Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-06-23
2004-03-23
Scheiner, Laurie (Department: 1648)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C424S188100, C424S208100
Reexamination Certificate
active
06710173
ABSTRACT:
The invention disclosed herein was made with Government support under NIH Grant No. R01 Al 45463-01 from the Department of Health and Human Services. Accordingly, the government has certain rights in this invention.
Throughout this application, various publications are referenced. The disclosure of these publications is hereby incorporated by reference into this application to describe more fully the art to which this invention pertains.
BACKGROUND OF THE INVENTION
The human immunodeficiency virus (HIV) is the agent that causes AIDS, a lethal disease characterized by deterioration of the immune system. The initial phase of the HIV replicative cycle involves the attachment of the virus to susceptible host cells followed by fusion of viral and cellular membranes. These events are mediated by the exterior viral envelope glycoproteins, which are first synthesized as a fusion-incompetent precursor envelope glycoprotein (env) known as gp160. The gp160 glycoprotein is endoproteolytically processed to the mature envelope glycoproteins gp120 and gp41, which are noncovalently associated on the surface of the virus. The gp120 surface protein contains the high affinity binding site for human CD4, the primary receptor for HIV, as well as domains that interact with fusion coreceptors, such as the chemokine receptors CCRS and CXCR4. The gp41 protein spans the viral membrane and contains at its amino-terminus a sequence of amino acids important for the fusion of viral and cellular membranes. The HIV envelope glycoproteins assemble as noncovalent oligomers, almost certainly trimers, of gp120/gp41 on the virus surface. The detailed events of viral entry remain poorly understood but involve gp120 binding first CD4 then a fusogenic chemokine receptor, followed by gp41-mediated virus-cell fusion.
Because of their location on the virion surface and central role in mediating viral entry, the HIV envelope glycoproteins provide important targets for HIV vaccine development. Although most HIV-infected individuals mount a robust antibody (Ab) response to the envelope glycoproteins, most anti-gp120 and anti-gp41 Abs produced during natural infection bind weakly or not at all to virions and are thus functionally ineffective. These Abs are probably elicited and affinity matured against “viral debris” comprising gp120 monomers or improperly processed oligomers released from virions or infected cells. (Burton and Montefiori, AIDS, 11 [Suppl A]:587, 1997)
Several preventive HIV-1 subunit vaccines have been tested in Phase I and II clinical trials and a multivalent formulation is entering Phase III testing. These vaccines have contained either monomeric gp120 or unprocessed gp160 proteins. In addition, the vaccines mostly have been derived from viruses adapted to grow to high levels in immortalized T cell lines (TCLA viruses). These vaccines have consistently elicited Abs which neutralize the homologous strain of virus and some additional TCLA viruses. However, the Abs do not potently neutralize primary HIV-1 isolates (Mascola et al., J. Infec. Dis. 173:340, 1996). Compared with TCLA strains, the more clinically relevant primary isolates typically possess a different cellular tropism, show a different pattern of coreceptor usage, and have reduced sensitivity to neutralization by soluble CD4 and Abs. These differences primarily map to the viral envelope glycoproteins (Moore and Ho, AIDS, 9 [Suppl A]:S117-S136, 1995).
The Importance of Oligomerization in Envelope Glycoprotein Structure
There is a growing awareness that current-generation HIV subunit vaccines do not adequately present key neutralization epitopes as they appear on virions (Parren et al, Nat. Med. 3:366, 1997). There are several ways in which the native structure of virions affects the presentation of antibody epitopes. Firstly, much of the surface area of gp120 and gp41 is occluded by inter-subunit interactions within the trimer. Hence several regions of gp120, especially around the N- and C-termini, that are well exposed (and highly immunogenic) on the monomeric form of the protein, are completely inaccessible on the native trimer (Moore et al, J. Virol 68:469, 1994). This means that a subset of Abs raised to gp120 monomers are irrelevant, whether they arise during natural infection (because of the shedding of gp120 monomers from virions or infected cells) or after gp120 subunit vaccination. This provides yet another level of protection for the virus; the immune system is decoyed into making Abs to shed gp120 that are poorly reactive, and hence ineffective, with virions.
A second, more subtle problem is that the structure of key gp120 epitopes can be affected by oligomerization. A classic example is provided by the epitope for the broadly neutralizing human MAb IgG1b12 (Burton et al. Science 266:1024, 1994). This epitope overlaps the CD4-binding site on gp120 and is present on monomeric gp120. However, IgG1b12 reacts far better with native, oligomeric gp120 than might be predicted from its monomer reactivity, which accounts for its unusually potent neutralization activity (77,99-103). Thus the IgG1b12 epitope is oligomer-dependent, but not oligomer-specific. The converse situation is more common, unfortunately; many Abs that are strongly reactive with CD4-binding site-related epitopes on monomeric gp120, fail to react with the native trimer, and consequently do not neutralize the virus. In some undefined way, oligomerization of gp120 adversely affects the structures recognized by these Mabs. (Fouts et al., J Virol 71: 2779, 1997).
A third example of the problems caused by the native structure of the HIV-1 envelope glycoproteins is provided by gp41 MAbs. Only a single gp41 MAb (2F5) is known to have strong neutralizing activity against primary viruses (Trkola et al., J Virol, 69: 6609, 1995), and among those tested, 2F5 alone is thought to recognize an intact, gp120-gp41 complex (Sattentau et al, Virology 206: 713, 1995). All other gp41 MAbs that bind to virions or virus-infected cells probably react with fusion-incompetent gp41 structures from which gp120 has dissociated. Since the most stable form of gp41 is this post-fusion configuration (Weissenhorm et al, Nature, 387: 426, 1997), it can be supposed that most anti-gp41 Abs are raised (during natural infection or after gp160 vaccination) to an irrelevant gp41 structure that is not present on the pre-fusion form.
Despite these protective mechanisms, most HIV-1 isolates are potently neutralized by a limited subset of broadly reactive human monoclonal antibodies (MAbs), so induction of a relevant humoral immune response is not impossible. Mab IgG1b12, blocks gp120-CD4 binding; a second (2G12; Trkola et al. J Virol 70: 1100, 1996) acts mostly by steric hindrance of virus-cell attachment; and 2F5 acts by directly compromising the fusion reaction itself. Critical to understanding the neutralization capacity of these MAbs is the recognition that they react preferentially with the fusion-competent, oligomeric forms of the envelope glycoproteins, as found on the surfaces of virions and virus-infected cells. (Parren et al J. Virol 72: 3512, 1998). This distinguishes them from their less active peers. The limited number of MAbs that are oligomer-reactive explains why so few can neutralize primary viruses. Thus with rare exceptions, neutralizing anti-HIV Abs are capable of binding infectious virus while non-neutralizing Abs are not (Fouts et al AIDS Res Human Retrovir. 14: 591, 1998). Neutralizing Abs also have the potential to clear infectious virus through effector functions, such as complement-mediated virolysis.
Modifying the Antigenic Structure of the HIV Envelope Glycoproteins
HIV-1 has evolved sophisticated mechanisms to shield key neutralization sites from the humoral immune response, and in principle these mechanisms can be “disabled” in a vaccine. One example is the V3 loop, which for TCLA viruses in particular is an immunodominant epitope that directs the antibody response away from more broadly conserved neutralization epitopes. HIV-1 is also protected from humoral immunity
Binley James M.
Maddon Paul J.
Moore John P.
Olson William C.
Schuelke Norbert
Cooper & Dunham LLP
Parkin Jeffrey S.
Progenics Pharmaceuticals Inc.
Scheiner Laurie
White John P.
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