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An efficient one-pot procedure for the solid-phase synthesis of new tetracyclic 1,3,5-triazino[1,2-a]benzimidazolium derivatives starting from resin-bound benzimidazoles is described. The synthetic strategy involves an unprecedented one-pot Aza-Wittig/heterocyclization/substitution reaction sequence using halogenoalkyl isocyanates. The structure of the tetracyclic ring system was determined by two-dimensional NMR experiments and X-ray analysis.

The parallel synthesis of a large number of 2-imino-4-oxo-1,3,5-triazino[1,2-a]benzimidazole derivatives via a solid-phase 1,3,5-triazino-annulation reaction is described. The solid-phase approach involves the in situ generation of iminophosphorane derivatives derived from resin-bound 2-aminobenzimidazoles employing Mitsunobu conditions. The subsequent Aza-Wittig reaction of the iminophosphoranes with isocyanates leads to highly reactive carbodiimides, which undergo an intramolecular heterocyclization reaction to form tetrasubstituted 2-imino-4-oxo-1,3,5-triazino[1,2-a]benzimidazoles in high yields (74−94%) and good purity (>80%).

The solid-phase synthesis of novel imidazolines and dihydroimidazolylbenzimidazoles is described. Resin-bound diamines, derived from resin-bound N-acylated amino acid amides, were cyclized using Vilsmeier reagent to yield imidazolines following cleavage. Similarly, cyclization of resin-bound tetraamines having two secondary amines and an o-dianiline yielded dihydroimidazolylbenzimidazoles following cleavage.

The solid-phase synthesis of 1,3-disubstituted and 1,3,5-trisubstituted 1,3,5-triazine-2,4,6-triones from MBHA and Wang resin is described. Reaction of resin-bound amino acids with isocyanates yield resin-bound ureas, which further react with chlorocarbonyl isocyanate in toluene at 65 °C to selectively afford the resin-bound 1,3-disubstituted 1,3,5-triazine-2,4,6-triones. Selective alkylation at the N-5 position of the resin-bound 1,3-disubstituted 1,3,5-triazine-2,4,6-triones was accomplished by treatment with alkyl halides in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The desired products were cleaved from their solid support and obtained in good yield and purity. The method can be employed in production of toltrazuril analogue libraries for identification of new anticoccidial agents.

An efficient method for the solid-phase synthesis of trisubstituted [1,3,5]triazino[1,2-a]benzimidazole-2,4(3H,10H)-diones from resin-bound amino acids is described. N-acylation of the primary amine of a resin-bound amino acid with 4-fluoro-3-nitrobenzoic acid, followed by displacement of the fluoro group and reduction of the nitro group, generated a resin-bound o-dianilino derivative. The dianilino compound was treated with cyanogen bromide to generate the corresponding iminobenzimidazole, which, following treatment with N-(chlorocarbonyl)isocyanate, afforded the resin-bound triazinodione derivative. Alkylation of the triazinodione compound with an alkyl halide yielded, following cleavage of the solid-support, the trisubstituted [1,3,5]triazino[1,2-a]benzimidazole-2,4(3H,10H)-dione.

The solid-phase syntheses of dihydroimidazolyl 2-alkylthiobenzimidazoles, dihydroimidazolyl 2-alkylsulfonylbenzimidazoles, dihydroimidazolyl dihydroquinoxalin-2,3-diones, and dihydroimidazolyl dihydrobenzimidazol-2-imines are described. Following reduction of a resin-bound amino acid amide, the primary amine of the resulting resin-bound diamine was N-acylated with 4-fluoro-3-nitrobenzoic acid. Treatment with POCl3 led to formation of a dihydroimidazole derivative via dehydrative cyclization. The resin-bound dihydroimidazole derivative was then used as the key starting material for the synthesis of the aforementioned biheterocycles. Following cleavage, the resulting compounds, obtained in moderate yield and good purity, were characterized by LC−MS and ¹H NMR and ¹³C NMR spectroscopy.

An efficient method for the preparation of 1,2,5-trisubstituted 4-imidazolidinones is presented. The synthetic approach is based on the formation of an N-[1-(benzotriazol-1-yl)alkyl] moiety on the amino group of a MBHA resin-bound amino acid. The nucleophilic substitution of the benzotriazole group with an amidic nitrogen results in the formation of a five-membered imidazolidinone ring. The reaction is nonstereospecific and produces diastereomers in ratios that vary depending on the substituents on the ring. A variety of N-α-alkylated amino acids were cyclized with aromatic, aliphatic, and heterocyclic aldehydes to determine optimal reaction conditions and to select building blocks for the future preparation of a large, diverse range of individual trisubstituted imidazolidinones as well as a mixture-based combinatorial library.

An efficient method for the solid-phase synthesis of hydantoins and thiohydantoins tethered to ureas, starting from a resin-bound amino acid, is presented. Following reduction of the amide with borane−THF, a second amino acid was selectively coupled to the primary amine followed by treatment of the secondary amine by an isocyanate to generate the corresponding urea. Hydantoin and thiohydantoin formation was achieved through the use of carbonyldiimidazole and thiocarbonyldiimidazole, respectively. Cleavage from the solid support using hydrogen fluoride, followed by extraction and lyophilization, provided the desired urea-linked heterocyclic compounds in good yield and high purity.

Efficient methods for the solid-phase synthesis of imidazoline-tethered 2,3-diketopiperazines, cyclic ureas, and cyclic thioureas are described. Following the exhaustive reduction of resin-bound dipeptides derived from orthogonally protected diamino acids, the primary amine of the resulting tetraamines was selectively protected with Dde. The compounds were then selectively cyclized via their secondary amines with three different diimidazole derivatives ((COIm)2, COIm2, CSIm2). Upon Dde removal, the compounds were selectively N-acylated and dehydratively cyclized with POCl3 to afford the imidazoline-tethered analogues in moderate yield and high purity. These procedures have been extended to prepare mixture-based combinatorial libraries. Details of the selection of building blocks for preparation of the positional scanning libraries based on the “libraries from libraries” approach are discussed.

An efficient method for the solid-phase synthesis of cyclic guanidines from N-acylated amino acid amides, bis cyclic guanidines from N-acylated dipeptides derived from orthogonally protected diamino acids, and N-acylated guanidines from disubstituted cyclic guanidines is described. The exhaustive reduction of N-acylated amino acid amides yields diamines that on treatment with cyanogen bromide lead to the formation of cyclic guanidines. Resin-bound orthogonally protected diamino acids (i.e., N^α-Fmoc-N^x-(Boc)-diamino acid, x = β, γ, δ, ε) were N-acylated following removal of the Fmoc group. Removal of the Boc functionality from the side chain then generated a primary amine. Subsequent coupling of Boc amino acids, followed by removal of the Boc group, generated dipeptides that were N-acylated. Exhaustive reduction of amide bonds of the N-acylated dipeptides generated tetraamines having four secondary amines, which upon cyclization with cyanogen bromide afforded the resin-bound trisubstituted bis cyclic guanidines. Treatment of the resin-bound disubstituted cyclic guanidines with carboxylic acids gave N-acylated guanidines. On the basis of their high yield and purity, bis cyclic guanidines derived from N^α-Fmoc-N^ε-Boc-lysine and N-acylated guanidines were chosen for preparation of mixture-based combinatorial libraries. Details of the preparation of these positional scanning libraries using the “libraries from libraries” concept are presented.

The general concept of tethered combinatorial libraries of compounds in which two pharmacophores are found is described. In particular, an improved method for the solid-phase synthesis of bicyclic guanidines from reduced N-acylated dipeptides, and its use in the synthesis of urea-linked bicyclic guanidines, is described. The exhaustive reduction of glutamine-containing resin-bound N-acylated dipeptides, using borane-THF, generated compounds containing three secondary amines and one primary amine. Following selective trityl protection of the primary amine, treatment of the three secondary amines with thiocarbonyldiimidazole (CSIm2) and mercuric acetate (Hg(OAc)2) generated the resin-bound bicyclic guanidines. Following trityl deprotection, an Fmoc-amino acid was coupled. Upon removal of the Fmoc protecting group, the resulting primary amine was treated with hexyl isocyanate to generate the urea-linked bicyclic guanidines. The desired products were cleaved from the resin using hydrogen fluoride. The selection of building blocks and characterization of controls for the synthesis of a combinatorial library is discussed.

CD4⁺ T lymphocytes usually recognize peptides of 12-16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4⁺ T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4⁺ TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4⁺ TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4⁺ HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.

CD4(+) T lymphocytes usually recognize peptides of 12-16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4(+) T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4(+) TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4(+) TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4(+) HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.

An efficient method for the solid-phase synthesis of 1,3,4-trisubstituted-2-imidazolidones and 1,3,4-trisubstituted-2-imidazolidinethiones from reduced N-acylated dipeptides is described. The complete reduction of the amide bonds of an N-acylated dipeptide with borane in THF results in two secondary and one tertiary amine. Reaction of the resulting resin-bound polyamine 4 with carbonyldiimidazole or thiocarbonyldiimidazole affords, respectively, cyclic ureas 6 and cyclic thioureas 7 in high yield and purity. Details on the selection of the building blocks and characterization of the controls for the libraries' synthesis will be presented. These procedures have also been used to generate parallel arrays and mixture-based combinatorial libraries of cyclic ureas and thioureas.

Synthetic peptides corresponding to sequences in the human liver gap junction protein were chemically synthesized and used for generation of peptide antisera to defined sequences in the protein. The antibodies were affinity purified and characterized by demonstrating that they specifically recognized both their corresponding synthetic peptide (as indicated by dot blot analysis) and the native 32‐kd gap junction protein (by immunoblotting). The specificity of a subset of the different site‐specific antibodies was subsequently confirmed by demonstration of their binding to specific gap junction fragments produced by treatment with a lysine‐specific endoproteinase. Immunoelectron microscopy was used to localize the specific peptide antibody epitopes to either the cytoplasmic or extracellular surfaces of the gap junction. Results indicate a transmembrane orientation for the protein with the amino and carboxyl termini located on the cytoplasmic side of the membrane. Based on these data, a model is proposed for the transmembrane folding of the gap junction protein.

Fifteen hexapeptides having high affinity for the opioid-like receptor ORL1 were identified from a combinatorial library containing more than 52 million different hexapeptides. The five compounds with the highest affinity were characterized further by use of a variety of in vitro models. Binding studies indicated that these five peptides have affinity for ORL1 in the nanomolar range, similar to the recently discovered endogenous ligand called nociceptin and orphanin FQ (N/OFQ). The activity of these compounds was investigated in three different assays: stimulation of [35S]GTPgammaS binding and inhibition of forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells transfected with ORL1, and inhibition of electrically induced contractions in the mouse vas deferens. In each assay, the five hexapeptides acted as partial agonists. The EC50 values for stimulation of [35S]GTPgammaS binding and inhibition of cAMP accumulation were in the range of that for N/OFQ, but maximal effects ranged from 70 to 90% of N/OFQ in the cAMP assay, and 30 to 60% of N/OFQ in the GTPgammaS assay. The positive hexapeptides identified were found to have minimal structural similarity to N/OFQ. The peptides are positively charged, which could enable them to bind to the negatively charged second extracellular loop thought to be a likely binding site for N/OFQ.

Abstract: Here we review the use of combinatorial libraries in opioid receptor assays. Following a brief description of the history of the combinatorial field, methods for the generation of synthetic libraries and the deconvolution of mixture-based libraries are presented. Case studies involving opioid assays used to demonstrate the viability of combinatorial libraries are described. The identification of new opioid peptides from combinatorial libraries is reviewed. The peptides found are composed of L-amino acids, D-amino acids, or L-, D-, and unnatural amino acids, and range from tetrapeptides to decapeptides. Likewise, new opioid compounds identified from peptidomimetic libraries, such as peptoids and alkylated dipeptides, and those identified from acyclic (e.g., polyamine, urea) and heterocyclic (e.g., bicyclic guanidine) libraries, are reviewed. © 2000 John Wiley & Sons, Inc. Biopoly 51: 379–390, 1999

Rabbits and rats were given intravenous injections of tritiated human beta-endorphin. The levels of beta-endorphin were followed by the decrease in radioactivity in the plasma of rats or rabbits and by the increase in radioactivity in the cerebrospinal fluid of the rabbit. The results were identical with the tritium label on either tyrosine-1 or -27. The plasma distribution times were 2 and 5 min in the rat and rabbit, respectively, with a later clearance time of approximately 1-8 hr. In the rat, approximately 50% of the radioactivity in the plasma was found to be intact human beta-endorphin 45 min after injection. Radioactivity appeared in the cerebrospinal fluid of the rabbit within 30 sec after injection and reached a plateau in approximately 60-90 min after injection. Approximately 75% of the radioactivity in the cerebrospinal fluid of the rabbit was intact human beta-endorphin. In the brain hemispheres of the rat and the rabbit, the only significant radiolabeled product was found to be radioactive tyrosine. Moreover, rat plasma levels of beta-endorphin decreased dramatically after hypophysectomy, which only slightly lowered the levels in the brain. It appears that beta-endorphin, upon entry into the plasma, is either not significantly taken up into the brain or is broken down with extreme rapidity upon entry into the brain, although it apparently does enter the cerebrospinal fluid.

Because cytotoxic T lymphocytes (CTL) may be important for preventing direct cell-to-cell transmission of human immunodeficiency virus (HIV), the agent responsible for acquired immunodeficiency syndrome, we have begun to investigate the epitope specificity and immune response (Ir) gene control of anti-HIV CTL responses in experimental animals. Mice were infected with a recombinant vaccinia virus expressing the HIV gp160 envelope gene, and the primed lymphocytes were restimulated in vitro with a transfected histocompatible cell line expressing the same gene. Our results show that H-2d mice are CTL high responders and H-2k mice are low responders to the HIV gp160 envelope protein under these conditions. Moreover, the H-2d mice respond predominantly to a single immunodominant site represented by a 15-residue synthetic peptide conforming to the amphipathic alpha-helix model of T-cell epitopes and seen by CD4- CD8+ CTL in association with the Dd class I major histocompatibility complex (MHC) molecules. The facts that CTL responses were detected in the context of only one of four class I MHC molecules tested and that the response was limited predominantly to a single epitope indicate that the CTL repertoire elicited by the HIV envelope protein in association with murine class I MHC molecules may be very limited. In addition, this epitope occurs in a highly variable segment of the envelope protein. This puts constraints on the use of a single peptide sequence from this region in a vaccine, as such a vaccine would have to be polyvalent. Nevertheless, this same variability suggests that this region may be under selective pressure from human CTL, and therefore that this site may be immunodominant in humans as well as mice and so of clinical importance in vaccine development.

We have generated antibodies against a synthetic peptide corresponding to the sequence of human von Willebrand factor (vWF) between residues Glu1737-Ser1750 which includes the Arg-Gly-Asp sequence common to several adhesive molecules. Two anti-peptide antibodies, one polyclonal, and one monoclonal reacted with native vWF and inhibited its binding to platelet glycoprotein (GP) IIb-IIIa, but showed negligible cross-reactivity with fibrinogen, fibronectin, and vitronectin, three other molecules that contain the sequence Arg-Gly-Asp and bind to platelets. The structural bases for the specificity of the two antibodies were evaluated by testing the ability of peptides homologous to the parent sequence, but with single amino acid substitutions, to neutralize the binding of the two antibodies to vWF. The substitution of Pro1743, the residue immediately adjacent to the Arg-Gly-Asp sequence on the amino-terminal side, with Phe resulted in a peptide that failed to interact with either antibody. Thus, Pro1743 is important for maintaining a peptide conformation recognized by two antibodies specific for the GP IIb-IIIa-binding domain of vWF. Other residues important for optimal peptide reactivity with the polyclonal antibody were Ser1742, Arg1744, and Gly1745, whereas Gly1741, Gly1745, and Asp1746, but not Arg1744, were important for reactivity with the monoclonal antibody. The epitopes of both antibodies, therefore, included at least 2 of the residues in the sequence Arg-Gly-Asp considered the common cell-binding site of adhesive molecules that interact with GP IIb-IIIa. Nevertheless, both antibodies reacted only with vWF. These studies demonstrate that peptide-specific antibodies, unlike the promiscuous GP IIb-IIIa receptor, can recognize distinctive structural characteristics of the cell-binding domain of adhesive molecules imposed by residues adjacent to the sequence Arg-Gly-Asp.

The Plasmodium yoelii sporozoite surface protein 2 (PySSP2) is the target of protective cellular immunity. Cytotoxic T cells specific for the Plasmodium falciparum analog PfSSP2, also known as thrombospondin-related anonymous protein (TRAP), are induced in human volunteers immunized with irradiated sporozoites. PfSSP2 is an important candidate antigen for a multicomponent malaria vaccine. We generated and characterized three monoclonal antibodies (MAbs) specific for PfSSP2/TRAP. The MAbs PfSSP2.1 (immunoglobulin G1 [IgG1]), PfSSP2.2 (IgG2a), and PfSSP2.3 (IgM) were species specific and identified three distinct B-cell epitopes containing sequences DRYI, CHPSDGKC, and TRPHGR, respectively. PfSSP2.1 partially inhibited P. falciparum liver-stage parasite development in human hepatocyte cultures (42 and 86% in two experiments at 100 microg/ml). Mice immunized with vaccinia virus expressing full-length PfSSP2 protein produced antibodies to (DRYIPYSP)3, and humans living in malaria-endemic areas (Indonesia and Kenya), who have lifelong exposure and partial clinical immunity to malaria, had antibodies to both (DRYIPYSP)3 and (CHPSDGKCN)2. Mice immunized with multiple antigen peptides MAP4 (DRYIPYSP)3P2P30 and MAP4 (CHPSDGKCN)3P2P30 in TiterMax developed antibodies to sporozoites that partially inhibited sporozoite invasion of human hepatoma cells (39 to 71% at a serum dilution of 1:50 in three different experiments). The modest inhibitory activities of the MAbs and the polyclonal antibodies to PfSSP2/TRAP epitopes do not suggest that a single-component vaccine designed to induce antibodies against PfSSP2/TRAP will be protective. Nonetheless, the MAbs directed against PfSSP2, and the peptides recognized by these MAbs, will be essential reagents in the development of PfSSP2/TRAP as a component of a multivalent P. falciparum human malaria vaccine.

Several cytotoxic T-lymphocyte (CTL) epitopes have been defined in hepatitis C virus (HCV) proteins. CTL may play an important role in the control of infection by HCV. Here, we identify a highly conserved antigenic site in the HCV core recognized by both murine and human CTL. Spleen cells from mice immunized with a recombinant vaccinia virus expressing the HCV core gene were restimulated in vitro with 11 peptides from the core protein. CTL from H-2d mice responded to a single 16-residue synthetic peptide (HCV 129-144). This conserved epitope was presented by a murine class I major histocompatibility molecule (H-2Dd) to conventional CD4- CD8+ CTL mapped by using transfectants expressing Dd, Ld, or Kd, but was not seen by CTL restricted by H-2b. The murine epitope was mapped to the decapeptide LMGYIPLVGA. The same 16-residue peptide was recognized by CTL from two HCV-seropositive patients but not by CTL from any seronegative donors. CTL from two HLA-A2-positive patients with acute and chronic hepatitides C recognized a 9-residue fragment (DLMGYIPLV) of the peptide presented by HLA-A2 and containing an HLA-A2-binding motif, extending only 1 residue beyond the murine epitope. Therefore, this conserved peptide, seen with murine CTL and human CTL with a very prevalent HLA class I molecule, may be a valuable component of an HCV vaccine against a broad range of HCV isolates. This study demonstrates that the screening for CTL epitopes in mice prior to human study may be useful.

An approach that enables identification of specific synthetic peptide inhibitors of plant viral infection is reported. Synthetic analogs of melittin that have sequence and structural similarities to an essential domain of tobacco mosaic virus coat protein were found to possess highly specific antiviral activity. This approach involves modification of residues located at positions analogous to those that are critical for virus assembly. The degree of inhibition found correlates well with sequence similarities between the viral capsid protein and the melittin analogs studied as well as with the induced conformational changes that result upon interaction of the peptides and ribonucleic acid.

A combinatorial library of 6,250,000 tetrapeptides in the mixture based positional scanning format was screened in binding assays for the three opioid receptors, mu, delta, and kappa. Three different binding profiles were found. Individual peptides were synthesized representing all possible combinations of the active amino acids identified from the screening data. New, highly active peptides selective for each of the three receptors were chosen. This study demonstrates the power of mixture-based combinatorial libraries to identify distinctly different ligands for closely related receptors.

We have identified the Factor VIII amino acid sequence Asp-Tyr-Asp-Asp-Thr-Ile-Ser (1663-1669) as the binding site of a Factor VIII activity neutralizing antibody (28 Bethesda units/mg). The binding site of another neutralizing antibody (10 Bethesda units/mg) overlapped only at Asp1663 and Tyr1664, whereas an antibody with minimal neutralizing activity (0.2 Bethesda units/mg) bound only at Asp1665-Ser1669. Residues comprising antibody binding sites were determined by blocking Factor VIII neutralization and/or binding to insolubilized Factor VIII with overlapping peptides, or with variant peptides in which a single amino acid was deleted or replaced with glycine. Eight additional antibodies to flanking sequences, and with similar affinities for Factor VIII, had little or no neutralizing activity (0-3.0 Bethesda units/mg). These studies suggest that Asp1663 and Tyr1664 may be structural features important to Factor VIII function.

Cytotoxic T lymphocytes (CTL) have been found to mediate protection in vivo against certain virus infections. CTL also may play an important role in control of infection by hepatitis C virus (HCV), but no CTL epitopes have yet been defined in any HCV protein. The nonstructural protein with homology to RNA polymerase should be a relatively conserved target protein for CTL. To investigate the epitope specificity of CTL specific for this protein, we used 28 peptides from this sequence to study murine CTL. Mice were immunized with a recombinant vaccinia virus expressing the HCV nonstructural region corresponding to the flavivirus NS5 gene (RNA polymerase), and the primed spleen cells were restimulated in vitro with peptides. CTL from H-2d mice responded to a single 16-residue synthetic peptide (HCV 2422 to 2437). This relatively conserved epitope was presented by H-2d class I major histocompatibility complex (MHC) molecules to conventional CD4- CD8+ CTL but was not recognized by CTL restricted by H-2b. Moreover, exon shuffle experiments using several transfectants expressing recombinant Dd/Ld and Kd demonstrated that this peptide is seen in association with alpha 1 and alpha 2 domains of the Dd class I MHC molecule. This peptide differs from the homologous segments of this nonstructural region from three other HCV isolates by one residue each. Variant peptides with single amino acid substitutions were made to test the effect of each residue on the ability to sensitize targets. Neither substitution affected recognition. Therefore, these conservative mutations affected peptide interaction neither with the Dd class I MHC molecule nor with the T-cell receptor. Because these CTL cross-react with all four sequenced isolates of HCV in the United States and Japan, if human CTL display similar cross-reactivity, this peptide may be valuable for studies of HCV diagnosis and vaccine development. Our study provides the first evidence that CD8+ CTL can recognize an epitope from the HCV sequence in association with a class I MHC molecule.

In earlier studies, we have reported that minor modifications in the amino acid sequence of melittin result in dramatic changes in its biological activity. In the current study, we have investigated the secondary structure of melittin analogues with either increased or decreased haemolytic activity in order to further our understanding of the structural features involved in the binding and/or insertion of peptides into a phospholipid membrane from solution. This was accomplished by analysing the c.d. spectra of the analogues in solutions of various ionic strength and, separately, in the presence of micelles. These studies permit the assessment of the effect of small sequence modifications (i.e. single amino acid omission or substitution) on the self-association-induced secondary structure of melittin in aqueous solution, as well as its binding affinity to micelles. It was found that amphipathicity, as well as interchain distances and the orientation of hydrophobic residues, were involved in the induction of stabilized structures.

Synthetic peptides corresponding to sequences in the human liver gap junction protein were chemically synthesized and used for generation of peptide antisera to defined sequences in the protein. The antibodies were affinity purified and characterized by demonstrating that they specifically recognized both their corresponding synthetic peptide (as indicated by dot blot analysis) and the native 32‐kd gap junction protein (by immunoblotting). The specificity of a subset of the different site‐specific antibodies was subsequently confirmed by demonstration of their binding to specific gap junction fragments produced by treatment with a lysine‐specific endoproteinase. Immunoelectron microscopy was used to localize the specific peptide antibody epitopes to either the cytoplasmic or extracellular surfaces of the gap junction. Results indicate a transmembrane orientation for the protein with the amino and carboxyl termini located on the cytoplasmic side of the membrane. Based on these data, a model is proposed for the transmembrane folding of the gap junction protein.

A positional scanning synthetic peptide combinatorial library containing approximately 52 million hexapeptides was used to identify potential inhibitory peptides for recombinant mouse prohormone convertase 1 (PC1) and PC2 and to provide information on the specificity of these enzymes. The library surveys revealed that a P6 Leu, a P4 Arg, a P2 Lys, and a P1 Arg were most inhibitory against PC1, and a P6 Ile and a P4 Arg were most inhibitory against PC2. Using information derived from the library surveys, hexapeptide sets were synthesized and screened for inhibition of PC1 and PC2. The data obtained revealed the preference of both enzymes for a P3 Val. At P5, many substitutions were well tolerated. PC1 and PC2 proved to differ mainly in the selectivity of their S6 subsites. In PC1, this subsite displayed a strong preference toward occupation by Leu; the Ki value for peptide Ac-Leu-Leu-Arg-Val-Lys-Arg-NH2 was 28 times lower than that for peptide Ac-Ile-Ile-Arg-Val-Lys-Arg-NH2. In contrast, PC2 discriminated little between Leu and Ile at P6, as evidenced by the small (1.5-fold) difference in Ki values for these two peptides. Several hexapeptides synthesized as a result of the screen were found to represent potent inhibitors of PC2 (with Ki values in the submicromolar range) and, particularly, of PC1 (with Ki values in the low nanomolar range). The most potent inhibitor, Ac-Leu-Leu-Arg-Val-Lys-Arg-NH2, proved to be the same peptide for both enzymes and inhibited PC1 and PC2 in a competitive, fast-binding manner with Ki values of 3.2 and 360 nM, respectively. The four most potent peptide inhibitors of PC1 and PC2 were also tested against soluble human furin and found to exhibit a different rank order of inhibition; for example, Ac-Leu-Leu-Arg-Val-Lys-Arg-NH2 was 440-fold less potent against furin than against PC1, with a Ki of 1400 nM.

Irradiated malaria sporozoites can induce CD8+ T cells that are required for protection against infection. However, the parasite antigens targeted by this immune response are unknown. We have discovered a 16-amino acid epitope from the Plasmodium yoelii circumsporozoite (CS) protein that is recognized by cytotoxic T cells from immune mice. Lymphocytes stimulated with this peptide can kill P. yoelii liver stage parasites in vitro in an MHC-restricted, antigen-specific manner. Thus, epitopes from the CS protein are presented on the surface of infected hepatocytes and can be targets for T cells, even though intact CS protein has not been detected on the surface of the infected hepatocyte. A vaccine that induced CTL to parasite antigens might protect humans against malaria by eliminating liver stage parasites.

Recently, an antiidiotype to human monoclonal IgM anti-IgG autoantibodies (rheumatoid factors) was found to react also with human IgG. This peculiar antiidiotype was called an 'epibody'. We describe the induction of a similar epibody by immunization with a synthetic peptide (corresponding to one hypervariable region of the IgM-RF Glo). The results confirm the existence of epibodies, and provide the possible molecular basis of the epibody phenomenon.

Antibody against a cross-reactive idiotype (CRI) on human IgM-rheumatoid factor (RF) antibodies was induced by immunization of rabbits with a synthetic peptide ( PSL2 ) corresponding to the second complementarity-determining region (CDR), and adjacent amino acid residues of the kappa light chain of the IgM-RF Sie . The anti-peptide antibody bound efficiently to IgM-RF proteins known to share a cross-reactive idiotype, and to their isolated kappa chains. The anti-CRI was absorbed by, and eluted from, a peptide-Sepharose affinity column. The antibody activity was inhibited by the free peptide in solution. The anti-peptide antibody thus identifies a public idiotype on human IgM-RF, that is largely dependent on the primary sequence of the second CDR of the light chain. Such peptide-induced antiidiotypes of predefined specificity may facilitate studies of the molecular basis of idiotypic cross-reactions, the inheritance and somatic diversification of antibody molecules, and the regulation of the idiotype network.

A synthetic peptide combinatorial library made up of 52,128,400 hexapeptides, each having an acetyl group at the N terminus and an amide group on the C terminus, was screened to find compounds able to displace tritiated [D-Ala2,MePhe4,Gly-ol5]enkephalin from mu opioid receptor binding sites in crude rat brain homogenates. Individual peptides with mu receptor affinity were found using an iterative process for successively determining the most active peptide mixtures. Upon completion of this iterative process, the three peptides with the highest affinity were Ac-RFMWMT-NH2, Ac-RFMWMR-NH2, and Ac-RFMWMK-NH2. These peptides showed high affinity for mu and kappa 3 opioid receptors, somewhat lower affinity for delta receptors, weak affinity for kappa 1 receptors, and no affinity for kappa 2 receptors. They were found to be potent mu receptor antagonists in the guinea pig ileum assay and relatively weak antagonists in the mouse vas deferens assay. These peptides represent a class of opioid receptor ligands that we have termed acetalins (acetyl plus enkephalin).

Cytotoxic T lymphocytes (CTL) against the circumsporozoite (CS) protein of malaria sporozoites protect against malaria in rodents. Although there is interest in developing human vaccines that induce CTL against the Plasmodium falciparum CS protein, humans have never been shown to produce CTL against any Plasmodium species protein or other parasite protein. We report that when peripheral blood mononuclear cells (PBMC) from three of four volunteers immunized with irradiated P. falciparum sporozoites were stimulated in vitro with a recombinant vaccinia virus expressing the P. falciparum CS protein or a peptide including only amino acids 368-390 of the P. falciparum CS protein [CS-(368-390)], the PBMC lysed autologous Epstein-Barr virus-transformed B cells transfected with the P. falciparum CS protein gene or incubated with CS-(368-390) tricosapeptide. Activity was antigen specific, genetically restricted, and dependent on CD8+ T cells. In one volunteer, seven peptides reflecting amino acids 311-400 were tested, and, as in B10.BR mice, CTL activity was only associated with the CS-(368-390) peptide. Development of an assay for studying human CTL against the CS and other malaria proteins and a method for constructing target cells by direct gene transfection provide a foundation for studying the role of CTL in protection against malaria.

Abstract:

T-cell-mediated cytotoxicity may play an important role in control of infection by the human immunodeficiency virus (HIV). In this study, we have identified and characterized a relatively conserved epitope in the HIV-1 reverse transcriptase recognized by murine and human cytotoxic T cells. This epitope was identified using a murine antigen-specific CD8+ class I major histocompatibility complex-restricted cytotoxic T-cell (CTL) line, a transfected fibroblast cell line expressing the HIV-1 pol gene, recombinant vaccinia viruses containing different truncated versions of the pol gene, and overlapping synthetic peptides. The optimal antigenic site was identified as residues 203-219 by synthesizing extended or truncated peptide analogs of the antigenic fragment. The optimal peptide was then tested for sensitization of autologous Epstein-Barr virus-transformed B-cell targets for killing by fresh human peripheral blood mononuclear cells. It was recognized by CTLs from several HIV-seropositive patients but not from any seronegative donor. Therefore, this peptide is a good candidate for inclusion in an AIDS vaccine. This study demonstrates that the same CTL epitope can be seen by murine and human CD8+ CTLs, as previously demonstrated for epitopes recognized by CD4+ helper T cells, and suggests the utility of screening for immunodominant CTL epitopes in mice prior to carrying out studies in humans.

The immunodeterminant regions of the Escherichia coli heat-labile toxin B subunit were identified by determining the antigenicity, by using enzyme-linked immunosorbent assays, of synthetically produced peptides corresponding to various segments of its 124-amino-acid sequence. The addition of the 18-amino-acid sequence of heat-stable toxin (ST) to some of these peptides enhanced their B subunit antigenicity. Peptide residues containing the 26 amino acids of B subunit sequence 58 to 83 joined to the 18-amino-acid sequence of ST yielded a 44-amino-acid peptide whose antigenicity was 50% that of both native B subunit and ST. This peptide was completely nontoxic when tested in Chinese hamster ovary tissue culture, suckling mouse, and rat ligated ileal loop assays. Peroral immunization of rats with the polymeric form of this peptide yielded a dose-dependent response of intestinal immunoglobulin A antitoxin titers to both the ST and B subunit components and provided strong protection against challenge with viable ST- and heat-labile toxin-producing E. coli strains. The immunogenicity of the synthetic peptide in rats was the same as that of ST and about 50% that of native B subunit. The completely synthetic peptide vaccine has the following advantages over previously described toxoid vaccines that consist of synthetic ST chemically cross-linked to native B subunit derived from bacterial cultures: it is produced by a single synthetic process, it is completely nontoxic, and it is immunogenic for both ST and B subunit.

Peroral immunization of volunteers on four weekly occasions with 750 micrograms of a conjugate containing 3,000 antigen units of a synthetically produced peptide of hyperantigenic Escherichia coli heat-stable (ST) toxin, conjugated with the heat-labile toxin B subunit as a carrier, raised serum immunoglobulin G antitoxin titers to ST by fourfold and intestinal immunoglobulin A antitoxin titers to ST by sevenfold over control values at five weeks postimmunization. The ability of jejunal aspirates from the immunized volunteers to neutralize ST in the suckling mouse assay correlated with the intestinal immunoglobulin A ST antitoxin response determined by enzyme-linked immunosorbent assay.

Monoclonal antibodies directed to Mycobacterium bovis BCG (BCG) and to M. tuberculosis H37Rv (H37Rv) were used in conjunction with affinity chromatography to prepare a mycobacterial component which was designated BCG-a. A synthetic peptide antigen was prepared based on the amino acid sequence of BCG-a and was designated BCG-a-P. Significant immunological similarities were found between BCG-a-P and antigens in extracts of BCG and H37Rv but not between BCG-a-P and antigens of nontuberculous mycobacteria. An enzyme-linked immunosorbent assay detected antibodies to BCG-a-P in sera from rabbits that had been immunized with BCG and H37Rv sonicates. In Western blot analysis, antibodies to BCG-a-P reacted to 10,000-molecular-weight components of extracts of BCG and H37Rv. Delayed cutaneous hypersensitivity reactions to BCG-a-P were elicited in guinea pigs immunized with sonicates of BCG and H37Rv but were weak or nonexistent in unimmunized animals or in animals immunized with sonicates of nontuberculous mycobacteria. This study points out the feasibility of using monoclonal antibodies to prepare and characterize synthetic mycobacterial peptides with a potential for immunodiagnostic purposes.

Class I-restricted CD8+ cytotoxic T lymphocytes (CTL) against the circumsporozoite protein (CSP) protect mice against the rodent malaria parasite, Plasmodium yoelii, and vaccines designed to produce protective CTL against the P. falciparum CSP (PfCSP) are under development. Humans and B10.BR (H-2k) mice have been shown to have CD8+ CTL activity against a 23-amino-acid region of the PfCSP (residues 368 to 390 from the PfCSP 7G8 sequence) that is too long to bind directly to class I major histocompatibility complex molecules. To identify within this 23-amino-acid peptide a shorter peptide that binds to an H-2k class I major histocompatibility molecule, a primarily CD8+ (97.8%) T-cell line (PfCSP TCL.1) was produced by immunizing B10.BR mice with recombinant vaccinia virus expressing the PfCSP and stimulating in vitro spleen cells from these immunized mice with L cells transfected with the PfCSP gene (LPF cells). PfCSP TCL.1 lysed LPF cells and L cells pulsed with peptide PfCSP 7G8 368-390. When 15 overlapping nonamer peptides spanning the 368 to 390 sequence were tested, only one peptide, PfCSP 7G8 375-383 (Y E N D I E K K I), which includes an H-2Kk-binding motif, E at amino acid residue 2, and I at residue 9, sensitized targets for lysis by PfCSP TCL.1. Furthermore, a 10(3)- to 10(4)-fold lower concentration of the nonamer than that of the 23-amino-acid peptide was required to sensitize target cells for lysis by PfCSP TCL.1. Presentation by H-2Kk was demonstrated by using 3T3 fibroblast cells transfected with the murine H-2Kk or H-2Dk genes, and only the H-2Kk transfectants were lysed by PfCSP TCL.1 after incubation with peptide PfCSP 7G8 375-383. Binding to H-2Kk was confirmed by competitive inhibition of binding of labelled peptides to affinity-purified Kk molecules. Substitution of the anchor amino acid residue, E, at position 2 with A dramatically reduced binding to Kk and eliminated the capacity of the peptide to sensitize target cells for killing. Variation of non-anchor residues did not markedly reduce binding to Kk but in some cases eliminated the capacity of the peptide to sensitize targets for cytolysis by PfCSP TCL.1, presumably by eliminating T-cell receptor-binding sites. These data suggest that similar studies with human T cells will be required for optimal development of peptide-based vaccines designed to produce protective class I-restricted CD8+ CTL against the PfCSP in humans.

This communication describes the preparation of antibodies to human interleukin 2 (IL-2), using as immunogens synthetic peptides derived from the predicted amino acid sequence of IL-2. Rabbits and mice were immunized with protein carrier conjugates of eight chemically synthesized IL-2-derived peptides, each consisting of 13-15 amino acids. The immune antisera were screened in a solid-phase ELISA for reactivity to a native human IL-2. Antibodies to four of the eight peptides were found by a variety of biological and immuno-chemical criteria to react against human IL-2. Furthermore, an affinity-purified antibody to one of the IL-2 peptides (peptide 84) specifically stained the cytoplasm of phytohemagglutinin-stimulated human peripheral blood lymphocytes or T-leukemic cells (Jurkat). Antibodies to synthetic IL-2 peptides should serve as useful probes for studying this lymphokine and for developing quantitative assays for measuring its levels in biological fluids and its association with disease.

The definition of human T-cell antigenic sites is important for subunit vaccine development of a peptide immunogen if the goal is to allow antibody boosting during infection or to stimulate antibody-independent T-cell immunity. To identify such sites on the circumsporozoite (CS) protein of Plasmodium falciparum, 29 overlapping synthetic peptides spanning the entire CS protein were made and tested for their ability to stimulate peripheral blood lymphocytes from 35 adults living in a P. falciparum malaria-endemic region of West Africa. Three immunodominant domains were located outside the repetitive region. These domains, however, occurred in the polymorphic regions of the molecule, suggesting that parasite mutation and selection has occurred in response to immune pressure from T cells. Such polymorphism may impose an obstacle for vaccine development.