Terminal deoxynucleotidyltransferase. Serological studies and radioimmunoassay

Detection of terminal deoxynucleotidyl transferase activity based on self-mediated nucleic acid elongation and elemental labeling inductively coupled plasma-mass spectrometry

Terminal deoxynucleotidyl transferase (TdT), a specialized DNA polymerase, is recognized as a promising biomarker for acute leukemia. Herein, taking the advantage of the self-mediated strand elongation property of TdT, a simple and sensitive method for TdT activity assay was developed based on gold nanoparticles (AuNPs) labeling inductively coupled plasma mass spectrometry (ICP-MS). In the presence of TdT, the primer DNA on magnetic beads is elongated with an adenine-rich single stranded long chain that can label poly-thymine modified AuNPs. After acid elution, the labeled AuNPs were detected by ICP-MS, and the signal intensity of 197Au reflected the TdT activity. Under the optimal conditions, the limit of detection for TdT activity is down to 0.054 U mL-1, along with good selectivity and strong tolerance to other interfering proteins. Furthermore, it achieves a straightforward and accurate detection of TdT activity in acute lymphoblastic leukemia cells without sample pre-processing and tool enzyme addition. Therefore, the proposed method shows great promise as a valuable tool for TdT-related biological research and leukemia therapeutics.

Dual Self-Amplification Homogeneous Electrochemiluminescence Biosensor for Terminal Deoxynucleotidyl Transferase Activity Based on Controlling the Surface Morphology and Charge of Reporter Nanoparticles

Terminal deoxynucleotidyl transferase (TdT) is upregulated in several types of leukemia and is considered a disease biomarker and a potential therapeutic target for leukemia. In this research, a homogeneous electrochemiluminescence (ECL) method based on the control of surface charge and morphology of tris (2,2'-bipyridine) ruthenium(II) chloride hexahydrate-doped silica nanoparticles (Ru@SiO2 NPs) has been designed for TdT activity detection. A small amount of short single-stranded DNA (ssDNA) was modified onto the surface of Ru@SiO2 NPs, and the nanoparticles with a slight positive charge experienced electrostatic attraction with the indium tin oxide (ITO) electrode with a negative charge, so relatively high ECL signals had been detected. Under the action of TdT, the ssDNA was significantly elongated, carrying numerous negative charges on its phosphate backbone, so the overall negative charge of the reporter nanoparticles was enhanced, resulting in a strong electrostatic repulsion with the ITO electrode. Simultaneously, the long ssDNA wrapped around the nanoparticles hindered the approach of the coreactant. Due to the dual effects, the ECL response of the system decreased. The constructed biosensor exhibited excellent sensitivity toward TdT over a range spanning from 1 to 100 U/L. The limit of detection is as low as 1.78 U/L. The developed approach was effectively applied to detect TdT activity in leukemic patients' leukocyte extracts.

Simple and label-free strategy for terminal transferase assay using a personal glucose meter

We herein developed a simple personal glucose meter (PGM)-based method for terminal transferase (TdT) activity assay by utilizing the glucose oxidase (GOx)-mimicking activity of cerium oxide nanoparticles (CeO₂ NPs). Using this strategy, the TdT activity was reliably determined down to 0.7 U mL^-1 with high selectivity against other non-specific enzymes.

Label-free and sensitive detection assay for terminal deoxynucleotidyl transferase via polyadenosine-coralyne fluorescence enhancement strategy

Terminal deoxynucleotidyl transferase (TdT) is a unique template-free polymerase that randomly adds multiple deoxyribonucleoside triphosphates (dNTPs) to the 3'-OH terminus of ssDNA. This characteristic makes TdT a versatile enzymatic tool in many fields. Moreover, aberrant TdT expression is a well-recognized biomarker of several leukemic diseases and is related to carcinogenesis. In this study, we developed a facile, rapid, label-free, and convenient assay for TdT detection. TdT-generated poly A tails formed a fluorescent enhancement complex in the presence of coralyne. To achieve a better signal-to-noise ratio, we used potassium thiocyanate (KSCN), instead of other halogen anions (KCl, KBr, KI, NaI) as the quenching agent of dissociate coralyne. Our results demonstrate that this assay is extremely facile, rapid, and label-free; at levels as low as 0.025 U/mL, TdT was distinctly detected within 55 min. And the determination of TdT activity in RBL-2H3 and Reh cells lysates exhibited a good sensing performance, demonstrating its potential applications in biochemical research and clinical diagnosis.

A luminescence switch-on probe for terminal deoxynucleotidyl transferase (TdT) activity detection by using an iridium(iii)-based i-motif probe

An iridium(iii) complex exhibiting higher responce towards i-motif DNA over dsDNA and ssDNA was employed for the construction of a TdT activity detection platform. The limit of detection for TdT was 0.25 U ML⁻¹.

Monoclonal antibodies that recognize a broad range of mammalian terminal deoxynucleotidyl transferases

Terminal deoxynucleotidyl transferase (TdT) is a useful marker for lymphocyte precursors in the bone marrow and thymus and for lymphoblastic leukemia and lymphoma cells. To simplify and enhance the detection and phenotypic analysis of these cells, we sought to develop monoclonal antibodies to this enzyme. In order to obtain antibodies that bind a variety of mammalian TdTs, mice were immunized with bovine TdT and the hybridoma secretions were screened by immunofluorescence assays on cultured TdT-positive and negative human lymphoblasts. Four monoclonal antibodies which bound specifically to TdT-positive lymphoblasts were characterized in detail. All four antibodies immunoprecipitated the native 60 kd TdT molecule from extracts of TdT-positive human lymphoblasts and bound specifically in immunoblot assays to the 43.8 and 11 kd proteolytic fragments of bovine thymus TdT. To assess whether the antibodies bound to related or distinct epitopes on bovine TdT, we measured the displacement of radiolabeled antibody from the immobilized enzyme by an excess of unlabeled heterologous antibody. These studies revealed that three of the antibodies competed for the same determinant on bovine TdT, while one antibody reacted with a distinct epitope. Antibody binding to either epitope, however, partially inhibited the enzymatic activity of bovine TdT. Specificity for TdT was tested by immunofluorescence and competition radioimmunoassays. In these assays, the antibodies did not stain a variety of known TdT-negative human hematopoietic cells and cell lines. both normal and neoplastic, nor were the antibodies displaced from purified bovine TdT by extracts of these TdT-negative cells. These results confirmed the cross-reactivity of the antibodies with human and bovine TdT. To assess cross-reactivity with TdT from other species, extracts of rabbit, mouse, and rat thymus were prepared and shown to specifically displace the antibodies from bovine TdT. Thus, these antibodies bound to TdT derived from at least five mammalian species. To determine whether these antibodies could be used to detect small subpopulations of TdT-positive cells, mixtures of TdT-positive and negative cells were prepared and stained with fluorescein conjugates of the antibodies. When assayed by flow cytometry, a population of 1% TdT-positive cells was easily detectable. We conclude that these monoclonal antibodies should be useful for the enumeration and analysis of TdT-positive cells in normal and neoplastic hematopoietic tissues from several mammalian sources, including man.

Distribution of terminal deoxynucleotidyl transferase activity between peaks I and II in host and donor thymic cells of bone-marrow-restored mice after X-irradiation

The terminal deoxynucleotidyl transferase (TdT) activity and its distribution between peaks I and II after chromatographic elution were studied on days 15 and 17 after X-irradiation, in host- and donor-derived thymic cells of lethally irradiated (9 Gy) mice restored with BM cells. It was found that the population derived from the surviving host thymocytes differed markedly from the donor-derived population. The cells of host origin has a low TdT activity especially in peak II and the ratio peak I/peak II remained close to 1 instead of 0.1 in controls. These alterations reflect a reduced replication rate and possibly a modification of the cellular metabolic activity (phosphorylation-dephosphorylation). In contrast, the donor-derived elements displayed a very high TdT activity related to their elevated rate of replication, and the ratio peak I/peak II which was close to 1 on day 15 returned rapidly to normal. The impaired replication ability and the metabolic alteration of the host cells might be attributed either to a specific property of the radiation-resistant thymocytes or to residual cellular injury or to a combination of both.

Effects of 6-hydroxydopamine upon primary and secondary thymus dependent immune responses

Adult male mice were treated with various doses of 6-hydroxydopamine in order to assess the effects of this drug upon thymic dependent immunity. A consistent decrease in primary antibody titers to sheep erythrocytes was observed following treatment with this drug. Serum levels of thymosin alpha 1 were increased by day three after 6-OHDA with a return to normal by day five. Thymocyte terminal deoxynucleotidyl transferase changes were biphasic with an initial decrease after 6-OHDA followed by an increase. Changes in mitogen responsiveness were observed but were not consistently reproducible. Involvement of both catecholamines and corticosteroids in bringing about these observed changes was discussed.

Enrichment of cell populations containing terminal deoxynucleotidyl transferase activity by free flow electrophoresis

Terminal deoxynucleotidyl transferase (TdT) is an enzyme that has been utilized as a biochemical marker for following certain leukemia patients during treatment and remission. The potential usefulness of this enzyme in predicting the onset of relapse before any morphological indications has been demonstrated in chronic myelogenous leukemia patients in blast phase of the disease. In order to be able to detect low levels of TdT activity, especially during remission phase, we have used the technique of free flow electrophoresis to enrich cell populations containing TdT. With this technique we have achieved up to 20-fold enrichment of TdT-positive cell populations from normal human bone marrow, cells from patients with acute lymphoblastic leukemia and chronic myelogenous leukemia in blast phase of the disease. TdT positive cells were not detected in patients with acute myelogenous leukemia and B cell lines. This technique should prove to be useful in early detection of relapse in patients in remission and for enrichment of cell populations containing other biochemical markers.

Enrichment of terminal deoxynucleotidyl transferase activity by cell separation

Terminal deoxynucleotidyl transferase is a unique DNA polymerase that can carry out DNA synthesis on an initiator molecule in the absence of a template. The usefulness of this enzyme as a biological marker for following patients during treatment and remission has been suggested. The potential usefulness of this enzyme in predicting the onset of relapse before any morphological indications has been demonstrated in chronic myelogenous leukemia patients in blast phase of the disease. In order to be able to detect low levels of TdT activity especially during remission phase, we have used cell separation techniques which can enrich cell populations containing TdT activity. A number of cell separation techniques have been developed to separate different cell types. We have used the techniques of unit gravity sedimentation and free flow electrophoresis to achieve enrichment of TdT positive cell populations. Our results show that up to 20 fold enrichment of TdT activity in normal human bone marrow can be accomplished by using cell separation techniques. With the use of free flow electrophoresis, we have achieved enrichment of TdT positive cell populations from normal human bone marrow, cells from patients with acute lymphoblastic leukemia and chronic myelogenous leukemia in blast phase of the disease. No TdT positive cells were detected in patients with acute myelogenous leukemia. These cell separation techniques should prove to be useful in early detection of relapse in patients in remission.

Cooperation of terminal deoxynucleotidyl transferase with DNA polymerase alpha in the replication of ultraviolet-irradiated DNA

The amount of DNA synthesis in vitro with the ultraviolet-irradiated poly-(dT) . oligo(rA) template initiators catalysed by DNA polymerase alpha (Masaki, S. and Yoshida, S., Biochim. Biophys. Acta 521, 74--88) decreased with the dose of ultraviolet-irradiation. The ultraviolet irradiation to the template, however did not affect the rate of incorporation of incorrect deoxynucleotides into the newly synthesized poly(dA). The addition of terminal deoxynucleotidyl transferase to this system enhanced the DNA synthesis to a level which is comparable to that of the control and it concomitantly increased the incorporation of the mismatched deoxynucleotide into the newly synthetized poly(dA) strands. On the other hand, with an unirradiated template initiator, the misincorporation was only slightly enhanced by the addition of terminal deoxynucleotidyl transferase. The sizes of newly synthetized DNA measured by sedimentation velocities were found to be smaller with the ultraviolet-irradiated templates but they increased to the control level with the addition of terminal deoxynucleotidyl transferase to the systems. These results suggest that terminal deoxynucleotidyl transferase can help DNA polymerase alpha to "bypass" thymine dimers in vitro by the formation of mismatched regions at the positions opposite to pyrimidine dimers on the template.

Terminal deoxynucleotidyl transferase positive lymphoblastic lymphoma: a study of 15 cases

The investigation was undertaken to define the features of lymphoblastic lymphoma. Fifteen lymph node biopsies from a group of 82 specimens studied for the enzyme terminal deoxynucleotidyl transferase (TdT) fulfilled morphological criteria for this diagnosis. These criteria required a diffuse infiltrate of relatively uniform, immature lymphoid cells with basophilic cytoplasm; round, oval or lobulated nuclei with evenly dispersed chromatin; rare or inconspicuous nucleoli; and numerous mitotic figures. Examination of 1-micron thick, plastic-embedded, Giemsa-stained tissue sections revealed convoluted nuclei in more than 50% of neoplastic cells in four cases: in six specimens there was an admixture of cells with grooved, hyperlobulated, and round nuclei, and in five the round or oval nuclei were non-convoluted. Specimens from all 15 patients were positive for TdT by fluorescent antibody and biochemical assays. The percentage of cells from involved nodes reacting by indirect immunofluorescence with an antiserum against bovine TdT ranged from 4 to 90% (mean of 52%), and the mean level of biochemically measured enzyme activity was 8.7 units/g of tissue (range of 1.9 to 27.5). Cytochemical stains for acid phosphatase were positive in 13 of the 15 cases. In eight samples more than 50% of cells formed rosettes with sheep erythrocytes, while the E rosettes varied from 14 to 38% in the other seven. The percentage of cells with complement receptors varied widely (range of 6 to 80), but cells bearing surface immunoglobulin or IgGfc receptors were not increased. All patients presented with supradiaphragmatic lymphaedenopathy, eight with an anterior mediastinal mass. Two-thirds of the patients were male, and the mean age was 20 years (range 4 to 46 years). None were leukemic at the time of diagnosis, but eight patients subsequently developed acute lymphoblastic leukemia. Involvement of the central nervous system was observed in four of the 15, and of the testes in two. Ten patients have died of their disease with a median survival of 8 months (range 4 to 20), and five are alive 3--8 months after diagnosis. We observed no differences in clinical findings at presentation, incidence of mediastinal involvement or leukemic dissemination, content of TdT, acid phosphatase staining, or immunologic cell surface characteristics between the convoluted and non-convoluted types of lymphoblastic lymphoma. Distinctive morphologic, cell surface, biochemical, and clinical features of lymphoblastic lymphoma can be identified irrespective of the presence or absence of convoluted nuclei.

The effect of different buffers on terminal deoxynucleotidyl transferase activity

The polymerization of dATP, dCTP, and dGTP onto the defined length initiator, d(pA)10, has been carried out in four buffers. The relative effectiveness of the buffers for the polymerization of each deoxynucleoside triphosphate decreased in the order: cacodylate, 2(N-morpholino)ethane sulfonic acid, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, and Tris. With the poorer buffers, activity could be increased by the addition of KCl: this effect is not primarily due to an increase in ionic strength. With dGTP as the substrate, but not with dATP or dCTP, activity increased when the concentration of the more active buffers was raised beyond 0.2 M.

Terminal deoxynucleotidyl transferase in the diagnosis of leukemia and malignant lymphoma

Neoplastic cells from 253 patients with leukemia and 46 patients with malignant lymphoma were studied for the presence of terminal deoxynucleotidyl transferase (TdT) by biochemical and fluorescent antibody technics. TdT was detected in circulating blast cells from 73 of 77 patients with acute lymphoblastic leukemia, 24 of 72 patients with chronic myelogenous leukemia examined during the blastic phase of the disorder and in cell suspensions of lymph nodes from nine of nine patients with diffuse lymphoblastic lymphoma. Blast cells from six of 10 patients with acute undifferentiated leukemia were TdT positive, but the enzyme was found in only two of 55 patients with acute myeloblastic leukemia. TdT was not detected in other lymphocytic or granulocytic leukemias or in other types of malignant lymphomas. The fluorescent antibody assay for TdT permits rapid and specific identification of the enzyme in single cells. The TdT assay is clinically useful in confirming the diagnosis of acute lymphoblastic leukemia, evaluating patients with blastic chronic myelogenous leukemia, and distinguishing patients with lymphoblastic lymphoma, whose natural history includes rapid extranodal dissemination, from patients with other poorly differentiated malignant lymphomas.