The present invention relates to peptides suitable for use in vaccination against AIDS.
The human immunodeficiency virus (HIV) is responsible for the disease that has come to be known as acquired immune deficiency syndrome (AIDS). Although initially recognized in 1981, no cure has yet been found for this inevitably fatal disease. HIV is spread by a variety of means such as sexual contact, infected blood or blood products and perinatally. Due to the complexity of HIV infection and the paucity of effective therapies, eradication of AIDS will most likely occur by preventing new infections rather than curing those persons already infected. To this end a great deal of effort has been expended in developing methods for detecting and preventing infection. Diagnostic procedures have been developed for identifying infected persons, blood and other biological products.
Like most viruses, HIV often elicits the production of neutralizing antibodies, unlike many other viruses and other infectious agents for which infection leads to protective immunity, however, HIV specific antibodies are insufficient to halt the progression of the disease. Therefore, in the case of HIV, a vaccine that elicits the immunity of natural infection could prove to be ineffective. In fact, vaccines prepared from the HIV protein gp160 appear to provide little immunity to HIV infection although they elicit neutralizing antibodies. The failure to produce an effective anti-HIV vaccine has led to the prediction that an effective vaccine will not be available until the end of the 1990's.
The HIV genome has been well characterized. Its approximately 10Kb encode sequences that contain regulatory segments for HIV replication as well as the gag, pol and env genes coding for the core proteins, the reverse transcriptase-protease-endonuclease, and the internal and external envelope glycoproteins respectively.
The HIV env gene encodes the intracellular glycoprotein, gp160, which is normally processed by proteolytic cleavage to form gp120, the external viral glycoprotein, and gp41, the viral transmembrane glycoprotein. The gp120 remains associated with HIV virions by virtue of noncovalent interactions with gp41. These noncovalent interactions are weak, consequently most of the gp120 is released from cells and virions in a soluble form.
Previous studies have shown that the proteins encoded by the gag and especially the env regions of the HIV-1 genome are immunogenic since antibodies to the products of the gag and env genes are found in the sera of HIV infected, AIDS and ARC ("AIDS Related Condition") patients.
It has previously been shown that some antibodies obtained from sera of AIDS and ARC patients, as well as asymptomatic individuals infected with the virus are specific to gp120 and gp160. Occasionally these antibodies, are neutralizing. The envelope glycoproteins are the HIV-1 antigen most consistently recognized by antibodies in AIDS and ARC patient sera. Allan et al., "Major Glycoprotein Antigens that Induce Antibodies in AIDS Patients are Encoded by HTLV-III", Science, 228:1091-1094 (1985); and Barin et al., "Virus Envelope Protein of HTLV-III Represents Major Target Antigen for Antibodies in AIDS Patients", Science, 228:1094-1096 (1985). In addition, antibodies in patient sera also recognize epitopes of the viral core proteins encoded by the gag gene.
Immunologically important HIV-1 antigens for use in diagnosis and as potential vaccine compositions have been prepared by cloning portions of the HIV-1 genome in various expression systems such as bacteria, yeast or vaccinia. Cabradilla et al., "Serodiagnosis of Antibodies to the Human AIDs Retrovirus With a Bacterially Synthesized env Polypeptide", Biotechnology, 4:128-133 (1986); and Chang et al., "Detection of Antibodies to Human T-Cell Lymphotropic Virus-III (HTLV-III) With an Immunoassay Employing a Recombinant Escherichia coli--Derived Viral Antigenic Peptide", Biotechnology, 3:905-909 (1985). HIV-1 antigens produced by recombinant DNA methods, however, must still be exhaustively purified to avoid adverse reactions upon vaccination and false positive reactions in ELISA assays due to any antibody reactivity to antigens of the expression system which may contaminate the HIV-1 antigen preparation. Also, denaturation of HIV-1 antigens during purification may destroy important antigen activity. Preparation of proteins from intact viruses can also result in contamination by intact virus.
Several publications have presented data showing immunologic reactivity of selected synthetic peptides corresponding to antigenic proteins of HIV-1. In one study, a peptide having the amino acid sequence Tyr-Asp-Arg-Pro-Glu-Gly-Ile-Glu-Glu-Glu-Gly-Gly-Glu-Arg-Asp-Arg-Asp-Arg-Se r-Gly-Cys which corresponds to amino acid residues 735-752 of HIV-1 was synthesized. Kennedy et al., "Antiserum to a Synthetic Peptide Recognizes the HTLV-III Envelope Glycoprotein", Science, 231:1556-1559 (1986). This peptide, derived from a portion of gp41, was used to immunize rabbits in an attempt to elicit a neutralizing antibody response to HIV-1. Furthermore, several sera from AIDS patients known to contain anti-gp41 antibodies were weakly reactive with this peptide, thus indicating that this peptide contains at least one epitope recognized, to some extent, by antibodies to native gp160/gp41. However, this peptide has not been shown to elicit neutralizing antibodies in mammals other than rabbits nor has it been suggested for use as a human vaccine.