1. Field of the Invention
This invention relates to a peptide which has an affinity for gp120, HIV (human immunodeficiency virus) envelope protein.
2. Description of the Related Art
The therapy for HIV infection is usually chemotherapy, such as the nucleotide derivative AZT (3′-azido-3′-deoxythmidine). This AZT therapy or protease inhibitor, which was later developed, prolongs the life of HIV patients, but there are some problems, these are derived from the chemotherapy itself.
The problems are shown as follows: The first is chronic poisoning due to long term administration, the second is the appearance of an HIV virus resistant to the medicine during the therapy, the third is the appearance of malignant tumors in prolongation of the HIV patient's life, the fourth is that the recovery of the immune system can not be monitored, the fifth is that there is not a method to monitor treatment effect, etc. Since such chemotherapy is not basic therapy for HIV infections, most people anticipate the development of a vaccine.
Generally, the vaccine is an inactive treatment (in active vaccine) of a microbe of viruses; a weak activity virus which loses pathogenesis or a pseudo virus (live vaccine) which has no fatal effects to humans. However, although HIV itself is natively a weak activity virus, it is well known to stay long after having once invaded the body. In addition, the host cell of HIV is mainly a lymphocyte, which controls the immune system; furthermore, HIV spreads over hemophilic patients through blood-preparation. From these finding, even if it is assumed that we selected either an in-active or a weak vaccine, the development of an HIV vaccine has many problems with safety.
Accordingly, an HIV vaccine is being developed which utilizes a part of the HIV envelope protein and inhibits further infection.
From such an idea, many researchers performed an epitope analysis of gp120 in the HIV enveloped protein, and then, watched the V3 region (3rd hypervariable region) of gp120 as an epitope. But it was a true hypervariable region [Palker T. J., et al., Proc. Natl. Acad. Sci. USA 85:2709-2713, 1988; Rusche J. R., et al., ibid 85:3198-3202, 1988; Gouddsmit J., et all., ibid 85:4478-4482.1988; Matsushita S., et al., J. Virol. 62:2107-2114, 1988]. After this, a vaccine which used a part of this region as antigen was administrated to an HIV infected monkey as an infection inhibitory experiment, but the effectiveness has not yet been reported.
As well as this, Tam et al. devised further antigenecity for the above-mentioned peptide antigen (Tam et. al., Japanese patent publication (Tokuhyo) No. H 3-503539), but have not yet had success because in most parts of the V region, particularly in the V3 which is a convenient region for antibody preparation, mutation or deletion occurs.
In addition, a neutralized antibody, which inhibits the infection against lymphocyte, is developed. For example, in Japanese Patent Application No. 63-171385, after the production of a monoclonal antibody by using a part of the above mentioned peptide as antigen, a method is reported, which produces anti HIV chimera antibodies on hybridization due to genetic engineering at the level of the protein as the Fab′ itself. But, although with such neutralizing antibodies it is possible to inhibit HIV infection to the lymphocyte at laboratory level, an antibody that can be used practically has not yet been developed.
As mentioned above, chemotherapy has some problems; drug tolerance in the virus and side effects in the host, another idea to solve the problem of removing the virus from the body is by plasmapheresis. Although this method to remove the HIV virus by using a pore size membrane filter (smaller than virus size) for plasmapheresis has been definitely proposed it is not yet possible to make a uniform pore size membrane. It is also possible that the pores will become clogged during plasmapheresis resulting in the deterioration of the membrane due to pressure. As mentioned above there are many technical problems which have to be settled. So, a method to use CD4 derived from human lymphocyte having specific affinity to HIV, as absorbed carrier in column for plasmapheresis is also proposed. It cannot be used as a medical procedure because of the lost affinity due to decay by autoclave treatment. In addition, there are also methods using thermostable molecules, a high molecule polymer or color ligand as an affinity carrier to HIV. However, as these molecules do not originally have specific binding ability to HIV, they cannot be used because they bind to blood ingredients faster than to HIV.
In this way, aiming at the development of an HIV treatment medicine, research to produce a vaccine and neutralizing antibody is flourishing, but useful medicine has not yet been developed.
The inventors paid attention to this present situation and developed a superior peptide to have the same degree or more affinity for gp120 compared to antibodies and to be resistant to autoclave treatment, and have already made a patent application (Japanese Patent Application No. H 8-351474 and Japanese Patent Application No. 8-351475). This peptide basically consists of a three amino acid sequence, but from a study of the sequel, we found that an affinity to gp120 of this peptide deteriorated by number and a kind of the amino acid which ranged in it. So, we knew that we needed to develop a more stable peptide.