Immunization with a killed or inactivated viral vaccine provides significant protection in animals against challenge with certain corresponding pathogenic coronaviruses (CoVs). However, the promise of this approach in humans is hampered by serious concerns over the risk of leaking live severe acute respiratory syndrome (SARS) viruses. In this study, we generated a SARS vaccine candidate by using the live-attenuated modified vaccinia virus Ankara (MVA) as a vector. The full-length SARS-CoV envelope Spike (S) glycoprotein gene was introduced into the deletion III region of the MVA genome. The newly generated recombinant MVA, ADS-MVA, is replication incompetent in mammalian cells and highly immunogenic in terms of inducing potent neutralizing antibodies in mice, rabbits, and monkeys. After two intramuscular vaccinations with ADS-MVA alone, the 50% inhibitory concentration in serum was achieved with reciprocal sera dilutions of more than 1,000-to 10,000-fold in these animals. Using fragmented S genes as immunogens, we also mapped a neutralizing epitope in the region of N-terminal 400 to 600 amino acids of the S glycoprotein (S400-600), which overlaps with the angiotensin-converting enzyme 2 (ACE2) receptor-binding region (RBR; S318-510). Moreover, using a recombinant soluble RBR-Fc protein, we were able to absorb and remove the majority of the neutralizing antibodies despite observing that the full S protein tends to induce a broader spectrum of neutralizing activities in comparison with fragmented S proteins. Our data suggest that a major mechanism for neutralizing SARS-CoV likely occurs through blocking the interaction between virus and the cellular receptor ACE2. In addition, ADS-MVA induced potent immune responses which very likely protected Chinese rhesus monkeys from pathogenic SARS-CoV challenge.
Most of the SARS-CoV-infected patients spontaneously recovered without clinical intervention while a small percentage succumbed to the disease. Here, we characterized temporal changes in N protein-specific and S glycoprotein-specific neutralizing antibody (Nab) responses in infected patients who have either recovered from or succumbed to SARS-CoV infection. Recovered patients were found to have higher and sustainable levels of both N protein-specific and S glycoprotein-specific Nab responses, suggesting that antibody responses likely play an important role in determining the ultimate disease outcome of SARS-CoV-infected patients.
Summary
Maturation of a vascular plexus is a critical and yet incompletely understood process in organ development, and known maturation factors act universally in all vascular beds. In this study, we show that CXCL12 is an organ-specific maturation factor of particular relevance in coronary arterial vasculature. In vitro, CXCL12 does not influence nascent vessel formation but promotes higher order complexity of preinitiated vessels. In the heart, CXCL12 is expressed principally by the epicardium and its receptor CXCR4 is expressed by coronary endothelial cells. CXCL12 is not a chemotactic signal for endothelial cell migration, but rather acts in a paracrine manner to influence the maturation of the coronary vascular plexus. Mutants in CXCL12 signaling show an excess of immature capillary chains and a selective failure in arterial maturation, and become leaky with the onset of coronary perfusion. Failed maturation of the coronary system explains the late-gestation lethality of these mutants.
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