SARS-CoV-2 antibodies from children exhibit broad neutralization and belong to adult public clonotypes.

From the beginning of the COVID-19 pandemic, children have exhibited different susceptibility to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, reinfection, and disease compared with adults. Motivated by the established significance of SARS-CoV-2-neutralizing antibodies in adults, here we characterize SARS-CoV-2-specific antibody repertoires in a young cohort of individuals aged from 5 months to 18 years old. Our results show that neutralizing antibodies in children possess similar genetic features compared to antibodies identified in adults, with multiple antibodies from children belonging to previously established public antibody clonotypes in adults. Notably, antibodies from children show potent neutralization of circulating SARS-CoV-2 variants that have cumulatively resulted in resistance to virtually all approved monoclonal antibody therapeutics. Our results show that children can rely on similar SARS-CoV-2 antibody neutralization mechanisms compared to adults and are an underutilized source for the discovery of effective antibody therapeutics to counteract the ever-evolving pandemic.

Augmentation of the Riboflavin-Biosynthetic Pathway Enhances Mucosa-Associated Invariant T (MAIT) Cell Activation and Diminishes Mycobacterium tuberculosis Virulence.

Mucosa-associated invariant T (MAIT) cells play a critical role in antimicrobial defense. Despite increased understanding of their mycobacterial ligands and the clinical association of MAIT cells with tuberculosis (TB), their function in protection against Mycobacterium tuberculosis infection remains unclear. Here, we show that overexpressing key genes of the riboflavin-biosynthetic pathway potentiates MAIT cell activation and results in attenuation of M. tuberculosis virulence in vivo. Further, we observed greater control of M. tuberculosis infection in MAIThi CAST/EiJ mice than in MAITlo C57BL/6J mice, highlighting the protective role of MAIT cells against TB. We also endogenously adjuvanted Mycobacterium bovis BCG with MR1 ligands via overexpression of the lumazine synthase gene ribH and evaluated its protective efficacy in the mouse model of M. tuberculosis infection. Altogether, our findings demonstrate that MAIT cells confer host protection against TB and that overexpression of genes in the riboflavin-biosynthetic pathway attenuates M. tuberculosis virulence. Enhancing MAIT cell-mediated immunity may also offer a novel approach toward improved vaccines against TB. IMPORTANCE Mucosa-associated invariant T (MAIT) cells are an important subset of innate lymphocytes that recognize microbial ligands derived from the riboflavin biosynthesis pathway and mediate antimicrobial immune responses. Modulated MAIT cell responses have been noted in different forms of tuberculosis. However, it has been unclear if increased MAIT cell abundance is protective against TB disease. In this study, we show that augmentation of the mycobacterial MAIT cell ligands leads to higher MAIT cell activation with reduced M. tuberculosis virulence and that elevated MAIT cell abundance confers greater control of M. tuberculosis infection. Our study also highlights the potential of endogenously adjuvanting the traditional BCG vaccine with MR1 ligands to augment MAIT cell activation. This study increases current knowledge on the roles of the riboflavin-biosynthetic pathway and MAIT cell activation in M. tuberculosis virulence and host immunity against TB.

HLA-E Presents Glycopeptides from the Mycobacterium tuberculosis Protein MPT32 to Human CD8+ T cells.

Infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis, remains a global health concern. Both classically and non-classically restricted cytotoxic CD8+ T cells are important to the control of Mtb infection. We and others have demonstrated that the non-classical MHC I molecule HLA-E can present pathogen-derived peptides to CD8+ T cells. In this manuscript, we identified the antigen recognized by an HLA-E-restricted CD8+ T cell clone isolated from an Mtb latently infected individual as a peptide from the Mtb protein, MPT32. Recognition by the CD8+ T cell clone required N-terminal O-linked mannosylation of MPT32 by a mannosyltransferase encoded by the Rv1002c gene. This is the first description of a post-translationally modified Mtb-derived protein antigen presented in the context of an HLA-E specific CD8+ T cell immune response. The identification of an immune response that targets a unique mycobacterial modification is novel and may have practical impact in the development of vaccines and diagnostics.

Endosomal MR1 Trafficking Plays a Key Role in Presentation of Mycobacterium tuberculosis Ligands to MAIT Cells.

Mucosal-Associated Invariant T (MAIT) cells, present in high frequency in airway and other mucosal tissues, have Th1 effector capacity positioning them to play a critical role in the early immune response to intracellular pathogens, including Mycobacterium tuberculosis (Mtb). MR1 is a highly conserved Class I-like molecule that presents vitamin B metabolites to MAIT cells. The mechanisms for loading these ubiquitous small molecules are likely to be tightly regulated to prevent inappropriate MAIT cell activation. To define the intracellular localization of MR1, we analyzed the distribution of an MR1-GFP fusion protein in antigen presenting cells. We found that MR1 localized to endosomes and was translocated to the cell surface upon addition of 6-formyl pterin (6-FP). To understand the mechanisms by which MR1 antigens are presented, we used a lentiviral shRNA screen to identify trafficking molecules that are required for the presentation of Mtb antigen to HLA-diverse T cells. We identified Stx18, VAMP4, and Rab6 as trafficking molecules regulating MR1-dependent MAIT cell recognition of Mtb-infected cells. Stx18 but not VAMP4 or Rab6 knockdown also resulted in decreased 6-FP-dependent surface translocation of MR1 suggesting distinct pathways for loading of exogenous ligands and intracellular mycobacterially-derived ligands. We postulate that endosome-mediated trafficking of MR1 allows for selective sampling of the intracellular environment.

Human lung epithelial cells contain Mycobacterium tuberculosis in a late endosomal vacuole and are efficiently recognized by CD8⁺ T cells.

Mycobacterium tuberculosis (Mtb) is transmitted via inhalation of aerosolized particles. While alveolar macrophages are thought to play a central role in the acquisition and control of this infection, Mtb also has ample opportunity to interact with the airway epithelium. In this regard, we have recently shown that the upper airways are enriched with a population of non-classical, MR1-restricted, Mtb-reactive CD8⁺ T cells (MAIT cells). Additionally, we have demonstrated that Mtb-infected epithelial cells lining the upper airways are capable of stimulating IFNγ production by MAIT cells. In this study, we demonstrate that airway epithelial cells efficiently stimulate IFNγ release by MAIT cells as well as HLA-B45 and HLA-E restricted T cell clones. Characterization of the intracellular localization of Mtb in epithelial cells indicates that the vacuole occupied by Mtb in epithelial cells is distinct from DC in that it acquires Rab7 molecules and does not retain markers of early endosomes such as Rab5. The Mtb vacuole is also heterogeneous as there is a varying degree of association with Lamp1 and HLA-I. Although the Mtb vacuole shares markers associated with the late endosome, it does not acidify, and the bacteria are able to replicate within the cell. This work demonstrates that Mtb infected lung epithelial cells are surprisingly efficient at stimulating IFNγ release by CD8⁺ T cells.

Demographic and ecological effects on patterns of parasitism in eastern chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania.

From January 2006 to January 2008, we collected 1,045 fecal samples from 90 individually-recognized, free-ranging, eastern chimpanzees (Pan troglodytes schweinfurthii) inhabiting Gombe National Park, Tanzania to determine how patterns of parasitism are affected by demographic and ecological covariates. Seventeen parasite species were recovered, including eight nematodes (Oesophagostomum sp., Necator sp., Probstmayria gombensis, Strongyloides fulleborni, Ascaris sp., Trichuris sp., Abbreviata caucasica, and an unidentified strongyle), 1 cestode (Bertiella sp.), 1 trematode (Dicrocoeliidae), and 7 protozoa (Entamoeba coli, Entamoeba histolytica/dispar, Iodamoeba bütschlii, Troglodytella abrassarti, Troglocorys cava, Balantidium coli, and an unidentified protozoa). Significant differences were observed in interannual infection prevalence and parasite richness between 2006 and 2007. Intercommunity comparisons demonstrated higher prevalence of parasites for the Mitumba compared with Kasekela chimpanzee community. Prevalence of several parasites was strongly correlated with monthly rainfall patterns for both 2006 and 2007. Subadult chimpanzees had lower prevalence for most parasite species compared with adults in both years and also yielded a lower average parasite species richness. No significant differences were observed between males and females in prevalence in 2006. However, in 2007 the prevalence of S. fulleborni and I. bütschlii were higher in males than in females. Parasite prevalence and richness were substantially higher in this multiyear study compared with previous short-term studies of the gastrointestinal parasites of Gombe chimpanzees. This coupled with the significant interannual and interseasonal variation, demonstrated in this study, emphasizes the importance of multiyear monitoring with adequate sample size to effectively determine patterns of parasitism in wild primate populations.