Terminal deoxynucleotidyl transferase is found in prothymocytes

Differentiation of murine bone marrow stem cells in vitro: long-term growth promoted by a lymphocyte-derived mediator

In attempts to induce differentiation of lymphoid cells from hematopoietic stem cells in vitro, the effects of allogeneic effect factor on the growth of murine bone marrow cultures were studied. Allogeneic effect factor is a soluble mediator derived from mixed secondary murine leukocyte cultures. For several weeks it supported the growth of bone marrow cultures, as indicated by the maintenance of stem cell activity, cellular proliferation, and heterogeneity. Another lymphokine, T cell growth factor, did not, Pre-T lymphocytes could be detected in these cultures for several weeks.

Methods and clinical relevance of terminal deoxynucleotidyl transferase determination in leukemic cells

Terminal deoxynucleotidyl transferase (TdT) is a unique DNA polymerase which is only found in immature cells of lymphoid lineage (pre-T/pre-B). Because of this restricted distribution of TdT, biochemical and immunofluorescence techniques have been employed to determine the distribution of TdT phenotypes in human leukemias and lymphomas, showing high levels of TdT in approximately 95% of acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LBL), approximately 50% of patients with acute undifferentiated leukemia (AUL), approximately 10 of patients with acute nonlymphoblastic leukemia (ANLL), and approximately 30% of patients with chronic myeloid leukemia (CML) and other myeloproliferative (MPS) or myelodysplastic (MDS) syndromes in blast crisis. High levels of TdT activity are associated with a clinical response to remission inducing therapy with vincristine and prednisone in a high proportion of patients (50%-90%), irrespective of clinical and morphologic diagnosis. Preliminary studies furthermore suggest that TdT might serve as a sensitive indicator of subclinical disease in ALL in complete remission.

Terminal deoxynucleotidyl transferase during the development of chicken thymus

Antibodies specific for chicken terminal deoxynucleotidyl transferase (TdT) were used to develop immunoperoxidase and immunofluorescence assays. The cellular distribution and localisation of TdT during the development of chicken thymus were studied. TdT began to appear in the embryonic thymus in the cytoplasm of large cells, between 11 and 12 days of incubation. Thereafter, the proportion of TdT-positive cells increased and TdT was detected in both nucleus and cytoplasm. The first appearance of TdT positive cells, their increasing proportion and the intracellular localisation of TdT will be discussed in correlation with the developmental stages of the thymus.

Terminal deoxynucleotidyl transferase expression in a Thy-l alloantigen variant lymphoma cell line

Terminal deoxynucleotidyl transferase (TdT) expression was examined in the clones of the radiation induced murine leukemia, RL male 1, which differ in Thy-1.2 alloantigen expression and tumourigenicity in syngeneic mice. Both cell lines displayed predominant cytoplasmic localization of TdT and equal sensitivities to specific TdT inhibitors. The R1 male 1.3 + cell line (Thy-1.2 positive and tumourigenic) demonstrated overall higher levels of TdT activity and different elution patterns on phosphocellulose chromatography compared with the RL male 1.4 - (Thy-1.2 negative and poorly tumourgenic) cell line. These findings suggest an association of TdT expression with tumourigenicity properties in leukemic T lymphocytes.

A micromethod for determination of terminal deoxynucleotidyl transferase (TdT) in the diagnostic evaluation of acute leukemias

A micromethod for the determination of TdT in peripheral leukocytes and bone marrow cells has been developed that allows unequivocal identification and quantitation of TdT in less than 1 X 10(6) leukocytes from ALL patients, i.e., in 1 ml of peripheral blood and/or 0.5 ml of bone marrow obtained during routine clinical sampling. The method involves disruption of cell pellet with high salt and detergent followed by centrifugation of extracts at 12,000 X g and partial purification on phosphocellulose matrix by a batch elution technique using a standard laboratory microcentrifuge. Using this microassay, TdT activities have been determined in 500 samples of peripheral blood and bone marrow of 240 adult patients with acute leukemias (86 ALL, 108 ANLL, 44 blastic CML, two acute leukemias following P. vera). From an analysis of our data based on TdT activity, cell surface markers and growth patterns in soft agar and observations published in the literature, it can be concluded that the frequencies of TdT + phenotypes in the various clinical-morphological diagnostic groups are approximately 95% in ALL, 10% in ANLL, 50% in AUL, and 35% in blastic CML. Since the presence of high TdT activity is clearly associated with clinical response to specific forms of chemotherapy in blastic CML and most probably, also in ANLL, the determination of TdT should be considered in all cases of acute leukemias to objectively define prognostically important subgroups which can not be diagnosed by conventional means.

Analysis of rat hemopoietic cells on the fluorescence-activated cell sorter. II. Isolation of terminal deoxynucleotidyl transferase-positive cells

A method is described by which highly enriched populations of viable terminal deoxynucleotidyl transferase-positive (TdT+) cells can be isolated from rat bone marrow by use of the fluorescence-activated cell sorter. Such cells have been postulated to be progenitors of thymocytes and, possibly, of B lymphocytes, and may serve as the targets of neoplastic transformation in acute lymphoblastic leukemia. The separation procedure is based on differences in relative low-angle light scatter and relative fluorescence intensity for Thy-1 antigen between TdT+ cells and other lymphohemopoietic cell populations in bone marrow. Simultaneous sorting of bone marrow cells according to these two parameters resulted in a mean 87% purification of TdT+ cells. The morphological characteristics of the isolated TdT+ cells are described at the light and electron miscroscopic levels.

Induction of differentiation in human marrow T cell precursors by the synthetic serum thymic factor, FTS

The serum thymic factor, 'facteur thymique serique' (FTS), was analysed in vitro for its ability to induce differentiation of normal human marrow T cell precursors into cells with T lymphocyte characteristics. FTS has been isolated, characterized, sequenced and synthesized. In the mouse, natural and synthetic FTS have similar activities in vitro in the rosette inhibition assay. Both substances influence a variety of T cell differentiation markers and functions in vivo. In this study, we found that synthetic FTS induced appearance of two T cell surface markers, HTLA phenotypes and the ability to form E rosettes, on a selective population of normal human marrow cells sedimenting in layers II or III of a Ficoll discontinuous density gradient. In addition, a population of lymphoid cells also found in layer III, which bears receptors for peanut agglutinin (PNA), was decreased in number following exposure to FTS. In the same gradient layer, cells which expressed terminal deoxyribonucleotidyl transferase (TdT) activity showed decreased activity after treatment with FTS. Functional activities characteristic of T lymphocytes were also enhanced in marrow cells of gradient layer III after preincubation with FTS. These T cell functions were demonstrated in marrow cells by their ability to respond and to stimulate allogeneic peripheral blood lymphocytes (PBL) in mixed lymphocyte reactions and by responses to phytomitogens, PHA, Con A and pokeweed. These changes were not observed in marrow cells of gradient layers I, IV and V or after incubation with an FTS analogue that lacked biological and antigenic activity in the mouse system.

Terminal transferase enzyme assay and immunological membrane markers in the diagnosis of leukaemia: a multiparameter analysis of 300 cases

Multiparameter analyses have been carried out with recently developed enzyme and membrane markers in 300 patients with various leukaemias including ALL, AML, but excluding Ph1 positive leukaemias. TdT enzyme levels were particularly valuable in the differential diagnosis of adult acute lymphoid and myeloid leukaemias. The levels were raised in 108 (94%) of the 115 patients who were considered to be non-T, non-B ALL on membrane marker and morphological analysis; all seven cases giving negative TdT results in this group were young children. Unexpectedly high levels were seen only in three (4.1%) of 73 cases of acute myeloid leukaemia verified by histochemistry and membrane markers. Anti-ALL serum was a most useful reagent in childhood leukaemias but blasts from 19 patients (10% of childhood ALL cases and 29% of adult ALL cases) failed to react with the serum in spite of TdT positivity. Strongly ALL+ blasts were seen only in non-T, non-B ALL and some undifferentiated leukaemias. Weakly ALL+ blasts were seen in seven of 32 cases of thymic ALL (Thy-ALL) but in other respects these blasts expressed Thy-ALL features, such as strong reactivity with anti-T cell (HuTLA) serum, negativity with anti-Ia-like serum and raised TdT. The combination of tests was particularly useful in 32 cases of undifferentiated leukaemia: in 10 of these cases TdT positivity indicated the probable 'lymphoblast', nature of blast cells: the remaining 22 cases remained unclassifiable with the markers used. The analysis revealed other interesting variant forms of leukaemias.

Promotion of hematopoietic stem cell differentiation in vitro by a soluble mediator, allogeneic effect factor

This study was designed to investigate the effects of allogenic effect factor (AEF), a soluble mediator derived from short-term mixed lymphocyte cultures (MLC) of in vitro alloantigen-primed T cells, on cultures of murine bone marrow cells. Cultures established under suboptimal conditions namely, in the absence of a pre-established adherent cell layer as required in conventional Dexter-type cultures--declined and lost their stem cell activity rapidly. In contrast, supplementation of these cultures, at initiation and thereafter, with AEF, but not with T cell growth factor (TCGF), induced cell growth and proliferation for several weeks. Such AEF-supplemented cultures exhibited cellular heterogeneity and stem cell activity for significantly longer periods than the control cultures. Even in conventional Dexter cultures, established under optimal conditions, AEF had a beneficial effect on cellular growth and proliferation and myeloid progenitor cell (CFU-C) activity. Furthermore, cell capable of synergizing with suboptimal numbers of mature T cells in con A-induced mitogenic responses, shown by others to be pre-T cells, were detected in the AEF-supplemented cultures for several weeks.

Nucleotide-metabolizing enzymes and lymphocyte differentiation

Inherited deficiencies of adenosine deaminase and purine nucleoside phosphorylase have been found to be associated with certain immunodeficiency syndromes which are characterized by deficiencies of mature peripheral lymphocytes. The immunodeficiency states associated with these enzyme deficiencies are thought to arise from blocks in lymphocyte differentiation. Deficiencies of these enzymes have profound and apparently selective effects on lymphocyte differentiation. Their discovery has focused attention on previously unknown relationships between purine nucleotide metabolism and lymphocyte development and function. In this article three aspects of nucleotide-metabolizing enzymes and lymphocyte differentiation will be discussed: 1) the distribution of the enzymes among lymphocyte populations at differing stages of differentiation; 2) the possible biochemical mechanisms which give rise to the immunodeficiencies; 3) the stages of lymphocyte differentiation which are affected by the enzyme deficiencies.

A synthetic pentapeptide with biological activity characteristic of the thymic hormone thymopoietin

The pentapeptide arginyl-lysyl-aspartyl-valyl-tyrosine, corresponding to amino acid residues 32--36 in thymopoietin, was synthesized. In vitro, this pentapeptide induced the differentiation of murine prothymocytes to thymocytes and inhibited differentiative induction of cells of the B lineage. This combination of actions is presently unique to the parent molecule thymopoietin. In vivo, the pentapeptide reduced the high numbers of autologous rosette-forming cells normally present in the spleens of athymic mice; this also is a property of thymopoietin. These results suggest that this readily synthesized pentapeptide corresponds to an active site of thymopoietin and might serve as a therapeutic substitute for thymopoietin.

Influence of thymosin on E-rosette formation of lymphoid cells in leukemic and nonleukemic children

The influence of two thymosin and two spleen control preparations on the E-rosette formation of peripheral blood lymphocytes and leukemic cells from non-leukemic children with depressed T cell values and leukemic children was investigated. Both thymosin preparations but also one of the control preparations induced a significant increase in the mean percentage of E-rosette forming PBL in the non-leukemic children with depressed T cell values. Thymosin and spleen preparations, however, did not convert the non-erythrocyte binding blasts to erythrocyte binding cells in either common or pre-T-ALL.

Lymphocytes. 2. Differentiation. Differentiation of lymphoid precursor cells

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Radiation leukemia in C57BL/6 mice. III. Correlation of altered expression of terminal deoxynucleotidyl transferase to induction of leukemia

The expression of terminal deoxynucleotidyl transferase (TdT) in the thymus and bone marrow of irradiated mice has been examined. Mice given the leukemogenic regimen of irradiation of four weekly doses of 175 rads starting at 1 mo of age show a long-term elimination of TdT activity in the bone marrow and a reduction of TdT activity in thymocytes. In such mice, the reappearance of normal levels of TdT in the thymus appears to only be associated with the onset of overt leukemia. This effect on TdT expression was shown to be uniquely associated with the leukemogenic regimen of irradiation in that nonleukemogenic irradiation or variations such as bone marrow reconstitution or age which reduce leukemias did not show the same phenotypic effects on TdT expression. The basis for the loss of TdT-positive cells was shown not to be due to the lack of the requisite factors involved in differentiation, but rather to the ability of leukemogenic doses of irradiation to reduce or eliminate an inducible bone marrow stem cell. These results are discussed with respect to the possible mechanisms involved in radiation-induced leukemias in mice.

Demonstration of Thy-1 antigen on pluripotent hemopoietic stem cells in the rat

Three approaches were used to demonstrate the presence of Thy-1 antigen on the surface of pluripotent hemopoietic stem cells in the rat. In the first, stem cells from fetal liver, neonatal spleen, and adult bone marrow were prevented from forming hemopoietic colonies in the spleens of irradiated recipients spleen (colony-forming unit assay) by incubation with antibodies to Thy-1 antigen. Highly specific rabbit heteroantiserum to purified rat brain Thy-1 antigen and mouse alloantisera to Thy-1.1-positive thymocytes were equally effective. This inhibition was neutralized by purified Thy-1 antigen. In a second series of experiments, Thy-1-positive and Thy-1-negative populations of nucleated bone marrow cells were separated by the FACS. All of the hemopoietic stem cell activity was recovered in the Thy-1-positive population. The stem cells were among the most strongly positive for Thy-1 antigen, being in the upper 25th percentile for relative fluorescence intensity. The relationships of Thy-1 antigen to the rat bone marrow lymphocyte antigen (BMLA) was shown in a third series of experiments. Rabbit anti-BMLA serum, which is raised against a null population of lymphocyte-like bone marrow cells, has been shown to have anti-stem cell activity. Here we demonstrate by double immunofluorescence, cocapping, and differential absorption studies that Thy-1 and BMLA are parts of the same molecule.

T-cell lymphoma induction by radiation leukemia virus in athymic nude mice

We report the development of extrathymic lymphoblastic lymphomas in RadLV-inoculated congenitally athymic nude mice. Thus, a leukemogenic virus which appears to require the presence of a thymus for its replication in normothymic mice can infect and transform target cells in the absence of this organ in the athymic host. The cells of one of these lymphomas have been established in vitro as a permanent cell line, BALB/Nu1. This cell line as well as a lymphoma induced in NIH/Swiss nude mice exhibit several T-cell markers, including terminal deoxynucleotidyl transferase activity, Thy-1.2, and Ly-2.2, but not Ly-1.2 nor TL. Ig determinants were not detected. The characteristics of the tumor cells support the view that cells with T-cell markers may normally exist in nude mice and undergo neoplastic transformation and clonal expansion after infection with a leukemogenic virus. The alternative possibility that virus-induced differentiation of prothymocytes may lead to the expression of Thy-1.2 and Ly-2.2 antigens is also considered. BALB/Nu1 cells release large numbers of type C viral particles. The virus, designated radiation leukemia virus (RadLV)/Nu1, has RTase activity and the protein profile characteristic of murine leukemia virus (MuLV). In radioimmunoassays, it cross-reacts completely with RadLV/VL3, a virus obtained from RadLV-induced C57BL/Ka thymic lymphoma cells in culture, and slightly with a xenotropic virus (BALB:virus-2) and with AKR MuLV. On inoculation into C57BL/Ka mice it has thymotropic and leukemogenic activity. In vitro it is B-tropic, poorly fibrotropic, and has limited xenotropic activity. Thus, RadLV/Nu1 appears to be biologically and serologically similar or identical to its parent virus, RadLV.

The immunological classification of acute lymphoblastic leukemias

The main methods used in order to assess the immunological markers on the blast cells from patients with acute lymphoblastic leukemia (ALL) are critically evaluated. The classification of ALL according to the phenotype of the leukemic cells and their presumed origin is reviewed. The correlations with clinical features and prognosis, as well as their possible therapeutic implications, are discussed.

Hematopoietic thymocyte precursors: IV. Enrichment of the precursors and evidence for heterogeneity

A method has been developed for the enrichment of the hematopoietic precursors of thymocytes from spleen and bone marrow cells. Up to 40-fold enrichments were obtained resulting in preparations in which as few as 10(5) cells produced prompt repopulation of the thymus of an irradiated mouse. Precursor cells from bone marrow appear to contain the enzyme terminal deoxyribonucleotidyl transferase (Tdt), an agent suggested as a potential somatic mutator. This enzyme (Tdt) was not detectable in any spleen cell preparation examined, including one in which a 40-fold enrichment of thymocyte precursors had been produced. This is the first difference reported between the splenic and bone marrow precursors of thymocytes.

Induction in vivo and in vitro of terminal deoxynucleotidyl transferase by thymosin in bone marrow cells from athymic mice

Terminal deoxynucleotidyl transferase (TdT) expression in bovine serum albumin (BSA) gradient-fractionated bone marrow cells was examined in NIH Swiss nu/nu and thymectomized C57BL/6 mice. In nude mice, TdT levels were approximately 10% of those of thymus-bearing littermates. In C57BL/6 mice, thymectomy caused a time-dependent loss of TdT activity in bone marrow cells. To determine whether or not not the apparent thymic requirement for TdT expression in bone marrow was mediated by thymic hormones, we examined the effects of thymosin fraction 5. Treatment of either NIH Swiss nu/nu or thymectomized C57BL/6 mice with thymosin fraction 5 restored the levels of TdT activity in BSA gradient-fractionated bone marrow cells to normal. Moreover, treatment of BSA gradient-fractionated bone marrow cells from NIH Swiss nu/nu or thymectomized C57BL/6 mice in tissue culture with thymosin fraction 5 induced TdT expression. In tissue culture, TdT induction was optimal with 25 ng/ml of thymosin fraction 5, it occurred within 6 h, and it was completely inhibited by actinomycin D. The effect was specific in that neither control nor spleen fraction 5-treated cells were induced to express TdT. These data demonstrate that TdT expression in bone marrow cells is under the direct control of thymic polypeptide hormones.

Differentiation of functionally active mouse T lymphocytes from functionally inactive bone marrow precursors II. Limited recovery of T-cell responses from mouse bone marrow in tissue culture

The limited differentiation of mature T cell function from mouse bone marrow in tissue culture is described and compared with similar differentiation occuring in vivo in irradiated bone marrow protected mice. Data are presented to show that a pool of precursors, similar in size to that able to produce early (transient?) regeneration in thymectomized recipients, is responsible for the development of mitogen responsive T cells active in MLC (proliferation) and CML (development of cytotoxic cells) assays. In contrast, a helper cell population which augments antibody formation from T-depleted normal spleen cells derives from a pool of similar precursors yet does not seem to be theta positive. Similarly, larger cells (perhaps typical of those giving rise to suppressor T cells in vivo) give rise to a suppressor cell pool after 4 days of culture, though again only a fraction of this suppressor activity could be attributed to theta positive cells. It is suggested that much of the data for regenration of T lymphocytes in vitro from T-depleted sources needs to be re-interpreted in terms of this evidence for a pool of post-thymic precursors of T cells in such T-deficient cell populations.

Intracellular distribution of terminal deoxynucleotidyl transferase in rat bone marrow and thymus

A subset of bone marrow cells that contains terminal deoxynucleotidyl transferase (DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) can be identified in adult rats by immunofluorescence using affinity-column-purified antibody to homogeneous calf transferase. The transferase-positive cells comprise approximately 1.8% of bone marrow cells. Correcting the specific activity of terminal transferase in total bone marrow cells (0.21 units per 10(8) cells) for the percentage of transferase-positive bone marrow cells (1.8%) gives 11.7 units per 10(8) cells, a value approximately half that found for transferase-positive thymocytes. Fluorescence appears to be restricted to the nucleus of transferase-positive bone marrow cells, in contrast to the predominantly cytoplasmic fluorescence of small thymocytes from adult rats. Some large thymocytes contain intranuclear transferase fluorescence patterns similar to those seen in bone marrow. These thymocytes are especially numerous in neonatal rat thymus, where they are localized in the subcapsular region of the cortex. Thymocytes with combined patterns of nuclear and cytoplasmic transferase are also present. In addition, Thy-1.1 antigen, which is present on thymic and prethymic cells but not on the majority of post-thymic cells in the rat, is also present on transferase-positive bone marrow cells. The results suggest that the transferase-positive subset of bone marrow cells may contain the immediate progenitors of cortical thymocytes in the rat. The nuclear location of fluorescence may indicate the site of physiological activity of terminal transferase in thymocytes and their precursors.