Immunogenicity of quadrivalent meningococcal conjugate vaccine in frequent platelet donors.

Frequent plateletpheresis is associated with severe lymphopenia of uncertain clinical significance. We assessed the functional impact of frequent platelet donations and associated lymphopenia on the response to neoantigens. We conducted a prospective study of 102 platelet donors (HIV uninfected) who were naive to meningococcal vaccination recruited at Brigham and Women's Hospital. One dose of quadrivalent meningococcal conjugate vaccine was administered. Seroresponse was defined as a fourfold increase of serum bactericidal antibody titers and seroprotection was defined as postvaccination titers of ≥1:8, for each of the 4 vaccine antigens (A, C, W, and Y). Mean age of participants was 61 years, 69% were male, and medial number of platelet donations in prior year was 14 (interquartile range, 4-20). Frequent platelet donors had a low CD4 count (14% with ≤200/µL and 34% with ≤350/µL). Seroresponse rates varied from 68% for serogroup Y to 86% for serogroup A and were higher for participants with baseline titers of <1:8. Postvaccination seroprotection rates varied from 76% for serogroup Y to 96% for serogroup A. After adjustments for age, sex, and frequent donations, lower total lymphocyte or lower CD4 counts were not associated with lower responses. These data suggest no impairment by plateletpheresis-associated lymphopenia on response to these neoantigens. This trial was registered at www.clinicaltrials.gov as #NCT04224311.

Nanaerobic growth enables direct visualization of dynamic cellular processes in human gut symbionts.

Mechanistic studies of anaerobic gut bacteria have been hindered by the lack of a fluorescent protein system to track and visualize proteins and dynamic cellular processes in actively growing bacteria. Although underappreciated, many gut "anaerobes" are able to respire using oxygen as the terminal electron acceptor. The oxygen continually released from gut epithelial cells creates an oxygen gradient from the mucus layer to the anaerobic lumen [L. Albenberg et al., Gastroenterology 147, 1055-1063.e8 (2014)], with oxygen available to bacteria growing at the mucus layer. Here, we show that Bacteroides species are metabolically and energetically robust and do not mount stress responses in the presence of 0.10 to 0.14% oxygen, defined as nanaerobic conditions [A. D. Baughn, M. H. Malamy, Nature 427, 441-444 (2004)]. Taking advantage of this metabolic capability, we show that nanaerobic growth provides sufficient oxygen for the maturation of oxygen-requiring fluorescent proteins in Bacteroides species. Type strains of four different Bacteroides species show bright GFP fluorescence when grown nanaerobically versus anaerobically. We compared four different red fluorescent proteins and found that mKate2 yields the highest red fluorescence intensity in our assay. We show that GFP-tagged proteins can be localized in nanaerobically growing bacteria. In addition, we used time-lapse fluorescence microscopy to image dynamic type VI secretion system processes in metabolically active Bacteroides fragilis The ability to visualize fluorescently labeled Bacteroides and fluorescently linked proteins in actively growing nanaerobic gut symbionts ushers in an age of imaging analyses not previously possible in these bacteria.

A proteolytically activated antimicrobial toxin encoded on a mobile plasmid of Bacteroidales induces a protective response.

Phocaeicola vulgatus is one of the most abundant and ubiquitous bacterial species of the human gut microbiota, yet a comprehensive analysis of antibacterial toxin production by members of this species has not been reported. Here, we identify and characterize a previously undescribed antibacterial protein. This toxin, designated BcpT, is encoded on a small mobile plasmid that is largely confined to strains of the closely related species Phocaeicola vulgatus and Phocaeicola dorei. BcpT is unusual in that it requires cleavage at two distinct sites for activation, and we identify bacterial proteases that perform this activation. We further identify BcpT's receptor as the Lipid A-core glycan, allowing BcpT to target species of other Bacteroidales families. Exposure of cells to BcpT induces a response involving an unusual sigma/anti-sigma factor pair that is likely triggered by cell envelope stress, resulting in the expression of genes that partially protect cells from multiple antimicrobial toxins.