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A Phase 1 Study in Healthy Subjects to Evaluate the Safety and Pharmacokinetics of a Human Monoclonal Antibody (S315) Against Diphtheria Toxin.

Diphtheria is a recurrent threat with endemic still occurs in many parts of the world. The standard of care is horse serum-derived diphtheria antitoxin (eDAT), which is in critical short supply globally. S315 is a fully human, monoclonal immunoglobulin G1 neutralizing antibody, specific to the receptor-binding domain of diphtheria toxin. S315 is intended to be a safer, more readily available alternative to replace eDAT. This first-in-human, randomized, double-blind, dose escalation study evaluated the safety, tolerability, and pharmacokinetics of S315 in healthy adults. Cohorts of study subjects received single intravenous infusions of S315 (480 mg, 960 mg, 1920 mg, 3840 mg, and 7680 mg) or matched placebo. Safety was assessed by standard clinical and laboratory evaluations. Serum S315 concentrations were measured by enzyme-linked immunosorbent assay (ELISA) and an in vitro diphtheria toxin neutralization assay, followed by pharmacokinetic analyses. Forty-one subjects were enrolled. S315 was safe and well tolerated. Most adverse events were mild or moderate. Peak mean serum concentrations ranged from 199 µg/mL to 2872 µg/mL (ELISA) and from 234 AU/mL to 1147 AU/mL (neutralization assay), with low variability. Mean serum half-life ranged from 12 to 27 days (ELISA) and from 17 to 22 days (neutralization assay). S315 was generally safe and well tolerated by healthy subjects. Pharmacokinetic data suggest that S315 serum neutralizing activity is an order of magnitude greater than that attained by eDAT. The results of this study support continued development of S315 as a replacement for eDAT to address critical global supply issues. Clinical Trials Registration. NCT04075175.

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Compartmentalized HIV-1 reservoir in intestinal monocytes/macrophages on antiretroviral therapy.

The persistence of latently infected cells prevents a cure of HIV. The intestinal mucosa contains numerous target cells, and high levels of HIV-1 DNA persist in this compartment under ART. While CD4+ T cells are the best characterized reservoir of HIV-1, the role of long-lived intestinal macrophages in HIV-1 persistence on ART remains controversial. We collected duodenal and colonic biopsies from 12 people living with HIV (PLWH) on suppressive ART, enrolled in the ARNS EP61 GALT study. Total, integrated, intact and defective HIV-1 proviruses were quantified from sorted T cells and monocytes/macrophages. HIV-1 env quasispecies were analyzed by single-molecule next-generation sequencing and env-pseudotyped viruses were constructed to assess macrophage versus T-tropism. Total HIV-1 DNA levels in intestinal T cells were significantly higher than those in monocytes/macrophages (P<0.0001). Unintegrated HIV-1 DNA was detected in one-third of T-cell and monocyte/macrophage-positive samples. Intact HIV-1 proviruses were detected using the intact proviral DNA assay in 4/16 T-cell samples and 1/6 monocyte/macrophage samples with detectable HIV-1 DNA. HIV-1 sequences were compartmentalized between intestinal monocytes/macrophages and T cells in some subjects. Phenotypic analysis of pseudotyped viruses expressing HIV-1 envelopes from colonic monocytes/macrophages revealed T-tropism rather than M-tropism. Our results show that monocytes/macrophages from the intestinal mucosa of PLWH on ART can contain HIV-1 DNA, including intact or unintegrated forms, but at much lower levels than those found in T cells, and with some compartmentalization although they do not exhibit a specific macrophage tropism, raising the question of the mechanisms of infection involved.

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