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Lassa virus-like particles displaying all major immunological determinants as a vaccine candidate for Lassa hemorrhagic fever.

Branco LM, Grove JN, Geske FJ, Boisen ML, Muncy IJ, Magliato SA, Henderson LA, Schoepp RJ, Cashman KA, Hensley LE, Garry RF - Virol. J. (2010)

Bottom Line: Although VLP did not contain the same host cell components as the native virion, electron microscopy analysis demonstrated that LASV VLP appeared structurally similar to native virions, with pleiomorphic distribution in size and shape.These results established that modular LASV VLP can be generated displaying high levels of immunogenic viral proteins, and that small laboratory scale mammalian expression systems are capable of producing multi-milligram quantities of pseudoparticles.These VLP are structurally and morphologically similar to native LASV virions, but lack replicative functions, and thus can be safely generated in low biosafety level settings.

View Article: PubMed Central - HTML - PubMed

Affiliation: Tulane University Health Sciences Center, New Orleans, LA, USA.

ABSTRACT

Background: Lassa fever is a neglected tropical disease with significant impact on the health care system, society, and economy of Western and Central African nations where it is endemic. Treatment of acute Lassa fever infections has successfully utilized intravenous administration of ribavirin, a nucleotide analogue drug, but this is not an approved use; efficacy of oral administration has not been demonstrated. To date, several potential new vaccine platforms have been explored, but none have progressed toward clinical trials and commercialization. Therefore, the development of a robust vaccine platform that could be generated in sufficient quantities and at a low cost per dose could herald a subcontinent-wide vaccination program. This would move Lassa endemic areas toward the control and reduction of major outbreaks and endemic infections. To this end, we have employed efficient mammalian expression systems to generate a Lassa virus (LASV)-like particle (VLP)-based modular vaccine platform.

Results: A mammalian expression system that generated large quantities of LASV VLP in human cells at small scale settings was developed. These VLP contained the major immunological determinants of the virus: glycoprotein complex, nucleoprotein, and Z matrix protein, with known post-translational modifications. The viral proteins packaged into LASV VLP were characterized, including glycosylation profiles of glycoprotein subunits GP1 and GP2, and structural compartmentalization of each polypeptide. The host cell protein component of LASV VLP was also partially analyzed, namely glycoprotein incorporation, though the identity of these proteins remain unknown. All combinations of LASV Z, GPC, and NP proteins that generated VLP did not incorporate host cell ribosomes, a known component of native arenaviral particles, despite detection of small RNA species packaged into pseudoparticles. Although VLP did not contain the same host cell components as the native virion, electron microscopy analysis demonstrated that LASV VLP appeared structurally similar to native virions, with pleiomorphic distribution in size and shape. LASV VLP that displayed GPC or GPC+NP were immunogenic in mice, and generated a significant IgG response to individual viral proteins over the course of three immunizations, in the absence of adjuvants. Furthermore, sera from convalescent Lassa fever patients recognized VLP in ELISA format, thus affirming the presence of native epitopes displayed by the recombinant pseudoparticles.

Conclusions: These results established that modular LASV VLP can be generated displaying high levels of immunogenic viral proteins, and that small laboratory scale mammalian expression systems are capable of producing multi-milligram quantities of pseudoparticles. These VLP are structurally and morphologically similar to native LASV virions, but lack replicative functions, and thus can be safely generated in low biosafety level settings. LASV VLP were immunogenic in mice in the absence of adjuvants, with mature IgG responses developing within a few weeks after the first immunization. These studies highlight the relevance of a VLP platform for designing an optimal vaccine candidate against Lassa hemorrhagic fever, and warrant further investigation in lethal challenge animal models to establish their protective potential.

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Electron micrographs of LASV VLP budding from the surface of HEK-293T/17 cells expressing LASV Z alone or in combination with GPC and NP genes, and high magnification of LASV pseudoparticles. Cells expressing LASV Z (6A), Z+NP (6B), or Z+NP+GPC (6C) were harvested at 72 hours post transfection, fixed in glutaraldehyde, and embedded in agarose plugs. Cell pellets were processed for EM analysis and were imaged. Images were printed on photographic paper and were subsequently scanned and saved as high resolution tiff files. LASV Z VLP budded from the surface of cells as empty particles, noted by the lack of electron dense cores (6A). By contrast, LASV Z+NP and Z+NP+GPC appear as electron dense particles containing subcellular structures (6A and 6B). LASV VLP budding from the surface of transfected cells or approaching the cell surface are marked by black arrows. Budded LASV Z+NP+GPC VLP appeared as round, dense structures enveloped in a bilayer structure, presumably a lipid envelope, and were associated with electron dense subcellular organelles (6D). These organelles were not identified as ribosomes in these studies. Cellular ribosomes are known to associate with and be packaged into native LASV virions. The bar in each Figure equals 100 nm.
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Figure 6: Electron micrographs of LASV VLP budding from the surface of HEK-293T/17 cells expressing LASV Z alone or in combination with GPC and NP genes, and high magnification of LASV pseudoparticles. Cells expressing LASV Z (6A), Z+NP (6B), or Z+NP+GPC (6C) were harvested at 72 hours post transfection, fixed in glutaraldehyde, and embedded in agarose plugs. Cell pellets were processed for EM analysis and were imaged. Images were printed on photographic paper and were subsequently scanned and saved as high resolution tiff files. LASV Z VLP budded from the surface of cells as empty particles, noted by the lack of electron dense cores (6A). By contrast, LASV Z+NP and Z+NP+GPC appear as electron dense particles containing subcellular structures (6A and 6B). LASV VLP budding from the surface of transfected cells or approaching the cell surface are marked by black arrows. Budded LASV Z+NP+GPC VLP appeared as round, dense structures enveloped in a bilayer structure, presumably a lipid envelope, and were associated with electron dense subcellular organelles (6D). These organelles were not identified as ribosomes in these studies. Cellular ribosomes are known to associate with and be packaged into native LASV virions. The bar in each Figure equals 100 nm.

Mentions: Electron microscopy (EM) was employed to dissect the morphological properties of VLP generated by expression of Z matrix protein alone, or in combination with NP and GPC. Expression of LASV Z gene alone was sufficient to induce budding of low electron density empty VLP from the surface of transfected cells (Figure 6A). By contrast, expression of Z in conjunction with NP or NP+GPC resulted in the generation of electron dense VLP with granular material associated with the pseudoparticles (Figure 6B,C,D). The granular structures were similar in size to cellular ribosomes, or ~ 20 nm (Figure 6D), but identification of these subcellular organelles as the granular elements, as well as their physical association and incorporation in VLP were not investigated in these studies. LASV VLP displayed pleiomorphic morphology by EM, with sizes ranging from 100 - 250 nm, and enveloped by a bilayer structure (Figure 6D).


Lassa virus-like particles displaying all major immunological determinants as a vaccine candidate for Lassa hemorrhagic fever.

Branco LM, Grove JN, Geske FJ, Boisen ML, Muncy IJ, Magliato SA, Henderson LA, Schoepp RJ, Cashman KA, Hensley LE, Garry RF - Virol. J. (2010)

Electron micrographs of LASV VLP budding from the surface of HEK-293T/17 cells expressing LASV Z alone or in combination with GPC and NP genes, and high magnification of LASV pseudoparticles. Cells expressing LASV Z (6A), Z+NP (6B), or Z+NP+GPC (6C) were harvested at 72 hours post transfection, fixed in glutaraldehyde, and embedded in agarose plugs. Cell pellets were processed for EM analysis and were imaged. Images were printed on photographic paper and were subsequently scanned and saved as high resolution tiff files. LASV Z VLP budded from the surface of cells as empty particles, noted by the lack of electron dense cores (6A). By contrast, LASV Z+NP and Z+NP+GPC appear as electron dense particles containing subcellular structures (6A and 6B). LASV VLP budding from the surface of transfected cells or approaching the cell surface are marked by black arrows. Budded LASV Z+NP+GPC VLP appeared as round, dense structures enveloped in a bilayer structure, presumably a lipid envelope, and were associated with electron dense subcellular organelles (6D). These organelles were not identified as ribosomes in these studies. Cellular ribosomes are known to associate with and be packaged into native LASV virions. The bar in each Figure equals 100 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2984592&req=5

Figure 6: Electron micrographs of LASV VLP budding from the surface of HEK-293T/17 cells expressing LASV Z alone or in combination with GPC and NP genes, and high magnification of LASV pseudoparticles. Cells expressing LASV Z (6A), Z+NP (6B), or Z+NP+GPC (6C) were harvested at 72 hours post transfection, fixed in glutaraldehyde, and embedded in agarose plugs. Cell pellets were processed for EM analysis and were imaged. Images were printed on photographic paper and were subsequently scanned and saved as high resolution tiff files. LASV Z VLP budded from the surface of cells as empty particles, noted by the lack of electron dense cores (6A). By contrast, LASV Z+NP and Z+NP+GPC appear as electron dense particles containing subcellular structures (6A and 6B). LASV VLP budding from the surface of transfected cells or approaching the cell surface are marked by black arrows. Budded LASV Z+NP+GPC VLP appeared as round, dense structures enveloped in a bilayer structure, presumably a lipid envelope, and were associated with electron dense subcellular organelles (6D). These organelles were not identified as ribosomes in these studies. Cellular ribosomes are known to associate with and be packaged into native LASV virions. The bar in each Figure equals 100 nm.
Mentions: Electron microscopy (EM) was employed to dissect the morphological properties of VLP generated by expression of Z matrix protein alone, or in combination with NP and GPC. Expression of LASV Z gene alone was sufficient to induce budding of low electron density empty VLP from the surface of transfected cells (Figure 6A). By contrast, expression of Z in conjunction with NP or NP+GPC resulted in the generation of electron dense VLP with granular material associated with the pseudoparticles (Figure 6B,C,D). The granular structures were similar in size to cellular ribosomes, or ~ 20 nm (Figure 6D), but identification of these subcellular organelles as the granular elements, as well as their physical association and incorporation in VLP were not investigated in these studies. LASV VLP displayed pleiomorphic morphology by EM, with sizes ranging from 100 - 250 nm, and enveloped by a bilayer structure (Figure 6D).

Bottom Line: Although VLP did not contain the same host cell components as the native virion, electron microscopy analysis demonstrated that LASV VLP appeared structurally similar to native virions, with pleiomorphic distribution in size and shape.These results established that modular LASV VLP can be generated displaying high levels of immunogenic viral proteins, and that small laboratory scale mammalian expression systems are capable of producing multi-milligram quantities of pseudoparticles.These VLP are structurally and morphologically similar to native LASV virions, but lack replicative functions, and thus can be safely generated in low biosafety level settings.

View Article: PubMed Central - HTML - PubMed

Affiliation: Tulane University Health Sciences Center, New Orleans, LA, USA.

ABSTRACT

Background: Lassa fever is a neglected tropical disease with significant impact on the health care system, society, and economy of Western and Central African nations where it is endemic. Treatment of acute Lassa fever infections has successfully utilized intravenous administration of ribavirin, a nucleotide analogue drug, but this is not an approved use; efficacy of oral administration has not been demonstrated. To date, several potential new vaccine platforms have been explored, but none have progressed toward clinical trials and commercialization. Therefore, the development of a robust vaccine platform that could be generated in sufficient quantities and at a low cost per dose could herald a subcontinent-wide vaccination program. This would move Lassa endemic areas toward the control and reduction of major outbreaks and endemic infections. To this end, we have employed efficient mammalian expression systems to generate a Lassa virus (LASV)-like particle (VLP)-based modular vaccine platform.

Results: A mammalian expression system that generated large quantities of LASV VLP in human cells at small scale settings was developed. These VLP contained the major immunological determinants of the virus: glycoprotein complex, nucleoprotein, and Z matrix protein, with known post-translational modifications. The viral proteins packaged into LASV VLP were characterized, including glycosylation profiles of glycoprotein subunits GP1 and GP2, and structural compartmentalization of each polypeptide. The host cell protein component of LASV VLP was also partially analyzed, namely glycoprotein incorporation, though the identity of these proteins remain unknown. All combinations of LASV Z, GPC, and NP proteins that generated VLP did not incorporate host cell ribosomes, a known component of native arenaviral particles, despite detection of small RNA species packaged into pseudoparticles. Although VLP did not contain the same host cell components as the native virion, electron microscopy analysis demonstrated that LASV VLP appeared structurally similar to native virions, with pleiomorphic distribution in size and shape. LASV VLP that displayed GPC or GPC+NP were immunogenic in mice, and generated a significant IgG response to individual viral proteins over the course of three immunizations, in the absence of adjuvants. Furthermore, sera from convalescent Lassa fever patients recognized VLP in ELISA format, thus affirming the presence of native epitopes displayed by the recombinant pseudoparticles.

Conclusions: These results established that modular LASV VLP can be generated displaying high levels of immunogenic viral proteins, and that small laboratory scale mammalian expression systems are capable of producing multi-milligram quantities of pseudoparticles. These VLP are structurally and morphologically similar to native LASV virions, but lack replicative functions, and thus can be safely generated in low biosafety level settings. LASV VLP were immunogenic in mice in the absence of adjuvants, with mature IgG responses developing within a few weeks after the first immunization. These studies highlight the relevance of a VLP platform for designing an optimal vaccine candidate against Lassa hemorrhagic fever, and warrant further investigation in lethal challenge animal models to establish their protective potential.

Show MeSH
Related in: MedlinePlus