Enhancing RNA repair efficiency by combining trans-splicing ribozymes that recognize different accessible sites on a target RNA.

Recent reports have demonstrated that trans-splicing ribozymes can be employed to repair mutant RNAs. One key factor that influences RNA repair efficiency is the accessibility of the substrate RNA for ribozyme binding, which is complicated by the fact that RNAs may assume multiple conformations and have proteins bound to them in vivo. Here we describe a strategy to map accessible sites on sickle beta-globin (beta(s)-globin) transcripts in vitro and in vivo and to use this information to enhance RNA repair efficiency. Two sites upstream of the sickle mutation were identified as accessible in some fraction of the beta-globin RNA by mapping with a ribozyme library and the accessibility of those sites was assessed by in vitro cleavage analyses. Ribozymes targeting either site could only convert a certain fraction of the beta(s)-globin RNA to product but not drive the reaction to completion. However, cleavage and splicing reactions were driven further toward completion when the two ribozymes were both added to the reactions, suggesting that the substrate RNA is present in multiple conformations in vitro. These two ribozymes were each able to repair beta(s)-globin transcripts in erythrocyte precursors derived from peripheral blood from individuals with sickle cell disease. Moreover, the relative accessibility of the targeted sites in vivo is as predicted by mapping and in vitro analyses. These results demonstrate that this novel RNA mapping strategy represents an effective means to determine the accessible regions of target RNAs and that combinations of trans-splicing ribozymes can be employed to enhance RNA repair efficiency of clinically relevant transcripts such as beta(s)-globin RNA.

An in vitro system for efficiently evaluating gene therapy approaches to hemoglobinopathies.

A variety of gene therapy strategies are under development for the treatment of sickle cell anemia and other hemoglobinopathies. A number of alternative vectors have been developed to transfer and express the beta-globin gene and other therapeutic molecules, but none has resulted in efficient transduction and stable long-term expression in primary hematopoietic cells. One reason for this problem is that most vectors are initially evaluated in immortalized cell lines which may not faithfully recapitulate the biology of primary erythroid cells. In order to provide a more relevant system for efficiently evaluating alternative vector constructs for beta-globin disorders, we have developed (1) a simple method for generating primary human red blood cell (RBC) precursors in liquid culture established with mononuclear cells obtained from normal donors as well as patients with Hb SC disease; (2) a high titer retroviral vector which can be easily modified to optimize gene transfer and transgene expression; and (3) methods for transducing the RBC precursors at high efficiency. The development of simple and efficient methods and reagents for generating and transducing primary human RBC precursors provides a facile and effective means for screening alternative gene therapy strategies. Gene Therapy (2000) 7, 215-223.

Graft-versus-leukemia-induced complete remission following unrelated umbilical cord blood transplantation for acute leukemia.

A 15-year-old female received an unrelated three of six HLA antigen matched umbilical cord blood (UCB) transplant for refractory, relapsed T-cell ALL. Conditioning consisted of TBI, melphalan, and anti-thymocyte globulin (ATG), with cyclosporin A (CsA) and solumedrol for GVHD prophylaxis. She engrafted and a day 34 bone marrow aspirate showed 100% donor cells and no evidence of leukemia. The post-transplant course was complicated by mild grade I acute GVHD involving skin, and limited chronic GVHD of the gut which resolved with the addition of 1 mg/kg/day of steroids to her CsA prophylaxis. One hundred and ninety days after transplantation the patient developed pancytopenia and was subsequently found to have a leukemic relapse. Immunosuppression was discontinued and she was started on G-CSF and erythropoietin. Moderate skin and gut GVHD developed which was treated with both topical and low-dose oral steroids. Over the next few weeks she became transfusion independent and a follow-up bone marrow aspirate showed complete remission. She continued in complete remission for 4 months, at which time localized leukemic relapse was found in a soft tissue breast mass in spite of continued bone marrow remission. While the patient ultimately died of progressive disease, this case demonstrates that mismatched UCB in conjunction with G-CSF is capable of generating a GVL effect that can induce a complete remission.

Sebaceous gland carcinoma: a subtle second malignancy following radiation therapy in patients with bilateral retinoblastoma.

BACKGROUND: Second primary malignancies are common after bilateral retinoblastoma; their estimated incidence has been as high as 51% 50 years after diagnosis. Fifteen patients who developed sebaceous gland carcinoma after radiation therapy have been reported in the literature, five of whom were treated for bilateral retinoblastoma. METHODS: The authors conducted a retrospective chart review of patients treated for bilateral retinoblastoma at Duke University Medical Center who later developed sebaceous gland carcinoma. RESULTS: This article reports two patients who developed sebaceous gland carcinoma after radiation therapy for bilateral retinoblastoma. CONCLUSIONS: Delay in diagnosis is often associated with sebaceous gland carcinoma. Because high mortality is observed with metastatic disease, the recognition of this association is important for anyone who follows patients with a history of bilateral retinoblastoma or prior cranial radiation therapy.

Ribozyme-mediated repair of sickle beta-globin mRNAs in erythrocyte precursors.

Sickle cell anemia is the most common heritable hematological disease, yet no curative treatment exists for this disorder. Moreover, the intricacies of globin gene expression have made the development of treatments for hemoglobinopathies based on gene therapy difficult. An alternative genetic approach to sickle cell therapy is based on RNA repair. A trans-splicing group I ribozyme was used to alter mutant beta-globin transcripts in erythrocyte precursors derived from peripheral blood from individuals with sickle cell disease. Sickle beta-globin transcripts were converted into messenger RNAs encoding the anti-sickling protein gamma-globin. These results suggest that RNA repair may become a useful approach in the treatment of genetic disorders.

Tumor-elicited polymorphonuclear cells, in contrast to "normal" circulating polymorphonuclear cells, stimulate invasive and metastatic potentials of rat mammary adenocarcinoma cells.

Circulating polymorphonuclear cell (PMN) levels rise in proportion to the metastatic potential of the tumor in 13762NF mammary adenocarcinoma tumor-bearing rats. These tumor-elicited PMNs (tcPMNs) secrete high levels of the basement-membrane-degrading enzymes, type IV collagenase and heparanase, suggesting that metastatic tumor cells stimulate neutrophilia so that the tcPMNs might assist tumor cell extravasation during metastasis. To test this hypothesis, purified proteose peptone-elicited PMNs from peritoneal exudate, circulating normal PMNs, and tcPMNs were evaluated for their effects on in vitro invasive and in vivo metastatic potentials of syngeneic 13762NF mammary adenocarcinoma tumor cells. tcPMNs caused a dose-dependent increase in invasion through a reconstituted basement membrane barrier in an in vitro invasion assay. At PMN:tumor cell ratios of 30:1, invasion potential significantly (P less than 0.05) rose to 26-fold, 40-fold, and 37-fold for poorly metastatic MTLn2 cells, highly metastatic MTLn3 cells, and moderately metastatic MTF7 cells, respectively. In contrast, purified proteose peptone-elicited PMNs and circulating normal PMNs did not significantly alter invasive potential. Intravenous coinjections of purified proteose peptone-elicited PMNs did not change the number of experimental lung metastases, but tcPMNs at ratios to 50:1 significantly raised the mean number of metastases 23-fold for MTLn2, 3- to 4-fold for MTLn3, and 1.6- to 1.8-fold for MTF7. These results demonstrate that tcPMNs contribute to the metastatic propensity of mammary adenocarcinoma clones by increasing efficiency of invasion through basement membrane.