Chemistry: molecular biology and microbiology – Process of mutation – cell fusion – or genetic modification – Introduction of a polynucleotide molecule into or...
Reexamination Certificate
1998-10-20
2003-11-04
Guzo, David (Department: 1636)
Chemistry: molecular biology and microbiology
Process of mutation, cell fusion, or genetic modification
Introduction of a polynucleotide molecule into or...
C435S320100, C435S069100, C435S325000, C435S366000, C435S369000, C435S235100, C435S091400, C435S091410, C435S091420, C435S456000, C435S457000, C536S023100, C536S023720
Reexamination Certificate
active
06642051
ABSTRACT:
TECHNICAL FIELD
This invention is in the field of viral constructs for gene delivery. More specifically, the invention is in the field of recombinant DNA constructs for use in the production of adeno-associated virus (AAV) vectors for gene delivery.
BACKGROUND
Vectors based on adeno-associated virus (AAV) are believed to have utility for gene therapy but a significant obstacle has been the difficulty in generating such vectors in amounts that would be clinically useful for human gene therapy applications. This is a particular problem for in vivo applications such as direct delivery to the lung. Another important goal in the gene therapy context, discussed in more detail herein, is the production of vector preparations that are essentially free of replication-competent virions. The following description briefly summarizes studies involving adeno-associated virus and AAV vectors, and then describes a number of novel improvements according to the present invention that are useful for efficiently generating high titer recombinant AAV vector (rAAV) preparations suitable for use in gene therapy.
Adeno-associated virus is a defective parvovirus that grows only in cells in which certain functions are provided by a co-infecting helper virus. General reviews of AAV may be found in, for example, Carter, 1989
, Handbook of Parvoviruses
, Vol. I, pp. 169-228, and Berns, 1990
, Virology
, pp. 1743-1764, Raven Press, (New York). Examples of co-infecting viruses that provide helper functions for AAV growth and replication are adenoviruses, herpesviruses and, in some cases, poxviruses such as vaccinia. The nature of the helper function is not entirely known but it appears that the helper virus indirectly renders the cell permissive for AAV replication. This belief is supported by the observation that AAV replication may occur at low efficiency in the absence of helper virus co-infection if the cells are treated with agents that are either genotoxic or that disrupt the cell cycle.
Although AAV may replicate to a limited extent in the absence of helper virus, under such conditions as noted above, more generally infection of cells with AAV in the absence of helper functions results in the proviral AAV genome integrating into the host cell genome. Unlike other viruses, such as many retroviruses, it appears that AAV generally integrates into a unique position in the human genome. Thus, it has been reported that, in human cells, AAV integrates into a unique position (referred to as an “AAV integration site”) which is located on chromosome 19. See, e.g., Weitzman et al. (1994)
Proc. Nat'l. Acad. Sci. USA
91: 5808-5812. If host cells having an integrated AAV are subsequently superinfected with a helper virus such as adenovirus, the integrated AAV genome can be rescued and replicated to yield a burst of infectious progeny AAV particles. A sequence at the AAV integration site, referred to as “P1,” shares homology with the AAV inverted terminal repeat (ITR) sequence, exhibits activity in a cell-free replication system, and is believed to be involved in both the integration and rescue of AAV. See, e.g., Weitzman et al., id., Kotin et al. (1992)
EMBO J
. 11:5071-5078, and Urcelay et al.,
J. Virol
. 69: 2038-2046. The fact that integration of AAV appears to be efficient and site-specific makes AAV a useful vector for introducing genes into cells for uses such as human gene therapy.
AAV has a very broad host range without any obvious species or tissue specificity and can replicate in virtually any cell line of human, simian or rodent origin provided that an appropriate helper is present. AAV is also relatively ubiquitous and has been isolated from a wide variety of animal species including most mammalian and several avian species.
AAV is not associated with the cause of any disease. Nor is AAV a transforming or oncogenic virus, and integration of AAV into the genetic material of human cells generally does not cause significant alteration of the growth properties or morphological characteristics of the host cells. These properties of AAV also recommend it as a potentially useful human gene therapy vector because most of the other viral systems proposed for this application, such as retroviruses, adenoviruses, herpesviruses, or poxviruses, are disease-causing.
Although various serotypes of AAV are known to exist, they are all closely related functionally, structurally, and at the genetic level (see, e.g., Blacklow, 1988, pp. 165-174 of
Parvoviruses and Human Disease
, J. R. Pattison (ed.); and Rose, 1974
, Comprehensive Virology
3: 1-61). For example, all AAV serotypes apparently exhibit very similar replication properties mediated by homologous rep genes; and all bear three related capsid proteins such as those expressed in AAV2. The degree of relatedness is further suggested by heteroduplex analysis which reveals extensive cross-hybridization between serotypes along the length of the genome; and the presence of analogous self-annealing segments at the termini that correspond to inverted terminal repeats (ITRs). The similar infectivity patterns also suggest that the replication functions in each serotype are under similar regulatory control. Thus, although the AAV2 serotype was used in various illustrations of the present invention that are set forth in the Examples, general reference to AAV herein encompasses all AAV serotypes, and it is fully expected that the methods and compositions disclosed herein will be applicable to all AAV serotypes.
AAV particles are comprised of a proteinaceous capsid having three capsid proteins, VP1, VP2 and VP3, which enclose a DNA genome. The AAV2 DNA genome, for example, is a linear single-stranded DNA molecule having a molecular weight of about 1.5×10
6
daltons and a length of about 5 kb. Individual particles package only one DNA molecule strand, but this may be either the “plus” or “minus” strand. Particles containing either strand are infectious and replication occurs by conversion of the parental infecting single strand to a duplex form and subsequent amplification of a large pool of duplex molecules from which progeny single strands are displaced and packaged into capsids. Duplex or single-strand copies of AAV genomes can be inserted into bacterial plasmids or phagemids and transfected into adenovirus-infected cells; these techniques have facilitated the study of AAV genetics and the development of AAV vectors.
The AAV genome, which encodes proteins mediating replication and encapsidation of the viral DNA, is generally flanked by two copies of inverted terminal repeats (ITRs). In the case of AAV2, for example, the ITRs are each 145 nucleotides in length, flanking a unique sequence region of about 4470 nucleotides that contains two main open reading frames for the rep and cap genes (Srivastiva et al., 1983
, J. Virol
., 45:555-564; Hermonat et al.,
J. Virol
. 51:329-339; Tratschin et al., 1984a,
J. Virol
., 51:611-619). The AAV2 unique region contains three transcription promoters p5, p19, and p40 (Laughlin et al., 1979
, Proc. Natl. Acad. Sci. USA
, 76:5567-5571) that are used to express the rep and cap genes. The ITR sequences are required in cis and are sufficient to provide a functional origin of replication (ori), signals required for integration into the cell genome, and efficient excision and rescue from host cell chromosomes or recombinant plasmids. It has also been shown that the ITR can function directly as a transcription promoter in an AAV vector. See Flotte et al., 1993, supra; and Carter et al., U.S. Pat. No. 5,587,308.
The rep and cap gene products are required in trans to provide functions for replication and encapsidation of viral genome, respectively. Again, using AAV2 for purposes of illustration, the rep gene is expressed from two promoters, p5 and p19, and produces four proteins. Transcription from p5 yields an unspliced 4.2 kb mRNA encoding a first Rep protein (Rep78), and a spliced 3.9 kb mRNA encoding a second Rep protein (Rep68). Transcription from p19 yields an unspliced mRNA encoding a third Rep protein (Rep52), and a splice
Burstein Haim
Lockert Dara H.
Lynch Carmel M.
Stepan Anthony M.
Guzo David
Morrison & Foerster / LLP
Targeted Genetics Corporation
LandOfFree
Amplifiable adeno-associated virus(AAV) packaging cassettes... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Amplifiable adeno-associated virus(AAV) packaging cassettes..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Amplifiable adeno-associated virus(AAV) packaging cassettes... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3138668