New Generation Live Vaccines against Human Respiratory Syncytial Virus Designed by Reverse Genetics

Abstract

Development of a live pediatric vaccine against human respiratory syncytial virus (RSV) is complicated by the need to immunize young infants and the difficulty in balancing attenuation and immunogenicity. The ability to introduce desired mutations into infectious virus by reverse genetics provides a method for identifying and designing highly defined attenuating mutations. These can be introduced in combinations as desired to achieve gradations of attenuation. Attenuation is based on several strategies: multiple independent temperature-sensitive point mutations in the polymerase, a temperature-sensitive point mutation in a transcription signal, a set of non-temperature-sensitive mutations involving several genes, deletion of a viral RNA synthesis regulatory protein, and deletion of viral IFN ␣/␤ antagonists. The genetic stability of the live vaccine can be increased by judicious choice of mutations. The virus also can be engineered to increase the level of expression of the protective antigens. Protective antigens from antigenically distinct RSV strains can be added or swapped to increase the breadth of coverage. Alternatively, the major RSV protective antigens can be expressed from transcription units added to an attenuated parainfluenza vaccine virus, making a bivalent vaccine. This would obviate the difficulties inherent in the fragility and inefficient in vitro growth of RSV, simplifying vaccine design and use.

Bovine respiratory syncytial virus infection

“…Furthermore, the mucosal route of vaccination is more resistant to the immunosuppressive effects of maternal antibodies than the parenteral route of administration [13,38]. Whilst it is possible to generate live, attenuated viruses by passage in cell culture, it has been difficult to produce a genetically stable HRSV with an appropriate balance between attenuation and immunogenicity [34,169]. Furthermore, we have increased the virulence of a BRSV isolate by sequential passage in gnotobiotic calves 8 .…”

High-throughput screening of stabilizers for Respiratory Syncytial Virus: Identification of stabilizers and their effects on the conformational thermostability of viral particles

“…13 The first vaccine attempt not only failed to protect recipients against infection but also exacerbated the disease after natural infection resulting in the hospitalization of 80% of the enrolled patients and two deaths. 14 Currently, a number of vaccines candidates are being investigated, including live attenuated RSV, 15 protein subunits, 16 DNA vaccines 17 and vector delivery systems. 18 In addition to resembling the natural disease, live attenuated vaccines strategies have the advantage of producing a balanced immune response with the production of both secretory and serum antibodies.…”

Mucosal inoculation with an attenuated mouse pneumovirus strain protects against virulent challenge in wild type and interferon-gamma receptor deficient mice

“…Although several parenteral vaccines are licensed and have been shown to be effective for use against hRSV in cattle [8][9][10][11], there is currently no vaccine available for the prevention of hRSV in human infants [12][13][14][15]. Recent interest in the use of intranasal vaccines for respiratory diseases in children has emerged, and an intranasal vaccine for influenza has recently been shown to be safe and effective in young children [16].…”