Non-canonical effects of anthrax toxins on haematopoiesis: implications for vaccine development

Fifteen Years of Sm-p80-Based Vaccine Trials in Nonhuman Primates: Antibodies From Vaccinated Baboons Confer Protection in vivo and in vitro From Schistosoma mansoni and Identification of Putative Correlative Markers of Protection

Recent advances in systems biology have shifted vaccine development from a largely trial-and-error approach to an approach that promote rational design through the search for immune signatures and predictive correlates of protection. These advances will doubtlessly accelerate the development of a vaccine for schistosomiasis, a neglected tropical disease that currently affects over 250 million people. For over 15 years and with contributions of over 120 people, we have endeavored to test and optimize Sm-p80-based vaccines in the non-human primate model of schistosomiasis. Using RNA-sequencing on eight different Sm-p80-based vaccine strategies, we sought to elucidate immune signatures correlated with experimental protective efficacy. Furthermore, we aimed to explore the role of antibodies through in vivo passive transfer of IgG obtained from immunized baboons and in vitro killing of schistosomula using Sm-p80-specific antibodies. We report that passive transfer of IgG from Sm-p80-immunized baboons led to significant worm burden reduction, egg reduction in liver, and reduced egg hatching percentages from tissues in mice compared to controls. In addition, we observed that sera from Sm-p80-immunized baboons were able to kill a significant percent of schistosomula and that this effect was complement-dependent. While we did not find a universal signature of immunity, the large datasets generated by this study will serve as a substantial resource for further efforts to develop vaccine or therapeutics for schistosomiasis.

Erythropoiesis suppression is associated with anthrax lethal toxin-mediated pathogenic progression

Anthrax is a disease caused by the bacterium Bacillus anthracis, which results in high mortality in animals and humans. Although some of the mechanisms are already known such as asphyxia, extensive knowledge of molecular pathogenesis of this disease is deficient and remains to be further investigated. Lethal toxin (LT) is a major virulence factor of B. anthracis and a specific inhibitor/protease of mitogen-activated protein kinase kinases (MAPKKs). Anthrax LT causes lethality and induces certain anthrax-like symptoms, such as anemia and hypoxia, in experimental mice. Mitogen-activated protein kinases (MAPKs) are the downstream pathways of MAPKKs, and are important for erythropoiesis. This prompted us to hypothesize that anemia and hypoxia may in part be exacerbated by erythropoietic dysfunction. As revealed by colony-forming cell assays in this study, LT challenges significantly reduced mouse erythroid progenitor cells. In addition, in a proteolytic activity-dependent manner, LT suppressed cell survival and differentiation of cord blood CD34⁺-derived erythroblasts in vitro. Suppression of cell numbers and the percentage of erythroblasts in the bone marrow were detected in LT-challenged C57BL/6J mice. In contrast, erythropoiesis was provoked through treatments of erythropoietin, significantly ameliorating the anemia and reducing the mortality of LT-treated mice. These data suggested that suppressed erythropoiesis is part of the pathophysiology of LT-mediated intoxication. Because specific treatments to overcome LT-mediated pathogenesis are still lacking, these efforts may help the development of effective treatments against anthrax.

Effects by anthrax toxins on hematopoiesis: a key role for cytokines as mediators

An understanding of anthrax toxins on the emerging immune system and blood production are significant to medicine. This study examined the effects of anthrax toxin on hematopoiesis and determined roles for cytokines. Anthrax holotoxin toxin is three components: protective antigen (PA) binds to the target cell and mediates the entry of lethal factor (LF) and edema factor (EF). Anthrax toxin dramatically inhibits signaling in immune cells. We first identified the cell subsets that interacted with the protective antigen (PA) and then studied the effects on hematopoietic progenitors in clonogenic assays: granulocytic-monocytic (CFU-GM) and late erythroid (CFU-E). Multi-color immunofluorescence with FITC-PA indicated its interaction with early and late myeloid cells. Clonogenic assays, in the presence or absence of holotoxin and individual toxin proteins resulted in significant suppression by hologenic toxic alone, despite the presence of growth-promoting cytokines. Antibodies to anthrax receptor (ATR1) reversed the suppressive effects, indicating specificity. Monomeric proteins showed different effects on myeloid and erythroid progenitors. Suppression was not due to cell death, based on undetectable active caspase 3. Cytokine array analyses with supernatants from toxin-stimulated stroma showed an increase in the hematopoietic suppressor, MIP-1α. This finding, in addition to our previous studies, showing an increase in IL-10, suggested indirect roles for cytokines in toxin-mediated hematopoietic suppression. The chemokine, SDF-1α was increased. Since SDF-1 is involved in the mobilization of hematopoietic cells, it is likely that anthrax holotoxin could induce cell exit from BM. In summary, anthrax holotoxin, but not individual toxins, exerted hematopoietic effects on myeloid and erythroid progenitors via specific receptor, partly through the induction of cytokines.