Safety and efficacy of azacitidine in Belgian patients with high-risk myelodysplastic syndromes, acute myeloid leukaemia, or chronic myelomonocytic leukaemia: results of a real-life, non-interventional post-marketing survey.

OBJECTIVES: We evaluated azacitidine (Vidaza(®)) safety and efficacy in patients with myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML), and chronic myelomonocytic leukaemia (CMML), in a real-life setting. Treatment response, dose, and schedule were assessed. METHODS: This non-interventional, post-marketing survey included 49/50 patients receiving azacitidine at 14 Belgian haematology centres from 2010-2012. Treatment-emergent adverse events (TEAEs), including treatment-related TEAEs, and serious TEAEs (TESAEs) were recorded throughout the study. Treatment response [complete response (CR), partial response (PR), haematological improvement (HI), stable disease (SD), treatment failure (TF)) and transfusion-independence (TI) were evaluated at completion of a 1-year observation period (1YOP) or at treatment discontinuation, and overall survival (OS), at study conclusion. RESULTS: The median age of patients was 74·7 (range: 43·9-87·8) years; 69·4% had MDS, 26·5% had primary or secondary AML, and 4·1% had CMML. Treatment-related TEAEs, grade 3-4 TEAEs, and TESAEs were reported in 67·3%, 28·6%, and 18·4% of patients, respectively. During 1YOP, patients received a median of 7 (1-12) treatment cycles. Treatment response was assessed for 38/49 patients. Among MDS and CMML patients (n = 29), 41·4% had CR, PR, or HI, 41·4% had SD, and 17·2% had TF. Among AML patients (n = 9), 44·4% had CR or PR, 33·3% had SD, and 22·2% had TF. TI was observed in 14/32 (43·8%) patients who were transfusion-dependent at baseline. Median (95% confidence interval) OS was 490 (326-555) days; 1-year OS estimate was 0·571 (0·422-0·696). CONCLUSIONS: Our data support previous findings that azacitidine has a clinically acceptable safety profile and shows efficacy.

Azacitidine access program for Belgian patients with myelodysplastic syndromes, acute myeloid leukemia or chronic myelomonocytic leukemia.

OBJECTIVE: Azacitidine (Vidaza *) is approved in Europe for treatment of myelodysplastic syndromes (MDS), acute myeloid leukemia (AML) with 20-30% bone marrow (BM) blasts, and chronic myelomonocytic leukemia (CMML) with 10-29% BM blasts and no myeloproliferative syndrome (i.e. <13.000/µL white blood cells). In Belgium, the azacitidine reimbursement process can take several months, and is often delayed at submission for medical assessment by the Belgian National Institute for Health and Disability Insurance of incomplete patient dossiers, due to disease complexity and classification, and administrative burden. We describe the Vidaza Access Program and its application to an initial 175 patients. Individual medical dossiers were reviewed for completeness to facilitate patient access to treatment in Belgium. METHODS: A standardized anonymized patient information form is completed by the physician and sent for review to the Belgian Celgene Medical Department. The form is reviewed within three working days and, for complete dossiers, Celgene grants a financial guarantee for treatment with azacitidine. The patient can then be treated without the hospital being subjected to financial risk. RESULTS: Between January 2013 and June 2014, 63 physicians (53 Belgian hospitals) recruited 175 patients. In total, 163 patient dossiers were approved by Celgene (120 MDS, 36 AML, and 7 CMML), of which 104 dossiers were also approved by the review committee and 49 have been waiting for a final decision for a median of 6 months; no information is currently available for the remaining 10. No dossiers approved by Celgene have been rejected by the review committee. CONCLUSIONS: The Celgene Vidaza Access Program offers support to healthcare professionals in the appropriate use of azacitidine. By facilitating the assessment of patient dossiers and providing a financial guarantee for prescribers and hospitals, treatment can be initiated more rapidly and patients may better benefit from azacitidine treatment.

Myelofibrosis patients in Belgium: disease characteristics.

OBJECTIVE: To date, only a small number of epidemiological studies on myelofibrosis have been performed. The current study aimed to characterize the myelofibrosis patient population in Belgium according to pre-defined disease parameters (diagnosis, risk categories, hemoglobin <10 g/dl, spleen size, constitutional symptoms, platelet count, myeloblast count), with a view to obtaining a deeper understanding of the proportion of patients that may benefit from the novel myelofibrosis therapeutic strategies. METHODS: A survey was used to collect data on prevalence and disease parameters on all myelofibrosis patients seen at each of 18 participating hematologic centers in 2011. Aggregated data from all centers were used for analysis. Analyses were descriptive and quantitative. RESULTS: A total of 250 patients with myelofibrosis were captured; of these, 136 (54%) were male and 153 (61%) were over 65 years old. One hundred sixty-five (66%) of myelofibrosis patients had primary myelofibrosis and 85 (34%) had secondary myelofibrosis. One hundred ninety-three myelofibrosis patients (77%) had a palpable spleen. About a third of patients (34%) suffered from constitutional symptoms. Two hundred twenty-two (89%) myelofibrosis patients had platelet count ≧50 000/µl and 201 (80%) had platelet count ≧100 000/µl. Of 250 patients, 85 (34%) had a myeloblast count ≧1%. Six (2%) patients had undergone a splenectomy. Thirteen (5·2%) patients had undergone radiotherapy for splenomegaly. CONCLUSIONS: The results of this survey provide insight into the characteristics of the Belgian myelofibrosis population. They also suggest that a large proportion of these patients could stand to benefit from the therapies currently under development.

Multiple myeloma presenting as hepatic nodular lesion.

The diffuse infiltration by plasma cells in the liver is not uncommon in multiple myeloma (MM). However, a MM with hepatic mass is very unusual. We report a case of a 75-year-old male with hepatomegaly and a lesion occupying a voluminous space in the liver. A lambda light chain multiple myeloma was found in the check-up of this hepatic mass. We also provide a literature review.

Lenalidomide in relapsed refractory myeloma patients: impact of previous response to bortezomib and thalidomide on treatment efficacy. Results of a medical need program in Belgium.

The prognosis of multiple myeloma patients has significantly improved since the introduction of the novel agents thalidomide, bortezomib and lenalidomide. We report the data of a medical need programme with lenalidomide plus dexamethasone, conducted in Belgium between August 2007 and March 2008, and including 98 relapsed refractory multiple myeloma patients. In addition to chemotherapy and steroids, all patients had received prior treatment with bortezomib, and 84% of them had been exposed to thalidomide. In 52 patients response data could be retrieved by post-hoc analysis. A partial remission or better was achieved in 52% (49% partial and 3% complete response) of patients, despite a median of 5 previous anti-myeloma treatment lines. Responses were rapid while the majority of patients received lenalidomide with once weekly (also called low-dose) dexamethasone. Treatment with lenalidomide plus dexamethasone did prolong overall survival by nearly half a year in this population with end-stage myeloma. Overall response and quality of response were independent of previous response to thalidomide and bortezomib, although the time to progression tended to be shorter in thalidomide- and bortezomib-refractory patients. It can be concluded that lenalidomide plus dexamethasone is an effective and safe treatment regimen in highly refractory multiple myeloma patients, and that these responses are irrespective of previous exposure or sensitivity to thalidomide and bortezomib.

Immune thrombocytopenic purpura at the diagnosis of Hodgkin disease.

We describe the case of a 76-year-old male presenting a thrombocytopenia at the diagnosis of Hodgkin disease. Basing on bone marrow biopsy and evolution, we diagnosed an immune thrombocytopenia and treated with intravenous gammaglobulins. The platelet count normalized in a few days under this therapy. Immune thrombocytopenia purpura (ITP) is a rare complication of Hodgkin disease (HD). It seems to be due to the production of antibodies directed against platelet membrane proteins. The patient's and the lymphoma's characteristics are not predictive for it to happen. The evolution of HD is also not influenced by its occurrence. Various treatments (including corticoids and immunomodulating agents) have been tried with different efficiencies.

Antileukemic activity of valproic acid in chronic lymphocytic leukemia B cells defined by microarray analysis.

Epigenetic code modifications by histone deacetylase inhibitors have recently been proposed as potential new therapies for hematological malignancies. Chronic lymphocytic leukemia (CLL) remains incurable despite the introduction of new treatments. CLL B cells are characterized by an apoptosis defect rather than excessive proliferation, but proliferation centers have been found in organs such as the bone marrow and lymph nodes. In this study, we analyzed gene expression modifications in CLL B cells after treatment with valproic acid (VPA), a well-tolerated anti-epileptic drug with HDAC inhibitory activity. CLL B cells obtained from 14 patients were treated in vitro with a concentration of 1 mM VPA for 4 h. VPA effects on gene expression were thereafter studied using Affymetrix technology, and some identified genes were validated by real-time PCR and western blot. We observed that VPA induced apoptosis by downregulating several anti-apoptotic genes and by upregulating pro-apoptotic genes. Furthermore, VPA significantly increased chemosensitivity to fludarabine, flavopiridol, bortezomib, thalidomide and lenalidomide. VPA inhibited the proliferation of CpG/IL2-stimulated CLL B cells and modulated many cell cycle messenger RNAs. In conclusion, exposure of CLL B cells to VPA induced apoptosis, potentiated chemotherapeutic agent effects and inhibited proliferation. These data strongly suggest the use of VPA in CLL treatment, particularly in combination with antileukemia agents.

Rituximab in auto-immune haemolytic anaemia and immune thrombocytopenic purpura: a Belgian retrospective multicentric study.

OBJECTIVES: For better characterizing the effect of anti-CD20 therapy, we analysed the use of rituximab in Belgian patients experiencing auto-immune haemolytic anaemia (AIHA) and immune thrombocytopenic purpura (ITP). DESIGN: We performed a retrospective multicentric analysis of patients with AIHA and ITP treated with rituximab in Belgium. SETTING: Haematological departments were invited to fill in a questionnaire about patient and disease characteristics. SUBJECTS: All patients with AIHA and ITP, both primary and secondary to other diseases, who received one or more courses of rituximab during their disease course were included. Sixty-eight courses of rituximab in 53 patients with AIHA and 43 courses in 40 patients with ITP were analyzed. INTERVENTION: Response rates, duration of response and factors predictive for response were assessed. RESULTS: All patients were given rituximab after failing at least one previous line of treatment, including splenectomy in 19% and 72.5% of AIHA-patients and ITP-patients respectively. Overall response rates were 79.2% in AIHA and 70% in ITP, with a median follow-up since first rituximab administration of 15 months (range 0.5-62) in AIHA and 11 months (range 0-74) in ITP. Progression free survival at 1 and 2 years were 72% and 56% in AIHA and 70% and 44% in ITP. In this retrospective analysis we were not able to identify pretreatment characteristics predictive for response to rituximab. Nine patients with AIHA and three patients with ITP were given one or more additional courses of rituximab. Most of these patients, who had responded to a previous course, experienced a new response comparable to the previous one, both in terms of quality and of duration of response. Finally, the outcome of patients who failed to respond to rituximab therapy was poor both in terms of response to subsequent therapy and in terms of survival. CONCLUSIONS: This study confirms that rituximab induces responses in a majority of previously treated patients with AIHA and ITP. Response duration generally exceeds 1 year. Retreatment with rituximab in responding patients is most often successful. The outcome of patients who fail on rituximab is poor. We were not able to identify pretreatment patient characteristics predicting for response.

RGDS and DGEA-induced [Ca2+]i signalling in human dermal fibroblasts.

A pulse of short peptides, RGDS and DGEA in the millimolar range, immediately elicits in normal human fibroblasts a transient increase of intracellular Ca2+ ([Ca2+]i). In the present study, we show that this [Ca2+]i occurs in an increasing number of cells as a function of peptides concentration. It is specific of each peptide and inhibited at saturating concentration of the peptide in the culture medium. The [Ca2+]i transient depends on signalling pathways slightly different for DGEA and RGDS involving tyrosine kinase(s) and phosphatase(s), phospholipase C, production of inositol-trisphosphate and release of Ca2+ from the cellular stores. GFOGER, the classical collagen binding peptide of alpha1- alpha2- and alpha11-beta1 integrins, in triple helical or denatured form, does not produce any Ca2+ signal. The [Ca2+]i signalling induced by RGDS and DGEA is inhibited by antibodies against beta1 integrin subunit while that mediated by RGDS is also inhibited by antibodies against the alpha3 integrin. Delay in the acquisition of responsiveness is observed during cell adhesion and spreading on a coat of fibronectin for RGDS or collagen for DGEA or on a coat of the specific integrin-inhibiting antibodies but not by seeding cells on GFOGER or laminin-5. This delay is suppressed specifically by collagenase acting on the collagen coat or trypsin on the fibronectin coat. Our results suggest that free integrins and associated focal complexes generate a Ca2+ signal upon recognition of DGEA and RGDS by different cellular pathways.

Translocation t(1;6)(p35.3;p25.2): a new recurrent aberration in "unmutated" B-CLL.

Although reciprocal chromosomal translocations are not typical for B-cell chronic lymphocytic leukemia (B-CLL), we identified the novel t(1;6)(p35.3;p25.2) in eight patients with this disorder. Interestingly, all cases showed lack of somatically mutated IgV(H). Clinical, morphological, immunologic, and genetic features of these patients are described. Briefly, the age ranged from 33 to 81 years (median: 62.5 years) and the sex ratio was 6M:2F. Most of the patients (6/8) presented with advanced clinical stage. Therapy was required in seven cases. After a median follow-up of 28 months, five patients are alive and three died from disease evolution. Three cases developed transformation into diffuse large B-cell lymphoma. Translocation t(1;6) was found as the primary karyotypic abnormality in three patients. Additional chromosomal aberrations included changes frequently found in unmutated B-CLL, that is, del(11)(q), trisomy 12 and 17p aberrations. Fluorescence in situ hybridization analysis performed in seven cases allowed us to map the t(1;6) breakpoints to the 1p35.3 and 6p25.2 chromosomal bands, respectively. The latter breakpoint was located in the genomic region coding for MUM1/IRF4, one of the key regulators of lymphocyte development and proliferation, suggesting involvement of this gene in the t(1;6). Molecular characterization of the t(1;6)(p35.3;p25.2), exclusively found in unmutated subtype of B-CLL, is in progress.

Clinical and pathological features of 14 non-Hodgkin's lymphomas associated with coeliac disease.

BACKGROUND: It is well established that enteropathy associated T-cell lymphoma is associated with malabsorption which is due to gluten sensitivity (coeliac disease). Our study was performed to define the clinical features, histological subtypes, response to treatment, and outcome of the association of coeliac disease and T-cell lymphoma. PATIENTS AND METHODS: A retrospective study was performed in the UCL Group of Hematology to collect data on patients with a diagnosis of non-Hodgkin's lymphoma and coeliac disease. Fifteen cases were observed between 1985 and 1999. Case records for all but one patient were available and the pathological specimens of 14 patients were reviewed by two pathologists. RESULTS: Six previously diagnosed coeliac patients developed lymphoma; interval between coeliac symptoms and onset of the lymphoma ranged from 2 to 48 years (median 16 years). Five patients had coeliac disease and non-Hodgkin's lymphoma diagnosed concomitantly or less than 6 months before the symptoms leading to the diagnosis of lymphoma. Three patients had the diagnosis of coeliac disease after lymphoma diagnosis (1, 8 and 10 years later respectively). Ten non-Hodgkin's lymphomas were of T-cell origin and 4 were B-cell lymphomas. Eight out of 14 presented on a surgical emergency. Thirteen were treated using chemotherapy. The median survival from the diagnosis of enteropathy associated T-cell lymphoma was 12 months (range 1-126). CONCLUSIONS: Lymphomas associated with coeliac disease are heterogeneous and their diagnosis is difficult. The enteropathy-associated T-cell lymphoma is the most frequent, aggressive and fatal complication of coeliac disease but it is not rare to observe association with B-cell lymphoma. Chemotherapy is highly toxic in those patients. Despite a poor prognosis, long-term survival can be expected in a fraction of these patients.

Antibody-targeted chemotherapy of older patients with acute myeloid leukemia in first relapse using Mylotarg (gemtuzumab ozogamicin).

We analyzed the safety and efficacy of Mylotarg (gemtuzumab ozogamicin, an antibody-targeted chemotherapy consisting of a humanized anti-CD33 antibody linked to calicheamicin, a potent antitumor antibiotic) in the treatment of 101 patients > or =60 years of age with acute myeloid leukemia (AML) in untreated first relapse in three open-label trials. Mylotarg is administered as a 2-h intravenous infusion at 9 mg/m(2) for two doses with 14 days between doses. The overall remission rate was 28%, with complete remission (CR) in 13% of patients and complete remission with incomplete platelet recovery (CRp) in 15%. Median survival was 5.4 months for all patients and 14.5 months and 11.8 months for patients achieving CR and CRp, respectively. CD33 antigen is present on normal hematopoietic progenitor cells; thus, an expected high incidence of grade 3 or 4 neutropenia (99%) and thrombocytopenia (99%) was observed. The incidences of grade 3 or 4 elevations of bilirubin and hepatic transaminases were 24% and 15%, respectively. There was a low incidence of grade 3 or 4 mucositis (4%) and infections (27%) and no treatment-related cardiotoxicity, cerebellar toxicity, or alopecia. Mylotarg is an effective treatment for older patients with CD33-positive AML in first relapse and has acceptable toxicity.

Angioimmunoblastic lymphadenopathy following ciprofloxacin administration.

Angioimmunoblastic lymphadenopathy (AILD) is a rare disorder characterised by generalised lymphadenopathy, fever, hepatosplenomegaly, immune hemolytic anemia and polyclonal hypergammaglobulinemia. We report the occurrence of histology-proven AILD in a patient who had received ciprofloxacin. We suggest that this drug may be added to the list of agents susceptible to elicit AILD.

Long-term follow-up confirms the benefit of all-trans retinoic acid in acute promyelocytic leukemia. European APL group.

First results of a randomized trial (APL91 trial) and other randomized or non-randomized studies have shown that ATRA followed by chemotherapy significantly increased event-free survival (EFS) and survival, and decreased the incidence of relapse by comparison to chemotherapy alone in newly diagnosed APL. We present here long-term follow-up of the APL91 trial. In this trial, 101 patients had been randomized between ATRA followed by three courses of daunorubicin-AraC chemotherapy (ATRA group) and the same chemotherapy alone (chemotherapy group). Results were reanalyzed 73 months after closing of patient entry. Updated results of APL 91 trial found a Kaplan-Meier estimate of EFS and relapse rate at 4 years of 63% and 31% in the ATRA group, as compared to 17% and 78% in the chemotherapy group (P= 10(-4) and relative risk 2.95, P= 10(-4) and relative risk 3.68, respectively). Kaplan-Meier survival at 4 years was 76% in the ATRA group and 49% in the chemotherapy group (P= 0.026, relative risk 2.7). In the chemotherapy group, seven of the 27 relapses occurred after 18 months, but no relapse was seen after 43 months. In the ATRA group, four of the 17 relapses occurred after 18 months, including two late relapses (at 58 and 74 months). In the chemotherapy group, 23 of the 25 patients who relapsed achieved a second CR with ATRA, and the Kaplan-Meier estimate of second relapse was 40% at 30 months. In the ATRA group, the 10 patients who relapsed and were retreated with ATRA achieved a second CR. In conclusion, long-term results of APL91 trial confirm the superiority of the combination of ATRA and chemotherapy over chemotherapy alone in newly diagnosed APL, and that ATRA should be incorporated in the front-line treatment of APL.

Phase I/II study of 2-chloro-2'-deoxyadenosine with cyclophosphamide in patients with pretreated B cell chronic lymphocytic leukemia and indolent non-Hodgkin's lymphoma.

Because of their substantial in vitro synergy, we conducted a dose-escalation study of cyclophosphamide (CP) added to 2-chloro-2'-deoxyadenosine (CdA) in patients with previously treated chronic lymphocytic leukemia and non-Hodgkin's lymphoma. CdA was given at a fixed dose (5.6 mg/m2/day) as a 2-h intravenous (i.v.) infusion, immediately followed by a 1-h i.v. infusion of CP, for 3 days. The initial daily CP dose was 200 mg/m2, and was escalated by 100 mg/m2 increments in successive cohorts of three to six patients to determine the maximum-tolerated dose (MTD). Additional patients were included at the MTD to extend toxicity and response analysis. Twenty-six patients received 68 cycles of chemotherapy. The MTD of CP after CdA 5.6 mg/m2, was 300 mg/m2. Acute neutropenia was the dose-limiting toxicity of this regimen, which was otherwise well tolerated. Delivery of repeated cycles was not feasible in eight patients (31%) because of prolonged thrombocytopenia. Severe infections were seen in three of 68 cycles (4%). The overall response rate was 58% (15 of 26; 95% CI, 36-76%), with 15% complete responses and 42% partial responses. These data show the feasibility of the association of CdA with CP. Given the response rate observed, further studies of this regimen are warranted in untreated patients, in particular with chronic lymphocytic leukemia and with Waldenström macroglobulinemia.

Hypercalcemia, chronic lymphocytic leukemia and multiple myeloma: uncommon association.

A fifty-nine year old woman is admitted with severe hypercalcemia and other metabolic disorders. The buffy coat showed plasmoblasts in association with chronic lymphocytic leukemia cells (CLL). Immunophenotyping revealed different light chains on CLL cells and in plasmoblasts. We discuss the association of hypercalcemia and CLL, its physiopathology and the distinction with Richter's Syndrome. We also review literature descriptions of the uncommon association of CLL and Multiple Myeloma and raise the question of its clonal origin.

VAD or VMBCP in multiple myeloma refractory to or relapsing after cyclophosphamide-prednisone therapy (protocol MY 85).

263 patients (median age 65+/-10 years) with multiple myeloma were treated with cyclophosphamide-prednisone. Out of this cohort, 103 patients had progressive disease and were randomly assigned to either VAD (vincristine, doxorubicin, dexamethasone; 50 cases) or VMBCP (vincristine, BCNU, cyclophosphamide, melphalan and prednisone; 53 cases). There were no statistical differences between the two groups with the respect to clinical, biological and radiological parameters. There was no difference in survival between the VAD and VMBCP groups. The 4 months response rate was similar in the two groups (50% VAD, 56% VMBCP). With multivariate analysis for survival (Cox model), two factors had a statistically significant impact: Karnofsky index (> 60) and albuminaemia (< 34 g/l). With both Karnofsky index > 60 and albuminaemia > or = 34 g/l, the median survival was 29 months v 2 months with a Karnofsky index < or = 60 and albuminaemia < 34 g/l (P<0.05). In conclusion, VAD or VMBCP had similar activity for salvage treatment in MM refractory or relapsing to first-line treatment with cyclophosphamide-prednisone.

2-Chlorodeoxyadenosine with or without daunorubicin in relapsed or refractory acute myeloid leukemia.

2-Chlorodeoxyadenosine (2-CdA) is a purine analogue which has proved to be active in acute myeloid leukemia (AML), especially in children. In adults, results yielded by 2-CdA alone or with ara-C were less encouraging. Here we report on the efficacy of 2-CdA with or without daunorubicin (DNR) in 19 relapsing or refractory adult AML patients, with a median age of 57 years. 2-CdA was administered as a continuous infusion to all patients at a dose of 0.1 mg/kg per day for 7 days. For 14 patients, DNR was added at a dose of 50 mg/m2 per day on days 5, 6, and 7. Antileukemic activity was observed in all the patients, but no single complete remission was achieved. One patient had a long-lasting partial response (response rate=5%). The remaining patients died of progressive AML (n=7), uncontrollable infection with persistent disease (n=10), and cerebral hemorrhage (n=1). Median survival from start of 2-CdA therapy was 56 days. Long-lasting neutropenia and transfusion-dependent thrombopenia were encountered in all 16 evaluable patients. Grade 4 hepatic toxicity occurred in one patient. Other side effects included nausea in six, mucositis in three, and mental disturbances in three patients. Compared with 2-CdA alone, the addition of DNR to 2-CdA changed neither the response rate nor the toxicities. In conclusion, our data do not support the use of 2-CdA +/- DNR for relapsing or refractory adult AML patients, at least as used in the present regimen.

Ultrastructural distribution of DNA within plant meristematic cell nucleoli during activation and the subsequent inactivation by a cold stress.

We have investigated the precise location of DNA within the meristematic cell nucleolus of Zea mays root cells and Pisum sativum cotyledonary buds, in the course of their activation and induced inactivation following a subsequent treatment at low temperature. For this purpose, we combined the acetylation method, providing an excellent distinction between the various nucleolar components, with the in situ terminal deoxynucleotidyl transferase-immunogold technique, a highly sensitive method for detecting DNA at the ultrastructural level. In addition to the presence of DNA in the condensed chromatin associated with the nucleolus, we demonstrated that a significant label was detected in the nucleolus of quiescent cells in both plant models. Evident labels were also found in the dense fibrillar component of actived nucleoli. Whereas in inactivated nucleoli no significant label was observed within the dense fibrillar component, an intense label was seen over the large heterogeneous fibrillar centres only during inactivation. The granular component was never significantly labelled. These results appear to indicate that the DNA present in the dense fibrillar component of activated nucleoli withdraws from this structure during its inactivation and becomes incorporated in the large fibrillar centres. These observations suggest that in plant cells inactivation of rRNA genes is clearly accompanied by changes in the conformation of ribosomal chromatin.