, suggesting a secondary effect via transgenic stromal cells. (J Allergy Clin Immunol 1997;100:S87-96.)

Human Granulocyte-Macrophage Colony-Stimulating Factor (hGM-CSF) Induces Inhibition of Intrathymic T-Cell Development in hGM-CSF Receptor Transgenic Mice

AbstractThymocytes show differential cytokine responses, depending on the stage of differentiation. Whether these responses are due to preferential cytokine receptor expression or due to downstream signaling mechanisms is unknown. In this study, we examined the relationship between receptor expression and T-cell proliferation or differentiation using thymocytes from transgenic mice constitutively expressing the human granulocyte-macrophage colony-stimulating factor (hGM-CSF ) receptor. Transgenic CD4−CD8−, CD4+CD8−, and CD4−CD8+ cells proliferated when cultured with hGM-CSF in vitro, whereas CD4+CD8+ cells failed to proliferate. To examine the effect of hGM-CSF receptor signaling on T-cell development, we used fetal thymic organ cultures. The addition of exogenous hGM-CSF resulted in the failure of CD4−CD8− cells to differentiate into CD4+CD8+ cells. To more closely identify this maturational inhibition, we reconstituted normal fetal lobes with sorted pro-T–, pre-T–, or post-pre-T–precursor cells from transgenic mice. The addition of hGM-CSF to these cultures led to a block in both pro-T– and pre-T–cell differentiation, whereas the more mature post-pre-T cells differentiated normally. We propose that hGM-CSF receptor signaling during T-cell development results in a stage-specific inhibition of thymic precursor maturation.

Interleukin 7-induced expression of specific T cell receptor gamma variable region genes in murine fetal liver cultures.

We previously reported that culture of murine fetal liver (FL) cells with interleukin 7 (IL-7) results in expression of high levels of T cell receptor (TCR) gamma transcripts by a population of cells expressing Thy-1 and Pgp-1, suggesting that IL-7 promotes the growth and/or differentiation of pre-T cells. We demonstrate herein that culture of FL cells for 7 d with IL-7 caused the rearrangement and expression of TCR gamma variable (V) region genes V gamma 4 and V gamma 6, but not V gamma 5 or V gamma 7. Since this effect was not blocked by hydroxyurea, it appeared to represent induction of expression of these genes by IL-7 rather than expansion of a preexisting positive population. We also show that IL-7 induced RAG-1 and RAG-2 mRNA expression by FL cells. These data provide evidence that specific TCR gamma/delta V region genes can be rearranged and expressed by T lineage cells before their migration to the thymus, in response to IL-7.

Development of αβ T cells

Developing T cells in the thymus are subject to a screening process, through interactions with thymic stromal cells, from which T cells with appropriate T-cell receptors are selected. The recent generation of T-cell receptor transgenic mice and mice homozygous for disrupted T-cell receptor genes have now supplied tools that improve the prospect for a better understanding of the molecular mechanisms of this thymic selection process. In addition these model systems appear to indicate a role for a, not yet fully characterized, pre-T cell receptor complex in survival and further differentiation of pre-T cells.

IL 7-induced T cell receptor-gamma gene expression by pre-T cells in murine fetal liver cultures.

IL-7 has previously been shown to stimulate proliferation of immature CD4-CD8- thymocytes from fetal and adult mice. We show that IL-7 mRNA levels are much higher in the day-14 fetal thymus than in the adult thymus, i.e., when the thymus is primarily composed of CD4-CD8- cells. Inasmuch as IL-7 may, therefore, be one of the first cytokines to which pre-T cells from the fetal liver are exposed when they migrate to the thymus during development, we hypothesized that IL-7 may promote differentiation of pre-T cells from the fetal liver. We found that human rIL-7 promotes growth of cells obtained from the liver of fetal mice at day 14 of gestation. Moreover, we found that IL-7 stimulated expression of mRNA encoding TCR-gamma, alpha-, and beta-genes. The size of the transcripts induced by IL-7 suggests that TCR-gamma was expressed in a rearranged form in response to IL-7, whereas TCR-alpha and -beta genes appeared to be expressed from nonrearranged loci. Culture of fetal liver cells for 7 days with IL-7 also caused the appearance of a population of cells expressing Thy-1 and Pgp-1 Ag, a phenotype similar to that seen in the early (day-14) fetal thymus. The Thy-1+ Pgp-1+ population was enriched in TCR-gamma mRNA, as determined by flow cytometric sorting followed by Northern blot analysis. These data support the hypothesis that IL-7 can stimulate some of the early events associated with thymocyte differentiation in the fetus.

A role for interleukin 4 in the differentiation of mature T cell receptor gamma/delta + cells from human intrathymic T cell precursors.

We have analyzed the effect of human recombinant interleukin 4 (rIL-4) on the growth and differentiation of human intrathymic pre-T cells (CD7+2+1-3-4-8-). We describe that this population of T cell precursors proliferates in response to rIL-4 (in the absence of mitogens or other stimulatory signals) in a dose-dependent way. The IL-4-induced proliferation is independent of the IL-2 pathway, as it cannot be inhibited with an anti-IL-2 receptor alpha chain antibody. In our culture conditions, rIL-4 also promotes the differentiation of pre-T cells into phenotypically mature T cells. Although both CD3/T cell receptor (TCR)-alpha/beta + and CD3-gamma/delta + T cells were obtained, the preferential differentiation into TCR-gamma/delta + cells was a consistent finding. These results suggest that, in addition to IL-2, IL-4 plays a critical role in promoting growth and differentiation of intrathymic T cell precursors at early stages of T cell development.

Bone marrow cytotoxic precursor T cells: Alloantigen-induced cytotoxic T-cell responses by murine bone marrow cells in vitro

When bone marrow cells, obtained from C57BL/6 mice, were incubated in vitro with irradiated BALB/c spleen cells, cytotoxic activity against P815 tumor cells developed at 5–7 days of culture. This cytotoxic activity was T cell mediated and specific for the H-2 type of the allogeneic spleen cells used as stimulators. The generation of this cytotoxic T-cell activity was dependent on T cells present in the bone marrow since T-cell-depleted bone marrow cells failed to generate a cytotoxic response in vitro. The correct ratio of bone marrow cells to allogeneic stimulator cells was critical for demonstrating an in vitro cytotoxic response. Further, bone marrow cells incubated in culture medium not supplemented with 2-mercaptoethanol (2-ME) failed to generate alloantigen induced cytotoxic responses. Cytotoxic activity generated by bone marrow cells was always lower than the cytotoxic activity generated by alloantigen stimulated spleen cells. However, the level of cytotoxic activity generated by bone marrow cells was not in proportion to the initial low number of T cells present in that tissue. Before in vitro culture with alloantigen, 3% of the bone marrow cells were Thy-1.2 + as compared to 40% of the spleen cells being Thy-1.2 +. After 5 days of culture with alloantigen, 28% of the bone marrow cells were Thy-1.2 +, representing a sixfold increase in the absolute number of T cells. The possibility that differentiation of pre-T cells into cytotoxic effector T cells is taking place in this in vitro response is considered.