Overexpression of tumstatin in genetically modified megakaryocytes changes the proangiogenic effect of platelets

Background Thrombocytopenia is a common side effect of tumor chemotherapy, the main management approach to which is based on platelet ( PLT ) transfusion. However, PLTs , containing angiogenesis regulators, play a major role in boosting tumor growth and metastasis. The purpose of the study was to determine whether PLTs have the capacity to overexpress tumstatin by modified megakaryocyte ( MK ) and PLT precursors using lentivirus‐mediated gene transfer, which might lead to alteration in proangiogenic effect of PLTs. Study Design and Methods CD 34+ hematopoietic stem cells ( HSCs ) were transduced with recombinant lentivirus carrying tumstatin and induced to produce MK s and PLTs in the culture medium containing a cytokine cocktail. Flow cytometry and aggregation test were used to detect the generation and function of MK s and PLTs . W estern blot analysis and confocal microscopy were applied to examine the expression and distribution of tumstatin in transgenic MK s and PLTs . Capillary tube formation of human umbilical vein endothelial cells ( HUVECs ) was used to evaluate the inhibitory effect of transgenic PLTs . Results CD 34+ HSCs can be efficiently transduced with lentivirus vectors and successfully differentiated into MK s and PLTs . Large amounts of functional MK s and PLTs could be generated and had correct biologic characteristics. The tests demonstrated the feasibility of tumstatin expression in MK s and PLTs under control of the cytomegalovirus promoter, that thus tumstatin was stored in the α‐granules of PLTs , and that the releasate of thrombin or A 543 cell–stimulated transgenic PLTs obviously inhibited the growth of capillary tube network structures of HUVECs . Conclusion Gene‐modified CD 34+ HSCs not only successfully differentiated into MK s and PLTs but also expressed tumstatin protein. Release of tumstatin in transgenic PLT granules led to antiangiogenic effect of PLTs .