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SUMMARY: Cellular therapeutic agents considerably contribute to the optimal treatment of patients with hematological malignancies such as leukemia or nonhematological disorders. Over the last 50 years especially the transplantation of autologous and allogeneic stem cells from different sources after high-dose or myeloablative chemotherapy became a well-established standard therapy that cures or alleviates the symptoms in more than 50,000 patients/year worldwide. In the near future, the current progress in fundamental research on stem cells and immunobiology will allow for the clinical implementation of novel advanced cellular therapies, including gene therapeutic options. The European and German legislation have realized the need of international regulations for improved standardization and harmonization of stem cell transplants, associated cell-therapeutic agents as well as various tissue-engineered preparations in the emerging field of regenerative medicine. The Tissue Directive 2004/23/EC, issued and ratified by the European Parliament in March 2004, and its national transition into the German Tissue Act which came into force in July 2007 define the quality and safety standards for the donation, procurement, testing, processing, preservation, storage, and distribution of human tissues and cells. These standards are of high relevance to ensure the efficient prevention of the transmission of viral and nonviral infectious pathogens and to achieve the same safeguards as in the population's blood supply. This review discusses the pros and cons of the new legislation and argues for keeping the administrative and regulative demands in reasonable limits and for offering innovative approaches of cellular therapies to the European citizens.

Actin polymerization is a key process for many cellular events during development. To a large extent, the formation of filamentous actin is controlled by the WASP and WAVE proteins that activate the Arp2/3 complex in different developmental processes. WAVE function is regulated through a protein complex containing Sra1, Kette and Abi. Using biochemical, cell biological and genetic tools, we show here that the Abi protein also has a central role in activating WASP-mediated processes. Abi binds WASP through its carboxy-terminal domain and acts as a potent stimulator of WASP-dependent F-actin formation. To elucidate the biological function of abi in Drosophila melanogaster, we studied bristle development, a process known to require wasp function. Reduction of abi function leads to a loss of bristles similar to that observed in wasp mutants. Activation of Abi results in the formation of ectopic bristles, a phenotype that is suppressed by a reduction of wasp activity but is not affected by the reduction of wave function. Thus, in vivo Abi may set the balance between WASP and WAVE in different actin-based developmental processes.

Regulation of growth cone and cell motility involves the coordinated control of F-actin dynamics. An important regulator of F-actin formation is the Arp2/3 complex, which in turn is activated by Wasp and Wave. A complex comprising Kette/Nap1, Sra-1/Pir121/CYFIP, Abi and HSPC300 modulates the activity of Wave and Wasp. We present the characterization of Drosophila Sra-1 (specifically Rac1-associated protein 1). sra-1 and kette are spatially and temporally co-expressed,and both encoded proteins interact in vivo. During late embryonic and larval development, the Sra-1 protein is found in the neuropile. Outgrowing photoreceptor neurons express high levels of Sra-1 also in growth cones. Expression of double stranded sra-1 RNA in photoreceptor neurons leads to a stalling of axonal growth. Following knockdown of sra-1function in motoneurons, we noted abnormal neuromuscular junctions similar to what we determined for hypomorphic kette mutations. Similar mutant phenotypes were induced after expression of membrane-bound Sra-1 that lacks the Kette-binding domain, suggesting that sra-1 function is mediated through kette. Furthermore, we could show that both proteins stabilize each other and directly control the regulation of the F-actin cytoskeleton in a Wasp-dependent manner.