Molecular studies of visna virus gene expression: analysis of envelope gene expression in transgenic sheep

Genome Editing Strategies to Protect Livestock from Viral Infections

The livestock industry is constantly threatened by viral disease outbreaks, including infections with zoonotic potential. While preventive vaccination is frequently applied, disease control and eradication also depend on strict biosecurity measures. Clustered regularly interspaced palindromic repeats (CRISPR) and associated proteins (Cas) have been repurposed as genome editors to induce targeted double-strand breaks at almost any location in the genome. Thus, CRISPR/Cas genome editors can also be utilized to generate disease-resistant or resilient livestock, develop vaccines, and further understand virus-host interactions. Genes of interest in animals and viruses can be targeted to understand their functions during infection. Furthermore, transgenic animals expressing CRISPR/Cas can be generated to target the viral genome upon infection. Genetically modified livestock can thereby reduce disease outbreaks and decrease zoonotic threats.

Stromelysin-1 (MMP-3) expression driven by a macrophage-specific promoter results in reduced viability in transgenic mice

Macrophage expression of matrix degrading metalloproteinases (MMPs) in human atheroma has been found to occur in rupture-prone areas of plaques. To investigate the effect of metalloproteinase activity on plaque stability, we attempted to generate mice that expressed a stromelysin-1 (MMP-3) transgene specifically in macrophages. Promoter sequences taken from a macrophage-tropic lentivirus (visna) were used to drive transgene expression. The transgene construct was expressed in macrophages in vitro and its autoactivation was established by casein zymography. Transgenic mice generated with this construct died at or before birth. No gross anatomical changes were observed in these mice. Embryos arising from a second round of oocyte injections with the transgene were examined at day 16 of gestation. Of the products of conception, approximately 40% resulted in vacant conceptuses. Only one animal of 38 examined carried the transgene and its expression of MMP-3 mRNA at E16 was faintly detected by RT-PCR. When a non-toxic reporter gene, luciferase, was substituted for the MMP-3 cDNA, healthy transgenic mice were produced that expressed the reporter gene in a wide variety of tissue macrophages, including those located in the brain, testis, lung, and thymus. These studies suggest that constitutive expression of MMP-3 in diverse populations of tissue macrophages leads to prenatal or neonatal death in the mouse. It appears likely that more sophisticated transcriptional control of MMP-3 expression will be required in order to generate stromelysin-1 transgenic mice that could be useful models for studying overexpression of this metalloproteinase's activity in the lesional macrophages of atherosclerotic plaques.

Late postnatal transmission of human immunodeficiency virus type 1 infection from mothers to infants in Dar es Salaam, Tanzania

OBJECTIVE

To study late postnatal transmission of human immunodeficiency virus type 1 in a cohort of children born to HIV-1-seropositive mothers who delivered at Muhimbili Medical Centre in Dar es Salaam, Tanzania.

MATERIALS AND METHODS

Since 1991 a prospective cohort study of mother-to-child transmission of HIV-1 has been conducted at Muhimbili Medical Centre in Dar es Salaam. HIV-1-seropositive mothers and age-matched seronegative controls were recruited into the cohort at delivery together with their newborns. Diagnosis of HIV-1 infection in children was based on polymerase chain reaction, HIV-1 p24 antigen tests and HIV antibody tests. Late postnatal transmission was defined as HIV-1 infection occurring after 6 months of age in a child who was uninfected at 6 months of age and who had an HIV-1-seropositive mother. Children born to HIV-seronegative mothers were used as controls. Breast-feeding was universal in this cohort. CD4 and CD8 T lymphocytes were assayed by flow cytometry in the mothers.

RESULTS

Among 139 children born to HIV-1-seropositive mothers and known to be HIV-uninfected at 6 months of age, 8 children became HIV-1-infected at the end of their first year of life or later. No conversions were observed in children younger than 11 months. The 8 conversions were observed during a follow-up covering 1555 child months between 6 and 27 months of age corresponding to a conversion rate of 6.2 per 100 child years. Among 260 children with HIV-seronegative mothers no child became HIV-infected during the follow-up. The percentage of CD4 T lymphocytes was similar in mothers with early and late transmission but was significantly lower in transmitting than in nontransmitting mothers.

CONCLUSION

Because no HIV-1 infection occurred in children with HIV-seronegative mothers, we conclude that the observed infections at the end of the first year of life or later among children born to HIV-seropositive women were caused by late transmission from mother to child, most likely through breast-feeding.

Maedi-Visna and ovine progressive pneumonia

Maedi-Visna and ovine progressive pneumonia are disease of sheep that are caused by ovine lentivirus and characterized by chronic inflammation of the lungs, mammary glands, joints, and central nervous system. Although tremendous progress in research has led to a better understanding of the pathogenesis of these diseases, many questions still remain. Much of the mystery is the result of the complexity of the ovine lentivirus genome and the intricate interactions of the virus with the host during replication. Discoveries in molecular virology are shedding light on these interactions and novel approaches to prevent and control lentivirus infections are being explored. There is hope that some of these approaches will eventually be used to eradicate these diseases.

Pattern of HIV viraemia and CD4 levels in relation to pregnancy in HIV-1 infected women

The objective was to study HIV-1 viraemia and CD4 levels during and 6 months after pregnancy. HIV cultures on peripheral blood mononuclear cells (PBMC) and plasma from 225 samples were performed in 90 HIV-1 infected women with 59 continued and 35 terminated pregnancies. P-24 antigen and HIV-DNA were also studied. 34 women originated from European, 44 from African and 10 from other countries while 2 were of unknown origin. HIV was detected in 30% of the plasma cultures from the first trimester and in approximately 50% thereafter. Repeated plasma isolations did not give an indication of HIV activation, nor did the cross-sectional time-to-culture positivity in plasma and in PBMC, PBMC isolation frequencies, HIV-DNA and CD4 levels. The plasma viraemia frequencies were generally higher and the CD4 levels lower in the African women than in the European ones. Six months after delivery there was a significant decrease in the CD4 cell counts compared to delivery, but not when compared to the values during the first or second trimesters. The results showed that HIV activity during pregnancy was relatively stable, followed by indications of resumed activity during the first 6 months after delivery.