The current outbreak of Ebola virus (EBOV) in West Africa is unprecedented, causing more cases and fatalities than all previous outbreaks combined, and has yet to be controlled1. Several postexposure interventions have been employed under compassionate use to treat a number of patients repatriated to Europe and the United States2. However, the in vivo efficacy of these interventions against the new outbreak strain of EBOV is unknown. Here, we show that lipid nanoparticle (LNP)-encapsulated siRNAs rapidly adapted to target the Makona outbreak strain of EBOV are able to protect 100% of rhesus monkeys against lethal challenge when treatment was initiated at 3 days postexposure while animals were viremic and clinically ill. Although all infected animals showed evidence of advanced disease including abnormal hematology, blood chemistry, and coagulopathy, siRNA-treated animals had milder clinical features and fully recovered while the untreated control animals succumbed. These results represent the first successful demonstration of therapeutic anti-EBOV efficacy against the new outbreak strain in nonhuman primates (NHPs) and highlight the rapid development of LNP-delivered siRNA as a countermeasure against this highly lethal human disease.

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RNA silencing ͉ silencing suppressor ͉ cucumber mosaic virus ͉ Y-satellite P lants have three overlapping but distinct RNA silencing pathways that involve small interfering RNAs (siRNAs) and micro RNAs (miRNAs) (1). In the siRNA-related pathways, perfectly complementary dsRNAs are cleaved into siRNAs having two distinct size classes, 21-22 and 24 nt, by RNase III-type Dicer enzymes (2). These siRNAs are then incorporated into RNAinduced silencing complexes (RISCs) that guide the specific degradation of RNA in the cytoplasm (and possibly the nucleus) and͞or cytosine methylation of DNA in the nucleus (1, 3, 4). miRNAs are predominately 21-22 nt in length and are formed by the Dicer-mediated cleavage of hairpin-structured RNAs (5, 6). Both siRNAs and miRNAs play important roles in the control of spatial and temporal expression of key regulatory genes and can act through RISC-mediated mRNA cleavage (6, 7). The different pathways leading to the biogenesis of siRNAs and miRNAs in plants involve multiple protein factors that include the Dicer-like proteins (7, 8) and RNA-dependent RNA polymerases (9). A recent study has revealed that the 3Ј-terminal nucleotides of miRNAs in plants are methylated at their 2Ј or 3Ј hydroxyls by HEN1 (10), a protein previously shown to be required for the accumulation of miRNAs and sense transgene-derived siRNAs in Arabidopsis (11). It remains unclear, however, whether siRNAs are also methylated in plants, because HEN1 fails to methylate perfectly complementary duplex siRNAs in vitro (10).RNA silencing, and the siRNA pathway in particular, is a natural antiviral defense mechanism in plants (12). Consequently, many plant viruses encode proteins that can suppress RNA silencing by a variety of mechanisms. These silencing suppressors have become important tools in the elucidation of RNA silencing pathways in plants because they act differentially on the silencing machinery.

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Programmed death-ligand 1 is a glycoprotein expressed on antigen presenting cells, hepatocytes, and tumors which upon interaction with programmed death-1, results in inhibition of antigen-specific T cell responses. Here, we report a mechanism of inhibiting programmed death-ligand 1 through small molecule-induced dimerization and internalization. This represents a mechanism of checkpoint inhibition, which differentiates from anti-programmed death-ligand 1 antibodies which function through molecular disruption of the programmed death 1 interaction. Testing of programmed death ligand 1 small molecule inhibition in a humanized mouse model of colorectal cancer results in a significant reduction in tumor size and promotes T cell proliferation. In addition, antigen-specific T and B cell responses from patients with chronic hepatitis B infection are significantly elevated upon programmed death ligand 1 small molecule inhibitor treatment. Taken together, these data identify a mechanism of small molecule-induced programmed death ligand 1 internalization with potential therapeutic implications in oncology and chronic viral infections.

Although significant progress has been made in developing therapeutics against Zaire ebolavirus, these therapies do not protect against other Ebola species such as Sudan ebolavirus (SUDV). Here, we describe an RNA interference therapeutic comprising siRNA targeting the SUDV VP35 gene encapsulated in lipid nanoparticle (LNP) technology with increased potency beyond formulations used in TKM-Ebola clinical trials. Twenty-five rhesus monkeys were challenged with a lethal dose of SUDV. Twenty animals received siRNA-LNP beginning at 1, 2, 3, 4 or 5 days post-challenge. VP35-targeting siRNA-LNP treatment resulted in up to 100% survival, even when initiated when fever, viraemia and disease signs were evident. Treatment effectively controlled viral replication, mediating up to 4 log10 reductions after dosing. Mirroring clinical findings, a correlation between high viral loads and fatal outcome was observed, emphasizing the importance of stratifying efficacy according to viral load. In summary, strong survival benefit and rapid control of SUDV replication by VP35-targeting LNP confirm its therapeutic potential in combatting this lethal disease.

Marburg virus (MARV) and the closely related filovirus Ebola virus cause severe and often fatal hemorrhagic fever (HF) in humans and nonhuman primates with mortality rates up to 90%. There are no vaccines or drugs approved for human use, and no postexposure treatment has completely protected nonhuman primates against MARV-Angola, the strain associated with the highest rate of mortality in naturally occurring human outbreaks. Studies performed with other MARV strains assessed candidate treatments at times shortly after virus exposure, before signs of disease are detectable. We assessed the efficacy of lipid nanoparticle (LNP) delivery of anti-MARV nucleoprotein (NP)–targeting small interfering RNA (siRNA) at several time points after virus exposure, including after the onset of detectable disease in a uniformly lethal nonhuman primate model of MARV-Angola HF. Twenty-one rhesus monkeys were challenged with a lethal dose of MARV-Angola. Sixteen of these animals were treated with LNP containing anti-MARV NP siRNA beginning at 30 to 45 min, 1 day, 2 days, or 3 days after virus challenge. All 16 macaques that received LNP-encapsulated anti-MARV NP siRNA survived infection, whereas the untreated or mock-treated control subjects succumbed to disease between days 7 and 9 after infection. These results represent the successful demonstration of therapeutic anti–MARV-Angola efficacy in nonhuman primates and highlight the substantial impact of an LNP-delivered siRNA therapeutic as a countermeasure against this highly lethal human disease.

SummaryUsing a genetic screen in yeast we found that Mycobacterium tuberculosis PE-PGRS62 was capable of disrupting yeast vacuolar protein sorting, suggesting effects on endosomal trafficking. To study the impact of PE-PGRS62 on macrophage function, we infected murine macrophages with Mycobacterium smegmatis expressing PE-PGRS62. Infected cells displayed phagosome maturation arrest. Phagosomes acquired Rab5, but displayed a significant defect in Rab7 and LAMP-1 acquisition. Macrophages infected with M. smegmatis expressing PE-PGRS62 also expressed twoto threefold less iNOS protein when compared with cells infected with wild-type bacteria. Consistent with this, cells infected with a Mycobacterium marinum transposon mutant for the PE-PGRS62 orthologue showed greater iNOS protein expression when compared to cells infected with wildtype organisms. Complementation restored the ability of the mutant to inhibit iNOS expression. No differences in iNOS transcript levels were observed, suggesting that PE-PGRS62 effects on iNOS expression occurred post-transcriptionally. Marked differences in colony morphology were also seen in M. smegmatis expressing PE-PGRS62 and in the M. marinum transposon mutant, suggesting that PE-PGRS62 may affect cell wall composition. These findings suggest that PE-PGRS62 supports virulence via inhibition of phagosome maturation and iNOS expression, and these phenotypes may be linked to effects on bacterial cell wall composition.