1
|
Salmons B, Gunzburg WH. Long-Term Survival of Cellulose Sulphate-Encapsulated Cells and Metronomic Ifosfamide Control Tumour Growth in Pancreatic Cancer Models-A Prelude to Treating Solid Tumours Effectively in Pets and Humans. Life (Basel) 2023; 13:2357. [PMID: 38137959 PMCID: PMC10745020 DOI: 10.3390/life13122357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 10/10/2023] [Accepted: 11/23/2023] [Indexed: 12/24/2023] Open
Abstract
BACKGROUND The use of encapsulated cells for the in vivo delivery of biotherapeutics is a promising new technology to potentiate the effectiveness of cell-based therapies for veterinary and human application. One use of the technology is to locally activate chemotherapeutics to their short-lived highly active forms. We have previously shown that a stable clone of HEK293 cells overexpressing a cytochrome P450 enzyme that has been encapsulated in immunoprotective cellulose sulphate beads can be implanted near solid tumours in order to activate oxazaphosphorines such as ifosfamide and cyclophosphamide to the tumour-killing metabolite phosphoramide mustard. The efficacy of this approach has been shown in animal models as well as in human and canine clinical trials. In these previous studies, the oxazaphosphorine was only given twice. An analysis of the Kaplan-Meier plots of the results of the clinical trials suggest that repeated dosing might result in a significant clinical benefit. AIMS In this study, we aimed to (i) demonstrate the stable long-term expression of cytochrome P450 from a characterized, transfected cell clone, as well as (ii) demonstrate that one implanted dose of these encapsulated cytochrome P450-expressing cells is capable of activating multiple doses of ifosfamide in animal models. METHODOLOGY We initially used cell and molecular methods to show cell line stability over multiple passages, as well as chemical and biological function in vitro. This was followed by a demonstration that encapsulated HEK293 cells are capable of activating multiple doses of ifosfamide in a mouse model of pancreatic cancer without being killed by the chemotherapeutic. CONCLUSION A single injection of encapsulated HEK293 cells followed by multiple rounds of ifosfamide administration results in repeated anti-tumour activity and halts tumour growth but, in the absence of a functioning immune system, does not cause tumour regression.
Collapse
Affiliation(s)
- Brian Salmons
- Austrianova Singapore Pte Ltd., 2 International Business Park, The Strategy @ IBP #09-04, Singapore 609930, Singapore;
| | - Walter H. Gunzburg
- Institute of Virology, Department of Pathobiology, University of Veterinary Medicine, 1210 Vienna, Austria
| |
Collapse
|
2
|
Siddiqui AA, Peter S, Ngoh EZX, Wang CI, Ng S, Dangerfield JA, Gunzburg WH, Dröge P, Makhija H. A versatile genomic transgenesis platform with enhanced λ integrase for human Expi293F cells. Front Bioeng Biotechnol 2023; 11:1198465. [PMID: 37425360 PMCID: PMC10325659 DOI: 10.3389/fbioe.2023.1198465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Accepted: 06/06/2023] [Indexed: 07/11/2023] Open
Abstract
Reliable cell-based platforms to test and/or produce biologics in a sustainable manner are important for the biotech industry. Utilizing enhanced λ integrase, a sequence-specific DNA recombinase, we developed a novel transgenesis platform involving a fully characterized single genomic locus as an artificial landing pad for transgene insertion in human Expi293F cells. Importantly, transgene instability and variation in expression were not observed in the absence of selection pressure, thus enabling reliable long-term biotherapeutics testing or production. The artificial landing pad for λ integrase can be targeted with multi-transgene constructs and offers future modularity involving additional genome manipulation tools to generate sequential or nearly seamless insertions. We demonstrated broad utility with expression constructs for anti PD-1 monoclonal antibodies and showed that the orientation of heavy and light chain transcription units profoundly affected antibody expression levels. In addition, we demonstrated encapsulation of our PD-1 platform cells into bio-compatible mini-bioreactors and the continued secretion of antibodies, thus providing a basis for future cell-based applications for more effective and affordable therapies.
Collapse
Affiliation(s)
- Asim Azhar Siddiqui
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Sabrina Peter
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Eve Zi Xian Ngoh
- Singapore Immunology Network, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Cheng-I. Wang
- Singapore Immunology Network, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Shirelle Ng
- Austrianova Singapore Pte. Ltd., Singapore, Singapore
| | | | - Walter H. Gunzburg
- Austrianova Singapore Pte. Ltd., Singapore, Singapore
- Department of Pathobiology, Institute of Virology, University of Veterinary Medicine, Vienna, Austria
| | - Peter Dröge
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | | |
Collapse
|
3
|
Gunzburg WH, Aung MM, Toa P, Ng S, Read E, Tan WJ, Brandtner EM, Dangerfield J, Salmons B. Efficient protection of microorganisms for delivery to the intestinal tract by cellulose sulphate encapsulation. Microb Cell Fact 2020; 19:216. [PMID: 33243224 PMCID: PMC7691082 DOI: 10.1186/s12934-020-01465-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 10/28/2020] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND Gut microbiota in humans and animals play an important role in health, aiding in digestion, regulation of the immune system and protection against pathogens. Changes or imbalances in the gut microbiota (dysbiosis) have been linked to a variety of local and systemic diseases, and there is growing evidence that restoring the balance of the microbiota by delivery of probiotic microorganisms can improve health. However, orally delivered probiotic microorganisms must survive transit through lethal highly acid conditions of the stomach and bile salts in the small intestine. Current methods to protect probiotic microorganisms are still not effective enough. RESULTS We have developed a cell encapsulation technology based on the natural polymer, cellulose sulphate (CS), that protects members of the microbiota from stomach acid and bile. Here we show that six commonly used probiotic strains (5 bacteria and 1 yeast) can be encapsulated within CS microspheres. These encapsulated strains survive low pH in vitro for at least 4 h without appreciable loss in viability as compared to their respective non-encapsulated counterparts. They also survive subsequent exposure to bile. The CS microspheres can be digested by cellulase at concentrations found in the human intestine, indicating one mechanism of release. Studies in mice that were fed CS encapsulated autofluorescing, commensal E. coli demonstrated release and colonization of the intestinal tract. CONCLUSION Taken together, the data suggests that CS microencapsulation can protect bacteria and yeasts from viability losses due to stomach acid, allowing the use of lower oral doses of probiotics and microbiota, whilst ensuring good intestinal delivery and release.
Collapse
Affiliation(s)
- Walter H Gunzburg
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore. .,Institute of Virology, Department of Pathobiology, University of Veterinary Medicine, 1210, Vienna, Austria.
| | - Myo Myint Aung
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Pauline Toa
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Shirelle Ng
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Eliot Read
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Wee Jin Tan
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Eva Maria Brandtner
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore.,VIVIT - Vorarlberg Institute for Vascular Investigation and Treatment, Feldkirch, Austria
| | - John Dangerfield
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| | - Brian Salmons
- Austrianova Singapore, 41 Science Park Road, #03-15 The Gemini, Singapore, 117610, Singapore
| |
Collapse
|
4
|
Zavala G, Ramos MP, Figueroa-Valdés AI, Cisternas P, Wyneken U, Hernández M, Toa P, Salmons B, Dangerfield J, Gunzburg WH, Khoury M. Semipermeable Cellulose Beads Allow Selective and Continuous Release of Small Extracellular Vesicles (sEV) From Encapsulated Cells. Front Pharmacol 2020; 11:679. [PMID: 32528280 PMCID: PMC7253686 DOI: 10.3389/fphar.2020.00679] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 04/24/2020] [Indexed: 12/12/2022] Open
Abstract
The clinical benefit of therapies using Mesenchymal Stem Cells (MSCs) is attributable to their pleiotropic effect over cells and tissues, mainly through their secretome. This paracrine effect is mediated by secreted growth factors and extracellular vesicles (EV) including small EV (sEV). sEV are extra-cellular, membrane encompassed vesicles of 40 to 200 nm diameter that can trigger and signal many cellular responses depending on their cargo protein and nucleic acid repertoire. sEV are purified from cell culture conditioned media using several kits and protocols available that can be tedious and time-consuming, involving sequences of ultracentrifugations and density gradient separations, making their production a major challenge under Good Manufacturing Practices (GMP) conditions. We have developed a method to efficiently enrich cell culture media with high concentrations of sEV by encapsulating cells in semipermeable cellulose beads that allows selectively the release of small particles while offering a 3D culture condition. This method is based on the pore size of the capsules, allowing the release of particles of ≤ 200 nm including sEV. As a proof-of-principle, MSCs were encapsulated and their sEV release rate (sEV-Cap) was monitored throughout the culture and compared to sEV isolated from 2D seeded cells (sEV-2D) by repetitive ultracentrifugation cycles or a commercial kit. The isolated sEV expressed CD63, CD9, and CD81 as confirmed by flow cytometry analysis. Under transmission electron microscopy (TEM), they displayed the similar rounded morphology as sEV-2D. Their corresponding diameter size was validated by nanoparticle tracking analysis (NTA). Interestingly, sEV-Cap retained the expected biological activities of MSCs, including a pro-angiogenic effect over endothelial cells, neuritic outgrowth stimulation in hippocampal neurons and immunosuppression of T cells in vitro. Here, we successfully present a novel, cost, and time-saving method to generate sEV from encapsulated MSCs. Future applications include using encapsulated cells as a retrievable delivery device that can interact with the host niche by releasing active agents in vivo, including sEV, growth factors, hormones, and small molecules, while avoiding cell clearance, and the negative side-effect of releasing undesired components including apoptotic bodies. Finally, particles produced following the encapsulation protocol display beneficial features for their use as drug-loaded delivery vehicles.
Collapse
Affiliation(s)
- Gabriela Zavala
- Consorcio REGENERO, Chilean Consortium for Regenerative Medicine, Santiago, Chile.,Laboratory of Nano-Regenerative Medicine, Faculty of Medicine, Universidad de los Andes, Santiago, Chile
| | - María-Paz Ramos
- Consorcio REGENERO, Chilean Consortium for Regenerative Medicine, Santiago, Chile.,Laboratory of Nano-Regenerative Medicine, Faculty of Medicine, Universidad de los Andes, Santiago, Chile
| | - Aliosha I Figueroa-Valdés
- Consorcio REGENERO, Chilean Consortium for Regenerative Medicine, Santiago, Chile.,Laboratory of Nano-Regenerative Medicine, Faculty of Medicine, Universidad de los Andes, Santiago, Chile
| | - Pablo Cisternas
- Laboratory of Neurosciences, Centro de Investigación Biomédica, Universidad de los Andes, Santiago, Chile
| | - Ursula Wyneken
- Laboratory of Neurosciences, Centro de Investigación Biomédica, Universidad de los Andes, Santiago, Chile
| | - Macarena Hernández
- Consorcio REGENERO, Chilean Consortium for Regenerative Medicine, Santiago, Chile.,Laboratory of Nano-Regenerative Medicine, Faculty of Medicine, Universidad de los Andes, Santiago, Chile
| | - Pauline Toa
- Austrianova Singapore Pte Ltd, Singapore, Singapore
| | | | | | - Walter H Gunzburg
- Department of Pathobiology, Institute of Virology, University of Veterinary Medicine, Vienna, Austria
| | - Maroun Khoury
- Consorcio REGENERO, Chilean Consortium for Regenerative Medicine, Santiago, Chile.,Laboratory of Nano-Regenerative Medicine, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.,Cells for Cells, Santiago, Chile
| |
Collapse
|
5
|
Salmons B, Gunzburg WH. Release characteristics of cellulose sulphate capsules and production of cytokines from encapsulated cells. Int J Pharm 2018; 548:15-22. [PMID: 29933063 DOI: 10.1016/j.ijpharm.2018.06.040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/16/2018] [Accepted: 06/18/2018] [Indexed: 12/11/2022]
Abstract
The size and speed of release of proteins of different sizes from standard cellulose sulphate capsules (Cell-in-a-Box®) was investigated. Proteins with molecular weights of up to around 70kD can be released. The conformation, charge and concentration of the protein being released play a role in the release kinetics. Small proteins such as cytokines can be easily released. The ability to produce cytokines at a sustained and predefined level from encapsulated cells genetically engineered to overexpress such cytokines and implanted into patients may aid immunotherapies of cancer as well as infectious and other diseases. It will also allow allogeneic rather than autologous cells to be used. We show that cells encapsulated in polymers of cellulose sulphate are able to release cytokines such as interleukin-2 (IL-2) in a stimulated fashion e.g. using phorbol 12-myristate 13-acetate (PMA) plus ionomycin. Given the excellent documented safety record of cellulose sulphate in patients, these data suggest that clinical usage of the technology may be warranted for cancer treatment and other diseases.
Collapse
Affiliation(s)
- Brian Salmons
- Austrianova Singapore Pte Ltd, Synapse, 3 Biopolis Drive, Singapore
| | - Walter H Gunzburg
- Austrianova Singapore Pte Ltd, Synapse, 3 Biopolis Drive, Singapore; Institute of Virology, Dept. of Pathobiology, University of Veterinary Medicine, A1210 Vienna, Austria.
| |
Collapse
|
6
|
Lawson JS, Salmons B, Gunzburg WH. Commentary regarding Gannon et al. “Viral infections and breast cancer – A current perspective”. Cancer Lett 2018; 424:117-118. [DOI: 10.1016/j.canlet.2018.03.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 03/21/2018] [Indexed: 10/17/2022]
|
7
|
Affiliation(s)
- Walter H Gunzburg
- Department of Pathobiology, Institute of Virology, University of Veterinary Medicine Vienna, Austria
| | | |
Collapse
|
8
|
Salmons B, Gunzburg WH. Revisiting a role for a mammary tumor retrovirus in human breast cancer. Int J Cancer 2013; 133:1530-5. [DOI: 10.1002/ijc.28210] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Accepted: 04/09/2013] [Indexed: 12/12/2022]
Affiliation(s)
- Brian Salmons
- SG Austria; 20 Biopolis Way #05-518 Centros; Singapore; Singapore
| | - Walter H. Gunzburg
- Institute of Virology; Department of Pathobiology; University of Veterinary Medicine; Vienna; Austria
| |
Collapse
|
9
|
Hohenadl C, Gunzburg WH, Salmons B, Indik S. The 5' leader sequence of mouse mammary tumor virus enhances expression of the envelope and reporter genes. J Gen Virol 2011; 93:308-318. [PMID: 22113011 DOI: 10.1099/vir.0.035196-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mouse mammary tumor virus (MMTV) is a complex betaretrovirus, which utilizes a Rev-like auxiliary protein Rem to export the unspliced viral RNA from the nucleus. MMTV env mRNA appears to be exported via a distinct, Rem-independent, mechanism. Here, we analysed the effect of an extensively folded region coinciding with the 5' leader sequence on env gene expression. We found that the presence of the 5' leader stimulates expression of the envelope protein. Enhanced Env production was accompanied by increased cytoplasmic levels of env mRNA. The 5' leader promotes nucleocytoplasmic translocation and increases stability of env mRNA. The region responsible for this effect was mapped to the distal part of the 5' leader. Furthermore, the 5' leader inserted in the sense orientation into a heterologous luciferase expression construct increased luciferase activity.
Collapse
Affiliation(s)
- Christine Hohenadl
- Institute of Virology, Department of Pathobiology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Walter H Gunzburg
- Christian Doppler Laboratory for Gene Therapeutic Vector Development, Vienna, Austria.,Institute of Virology, Department of Pathobiology, University of Veterinary Medicine Vienna, Vienna, Austria
| | | | - Stanislav Indik
- Institute of Virology, Department of Pathobiology, University of Veterinary Medicine Vienna, Vienna, Austria
| |
Collapse
|
10
|
Salmons B, Brandtner EM, Hettrich K, Wagenknecht W, Volkert B, Fischer S, Dangerfield JA, Gunzburg WH. Encapsulated cells to focus the metabolic activation of anticancer drugs. Curr Opin Mol Ther 2010; 12:450-460. [PMID: 20677096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
One of the first strategies for cancer gene therapy was the use of suicide gene/prodrug combinations, originally delivered to tumor cells using viral vectors. A major limitation of this approach was the inefficiency of suicide gene delivery. An alternative strategy, in which the suicide genes are physically juxtaposed to the tumor, involves the implantation of encapsulated, genetically modified cells. Cell encapsulation technologies were originally developed for the treatment of acquired and genetic diseases, such as diabetes. In the application of this technology for the treatment of tumors, cells that are genetically modified to overexpress suicide genes are encapsulated and implanted near solid tumors; this process is then followed by systemic prodrug administration. This review discusses the various cells types, suicide genes and prodrugs that have been used in preclinical and clinical trials, as well as the data that have been obtained from these studies. Future improvements for the production of second-generation approaches are also discussed.
Collapse
Affiliation(s)
- Brian Salmons
- Austrianova Singapore Pte Ltd, 20 Biopolis Way, #05-518 Centros, Singapore 138668.
| | | | | | | | | | | | | | | |
Collapse
|
11
|
Salmons B, Gunzburg WH. Therapeutic Application of Cell Microencapsulation in Cancer. Advances in Experimental Medicine and Biology 2010; 670:92-103. [DOI: 10.1007/978-1-4419-5786-3_9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
|
12
|
Gunzburg WH, Salmons B. Stem cell therapies: on track but suffer setback. Curr Opin Mol Ther 2009; 11:360-363. [PMID: 19649980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
|
13
|
Lear MJ, Salmons B, Gunzburg WH, Dangerfield JA. Singapore R&D and globetrotting. Biotechnol J 2009; 4:179-85. [DOI: 10.1002/biot.200800131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
14
|
Metzner C, Salmons B, Gunzburg WH, Gemeiner M, Miller I, Gesslbauer B, Kungl A, Dangerfield JA. MMTV accessory factor Naf affects cellular gene expression. Virology 2006; 346:139-50. [PMID: 16310820 DOI: 10.1016/j.virol.2005.10.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Revised: 08/23/2005] [Accepted: 10/21/2005] [Indexed: 11/25/2022]
Abstract
Mouse mammary tumour virus (MMTV) encodes a viral superantigen (Sag) and a negative acting factor (Naf) which share parts of their coding sequence. Using 2-dimensional gel electrophoresis (2D-DIGE), we could show that at least 10 different cellular proteins were differentially expressed in Naf positive cells. Also, luciferase reporter expression was down-regulated in Naf expressing cells independent of the promoter used and further experiments suggested that this effect was due in part to a decrease in cellular growth rates. Although in Naf positive cells expression of the major sag containing transcript was strongly induced by the synthetic glucocorticoid dexamethasone, the hormone analogue neither influenced luciferase expression nor mRNA expression of selected cellular proteins identified by 2D-DIGE. Taken together, these data support the previous finding that Naf and Sag have separable activities and suggest that Naf may play a role in modulating host cell gene expression during MMTV infection.
Collapse
Affiliation(s)
- Christoph Metzner
- Research Institute of Virology and Biomedicine, University of Veterinary Medicine, A-1210 Vienna, Austria.
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Klein D, Leutenegger CM, Bahula C, Gold P, Hofmann-Lehmann R, Salmons B, Lutz H, Gunzburg WH. Influence of preassay and sequence variations on viral load determination by a multiplex real-time reverse transcriptase-polymerase chain reaction for feline immunodeficiency virus. J Acquir Immune Defic Syndr 2001; 26:8-20. [PMID: 11176264 DOI: 10.1097/00126334-200101010-00002] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Determination of retroviral load is an important tool in the investigation of the success of therapeutic or vaccination trials in patients infected with lentiviruses such as HIV, or with their simian (SIV) or feline (FIV) counterparts. We have developed an one-tube quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay based on the ABI Prism 7700 Sequence Detection System (TaqMan) to quantify the viral load of FIV-infected cats. Two different primer/probe systems were designed to detect a broad range of clade A FIV isolates. Both systems are characterized by excellent reproducibility, high sensitivity, and a wide range of quantification. As a consequence of this improved precision in the quantitative RT-PCR, preassay variations have greater impact on the accuracy of the viral load estimation. To compensate for these variations, we improved the assay and developed a multiplex real-time RT-PCR, which allows simultaneous calculation of the viral copy number and the individual recovery rate in an one-tube reaction. This enables the rapid and accurate calculation of copy number independent of preassay variations. In further studies, two additional real-time RT-PCR assays were designed and used to investigate the influence of sequence variations in the binding regions for either the primers or probe. Sequence mismatches in this region had a significant effect (up to 4 logarithmic decades) on reaction efficiency. In view of the inherent variability of retroviral sequences, these results underline the necessity to check reaction efficiencies before determining viral load.
Collapse
Affiliation(s)
- D Klein
- Institute of Virology, University of Veterinary Sciences, Vienna, Austria.
| | | | | | | | | | | | | | | |
Collapse
|
16
|
Affiliation(s)
- W H Gunzburg
- Institute of Virology, University of Veterinary Sciences, Vienna, Austria.
| |
Collapse
|