Overlapping epitopes that are recognized by CD8+ HLA class I-restricted and CD4+ class II-restricted cytotoxic T lymphocytes are contained within an influenza nucleoprotein peptide.

Viral epitopes that are recognized by both HLA class I-restricted and class II-restricted T cells have been defined for a type A influenza virus nucleoprotein (NP) peptide. CD8+ and CD4+ CTL lines have been generated against a synthetic peptide encompassing residues 335 to 349 of NP that are restricted by HLA-B37 and HLA-DQw5, respectively. Both of these CTL populations were capable of specifically lysing influenza A virus-infected targets, indicating that a naturally processed NP peptide(s) was being mimicked by the NP (335-349) peptide. Amino acid residues that are critical for recognition of this NP determinant in the context of HLA-B37 and HLA-DQw5 were investigated by the use of panels of truncated and alanine-substituted NP peptides. The results demonstrate that: 1) truncations in the amino- or carboxy-terminal ends differentially affect CD8+ and CD4+ CTL recognition; 2) the NP (335-349) sequence contains two octapeptide epitopes that share a core of six amino acid residues (NP 338-343); and 3) alanine substitutions at five of these residues abrogated recognition by at least one of the CD8+ and CD4+ CTL lines. Thus, these class I- and class II-restricted CTL lines recognize similar but distinct epitopes, and different structural features of the NP peptide are required for presentation by HLA-B37 and HLA-DQw5. Comparison of the amino acid sequences of the NP peptide presented by HLA-B37 and HLA-DQw5 with other peptides known to be presented by both class I and class II molecules revealed a common motif among these peptides.     

Multiple genetic mechanisms have contributed to the generation of the HLA-A2/A28 family of class I MHC molecules

The genetic events that produce diversity in class I MHC genes and proteins has been investigated by using a family of closely related HLA-A alleles. Five genes coding for HLA-A2.2Y, HLA-A2.3, and HLA-Aw68.2 have been isolated. Exon sequences are compared with the known sequences for HLA-A2.1, HLA-A2.2F, HLA-A2.4, HLA-Aw68.1, and HLA-Aw69. Pairwise comparison of the eight unique sequences shows that point mutation, reciprocal recombination, and gene conversion have all contributed significantly to the diversification of this family of alleles. These results are compared with those of other studies that have emphasized the role of gene conversion. A predominance of coding substitutions in the alpha 1 and alpha 2 domains is found, consistent with positive selection for polymorphism being a major factor in the fixation of these alleles. In the three cases examined, genes for phenotypically identical proteins gave identical nucleotide sequences, indicating that most, if not all, of the class I polymorphism is detectable by immunological methods. The apparent stability of the sequences suggests that the events generating some of the alleles occurred before the origin of modern Homo sapiens.     

Functional constraints of influenza A virus epitopes limit escape from cytotoxic T lymphocytes

Viruses can exploit a variety of strategies to evade immune surveillance by cytotoxic T lymphocytes (CTL), including the acquisition of mutations in CTL epitopes. Also for influenza A viruses a number of amino acid substitutions in the nucleoprotein (NP) have been associated with escape from CTL. However, other previously identified influenza A virus CTL epitopes are highly conserved, including the immunodominant HLA-A*0201-restricted epitope from the matrix protein, M1(58-66). We hypothesized that functional constraints were responsible for the conserved nature of influenza A virus CTL epitopes, limiting escape from CTL. To assess the impact of amino acid substitutions in conserved epitopes on viral fitness and recognition by specific CTL, we performed a mutational analysis of CTL epitopes. Both alanine replacements and more conservative substitutions were introduced at various positions of different influenza A virus CTL epitopes. Alanine replacements for each of the nine amino acids of the M1(58-66) epitope were tolerated to various extents, except for the anchor residue at the second position. Substitution of anchor residues in other influenza A virus CTL epitopes also affected viral fitness. Viable mutant viruses were used in CTL recognition experiments. The results are discussed in the light of the possibility of influenza viruses to escape from specific CTL. It was speculated that functional constraints limit variation in certain epitopes, especially at anchor residues, explaining the conserved nature of these epitopes.     

CD4+ cytolytic T cell clones restricted to HLA class II, DR beta I, and DR beta III chains

We have investigated the functional polymorphism of HLA class II antigens using CD4+ CTL clones. Seven CD4+ CTL clones were isolated from a healthy donor (HLA A2 A24; B8 B27; DRw17 DRw52a) by repeated stimulation with irradiated autologous EBV-transformed B cell lines (EBV-B). According to the HLA restriction specificity we divided CD4+ CTL clones into three subgroups: (i) DRw17-restricted CD4+ CTL clones; (ii) DRw52a-restricted CD4+ CTL clones; and (iii) the CD4+ CTL clones, of which the restriction specificity could not be assigned to products of a single HLA locus. Interestingly, DRw17-restricted CD4+ CTL clones distinguished between DRw17 and DRw18. Similarly, DRw52a-restricted CD4+ CTL clones distinguished between DRw52a, w52b, and w52c. There are four amino acids which differ between DRw17 and DRw18, whereas five differ between DRw52a and the other two alleles (DRw52b and DRw52c). The recent elucidation of the crystal structure of a human class I MHC molecule has identified the probable peptide binding site to be a cleft on the outer surface of the molecule, between two alpha-helices. On the basis of the theoretical model for HLA class II molecules, amino acid positions 26 and 28 (DRw17 vs DRw18) and amino acid positions 26, 28, and 74 (DRw52a vs the other two alleles) lie within the "cleft." We propose that amino acid positions 26 and 28 are very important sites with regard to the recognition of antigen-MHC complex by the TCR.     

The 45 pocket of HLA-A2.1 plays a role in presentation of influenza virus matrix peptide and alloantigens

Amino acid substitutions were introduced into the 45 pocket of HLA-A2.1 to determine the potential role of this structurally defined feature of class I molecules in viral peptide and alloantigen presentation. The 45 pocket lies below the alpha 1-domain alpha-helix and is composed of five amino acids, three of which differ between HLA-A2.1 and HLA-B37. These two class I molecules have previously been shown to have largely non-overlapping peptide-binding specificities. Site-directed mutagenesis was used to replace the hydrophobic residues at positions 24, 45, and 67 in the 45 pocket of HLA-A2.1 with the hydrophilic amino acids found in these positions in HLA-B37. Thus, three single amino acid mutants were produced: 24A----S, 45 M----T, and 67V----S. These mutants were transfected into HMy2.C1R cells and assessed for their ability to present influenza virus matrix M1 57-68 peptide and HTLV-I Tax-1 2-25 peptide to HLA-A2.1-restricted, peptide-specific CTL and to present alloantigens to HLA-A2-allospecific CTL lines. Each of these substitutions in the 45 pocket produced a molecule that failed to present the M1 peptide to most M1 peptide-specific CTL lines. In contrast, none of these mutations affected presentation of the Tax-1 peptide to Tax-1-specific CTL lines, which indicates that these mutant HLA-A2 molecules can function in viral peptide presentation. Two of the three substitutions in the 45 pocket resulted in lack of recognition by a subset of HLA-A2 allospecific CTL lines. These results demonstrate that the amino acid side chains in the 45 pocket can strongly influence peptide presentation and suggest that the 45 pocket may play a role in determining peptide-binding specificity.     

Macrophages escape inhibition of major histocompatibility complex class I-dependent antigen presentation by cytomegalovirus

The mouse cytomegalovirus (MCMV) m152- and m06-encoded glycoproteins gp40 and gp48, respectively, independently downregulate major histocompatibility complex (MHC) class I surface expression during the course of productive MCMV infection in fibroblasts. As a result, presentation of an immediate-early protein pp89-derived nonapeptide to H-2L(d)-restricted CD8(+) cytotoxic T cells is completely prevented in fibroblasts. Here we demonstrate that MCMV-infected primary bone marrow macrophages and the macrophage cell line J774 constitutively present pp89 peptides during permissive MCMV infection to cytotoxic T lymphocytes (CTL). In contrast to fibroblasts, expression of the m152 and m06 genes in macrophages does not affect surface expression of MHC class I. Assessment of pp89 synthesis and quantification of extracted peptide revealed a significantly higher efficiency of macrophages than of fibroblasts to process pp89 into finally trimmed peptide. The yield of pp89 peptide determined in MCMV-infected tissues of bone marrow chimeras confirmed that bone marrow-derived cells represent a prime source of pp89 processing in parenchymal organs. The finding that macrophages resist the viral control of MHC I-dependent antigen presentation reconciles the paradox of efficient induction of CMV-specific CD8(+) CTL in vivo despite extensive potential of CMVs to subvert MHC class I.     

Comparison between two peptide epitopes presented to cytotoxic T lymphocytes by HLA-A2. Evidence for discrete locations within HLA-A2

An influenza B virus nucleoprotein (BNP) peptide, residues 82-94, defined by limited sequence homology with an HLA-A2-restricted peptide from influenza A matrix protein, was recognized by HLA-A2-restricted CTL. Reciprocal inhibition of T cell recognition by the two peptides suggest that the BNP peptide may have lower avidity for HLA-A2 molecules than the matrix peptide. The interaction between this peptide and HLA-A2 was explored by studying the CTL recognition of BNP 82-94 presented by mutant HLA-A2 molecules. Mutations at residues 9, 99, 70, 74, 152 and 156 were found to abolish T cell recognition of the BNP peptide. These results were compared with results previously obtained with the influenza A matrix peptide and suggest that the two peptides bind differently in the peptide binding site.     

Differential effects of amino acid substitutions in the beta-sheet floor and alpha-2 helix of HLA-A2 on recognition by alloreactive viral peptide-specific cytotoxic T lymphocytes

Crystallographic studies of the HLA-A2 molecule have led to the assignment of a putative peptide binding site that consists of a groove with a beta-pleated sheet floor bordered by two alpha-helices. A CTL-defined variant of HLA-A2, termed HLA-A2.2F, differs from the common A2.1 molecule by three amino acids: a Leu to Trp substitution at position 156 in the alpha-2 helix, a Val to Leu substitution at position 95 in the beta-sheet floor of the groove, and a Gln to Arg substitution at position 43 in a loop outside of the groove. Another HLA-A2 variant, termed CLA, has a single Phe to Tyr substitution at position 9 that is sterically located adjacent to position 95 in the beta-sheet floor of the groove. We have determined which of the amino acid substitutions at positions 9, 43, 95, or 156 could individually affect recognition by panels of A2.1 allospecific and A2.1-restricted influenza viral matrix peptide-specific CTL lines, using a panel of site-directed mutants and CLA. Recognition by allospecific CTL lines was generally unaffected by any one of the amino acid substitutions, but was eliminated by the double substitution at positions 95 and 156. Allorecognition by some CTL lines was eliminated by a single substitution at position 9 or 95. In contrast, recognition by A2.1-restricted matrix peptide specific CTL was totally eliminated by a single substitution at position 9 or 156. The substitution at position 43 in a loop away from the peptide binding groove had no effect on allorecognition or matrix peptide recognition. These results indicate that amino acid residues in the floor or alpha-2 helical wall of the peptide binding groove of the HLA-A2 molecule can differentially affect allorecognition and viral peptide recognition.     

烟曲霉抗原Asp f16HLA-A*0201限制性的CD8+CTL抗原表位生物信息学预测与实验室鉴定

目的 预测与鉴定烟曲霉抗原Asp f16的HLA-A *0201限制性CD8+细胞毒性T细胞(CTL)抗原表位.方法 以国人常见的HLA-A*0201位点为靶点,依据生物信息学软件扫描烟曲霉特异性抗原Asp f16的全部427个氨基酸序列.使用HLA-A *0201转基因小鼠制备骨髓来源的树突状细胞(DC)和CTL.流式细胞仪技术检测DC表面MHC Ⅱ类抗原,CD80,CD86和CD11c的表达来验证其是否成熟.ELISPOT试验检测烟曲霉抗原多肽特异性CTL产生的细胞因子IFN-γ.四聚体(Tetramer)试验证实烟曲霉特异性CTL与抗原肽,HLA-A*0201分子复合体的亲和性.结果 根据与MHC I类分子结合的半衰期评分,选择了3个HLA-A*0201限制性抗原表位.流式细胞仪分析示成熟DC高表达HLA Ⅱ类抗原,CD80,CD86和CD11c.Tetramer试验证实烟曲霉特异性T细胞受体与抗原肽,HLA-A*0201分子复合体的高亲和性.ELISPOT实验结果 表明烟曲霉抗原肽体外可以活化CD8+CTL,被负载了抗原肽的DC刺激活化后可以产生IFN-γ.结论 本研究成功鉴定烟曲霉抗原Asp f16的HLA-A*0201限制性CD8+CTL表位,可作为疫苗设计的候选表位,为进一步研发新型抗烟曲霉疫苗提供参考.     

Cytotoxic-T-lymphocyte human papillomavirus type 16 E5 peptide with CpG-oligodeoxynucleotide can eliminate tumor growth in C57BL/6 mice

Previously, we identified human papillomavirus type 16 (HPV-16) E5 as a tumor rejection antigen that can induce cytotoxic T lymphocytes (CTLs) to protect against tumor growth (D. W. Liu et al., J. Virol. 74:9083-9089, 2000). In the present study, we further mapped the CTL epitope of E5 protein by analyzing E5-specific CD8(+) gamma interferon-positive (IFN-gamma(+)) double-positive cells in C57BL/6 mice with flow cytometry. The results showed the region spanning amino acids 25 to 33 (VCLLIRPLL) contained the potential D(b)-restricted CTL epitope. Subsequently, to determine whether peptide E5 25-33-based vaccination could induce E5-specific CTL activity, syngeneic animals received E5 25-33 emulsified with either CpG oligodeoxynucleotide (CpG ODN 1826) or Freund's adjuvant, and the growth of the tumors was monitored. The results showed that although both adjuvants induced E5-specific CD8(+) IFN-gamma(+) T cells and eradicated E5-containing tumor growth, CpG ODN was found to stimulate stronger CTL response than Freund's adjuvant. We also compared the immune response of the effector/memory/recall phase induced by E5 25-33 peptide or by E5 protein that was synthesized in vivo by adenovirus-based E5 gene delivery. E5 25-33 peptide plus CpG ODN was shown to be a superior vaccine compared to the adenovirus-based E5 gene. Interestingly, their chronological patterns of immune response were similar, suggesting that E5 25-33 is a major CTL peptide of E5 protein.     

A single amino acid substitution in HLA-A2 can alter the selection of the cytotoxic T lymphocyte repertoire that responds to influenza virus matrix peptide 55-73

Previous studies have demonstrated that certain amino acid substitutions in the alpha two domain at positions 152 and 156 in the alpha two helix of the HLA-A2 molecule can affect presentation of the influenza virus matrix peptide M1 55-73 without abolishing binding of the M1 peptide. HLA-A2.1-restricted M1 55-73 peptide-specific CTL lines obtained from almost all HLA-A2.1+ individuals fail to recognize the M1 peptide presented by site-directed mutants of HLA-A2 that have either a Val----Ala or Val----Gln substitution at position 152 or a Leu----Trp substitution at position 156. Only one HLA-A2+ individual (donor Q66, HLA-A2,-B53,-B63) has been found who is able to generate a unique repertoire of HLA-A2-restricted M1 peptide-specific CTL that can recognize peptide presented by HLA-A2 mutants with either an Ala or Gln substitution at position 152 or a Trp substitution at position 156. These Q66 M1 peptide-specific CTL could be selected by stimulation with M1 peptide-pulsed transfectants that express the mutant HLA-A2 gene with the Trp substitution at 156. To determine if the presence of the unique CTL repertoire could be attributed to a variant HLA-A2 molecule in Q66, sequences were determined from polymerase chain reaction-amplified segments of the HLA-A2 RNA. Two different HLA-A2 genes were found expressed in Q66 cells: one is identical to HLA-A2.1 and the other is identical to HLA-A2.2F (Gln----Arg at position 43, Val----Leu at position 95, and Leu----Trp at position 156). These results demonstrate that a different CTL repertoire specific for HLA-A2 plus the M1 55-73 peptide is generated in an individual that expresses both HLA-A2.1 and HLA-A2.2F compared to individuals who express HLA-A2.1 alone, and that the unique repertoire can be selected by the presence of an HLA-A2 molecule with a single amino acid substitution at position 156.     

Creation of an HLA-A2/HLA-Aw69 alloantigenic determinant on an HLA-A3 molecule by site-directed mutagenesis

The HLA-A2 and HLA-Aw69 molecules share an antigenic determinant not expressed by HLA-Aw68 and HLA-A3. Comparison of the amino acid (aa) sequences of these molecules and previous studies of the antigenic determinant expressed by different HLA-A2 X HLA-A3 hybrid molecules had established that three aa at positions 95, 97, and 107 were possibly involved in the formation of this determinant. The HLA-A3 gene was therefore mutagenized to replace successively at these positions the HLA-A3-specific aa by the HLA-A2 residues. A single substitution at position 107 of a glycine by a tryptophan residue is sufficient for full expression by HLA-A3 molecules of the HLA-A2/Aw69 shared antigenic determinant without modification of the other serological reactivities characteristic of the HLA-A3 molecules. Previous studies of ethyl methanesulfonate mutants having shown the involvement of aa 161 in this determinant, we assume that the two aa residues 107 and 161 are close to each other.     

A partially agonistic peptide acts as a selective inducer of apoptosis in CD8+ CTLs.

We have analyzed the effect of partially agonistic peptides on the activation and survival of CTL clones specific for a highly immunogenic HLA A11-restricted peptide epitope derived from the EBV nuclear Ag-4. Several analogues with substitutions of TCR contact residues were able to trigger cytotoxic activity without induction of IL-2 mRNA and protein or T cell proliferation. Triggering with these partial agonists in the absence of exogenous IL-2 resulted in down-regulation of the cytotoxic potential of the specific CTLs. One analogue selectively triggered apoptosis as efficiently as the original epitope, subdividing the partial agonists into apoptosis-inducing and noninducing ligands. Analysis of early T cell activation events, induction of Ca2+ influx, and acid release did not reveal significant differences between the two types of analogue peptides. These results demonstrate that some partial agonists can dissociate the induction of CTL death from CTL activation. Peptides with such properties may serve as useful tools to study signal transduction pathways in CD8+ lymphocytes and as therapeutic agents modulating natural immune responses.     

Subsite preferences of pepstatin-insensitive carboxyl proteinases from prokaryotes: kumamolysin, a thermostable pepstatin-insensitive carboxyl proteinase

Kumamolysin, a carboxyl proteinase from Bacillus novosp. MN-32, is characterized by its thermostability and insensitivity to aspartic proteinase inhibitors such as pepstatin, diazoacetyl-DL-norleucine methylester, and 1,2-epoxy-3-(p-nitro-phenoxy)propane. Here, its substrate specificity was elucidated using two series of synthetic chromogenic substrates: P(5)-P(4)-P(3)-P(2)-Phe*Nph (p-nitrophenylalanine: *cleavage site)-P(2)'-P(3)', in which the amino acid residues at the P(5)-P(2), P(2)' and P(3)' positions were systematically substituted. Among 74 substrates, kumamolysin was shown to hydrolyze Lys-Pro-Ile-Pro-Phe-Nph-Arg-Leu most effectively. The kinetic parameters of this peptide were K(m) = 41+/-5 microM, k(cat) = 176+/- 10 s(-1), and k(cat)/K(m) = 4.3+/-0.6 mM(-1) x s(-1). These systematic analyses revealed the following features: (i) Kumamolysin had a unique preference for the P(2) position. Kumamolysin preferentially hydrolyzed peptides having an Ala or Pro residue at the P(2) position; this was also observed for the pepstatin-insensitive carboxyl proteinase from Bacillus coagulans J-4 [J-4; Shibata et al. (1998) J. Biochem. 124, 642-647]. Other carboxyl proteinases, including Pseudomonas sp. 101 pepstatin-insensitive carboxyl proteinase (PCP) and Xanthomonas sp. T-22 pepstatin-insensitive carboxyl proteinase (XCP), preferred peptides having hydrophobic and bulky amino acid residue such as Leu at the P(2) position. (ii) Kumamolysin preferred such charged amino acid residues as Glu or Arg at the P(2)' position, suggesting that the S(2)' subsite of kumamolysin is occupied by hydrophilic residues, similar to that of PCP, XCP, and J-4. In general, the S(2)' subsite of pepstatin-sensitive carboxyl proteinases (aspartic proteinases) is hydrophobic in nature. Thus, the hydrophilic nature of the S(2)' subsite was confirmed to be a distinguishing feature of pepstatin-insensitive carboxyl proteinases from prokaryotes.     

HLA-A*0201 T-cell epitopes in severe acute respiratory syndrome (SARS) coronavirus nucleocapsid and spike proteins

The immunogenicity of HLA-A*0201-restricted cytotoxic T lymphocyte (CTL) peptide in severe acute respiratory syndrome coronavirus (SARS-CoV) nuclear capsid (N) and spike (S) proteins was determined by testing the proteins' ability to elicit a specific cellular immune response after immunization of HLA-A2.1 transgenic mice and in vitro vaccination of HLA-A2.1 positive human peripheral blood mononuclearcytes (PBMCs). First, we screened SARS N and S amino acid sequences for allele-specific motif matching those in human HLA-A2.1 MHC-I molecules. From HLA peptide binding predictions (http://thr.cit.nih.gov/molbio/hla_bind/), ten each potential N- and S-specific HLA-A2.1-binding peptides were synthesized. The high affinity HLA-A2.1 peptides were validated by T2-cell stabilization assays, with immunogenicity assays revealing peptides N223-231, N227-235, and N317-325 to be the first identified HLA-A*0201-restricted CTL epitopes of SARS-CoV N protein. In addition, previous reports identified three HLA-A*0201-restricted CTL epitopes of S protein (S978-986, S1203-1211, and S1167-1175), here we found two novel peptides S787-795 and S1042-1050 as S-specific CTL epitopes. Moreover, our identified N317-325 and S1042-1050 CTL epitopes could induce recall responses when IFN-gamma stimulation of blood CD8+ T-cells revealed significant difference between normal healthy donors and SARS-recovered patients after those PBMCs were in vitro vaccinated with their cognate antigen. Our results would provide a new insight into the development of therapeutic vaccine in SARS.     

Identification of residues necessary for clonally specific recognition of a cytotoxic T cell determinant.

The residues in an influenza nucleoprotein (NP) cytotoxic T cell determinant necessary for cytotoxic T cell (CTL) recognition, were identified by assaying the ability of hybrid peptides to sensitize a target cell to lysis. The hybrid peptides were formed by substituting amino acids from one determinant (influenza NP 147-158) for the corresponding residues of a second peptide (HLA CW3 171-182) capable of binding to a common class I protein (H-2Kd). Six amino acids resulted in partial recognition; however, the presence of a seventh improved the potency of the peptide. Five of the six amino acids were shown to be required for recognition. The spacing of the six amino acids was consistent with the peptide adopting a helical conformation when bound. The importance of each amino acid in CTL recognition and binding to the restriction element was investigated further by assaying the ability of peptides containing point substitutions either to sensitize target cells or to compete with the natural NP sequence for recognition by CTL. The T cell response was much more sensitive to substitution than the ability of the peptide to bind the restriction element. Collectively the separate strategies identified an approximate conformation and orientation of the peptide when part of the complex and permitted a potential location in the MHC binding site to be identified. The model provides a rationalization for analogues which have previously been shown to exhibit greater affinity for the class I molecule and suggests that the binding site in major histocompatibility complex (MHC) class I molecules might have greater steric constraints that the corresponding area of class II proteins.     

Molecular analysis of the serologically defined HLA-Aw19 antigens. A genetically distinct family of HLA-A antigens comprising A29, A31, A32, and Aw33, but probably not A30

The HLA-Aw19 complex consists of a number of serologically cross-reactive Ag (i.e., A29, A30, A31, A32, and Aw33) which exhibit an epitope shared by HLA-B and -C proteins. To investigate the structural basis for these serologic cross-reactivities, we have cloned and determined the nucleotide sequences for A30, A31, and Aw33, and compared the predicted amino acid sequences with those already available for A29, A32, and other class I allelic products. All alleles of the Aw19 group contained A-locus-specific sequences, exhibiting "A-ness." The structural similarities between Aw19 polypeptides were found in the alpha 1 and alpha 2 domains, where shared amino acid residues were identified that correlated with observed serological reactivity patterns. Seven Aw19-specific nucleotides were found. Two of these were silent substitutions, but the remaining five resulted in Aw19-specific amino acid residues. Each of the HLA-A alleles can be classified into one of the five serologically cross-reacting groups. In the Aw19 group, the alleles A29, A31, A32, and Aw33 are closely related serologically as well as genetically whereas A30 probably belongs to the A1/A3/A11 group. The similarity between A30 and the other Aw19 alleles may have resulted from two independent gene conversions affecting exons 2 and 3. Additional mutations or gene conversion-like events in A30 were also noted. It is postulated that gene conversions have played a significant role in the divergence of the Aw19 alleles. However, each serologically cross-reactive Aw19 allotype appears to have arisen directly from a common ancestral allele. A30 was the only exception, and this allele may represent an unusual allotype, which is subject to a high rate of genetic changes, as is seen in the H-2Kb gene of the mouse.     

The covalent structure of collagen. The amino-acid sequence of alpha2-CB4 from calf-skin collagen.

Sequencing of chymotrypsin, trypsin, collagenase- and hydroxylamine-derived peptides, using the automated Edman degradation procedure, yielded the complete amino acid sequence of alpha2-CB4 from calf skin collagen (321 residues). Together with the data from earlier work, an uninterrupted sequence in the helical region of the alpha2-chain from residues 1-393 is now known. Glycine is found in every third position of the peptide. Hydroxylation of proline and lysine occurs only in the Y-position of the triplet Gly-X-Y and is not complete in every position. Some residues, such as glutamic acid, leucine, phenylalanine and arginine, are distributed non-randomly between the X and Y-positions and this non-random distribution is different in the alpha1 and alpha2-chains. Comparison of the N-terminal 393 residues from the helical region of the alpha1 and alpha2-chains revealed a nearly identical distribution of charged polar residues arginine, lysine, glutamic and aspartic acids. The distribution of the triplet Gly-Pro-Hyp is simialr in both chains. The remaining residues in the alpha2-chain exhibit a high degree of substitutions when compared with those in the alpha1-chain. Approximately one in every two residues in both the X and Y-positions are substituted.     

Mutations inside but not outside the peptide binding cleft of the H-2 Ld molecule affects CTL recognition and binding of the nucleoprotein peptide from the lymphocytic chroriomeningitis

In order to investigate the role of residues inside and outside the peptide binding cleft of the L² molecule in peptide presentation to cytotoxic T lymphocytes (CTL), we constructed a series of point mutations in the L ^d gene. We determined the effects of the mutations in the L^d molecule on the binding and recognition of an L^d-restricted CTL epitope derived from the nucleoprotein (NP) of the lymphocytic phoriomeningitis virus (LCMV). Each of the mutations within the L^d peptide binding cleft resulted in a complete loss of CTL recognition. Addition of the LCMV NP peptide to cells expressing these mutants did not increase surface L^d expression, suggesting that the mutations altered peptide binding. Mutations involving pockets D and E within the cleft affected LCMV peptide binding and recognition as drastically as those in pocket B, which was predicted to interact with a main anchor residue of the peptide. In striking contrast, the mutations located outside the cleft did not change either recognition or binding. These results demonstrate that the L^d residues in the peptide binding cleft are the main determinants dictating LCMV NP peptide binding, and that the residues in each of the pockets within the cleft play a role in this interaction. Surprisingly, one mutation outside the peptide binding cleft, T92S, abrogated CTL lysis of target cells treated with the LCMV NP peptide, but not virus-infected cells. These data show that this mutation selectively altered the presentation of the LCMV NP peptide introduced to the cell exogenously, but not endogenously. This implies that the pathway by which peptides associate with class I molecules within the cell differs from that of exogenous peptide binding.     

Human kallikrein 4 signal peptide induces cytotoxic T cell responses in healthy donors and prostate cancer patients

Immunotherapy is a promising new treatment for patients with advanced prostate and ovarian cancer, but its application is limited by the lack of suitable target antigens that are recognized by CD8⁺ cytotoxic T lymphocytes (CTL). Human kallikrein 4 (KLK4) is a member of the kallikrein family of serine proteases that is significantly overexpressed in malignant versus healthy prostate and ovarian tissue, making it an attractive target for immunotherapy. We identified a naturally processed, HLA-A*0201-restricted peptide epitope within the signal sequence region of KLK4 that induced CTL responses in vitro in most healthy donors and prostate cancer patients tested. These CTL lysed HLA-A*0201⁺ KLK4 ⁺ cell lines and KLK4 mRNA-transfected monocyte-derived dendritic cells. CTL specific for the HLA-A*0201-restricted KLK4 peptide were more readily expanded to a higher frequency in vitro compared to the known HLA-A*0201-restricted epitopes from prostate cancer antigens; prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA) and prostatic acid phosphatase (PAP). These data demonstrate that KLK4 is an immunogenic molecule capable of inducing CTL responses and identify it as an attractive target for prostate and ovarian cancer immunotherapy.