Safety and immunogenicity of VLPCOV-02, a SARS-CoV-2 self-amplifying RNA vaccine with a modified base, 5-methylcytosine

Continuing emergence of variants of concern resulting in reduced SARS-CoV-2 vaccine efficacy necessitates additional prevention strategies. The structure of VLPCOV-01, a lipid nanoparticle-encapsulated, self-amplifying RNA COVID-19 vaccine with a comparable immune response to BNT162b2, was revised by incorporating a modified base, 5-methylcytosine, to reduce reactogenicity, and an updated receptor-binding domain derived from the Brazil (gamma) variant. Interim analyses of a phase 1 dose-escalation booster vaccination study with the resulting construct, VLPCOV-02, in healthy, previously vaccinated Japanese individuals (N = 96) are reported (jRCT2051230005). A dose-related increase in solicited local and systemic adverse events was observed, which were generally rated mild or moderate. The most commonly occurring events were tenderness, pain, fatigue, and myalgia. Serum SARS-CoV-2 immunoglobulin titers increased during the 4 weeks post-immunization. VLPCOV-02 demonstrated a favorable safety profile compared with VLPCOV-01, with reduced adverse events and fewer fever events at an equivalent dose. These findings support further study of VLPCOV-02.

Incorporation of 5 methylcytidine alleviates innate immune response to self-amplifying RNA vaccine

In order to improve vaccine effectiveness and safety profile of existing synthetic RNA-based vaccines, we have developed a self-amplifying RNA (saRNA)-based vaccine expressing membrane-anchored receptor binding domain (RBD) of SARS-CoV-2 S protein (S-RBD) and have demonstrated that a minimal dose of this saRNA vaccine elicits robust immune responses. Results from a recent clinical trial with 5-methylcytidine (5mC) incorporating saRNA vaccine demonstrated reduced vaccine-induced adverse effects while maintaining robust humoral responses. In this study, we investigate the mechanisms accounting for induction of efficient innate and adaptive immune responses and attenuated adverse effects induced by the 5mC-incorporated saRNA. We show that the 5mC-incorporating saRNA platform leads to prolonged and robust expression of antigen, while induction of type-I interferon (IFN-I), a key driver of reactogenicity, is attenuated in peripheral blood mononuclear cells (PBMCs), but not in macrophages and dendritic cells. Interestingly, we find that the major cellular source of IFN-I production in PBMCs is plasmacytoid dendritic cells (pDCs), which is attenuated upon 5mC incorporation in saRNA. In addition, we demonstrate that monocytes also play an important role in amplifying proinflammatory responses. Furthermore, we show that the detection of saRNA is mediated by a host cytosolic RNA sensor, RIG-I. Importantly, 5mC-incorporating saRNA vaccine candidate produced robust IgG responses against S-RBD upon injection in mice, thus providing strong support for the potential clinical use of 5mC-incorporating saRNA vaccines.

Safety and immunogenicity of SARS-CoV-2 self-amplifying RNA vaccine expressing an anchored RBD: A randomized, observer-blind phase 1 study

VLPCOV-01 is a lipid nanoparticle-encapsulated self-amplifying RNA (saRNA) vaccine that expresses a membrane-anchored receptor-binding domain (RBD) derived from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. A phase 1 study of VLPCOV-01 is conducted (jRCT2051210164). Participants who completed two doses of the BNT162b2 mRNA vaccine previously are randomized to receive one intramuscular vaccination of 0.3, 1.0, or 3.0 μg VLPCOV-01, 30 μg BNT162b2, or placebo. No serious adverse events have been reported. VLPCOV-01 induces robust immunoglobulin G (IgG) titers against the RBD protein that are maintained up to 26 weeks in non-elderly participants, with geometric means ranging from 5,037 (95% confidence interval [CI] 1,272-19,940) at 0.3 μg to 12,873 (95% CI 937-17,686) at 3 μg compared with 3,166 (95% CI 1,619-6,191) with 30 μg BNT162b2. Neutralizing antibody titers against all variants of SARS-CoV-2 tested are induced. VLPCOV-01 is immunogenic following low-dose administration. These findings support the potential for saRNA as a vaccine platform.

saRNA vaccine expressing membrane-anchored RBD elicits broad and durable immunity against SARS-CoV-2 variants of concern

Several vaccines have been widely used to counteract the global pandemic caused by SARS-CoV-2. However, due to the rapid emergence of SARS-CoV-2 variants of concern (VOCs), further development of vaccines that confer broad and longer-lasting protection against emerging VOCs are needed. Here, we report the immunological characteristics of a self-amplifying RNA (saRNA) vaccine expressing the SARS-CoV-2 Spike (S) receptor binding domain (RBD), which is membrane-anchored by fusing with an N-terminal signal sequence and a C-terminal transmembrane domain (RBD-TM). Immunization with saRNA RBD-TM delivered in lipid nanoparticles (LNP) efficiently induces T-cell and B-cell responses in non-human primates (NHPs). In addition, immunized hamsters and NHPs are protected against SARS-CoV-2 challenge. Importantly, RBD-specific antibodies against VOCs are maintained for at least 12 months in NHPs. These findings suggest that this saRNA platform expressing RBD-TM will be a useful vaccine candidate inducing durable immunity against emerging SARS-CoV-2 strains.

HER2 expression in oesophageal carcinoma and Barrett's oesophagus associated adenocarcinoma: An Australian study

BACKGROUND

Several studies have evaluated the prognostic value of HER2 in oesophageal cancer, but the prognostic influence of HER2 overexpression in oesophageal cancer remains uncertain. The aim of this study was to assess the incidence of HER2 positivity and relationship with clinicopathological features in patients with oesophageal cancer.

DESIGN

The study cohort consisted of 269 patients diagnosed with oesophageal carcinoma in a single institution. HER2 expression was analysed by immunohistochemistry (IHC) and silver in situ hybridization (SISH) in 152 archival oesophageal cancer specimens. Survival analysis was assessed using Hazard models.

RESULTS

HER2 expression was IHC3+ in 14 (9.2%), IHC2+ in 14 (9.2%), IHC1+ in 57 (37.5%), and IHC0 in 67 (44.1%) cases. SISH results confirmed that 15 specimens (9.9%) were HER2 gene amplified. Among 27 squamous cell carcinomas (SCCs) only 3.7% were HER2 positive whereas 11.2% of 125 adenocarcinomas were HER2 positive. The HER2 positive tumours were more likely to occur in men (OR: 5.00, 95% CI: 1.69-14.29), smokers (OR: 10.00, 95% CI: 4.17-25) and in patients with Barrett's oesophagus (OR: 8.33, 95% CI: 3.71-20.00). There was no significant difference in survival between the (HER2 +ve, 14.3 months vs HER2 -ve, 24.6 months, p = 0.42) CONCLUSION: A HER2 prevalence rate of 9.9% was found among patients with oesophageal cancer and no correlation with survival was detected overall.

Aberrant p16(INK4A) and DPC4/Smad4 expression in intraductal papillary mucinous tumours of the pancreas is associated with invasive ductal adenocarcinoma

BACKGROUND AND AIMS

Intraductal papillary mucinous tumours (IPMT) of the pancreas constitute a unique pathological entity with an overall incidence of associated invasive malignancy of 20%. The malignant potential of an individual IPMT cannot be accurately predicted. Preoperative estimation of the risk of associated invasive malignancy with IPMT would be of significant clinical benefit. As aberrations in cell cycle regulatory genes are associated with the progression of precursor pancreatic ductal lesions to invasive adenocarcinoma, we examined expression of key cell cycle regulatory genes in the cyclin D1/retinoblastoma pathway and the transforming growth factor beta/Smad4 signalling pathway in a cohort of patients with surgically resected IPMT.

METHODS

Sections of formalin fixed paraffin embedded pancreatic tissue from a cohort of 18 patients with IPMT were examined using immunohistochemistry for protein expression of cell cycle regulatory genes p16(INK4A), p21(CIP1), p27(KIP1), cyclin D1, pRb, and p53, as well as the cell signalling molecule Smad4. A comparison of expression levels was made between adenoma/borderline IPMT (10 patients) and intraductal papillary mucinous carcinoma (IPMC) (eight patients, four of whom harboured invasive carcinoma). Statistical analysis was performed using the chi(2) and Fisher's exact tests.

RESULTS

Aberrant expression of the proteins examined increased in frequency from adenoma/borderline IPMT to IPMC. Specifically, there was a significantly greater incidence of loss of p16(INK4A) expression in IPMC: 8/8 lesions (100%) compared with 1/10 (10%) adenoma/borderline IPMT (p<0.001). Similarly, loss of Smad4 expression was associated with IPMC: 3/8 (38%) versus adenoma/borderline IPMT 0/10 (p<0.03). Loss of Smad4 expression within the IPMT was the best marker for the presence of invasive carcinoma (p<0.001).

CONCLUSIONS

These data indicate that loss of p16(INK4A) and Smad4 expression occur more frequently in IPMC alone, or with associated invasive carcinoma, compared with adenoma/borderline IPMT. Aberrant protein expression of these cell cycle regulatory genes in IPMT and pancreatic intraepithelial neoplasia in the current model of pancreatic cancer progression suggest similarities in their development and may also represent the subsequent risk of invasive carcinoma.

Overexpression of p21(WAF1/CIP1) is an early event in the development of pancreatic intraepithelial neoplasia

Pancreatic cancer (PC) is thought to develop through a series of duct lesions termed pancreatic intraepithelial neoplasia (PanIN). Characterization of the molecular pathology of these lesions may lead to additional understanding of pancreatic ductal carcinogenesis. We examined the protein expression of four functionally related genes, p21(WAF1/CIP1) (CDKN1A), p53, cyclin D1 (CCND1), and DPC4/Smad4 (MADH4), aberrations of which are associated with PC, within 451 PanIN lesions present in the pancreata of 60 patients. p21(WAF1/CIP1) overexpression was present in the normal ducts of 9% of patients and increased progressively to 16% of patients with PanIN-1A lesions, to 32% of patients with PanIN-1B lesions, 56% of patients with PanIN-2 lesions, 80% of patients with PanIN-3 lesions, and 85% of patients with invasive carcinomas (P < 0.01). p53 and cyclin D1 overexpression occurred predominantly in PanIN-3 lesions (P < 0.01), and loss of DPC4/Smad4 expression occurred predominantly in PanIN-3 lesions and invasive carcinoma (P < 0.01). In addition, p21(WAF1/CIP1) overexpression occurred independently of p53 and DPC4/Smad4 expression within invasive carcinoma and PanIN-3 lesions. Cyclin D1 overexpression or loss of DPC4/Smad4 expression was apparent in 85% of invasive carcinomas but in only 14% of PanIN-2 lesions. These data demonstrate that overexpression of p21(WAF1/CIP1) occurs early in the development of PanIN, before aberrations in p53, cyclin D1, and DPC4/Smad4 expression. p21(WAF1/CIP1) overexpression, independent of p53 and/or DPC4/Smad4 expression, may reflect increased Ras activity, either directly through activating K-ras mutations or as a consequence of HER-2/neu (ERBB2) overexpression, both of which are common in PC and in early events in the development of PanIN. These data support further the current progression model for PC and demonstrate that aberrant expression of key cell cycle regulatory genes may be important in the early development and progression of PanIN.

Suggestions for HER-2/neu testing in breast carcinoma, based on a comparison of immunohistochemistry and fluorescence in situ hybridisation

The arrival of Herceptin (Trastuzumab), an antibody against the HER-2 oncogene found in a proportion of breast carcinomas and other carcinomas, has emphasised the need for a standardised technique for demonstrating overexpression of HER-2. We compared the Dako A485 antibody and Dako HercepTest kit (HT) on a series of 122 breast carcinomas. Fluorescence in situ hybridisation (FISH) (Vysis) was performed on all cases with positive or equivocal immunohistochemical results. The Dako A485 showed HER-2 overexpression in 53% of carcinomas, while the HT showed 21% positive (HT 2+ 8%, HT 3+ 13%) and 79% negative (HT 0 67%, HT 1+ 12%). FISH for HER-2 gene amplification on all the HT 1+ and HT 2+ cases was negative, whereas FISH analysis of all HT 3+ cases was positive, with the exception of one case which could not be analysed for technical reasons. When histological subtype was analysed, only grade 3 infiltrating duct carcinomas were FISH-positive, suggesting that histological grading and subtyping may be able to triage carcinomas suitable for HER-2 testing. We suggest that the HT or a similar standardised immunohistochemical study for HER-2 can be used to screen breast carcinomas. We then recommend FISH where the carcinoma is HT 2+. FISH may also be appropriate in high grade, HT 1+ carcinomas where there are doubts regarding optimal tissue fixation or block storage conditions.

Conventional patterns of human intestinal proliferation in a severe-combined immunodeficient xenograft model

The present work describes the pattern of human intestinal proliferation in an immunodeficient murine xenograft model, which we have shown to closely mimic cell division in normal paediatric gut. Cellular proliferation was measured using a double-label technique combining MIB-1 immunohistochemistry and [3H]thymidine autoradiography, to critically compare values for the tissue growth fraction (G1, G2, S- and M-phase cells) and DNA synthesizing (S-phase) cells in xenograft epithelium, lamina propria, muscularis externa and intraepithelial lymphocytes. The MIB-1 monoclonal antibody (which recognises the cell-cycle dependent nuclear antigen Ki-67) specifically labelled proliferating human cells within the xenografts and did not cross-react with dividing murine cells. This was confirmed using ultrastructural in situ hybridisation with human- and mouse-specific DNA probes to identify the genetic origin of proliferating cells. In general, we found a good tissue correlation between MIB-1 and [3H]thymidine labelling, the only exception being an apparent dysregulation of Ki-67 antigen expression in regenerating xenograft epithelium. In developed xenograft intestine, the highest levels of proliferation were consistently recorded within the crypt epithelium, where 15.7%-26.7% of cells were actively cycling and S-phase occupied approximately half of the cell cycle. The frequency distribution of proliferating epithelial cells within small and large intestinal xenograft crypts was clearly tissue-specific, showing typical patterns of cell division. Therefore, the presence of functional pluripotent epithelial stem cells and conventional spatio-temporal patterns in cellular proliferation, migration, de-cycling, lineage commitment and cytodifferentiation now makes this an attractive experimental model with which to study human intestinal crypt responses to various types of tissue manipulation, e.g. cytotoxic, radiotherapeutic, dietary, endocrine and gene-targeting therapy.

Non-isotopic in situ hybridization at the ultrastructural level

Non-isotopic in situ hybridization techniques are becoming increasingly widely used at the ultrastructural level, permitting rapid localization of nucleic acid targets with a high degree of resolution. Technical considerations dictate that the great specificity of the method cannot be matched by a similar degree of sensitivity; the value of non-isotopic ultrastructural in situ hybridization lies in its unique ability to localize nucleic acid targets in relation to submicroscopic cellular structures. This article presents an overview of non-isotopic ultrastructural hybridization methods and applications.

Human intestinal development in a severe-combined immunodeficient xenograft model

The present work describes a severe-combined immunodeficient murine xenograft model used to investigate human gastrointestinal ontogenesis. Specifically, the study has tested whether carefully selected regions of human fetal gut are able to undergo region-specific morphogenesis and epithelial cytodifferentiation when transplanted subcutaneously into immunodeficient mice. In addition, double-label in situ hybridisation techniques, utilising specific human and mouse DNA probes, have been adopted to characterise host and donor cell types and to investigate the potential developmental roles for non-epithelial cells in the regulation of epithelial differentiation pathways in vivo. Human fetal small and large bowel developed to form a characteristic mucosa 10 weeks after transplantation, which displayed clear region-specific structural and functional gradients. The initial phase of xenograft epithelialisation closely resembled the stratified type of epithelium which is present during early fetal gastrointestinal development. Idiosyncratic epithelial differentiation pathways were recorded during xenograft regeneration, with an absence of Paneth cells and an abundance of enteroendocrine cells when compared with developed xenograft and paediatric intestine. Such differences may, therefore, be important in ensuring rapid and region-specific development in the absence of conventional luminal stimuli and hormonal changes that occur normally during pregnancy. In situ hybridisation demonstrated an exclusively human origin for the intestinal xenograft epithelium and muscularis mucosa and externa. Although the submucosa and lamina propria were comprised of a chimeric mixture, murine cells were rarely seen to contact with the epithelium, which interacted primarily with human myofibroblasts and human intraepithelial lymphocytes. It is proposed that a 'selection' process operates to maintain species-specific cellular interactions, and this mechanism may subsequently play an important role in regulating epithelial cell differentiation, orchestrated in part by juxtaposed non-epithelial cell types.

Combined immunocytochemistry and non-isotopic in situ hybridization for the ultrastructural investigation of human parvovirus B19 infection

Parvovirus B19 is a single-stranded DNA virus with a specific tropism for human erythroid precursor cells. The virus codes for two overlapping structural (capsid) proteins and one non-structural protein which is thought to perform essential functions in viral replication, transcription and packaging. The ultrastructural localization of these proteins was achieved in cultured haemopoietic cells derived from fetal liver which had been infected in vitro and subsequently embedded in LR White acrylic resin. Postembedding immunogold detection of B19 structural and non-structural proteins was combined with localization of viral nucleic acid by in situ hybridization using a digoxigenin-labelled probe and different sized gold labels. The majority of the B19 capsid protein and DNA present in cells harvested 48 hours post-infection co-localized within the centri-nuclear region of erythroid cells demonstrating characteristic chromatin margination. Relatively little DNA hybridization signal was present over paracrystalline inclusions strongly labelled with anti-capsid protein monoclonal antibody R92F6. Viral DNA and capsid protein were co-localized in apparent egress from the nucleus through nuclear pores. B19 non-structural protein was detected in association with both nuclear and cytoplasmic arrays of capsids, supporting the view that this protein plays an important role in viral packaging and remains associated with the complete viral particle until its release from the cell. Co-localization of viral nucleic acid and proteins at the ultrastructural level is a flexible, rapid and highly specific tool for examination of viral life-cycles within cells.

Intracellular localization of parvovirus B19 nucleic acid at the ultrastructural level by in situ hybridization with digoxigenin-labelled probes

Conditions suitable for immunogold detection of digoxigenin-labelled DNA probes hybridized to parvovirus B19-infected erythroid cells embedded in Lowicryl K4M and LR White acrylic resins were established at the electron microscope level. The protocol was initially optimized using a positive control probe for whole human DNA which produced signal over the heterochromatin of all nucleated cells. In cultures harvested 2 days postinfection, B19 nucleic acid was detected mainly within the centrinuclear region of erythroid cells exhibiting characteristic margination of the chromatin. The B19 hybridization signal was largely unaffected by denaturation and was resistant to RNase digestion but sensitive to DNase digestion, indicating that it was mainly single-stranded B19 DNA. Relatively few gold particles were found over crystalline arrays of viral capsids, consistent with the observation that they are composed of mainly 'empty' capsids. B19 nucleic acid was detected in apparent transit from nucleus to cytoplasm through pores in the nuclear membrane. While the sensitivity of this system is limited by the fact that hybridization occurs only at the surface of the section, it is a rapid and specific means of localizing viral nucleic acids with a high degree of resolution.

Ultrastructural features of fetal erythroid precursors infected with parvovirus B19 in vitro: evidence of cell death by apoptosis

Human parvovirus B19 cannot be cultured in standard cell lines and relatively little is known about the intracellular life-cycle of the virus. In this study, ultrastructural features of B19 infection were examined using haemopoietic cell suspension cultures derived from human fetal liver. Erythroblasts from infected cultures frequently contained crystalline arrays of both full and empty virus-like particles. The number and size of these arrays increased with the duration of culture, and their location changed from exclusively nuclear at 24 h post-infection to both nuclear and cytoplasmic at 3 days post-infection. Arrays were occasionally found in cytoplasmic protuberances which appeared to be pinching off from the cell. The location of the arrays corresponded to the distribution of viral capsid protein determined by immunolabelling at the light microscope level. Cells containing viral crystalline arrays also exhibited nucleolar degeneration, extreme margination of the nuclear heterochromatin, and cytoplasmic vacuolation. These features are typical of cells undergoing individual programmed cell death or 'apoptosis'. The triggering of apoptosis in erythroid precursors by parvovirus B19 may help to explain the apparent lack of a strong inflammatory response to fetal B19 infection and may have implications for understanding the mechanisms of viral spread throughout the host.

In vitro culture for the detection of infectious human parvovirus B19 and B19-specific antibodies using foetal haematopoietic precursor cells

The inability to culture human parvovirus B19 in standard cell lines has rendered investigation of clinical samples for the presence of infectious virus problematic. Using haematopoietic precursors derived from first trimester foetal liver as targets for infection, and non-isotopic in situ hybridization to detect intracellular viral DNA, we have assessed infectivity in stored serum samples taken from nine volunteers at different stages following intranasal inoculation with parvovirus B19. Infectious virus was detected as early as 3 days after inoculation, the cessation of infectivity correlating with the rise in specific IgM. In all but two samples, infectivity correlated with the detection of B19 DNA by dot-blot hybridization, although in vitro culture was 10-fold more sensitive than dot-blot hybridization. B19 DNA was detected by the polymerase chain reaction in serum from one volunteer up to 36 days after inoculation, although samples containing specific antibody were non-infectious. Infection of erythroid precursors was completely inhibited by preincubation of virus with serum containing high titre B19-specific IgM and IgG. Unexpectedly, this was associated with a strong B19 DNA hybridization signal within the cytoplasm of phagocytic macrophages. This culture and detection system is a rapid and sensitive means of detecting infectious virus in serum samples, and of assessing the neutralizing ability of B19-specific antibodies.

Immunophenotyping of fetal haemopoietic cells permissive for human parvovirus B19 replication in vitro

Human parvovirus B19 is known to inhibit erythroid colony formation in vitro, but the precise stage of differentiation at which erythroid precursors become capable of supporting viral replication has not been accurately determined. In order to address this issue, haemopoietic cells derived from first trimester fetal liver were cultured in medium containing B19 antigen-positive serum. Infected cells were phenotyped by combining immunohistology for cell-type specific antigens with non-isotopic in situ hybridization for B19 nucleic acid. Strong nuclear hybridization signal was detected as early as 8 h after infection in erythroid precursors labelling with antibodies to glycophorin A, glycophorin C, CD43, CD36 and HLA-ABC (pronormoblast or normoblast phenotype). Giant erythroid precursors labelling with the same five antibodies were a pathognomonic feature of infected cultures, but contained relatively little B19 nucleic acid. Hybridization signal was not detected in progenitor cells of more primitive erythroid phenotype or in nuclei of cells of other lineages, though B19 DNA was occasionally localized within the cytoplasm of macrophages. Double-labelling with antibody Ki-67 confirmed that proliferating cells were targets for B19 infection. Co-detection of cell-type specific antigens and viral nucleic acid is a powerful tool for investigating host cell specificity, and suggests that proliferating late erythroid precursors are the only haemopoietic cells fully permissive for B19 infection.

Non-isotopic in situ hybridisation and immunophenotyping of infected cells in the investigation of human fetal parvovirus infection

AIMS

To compare the use of biotinylated and digoxigenin labelled probes for diagnosis of human fetal parvovirus B19 infection in formalin fixed, paraffin wax embedded tissues; and to assess the cellular distribution of the virus in positive cases.

METHODS

Sections of lung tissue from 23 cases of anatomically normal non-immune fetal hydrops presenting between 1984 and 1989, and from 13 control cases of hydrops due to chromosomal abnormality were probed for B19 DNA by in situ hybridisation using both biotinylated and digoxigenin labelled probes. The distribution of the virus was then investigated in all cases of fetal B19 infection confirmed in this laboratory to date (n = 11) by combining in situ hybridisation for viral DNA (using the digoxigenin system) with immunohistological labelling for a range of cellular antigens.

RESULTS

Five unequivocal cases of B19 infection were identified among the 23 fetuses with unexplained hydrops using both probe labels. When combined with data from previous studies of the period 1974-1983, the results indicate that B19 infection was responsible for 27% of cases of anatomically normal non-immune hydrops and 8% of all cases, of non-immune hydrops presenting to this hospital over 15 years. False positive signal was seen in an additional three cases, using biotinylated probes. Digoxigenin labelled probes gave greater specificity and permitted detailed investigation of tissues high in endogenous biotin. Though most cells containing B19 DNA colabelled as erythroid precursors, viral DNA was frequently detected within mononuclear-phagocytic cells. In three cases viral signal was also found within occasional myocardial cells labelled by antibody to desmin.

CONCLUSIONS

A relatively high proportion of cases of anatomically normal, non-immune hydrops are caused by B19 infection. Digoxigenin is a more reliable probe label than biotin for in situ hybridisation in archival fetal tissues. Double labelling for cellular antigens and viral nucleic acid is a powerful technique for investigating virus-host cell interactions, and provides evidence that cell types other than those of erythroid lineage may have a role in human fetal parvovirus infection.

Clinical and histopathological features of parvovirus B19 infection in the human fetus

OBJECTIVE

To provide a comprehensive description of the clinical and histopathological features associated with parvovirus B19 infection of the human fetus.

SUBJECTS

All cases of parvovirus B19-related fetal death presenting to the John Radcliffe Hospital, Oxford, over a 16 year period. Diagnosis was confirmed retrospectively by non-isotopic in situ hybridization for parvovirus B19 DNA.

RESULTS

The ten cases occurred in two clusters (1979-80 and 1988-89) and presented between 15 and 29 weeks gestation. In at least three cases maternal infection was asymptomatic. Nine fetuses were grossly hydropic at necropsy. Histological features common to all cases included the presence of typical intranuclear inclusions in erythroid precursor cells and evidence of vasculitis within placental villi. Inflammatory changes were also present in the myocardium of four cases, with evidence of subendocardial fibroelastosis in three.

CONCLUSIONS

Histological features of fetal parvovirus B19 infection are similar across a range of gestational ages. The heart failure and hydropic state associated with fetal parvovirus infection may be of multifactorial aetiology, and not due to fetal anaemia alone.

Optimization of non-isotopic in situ hybridization on formalin-fixed, paraffin-embedded material using digoxigenin-labelled probes and transgenic tissues

The sensitivity of non-isotopic in situ hybridization (NISH), particularly on formalin-fixed, paraffin-embedded (FFPE) clinical tissues, has been the subject of controversy. Generally, NISH has been regarded as being less sensitive than radiolabelled procedures, although some reports have contradicted this. Accordingly, tissues from mice which were transgenic for variable amounts of the human alpha-1-antitrypsin gene were used to optimize the NISH procedure and to estimate the sensitivity. This approach showed that prolonged incubation of slides in final substrate resulted in high sensitivity--about 13 kb of target DNA. However, this prolonged incubation crucially depended on achieving minimal non-specific background staining. Many factors affected the degree of background staining, but five were particularly important. First, the method of mounting cut sections onto slides. Second, the length of the probe (ideally less than 400 bp). Third, the procedure for proteolytic digestion. Fourth, the denaturation technique, and fifth, the quality of the dextran sulphate used in the hybridization mix. The optimized protocol showed variable patterns of mRNA distribution in the transgenic mouse livers, while DNA distribution appeared uniform.

Immunohistological detection of human parvovirus B19 in formalin-fixed, paraffin-embedded tissues

Human parvovirus B19 is a cause of aplastic crises in patients with haemolytic anaemias, prolonged bone marrow failure in the immunosuppressed, and fetal death secondary to non-immune hydrops. The immunohistological detection of parvovirus B19 in formalin-fixed, paraffin-embedded tissues has not previously been reported, and definitive diagnosis of infection in such specimens has relied on the use of specialized DNA hybridization and amplification techniques. A new monoclonal antibody to B19 capsid proteins, R92F6, was found to be capable of labelling infected cells in paraffin-embedded tissues from all 19 cases of parvovirus-related fetal hydrops tested, and in bone marrow from a child with congenital immunodeficiency and chronic parvovirus infection. Viral antigen was detected both in cytoplasmic and in nuclear distributions using the alkaline phosphatase anti-alkaline phosphatase (APAAP) technique without preceding proteolytic digestion. The viral epitope recognized appears to be highly conserved, as specimens were obtained over a 13-year period from widely spaced locations in the U.K. Antibody R92F6 should facilitate rapid diagnosis of parvovirus B19 infection in routinely processed and archival specimens.

A nude mouse xenograft model of fetal intestine development and differentiation

This report describes a novel in vivo model of intestinal differentiation. Fourteen day, undifferentiated fetal rat small intestine, stripped of the major part of its mesenchyme, suspended in a type I collagen gel and then xenografted into a nude mouse, undergoes small intestinal morphogenesis and cytodifferentiation. All four major epithelial lineages, namely Paneth, goblet, columnar and endocrine are present. Double-label nonisotopic in situ hybridization, employing biotinylated and digoxigenin-labelled whole rat DNA and whole mouse DNA probes, was performed to distinguish donor cells from host cell types. The outer longitudinal smooth muscle layer, and the major part of the lamina propria, including pericryptal fibroblasts, are of host mouse origin; the inner circular smooth muscle layer is of donor rat origin. Cells of the muscularis propria and lamina propria acquired smooth muscle alpha-actin, presumably under the influence of the donor endoderm. Furthermore, this xenograft develops a host vascular network, and cells with the morphological appearance of lymphocytes are present within the intestinal epithelium. The production of chemotactic factors by the endoderm is postulated because grafting of collagen gel alone results in a minimal invasion by stromal cells which do not express smooth muscle alpha-actin.

Auditory brainstem of the ferret: maturation of the brainstem auditory evoked response

A longitudinal study of developmental changes in the brainstem auditory evoked response (BAER) was made on 19 ferrets between postnatal days 25 (P25) and 50. Responses to free-field click stimuli were recorded from anaesthetized animals, and compared with data obtained from 8 adult ferrets. A reproducible BAER was first recordable on P27, although the response onset was generally later in smaller animals. BAER onset preceded eye opening, which started on P32. Adult-like thresholds were observed in all animals by P40, but the age at which they were attained was also dependent on size. The BAER in the adult ferret consists of 4 main vertex-positive peaks occurring in the first 5 ms following transient acoustic stimulation. In the youngest animals the presence of an additional peak (between II and III) and the slurring of peaks III and IV were consistent features. The individual peaks undergo an asymmetrical pattern of development, with mean peak I latency attaining an adult value at P40, while mean peak IV latency is still 115% of the mean adult value at that age. BAERs could routinely be recorded using high stimulus presentation rates (greater than 40/s), though an increase in absolute and interpeak latencies occurred, the extent of which decreased with age. The pattern of BAER development in the ferret is compared with that in other species, and the concept of the 'silent period' (period between conception and onset of hearing) as a standard unit of auditory development is introduced.

Changes in the brainstem auditory evoked response of the rabbit during the first postnatal month

Brainstem auditory evoked responses (BAERs) were recorded in 73 albino rabbits during the first postnatal month. Responses could not be evoked before the ninth day post-term using free field click stimulation at 60 dBHL. The onset of BAERs to these stimuli on or after day 9 was coincident with the onset of behavioural responses to sounds and, in the majority of animals, with eye opening. The onset of BAERs was delayed in animals with low body weight. The intensity required to evoke detectable BAERs in normally grown animals decreased rapidly after day 9 post-term. The most significant changes in the form of the BAER in the first postnatal month were an increase in the amplitude of peak III and the separation of peaks IV and V. Peak I and the negative dip after peak V (Vn) were consistent features of the BAER during development. The latencies of these deflections and the interval between them decreased by approximately 1.5 and 4 ms respectively up to the end of the first month post-term. On days 9 and 10 post-term, stimulation at a higher rate (40 Hz) failed to evoke a BAER in some animals. In other animals the change in stimulation rate from 10 to 40 Hz produced a large increase in the latency of peak V. The unusually large changes in the latencies of peaks and the interpeak intervals during the development of the rabbit indicate that this animal may be particularly suitable for studies of perinatal complications on development of the brainstem when the BAER is to be used as non-invasive measure of neural function.