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Feline foamy virus in domestic cats: use as a vaccine vector, characterization of infection, and association with other diseases

Date

2019

Authors

Ledesma-Feliciano, Carmen Denise, author
VandeWoude, Sue, advisor
Quimby, Jessica, committee member
Schountz, Tony, committee member
Basaraba, Randall, committee member
Frye, Melinda, committee member

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Abstract

Foamy viruses (FVs) are retroviruses from the Spumaretrovirinae subfamily. FVs are globally prevalent retroviruses with a unique molecular biology. FVs establish apparently apathogenic lifelong infections. Due to this, FVs are considered attractive vectors for vaccine and gene therapy development. Feline foamy virus (FFV) infects domestic cats and has widespread and high prevalence around the world. However, FFV has also been isolated from cats suffering from concurrent disease, including renal syndromes and other retroviral co- infections such as feline immunodeficiency virus (FIV). Much remains unknown about FFV infection and in vivo experimental infections are rare in the literature. To test FFV's use as a vaccine vector and understand the interaction between viral proteins and host antiviral restriction factors, we developed an infective chimeric vaccine containing lentiviral FIV vif replacing FFV bet. FFV Bet and FIV Vif counteract feline innate APOBEC3 (feA3) restriction factors through different mechanisms. FeA3 action on retroviral genomes lead to hypermutation and degradation of viral DNA. In vitro, we show that vif can replace bet to yield replication-competent chimeric viruses. We experimentally inoculated 12 domestic cats (n=4 per group in naïve, wild-type, and chimera-inoculated groups) with the FFV-Vif chimera and wild- type FFV in order to compare viral replication kinetics through PCR and specific antibody development through ELISA. Inoculation with the chimeric vector resulted in the development of a specific immune response against FFV Gag and Bet and FIV Vif proteins. In addition, we show that the domestic cat can be superinfected with different strains of FFV. The chimeric virus displayed attenuated infection in vivo, as provirus was not detected in PBMC for any chimera-only inoculated animals. Thus, Bet may have additional functions other than A3 antagonism required for successful in vivo infection. Our studies further exemplify how FV vaccine vectors are an attractive tool to counteract lentiviral infections and poses the possibility to induce immunity against other lentiviral antigens. In order to further characterize wild-type infection, we also collected blood, saliva, and urine over a 6-month time-period with a necropsy and tissue collection at the end of the study. Animals were monitored daily for clinical signs of disease and temperature and weight data were collected weekly. None of the cats showed clinical signs of infection and complete blood count and chemistry were unremarkable. However, we found significant differences in blood urea nitrogen, one of the markers used to assess renal function, when comparing infected versus control animals. All animals inoculated with wild-type virus showed a persistent proviremia (in PBMCs) and viral tissue tropism was primarily lymphoid with the exception of one cat that had an expanded tissue tropism to other lymphoid tissues and oral mucosa. This animal had altered viral kinetics compared to the rest of infected animals, in addition to a negative correlation between lymphocyte count and viral load. Histopathological analysis showed evidence of microscopic pathology in the kidneys, lung, and brain of infected animals. This same cat had an increase in urine protein at the time of highest PBMC proviremia. Additionally, transmission electron microscopy showed ultrastructural changes indicative of transient renal injury in the kidneys of infected animals. We additionally found electron dense structures in the cytoplasm of tubular epithelial of as of yet unknown origin. Due to the renal changes we saw in the experimental study and pathology reported in the literature, we conducted a survey of FFV in pet cats in the USA and Australia (AU) suffering from chronic kidney disease (CKD) and compared findings to age- and sex-matched controls without CKD. We found an association between CKD and FFV in males, and males in general are also at a significantly increased risk of FFV infection. We then assessed through an FFV serosurvey whether FFV was associated with FIV and causing potentiation of FIV disease in two cohorts of naturally FIV-infected cats. One of the groups consisted of cats living in 1-2 cat households that did not experience much FIV-related morbidity and mortality, while the second group of cats housed in a large multicat household suffered from severe clinical symptoms and mortality. We hypothesized the reason for this discrepancy could be an increase in FFV/FIV co-infection rate in the group of cats with higher morbidity and mortality. We found that FFV is associated with FIV in these groups and that males are also at an increased risk for FFV infection. Finally, we conducted an in vitro co- infection study to assess potentiated infection as determined by more rapid development of cytopathic effects (CPE) and higher viral titers in the supernatant. GFox cells were inoculated with FFV and FIV in single, and dual simultaneous and staggered inoculations. A p26 ELISA was used to determine amount of FIV reactivity in the cells, while a chemiluminescent β- galactosidase assay was used to detect amount of β -gal produced in FeFAB FFV reporter cells. The in vitro assays showed increased permissivity of either virus following an initial infection of the other virus, showing these two retroviruses can accelerate and potentiate a secondary infection regardless of which virus infected initially. Overall, we have demonstrated the suitability of FFV as a vaccine vector candidate. Additionally, we have documented that FFV may cause subclinical alterations that in certain cohorts of domestic cats, may contribute to disease development in chronic cases. Finally, we showed that FFV interacts with another retrovirus and could potentially affect FIV-related disease. More studies should focus on the effects of FFV in chronic infections in addition to the effect of FFV on co-morbidities in a chronic timeline.

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Subject

chronic kidney disease
feline immunodeficiency virus
retrovirus
feline foamy virus
cat
foamy virus

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