SV40-immortalized human fibroblasts as a source of SV40 infectious virions

Immortalized erythroid cells as a novel frontier for in vitro blood production: current approaches and potential clinical application

BACKGROUND

Blood transfusions represent common medical procedures, which provide essential supportive therapy. However, these procedures are notoriously expensive for healthcare services and not without risk. The potential threat of transfusion-related complications, such as the development of pathogenic infections and the occurring of alloimmunization events, alongside the donor's dependence, strongly limits the availability of transfusion units and represents significant concerns in transfusion medicine. Moreover, a further increase in the demand for donated blood and blood transfusion, combined with a reduction in blood donors, is expected as a consequence of the decrease in birth rates and increase in life expectancy in industrialized countries.

MAIN BODY

An emerging and alternative strategy preferred over blood transfusion is the in vitro production of blood cells from immortalized erythroid cells. The high survival capacity alongside the stable and longest proliferation time of immortalized erythroid cells could allow the generation of a large number of cells over time, which are able to differentiate into blood cells. However, a large-scale, cost-effective production of blood cells is not yet a routine clinical procedure, as being dependent on the optimization of culture conditions of immortalized erythroid cells.

CONCLUSION

In our review, we provide an overview of the most recent erythroid cell immortalization approaches, while also describing and discussing related advancements of establishing immortalized erythroid cell lines.

Association Between Simian Virus 40 and Human Tumors

Simian virus 40 (SV40) is a small DNA tumor virus of monkey origin. This polyomavirus was administered to human populations mainly through contaminated polio vaccines, which were produced in naturally infected SV40 monkey cells. Previous molecular biology and recent immunological assays have indicated that SV40 is spreading in human populations, independently from earlier SV40-contaminated vaccines. SV40 DNA sequences have been detected at a higher prevalence in specific human cancer specimens, such as the brain and bone tumors, malignant pleural mesotheliomas, and lymphoproliferative disorders, compared to the corresponding normal tissues/specimens. However, other investigations, which reported negative data, did not confirm an association between SV40 and human tumors. To circumvent the controversies, which have arisen because of these molecular biology studies, immunological researches with newly developed indirect ELISA tests were carried out in serum samples from patients affected by the same kind of tumors as mentioned above. These innovative indirect ELISAs employ synthetic peptides as mimotopes/specific SV40 antigens. SV40 mimotopes do not cross-react with the homologous human polyomaviruses, BKPyV, and JCPyV. Immunological data obtained from indirect ELISAs, using SV40 mimotopes, employed to analyze serum samples from oncological patients, have indicated that these sera had a higher prevalence of antibodies against SV40 compared to healthy subjects. The main data on (i) the biology and genetics of SV40; (ii) the epidemiology of SV40 in the general population, (iii) the mechanisms of SV40 transformation; (iv) the putative role of SV40 in the onset/progression of specific human tumors, and (v) its association with other human diseases are reported in this review.

Serological evidence of an early seroconversion to Simian virus 40 in healthy children and adolescents

At present Simian virus 40 (SV40) infection in humans appears to be transmitted independently from early contaminated vaccines. In order to test the spread of SV40 infection in children, an immunologic assay employing specific SV40 synthetic peptides corresponding to its viral protein (VP) antigens was employed to estimate the seroprevalence of this polyomavirus in Italian infants and adolescents. Serum samples from 328 children and adolescents, up to 17 years, were investigated. Serum antibodies against SV40 VPs were detected by indirect enzyme-linked immunosorbent assays. The seroprevalence of this polyomavirus was calculated after stratifying the subjects by age. Anti-viral capsid protein 1-2-3 SV40 IgG antibodies were detected in 16% of the study participants. The prevalence of antibodies against SV40 VPs tended to increase with age in children, up to 10 year old (21%). Then, in the cohort of individuals aged 11–17 years, the prevalence decreased (16%). A higher prevalence rate (23%) of SV40 VP antibodies was detected in the cohorts of 1–3 year and 7–10 year old children, than in children and adolescents of the other age groups. This age corresponds to children starting nursery and primary school, respectively, in Italy. IgM antibodies against SV40 VP mimotopes were detected in 6–8 month old children suggesting that SV40 seroconversion can occur early in life. SV40 VP antibodies are present at low prevalence in Italian children (16%), suggesting that SV40 infection, although acquired early in life, probably through different routes, is not widespread. The low SV40 seroprevalence suggests that SV40 is less transmissible than other common polyomaviruses, such as BKV and JCV. Alternatively, our immunologic data could be due to another, as yet undiscovered, human polyomavirus closely related to SV40.

Extended lifespan of normal human B lymphocytes experimentally infected by SV40 or transfected by SV40 large T antigen expression vector

SV40 footprints were detected in different lymphoproliferative disorders and in blood specimens of healthy donors. However, little is known on the ability of SV40 to infect/transform normal human B-lymphocytes. In this in vitro study, experimental SV40 infection and SV40 Tag transfection of normal human B-lymphocytes from healthy blood donors were carried out. In SV40 infected/transfected purified B-cells, during the time course analyses, viral DNA sequences were detected by PCR, while Tag mRNA and protein were revealed by RT-PCR and immunocytochemistry, respectively. Trypan blue and Alamar blue assays showed an increase in number of cells and cell viability of infected/transfected B-cells up to day 50, then a drastic and constant cell number reduction was observed in cultures. Approximately 50% of both infected and transfected B-cells appeared morphologically transformed. SV40 viral progeny and its titer from infected B-cells was determined by plaque assay in permissive CV-1 cells. Our data indicate that human B-cells can be efficiently infected by SV40, release a viral progeny, while at the same time are transformed. SV40 infected/Tag transfected B-cells may represent an experimental model of study for investigating new biomarkers and targets for innovative therapeutic approaches in human B-cell malignancies.

Telomerase immortalization of principal cells from mouse collecting duct

Recently, the use of overexpression of telomerase reverse transcriptase (TERT) has led to the generation of immortalized human cell lines. However, this cell immortalization approach has not been reported in well-differentiated mouse cells, such as renal epithelial cells. We sought to establish and then characterize a mouse collecting duct cell line, using ectopic expression of mTERT. Isolated primary cortical collecting duct (CCD) cell lines were transduced with mouse (m)TERT, using a lentiviral vector. mTERT-negative cells did not survive blasticidin selection, whereas mTERT-immortalized cells proliferated in selection media for over 40 subpassages. mTERT messenger RNA and telomerase activity was elevated in these cells, compared with an SV40-immortalized cell line. Flow cytometry with Dolichos biflorus agglutinin was used to select the CCD principal cells, and we designated this cell line mTERT-CCD. Cells were well differentiated and exhibited morphological characteristics typically found in renal epithelial cells, such as tight junction formation, microvilli, and primary cilia. Further characterization using standard immunofluorescence revealed abundant expression of aquaporin-2 and the vasopressin type 2 receptor. mTERT-CCD cells exhibited cAMP-stimulated/benzamil-inhibited whole cell currents. Whole cell patch-clamp currents were also enhanced after a 6-day treatment with aldosterone. In conclusion, we have successfully used mTERT to immortalize mouse collecting duct cells that retain the basic in vivo phenotypic characteristics of collecting duct cells. This technique should be valuable in generating cell lines from genetically engineered mouse models.

Gene transfer using recombinant simian virus 40 viral vectors into mice bone marrow progenitor cells depressed the immunogenicity of keratinocyte stem cells

Hematopoietic stem cell (HSC) gene transfer has been attempted almost entirely ex vivo and has been limited by loss of self-renewal capacity and transplantation-related defects in homing and engraftment. Herein we have attempted to overcome these limitations by injecting vectors directly into the bone marrow (BM) to transduce HSCs in their native environment. Simian virus 40 (SV40)-derived gene delivery vectors were used because they efficiently transduce resting CD34+ cells. Neonatal C57BL/6 (H-2b) mice (3 days old) received SV(Nef-FLAG), carrying FLAG marker epitope directly into both femoral marrow cavities. Keratinocyte stem cells (KSCs) were purified at 7 and 14 days after SV40 injection. The KSCs from 10-day-old C57BL/6 mice were designated as controls. Flow cytometric (FCM) analyses indicated that KSCs from transgenic mice showed strong down-regulation of surface immunological molecules CD40, CD80, CD86, and human major histocompatibility complex class I chain-related antigen A (MICA). Mixed lymphocyte reaction (MLR) assays showed that transgenic KSCs depressed allogeneic T-cell proliferation. Immunofluorescence showed transgenic KSCs expressed FLAG for the entire study as well as high levels of transforming growth factor (TGF)-beta and BCL-2. Thus, direct intramarrow administration of recombinant SV40 yielded efficient gene transfer to mice BM progenitor cells. KSCs with low immunogenicity may be obtained for further investigations of skin transplantation immunity.

Mesothelioma mortality in Europe: impact of asbestos consumption and simian virus 40

Background

It is well established that asbestos is the most important cause of mesothelioma. The role of simian virus 40 (SV40) in mesothelioma development, on the other hand, remains controversial. This potential human oncogene has been introduced into various populations through contaminated polio vaccines. The aim of this study was to investigate whether the possible presence of SV40 in various European countries, as indicated either by molecular genetic evidence or previous exposure to SV40-contaminated vaccines, had any effect on pleural cancer rates in the respective countries.

Methods

We conducted a Medline search that covered the period from January 1969 to August 2005 for reports on the detection of SV40 DNA in human tissue samples. In addition, we collected all available information about the types of polio vaccines that had been used in these European countries and their SV40 contamination status.

Results

Our ecological analysis confirms that pleural cancer mortality in males, but not in females, correlates with the extent of asbestos exposure 25 – 30 years earlier. In contrast, neither the presence of SV40 DNA in tumor samples nor a previous vaccination exposure had any detectable influence on the cancer mortality rate in neither in males (asbestos-corrected rates) nor in females.

Conclusion

Using the currently existing data on SV40 prevalence, no association between SV40 prevalence and asbestos-corrected male pleural cancer can be demonstrated.