Human megakaryocytic microparticles induce de novo platelet biogenesis in a wild-type murine model

Platelet transfusions are used to treat idiopathic or drug-induced thrombocytopenia. Platelets are an expensive product in limited supply, with limited storage and distribution capabilities because they cannot be frozen. We have demonstrated that, in vitro, human megakaryocytic microparticles (huMkMPs) target human CD34(+) hematopoietic stem and progenitor cells (huHSPCs) and induce their Mk differentiation and platelet biogenesis in the absence of thrombopoietin. In this study, we showed that, in vitro, huMkMPs can also target murine HSPCs (muHSPCs) to induce them to differentiate into megakaryocytes in the absence of thrombopoietin. Based on that, using wild-type BALB/c mice, we demonstrated that intravenously administering 2 x 10(6) huMkMPs triggered de novo murine platelet biogenesis to increase platelet levels up to 49% 16 hours after administration. huMkMPs also largely rescued low platelet levels in mice with induced thrombocytopenia 16 hours after administration by increasing platelet counts by 51%, compared with platelet counts in thrombocytopenic mice. Normalized on a tissue-mass basis, biodistribution experiments show that MkMPs localized largely to the bone marrow, lungs, and liver 24 hours after huMkMP administration. Beyond the bone marrow, CD41(+) (megakaryocytes and Mk-progenitor) cells were frequent in lungs, spleen, and especially, liver. In the liver, infused huMKMPs colocalized with Mk progenitors and muHSPCs, thus suggesting that huMkMPs interact with muHSPCs in vivo to induce platelet biogenesis. Our data demonstrate the potential of huMkMPs, which can be stored frozen, to treat thrombocytopenias and serve as effective carriers for in vivo, target-specific cargo delivery to HSPCs.