Epitope-dependent mechanisms of CD27 neutralization revealed by X-ray crystallography.

CD27 is a T and B cell co-stimulatory protein of the TNF receptor superfamily dependent on the availability of the TNF-like ligand CD70. Two anti-CD27 neutralizing monoclonal antibodies were obtained from mouse hybridoma and subsequently humanized and optimized for binding the target. The two antibodies are similar in terms of their CD27-binding affinity and ability to block NF-κB signaling, however their clearance rates in monkeys are very different. The pharmacokinetics profiles could be epitope dependent. To identify the epitopes, we determined the crystal structure of the ternary complex between CD27 and the Fab fragments of these non-competing antibodies. The structure reveals the binding modes of the antibodies suggesting that their mechanisms of action are distinctly different and provides a possible explanation of the in vivo data.

Differential Expression of Immune Checkpoint Modulators on In Vitro Primed CD4(+) and CD8(+) T Cells.

PD-1, TIM-3, and LAG-3 are molecules shown to have immune modulatory properties, and although initially classified as indicators of T cell hyporesponsiveness, it has become clear that they are also associated with the normal course of T cell activation. Functional studies have focused mainly on CD8(+) T cells during chronic inflammation due to interest in co-opting the cellular immune response to eliminate viral or cancerous threats; however, there remains a relative lack of data regarding the expression of these molecules on CD4(+) T cells. Here, we report that expression of the immune checkpoint (IC) molecules PD-1, LAG-3, and TIM-3 are differentially expressed on CD4(+) and CD8(+) T cells in the allogeneic response resulting from a mixed lymphocyte reaction. In these studies, PD-1 expression is higher on CD4(+) T cells compared to CD8(+) T cells. In contrast, TIM-3 is expressed at higher levels on CD8(+) T cells compared to CD4(+) T cells with an apparent reciprocity in that PD-1(+) CD4(+) T cells are frequently TIM-3(lo/-), while TIM-3-expressing CD8(+) T cells are largely PD-1(lo/-). In addition, there is a decrease in the frequency of TIM-3(+) CD4(+) cells producing IFN-γ and IL-5 compared to TIM-3(+) CD8(+) cells. Lastly, the memory T cell phenotype within each IC-expressing subset differs between CD4(+) and CD8(+) T cells. These findings highlight key differences in IC expression patterns between CD4(+) and CD8(+) T cells and may allow for more effective therapeutic targeting of these molecules in the future.

Phospholipogenic pharmaceuticals are associated with a higher incidence of histological findings than nonphospholipogenic pharmaceuticals in preclinical toxicology studies.

While phospholipidosis is thought to be an adaptive response to chemical challenge, many phospholipogenic compounds are known to display adverse effects in preclinical species and humans. To investigate the link between phospholipogenic administration and incidence of preclinical histological signals, an internal AstraZeneca in vivo toxicology report database was searched to identify phospholipogenic and nonphospholipogenic compounds. The datasets assembled comprised 46 phospholipogenic and 62 nonphospholipogenic compounds. The phospholipogenic potential of these compounds was confirmed by a pathologist's interpretation and was supported by well-validated in silico and in vitro models. The phospholipogenic dataset contained 37 bases, 4 neutral compounds, 3 zwitterions, and 1 acid, whereas the nonphospholipogenic dataset contained 9 bases, 34 neutrals, 1 zwitterion, and 18 acids. Histologic findings were tracked for adrenal gland; bone marrow; kidney; liver; lung; lymph node; spleen; thymus; and reproductive organs. On average, plasma exposures were higher in animals dosed with the nonphospholipogenics. Phospholipogenics yielded proportionally more histologic changes (exclusive of phospholipidosis itself) in all organs. Statistically significant higher frequencies of liver necrosis, alveolitis/pneumonitis, as well as lymphocytolysis in the thymus, lymph nodes, and spleen occurred in response to phospholipogenics compared to that for nonphospholipogenics.

Relationship of pleconaril susceptibility and clinical outcomes in treatment of common colds caused by rhinoviruses.

Pleconaril, a specific inhibitor of human picornaviruses, showed therapeutic efficacy against community-acquired colds caused by rhinoviruses in two placebo-controlled trials. Virological assessments were conducted during these trails, including virus culture and drug susceptibility testing. Nasal mucus samples collected from the enrolled patients were tested for the presence of picornavirus by reverse transcriptase PCR and culture. In total, 827 baseline nasal mucus samples were positive by virus culture (420 in the placebo group and 407 in the pleconaril group). Pleconaril treatment was associated with a more rapid loss of culturable virus. By study day 3, the number of samples positive by culture fell to 282 for the placebo-treated subjects and 202 for the pleconaril-treated subjects (P < 0.0001); and by day 6, the number of samples in the two groups positive by culture fell to 196 and 165, respectively (P = 0.07). The clinical benefit correlated strongly with the pleconaril susceptibility of the baseline virus isolate. Pleconaril-treated subjects infected with the more highly susceptible viruses (50% effective concentration < or = 0.38 microg/ml) experienced a median 1.9- to 3.9-day reduction in symptom duration compared with that for the placebo-treated subjects. By contrast, subjects whose baseline virus isolate susceptibility was >0.38 microg/ml did not benefit from pleconaril treatment. These results indicate that the magnitude of symptomatic improvement in pleconaril-treated subjects with community-acquired colds is related to the drug susceptibility of the infecting virus, clearly linking the antiviral effects of the drug to clinical efficacy. Post-baseline virus isolates with reduced susceptibility or full resistance to pleconaril were recovered from 10.7% and 2.7% of drug-treated subjects, respectively. These patients shed low levels of virus and had no unusual clinical outcomes. Nevertheless, studies on the biologic properties and transmissibility of these variant viruses are warranted.

An orally bioavailable antipoxvirus compound (ST-246) inhibits extracellular virus formation and protects mice from lethal orthopoxvirus Challenge.

ST-246 is a low-molecular-weight compound (molecular weight = 376), that is potent (concentration that inhibited virus replication by 50% = 0.010 microM), selective (concentration of compound that inhibited cell viability by 50% = >40 microM), and active against multiple orthopoxviruses, including vaccinia, monkeypox, camelpox, cowpox, ectromelia (mousepox), and variola viruses. Cowpox virus variants selected in cell culture for resistance to ST-246 were found to have a single amino acid change in the V061 gene. Reengineering this change back into the wild-type cowpox virus genome conferred resistance to ST-246, suggesting that V061 is the target of ST-246 antiviral activity. The cowpox virus V061 gene is homologous to vaccinia virus F13L, which encodes a major envelope protein (p37) required for production of extracellular virus. In cell culture, ST-246 inhibited plaque formation and virus-induced cytopathic effects. In single-cycle growth assays, ST-246 reduced extracellular virus formation by 10 fold relative to untreated controls, while having little effect on the production of intracellular virus. In vivo oral administration of ST-246 protected BALB/c mice from lethal infection, following intranasal inoculation with 10x 50% lethal dose (LD(50)) of vaccinia virus strain IHD-J. ST-246-treated mice that survived infection acquired protective immunity and were resistant to subsequent challenge with a lethal dose (10x LD(50)) of vaccinia virus. Orally administered ST-246 also protected A/NCr mice from lethal infection, following intranasal inoculation with 40,000x LD(50) of ectromelia virus. Infectious virus titers at day 8 postinfection in liver, spleen, and lung from ST-246-treated animals were below the limits of detection (<10 PFU/ml). In contrast, mean virus titers in liver, spleen, and lung tissues from placebo-treated mice were 6.2 x 10(7), 5.2 x 10(7), and 1.8 x 10(5) PFU/ml, respectively. Finally, oral administration of ST-246 inhibited vaccinia virus-induced tail lesions in Naval Medical Research Institute mice inoculated via the tail vein. Taken together, these results validate F13L as an antiviral target and demonstrate that an inhibitor of extracellular virus formation can protect mice from orthopoxvirus-induced disease.