wherein the amino acids of the chain have the following meaning;

wherein Xaa in position 1 is Tyr, Trp, Phe or Gly

wherein the Xaa in position 1 is Trp or Tyr

The sequences contribute with CTL-epitopes and can activate the cellular immune system. The amino acid changes implemented within the frame of the CTL-epitopes are designed to achieve enhanced binding. Other amino acid changes have been conducted in order to facilitate the synthesis of the peptide and/or to increase the solubility of the peptide.

A method for detecting antibodies, induced by HIV-1 or HIV-1 specific peptides or proteins, in a sample of body fluid using the present antigens is a further embodiment of the invention. Also immunoassay kit designed for this detection and antibodies capable of selectively reacting with the said antigens are encompassed by the present invention.

Description of the Preparation of the Peptides

The peptides of the invention can be produced by any known method of producing a linear amino acid sequence, such as recombinant DNA techniques. A nucleic acid sequence which encodes a peptide of the invention or a multimer of the said peptides, is introduced into an expression vector. Suitable expression vectors are for instance plasmids, cosmids, viruses and YAC (yeast artificial chromosome) which comprise necessary control regions for replication and expression. The expression vector may be stimulated to expression in a host cell. Suitable host cells are for example bacteria, yeast cells and mammalian cells. Such techniques are well known in the art and described for instance by Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, 1989. Other well-known techniques are degradation or synthesis by coupling of one amino acid residue to the next one in liquid phase or preferably on a solid phase (resin) for instance by the so-called Merrifield synthesis. See for instance Barany and Merrifield in the Peptides, Analysis, Synthesis, Biology, Vol. 2, E. Gross and Meinhofer, Ed. (Acad. Press, N.Y., 1980), Kneib-Coronier and Mullen Int. J. Peptide Protein Res. 30, p. 705-739 (1987) and Fields and Noble Int.J.Peptide Protein Res., 35, p. 161-214 (1990).

In case a linked or cyclic peptide is desired, the amino acid sequence is subjected to a chemical oxidation step in order to cyclize or link the two cysteine residues between two peptide sequences, when the appropriate linear amino acid sequences are synthesized, see Akaji et al., Tetrahedron Letter, 33, 8, p. 1073-1076, 1992.

General Description of Synthesis

All peptide derivatives prepared in the Examples given below were synthesized on a Milligen 9050 Peptide Synthesizer using a standard program. The resin used was Tenta Gel P RAM with a theoretical loading of 0.20 meq/g (RAPP POLYMERE GmbH, Tübingen). The final product of the synthesis was dried in vacuo overnight. The peptide was then cleaved from the resin by treatment with 90% trifluoroacetic acid in the presence of ethane dithiol (5%) and water (5%) as scavengers (1.5 hours at RT). Then the resin was filtered and washed on filter with additional trifluoroacetic acid (100%) (2×20 ml). The combined filtrates were evaporated in vacuo (water bath at RT) and the residue was triturated with ethyl ether (200 ml) and the precipitated product filtered off. The solid was promptly dissolved on filter with glacial acetic acid (100 ml) and added to 1.5 l of 20% acetic acid in methanol and treated with 0.1 M solution of iodine in methanol until a faint brown colour remained. Then Dowex 1×8 ion exchange in acetate form (15 g) (Bio-Rad, Richmond, Calif.) was added and the mixture filtered. The filtrate was evaporated and the residue freeze-dried from acetic acid. The product was then purified by reversed phase liquid chromatography on a column filled with Kromasil® 100-5 C8 (EKA Nobel, Surte, Sweden) in a suitable system containing acetonitrile in 0.1% trifluoroacetic acid water solution. The samples collected from the column were analyzed by analytical high performance liquid chromatography (HPLC) (Beckman System Gold, USA) equipped with a Kromasil® 100-5 C8 Column (EKA Nobel, Surte, Sweden). Fractions containing pure substance were pooled, the solvent was evaporated and the product freeze-dried from acetic acid. The final HPLC analysis was performed on final product, and the structure of the peptide was confirmed by amino acid analysis and mass spectrometry (LDI-MS).

All amino acids used during the synthesis were L-amino acids and they were protected with a fluorenylmethoxy-carbonyl group at the α-amino function. The side chains were protected as follows: