The COVID-19 pandemic caused by SARS-CoV-2 imposes an urgent need for rapid development of an efficient and cost-effective vaccine, suitable for mass immunization. Here, we show the development of a replication competent recombinant VSV-∆G-spike vaccine, in which the glycoprotein of VSV is replaced by the spike protein of SARS-CoV-2. In-vitro characterization of this vaccine indicates the expression and presentation of the spike protein on the viral membrane with antigenic similarity to SARS-CoV-2. A golden Syrian hamster in-vivo model for COVID-19 is implemented. We show that a single-dose vaccination results in a rapid and potent induction of SARS-CoV-2 neutralizing antibodies. Importantly, vaccination protects hamsters against SARS-CoV-2 challenge, as demonstrated by the abrogation of body weight loss, and  alleviation of the extensive tissue damage and viral loads in lungs and nasal turbinates. Taken together, we suggest the recombinant VSV-∆G-spike as a safe, efficacious and protective vaccine against SARS-CoV-2.

The mechanisms of hematopoietic progenitor cell egress and clinical mobilization are not fully understood. Herein, we report that in vivo desensitization of Sphingosine-1-phosphate (S1P) receptors by FTY720 as well as disruption of S1P gradient toward the blood, reduced steady state egress of immature progenitors and primitive Sca-1 ؉ /c-Kit ؉ /Lin ؊ (SKL) cells via inhibition of SDF-1 release. Administration of AMD3100 or G-CSF to mice with deficiencies in either S1P production or its receptor S1P 1 , or pretreated with FTY720, also resulted in reduced stem and progenitor cell mobilization. Mice injected with AMD3100 or G-CSF demonstrated transient increased S1P levels in the blood mediated via mTOR signaling, as well as an elevated rate of immature c-Kit ؉ /Lin ؊ cells expressing surface S1P 1 in the bone marrow (BM). Importantly, we found that S1P induced SDF-1 secretion from BM stromal cells including Nestin ؉ mesenchymal stem cells via reactive oxygen species (ROS) signaling. Moreover, elevated ROS production by hematopoietic progenitor cells is also regulated by S1P. Our findings reveal that the S1P/S1P 1 axis regulates progenitor cell egress and mobilization via activation of ROS signaling on both hematopoietic progenitors and BM stromal cells, and SDF-1 release. The dynamic cross-talk between S1P and SDF-1 integrates BM stromal cells and hematopoeitic progenitor cell motility. (Blood. 2012;119(11):2478-2488) IntroductionMotility is a key feature of hematopoietic stem and progenitor cells (HSPCs). These cells are continuously released at basal levels from the bone marrow (BM) reservoir to the circulation during steady state homeostasis together with maturing leukocytes, and at increased rates on stress situations, such as bleeding or inflammation. 1,2 The complex process of HSPC trafficking is orchestrated by various cytokines, chemokines, proteolytic enzymes, and adhesion molecules 3-5 through a dynamic interplay between the immune and nervous systems within the bone microenvironment. 1,2,6-8 HSPC mobilization can be clinically induced by a variety of cytokines and drugs, such as granulocyte colony stimulating factor (G-CSF, the most commonly used agent), 9,10 sulfated polysaccharides, 11,12 and recently also by AMD3100. 13,14 Repetitive G-CSF administrations cause mobilization by inducing proliferation and differentiation of HSPC, thus increasing their pool size, accompanied by reduced retention in the BM microenvironment. 15 The chemokine stromal cell-derived factor-1 (SDF-1, also termed CXCL12), which is the most powerful chemoattractant of both human and murine HSPCs, 16,17 and its major receptor CXCR4 are key players in HSPC mobilization. 10,12,13,[18][19][20][21] SDF-1 is transiently increased in the murine BM during G-CSF stimulation followed by its downregulation at both protein 18,22 and mRNA 23 levels, reaching a nadir at the peak of HSPC mobilization. 18 The intensified SDF-1/CXCR4 interactions induce enhanced production of reactive oxygen species (ROS) through activation of the HGF/c-Met path...

Mechanisms governing stress-induced hematopoietic progenitor cell mobilization are not fully deciphered. We report that during granulocyte colony-stimulating factor-induced mobilization c-Met expression and signaling are up-regulated on immature bone marrow progenitors. Interestingly, stromal cell-derived factor 1/CXC chemokine receptor-4 signaling induced hepatocyte growth factor production and IntroductionDuring steady state conditions, adhesive interactions between the bone marrow (BM) stromal cells and primitive hematopoietic cells mostly result in stem cell retention, in a noncycling and nonmotile mode. However, low levels of progenitor cells are continuously released from the BM to the blood circulation as part of homeostasis. This process is dramatically amplified during emergency situations because of damage and cell death, as part of host defense and repair, in response to stress signals, including cytokines such as granulocyte colony-stimulating factor (G-CSF). Repetitive G-CSF stimulations are commonly used in the clinic, mimicking emergency situations to harvest stem and progenitor cells from the circulation for transplantation protocols. 1,2 The BM reservoir of immature and maturing leukocytes is dynamic, replenishing the blood with new cells on demand. These dynamic changes are achieved through a complex interplay between the immune and nervous systems, the bones and the BM microenvironment, involving cytokines, chemokines, proteolytic enzymes, and adhesion molecules. 3 In particular, oscillations in BM levels of stromal cell-derived factor 1 (SDF-1; transiently increased and subsequently degraded) and CXC chemokine receptor-4 (CXCR4) activation play a crucial role in promoting progenitor cell egress. 4,5 The cytokine hepatocyte growth factor (HGF) and its receptor c-Met control complex biologic programs known as "invasive growth" and tumor spreading. 6 Reactive oxygen species (ROS) are constantly generated during intracellular metabolism and in response to cytokines. Although excess ROS can cause oxidative damage to DNA, moderate levels have important roles in cell signaling, regulating different physiologic and pathologic cellular processes, including cell-cycle progression, migration, and invasion. 7 Finally, redox signaling has emerged as an important regulator of hematopoietic stem cell (HSC) self-renewal and lifespan. 8,9 The Forkhead Box, class O (FOXO) family of Forkhead transcription factors is a regulator of oxidative stress. 10 Loss of FOXO function in HSCs results in increased ROS levels, defective maintenance of quiescence, and reduced long-term repopulating ability. 11,12 FOXOs are a direct substrate of the protein kinase Akt, a mammalian target of rapamycin inhibition (mTOR) target, 13 which inactivates them by phosphorylation. 14 In this study, we demonstrate that c-Met expression levels on immature and maturing leukocytes in the BM reservoir are dynamic and dramatically increased when urgent requirements for enhanced leukocyte production and recruitment emerge. Moreover, full c-Me...

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The signal-recognition particle (SRP) mediates the translocation of membrane and secretory proteins across the endoplasmic reticulum upon interaction with the SRP receptor. In trypanosomes, the main RNA molecule is the spliced-leader (SL) RNA, which donates the SL sequence to all messenger RNA through trans-splicing. Here, we show that RNA interference silencing of the SRP receptor (SRa) in Trypanosoma brucei caused the accumulation of SRP on ribosomes and triggered silencing of SL RNA (SLS). SLS was elicited due to the failure of the SL RNAspecific transcription factor tSNAP42 to bind to its promoter. SL RNA reduction, in turn, eliminated mRNA processing and resulted in a significant reduction of all mRNA tested. SLS was also induced under pH stress and might function as a master regulator in trypanosomes. SLS is reminiscent of, but distinct from, the unfolded protein response and can potentially act as a new target for parasite eradication.