The International Prognostic Scoring System (IPSS) for childhood myelodysplastic syndrome (MDS) and juvenile myelomonocytic leukemia (JMML)

The International Prognostic Scoring System (IPSS) for myelodysplastic syndrome (MDS) is based upon weighted data on bone marrow (BM) blast percentage, cytopenia, and cytogenetics, separating patients into four prognostic groups. We analyzed the value of the IPSS in 142 children with de novo MDS and 166 children with juvenile myelomonocytic leukemia (JMML) enrolled in retro- and prospective studies of the European Working Group on childhood MDS (EWOG-MDS). Survivals in MDS and JMML were analyzed separately. Among the criteria considered by the IPSS score, only BM blasts <5% and platelets >100 x 10(9)/l were significantly associated with a superior survival in MDS. In JMML, better survival was associated with platelets >40 x 10(9)/l, but not with any other IPSS factors including cytogenetics. In conclusion, the IPSS is of limited value in both pediatric MDS and JMML. The results reflect the differences between myelodysplastic and myeloproliferative diseases in children and adults.

Retrospektive Analyse des klinischen Verlaufs bei 12 Kindern mit der Verdachtsdiagnose einer essenziellen Thrombozythämie

BACKGROUND

Essential Thrombocythemia (ET) is an acquired myeloproliferative disorder (MPD) characterized by excessive production of platelets. The disorder is usually affecting adults and is rarely diagnosed in children.

PATIENTS AND METHODS

In this retrospective study we describe 12 children aged 5-16 years in whom ET was presumed.

RESULTS

Median follow-up was 59 months (range 10-72). At diagnosis 7 patients had clinical symptoms (syncope, poor concentration, fatigue, abdominal pain and mild bleeding), 5 patients were diagnosed accidentally (operation, allergy, enuresis, pneumonia, routine examination). Median platelet count at diagnosis was 1 325 x 10 (9)/L (range 600-3 050). In 11 cases bone marrow morphology was consistent with ET, one patient had chronic idiopathic myelofibrosis. Cytogenetics were normal in all studied cases. Within 6 months after the initial presentation one patient who was diagnosed accidentally developed thrombosis, another patient had mild bleeding. 8 patients were treated with acetylsalicylic acid (in addition, 1 patient received hydroxyurea, 2 patients received anagrelide). On last follow-up all patients were alive, none had developed leukemia. 5 patients experienced hematological remission. 2 of these children had not received any therapy.

CONCLUSIONS

Many patients had symptoms attributable to ET. The clinical course is heterogeneous with complete normalization of platelets in the absence of cytoreductive therapy in some children. Due to the low incidence of ET in children indications for therapy are unclear and can only be deduced from findings obtained from studies in adults.

Juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia is an aggressive neoplasia of early childhood. Only allogeneic stem cell transplantation (SCT) offers long-term cure. In the absence of an HLA-matched family donor, early SCT from an unrelated donor is the treatment of choice for most children. With clear evidence of a graft-versus-leukemia effect and a high post-transplant relapse rate, the outcome of SCT depends, in part, on the management of immunosuppression during the procedure. The impact of pretransplant cytoreductive treatment, such as intensive chemotherapy, splenectomy, or 13-cis retinoic acid, is unclear. Hypersensitivity for granulocyte-macrophage colony-stimulating factor and pathologic activation of the Ras/MAPK pathway play an important role in the pathophysiology of juvenile myelomonocytic leukemia and provide the opportunity for several novel therapeutic approaches.

Semi-synthetic DNA–protein conjugates: novel tools in analytics and nanobiotechnology

This article reports on the syntheses, characterization and applications of semi-synthetic conjugates composed of nucleic acids, proteins and inorganic nanoparticles. For example, self-assembled oligomeric networks consisting of streptavidin and double-stranded DNA are applicable as reagents in immunoassays, model systems for ion-switchable nanoparticle networks as well as nanometer-scaled ‘soft material’ standards for scanning probe microscopy. Covalent conjugates of single-stranded DNA and streptavidin are utilized as biomolecular adapters for the immobilization of biotinylated macromolecules at solid substrates via nucleic acid hybridization. This ‘DNA-directed immobilization’ allows for reversible and site-selective functionalization of solid substrates with metal and semiconductor nanoparticles or, vice versa, for the DNA-directed functionalization of gold nanoparticles with proteins, such as immunoglobulins and enzymes. This approach is applicable for the detection of chip-immobilized antigens. Moreover, covalent DNA–protein conjugates allow for their selective positioning along single-stranded nucleic acids, and thus for the construction of nanometre-scale assemblies composed of proteins and/or nanoclusters. Examples include the fabrication of functional biometallic nanostructures from gold nanoparticles and antibodies, applicable as diagnostic tools in bioanalytics.

Hematologic features and clinical course of an infant with Pearson syndrome caused by a novel deletion of mitochondrial DNA

OBJECTIVE

Pearson bone marrow-pancreas syndrome (PS) is a rare, usually fatal mitochondrial disorder involving the hematopoietic system in early infancy. Due to the diversity of clinical symptoms, the diagnosis can be difficult. The authors describe a boy with severe hypoplastic anemia in whom extensive clinical, biochemical, and morphologic findings led to the diagnosis of PS, and molecular analysis revealed a novel deletion of mitochondrial DNA from nucleotide position 10.371 to 14.607.

METHODS

The patient is a 2-year-old boy who presented at age 5 months with hypoplastic macrocytic anemia. His first months of life and the family history were uneventful. Extensive pretransfusion evaluations did not reveal a metabolic, infectious, or hematologic-neoplastic etiology, and he had no evidence of exocrine pancreatic insufficiency. However, a second bone marrow aspirate at age 7 months showed a reduced cell number, vacuolated erythroblasts and myeloblasts, and ringed sideroblasts, so PS was suspected.

RESULTS

Additional molecular analysis from the boy's blood leukocytes revealed a deletion of mitochondrial DNA from nucleotide position 10.371 to 14.607, which was absent in his mother's blood cells, consistent with a sporadic mutation as commonly seen in PS. The muscle histology and the respiratory chain enzymes were normal.

CONCLUSIONS

Mitochondriopathies should be considered in children with persistent non-neuromuscular symptoms such as unexplained refractory anemia. Due to the often-fatal course of PS, the rapid detection of mitochondrial DNA deletions is imperative for diagnosis and family counseling.

Juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia is an aggressive neoplasia of early childhood. Only allogeneic stem cell transplantation (SCT) offers a long-term cure. In the absence of an HLA-matched family donor, early SCT from an unrelated donor will be the treatment of choice for most children. With clear evidence of a graft-versus-leukemia effect and a high post-transplant relapse rate, outcome of SCT will depend, in part, on the management of immunosuppression during the procedure. The impact of pretransplant cytoreductive treatment, such as intensive chemotherapy, splenectomy, or 13-cis retinoic acid, is unclear. Hypersensitivity for granulocyte-macrophage colony-stimulating factor and pathologic activation of the Ras/MAPK pathway play an important role in the pathophysiology of juvenile myelomonocytic leukemia and will provide the opportunity for several novel therapy approaches.

A pediatric approach to the WHO classification of myelodysplastic and myeloproliferative diseases

Myelodysplastic and myeloproliferative disorders are rare in childhood and there is no widely accepted system for their diagnosis and classification. We propose minimal diagnostic criteria and a simple classification scheme which, while based on accepted morphological features and conforming with the recent suggestions of the WHO, allows for the special problems of myelodysplastic diseases in children. The classification recognizes three major diagnostic groups: (1) juvenile myelomonocytic leukemia (JMML), previously named chronic myelomonocytic leukemia (CMML) or juvenile chronic myeloid leukemia (JCML); (2) myeloid leukemia of Down syndrome, a disease with distinct clinical and biological features, encompassing both MDS and AML occurring in Down syndrome; and (3) MDS occurring both de novo and as a complication of previous therapy or pre-existing bone marrow disorder (secondary MDS). The main subtypes of MDS are refractory cytopenia (RC) and refractory anemia with excess of blasts (RAEB). It is suggested retaining the subtype of RAEB-T with 20-30% blasts in the marrow until more data are available. Cytogenetics and serial assessments of the patients are essential adjuncts to morphology both in diagnosis and classification.

Nanostructured dna-protein aggregates consisting of covalent oligonucleotide-streptavidin conjugates

Covalent conjugates consisting of streptavidin and a 24-mer single-stranded DNA oligonucleotide have been oligomerized by cross-linking with a 5',5'-bis-biotinylated 169-base-pair double-stranded DNA (dsDNA) fragment. The oligomeric conjugates formed have been analyzed by nondenaturing gel electrophoresis and scanning-force microscopy (SFM). The comparison of analogous oligomers, prepared from native STV and the bis-biotinylated dsDNA fragment, revealed that the covalent STV-oligonucleotide hybrid conjugates self-assemble to generate oligomeric aggregates of significant smaller size, containing on average only about 2.5 times less dsDNA fragments per aggregate. Likely, this is a consequence of electrostatic or steric repulsion between the dsDNA and the single-stranded oligomer covalently attached to the hybrid, as indicated from control experiments. Nevertheless, the single-stranded oligonucleotide moiety within the oligomeric conjugates can be used as a selective molecular handle for further functionalization and manipulation. For instance, it was used for specific DNA-directed immobilization at a surface, previously functionalized with complementary capture oligonucleotides. Moreover, we demonstrate that macromolecules, such as STV and antibody molecules, which are tagged with the complementary oligonucleotide, specifically bind to the supramolecular DNA-STV oligomeric conjugates. This leads to a novel class of functional DNA-protein conjugates, suitable, for instance, as reagents in immuno-PCR or as building blocks in molecular nanotechnology.

Semi-synthetic nucleic acid-protein conjugates: applications in life sciences and nanobiotechnology

Semi-synthetic conjugates of nucleic acids and proteins can be generated by either covalent coupling chemistry, or else by non-covalent biomolecular recognition systems, such as receptor-ligands of complementary nucleic acids. These nucleic acid-protein conjugates are versatile molecular tools which can be applied, for instance, in the self-assembly of high-affinity reagents for immunological detection assays, the fabrication of laterally microstructured biochips containing functional biological groups, and the biomimetic 'bottom-up' synthesis of nanostructured supramolecular devices. This review summarizes the current state-of-the-art synthesis and characterization methods of artificial nucleic acid-protein conjugates, as well as applications and perspectives for future developments of such hybrid biomolecular components in life sciences and nanobiotechnology.

Dendrimer-activated solid supports for nucleic acid and protein microarrays

The generation of chemically activated glass surfaces is of increasing interest for the production of microarrays containing DNA, proteins, and low-molecular-weight components. We here report on a novel surface chemistry for highly efficient activation of glass slides. Our method is based on the initial modification of glass with primary amino groups using a protocol, specifically optimized for high aminosilylation yields, and in particular, for homogeneous surface coverages. In a following step the surface amino groups are activated with a homobifunctional linker, such as disuccinimidylglutarate (DSG) or 1,4-phenylenediisothiocyanate (PDITC), and then allowed to react with a starburst dendrimer that contains 64 primary amino groups in its outer sphere. Subsequently, the dendritic monomers are activated and crosslinked with a homobifunctional spacer, either DSG or PDITC. This leads to the formation of a thin, chemically reactive polymer film, covalently affixed to the glass substrate, which can directly be used for the covalent attachment of amino-modified components, such as oligonucleotides. The resulting DNA microarrays were studied by means of nucleic acid hybridization experiments using fluorophor-labeled complementary oligonucleotide targets. The results indicate that the novel dendrimer-activated surfaces display a surface coverage with capture oligomers about twofold greater than that with conventional microarrays containing linear chemical linkers. In addition, the experiments suggest that the hybridization occurs with decreased steric hindrance, likely a consequence of the long, flexible linker chain between the surface and the DNA oligomer. The surfaces were found to be resistant against repeated alkaline regeneration procedures, which is likely a consequence of the crosslinked polymeric structure of the dendrimer film. The high stability allows multiple hybridization experiments without significant loss of signal intensity. The versatility of the dendrimer surfaces is also demonstrated by the covalent immobilization of streptavidin as a model protein.

Bioorganic applications of semisynthetic DNA-protein conjugates

Semisynthetic DNA-protein conjugates are versatile molecular tools useful, for instance, in the self-assembly of high-affinity reagents for immunological detection assays, the fabrication of highly functionalized laterally microstructured biochips, and the biomimetic "bottom-up" synthesis of nanostructured supramolecular devices. This concept paper summarizes the current state-of-the-art concerning the synthesis, characterization, and applications of such hybrid molecules, and also draws perspectives on future developments.

[Improved treatment results in children with AML: Results of study AML-BFM 93]

BACKGROUND

In the multicenter trial AML-BFM 93 daunorubicin or idarubicin was randomly applied in all patients during induction in combination with cytarabine and etoposide. After induction all patients were stratified to the standard or high risk group. To improve outcome in high risk patients high dose cytarabine and mitoxantrone (HAM) was introduced. The placing of HAM as either the 2nd or 3rd therapy block was randomized to evaluate the efficacy and toxicity accordingly.

PATIENTS AND METHODS

471 children with de novo AML entered the trial AML-BFM 93 (161 standard risk, 310 high risk).

RESULTS

Overall, 387 of 471 (82 %) patients achieved remission, 5-year survival, event free survival (EFS), and disease free survival were 60 % SE 3 %, 51 % SE 2 % and 62 % SE 3 %, respectively. Idarubicin-based induction resulted in a significantly better blast cell reduction in the bone marrow on day 15 (25 of 144=17 % patients with > 5 % blasts compared to 46 of 149=31 % patients after daunorubicin, pchi(2)=0.01). This was, however, mainly seen in high risk patients treated with idarubicin (19 % vs. 38 %, pchi(2)=0.007). Cardiotoxicity, WHO grade 1 - 3 shortening fraction reduction after induction occurred in 6 % patients in both arms. In the total group of patients probabilities of five years event-free survival and disease-free survival were similar for patients treated with daunorubicin or idarubicin. However, in patients presenting with more than 5 % blasts on day 15 there was a trend for a better outcome after treatment with idarubicin (p logrank 0.06). Outcome in high risk patients was superior in study 93 compared to study 87 (remission rate and 5-year pEFS in study AML-BFM 93 vs. study 87: 78 % vs. 68 %, p=0.007, and 44 % vs. 31 %, p logrank=0.01). The placing of HAM as the 2nd or 3rd therapy block was of minor importance. However, patients who received the daunorubicin treatment during induction benefited from early HAM.

CONCLUSION

Compared to study AML-BFM 87 treatment results in study AML 93 improved significantly in high risk patients. This can partly be contributed to the better response on day 15 after idarubicin induction but is mainly due to the introduction of HAM.

Mucinous cystadenoma of the ovary in a 15-year-old girl

Benign neoplasms of the ovary originating from epithelial tissue are common tumors in adult women. They are, however, rarely seen in children or adolescent girls. Here the authors present a case of an ovarian mucinous cystadenoma in a premenarchal girl. To our knowledge, there are only 5 other cases reported in the literature.

Sensitivity of Ewing's sarcoma to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is able to kill transformed cells. We have studied the expression and functionality of the TRAIL apoptotic pathway in Ewing's sarcoma. We demonstrate that tumors from patients with Ewing's sarcoma express receptors TRAIL-R1 and -R2. Using a panel of nine Ewing's sarcoma cell lines TRAIL could induce apoptosis in seven cell lines. Preincubation with interferon-gamma rendered the two resistant cell lines sensitive. TRAIL was the most potent inducer of apoptosis when compared to Fas ligand or TNF. TRAIL-mediated apoptosis could be inhibited by various caspase-inhibitors. No difference in the surface expression of TRAIL-receptors was observed between sensitive and resistant cell lines. Also, all cell lines had similar levels of expression of Flice-like inhibitory protein (FLIP) on immunoblot. However, the two resistant cell lines had only very low level expression of caspase 8 on RNA and protein level. In summary, we show that Ewing's sarcoma expresses receptors for TRAIL, and that cells are exquisitely sensitive to TRAIL-mediated apoptosis. These results may warrant clinical trials with TRAIL in Ewing's sarcoma once the safety of TRAIL for humans has been established.

Nucleic acid supercoiling as a means for ionic switching of DNA--nanoparticle networks

Oligomeric nanoparticle networks, generated by the self-assembly of bis-biotinylated double-stranded DNA fragments and streptavidin, have been studied by scanning force microscopy (SFM). SFM imaging revealed the presence within the networks of irregular thick DNA molecules, which were often associated with distinct, Y-shaped structural elements. Closer analysis revealed that the Y structures are formed by condensation (thickening and shortening) of two DNA fragments, most likely through the supercoiling of two DNA molecules bound to adjacent binding sites of the streptavidin particle. The frequency of supercoiling was found to be dependent on the ionic strength applied during the immobilization of the oligomeric networks on mica surfaces. Potential applications of the structural changes as a means for constructing ion-dependent molecular switches in nanomaterials are discussed.

Evidence for linkage of familial Diamond-Blackfan anemia to chromosome 8p23.3-p22 and for non-19q non-8p disease

Diamond-Blackfan anemia (DBA) is a rare congenital hypoplastic anemia that usually presents early in infancy and is inherited in 10% to 20% of cases. Linkage analysis has shown that DBA in many of both dominant and recessive DBA families mapped to chromosome 19q13.2 leading to the cloning of a gene on chromosome 19q13.2 that encodes a ribosomal protein, RPS19. However, subsequently, mutations of the RPS19 gene have only been identified in 25% of all patients with DBA. This study analyzed 14 multiplex DBA families, 9 of which had 19q13.2 haplotypes inconsistent with 19q linkage. A genome-wide search for linked loci suggested the presence of a second DBA locus in a 26.4-centimorgan (cM) interval on human chromosome 8p. Subsequently, 24 additional DBA families were ascertained and all 38 families were analyzed with additional polymorphic markers on chromosome 8p. In total, 18 of 38 families were consistent with linkage to chromosome 8p with a maximal LOD score with heterogeneity of 3.55 at D8S277 assuming 90% penetrance. The results indicate the existence of a second DBA gene in the 26.4-cM telomeric region of human chromosome 8p23.3-p22, most likely within an 8.1-cM interval flanked by D8S518 and D8S1825. Seven families were inconsistent with linkage to 8p or 19q and did not reveal mutations in the RPS19 gene, suggesting further genetic heterogeneity. (Blood. 2001;97:2145-2150)

Idarubicin improves blast cell clearance during induction therapy in children with AML: results of study AML-BFM 93. AML-BFM Study Group

In the randomized trial AML-BFM 93 we compared 60 mg/m2/day daunorubicin with 12 mg/m2/day idarubicin for 3 days each, combined with cytarabine and etoposide during induction. Results showed a significant better blast cell reduction in the bone marrow on day 15 in patients of the idarubicin arm (25 of 144 = 17% of patients with > or = 5% blasts compared to 46 of 149 = 31% of patients after daunorubicin, Pchi2 = 0.01). This was, however, mainly seen in high risk patients treated with idarubicin (19% vs 38%, Pchi2 = 0.007). Cardiotoxicity, WHO grade 1-3 shortening fraction reduction after induction occurred in 6% patients in both arms. Bone marrow toxicity differed slightly with a median recovery time of neutrophils >500/microl of 25 days (daunorubicin) compared to 27 days (idarubicin), P = 0.05. In the total group of patients probabilities of 5 years event-free survival and disease-free survival were similar for patients treated with daunorubicin or idarubicin (49% +/- 4% vs 55% +/- 4% and 57% +/- 4% vs 64% +/- 4%, P logrank 0.29 and 0.15, respectively). However, in patients presenting with more than 5% blasts on day 15 there was a trend for a better outcome after treatment with idarubicin (P logrank 0.06). Together with the early effect seen for high risk patients these results indicate a better efficacy of idarubicin than of daunorubicin during induction with a similar rate of toxicity.

Self-assembled nanostructures based on DNA: towards the development of nanobiotechnology

DNA is a promising construction material for the supramolecular 'bottom-up' engineering of artificial nanostructured devices. The use of DNA for the selective positioning of macromolecular components, the fabrication of nanostructured DNA scaffolds, as well as the DNA-templated synthesis of nanometer-sized and mesoscopic complexes, consisting of inorganic and bioorganic compounds, are exciting areas of current research.

Frequency, natural course, and outcome of neonatal neutropenia

OBJECTIVE

We studied the frequency, onset, duration, and prognosis of neutropenia in a neonatal hospital population to define subgroups of neonates who might benefit from cytokine therapy.

STUDY DESIGN

The study comprised of 2 parts: in a first retrospective study (I), clinical data of neonates with sepsis (n = 168) were analyzed; in a second retrospective and prospective study (II), clinical data of neonates with neutropenia (n = 131) were studied. In study I, the analysis focused on septic neonates with and without neutropenia, and in study II, on neutropenic neonates with and without primary infection. In the prospective part of study II, granulocyte colony-stimulating factor (G-CSF) plasma concentrations were analyzed in neutropenic neonates (n = 32).

RESULTS

Thirty-eight percent of septic neonates were neutropenic. Neutropenia lasted <24 hours in 75% of these patients. It was recorded before or on the day of the clinical onset of sepsis in 87% of patients. The overall incidence of neutropenia was 8.1%. Seventy-two percent of these neutropenic episodes occurred in patients without infection at the time of diagnosis of neutropenia. In the latter patients, the risk of infection secondary to neutropenia was 9%, affecting only premature neonates. Neutropenic episodes without infection were of longer duration and were accompanied by lower G-CSF plasma concentrations than were episodes associated with infection. The percentage of neutropenic episodes primarily associated with infection was higher in VLBW neonates than in term neonates. Likewise, the risk of infection secondary to neutropenia (27%) and the mortality attributable to infection and neutropenia (28%) were significantly higher than in term newborns.

CONCLUSION

Considering the priming time for induction of neutrophilia, G-CSF therapy in neonates presenting with severe bacterial infection and neutropenia may be too late. In contrast, neutropenic very low birth weight neonates without primary infection might benefit from prophylactic G-CSF treatment.neonatal sepsis, neutropenia, granulocyte colony-stimulating factor.

Toxicity and effectiveness of high-dose idarubicin during AML induction therapy: results of a pilot study in children

BACKGROUND

Idarubicin (IDR) is one of the most effective, but also toxic drugs in the treatment of AML. The standard dose used in children and adults is 8-12 mg/m2 during induction.

PATIENTS AND METHODS

To improve outcome, we increased the IDR dose from 12 mg/m2 (standard dose in study AML-BFM 93), applied over three days during induction therapy (AIE = Ara-C, Idarubicin, Etoposide) to 14 mg/m2 in a pilot study including 17 patients (16 with de novo AML, one with secondary AML). Outcome and toxicities were compared with the other patients of study AML-BFM 93, treated with 3 x 12 mg/m2 IDR or 6 x 30 mg/m2 daunorubicin (DNR).

RESULTS

Patients of the pilot study achieved a good blast cell reduction in the bone marrow on day 15, a high CR rate of 94% and a low relapse rate (3/17 pts.), however, not significantly different to the IDR (12 mg/m2) group. Hematological toxicity was high, median duration until neutrophil recovery > 500/microliter was 25.0 (12-66) days, and similar to the IDR (12 mg/m2) and DNR groups. Duration of thrombocytopenia (time to > 20,000/microliter) was 21 (10-66) days in the pilot study compared to 19 (7-26) days in DNR patients (p = 0.08). Four of 17 pilot patients presented with severe WHO grades 3/4 of mucositis during induction. One patient died in long-lasting aplasia after the 3rd treatment block.

CONCLUSION

Results of this pilot study show that the IDR 14 mg/m2 regimen was effective but also toxic. According to our results which, however, are based on small patient numbers, an improved outcome compared to the IDR 12 mg/m2 regimen seems to be unlikely, therefore the possibly increased toxicity might not be acceptable.

Recurrent B-cell non-Hodgkin's lymphoma in two brothers with X-linked lymphoproliferative disease without evidence for Epstein-Barr virus infection

We present two male siblings suffering from recurrent manifestations of B-cell non-Hodgkin's lymphoma (NHL) and recurrent infections of the lower respiratory tract associated with bronchiectasis. Immunodeficiency could not be demonstrated by any laboratory investigation. In both patients, lymphomas developed without evidence for Epstein-Barr virus (EBV) infection, i.e. no antibody response to EBV-specific antigens, negative EBV-PCR (polymerase chain reaction) in peripheral blood cells, and absence of latent membrane protein (LMP) and EBV-encoded RNA (EBER) in lymphoma cells. Molecular analysis of the SH2D1A, the gene for X-linked lymphoproliferative disease (XLP) led to the identification of a deletion in the first exon in both patients. Therefore, we postulate that the genetic defect and the following dysregulation of the B-/T-cell interaction rendered these patients susceptible to the early onset of B-cell NHL and that EBV infection is not an obligate prerequisite.

Evaluation of single-stranded nucleic acids as carriers in the DNA-directed assembly of macromolecules

Current developments in nanosciences indicate that the self-assembly of macromolecules, such as proteins or metallic nanoclusters, can be conveniently achieved by means of nucleic acid hybridization. Within this context, we here report on the evaluation of single-stranded nucleic acids to be utilized as carrier backbones in DNA-directed self-assembly. A microplate solid-phase hybridization assay is described which allows rapid experimental determination of the hybridization efficiencies of various sequence stretches within a given nucleic acid carrier strand. As demonstrated for two DNA fragments of different sequence, the binding efficiencies of several oligonucleotides depend on the formation of specific secondary structure elements within the carrier molecule. A correlation of sequence-specific hybridization capability with modeled secondary structure is also obvious from experiments using the fluorescence gel-shift analysis. Electrophoretic studies on the employment of helper oligonucleotides in the formation of supramolecular conjugates of several oligonucleotide-tagged proteins indicate, that structural constraints can be minimized by disruption of intramolecular secondary structures of the carrier molecule. To estimate the influences of the chemical nature of the carrier, gel-shift experiments are carried out to compare a 170mer RNA molecule with its DNA analogue. Ternary aggregates, containing two protein components bound to the carrier, are formed with a greater efficiency on the DNA instead of the RNA carrier backbone.