The effector activity of antibodies is dependent on engagement with Fcγ receptors (FcγRs) and activation of the associated intracellular signaling pathways. Preclinical evaluation of therapeutic humanized or chimeric mAbs to study the interactions of their Fc regions with FcγRs is hampered by substantial structural and functional FcγR diversity among species. In this report, we used mice expressing only human FcγRs to evaluate the contribution of FcγR-mediated pathways to the neutralizing activity of an anti-anthrax toxin chimeric mAb. We observed that the protective activity of this mAb was highly dependent upon FcγR engagement, with minimal protection against anthrax toxin observed in FcγR-deficient mice following mAb administration. We generated anti-anthrax toxin mAbs with specific Fc domain variants with selectively enhanced affinity for particular human FcγRs and assessed their activity in FcγR-humanized mice. We determined that Fc domain variants that were capable of selectively engaging activating FcγRs substantially enhanced the in vitro and in vivo activity of anthrax toxin-neutralizing antibodies. These findings indicate that the application of Fc domain engineering is a feasible strategy to enhance toxin-neutralizing activity and suggest that engineered antitoxin antibodies will have improved therapeutic efficacy.

BACKGROUND: There is a growing understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease 2019 (COVID-19) in the general population. The unique immunology of pregnancy may result in variations from the reported course of disease. CASE: A 27-year-old primigravid woman presented with mild COVID-19 symptoms at 28 2/7 weeks of gestation, testing positive for SARS-CoV-2 infection by nasopharyngeal swab reverse transcription-polymerase chain reaction (RT-PCR). Antibody seroconversion was detected at 36 6/7 weeks of gestation. She presented for delivery at 38 1/7 weeks of gestation, and her SARS-CoV-2 RT-PCR test result was positive. Severe acute respiratory syndrome coronavirus 2 RNA remained detectable 34 days postpartum and 104 days from her initial positive test. CONCLUSION: Prolonged viral shedding of SARS-CoV RNA may occur in the pregnant patient. If prevalent, this complicates the interpretation of a positive SARS-CoV-2 RT-PCR test result in the asymptomatic gravid patient.

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Background It has been shown that the microbial polysaccharide Galactoxylomannan (GalXM) from the opportunistic fungus Cryptococcus neoformans is able to impair T-cell proliferation and to induce apoptosis in T lymphocytes following the interaction with CD45. GalXM administration in experimental arthritis is able to ameliorate synovitis, reduced the concentration of pro-inflammatory cytokines in affected joints and to prevent articular damage. Objectives Aim of the present study was to investigate the effects of GalXM on circulating T-cell subsets in rheumatoid arthritis (RA) to pursue potential therapeutic application. Methods Sixty RA patients and 40 HD were included in the study. RA and HD magnetic sorted-CD3+ T cells were cultured in presence or absence of GalXM (10 mg/ml) and activation stimuli (either anti-CD3 antibody of IL-6+TGFβ). Both apoptosis and proliferation assays were performed at different time-points. IL-17 expression and cleaved-caspase 3 were evaluated by flow cytometry, STAT-3 phosphorilation was assessed by western blot. Results GalXM selectively targeted RA Th17 cells. Indeed, GalXM was able to increase caspase-3 activation and eventually apoptosis rate of this cell subset. Moreover, it was able to reduce STAT3 phosphorilation culminating in reduced IL-17 production. Finally, Th17 cell proliferation was also reduced. In addition, we confirmed that CD45 expression on target T cells is required to mediate GAlXM immune-modulatory effects. Conclusions This study confirms immune-modulatory effects mediated by GalXM (increase of caspase-3 activation and apoptosis rate, reduction of proliferation, reduction of IL-17 synthesis) in RA Th17 cells. Since Th17 cells represent a pathogenic cell subset deeply involved in the development of rheumatoid synovitis, these findings may suggest possible therapeutic applications of GalXM in RA. References Pericolini E. et al. J Immunol 2009;182:6003 Pericolini E. et al PloS One 2010;5:e12720 Disclosure of Interest None Declared

Background and Objectives We previously demonstrated that the purified microbial polysaccharide Galactoxylomannan (GalXM) from the opportunistic fungus Cryptococcus neoformans is able to impair T-cell proliferation and to induce T lymphocyte apoptosis following the interaction with CD45 in normal subjects. Since T lymphocytes are crucially involved in the pathogenesis of rheumatoid arthritis (RA), aim of the present study was to investigate the effects of GalXM on circulatingT-cell subsets in RA and provide the rationale for potential therapeutic application of this compound. Materials and Methods Sixty RA patients and 40 healthy donors (HD) were included in the study. RA and HD magnetic sorted-CD3+, CD4+ or CD4+CD25high T cells were cultured in presence or absence of GalXM (10 ng/ml), Dex (10nM), MTX (10ng/ml) or FLLL31 (5µM). Lymphocyte apoptosis was performed at different time-points evaluating propidium iodide staining and in selected experiments cleaved caspase 3 staining by flow cytometry. Flow cytometry was also employed for phenotypic analysis of T cell subsets (CD4, CD25, CD127, FoxP3, IL-17, IL-10, IL-17, TGF-β1) and for the analysis of cell proliferation evaluating CFSE dilution. Western blot was employed to assess phospho-STAT3, STAT3, FoxP3 and T-bet expression in cell lysates. Cytokine concentration in culture supernatants (IL-21, IL-22, IL-23, IL-6, IL-17A, IFN-γ, IL-12p70, IL-8, TGF-β1 and IL-10) was assessed with commercial ELISA kits. Results GalXM selectively reduced proliferation and increased apoptosis rate in RA Th1 and Th17 cells. GalXM was also able to reduce STAT3 phosphorilation eventually leading to decreased IL-17 production in surviving Th17 cells. To note, GalXM strongly up-regulated FoxP3 expression in CD4+T cells, increased the percentage of non-conventional CD4+CD25-FOXP3+ Treg cells and enhanced suppressive activity of both CD4+CD25highFOXP3+and CD4+CD25-FOXP3+Treg cells. All these findings were further supported by a rebalance of effector/regulatory cytokines in culture supernatants. Conclusion Our results suggest that GalXM represents a powerful compound able to rebalance Treg/T-effector ratio in RA and therefore it is worth to be employed for therapeutic purposes in this disease.