Regulation of cellular proliferation in acute lymphoblastic leukemia by Casein Kinase II (CK2) and Ikaros

The IKZF1 gene encodes the Ikaros protein, a zinc finger transcriptional factor that acts as a master regulator of hematopoiesis and a tumor suppressor in leukemia. Impaired activity of Ikaros is associated with the development of high-risk acute lymphoblastic leukemia (ALL) with a poor prognosis. The molecular mechanisms that regulate Ikaros' function as a tumor suppressor and regulator of cellular proliferation are not well understood. We demonstrated that Ikaros is a substrate for Casein Kinase II (CK2), an oncogenic kinase that is overexpressed in ALL. Phosphorylation of Ikaros by CK2 impairs Ikaros' DNA-binding ability, as well as Ikaros' ability to regulate gene expression and function as a tumor suppressor in leukemia. Targeting CK2 with specific inhibitors restores Ikaros' function as a transcriptional regulator and tumor suppressor resulting in a therapeutic, anti-leukemia effect in a preclinical model of ALL. Here, we review the genes and pathways that are regulated by Ikaros and the molecular mechanisms through which Ikaros and CK2 regulate cellular proliferation in leukemia.

The immunophenotype of adult T acute lymphoblastic leukemia in Morocco

BACKGROUND

There is paucity of detailed studies of adult T cell acute lymphoblastic leukemia (T-ALL) in developing countries reflecting the condition of these patients including clinical and biological features.

OBJECTIVE

This study was carried out to analyze the immunophenotypic characteristics of 40 Moroccan patients with T-ALL and its association with biological and clinical features.

PATIENTS AND METHODS

Between 2006 and 2009, 130 adult patients diagnosed with acute lymphoblastic leukemia (ALL) were immunophenotyped by 3-color flow cytometry using a panel of monoclonal antibodies. Cases presenting features of a T-lineage phenotype were subjected to detailed analysis including immunophenotypic, clinical and biological parameters.

RESULTS

Proportion of T-ALL among ALL Moroccan patients was 31.0%. Median age of patients was 28 years. Twenty-nine patients were females and 11 were males. 45.0% of patients (18/40) had features of immature T-ALL stages (pro-T and pre-T ALL), 30.0% (12/40) of CD1a+ cortical T-ALL stage and 25.0% (10/40) had a characteristic phenotype of medullary T-ALL. The frequencies of progenitor cell markers CD10, CD34 and TdT expression were 14.0; 57.5% and 50.0% respectively. The aberrant expression of B lineage associated antigen CD79a were positive in 20.5% of the cases and the aberrant expression of myeloid antigens CD13 and/or CD33 was found in 22 (55.0%) cases. No significant association was encountered between TdT, CD34 or myeloid antigens positivity and high risk features at presentation as age, sex, and white blood cells. However, myeloid antigens (CD13 and/or CD33) was significantly associated with T-cell maturation stages (p = 0.009).

CONCLUSION

To the best of our knowledge, this is the first report from North Africa of immunophenotypic study on adult T-ALL. Our findings indicate that the proportion of T-ALL among ALL in Morocco is similar to that reported in others Mediterranean countries like France and Italy and that myeloid-associated antigens expression is frequently associated with immature immunophenotype.

Absence of N addition facilitates B cell development, but impairs immune responses

The programmed, stepwise acquisition of immunocompetence that marks the development of the fetal immune response proceeds during a period when both T cell receptor and immunoglobulin (Ig) repertoires exhibit reduced junctional diversity due to physiologic terminal deoxynucleotidyl transferase (TdT) insufficiency. To test the effect of N addition on humoral responses, we transplanted bone marrow from TdT-deficient (TdT(-/-)) and wild-type (TdT(+/+)) BALB/c mice into recombination activation gene 1-deficient BALB/c hosts. Mice transplanted with TdT(-/-) cells exhibited diminished humoral responses to the T-independent antigens α-1-dextran and (2,4,6-trinitrophenyl) hapten conjugated to AminoEthylCarboxymethyl-FICOLL, to the T-dependent antigens NP(19)CGG and hen egg lysozyme, and to Enterobacter cloacae, a commensal bacteria that can become an opportunistic pathogen in immature and immunocompromised hosts. An exception to this pattern of reduction was the T-independent anti-phosphorylcholine response to Streptococcus pneumoniae, which is normally dominated by the N-deficient T15 idiotype. Most of the humoral immune responses in the recipients of TdT(-/-) bone marrow were impaired, yet population of the blood with B and T cells occurred more rapidly. To further test the effect of N-deficiency on B cell and T cell population growth, transplanted TdT-sufficient and -deficient BALB/c IgM(a) and congenic TdT-sufficient CB17 IgM(b) bone marrow were placed in competition. TdT(-/-) cells demonstrated an advantage in populating the bone marrow, the spleen, and the peritoneal cavity. TdT deficiency, which characterizes fetal lymphocytes, thus appears to facilitate filling both central and peripheral lymphoid compartments, but at the cost of altered responses to a broad set of antigens.

Commercially available rabbit anti-human polyclonal antisera as a useful tool for immune system studies in veterinary species

We have used selected rabbit anti-human polyclonal antibodies as an example of useful and easily available tools for studies on immune system structure and development in important veterinary species, many of which also represent animal models in biomedicine. The cocktail of anti-human Igkappa-FITC/anti-Iglambda-RPE F(ab')(2) fragments was used for two-colour and, in combination with the cross-reactive anti-CD79alpha monoclonal antibody HM-57, for three-colour flow cytometry of canine, feline, bovine and porcine peripheral B-cells. A possible application of such immunoreagents in studies on primary B-cell differentiation has been suggested in pigs; the same approach can be used in other species of interest. Rabbit anti-human lactoferrin-FITC F(ab')(2) fragment was used for visualizing neutrophils in dogs, pigs and cattle and an application for two-colour immunophenotyping of canine granulocyte subsets has been designed. Affinity isolated rabbit anti-human CD3 and anti-human TdT have been shown to represent a ready-to-use tool for in situ studies on primary T-lymphopoiesis in pigs with possible extensions both to the B-lineage development in pigs and other animal models. Altogether, our study show that carefully selected polyclonal antibodies available on the market may possess broad cross-reactivity with important applications in veterinary research.

[Diagnostic value of anti-terminal deoxynucleotidyl transferase antibody (TdT) in hematologic pathology]

AIMS

The diagnosis of primitive hematologic malignancies depends on a panel of monoclonal antibodies which is growing over time. The distinction between immature (lymphoblastic lymphoma/acute lymphoblastic leukaemia) and mature lymphoma is sometimes difficult. In this study, we evaluated anti-TdT antibody in the diagnosis and classification of these proliferations.

MATERIALS AND METHODS

13 lesions were examined by immunohistochemistry: 4 B and T lymphoblastic lymphomas, 2 Burkitt's lymphomas, 5 B and T acute lymphoblastic leukemias and 2 acute monoblastic leukemias.

RESULTS

TdT expression is specific of immature lymphoid proliferations (T or B lymphoblasts). TdT is not expressed by mature B or T cell lymphomas such as Burkitt's lymphomas. Significant numbers of cases of acute myeloblastic leukemias are TdT positive but could be easily distinguished from lymphoblastic proliferations.

CONCLUSION

Anti-TdT antibody represents a useful marker for differentiating lymphoma/acute lymphoblastic leukemia from other lymphomas. This marker, available in routine diagnosis should be systematically included in the panel of antibodies used for immunophenotyping hematologic malignancies.

Rare detection of phenotypically immature lymphocytes in Hashimoto thyroiditis and rheumatoid arthritis

It has been suggested that recombination activating gene (RAG)-dependent revision of the immunoglobulin genes in germinal centres may contribute to local production of autoantibodies in Hashimoto thyroiditis (HT) and rheumatoid arthritis (RA). To test this hypothesis we examined HT and RA tissues for expression of RAG and terminal deoxynucleotidyl transferase (TdT) in situ. Paraffin-embedded tissues from 19 HT patients and from 20 RA patients were subjected to immunohistochemistry using TdT-specific antibodies. Expression of the RAGs was studied by in situ hybridisation. Tonsil sections were used as a control. Expression of TdT and RAGs was detected in extrafollicular lymphocytes in control tonsil sections. By contrast, only rare TdT-expressing cells were identified in 11 of 19 HT and in 2 of 20 RA samples. Germinal centre B-cells were consistently TdT- and RAG-negative. These results suggest that local RAG-dependent receptor revision in germinal centres is unlikely to contribute to production of autoantibodies in HT and RA. The presence of TdT-positive extrafollicular cells may represent an influx of immature cells in the context of chronic immune stimulation.

Flow cytometric analysis of acute leukemias. Diagnostic utility and critical analysis of data

CONTEXT

Acute leukemia displays characteristic patterns of surface antigen expression (CD antigens), which facilitate their identification and proper classification and hence play an important role in instituting proper treatment plans. In addition to enzyme cytochemical analysis, multiparameter flow cytometric analysis has become commonplace in most laboratories for that purpose. The essential role and caveats of flow cytometry in that regard, however, have received little scrutiny.

OBJECTIVE

To evaluate the expression of commonly used immunomarkers and patterns in various acute leukemias to help define the best use and role of multiparameter flow cytometry in the diagnosis and proper classification of acute leukemias.

DESIGN

We have retrospectively analyzed the immunophenotypic data from 508 de novo adult and pediatric acute leukemia patients, as studied using multiparameter flow cytometry in addition to routine morphologic and enzyme cytochemical analysis. Cytogenetic and/or molecular data were correlated in all 41 cases of acute promyelocytic leukemia (APL) and in 203 other cases of acute leukemia where those data were available. We have also determined the positive and negative predictive values of a combined CD34 and HLA-DR expression pattern for the differentiation of APL from other myeloid leukemias.

RESULTS

In acute myeloid leukemia (AML) other than APL, expression of CD34 was seen in 62% and expression of HLA-DR in 86% of all cases. Twenty-six (10%) of 259 cases of non-APL AML were negative for both CD34 and HLA-DR as opposed to 33 (80%) of 41 cases of APL. None of the cases of APL were positive for both CD34 and HLA-DR in contrast to 149 (58%) of 259 cases of non-APL AML. Fifty-three cases were found to be examples of minimally differentiated AML (AML M0) based on the lack of expression of cytoplasmic CD3 and cytoplasmic CD79a and expression of one or more myelomonocytic-associated antigens and/or myeloperoxidase. Expression of CD20 was seen in 40 (24%) of 168 cases of precursor B-cell acute lymphoblastic leukemia (pB-ALL) and 52 (29%) lacked CD34 expression. Five of 180 cases of pB-ALL and 2 cases of precursor T-cell ALL (pT-ALL) were negative for terminal deoxynucleotidyl transferase (TdT). Aside from cytoplasmic CD3, CD5 and CD7 were the most sensitive antigens present in all 21 cases of pT-ALL. CD33 was more sensitive but less specific than CD13 for myeloid lineage.

CONCLUSION

Aside from identification of blasts, flow cytometry was found to be especially useful in the correct identification of AML M0, differentiation of APL from AML M1/M2, and correct identification of TdT-negative ALL and unusual variants, such as transitional B-cell ALL and undifferentiated and biphenotypic acute leukemias.

Distinct and opposite diversifying activities of terminal transferase splice variants

The short splice variant of mouse terminal deoxynucleotidyl transferase (TdTS) catalyzes the addition of nontemplated nucleotides (N addition) at the coding joins of B cell and T cell antigen receptor genes. However, the activity and function of the long isoform of TdT (TdTL) have not been determined. We show here, in vitro and in vivo, that TdTL is a 3'-->5' exonuclease that catalyzes the deletion of nucleotides at coding joins. These findings suggest that the two TdT isoforms may act in concert to preserve the integrity of the variable region of antigen receptors while generating diversity.

MIC2, TdT, bcl-2, and CD34 expression in paraffin-embedded high-grade lymphoma/acute lymphoblastic leukemia distinguishes between distinct clinicopathologic entities

We propose that 12E7 (CD99) expression, along with TdT, bcl-2, and CD34 reactivity in lymphoblastic lymphoma (LyL)/acute lymphoblastic leukemia (ALL), distinguishes this group of neoplasms from small noncleaved cell lymphomas (SNCLs) in both pediatric and adult patients, thereby narrowing the differential diagnosis of high-grade non-Hodgkin's lymphomas and acute lymphoblastic leukemias in paraffin sections. 12E7 (CD99) is one of a group of available antibodies that recognizes the product of the mic-2 gene, which was originally identified in ALL. Despite this, most clinicopathological research has focused on the reactivity of 12E7 in a subset of the small round cell tumors of childhood. Although TdT is widely used in the subtyping of blastic leukemias, its use in the distinction of high-grade lymphomas in paraffin sections has been limited. We collected 24 cases of LyL/ALL (13 B-cell and 11 T-cell) and 15 cases of SNCL from 1984 through 1993. We confirmed the diagnoses using morphology and analysis of immunologic data. We performed immunohistochemistry with the 12E7 antibody, TdT, bcl-2, and CD34 on formalin-fixed, paraffin-embedded material. The patients' ages ranged from 4 to 81 years; nine of the study patients were children. Sixteen of the 24 LyL/ALLs stained with 12E7. In contrast, none of the 15 cases of SNCL reacted with this antibody (chi-square P < .0001). A larger percentage of T-cell LyL/ALLs reacted with 12E7 than did B-cell LyL/ALLs (82% v 54%). Sixteen of 20 LyL/ALLs reacted with the anti-TdT antibody, as compared with none of 11 SNCLs (chi-square P < .0001). Six LyL/ALLs were CD34 positive (of 23), and none of the SNCLs were CD34 positive (0 of 12) (chi-square P = .0519). Bcl-2-positive cases were found among both LyL/ ALLs and SNCLs, although they were more prevalent among LyL/ ALLs (92% v 25%; chi-square P < .0001). When one considers the differential diagnosis of a high-grade lymphoma/acute lymphoblastic leukemia, positive reactions with 12E7, TdT, bcl-2, and CD34 support the diagnosis of LyL/ALL over SNCL. Moreover, we present data that suggests that evaluating for TdT in formalin-fixed paraffin-embedded tissue is a more sensitive test than using either 12E7, bcl-2 or CD34 alone.

Increased peptide promiscuity provides a rationale for the lack of N regions in the neonatal T cell repertoire

Making use of mice deficient for terminal deoxynucleotidyl transferase (TdT) expression and a random peptide library, we have examined the diversity and peptide specificity of the neonatal T cell repertoire specific for a single H-2Db-restricted peptide. Consistent with the predicted decrease in repertoire diversity, polyclonal CTL lines and individual clones from different TdTo mice are more similar to each other than those from different wild-type mice in terms of their fingerprints of cross-reactivity to the library and their TCR sequences. We have also found that several TdTo CTL clones cross-react with many more library peptides than wild-type CTL clones. In a few instances, the degree of peptide promiscuity correlates with TCR sequence characteristics such as N region addition and homology-directed recombination, but not CDR3 loop length. Based on epitope titrations for each clone, TCR affinity for antigen is consistently high; thus, this reduced specificity for peptide may coincide with an accentuated affinity for the alpha helices of the MHC. Peptide promiscuity in the neonate may allow the relatively small numbers of T cells in the periphery to protect against a broader range of pathogens.

Mice lacking terminal deoxynucleotidyl transferase: adult mice with a fetal antigen receptor repertoire

TdT knock-out mice have established the role of this enzyme in vivo: TdT mediates the transition from the relatively limited fetal to the highly diverse adult antigen receptor repertoire by adding template independent "N" nucleotides and disrupting homology-directed recombination. Lacking this source of diversity, TdT degree mice harbor essentially fetal antigen receptor repertoires. In alpha beta TCRs, the TdT null mutation affects the length and diversity of the CDR3 loops thought to be important in "directing" MHC/peptide recognition. N- CDR3 loops appear to wield less influence than do their N+ counterparts--positive selection is more efficient in the TdT degree animals and the peripheral repertiore is more polyreactive and less peptide-oriented than is the N+ repertoire. However, this loss of specificity does not markedly diminish the response to specific peptides. Overall, mice harboring essentially fetal repertoires are robust and effectively respond to a wide variety of challenges to the immune system.

Efficient immune responses in mice lacking N-region diversity

Mice with a null mutation in the terminal deoxynucleotidyl transferase (TdT) gene harbor immunoglobulin and T cell receptor repertoires essentially devoid of N-region diversity. Consequently, the CDR3 loops important for antigen recognition are shorter and considerably less diverse than those of wild-type controls. We find surprisingly normal immune responses in TdT0 mice, as regards both efficiency and specificity. This provokes a reconsideration of the assumption that N-region diversity is required for an effective T and B cell repertoire.

Purification of Tetrahymena telomerase and cloning of genes encoding the two protein components of the enzyme

Telomerase is a ribonucleoprotein DNA polymerase that catalyzes the de novo synthesis of telomeric simple sequence repeats. We describe the purification of telomerase and the cloning of cDNAs encoding two protein subunits from the ciliate Tetrahymena. Two proteins of 80 and 95 kDa copurified and coimmunoprecipitated with telomerase activity and the previously identified Tetrahymena telomerase RNA. The p95 subunit specifically cross-linked to a radiolabeled telomeric DNA primer, while the p80 subunit specifically bound to radiolabeled telomerase RNA. At the primary sequence level, the two telomerase proteins share only limited homologies with other polymerases and polymerase accessory factors.

Clinical, morphologic, cytogenetic and prognostic implications of CD34 expression in childhood and adult de novo AML

Expression of CD34 by leukemic blasts was analyzed in 230 pediatric and 251 adult patients with de novo AML enrolled in two large multicenter trials (AML-BFM-87 and AMLCG respectively). The association between CD34 positivity and morphological classification according to FAB criteria, cytogenetic aberrations, immunophenotypic features and clinical characteristics was investigated. CD34 was expressed (> or = 20%) by leukemic cells from 45% of childhood and 43% of adult AML patients. CD34+ AML was often associated with M1/M2 morphology as well as the coexpression of CD7 and TdT. Translocation t(8;21), inv(16) and chromosome 5 and 7 aberrations were more frequently observed in CD34+ AML. There was a low frequency of CD34 expression in infant AML but no age dependency was evident in adult patients. CD34 expression exerted no influence on the rate of complete remissions (CR) after intensive multidrug induction therapy. In adults, 56% of the CD34-positive and 64% of CD34-negative cases achieved CR (P = 0.29), and the childhood trial even revealed a slight advantage for CD34+ AML with a CR rate of 80% vs. 71% for CD34-negative cases (P = 0.068). Long-term follow-up disclosed no significant differences in remission duration or event-free survival between the CD34-positive and CD34-negative groups. In conclusion, CD34+ AML patients comprise a heterogeneous group with good as well as poor risk factors. Though characterized by some distinct features, CD34 lacks prognostic significance in de novo AML patients submitted to intensive polychemotherapy.

Detection of terminal transferase in acute myeloid leukemia by flow cytometry

The purpose of this study was twofold: (1) to develop an optimized, reliable method for the flow cytometric analysis of the intranuclear DNA polymerase, terminal deoxynucleotidyl transferase (TdT) in acute myeloid leukemia, and (2) to establish the usefulness of a novel, fluorescein-isothiocyanate conjugated monoclonal anti-TdT antibody (HT-6) in double-fluorescence staining for surface antigens in the characterization of leukemic cells. Inclusion of an aldehyde blocking buffer in the staining protocol reduced background fluorescence sufficiently to allow for the detection of the low-level fluorescent TdT+ myeloblasts. When admixed to normal peripheral blood mononuclear cells, 0.4-0.5% of HLA-DR+ or myeloid surface antigen+, TdT+ double-stained myeloblasts could be reliably detected above background levels. Flow cytometric TdT measurements using the HT-6 antibody in 55 patients with TdT+ acute lymphocytic or myelocytic leukemia or blast crisis of chronic myelogenous leukemia were equal or superior to the results obtained with a mixture of monoclonal anti-TdT antibodies (anti-HTDT-Mix) and comparable to those obtained by the conventional slide method employing polyclonal rabbit anti-human TdT antiserum. This flow cytometric TdT determination in combination with surface antigen staining using a novel anti-TdT monoclonal antibody (HT-6) allows for the recognition of minimal leukemic blast cells during clinical remission in acute myeloid leukemia.

Production of interleukin-1 alpha and interleukin-2 by separate, phenotypically different leukaemia and human T cell lymphotropic virus-1-transformed T cell clones

The relationship between interleukin-1 (IL-1) and interleukin-2 (IL-2) production and immunophenotype marker profiles was studied in a panel of 29 leukaemia and human T cell lymphotropic virus-1 (HTLV-1)-transformed T cell lines. Culture supernatants from six of the 29 T cell lines tested increased IL-2 production by the MOLT-16 cell line in a manner similar to that of rIL-1 alpha or rIL-1 beta. The enhancing activity in the cell culture supernatants was inhibited by antibody against IL-1 alpha. Anti-IL-1 beta antibody had no inhibitory effect. All the cell lines producing IL-1 alpha had characteristics of activated mature T cells. They were terminal deoxyribonucleotidyl transferase (TdT)-, CD4+, CD8-, HLA-DR+ and all were strongly positive for IL-2R alpha (Tac antigen) expression. However, none of the IL-1 alpha producing cell lines secreted detectable IL-2. A significant quantity of IL-2 was found, after stimulation with phytohaemagglutinin, in supernatants from nine of the 29 cell lines tested. The majority of IL-2 producing cell lines originated from less mature, non-activated T cells, as they were characterized by the expression of TdT, lack of HLA-DR antigens and > 50% had no detectable IL-2R alpha. The results thus show that separate, phenotypically different leukaemia and HTLV-1-transformed T cell clones produce IL-1 alpha and IL-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow cytometric analysis of terminal deoxynucleotidyl transferase. A simplified method

The authors evaluated a new cell membrane permeabilization method for the flow cytometric detection of terminal deoxynucleotidyl transferase (TdT). In this method, gradient-separated leukocytes or unseparated blood or bone marrow cells were incubated in a commercially available diethylene glycol-based red blood cell lysing solution, which not only lyses red blood cells, but also permeabilizes leukocyte cell membranes; the light scattering properties of the cells are retained. The validity of the current method was demonstrated by the good concordance of the findings with previously published data as follows: (1) practically identical results were obtained when an established method for cell permeabilization was used in parallel on the same samples; (2) the proportion of TdT-positive cells in normal peripheral blood was negligible; (3) the proportion of TdT-positive cells in normal bone marrow averaged 1%, and a significant portion of TdT-positive cells in normal bone marrow expressed CD10 and CD34; and (4) TdT-positive cell populations were seen with the expected frequencies in various types of leukemia. This method for TdT flow cytometry provides significant advantages over previously used methods and is especially suitable for TdT detection in routine laboratories.

Production of a specific monoclonal antibody to terminal deoxynucleotidyl transferase (TdT) and the extensive studies of TdT in patients with hematological malignancies

Terminal deoxynucleotidyl transferase (TdT) was purified from calf thymus and a monoclonal antibody-producing clone was produced by the fusion of mouse myeloma cells and spleen cells of mice immunized with the purified enzyme. The antigens recognized by an immunoadsorbent column revealed TdT, whose molecular weight was 62 kDa. The extensive study of TdT in 196 patients with hematological disorders was done. The results from immunofluorescent analysis corresponded well to the results of biochemical assays of this enzyme. This monoclonal antibody will provide a useful means for the survey of leukemia and lymphoma patients.

Bone marrow involvement in non-Hodgkin's lymphoma: increased diagnostic sensitivity by combination of immunocytology, cytomorphology and trephine histology

Diagnostic results from cytomorphology and immunocytology of aspirated bone marrow (BM) were compared with the findings from standard trephine histology of 100 adult patients with non-leukaemic non-Hodgkin's lymphomas (NHL) in a retrospective study. Immunocytological investigations were performed by the immunoenzymatic APAAP-technique on BM smears monoclonal antibodies against CD19, Cd3, CD10 or TdT antigens and determination of positive cells in relation to total BM leucocytes. Corresponding results were obtained for trephine histology and for the combination of cytomorphology and immunocytology in 93/100 cases. Four cases with BM involvement by trephine histology were missed by the combination of immunocytology and cytomorphology. In turn, three cases negative by trephine histology, were found to be positive by the combination of immunocytology and cytomorphology. Immunocytochemistry considerably increased the number of true positive detected BM-infiltrations by cytomorphology in low grade B-cell lymphoma from 58% to 97%. For the diagnosis of BM involvement in high-grade NHL cytomorphology of the aspirate was of equal sensitivity to the biopsy and was always confirmed by immunocytology. The high diagnostic sensitivity of immunocytology was mainly due to high B-cell counts in BM involved by B-cell lymphoma (means = 38%, s = 23) in contrast to low B-cell counts in BM not involved by NHL (means = 4.5%, s = 3.8). We conclude from our data that immunocytology in addition to standard cytomorphology improves diagnostic sensitivity in the detection of BM involvement by NHL.

The human fetal omentum: a site of B cell generation

The fetal mouse omentum has been shown to be a source of precursors that exclusively reconstitutes Ly1+ B cells and the closely related Ly1- sister population, but not conventional B cells or T cells. We have extended these studies to compare B cell development in the human fetal omentum, liver, and spleen, and to demonstrate that the pro/pre-B cell compartment (CD24+, sIgM-) is detected in the omentum and liver but not spleen as early as 8 wk of gestation. From 8 to 12 wk of gestation, the proportions of IgM+ cells that were pre-B cells (cIgM+/sIgM-) in the omentum and liver were 53 +/- 15% and 45 +/- 13%, respectively, and IgM+ cells were not detectable in the spleen. After 12 wk, the percentage of pre-B cells was unchanged in the fetal liver (41 +/- 10%) but decreased significantly in the omentum (25 +/- 14%); pre-B cells were now detected in the spleen but at much lower percentages (2 +/- 3%) than either the omentum or liver. The nuclear enzyme, Tdt, was detected in approximately 25% of the CD24+ cells in the omentum and liver during the 8-12-wk time period, however, Tdt+ cells were not detected in the spleen. Approximately 40% of the mature B cells found in the omentum and spleen were CD5+ compared with only 20% in the liver. These results demonstrate that the fetal omentum, like the fetal liver and bone marrow, is a primary site of B cell development.

Terminal transferase expression in acute myeloid leukaemia: biology and prognosis

Clinical and biological features were assessed in 114 consecutive previously untreated adult acute myeloid leukaemia (AML) patients whose diagnosis was based on FAB criteria and detailed immunophenotyping. All patients received standard intensive chemotherapy. The main purpose of this study was to establish the prognostic value, if any, of terminal transferase (TdT) expression in myeloid leukaemia. TdT positive cells (7-80% of total blast cells) were detected in 40% of the cases. Among clinical characteristics, a low lactate dehydrogenase (LDH) (less than 250 I.U.) (P = 0.003), a low initial white blood cell count (less than 10 x 10(9)/l) (P = 0.002), and an absolute neutrophil count (less than 5 x 10(9)/l) (P = 0.02) were associated with TdT-positivity. FAB classification was not predictive of TdT expression, and there was no difference in the distribution of FAB subtypes between the groups. Multivariate analysis combining clinical and laboratory data indicated that a low expression of the monocytic antigen CD14 was predictive of TdT positivity in AML (P = 0.01). Karyotyping showed no difference in the pattern of occurrence of specific abnormalities between the TdT+ and the TdT- group. When clinical and immunophenotype data were included in a prognostic model, the patient's age was highly predictive of response (P less than 0.001), and only the CDw65 antigen contributed to the response model (P = 0.07). TdT+ patients with a low expression of CD11b achieved a higher frequency of response at a borderline level of significance (P = 0.06). Frequency of response to chemotherapy, the response duration or overall survival were not influenced by TdT expression.

The immunologic detection of minimal residual disease in acute leukemia

Certain combinations of differentiation antigens are expressed on leukemia blasts and are absent or extremely rare among normal progenitors in the fetal liver and fetal and regenerating bone marrow. These combinations include cCD3/TdT, a thymic feature retained on thymic-acute lymphoblastic leukemia (T-ALL) blasts outside the thymus, and the coexpression of TdT and myeloid markers (CD13, CD33) on a proportion of ALL and acute myeloid leukemia (AML). Thus, double marker immunofluorescence assays are operationally leukemia-specific and can be applied in 35% of acute leukemias for detecting minimal disease at a less than 10(-4) level; only rare cases, 2 of 35 in our study, switch these relevant features during relapse. The sensitivity and specificity of these assays was tested as follows. First, bone marrow samples taken from patients who had originally presented with blasts expressing the leukemia-associated combinations but were in full morphologic remission were studied, and varying numbers (less than 0.01% to 10% of the mononuclear fraction) of cells with aberrant features were identified in 11.6% of the cases. Second, the outcome of 19 patients with minimal disease identified immunologically while in complete morphologic remission was investigated: all 19 patients have developed systemic relapse within 4 to 25 (median 14.5) weeks. In contrast, 17 of 25 patients also morphologically in complete remission and without residual disease identifiable immunologically after repeated testing are still in morphologic and immunologic remission (follow-up 17 to 114 weeks, median 28 weeks). Only eight patients in this group have relapsed so far: in two patients the relapse was localized in the cerebrospinal fluid, while in six patients a systemic relapse was observed 6 to 51 (median 21.5) weeks after the last negative immunologic bone marrow examination. In conclusion, no false-positive results were detected with these sensitive assays, and the introduction of appropriately planned prospective studies, including the immunologic detection of residual leukemia, is justified on the basis of these observations.

Flow cytometric identification of intracellular antigens: detection of minimal residual leukemia

Recent advances in preparation of cells for flow cytometric analysis have enabled the sensitive detection of intracellular antigens. We have examined the utility of two color flow cytometry for the detection of minimal residual T cell acute lymphoblastic leukemia (T-ALL) using a combination of expression of the pan-T cell marker CD5 and intranuclear terminal deoxynucleotidyl transferase (TdT). CD5+TdT+ cells can be sensitively detected above background in remission bone marrows (0.03% sensitivity). Possible extension of this technique to the detection of minimal residual B-lineage ALL, acute myelogenous leukemia (AML), and non-hematologic malignancies is discussed.

Terminal transferase positive acute myeloid leukemia: immunophenotypic characterization and response to induction therapy

A quantitative evaluation of terminal deoxynucleotidyl transferase (TdT) was performed using a highly sensitive enzyme immunoassay (EIA) in 72 previously untreated patients with acute myeloid leukemia (AML). Biological analysis of the leukemic cells included in all cases cytochemistry, search for Ph' chromosome and immunophenotyping with both anti-lymphoid and anti-myeloid monoclonal antibodies (MoAbs). Thirteen AML cases (18 per cent) were considered TdT+ by EIA. According to the FAB classification, almost all of them (12 out of 13) were within the M1 and M2 subgroups. A mixed lymphoid-myeloid phenotype was observed in one of the 13 TdT+ cases, while in none of the others were lymphoid features detected. Nine of the 10 EIA TdT+ cases studied in parallel were TdT positive with the conventional immunofluorescence assay. All patients received standard protocol chemotherapy and in 61 (13 TdT+, 48 TdT--) the response to induction treatment was analysable. Only 3/13 TdT+ patients (23 per cent) achieved a complete remission (CR), while in the TdT- group 38 patients had a CR (79 per cent) and 10 were resistant (p less than 0.01). It is suggested that the incidence, biological interest and prognostic significance of TdT+ AML should encourage the routine and more accurate search for this marker in all patients with AML.

Translocation (6;9) may be associated with a specific TdT-positive immunological phenotype in ANLL

Two patients with acute nonlymphocytic leukemia (ANLL) (FAB-M4) and t(6;9)(p23;q34) are described. Immunological marker analysis revealed a phenotype of HLA-DR+/partly terminal deoxynucleotidyl transferase (TdT)+/CD13+ in both cases and CD33 positivity in one. The expression of CD13 and CD33 by TdT-positive cells was demonstrated by double immunofluorescence staining. Although it has been postulated that TdT plays a role in gene rearrangement, Southern blot analysis performed in one leukemia revealed that both the T cell receptor beta chain genes and the immunoglobulin heavy chain genes were in germ line configuration. Since we could not detect CD13+/TdT+ cells and CD33+/TdT+ cells in control bone marrow samples, double marker analysis was used to detect low numbers of residual leukemic cells during follow-up of one patient. A gradually increasing percentage of CD33+/TdT+ cells was detected in the bone marrow in a period of 6 months before hematological relapse. Although the t(6;9) may not be correlated to a specific French-American-British subtype, it may be associated with TdT-positive ANLL. Since TdT-positive ANLL seems to have a poor outcome, detection of TdT expression in ANLL patients is particularly important for diagnostic purposes. In addition, our results indicate that double immunological marker analysis for a myeloid marker and TdT allows detection of residual disease during follow-up.

Simultaneous evaluation of terminal deoxynucleotidyl transferase and myeloperoxidase in acute leukemias using an immunocytochemical method

The classification of acute leukemia is important for the selection of optimal therapy. Classification often rests on morphologic, cytochemical, and immunologic criteria, and the marker enzyme terminal deoxynucleotidyl transferase (TdT) has been considered to be a reliable indicator of lymphoblastic leukemias. Because TdT-positive cells sometimes are seen in leukemias otherwise identified as myeloblastic, the authors evaluated blasts identified as myeloid by the presence of myeloperoxidase (MPO) for the simultaneous expression of TdT. The blasts in the bone marrow aspirate or peripheral blood of unselected patients with hematologic malignancies were evaluated and 60 cases are shown. The French-American-British system and, in some patients, cytochemical and immunologic studies were used to classify the leukemias. The authors demonstrated that blasts simultaneously contained MPO and TdT in 29% of patients with acute myeloblastic leukemia and 3% of patients with acute lymphocytic leukemia (ALL). This finding supports the hypothesis that TdT is an expression of cell primitivity rather than a marker for lymphoblastic cells.

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.

Leukemia diagnosis and testing of complement-fixing antibodies for bone marrow purging in acute lymphoid leukemia

In this paper a microplate method is described for diagnosing acute leukemia and for investigating the reactivity of monoclonal antibodies (MoAbs) against membrane antigens in combination with rabbit or murine antibodies to nuclear terminal transferase (TdT). The speed of this method facilitates the investigation of fresh leukemic cells from individual patients and assesses the cytolytic efficacy of the relevant MoAbs in the presence of complement (C'). Lymphoblasts (TdT+) are mixed in equal proportions with known numbers of "inert" cells, eg, RBC or nonleukemic bone marrow (BM). Following incubation with MoAbs and C' the ratio of residual TdT+ cells and inert cells is determined on cytospin preparations. Initially, percentages of TdT+ cells are counted in a unit volume of 5,000 inert cells, followed by the scanning of greater than 2 X 10(4) inert cells on entire slides. With this method more than 4 log cytoreduction of TdT + cells is detected. The method is also applicable for studying the cytolysis of malignant B cells by using mostly monoclonal lg expression rather than TdT for the identification of residual B cells. Ten representative patients selected from a group of greater than 100 are reported. In some cases cytoreduction of greater than 4 log with no identifiable residual TdT + cells is achieved by a single C'-fixing MoAb: anti-CD10 (RFAL3) in common acute lymphoid leukemia (ALL) and anti-CD7 (RFT2) in T cell ALL (T-ALL). Other cases require cocktails of anti-CD10, anti-CD19, and anti-CD24 in common ALL or anti-CD7 and anti-CD8 in T-ALL. In T-ALL a few TdT + cells remain that exhibit the features of normal TdT + BM cells (CD7-, HLA-DR+). This is particularly noticeable when patients are studied in partial remission or if nonleukemic BM is used as a source of inert cells. The methods described here contribute to establishing a range of MoAbs (ie, of IgM class) and techniques for efficient purging and to comparing the efficacy of "clean-up," in remission, of common ALL, T-ALL, and B cell malignancies.

TdT activity in acute myeloid leukemias defined by monoclonal antibodies

Blast cells from eight out of 71 patients diagnosed with acute myeloid leukemia (AML) by morphological, cytochemical, and immunological criteria showed TdT activity. Their distribution according to the FAB classification was one M1, one M2, one M4, two M5a, one M5b, one M6, and one undifferentiated case. The TdT+ AML cases did not show major clinical and hematological differences when compared with the classical TdT- AML patients. Other phenotypical aberrations in the expression of membrane antigens, apart from the presence of nuclear TdT, were not observed in these TdT+ cases after study with a large panel of monoclonal antibodies. A higher incidence of TdT+ cases was found among the monocytic variants of AML (M4 and M5)--four cases--than in the granulocytic variants (M1, M2, and M3)--2 cases. These TdT+ cases should be distinguished from mixed leukemias by double labeling techniques, assessing in the TdT+ AML the coexpression of TdT and myeloid markers in individual cells as shown in four of our cases.

Detection of terminal deoxynucleotidyl transferase in acute leukemias using monoclonal antibodies directed against native and denatured sites

Monoclonal antibodies (MoAb) directed against human terminal deoxynucleotidyl transferase (TdT) have been developed recently. The authors evaluated the reactivity of two TdT MoAb, one directed against a native site and the other against a denatured site, in bone marrow samples from patients with acute lymphoblastic leukemia (ALL) and acute myelogenous leukemia (AML). Results were correlated with the immunophenotype and compared with those obtained with an anti-TdT polyclonal antibody (PoAb). The authors found that 39 of the 45 children (87%) with ALL were positive with the anti-TdT PoAb, while only 25 of 45 (56%) were positive using MoAb. In the 41 of 45 cases of ALL for which marker studies were available, there was no relationship between immunophenotype and reactivity with the PoAb or either MoAb. Five cases of AML were studied and two were positive using the PoAb, but none showed staining with the MoAb. The authors' findings demonstrate that, although MoAb may be used to detect TdT in acute leukemia, the two MoAb used do not correlate with immunophenotype and are less sensitive than the PoAb. However, the MoAb appears to demonstrate more specificity for ALL than the PoAb, since it was not reactive in PoAb+ AML.

Detection of TdT in AML blasts by immunological and biochemical techniques

The cellular level of terminal deoxynucleotidyl transferase (TdT) was measured in blasts from patients with AML. Parallel determinations were made using an immunoassay and polymerizing reaction. There was a good correlation between the two techniques (r = 0.92) and detectable levels of the enzyme was found in approximately 50% of the cases. The TdT levels found in AML blasts were 1/10 - 1/100 of that reported for cells of lymphoid origin.

Evaluation of a new enzyme-linked immunoassay for terminal deoxynucleotidyl transferase in haematologic malignancies

We have evaluated a new solid phase enzyme immunoassay (EIA) for detection of terminal deoxynucleotidyl transferase (TDT). The EIA is greater than 100 times more sensitive than previously used tests for enzyme activity. In 284 clinical specimens of human peripheral blood and bone marrow, the EIA detected TdT antigen in 97% of peripheral blood and 100% of bone marrow samples that were positive for enzymatic activity. The excellent sensitivity and specificity of this new test suggests that it can be used in clinical situations where quantitative TdT measurements are desired.

The reproducibility of acute lymphoblastic leukemia phenotype determinations: evaluation of monoclonal antibody and conventional hematopoietic markers

Peripheral blood and/or bone marrow lymphoblasts from 25 patients with acute lymphoblastic leukemia (ALL) were tested with a panel of monoclonal antibodies (MoAbs) and conventional hematopoietic markers by three different laboratories. The results were analysed to evaluate the reproducibility of ALL phenotype determinations. Specimens were transported between laboratories by 24-h courier service and were classified on the basis of indirect immunofluorescence MoAb reactivities as follows: B-lineage ALL (BA-1+T-MCS-2-); T-lineage ALL (T+BA-1-MCS-2-); myeloid antigen ALL (MCS-2+BA-1-CALLA-T-) and unclassified ALL (BA-1-MCS-2-CALLA-T-). Conventional marker studies for surface immunoglobulin (sIg), cytoplasmic immunoglobulin (cIg), sheep erythrocyte rosette formation (E) and nuclear terminal deoxynucleotidyl transferase (TdT) were also performed. In the cases with sufficient marker data to permit classification, 90% (18/20) were identically classified by different laboratories and this concordance was statistically significant (p less than 0.05). The agreement between laboratories for individual MoAb and conventional marker analyses was statistically significant (p less than 0.05) for all markers with the exception of BA-2, cIg and TdT determinations. Six of 7 discordant BA-2 cases represented BA-2+ evaluations which had subsequent BA-2- results following specimen transportation. These findings suggest instability of the BA-2 antigen to transport conditions. A similar pattern of positive to negative evaluations following transportation was observed in 5/5 discordant results involving other MoAbs. Disagreement between laboratories for cIg and TdT determinations implies that the detection of cytoplasmic or nuclear antigens may be more prone to subjective interpretation than cell surface antigen marker analyses. Our findings suggest that immunofluorescence marker studies employing MoAbs to cell surface antigens are in general highly reproducible. Our results also indicate that specimen storage conditions and the cellular location of target antigens are important variables which may affect the reproducibility of ALL phenotype determinations.

Affinity purification and refined structural characterization of terminal deoxynucleotidyltransferase

A total of 56 stable murine hybridoma monoclones that produce homogeneous antibodies against human or calf terminal deoxynucleotidyltransferase have been established. All of the antibodies exhibited specific binding to various Mr forms of terminal transferase and eight possessed neutralizing activity. Results are presented that permitted characterization of ten of these antibodies with respect to their immunoglobulin class, their recognition of calf or human terminal-transferase Mr species by immunoblotting techniques and their recognition of distinct antigenic sites. Terminal transferase was purified in a single step by using an immunoaffinity column constructed with a monoclonal antibody exhibiting a high binding affinity for the enzyme. Single monoclonal antibodies were also used to bind selectively to terminal-transferase antigen in tissue slices and individual cells.

Simultaneous or sequential expression of lymphoid and myeloid phenotypes in acute leukemia

Acute mixed myeloid-lymphoid leukemia is uncommon. We report four cases in which myeloid and lymphoid cell markers were observed simultaneously or sequentially when 94 patients with acute leukemia were phenotyped according to the French-American-British (FAB) classification system, with cytochemical stains, and with immunologically defined differentiation markers (identified by monoclonal antibodies and antiterminal deoxynucleotidyl transferase [TdT]). In one case, conversion from acute lymphoblastic leukemia to acute myeloid leukemia was noted (FAB L1, TdT+ to FAB M4, Auer rods, TdT-). In another patient, two distinct populations of myeloid and lymphoid blast cells were observed simultaneously (TdT-, LeuM1+/TdT+, LeuM1-). In two additional patients, acute leukemia was characterized by the expression of both lymphoid and myeloid markers on the same cell (TdT+/Leu M1+, B4+/Leu M1+ and greater than or equal to 70% TdT+, T11+, My9+). The Philadelphia (Ph1) chromosome was negative in all cases, though other chromosomal abnormalities were noted in three out of four cases. Malignant transformation of a pluripotential stem cell for both lymphoid and myeloid lineages, with or without the Ph1 chromosome marker, could explain the coexistence of distinct populations of lymphoblasts and myeloblasts in acute leukemia. Acute leukemia with a biphenotypic profile may reflect genome depression accompanying neoplasia.

A new solid-phase immunoassay for terminal deoxynucleotidyl transferase: analysis of TdT antigen in cells, plasma, and serum

A solid-phase immunoassay for terminal deoxynucleotidyl transferase has been developed using a primary antibody-coated polystyrene bead and secondary antibody conjugated with horseradish peroxidase. The immunoassay was compared with assays for enzyme activity and detection of antigen with immunofluorescence using cells from peripheral blood and bone marrow from patients with leukemia or lymphoma. In each instance, the solid-phase immunoassay correlated correctly with cellular samples judged to be positive by other tests. However, the level of detection of terminal transferase antigen in plasma or serum of patients with leukemia did not reflect accurately the level of terminal transferase in neoplastic cells. The solid-phase immunoassay was greater than 100-fold more sensitive than conventional assays for enzyme activity, rendering it potentially useful for quantitatively monitoring terminal transferase in patients with leukemia.

Monoclonal antibodies to human terminal transferase

Human terminal deoxynucleotidyltransferase was used to produce mouse monoclonal antibodies. Three different assays were used to screen for terminal transferase antibodies and antibody-producing hybridoma cells: an enzyme binding assay, an enzyme-linked immunosorbent assay, and a "terminal transferase-specific antibody" cytochemical procedure that allows visualization of the homogeneity of the hybridoma clones producing antibodies to terminal transferase. Of the 12 mouse hybridoma clones isolated, seven produce IgG1 and five produce IgG2a immunoglobulins. Only one of these monoclonal antibodies is inhibitory to human terminal transferase activity. Four of the monoclonal antibodies react with terminal transferase peptides after separation on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while the remainder appear to recognize only native determinants on the human enzyme. Cross-reactivity studies with purified calf thymus enzyme show that although four of the monoclonal antibodies bind to native enzyme, none react with calf thymus terminal transferase peptides after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting structural differences within the cross-reactive determinants. A more general survey on the affinity of these monoclonal antibodies to human terminal transferase for the enzyme from other species using an enzyme-linked immunosorbent assay demonstrates that none of the monoclonal antibodies reacts with chicken thymus terminal transferase. The affinity of binding for terminal transferase from other mammals to this panel of monoclonal antibodies varies with the clones as expected, but few bind as strongly as the human enzyme. These results suggest that although antigenic determinants are conserved through evolution, fine structural changes within the determinants do occur.

Detection of circulating 'terminal transferase-positive' cells does not predict relapse in acute lymphoblastic leukemia

Serial samples of peripheral blood were obtained from 35 children with ALL over a period of 18 months. The mononuclear cells were examined for TdT by indirect immunofluorescence using an unpurified anti-calf thymus TdT as the primary antibody. This analysis failed to distinguish those children who were destined to relapse (n = 9) from those who remained in continuous complete remission. Rather, the exhibition of fluorescence was linked to the co-existence of infection, with a negative predictive value of 0.91. Putative 'TdT-positive' cells were concentrated in the T-lymphocyte fraction and the very process of E-rosette formation seemed to contribute to this phenomenon. It appears as if the anti-TdT reagent recognizes not only TdT but also a variety of antigens which are expressed on or in immature and activated lymphocytes.

Expression of terminal deoxynucleotidyl transferase in human thymus during ontogeny and development

Expression of the enzyme terminal deoxynucleotidyl transferase (TdT) was studied in human thymus during ontogeny and development. In five fetal thymus samples, the enzyme activity was barely detectable. At birth, the terminal transferase activity remained low. Maximum expression of the enzyme activity occurred between 10 and 40 mo of age. Analysis of six other enzyme activities, adenosine kinase, deoxyadenosine kinase, AMP deaminase, dAMP deaminase, 5' nucleotidase, and adenosine deaminase confirmed the normal status of the thymic tissue. A careful analysis of thymic architecture revealed that involution did not occur as a result of the disease process that necessitated cardiac surgery. By immunofluorescence, the TdT antigen was localized exclusively in the nucleus of cortical thymocytes. Protein immunoblotting studies indicated that human thymic terminal transferase exists as a single high m.w. species in individuals under 30 mo of age. Thereafter, a variant m.w. species is detectable. The increase in expression of this enzyme coincides with the increase observed in serum immunoglobulin levels during maturation and precedes the maximum development of the human thymus.

Demonstration of terminal deoxynucleotidyl transferase in single cells by indirect immunofluorescence--a methodological reappraisal

The optimal conditions for assaying terminal transferase by indirect immunofluorescence with commercially available reagents have been explored. Target tissues examined included fresh, stored and cultured human acute lymphoblastic leukemia cells; normal human peripheral blood and bone marrow; and calf thymus. Brief, cold fixation in glutaraldehyde/ethanol or omission of fixation proved to be satisfactory. The most suitable primary antibody was an unfractionated rabbit serum with specificity for anti-calf thymus TdT which cross-reacted with human material and was neutralized in high dilution by purified enzyme. Inferior reagents and techniques gave false negative results. Identification of TdT appears to be feasible even in tissue samples stored for several months and enumeration of cells is facilitated by ethidium bromide counterstaining.

Evaluation of methods of detecting terminal deoxynucleotidyl transferase in human hematologic malignancies. Comparison of immunofluorescence and enzymatic assays

Terminal transferase (TdT) activity and antigen have been measured in 267 specimens of human bone marrow and peripheral blood by using a biochemical assay for enzymatic activity and an immunofluorescence test for antigen. Oligo p(dA)50 and dGTP were used as reagents in the biochemical assay and either rabbit anti-calf TdT or rabbit anti-human TdT was used as the primary antibody for immunofluorescence. Because both false-positive and false-negative detection of TdT antigen occurs, the biochemical assay of TdT activity is considered the standard against which immunofluorescence assays must be measured. If specimens of cells contained TdT activity, then the immunofluorescence detected antigen in 91% of cases (rabbit anti-calf TdT) and 95% of cases (rabbit anti-human TdT). When no TdT activity was detected, the immunofluorescence test was positive in 7.8% of cases (rabbit anti-calf TdT) and 5.2% of cases (rabbit anti-human TdT). When air-dried slices were shipped by air mail to a distant location before being stained for immunofluorescence, TdT antigen was detected in only 33% of matched pair cases which contained TdT activity. From this study, the authors conclude that with current methodology, immunofluorescence tests for TdT antigen must be carried out on slides prepared in the testing laboratory and that such tests are reliable in more than 90% of cases. However, because a small percentage of results are false positives and false negatives, the authors suggest that if a patient's clinical response is not consistent with the immunofluorescence TdT result, an enzymatic assay for TdT activity be carried out.

Histochemical demonstration of terminal deoxynucleotidyl transferase in leukemia

White blood cells from 22 patients with leukemia and lymphoma were studied for the presence of terminal deoxynucleotidyl transferase with a peroxidase-antiperoxidase method. The enzyme was detected in leukemic cells of 5 patients with acute lymphoblastic leukemia and 1 patient with chronic myelogenous leukemia, whereas 16 patients with different forms of leukemia or lymphoma were negative for this enzyme. Comparative studies using a biochemical and an indirect immunofluorescence assay revealed complete concordance between these three methods.

Terminal deoxynucleotidyl transferase activity in neoplastic and nonneoplastic hematopoietic cells

Terminal deoxynucleotidyl transferase activity was investigated by enzyme assay and (or) an indirect immunofluorescence method with specimens from 151 patients who had a variety of neoplastic and nonneoplastic conditions: leukemia, 62; non-Hodgkin's lymphoma, 36; Hodgkin's disease, seven; lymph nodes without neoplasms, 21; normal peripheral blood, 15; normal bone marrow, ten. Immunologic studies were done on samples from 82 of these patients. Increased terminal deoxynucleotidyl transferase activity was found by both methods in patients who had acute lymphoblastic leukemia and the lymphoid blast crisis of chronic myelocytic leukemia and by the immunofluorescence method in patients who had lymphoblastic lymphoma. A single patient with acute monoblastic leukemia was found by both technics to have increased enzyme activity. Three B-cell proliferations were positive by the enzyme assay; none was positive with the immunofluorescence method. In the remaining 42 B-cell proliferations, the levels of terminal deoxynucleotidyl transferase activity were found to be normal by both the enzyme assay and the immunofluorescence method. Cytoplasmic positivity was observed in as much as 10% of the cells in 13 specimens that were otherwise negative and in eight samples in association with nuclear positivity. A comparison of terminal deoxynucleotidyl transferase activity in microunits/mg protein (enzyme assay) with the percentage of positive cells (immunofluorescence method) yielded a correlation coefficient of 0.62 (P less than 0.01).

Biochemical and immunological properties of human terminal deoxynucleotidyl transferase purified from blasts of acute lymphoblastic and chronic myelogenous leukemia

Terminal deoxynucleotidyl transferase was purified to homogeneity from the blasts of eight patients with leukemia and compared with purified transferase from normal human and calf thymus. In two cases phenylmethanesulfonylfluoride was added during purification to reduce proteolysis. Comparative kinetic analyses of the purified enzymes indicated no differences in catalytic properties. There was substantial variation in the molecular structure of terminal transferase on denaturing polyacrylamide gels: (a) a protein that migrated as a single polypeptide with M(r) = 62,000 was isolated from two patients with acute lymphoblastic leukemia and from MOLT-4 cells; (b) a protein that migrated as a single polypeptide with M(r) = 42,500 was isolated from two patients with acute lymphoblastic leukemia; (c) a protein that migrated as a single polypeptide with M(r) = 42,500 was isolated from two patients with chronic myelogenous leukemia in blast crisis; (d) a protein that migrated as two non-identical subunits of M(r) = 27,000 and 10,000, respectively, was isolated from two additional patients with chronic myelogenous leukemia in blast crisis. The subunit structure of d is characteristic of the homogeneous enzymes purified from human and calf thymus. Neutralizing and precipitating antibodies to terminal transferase from human lymphoblasts and calf thymus have been produced in rabbits and goats. Antisera directed against either human or calf antigens neutralize enzymatic activity and precipitate all forms of human terminal transferase. The multiple human forms give reactions of antigenic identity by immunodiffusion, but differ antigenically from the calf enzyme. The multiple forms of terminal transferase could represent physiological processing, artifactual degradation, or isozymes coded by several genes.

Unusual immunofluorescence patterns for terminal deoxynucleotidyl transferase in blast crisis chronic myelogenous leukemia

An unusual cytoplasmic distribution of terminal deoxynucleotidyl transferase (TdT) antigen in leukemic cells from two patients who had chronic myelogenous leukemia in blastic phase is described. In most leukemic cells that contain TdT, the intracellular location has been reported to be exclusively nuclear. The cells from these two patients demonstrated TdT staining in both the nucleus and the cytoplasm. The pattern is remarkably similar to that observed in thymocytes, in which bright cytoplasmic staining may also be seen. In the immunofluorescence procedures for detection of TdT in blasts from patients who have chronic myelogenous leukemia, significant cytoplasmic staining should not be mistaken for nonspecific absorption of immunoglobulins or specimen deterioration.