Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving nucleic acid
Reexamination Certificate
2001-11-16
2004-08-31
Park, Hankyel T. (Department: 1648)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving nucleic acid
C435S005000, C435S069700, C435S339100, C435S320100, C536S023100, C536S023720, C424S192100, C424S208100
Reexamination Certificate
active
06783939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to vaccines using viral antigens, and in particular, to vaccines for the treatment and prevention of human immunodeficiency virus (HIV) infection. The vaccines of this invention comprise alphavirus RNA replicon systems which contain nucleic acid sequence encoding antigens for eliciting an immune response to HIV.
2. Background
The successful control of the AIDS epidemic will require an effective vaccine for human immunodeficiency virus type 1 (HIV) that significantly reduces or prevents the spread of infection. Currently, several viral vector systems as well as naked DNA are at various stages of pre-clinical and clinical evaluation as candidate HIV vaccines. Recombinant poxviruses are the most widely studied virus vectors and are furthest along in clinical development (e.g., ALVAC).
The alphavirus-based replicon particle systems, such as the ones described in U.S. Pat. No. 5,792,462 and herein referred to as “VRPs,” have multiple distinct properties that make them attractive as an HIV vaccine delivery technology. These properties include: natural targeting to and expression in lymphoid tissues (an optimal site for induction of an immune response); high antigen expression levels, e.g., up to 20% of total cell protein; induction of balanced humoral, cellular, and mucosal immune responses; sustained efficacy over multiple simultaneous or sequential inoculations of the vector; and a high margin of safety.
Venezuelan equine encephalitis virus (VEE) is a member of the Alphaviruses group, which also includes the prototype Sindbis virus (SIN) and Semliki Forest virus (SFV), and is comprised of enveloped viruses containing plus-stranded RNA genomes within icosahedral capsids (Strauss, 1994). Alphavirus genomes are: approximately 11.5 kb long, capped, polyadenylated, and infectious under appropriate transfection conditions. The nucleocapsid is composed of 240 molecules of the capsid protein arranged as a T=4 icosahedron, and is surrounded by a lipoprotein envelope (Paredes et al., 1993). Protruding from the virion surface are 80 glycoprotein spikes, each of which is a trimer of virally encoded E1 and E2 glycoprotein heterodimers. The virions contain no host proteins.
Alphaviruses share replication strategies and genomic organization. The complete replicative cycle of alphaviruses occurs in the cytoplasm of infected cells. Expression from the alphavirus genome is segregated into two regions. The four enzymatic nonstructural proteins (nsP1-nsP4) are synthesized from the 5′ two-thirds of the genome-length RNA and are required for RNA replication. Immediately following infection, the nsPs are produced by translation of parental genomes and catalyze the synthesis of a full-length negative-sense copy of the genome. This serves as a template for the synthesis of progeny plus-stranded genomes.
The negative-sense copy of the genome also serves as the template for the synthesis of subgenomic mRNA at approximately 10-fold molar excess relative to genomic RNA in infected cells (Schlesinger and Schlesinger, 1990). Synthesis of subgenomic 26S mRNA is initiated from the highly active internal 26S mRNA promoter, which is functional only on the negative-sense RNA. The subgenomic mRNA corresponds to the 3′ one-third of the genome and encodes the alphavirus structural proteins.
Full-length, infectious cDNA clones of the RNA genome of VEE Davis et al., 1989) have been constructed, a panel of mutations which strongly attenuate the virus have been identified (Johnston and Smith, 1988; Davis et al., 1990), and various constellations of these attenuating mutations have been inserted into the clones to generate several live attenuated VEE vaccine candidates (Davis et al., 1991; 1995b; Grieder et al., 1995). The resulting vaccine candidates are avirulent and provide complete protection against lethal virus challenge in rodents, horses and nonhuman primates.
The alphavirus VRPs are propagation defective, single cycle vectors that contain a self-amplifying alphavirus RNA (replicon RNA) in which the structural protein genes of the virus are replaced by a heterologous antigen gene to be expressed. Alphavirus VRPs are typically made in cultured cells, referred to as packaging cells. Following introduction into mammalian cells, the replicon RNA is packaged into VRP by supplying the structural proteins in “trans,” i.e., the cells are co-transfected with both replicon RNA and one or more separate helper RNAs which together encode the full complement of alphavirus structural proteins. Importantly, only the replicon RNA is packaged into VRP, as the helper RNA(s) lack the cis-acting packaging sequence required for encapsidation. Thus, the VRPs are defective, in that they can only infect target cells in culture or in vivo, where they express the heterologous antigen gene to high level, but they lack critical portions of the VEE genome (i.e., the VEE structural protein genes) necessary to produce virus particles which could spread to other cells.
Delivery of the replicon RNA into target cells (for vaccination) is facilitated by the VRP following infection of the target cells. In the cytoplasm of the target cell, the replicon RNA is first translated to produce the viral replicase proteins necessary to initiate self-amplification and expression. The heterologous antigen gene is encoded by a subgenomic mRNA, abundantly transcribed from the replicon RNA, leading to high level expression of the heterologous antigen gene product. Since the VEE structural protein genes are not encoded by the replicon RNA delivered to the target cell, progeny virion particles are not assembled, thus limiting the replication to a single cycle within the infected target cell. Experimental VRP vaccines have been successful in vaccinating rodents against influenza virus, Lassa fever virus and Marburg virus (Pushko et al., 1997; Hevey et al., 1998). In nonhuman primates, VRP vaccines have demonstrated complete efficacy against lethal Marburg virus challenge (Hevey et al., 1998), shown partial but significant protection against SIV infection and disease (Davis et al., 2000) and induced an anti-HA response at a level consistent with protection of humans against influenza virus infection.
The alphavirus based replicon vector systems, and in particular the VEE-based systems, present several advantages in vaccination, including safety and high immunogenicity/efficacy. VEE is unique among the alphaviruses in that a live attenuated IND VEE vaccine, TC-83, (Kinney et al., 1989; Kinney et al., 1993) has been inoculated into approximately 8,000 humans. This allows direct safety and efficacy comparisons between human, nonhuman primate and rodent responses to the same VEE derivative. A large body of experience strongly suggests that the animal models generally reflect the human susceptibility and disease course, except that mice are far more susceptible to lethal VEE disease than humans or nonhuman primates. Furthermore, the VEE replicon vectors express high levels of the gene of interest in cell culture, and in vivo expression is targeted to lymphoid tissues, reflecting the natural tropism mediated by the VEE glycoproteins. Cells in the draining lymph node of VRP-inoculated mice contain detectable amounts of the desired gene product within hours of inoculation. This expression continues for up to five days.
To date, VRP vector vaccines have been used in over 2000 rodents and in 94 macaques at doses up to 5×10
8
i.u., with no indication of any clinical manifestations.
In work reported by Pushko et al. (1997), individual mice were immunized sequentially with Lassa virus N-VRP and influenza virus HA-VRP. Groups of mice, which received two inoculations of 3×10
4
or 3×10
6
i.u. of Lassa N-VRP followed by two inoculations of 2×10
5
i.u. of HA-VRP, all responded with serum antibodies to both antigens. The level of anti-influenza antibody induced in these sequentially inoculated mice was equivalent to a control group, which received two inocula
Caley Ian
Davis Nancy
Dryga Sergey
Johnston Robert
Keith Paula
Alphavax, Inc.
Myers Bigel Sibley & Sajovec P.A.
Park Hankyel T.
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