CD26/Dipeptidyl Peptidase IV (DPPIV) Regulates p38 Phosphorylation and Topoisomerase II Alpha Expression in the B-Lymphoma Line Jiyoye, Associated with Enhanced In Vitro and In Vivo Sensitivity to Doxorubicin.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3407-3407
Author(s):  
Toshiko Yamochi ◽  
Tadanori Yamochi ◽  
Ugur Aytac ◽  
Tsutomu Sato ◽  
Chikao Morimoto ◽  
...  
Keyword(s):  
T Cell ◽  
Topoisomerase Ii ◽  
Low Dose ◽  
Topoisomerase Ii Alpha ◽  
In Vitro Sensitivity ◽  
Alpha Level ◽  
Lymphoma Line ◽  
Cd26 Expression

Abstract CD26 is a 110 kDa surface glycoprotein with diverse functional properties, including having a key role in normal T-cell biology, being a marker of aggressive disease for selected T-cell malignancies and being involved in the development of certain cancers. Its extracellular domain encodes a membrane-associated dipeptidyl peptidase IV (DPPIV) activity capable of processing biological factors to alter their functional profiles. We have shown previously that expression of CD26 on the T cell line Jurkat is associated with increased topoisomerase II alpha level and in vitro sensitivity to topoisomerase II inhibitors (Aytac U et al. Cancer Res61:7204, 2001; Aytac U et al. Br J Cancer88:455, 2003; Sato K et al. Br J Cancer89:1366, 2003). We now show that CD26 expression, particularly its DPPIV enzyme activity, on the B-lymphoma line Jiyoye results in increased topoisomerase II alpha level and in vitro sensitivity to doxorubicin-induced apoptosis. Examining the molecular mechanisms involved in CD26-associated signaling, our present findings also indicate that CD26/DPPIV expression on Jiyoye cells is associated with increased phosphorylation of p38 and its upstream regulators MKK3/6 and ASK1. Importantly, inhibition of p38 phosphorylation decreases topoisomerase II alpha expression, suggesting a role for p38 in the regulation of topoisomerase II alpha. Finally, studies using a SCID mouse xenograft model with CD26 Jiyoye transfectants show that CD26 expression is associated with enhanced survival following treatment with low doses of doxorubicin. In particular, treatment with low-dose doxorubicin of SCID mice injected with CD26-negative parental Jiyoye cells does not lead to a statistically significant survival advantage over those treated with saline. On the other hand, SCID mice injected with CD26 Jiyoye transfectants show significantly greater survival when treated with low-dose doxorubicin than with saline alone, indicating that CD26 presence renders tumor cells more sensitive to doxorubicin in an in vivo model. Our data thus characterize the biochemical linkage among CD26 and other key intracellular molecules, while demonstrating that CD26 may have a role in tumor sensitivity to antineoplastic agents targeting topoisomerase II alpha. In addition, our work suggests that CD26/DPPIV may be an appropriate target for therapy for selected hematological malignancies of both B- and T-cell lineages.

γδ T cells for immune therapy of patients with lymphoid malignancies

Blood ◽  
2003 ◽  
Vol 102 (1) ◽  
pp. 200-206 ◽  
Author(s):  
Martin Wilhelm ◽  
Volker Kunzmann ◽  
Susanne Eckstein ◽  
Peter Reimer ◽  
Florian Weissinger ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Antitumor Activity ◽  
Low Dose ◽  
Γδ T Cells ◽  
Low Grade ◽  
Treatment Schedule ◽  
Γδ T Cell

Abstract There is increasing evidence that γδ T cells have potent innate antitumor activity. We described previously that synthetic aminobisphosphonates are potent γδ T cell stimulatory compounds that induce cytokine secretion (ie, interferon γ [IFN-γ]) and cell-mediated cytotoxicity against lymphoma and myeloma cell lines in vitro. To evaluate the antitumor activity of γδ T cells in vivo, we initiated a pilot study of low-dose interleukin 2 (IL-2) in combination with pamidronate in 19 patients with relapsed/refractory low-grade non-Hodgkin lymphoma (NHL) or multiple myeloma (MM). The objectives of this trial were to determine toxicity, the most effective dose for in vivo activation/proliferation of γδ T cells, and antilymphoma efficacy of the combination of pamidronate and IL-2. The first 10 patients (cohort A) who entered the study received 90 mg pamidronate intravenously on day 1 followed by increasing dose levels of continuous 24-hour intravenous (IV) infusions of IL-2 (0.25 to 3 × 106 IU/m2) from day 3 to day 8. Even at the highest IL-2 dose level in vivo, γδ T-cell activation/proliferation and response to treatment were disappointing with only 1 patient achieving stable disease. Therefore, the next 9 patients were selected by positive in vitro proliferation of γδ T cells in response to pamidronate/IL-2 and received a modified treatment schedule (6-hour bolus IV IL-2 infusions from day 1-6). In this patient group (cohort B), significant in vivo activation/proliferation of γδ T cells was observed in 5 patients (55%), and objective responses (PR) were achieved in 3 patients (33%). Only patients with significant in vivo proliferation of γδ T cells responded to treatment, indicating that γδ T cells might contribute to this antilymphoma effect. Overall, administration of pamidronate and low-dose IL-2 was well tolerated. In conclusion, this clinical trial demonstrates, for the first time, that γδ T-cell–mediated immunotherapy is feasible and can induce objective tumor responses. (Blood. 2003;102:200-206)

scholarly journals 735 Identification of a small molecule that prevents T cell exhaustion using machine learning algorithms paired with high-resolution single cell RNAseq

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A766-A766
Author(s):  
Isabelle Le Mercier ◽  
Sunny Sun ◽  
Dongmei Xiao ◽  
Laura Isacco ◽  
Daniel Treacy ◽  
...  
Keyword(s):  
T Cell ◽  
Low Dose ◽  
Machine Learning Algorithms ◽  
High Dose ◽  
T Cell Exhaustion ◽  
Tcr Signaling ◽  
Compound A ◽  
Cell Exhaustion

BackgroundT cell responses are tightly regulated and require a constant balance of signals during the different stages of their activation, expansion, and differentiation. As a result of chronic antigen exposure, T cells become exhausted in solid tumors, preventing them from controlling tumor growth.MethodsWe identified a transcriptional signature associated with T cell exhaustion in patients with melanoma and used our proprietary machine learning algorithms to predict molecules that would prevent T cell exhaustion and improve T cell function. Among the predictions, an orally available small molecule, Compound A, was highly predicted.ResultsCompound A was tested in an in vitro T cell Exhaustion assay and shown to prevent loss of proliferation and expression of immune checkpoint receptors. Transcriptionally, Compound A-treated cells looked indistinguishable from conventionally expanded, non-exhausted T cells. However, when assessed in a classical T cell activation assay, Compound A demonstrated dose dependent activity. At low dose, Compound A was immuno-stimulatory, allowing cells to divide further by preventing activation induced cell death. At higher doses, Compound A demonstrated immuno-suppressive activity preventing early CD69 upregulation and T cell proliferation. All together, these observations suggest that Compound A prevented exhaustion with a mechanism of action involving TCR signaling inhibition. While cessation of TCR signaling or rest has been recently associated with improved CAR-T efficacy by preventing or reversing exhaustion during the in vitro manufacturing phase, it is unclear if that mechanism would translate in vivo.Compound A was evaluated in the CT26 and MC38 syngeneic mouse models alongside anti-PD1. At low dose Compound A closely recapitulated anti-PD1 mediated cell behavior changes by scRNA-seq and flow cytometry in CT26 mice. At high dose, Compound A led to the accumulation of naive cells in the tumor microenvironment (TME) confirming the proposed mechanism of action. Low dose treatment was ineffective in MC38 mouse model but a pulsed treatment at high dose also recapitulated anti-PD1 activity in most animals. Importantly, we identified a new T cell population responding to anti-PD1 that was particularly increased in the MC38 mouse model; Compound A treatment also impacted this population.ConclusionsThese data confirm that mild TCR inhibition either suboptimal or fractionated can prevent exhaustion in vivo. However, this approach has a very limited window of activity between immuno-modulatory and immuno-suppressive effects, thereby limiting potential clinical benefit. Finally, these results demonstrate that our approach and platform was able to predict molecules that would prevent T cell exhaustion in vivo.

Post-Transplant Immune Suppressive Therapy Is Not Necessary In Related and Unrelated Reduced Intensity Conditioning Stem Cell Transplantation Using Low Dose Alemtuzumab In Vivo T Cell Depletion Combined with Alemtuzumab-Mediated In Vitro T Cell Depletion of the Graft

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2328-2328
Author(s):  
P.A. Von Dem Borne ◽  
C.J.M. Halkes ◽  
C.W.J. Starrenburg ◽  
W.A.F. Marijt ◽  
J.H.F. Falkenburg
Keyword(s):  
T Cell ◽  
Low Dose ◽  
Chronic Gvhd ◽  
Cell Depletion ◽  
Suppressive Therapy ◽  
T Cell Depletion ◽  
Post Transplant ◽  
Immune Suppressive Therapy

Abstract Abstract 2328 Introduction T cell depletion with alemtuzumab administered in vivo to the patient reduces the risk of graft-versus-host disease (GVHD) and graft rejection following reduced intensity conditioning allogeneic stem cell transplantation (RIC SCT). However, high doses of alemtuzumab can result in delayed immune reconstitution, increased non relapse mortality (NRM) due to infections, and potential loss of graft versus tumor responses. Recently, the feasibility of T cell depletion with low dose in vivo alemtuzumab was demonstrated in HLA-identical related RIC SCT. Dose reduction of alemtuzumab to 30 mg combined with post-transplant immune suppressive therapy with cyclosporine tapered from 3 months after transplantation resulted in a low risk of GVHD, no increase in NRM and improved lymphocyte recovery (Chakraverty et al, Blood pre-published online June 29, 2010). Early immunotherapeutic intervention after SCT with donor lymphocytes may be hampered by the administration of post-transplant immune suppressive therapy. We investigated whether in RIC SCT using low dose in vivo alemtuzumab, post-transplant immune suppressive therapy can be replaced by alemtuzumab-mediated in vitro T cell depletion of the graft just prior to infusion (“Campath in the bag”). Patient and donor characteristics Between 2007 and 2009, 29 patients were transplanted with an unrelated donor, and 28 patients with a related donor using a RIC regimen consisting of fludarabine (50 mg/m2 p.o. day -10 to -5), busulphan (3.2 mg/kg i.v. day -6 and -5) and alemtuzumab (15 mg i.v. day -4 and -3), followed by infusion of the graft after in vitro incubation with 20 mg alemtuzumab. No additional immune suppressive therapy was used after SCT. Unrelated donors were matched for HLA-A, B, C, DR and DQ, three patient donor combinations had one HLA-DQ mismatch. Median patient age was 59 years (range 21–72). Remission status at the time of transplant was: 47% CR, 37% PR, 9% SD, 7% PD. Indications were diverse (19 AML, 16 myeloma, 6 CLL, 5 low grade NHL, 3 aggressive T-NHL, 2 aggressive B-NHL, 2 SAA, 1 CML, 1 myelofibrosis, 1 CMML, 1 ALL). The unrelated and related transplanted group were comparable regarding age, disease and remission status. The median Gratwohl transplantation risk score was 3 in the related group (range 1–5), and 5 in the unrelated group (range 3–6). Results All patients engrafted; platelet numbers of 50 × 109/L were reached after a median of 11 days (range 0–38 days), neutrophil numbers of 0.5 × 109/L were reached after a median of 18 days (range 0–161 days) post transplant. Two patients had secondary graft failure. In patients transplanted with a related donor, grade 1–2 and 3–4 acute GVHD was observed in 36% and 4% of evaluable patients, respectively, resolving in all patients without development of chronic GVHD. NRM was 0% at 3 months and 4% at 1 year. Overall survival was 100% at 3 months and 89% at 1 year. In patients transplanted with an unrelated donor more acute GVHD was observed (59% grade 1–2, 15% grade 3–4 of evaluable patients). 24% of evaluable patients developed chronic GVHD, which was limited in 75% and extensive in 25% of these patients. Chronic GVHD resolved in most patients, one patient has ongoing extensive chronic GVHD. NRM was 7% at 3 months and 24% at 1 year. Overall survival was 93% at 3 months and 55% at 1 year. Conclusions RIC SCT using low dose alemtuzumab in vivo T cell depletion combined with alemtuzumab-mediated in vitro T cell depletion of the graft without additional post-transplant immune suppressive therapy is feasible in patients transplanted with related and unrelated donors. Results are excellent in patients transplanted with related donors with low NRM and high overall survival. Although results are good in patients transplanted with unrelated donors considering the high Gratwohl score in this group, further improvement is being sought by increasing the efficiency of T cell depletion. This RIC SCT regimen without post-transplant immune suppressive therapy is an appropriate platform for early cellular immunotherapeutic interventions including donor lymphocyte infusion after SCT. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Low-Dose Decitabine Augments the Activation and Anti-Tumor Immune Response of IFN-γ+ CD4+ T Cells Through Enhancing IκBα Degradation and NF-κB Activation

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiang Li ◽  
Liang Dong ◽  
Jiejie Liu ◽  
Chunmeng Wang ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Immune Response ◽  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Low Dose ◽  
T Cell Proliferation ◽  
Ifn Γ ◽  
Iκbα Degradation

BackgroundCD4+ T cells play multiple roles in controlling tumor growth and increasing IFN-γ+ T-helper 1 cell population could promote cell-mediated anti-tumor immune response. We have previously showed that low-dose DNA demethylating agent decitabine therapy promotes CD3+ T-cell proliferation and cytotoxicity; however, direct regulation of purified CD4+ T cells and the underlying mechanisms remain unclear.MethodsThe effects of low-dose decitabine on sorted CD4+ T cells were detected both in vitro and in vivo. The activation, proliferation, intracellular cytokine production and cytolysis activity of CD4+ T cells were analyzed by FACS and DELFIA time-resolved fluorescence assays. In vivo ubiquitination assay was performed to assess protein degradation. Moreover, phosphor-p65 and IκBα levels were detected in sorted CD4+ T cells from solid tumor patients with decitabine-based therapy.ResultsLow-dose decitabine treatment promoted the proliferation and activation of sorted CD4+ T cells, with increased frequency of IFN-γ+ Th1 subset and enhanced cytolytic activity in vitro and in vivo. NF-κB inhibitor, BAY 11-7082, suppressed decitabine-induced CD4+ T cell proliferation and IFN-γ production. In terms of mechanism, low-dose decitabine augmented the expression of E3 ligase β-TrCP, promoted the ubiquitination and degradation of IκBα and resulted in NF-κB activation. Notably, we observed that in vitro low-dose decitabine treatment induced NF-κB activation in CD4+ T cells from patients with a response to decitabine-primed chemotherapy rather than those without a response.ConclusionThese data suggest that low-dose decitabine potentiates CD4+ T cell anti-tumor immunity through enhancing IκBα degradation and therefore NF-κB activation and IFN-γ production.

scholarly journals Low-dose decitabine priming endows CAR T cells with enhanced and persistent antitumour potential via epigenetic reprogramming

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yao Wang ◽  
Chuan Tong ◽  
Hanren Dai ◽  
Zhiqiang Wu ◽  
Xiao Han ◽  
...  
Keyword(s):  
Dna Methylation ◽  
T Cells ◽  
T Cell ◽  
Dna Methyltransferase ◽  
Low Dose ◽  
Cytokine Production ◽  
Car T Cells ◽  
Car T

AbstractInsufficient eradication capacity and dysfunction are common occurrences in T cells that characterize cancer immunotherapy failure. De novo DNA methylation promotes T cell exhaustion, whereas methylation inhibition enhances T cell rejuvenation in vivo. Decitabine, a DNA methyltransferase inhibitor approved for clinical use, may provide a means of modifying exhaustion-associated DNA methylation programmes. Herein, anti-tumour activities, cytokine production, and proliferation are enhanced in decitabine-treated chimeric antigen receptor T (dCAR T) cells both in vitro and in vivo. Additionally, dCAR T cells can eradicate bulky tumours at a low-dose and establish effective recall responses upon tumour rechallenge. Antigen-expressing tumour cells trigger higher expression levels of memory-, proliferation- and cytokine production-associated genes in dCAR T cells. Tumour-infiltrating dCAR T cells retain a relatively high expression of memory-related genes and low expression of exhaustion-related genes in vivo. In vitro administration of decitabine may represent an option for the generation of CAR T cells with improved anti-tumour properties.

γδ T Cell-Mediated Immunotherapy of Malignancies with Zoledronate and IL-2.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2439-2439 ◽  
Author(s):  
Volker Kunzmann ◽  
Manfred Smetak ◽  
Brigitte Kimmel ◽  
Florian Weissinger ◽  
Karin Weigang-Koehler ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Low Dose ◽  
Hematological Malignancies ◽  
Γδ T Cells ◽  
Γδ T Cell ◽  
Hla Dr ◽  
Ifn Γ

Abstract Despite major advances in our understanding of the adaptive immunity towards tumors and the introduction of vaccine-based strategies, durable responses are rare and adaptive immunotherapeutic approaches are still not an established treatment modality. Several lines of evidence indicate that MHC-independent effector cells of the innate immune system such as natural killer (NK) cells or γδ T cells significantly contribute to the immune surveillance of tumors. As we have shown previously, aminobisphosphonates (ABP) such as pamidronate or zoledronate are potent γδ T cell stimulatory compounds by inducing secretion of proinflammatory cytokines (i.e. IFN-γ) and cell-mediated cytotoxicity against lymphoma and myeloma cells in vitro. The detection of ABP as γδ T cell stimulating drugs at pharmacologically achievable concentrations in humans opened the possibility to evaluate the consequences of selective γδ T cell stimulation in vivo. The concept of γδ T cell-mediated immunotherapy is currently validated in a Phase II clinical trial with zoledronate (4mg i.v., d 1) and low dose IL-2 (2 x 106 IU/m2 s.c., d 1–6) for patients with hematological (NHL, myeloma, AML) and non-hematological malignancies (renal cell carcinoma and malignant melanoma). The results of our first clinical pilot study with pamidronate/IL-2 in patients with lymphoid malignancies showed that selective activation and expansion of γδ T cells can be induced in vivo. However, 50% of patients with hematological malignancies failed to respond to pamidronate/IL-2 in vitro. Therefore, positive in vitro sensitivity testing was an essential inclusion criterion in this trial. Immunomonitoring of the first 12 patients included in the study showed that zoledronate/IL-2 is highly effective in activating and expanding γδ T cells in vivo (104 TCRδ2+/HLA-DR+ cells/μl (range 11-323) at day 8 of cycle 1 compared to 3 TCRδ2+/HLA-DR+ cells (range 0-15) before treatment). In addition, IFN-γ serum levels increased from 7 to 110 pg/ml (mean 44, n=6) at day 2 at cycle 1 (day 0: 2, range 0–5). So far, objective tumor responses were observed only in hematological malignancies (updated data will be presented). The application of zoledronate/IL-2 is generally well tolerated. In conclusion, effective γδ T cell activation/expansion can be achieved in vivo by the combination of zoledronate and low dose IL-2. Because of the potent anti-tumor effects of γδ T cells this strategy might be a new attractive immunotherapy approach for malignancies with preserved γδ T cell function.

Low-Dose Lenalidomide Improves CAR-Based Immunotherapy In CLL By Reverting T-Cell Defects In Vivo

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4171-4171
Author(s):  
Maria Teresa Sabrina Bertilaccio ◽  
Sarah Tettamanti ◽  
Greta Maria Paola Giordano Attianese ◽  
Giovanni Galletti ◽  
Silvia Arcangeli ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Low Dose ◽  
Leukemic Cells ◽  
Antigen Binding ◽  
Low Doses ◽  
Car T Cells ◽  
Car T

Abstract Chronic Lymphocytic Leukemia (CLL) is a chronic lymphoid malignancy characterized by immune suppression that is responsible for an increase in infection susceptibility but also concurs to a reduced ability of the immune system to promote an effective response against the leukemic cells. Tumor-immunosuppressive mechanisms are essentially due to the capacity of CLL cells of modifying the surrounding microenvironment including immune effectors likely contributing to disease progression but also to limited effectiveness of current immunotherapy approaches. Lenalidomide is an immunomodulatory agent (IMID) able to induce significant long-lasting responses in CLL patients. The exact mechanism of anti-tumor activity of lenalidomide remains undefined, but it also implies the modulation of tumor microenvironment through down-regulation of critical cytokines and activation of immune effector cells. In addition, lenalidomide was shown to reverse, in vitro, defects in immunological synapse formation between T cells and CLL cells, by interfering with several cytoskeletal molecules. Chimeric antigen receptors (CARs) molecules are emerging as a powerful tool to redirect T-cell specificity against leukemia. CARs are artificial molecules constituted by an extracellular-antigen-binding domain consisting of the variable chains of a monoclonal antibody, linked together as a single chain Fv (scFV), and an intracellular signaling region, usually the zeta chain of the TCR/CD3 complex, that is immediately triggered after antigen recognition. Therefore, CARs take advantage of both the antigen binding non MHC-restricted-properties of monoclonal antibodies and of the typical T-cell mediated effector functions. Given the characteristic T cell defects occurring in vivo in CLL patients, it becomes very intriguing to explore the possibility of a novel CLL therapy combining a CAR-based immunotherapy with low doses of lenalidomide, in order to maximize the effect of the immune attack by reverting in vivo the acquired T cell defects. We studied the in vivo cytotoxic effects on the tumor microenvironment upon lenalidomide treatment utilizing the Rag2-/-γc-/--xenograft model of human CLL based on transplantation of the CLL cell line MEC1 into Rag2-/-γc-/--mice. Utilizing the CAR.CD23 tool as previously published by our group, we also performed experiments where MEC-1-trasplanted-Rag2-/-γc-/- mice were injected with CAR.CD23 T cells from CLL patients together with lenalidomide at low concentrations, uneffective in monotherapy. In these animals, a decrease of the percentage of CD19+leukemic cells was observed in all lymphoid and non-lymphoid tissues after 20 days of treatment, as compared to controls treated with CAR.CD23 T cells or lenalidomide alone. This combination resulted also in improved survival of the treated cohort (NT+lenalidomide vs CAR+lenalidomide: p<0.03, n=7). The effect of the combination with low dose lenalidomide was more effective also when compared to the addition of human recombinant IL-2 as in traditional immunotherapeutic settings. In accordance to the in vivo efficacy, CAR T cells were observed in all leukemic sites suggesting an ability to migrate and home in vivo. In addition, when purified from the bone marrow CD23.CAR+T cells were still able to mount a tumor-specific cytotoxic response in vitro, reaching more than 50% of tumor lysis in both the conditions with lenalidomide and IL-2, compared to 20% of tumor lysis exerted by unmanipulated T cells. Indeed, ex vivo T cells were for the majority effector memory cells and the CD23.CAR was still expressed on their surface. These results conceivably support the use in the CLL therapeutical setting of low doses lenalidomide to improve CARs cytotoxic response and avoid the potential impairment of an effective immune response. Disclosures: No relevant conflicts of interest to declare.

The in vivo distribution and dynamics of DNA topoisomerase II in Drosophila embryonic nuclei and chromosomes

1993 ◽  
Vol 51 ◽  
pp. 74-75
Author(s):  
Jason R. Swedlow ◽  
Neil Osheroff ◽  
Tim Karr ◽  
John W. Sedat ◽  
David A. Agard
Keyword(s):  
Topoisomerase Ii ◽  
Biochemical Characterization ◽  
Developmental Cycle ◽  
Dna Topoisomerase Ii ◽  
Chromosomal Distribution ◽  
Dna Topoisomerase ◽  
Ideal System ◽  
Dnase Treatment

DNA topoisomerase II is an ATP-dependent double-stranded DNA strand-passing enzyme that is necessary for full condensation of chromosomes and for complete segregation of sister chromatids at mitosis in vivo and in vitro. Biochemical characterization of chromosomes or nuclei after extraction with high-salt or detergents and DNAse treatment showed that topoisomerase II was a major component of this remnant, termed the chromosome scaffold. The scaffold has been hypothesized to be the structural backbone of the chromosome, so the localization of topoisomerase II to die scaffold suggested that the enzyme might play a structural role in the chromosome. However, topoisomerase II has not been studied in nuclei or chromosomes in vivo. We have monitored the chromosomal distribution of topoisomerase II in vivo during mitosis in the Drosophila embryo. This embryo forms a multi-nucleated syncytial blastoderm early in its developmental cycle. During this time, the embryonic nuclei synchronously progress through 13 mitotic cycles, so this is an ideal system to follow nuclear and chromosomal dynamics.

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