Frape-1 and Frape-3: two different recombinant retroviruses encoding the same human marker gene

Selective in vitro expansion and efficient retroviral transduction of human CD34+ CD38- haematopoietic stem cells

Ex vivo expansion of primitive human haematopoietic stem cells (HSC) is clinically relevant for stem cell transplantation and gene therapy. Here, we demonstrate the selective expansion of CD34+CD38- cells from purified CD34+ cells upon stimulation with Flt3-ligand, stem cell factor and thrombopoietin. Over a 100-fold (range 80 to 128-fold) expansion of CD34+CD38- cells was observed with bone marrow and cord blood (CB). The expanded CD34+CD38- cells remained negative for lineage-specific markers and could be induced to differentiate into granulocytes, monocytes, megakaryocytes, erythrocytes, and T and B-lymphocytes in vitro. Lineage differentiation assays with single CD34+CD38- cells showed no loss of multilineage potential of expanded cells after ex vivo culture. We also demonstrated that the increase in frequency of CD34+CD38- cells was not as a result of the downregulation of CD38 expression during the culture. Quantitative analysis showed that the number of 6 week cobblestone area forming cells (CAFCwk6), a measure of proliferating HSC, in cytokine-stimulated CD34+ cells were increased by 20-fold. Expanded CD34+CD38- cells could be transduced efficiently with retroviruses encoding the low affinity nerve growth factor receptor (LNGFR) marker gene (17% to 44%, mean 27%), resulting in long-lasting expression of retroviral-encoded genes in progeny HSC and differentiated progenitors. We conclude that the combination Flt3-ligand (FL), stem cell factor and thrombopoietin (TPO) induced strong ex vivo proliferation of CD34+CD38- cells and that the absolute number of expanded cells with stem cell activity increased substantially in this population.

Contaminants from the transplant contribute to intimal hyperplasia associated with microvascular endothelial cell seeding

OBJECTIVES

seeding prosthetic grafts with fat-derived microvascular endothelial cells (MVEC) results not only in a non-thrombogenic EC layer, but also in intimal hyperplasia. Here we investigated incidence, composition, progression, and cause of this intimal hyperplasia.

DESIGN

EPTFE grafts with MVEC were implanted as carotid interpositions in six dogs with 1 month, and in three dogs with 4, 8 and 12 months follow-up. Grafts seeded without cells, implanted in the contralateral carotid, served as a control. In another three dogs labelled cells were seeded to investigate the contribution of the seeded cells (2-3 weeks).

MATERIALS AND METHODS

MVEC were isolated from the falciform ligament. Cells were pressure seeded on ePTFE grafts. Labelling was performed using retroviral gene transduction. The grafts were analysed with immunohistochemical techniques.

RESULTS

after 1 month, all patent non-seeded grafts (5/6) showed fibrin and platelet deposition, and all patent seeded grafts (5/6) were covered with a confluent endothelial monolayer on top of a multilayer of myofibroblasts, elastin and collagen. After long term follow-up, all non-seeded grafts were occluded, all patent seeded grafts (4 and 12 months) were covered with an EC-layer with intimal hyperplasia underneath. The thickness of the intima did not progress after 1 month. Transduced cells were found in the endothelial monolayer, hyperplastic intima and luminal part of the prosthesis.

CONCLUSIONS

MVEC seeding in dogs results in intimal hyperplasia in all patent grafts, which contains myofibroblasts. Contaminants from the transplant contribute to this intimal hyperplasia.

Gene transfer to induce angiogenesis in myocardial and limb ischaemia

Stimulation of angiogenesis/arteriogenesis by gene transfer methods offers hope for treating patients with myocardial and peripheral limb ischaemia who are not candidates for standard revascularisation procedures. Preclinical studies showed that adenoviral and plasmid vectors encoding various angiogenic cytokines were capable of inducing functionally significant angiogenesis in vitro and in animal models of chronic myocardial ischaemia. Early clinical studies using VEGF121-, FGF-4- and VEGF165-encoding vectors showed a reasonable safety profile with promising results. However, significant advances in vector technology including regulatable and longer-term expression, delivery strategies (local and organ/tissue specific), clinical trial design, and outcome measure development are needed before this investigational treatment becomes reality.

Gene transfer for angiogenesis in coronary artery disease

Angiogenesis is a promising novel therapeutic strategy to provide new venues for blood flow in patients with severe ischemic heart and peripheral vascular disease, who are not candidates for standard revascularization strategies. We describe the underlying mechanisms involved in physiologic and therapeutic angiogenesis, underscoring the relative importance of vasculogenesis, angiogenesis, and arteriogenesis. We then present the various gene transfer vectors including plasmid, viral, and cell-based vectors, and various delivery modalities. The available preclinical data are presented, followed by a description of preliminary clinical experience, with an emphasis on the preliminary nature of these results, which address safety and not efficacy. Finally, we discuss the promises and pitfalls of clinical angiogenesis and gene transfer studies, stressing the importance of proper design of clinical trials and adequate protection of research subjects.

Wnt signaling is required for thymocyte development and activates Tcf-1 mediated transcription

T cell factor / lymphocyte enhancer factor (Tcf/Lef) transcription factors complex with the transcriptional co-activator beta-catenin to transduce Wnt signals in a variety of developmental systems. The prototypic family member Tcf-1 is highly expressed in T lineage cells. Tcf1-/- mice are defective in cell cycling of early thymocyte stages. Here, we show that the interaction of beta-catenin with Tcf-1 is required for full thymocyte development. This interaction may be established by signals mediated by Wnt1 and Wnt4, leading to increased Tcf-dependent transcriptional activity in thymocytes, as demonstrated in Tcf-LacZ reporter mice. Transduction of fetal thymocytes with Wnt1 and Wnt4 results in increased survival in an in vitro cell culture system. Retroviral expression of soluble Wnt receptor mutants that block Wnt signaling inhibits thymocyte development. These results imply an important role for the Wnt cascade in thymocyte development.