Erythropoietin is a major regulator of thrombopoiesis in thrombopoietin-dependent and -independent contexts

Thrombopoietin (TPO), through activation of its cognate receptor Mpl, is the major regulator of platelet production. However, residual platelets observed in TPO- and Mpl-loss-of-function (LOF) mice suggest the existence of an additional factor to TPO in platelet production. As erythropoietin (EPO) exhibited both in vitro megakaryocytic potential, in association with other early-acting cytokines, and in vivo platelet activation activity, we sought to investigate its role in this setting. Here, we used multiple LOF models to decipher the reciprocal role of EPO and TPO in the regulation of platelet production in TPO-LOF and Mpl-LOF mice and of platelet size heterogeneity in wild-type mice. We first identified EPO as the major thrombopoietic factor in the absence of the TPO-Mpl pathway. Based on the study of several mouse models we found that the EPO-EPO receptor pathway acts on late-stage megakaryopoiesis and is responsible for large-sized platelet production, while the TPO-Mpl pathway promotes small-sized platelet production. On the basis of our data, EPO might be used for thrombocytopenia supportive therapy in congenital amegakaryocytopoiesis. Furthermore, as a distribution skewed toward large platelets is an independent risk factor and a poor prognosis indicator in atherothrombosis, the characterization of EPO's role in the production of large-sized platelets, if confirmed in humans, may open new perspectives in the understanding of the role of EPO-induced platelets in atherothrombosis.

Specific detection of type II human chorionic gonadotropin beta subunit produced by trophoblastic and neoplastic cells

BACKGROUND

The sequence of the beta-subunit of human chorionic gonadotropin (hCGβ) varies depending on whether hCGβ is encoded by type I or type II genes. Type II genes are upregulated in trophoblast and cancer but hCGβ can be detected in the serum of nonpregnant women and healthy individuals. We aimed to determine whether monoclonal antibody (mAb) FBT11-II specifically detects hCGβ encoded by type II genes (type II hCGβ).

METHODS

Competitive inhibition assays with synthetic peptides, immunocytochemical and immunohistochemical studies, type II hCGβ dosing immunoassays and sequencing of CGB genes were performed.

RESULTS

Competitive inhibition assays determined that mAb FBT11-II recognizes the type II hCGβ derived peptide. CGB mRNA sequencing of JEG-3 (trophoblastic) and T24 (bladder) cell lines confirmed that JEG-3 expresses type II genes while T24 expresses exclusively type I. FBT11-II only recognizes JEG-expressed hCGβ. Placenta immunohistochemical studies confirmed that type II hCGβ expression is restricted to the syncytiotrophoblast. Immunoassays detected type II hCGβ in serum of patients with either nontrophoblastic cancers or fetal Down syndrome.

CONCLUSION

Type II gene expression can be detected using FBT11-II. This specific recognition could improve the clinical usefulness of assays aimed at either managing aggressive tumors or screening for Down syndrome.

Comparative expression of hCG β-genes in human trophoblast from early and late first-trimester placentas

Human chorionic gonadotropin (hCG) displays a major role in pregnancy initiation and progression and is involved in trophoblast differentiation and fusion. However, the site and the type of dimeric hCG production during the first trimester of pregnancy is poorly known. At that time, trophoblastic plugs present in the uterine arteries disappear, allowing unrestricted flow of maternal blood to the intervillous space. The consequence is an important modification of the trophoblast environment, including a rise of oxygen levels from about 2.5% before 10 wk of amenorrhea (WA) to ∼8% after 12 WA. Two specific β-hCG proteins that differ from three amino acids have been described: type 1 (CGB7) and type 2 (CGB3, -5, and -8). Here, we demonstrated in situ and ex vivo on placental villi and in vitro in primary cultures of human cytotrophoblasts that type 1 and 2 β-hCG RNAs and proteins were expressed by trophoblasts and that these expressions were higher before blood enters in the intervillous space (8-9 vs. 12-14 WA). hCG was immunodetected in villous mononucleated cytotrophoblasts (VCT) and syncytiotrophoblast (ST) at 8-9 WA but only in ST at 12-14 WA. Furthermore, hCG secretion was fourfold higher in VCT cultures from 8-9 WA compared with 12-14 WA. Interestingly, VCT from 8-9 WA placentas were found to exhibit more fusion features. Taken together, we showed that type 1 and type 2 β-hCG are highly expressed by VCT in the early first trimester, contributing to the high levels of hCG found in maternal serum at this term.

Dominance and diversity in the primary human CD4 T cell response to replication-competent vaccinia virus

Vaccination with replication-competent vaccinia protects against heterologous orthopoxvirus challenge. CD4 T cells have essential roles helping functionally important Ab and CD8 antiviral responses, and contribute to the durability of vaccinia-specific memory. Little is known about the specificity, diversity, or dominance hierarchy of orthopoxvirus-specific CD4 T cell responses. We interrogated vaccinia-reactive CD4 in vitro T cell lines with vaccinia protein fragments expressed from an unbiased genomic library, and also with a panel of membrane proteins. CD4 T cells from three primary vaccinees reacted with 44 separate antigenic regions in 35 vaccinia proteins, recognizing 8 to 20 proteins per person. The integrated responses to the Ags that we defined accounted for 49 to 81% of the CD4 reactivity to whole vaccinia Ag. Individual dominant Ags drove up to 30% of the total response. The gene F11L-encoded protein was immunodominant in two of three subjects and is fragmented in a replication-incompetent vaccine candidate. The presence of protein in virions was strongly associated with CD4 antigenicity. These findings are consistent with models in which exogenous Ag drives CD4 immunodominance, and provides tools to investigate the relationship between Ab and CD4 T cell specificity for complex pathogens.

Major neutralizing sites on vaccinia virus glycoprotein B5 are exposed differently on variola virus ortholog B6

Immunization against smallpox (variola virus) with Dryvax, a live vaccinia virus (VV), was effective, but now safety is a major concern. To overcome this issue, subunit vaccines composed of VV envelope proteins from both forms of infectious virions, including the extracellular enveloped virion (EV) protein B5, are being developed. However, since B5 has 23 amino acid differences compared with its B6 variola virus homologue, B6 might be a better choice for such a strategy. Therefore, we compared the properties of both proteins using a panel of monoclonal antibodies (MAbs) to B5 that we had previously characterized and grouped according to structural and functional properties. The B6 gene was obtained from the Centers for Disease Control and Prevention, and the ectodomain was cloned and expressed in baculovirus as previously done with B5, allowing us to compare the antigenic properties of the proteins. Polyclonal antibodies to B5 or B6 cross-reacted with the heterologous protein, and 16 of 26 anti-B5 MAbs cross-reacted with B6. Importantly, 10 anti-B5 MAbs did not cross-react with B6. Of these, three have important anti-VV biologic properties, including their ability to neutralize EV infectivity and block comet formation. Here, we found that one of these three MAbs protected mice from a lethal VV challenge by passive immunization. Thus, epitopes that are present on B5 but not on B6 would generate an antibody response that would not recognize B6. Assuming that B6 contains similar variola virus-specific epitopes, our data suggest that a subunit vaccine using the variola virus homologues might exhibit improved protective efficacy against smallpox.

A protein-based smallpox vaccine protects mice from vaccinia and ectromelia virus challenges when given as a prime and single boost

The heightened concern about the intentional release of variola virus has led to the need to develop safer smallpox vaccines. While subunit vaccine strategies are safer than live virus vaccines, subunit vaccines have been hampered by the need for multiple boosts to confer optimal protection. Here we developed a protein-based subunit vaccine strategy that provides rapid protection in mouse models of orthopoxvirus infections after a prime and single boost. Mice vaccinated with vaccinia virus envelope proteins from the mature virus (MV) and extracellular virus (EV) adjuvanted with CpG ODN and alum were protected from lethal intranasal challenge with vaccinia virus and the mouse-specific ectromelia virus. Organs from mice vaccinated with three proteins (A33, B5 and L1) and then sacrificed after challenge contained significantly lower titers of virus when compared to control groups of mice that were not vaccinated or that received sub-optimal formulations of the vaccine. Sera from groups of mice obtained prior to challenge had neutralizing activity against the MV and also inhibited comet formation indicating anti-EV activity. Long-term partial protection was also seen in mice challenged with vaccinia virus 6 months after initial vaccinations. Thus, this work represents a step toward the development of a practical subunit smallpox vaccine.

Physical and immunological characterization of a recombinant secreted form of the membrane protein encoded by the vaccinia virus L1R gene

We reported that immunization with recombinant proteins derived from vaccinia virus (VV) particles could provide protection against infection. Here we describe the physical and antigenic properties of the L1R membrane protein. The recombinant protein (L1R(185t)) was secreted as a monomer and correct folding was suggested by the presence of three intramolecular disulfide bonds and binding to conformation-specific monoclonal antibodies (MAbs). Furthermore, anti-L1R(185t) rabbit antisera exhibited potent virus-neutralizing activity against the IMV form of VV. We raised six MAbs against L1R(185t). Three recognized linear epitopes (residues 118--128) and neutralized IMV infectivity. These MAbs blocked binding of each other to L1R(185t) but failed to block binding of two previously described neutralizing anti-L1R MAbs, 7D11 and 2D5. The latter two antibodies blocked each other in binding L1R(185t). Thus, two antigenic sites on L1R overlap functional domains and based on recent structural studies these are found in accessible regions of the IMV L1R protein.

Epitope-mapping studies define two major neutralization sites on the vaccinia virus extracellular enveloped virus glycoprotein B5R

Vaccinia extracellular enveloped virus (EEV) is critical for cell-to-cell and long-range virus spread both in vitro and in vivo. The B5R gene encodes an EEV-specific type I membrane protein that is essential for efficient EEV formation. The majority of the B5R ectodomain consists of four domains with homology to short consensus repeat domains followed by a stalk. Previous studies have shown that polyclonal antibodies raised against the B5R ectodomain inhibit EEV infection. In this study, our goal was to elucidate the antigenic structure of B5R and relate this to its function. To do this, we produced multimilligram quantities of vaccinia virus B5R as a soluble protein [B5R(275t)] using a baculovirus expression system. We then selected and characterized a panel of 26 monoclonal antibodies (MAbs) that recognize B5R(275t). Five of these MAbs neutralized EEV and inhibited comet formation. Two other MAbs were able only to neutralize EEV, while five others were able only to inhibit comet formation. This suggests that the EEV neutralization and comet inhibition assays measure different viral functions and that at least two different antigenic sites on B5R are important for these activities. We further characterized the MAbs and the antigenic structure of B5R(275t) by peptide mapping and by reciprocal MAb blocking studies using biosensor analysis. The epitopes recognized by neutralizing MAbs were localized to SCR1-SCR2 and/or the stalk of B5R(275t). Furthermore, the peptide and blocking data support the concept that SCR1 and the stalk may be in juxtaposition and may be part of the same functional domain.

Antisense oligonucleotides targeted to the domain IIId of the hepatitis C virus IRES compete with 40S ribosomal subunit binding and prevent in vitro translation

Initiation of protein synthesis on the hepatitis C virus (HCV) mRNA involves a structured element corresponding to the 5' untranslated region and constituting an internal ribosome entry site (IRES). The domain IIId of the HCV IRES, an imperfect RNA hairpin extending from nucleotides 253 to 279 of the viral mRNA, has been shown to be essential for translation and for the binding of the 40S ribosomal subunit. We investigated the properties of a series of antisense 2'-O-methyloligoribonucleotides targeted to various portions of the domain IIId. Several oligomers, 14-17 nt in length, selectively inhibited in vitro translation of a bicistronic RNA construct in rabbit reticulocyte lysate with IC(50)s <10 nM. The effect was restricted to the second cistron (the Renilla luciferase) located downstream of the HCV IRES; no effect was observed on the expression of the first cistron (the firefly luciferase) which was translated in a cap-dependent manner. Moreover, antisense 2'-O-methyloligoribonucleotides specifically competed with the 40S ribosomal subunit for binding to the IRES RNA in a filter- retention assay. The antisense efficiency of the oligonucleotides was nicely correlated to their affinity for the IIId subdomain and to their ability to displace 40S ribosomal subunit, making this process a likely explanation for in vitro inhibition of HCV-IRES-dependent translation.

Apical loop-internal loop interactions: a new RNA-RNA recognition motif identified through in vitro selection against RNA hairpins of the hepatitis C virus mRNA

We performed in vitro selection of oligoribonucleotides in order to identify high-affinity motifs recognizing RNA hairpins located at the 3' end (SL1) and at the 5' end (domain IV of the internal ribosome entry site) of the hepatitis C virus mRNA. We selected aptamers constituted by an internal loop complementary to the SL1 apical loop, flanked by G-C-rich double-stranded regions, able to form complexes with a K(d) of 70 nM, at 37 degrees C under ionic conditions close to intracellular ones. The complex involves selective apical loop (SL1)-internal loop (aptamer) interactions. Similar structurally organized aptamers were independently identified against domain IV and were shown to also give rise to such complexes. Apical loop-internal loop interaction could constitute a new recognition motif allowing specific intra- or intermolecular RNA-RNA association.