Molecular determinants of peptide binding to two common rhesus macaque major histocompatibility complex class II molecules

Major histocompatibility complex class II molecules encoded by two common rhesus macaque alleles Mamu-DRB1*0406 and Mamu-DRB*w201 have been purified, and quantitative binding assays have been established. The structural requirements for peptide binding to each molecule were characterized by testing panels of single-substitution analogs of the two previously defined epitopes HIV Env242 (Mamu-DRB1*0406 restricted) and HIV Env482 (Mamu-DRB*w201 restricted). Anchor positions of both macaque DR molecules were spaced following a position 1 (P1), P4, P6, P7, and P9 pattern. The specific binding motif associated with each molecule was distinct, but largely overlapping, and was based on crucial roles of aromatic and/or hydrophobic residues at P1, P6, and P9. Based on these results, a tentative Mamu class II DR supermotif was defined. This pattern is remarkably similar to a previously defined human HLA-DR supermotif. Similarities in binding motifs between human HLA and macaque Mamu-DR molecules were further illustrated by testing a panel of more than 60 different single-substitution analogs of the HLA-DR-restricted HA 307-319 epitope for binding to Mamu-DRB*w201 and HLA-DRB1*0101. The Mamu-DRB1*0406 and -DRB*w201 binding capacity of a set of 311 overlapping peptides spanning the entire simian immunodeficiency virus (SIV) genome was also evaluated. Ten peptides capable of binding both molecules were identified, together with 19 DRB1*0406 and 43 DRB*w201 selective binders. The Mamu-DR supermotif was found to be present in about 75% of the good binders and in 50% of peptides binding with intermediate affinity but only in approximately 25% of the peptides which did not bind either Mamu class II molecule. Finally, using flow cytometric detection of antigen-induced intracellular gamma interferon, we identify a new CD4(+) T-lymphocyte epitope encoded within the Rev protein of SIV.

Dendritic cells generated in vivo by a chimeric hematopoietic growth factor, progenipoietin-4, demonstrate potent immunological function

Recently, a dual receptor agonist for human Flt3 and G-CSF receptors, progenipoietin-4 (ProGP-4), was shown to be highly effective in expanding DC in vivo. In this study, we examined the immunological activity of ProGP-4-generated dendritic cell (DC) in an HLA-A2.1 transgenic mouse system. ProGP-4 DC were found to be approximately equivalent in presenting a cytotoxic T lymphocyte (CTL) peptide to a CTL line in vitro compared with bone marrow (BM)-derived DC and >20-fold more efficient than macrophages or B cells, and >100-fold better than BM-DC, macrophages, or B cells at presenting PADRE, a universal helper T cell epitope, to a T cell clone. The heightened epitope presentation by ProGP-4 DC was paralleled in vivo inasmuch as a >6-fold increase in CTL induction was observed compared with other APC populations following ex vivo loading with peptide. The in vitro and in vivo CTL responses stimulated by ProGP-4 DC could be further augmented by either culturing with tumor necrosis factor-alpha (TNF-alpha) or co-loading with PADRE. Collectively, our results indicate that peptide-loaded ProGP-4-generated DC demonstrate potent antigenicity and immunogenicity for CTL, making them an attractive component of epitope-based vaccines.

Overcoming T cell tolerance to the hepatitis B virus surface antigen in hepatitis B virus-transgenic mice

The sequence of the hepatitis B virus (HBV) major envelope (Env) protein (ayw subtype) was scanned for the presence of H-2(d,b) motifs. Following binding and immunogenicity testing, two new H-2(d)-restricted epitopes (Env.362 and Env.364) were identified. These epitopes induced CTLs capable of recognizing naturally processed HBV-Env, but were apparently generated with lower efficiency than the previously defined dominant Env.28 epitope. Next, HBV-transgenic mice that express all of the HBV proteins and produce fully infectious particles were immunized with a mixture of lipopeptides encompassing the Env.28, Env.362, and Env.364 epitopes. Significant CTL responses were obtained, but they had no effect on viral replication in the liver, nor did they induce an inflammatory liver disease. However, in adoptive transfer experiments, CTL lines generated from the HBV-transgenic mice following immunization were able to inhibit viral replication in vivo without causing hepatitis. This is in contrast to CTL lines derived from nontransgenic mice that displayed both antiviral and cytopathic effects, presumably because they displayed higher avidity for the viral epitopes than the transgenic CTLs. These results suggest that T cell tolerance to HBV can be broken with appropriate immunization but the magnitude and characteristics of the resultant T cell response are significantly different from the response in HBV-naive individuals since their antiviral potential is stronger than their cytotoxic potential. This has obvious implications for immunotherapy of chronic HBV infection.

Human memory CTL response specific for influenza A virus is broad and multispecific

Class I restricted cytotoxic T-lymphocyte (CTL) responses are thought to be focused against few immunodominant epitopes. In humans, an often quoted example of such narrow focus is the influenza A (FLU) matrix 58-66 specific memory CTL activity, detectable in HLA-A2 individuals as a result of natural infection. Herein, we analyzed the repertoire of memory, FLU-specific CTLs in A2 and A11 positive individuals. Eighteen A2.1 binding peptides, derived from the FLU-Puerto Rico/8/34 (PR8) isolate, elicited CTL activity in A2. 1/Kb transgenic mice upon direct immunization. These peptides were also tested for their capacity to recall memory CTL responses from peripheral blood mononuclear cells (PBMC) of human A2.1 donors. Besides the known dominant M1.58 peptide, 5 new epitopes (PA.46, PA. 225, PB1.413, NA.75 and M1.59) were identified. Similarly, eleven, A11-binding, FLU-PR8 peptides, which were immunogenic in HLA-A11/Kb transgenic mice, were assayed for induction of recall CTL responses using peripheral blood lymphocytes from a cohort of A11-positive donors. Eight different peptides (NP.188, NP.342, HA.63(,) HA.149, HA.450, M1.13, M1.178, and M2.70) induced memory CTL activity. Several of these peptides were found to be highly conserved amongst different FLU isolates, and also capable of binding multiple A2 and A11 supertype molecules. Finally, 37 HLA-B7 binding peptides were also identified. In conclusion, a previously unappreciated breadth of FLU-specific, memory CTL responses in humans was revealed. The relevance of these findings to the design of multiepitope vaccines is discussed.

Linear PADRE T helper epitope and carbohydrate B cell epitope conjugates induce specific high titer IgG antibody responses

Linear carbohydrate-peptide constructs based on the 13 amino acid nonnatural pan DR epitope (PADRE) and carbohydrate B cell epitopes are demonstrated to be potent immunogens. These data support our belief that PADRE should be considered as an alternative to more complex carriers for use in prophylaxis and therapeutic vaccines. Two model carbohydrate-PADRE glycoconjugates were used to demonstrate that PADRE could effectively provide T cell help for carbohydrate-specific Ab responses. Conjugates of PADRE covalently linked to the human milk oligosaccharide, lacto-N-fucopentose II or a dodecasaccharide derived from Salmonella typhimurium O-Ag induced high titer IgG Ab responses in mice, which were comparable to glycoconjugates employing human serum albumin (HSA) as the carrier protein. Different adjuvants, in combination with PADRE conjugates, allowed for the modulation of the isotype profile with alum supporting an IgG1 profile; QS-21 an IgG2a, 2b profile, while an alum/QS-21 mixture generated a balanced IgG1/IgG2b isotype profile. As defined by binding to synthetic glycoconjugates, dodecasaccharide-specific Abs exhibited fine specificity similar to protective polyclonal Ab responses previously reported for dodecasaccharide-protein conjugates. The same Abs bound to intact S. typhimurium cells, suggesting that biologically relevant specificities were produced. The affinity of the dodecasaccharide-specific Abs was further shown to be comparable to that of a well-characterized, high affinity monoclonal anti-carbohydrate Ab recognizing the same epitope.

Conserved MHC class I peptide binding motif between humans and rhesus macaques

Since the onset of the HIV pandemic, the use of nonhuman primate models of infection has increasingly become important. An excellent model to study HIV infection and immunological responses, in particular cell-mediated immune responses, is SIV infection of rhesus macaques. CTL epitopes have been mapped using SIV-infected rhesus macaques, but, to date, a peptide binding motif has been described for only one rhesus class I MHC molecule, Mamu-A*01. Herein, we have established peptide-live cell binding assays for four rhesus MHC class I molecules: Mamu-A*11, -B*03, -B*04, and -B*17. Using such assays, peptide binding motifs have been established for all four of these rhesus MHC class I molecules. With respect to the nature and spacing of crucial anchor positions, the motifs defined for Mamu-B*04 and -B*17 present unique features not previously observed for other primate species. The motifs identified for Mamu-A*11 and -B*03 are very similar to the peptide binding motifs previously described for human HLA-B*44 and -B*27, respectively. Accordingly, naturally processed peptides derived from HLA-B*44 and HLA-B*27 specifically bind Mamu-A*11 and Mamu-B*03, respectively, indicating that conserved MHC class I binding capabilities exist between rhesus macaques and humans. The definition of four rhesus MHC class I-specific motifs expands our ability to accurately detect and quantitate immune responses to MHC class I-restricted epitopes in rhesus macaques and to rationally design peptide epitope-based model vaccine constructs destined for use in nonhuman primates.

Immunization with the HBV core 18-27 epitope elicits CTL responses in humans expressing different HLA-A2 supertype molecules

The human leukocyte antigen (HLA)-A2 restricted HBV core 18-27 epitope is immunodominant in the context of HLA-A2.1 and subdominant in the context of the other HLA-A2 supertype molecules, as defined by frequency of recognition by memory cytotoxic T lymphocyte (CTL) responses from acute hepatitis B virus (HBV) patients, and on the basis of its binding affinity to purified HLA molecules in vitro. Herein, we show that immunization with a lipopeptide containing HBV core 18-27 epitope induces CTL responses in patients expressing different HLA-A2 supertype molecules, with indistinguishable frequency and magnitude. No difference in responses was noted between patients expressing either one or two different HLA-A2 supertype molecules. Thus, complexes of HBV core 18-27 bound to different HLA-A2 supertype alleles do not appear to act as altered peptide ligands, and do not cross antagonize CTL responses. These results substantiate the immunological relevance of the HLA supertypes concept, and illustrate its potential usefulness for the development of vaccines.

Utilization of MHC class I transgenic mice for development of minigene DNA vaccines encoding multiple HLA-restricted CTL epitopes

We engineered a multiepitope DNA minigene encoding nine dominant HLA-A2.1- and A11-restricted epitopes from the polymerase, envelope, and core proteins of hepatitis B virus and HIV, together with the PADRE (pan-DR epitope) universal Th cell epitope and an endoplasmic reticulum-translocating signal sequence. Immunization of HLA transgenic mice with this construct resulted in: 1) simultaneous CTL induction against all nine CTL epitopes despite their varying MHC binding affinities; 2) CTL responses that were equivalent in magnitude to those induced against a lipopeptide known be immunogenic in humans; 3) induction of memory CTLs up to 4 mo after a single DNA injection; 4) higher epitope-specific CTL responses than immunization with DNA encoding whole protein; and 5) a correlation between the immunogenicity of DNA-encoded epitopes in vivo and the in vitro responses of specific CTL lines against minigene DNA-transfected target cells. Examination of potential variables in minigene construct design revealed that removal of the PADRE Th cell epitope or the signal sequence, and changing the position of selected epitopes, affected the magnitude and frequency of CTL responses. Our results demonstrate the simultaneous induction of broad CTL responses in vivo against multiple dominant HLA-restricted epitopes using a minigene DNA vaccine and underline the utility of HLA transgenic mice in development and optimization of vaccine constructs for human use.

Altered helper T lymphocyte function associated with chronic hepatitis B virus infection and its role in response to therapeutic vaccination in humans

Theradigm-hepatitis B virus (HBV) is an experimental lipopeptide vaccine designed to stimulate induction of HBV-specific CTL responses in HLA-A2 individuals. Previous studies had demonstrated high immunogenicity in healthy volunteers, but comparatively weak CTL responses in chronically infected HBV patients. Herein, we examined helper T lymphocyte (HTL) responses in chronically infected patients. Despite normal proliferation and IL-2 secretion, IL-12 and IFN-gamma secretion in vitro in response to the vaccine was reduced compared with healthy volunteers. A similar pattern of cytokine secretion was observed following mitogen stimulation, suggesting a general altered balance of Th1/Th2 responses. Further analysis indicated that HTL recall responses to whole tetanus toxoid protein were reduced in chronically infected subjects, and reduced responsiveness correlated with the outcome of Theradigm-HBV immunization. Finally, experiments in HBV transgenic mice indicated that the nonnatural Pan DR HTL epitope, PADRE, is capable of inducing high levels of IFN-gamma secretion and that its inclusion in a lipopeptide incorporating an immunodominant Ld-restricted CTL epitope resulted in breaking tolerance at the CTL level. Overall, our results demonstrate an alteration in the quality of HTL responses induced in chronically infected HBV patients and suggest that use of a potent HTL epitope may be important to overcome CTL tolerance against specific HBV Ags.

Lipopeptide particles as the immunologically active component of CTL inducing vaccines

Using a bipalmitoylated lipopeptide consisting of an ovalbumin helper T-cell epitope covalently linked to an influenza virus cytotoxic T-lymphocyte (CTL) epitope, we addressed possible factors that may be critical for CTL induction. Antigen processing of lipopeptide appears to be required for T-cell induction since there was virtually no in vitro binding of lipopeptide to purified MHC molecules. A major portion of lipopeptide immunogenicity was due to its particulate nature inasmuch as CTL induction in mice correlated with insoluble lipopeptide constructs, whereas more soluble analogs were significantly less immunogenic. Immunohistological analysis of tissue from immunized animals revealed that lipopeptide migration from the s.c. injection site to the spleen could be detected as early as 1 h after immunization and cell-associated lipopeptide was observed on macrophages and dendritic cells, implicating both cell populations in the processing and presentation of lipopeptide particles to CTLs.

The optimization of helper T lymphocyte (HTL) function in vaccine development

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Recognition of a novel naturally processed, A2 restricted, HCV-NS4 epitope triggers IFN-gamma release in absence of detectable cytopathicity

Using short term CTL lines derived from HLA A2/Kb transgenic mice and IFN-gamma release assays we demonstrate that the NS4.1769 epitope, is generated from natural processing of the NS4 antigen, and presented in the context of the A2/Kb molecules. Interestingly, T cell recognition of the naturally processed form of the NS4. 1769 epitope was associated with significant IFN-gamma release, but no direct cytolytic activity. Epitopes of this phenotype might be of interest, in terms of therapy of chronic HCV infection by associating the benefit of localized lymphokine release with low or absent direct cytopathicity.

Pools of lipidated HTL-CTL constructs prime for multiple HBV and HCV CTL epitope responses

Various peptide-based approaches to simultaneous induction of multiple cytotoxic T lymphocyte (CTL) responses were evaluated as part of ongoing efforts to develop immunotherapeutic vaccines for use in humans. To this end, HLA (human histocompatibility leukocyte antigen)-A2-restricted epitopes from several specific viral proteins were tested in an HLA-A2 transgenic mouse model system, which mimics human CTL responses to these viral proteins. Multiple CTL responses were elicited by immunization with either peptides emulsified in incomplete Freund's adjuvant (IFA), or lipidated peptides administered in phosphate buffered saline (PBS). In the case of lipidated peptides, induction of CTL responses was crucially dependent on the presence of helper T lymphocyte (HTL) epitopes, and most efficient in the case of lipidated covalently linked HTL-CTL epitope constructs. CTL could also be induced by immunization with lipidated HTL epitopes simply mixed with CTL epitopes and formulated in PBS. However, this approach was highly dependent on the particular lipidated HTL/CTL combination utilized, and was marginally effective for simultaneous priming of multiple CTL responses. By contrast, all HTL/CTL combinations were potent immunogens when delivered as lipidated, covalently linked molecules. This was the most effective of the approaches analysed in terms of multi-epitope priming, as demonstrated by the induction of simultaneous CTL responses to a pool of five different epitopes.

Several common HLA-DR types share largely overlapping peptide binding repertoires

The peptide binding specificities of HLA-DRB1*0401, DRB1*0101, and DRB1*0701 have been analyzed by the use of large collections of synthetic peptides corresponding to naturally occurring sequences. The results demonstrated that nearly all peptides binding to these DR molecules bear a motif characterized by a large aromatic or hydrophobic residue in position 1 (Y, F, W, L, I, V, M) and a small, noncharged residue in position 6 (S, T, C, A, P, V, I, L, M). In addition, allele-specific secondary effects and secondary anchors were defined, and these parameters were utilized to derive allele-specific motifs and algorithms. By the combined use of such algorithms, peptides capable of degenerate DRB1*0101, DRB1*0401, and DRB1*0701 binding were identified. Additional experiments utilizing a panel of quantitative assays specific for nine additional common DR molecules identified a large set of DR molecules, which includes at least the DRB1*0101, DRB1*0401, DRB1*0701, DRB5*0101, DRB1*1501, DRB1*0901, and DRB1*1302 allelic products, characterized by overlapping peptide-binding repertoires. These results have implications for understanding the molecular interactions involved in peptide-DR binding, as well as the genetic and structural basis of MHC polymorphism. These results also have potential practical implications for the development of epitope-based prophylactic and therapeutic vaccines.

Identification of Db- and Kb-restricted subdominant cytotoxic T-cell responses in lymphocytic choriomeningitis virus-infected mice

Antiviral cytotoxic T-cells are critical for control of lymphocytic choriomeningitis virus (LCMV) infection in mice. In H-2b mice, the antiviral response is directed against three Db-restricted epitopes in the viral nucleoprotein (NP396-404) and glycoprotein (GP276-286 and GP33-41). Our present data revealed a clear hierarchy among these three epitopes, in which NP396-404 is immunodominant, followed by GP33-41 and GP276-286, respectively. In order to identify additional CTL epitopes in the LCMV nucleoprotein and glycoprotein, we used the motifs for Db2- and Kb-binding peptides, combined with MHC class I-binding assays. Out of 23 Db motif-fitting peptides, we identified 4 Db binders, one of which (GP92-101) turned out to be a new CTL epitope. Among 28 Kb motif-fitting peptides, 12 bound Kb, and one of these (NP205-212) was a CTL epitope. Both newly identified CTL peptides were recognized by LCMV-immune splenocytes after secondary in vitro stimulation. Both peptides bound their MHC class I molecules with intermediate affinity (470 and 170 nM for GP92-101 and NP205-212, respectively). Responses against these peptides were weaker than the responses against the three major epitopes. None of the high affinity binders were new epitopes, suggesting that high affinity binders are either immunodominant epitopes or no epitopes at all. Thus, analysis of 51 Kb and Db motif-fitting peptides yielded 2 new, subdominant epitopes. Immunization of C57BL/6 mice with these peptides, or vaccinia virus recombinants expressing these epitopes as minigenes, protected against chronic LCMV infection, demonstrating that immunization with subdominant epitopes can confer protection against chronic viral infection.

The hepatitis B virus-specific CTL responses induced in humans by lipopeptide vaccination are comparable to those elicited by acute viral infection

We have previously described the development of a lipopeptide-based vaccine, Theradigm-HBV, capable of inducing CTL responses in humans. This vaccine incorporates the HLA-A2.1-restricted CTL epitope hepatitis B core Ag 18-27, linked to the universal helper T lymphocyte (HTL) epitope tetanus toxoid (TT) 830-843. Herein, we report the results of a phase I trial designed to examine the effects of Theradigm-HBV dose and regimen on the magnitude and duration of the memory CTL response. A total of four injections of up to 5 mg/dose were found to be a safe and effective means of generating substantial memory CTL responses. Precursor frequency analysis demonstrated CTL responses of similar magnitude to those previously observed in patients who successfully cleared hepatitis B virus infection and to influenza-specific memory CTL responses induced by natural exposure to influenza virus. Theradigm-HBV induced CTL responses that persisted for more than 9 months after the last injection. HTL responses were associated with significant CTL responses, and sustained HTL activity was necessary for development of persistent memory CTL activity. These results represent the first demonstration of the importance of HTL activity for development of long-lived memory CTL responses in humans. In conclusion, our results show that lipopeptides safely induce specific CTL activity in humans of such magnitude and persistence as to be of potential therapeutic significance.

The hepatitis B virus-specific CTL responses induced in humans by lipopeptide vaccination are comparable to those elicited by acute viral infection

We have previously described the development of a lipopeptide-based vaccine, Theradigm-HBV, capable of inducing CTL responses in humans. This vaccine incorporates the HLA-A2.1-restricted CTL epitope hepatitis B core Ag 18-27, linked to the universal helper T lymphocyte (HTL) epitope tetanus toxoid (TT) 830-843. Herein, we report the results of a phase I trial designed to examine the effects of Theradigm-HBV dose and regimen on the magnitude and duration of the memory CTL response. A total of four injections of up to 5 mg/dose were found to be a safe and effective means of generating substantial memory CTL responses. Precursor frequency analysis demonstrated CTL responses of similar magnitude to those previously observed in patients who successfully cleared hepatitis B virus infection and to influenza-specific memory CTL responses induced by natural exposure to influenza virus. Theradigm-HBV induced CTL responses that persisted for more than 9 months after the last injection. HTL responses were associated with significant CTL responses, and sustained HTL activity was necessary for development of persistent memory CTL activity. These results represent the first demonstration of the importance of HTL activity for development of long-lived memory CTL responses in humans. In conclusion, our results show that lipopeptides safely induce specific CTL activity in humans of such magnitude and persistence as to be of potential therapeutic significance.

Human histocompatibility leukocyte antigen-binding supermotifs predict broadly cross-reactive cytotoxic T lymphocyte responses in patients with acute hepatitis

The present study was designed to determine if highly conserved hepatitis B virus (HBV)-derived peptides that bind multiple HLA class I alleles with high affinity are recognized as cytotoxic T lymphocyte (CTL) epitopes in acutely infected patients. Peripheral blood mononuclear cells from 67 patients with acute hepatitis B, and 12 patients convalescent from acute hepatitis B, were stimulated with three panels of peptides, each of which bind with high affinity to several class I alleles from the HLA-A2-, HLA-A3-, or HLA-B7-supertypes. In these patients, 8 of the 19 peptides tested were found to represent CTL epitopes recognized by two or more alleles in each supertype. Two sets of nested peptides were recognized in the context of alleles with completely unrelated peptide binding specificities. Finally, promiscuous recognition by the same CTL of a given peptide presented by target cells expressing different A2 subtypes was also commonly observed. In conclusion, several HBV-specific CTL epitopes, recognized by acutely infected or convalescent patients in the context of a wide range of HLA alleles have been identified. These results demonstrate the functional relevance of the supertype grouping of HLA class I molecules in a human viral disease setting. Furthermore, they represent a significant advance in the development of a totally synthetic vaccine to terminate chronic HBV infection and support the feasibility of a systematic approach to development of similar vaccines for prevention and treatment of other chronic viral infections.

Degenerate cytotoxic T cell epitopes from P. falciparum restricted by multiple HLA-A and HLA-B supertype alleles

We recently described human leukocyte antigen (HLA) A2, A3 and B7 supertypes, characterized by largely overlapping peptide-binding specificities and represented in a high percentage of different populations. Here, we identified 17 Plasmodium falciparum peptides capable of binding these supertypes and assessed antigenicity in both vaccinated and naturally exposed populations. Positive cytotoxic T lymphocyte recall and cytokine (interferon-gamma and tumor necrosis factor alpha) responses were detected for all peptides; all were recognized in the context of more than one HLA class I molecule; and at least 12 of the 17 were recognized in the context of all HLA alleles studied. These data validate the concept of HLA supertypes at the biological level, show that highly degenerate peptides are almost always recognized as epitopes, and demonstrate the feasibility of developing a universally effective vaccine by focusing on a limited number of peptide specificities.

Uncovering subdominant cytotoxic T-lymphocyte responses in lymphocytic choriomeningitis virus-infected BALB/c mice

The cytotoxic T-lymphocyte response against lymphocytic choriomeningitis virus (LCMV) in BALB/c mice is predominantly directed against a single, Ld-restricted epitope in the viral nucleoprotein (residues 118 to 126). To investigate whether any Kd/Dd-restricted responses were activated but did not expand during the primary response, we used a BALB/c mutant, BALB/c-H-2dm2, which does not express the Ld molecule. Splenocytes from LCMV-infected BALB/c mice were transferred into irradiated BALB/c-H-2dm2 mice and rechallenged with LCMV. Thus, they were exposed to an antigenic stimulus without the involvement of the immunodominant Ld-restricted epitope. In this adoptive transfer model, the donor splenocytes protected the recipient mice against chronic LCMV infection by mounting a potent Kd- and/or Dd-restricted secondary antiviral response. Analysis of a panel of Kd binding LCMV peptides revealed that residues 283 to 291 from the viral glycoprotein (GP(283-291)) comprise a major new epitope in the adoptive transfer model. Because the donor splenocytes were first activated during the primary infection in BALB/c mice, the GP(283-291) epitope is a subdominant epitope in BALB/c mice that becomes dominant after rechallenge in BALB/c-H-2dm2 mice. This study makes two points. First, it shows that subdominant CTL responses can be protective, and second, it provides a general experimental approach for uncovering subdominant CTL responses in vivo. This strategy can be used to identify subdominant T-cell responses in other systems.

Comparison of cytotoxic T lymphocyte responses induced by peptide or DNA immunization: implications on immunogenicity and immunodominance

To study the mechanisms that influence the immunogenicity and immunodominance of potential cytotoxic T lymphocyte (CTL) epitopes, we conducted a systematic analysis of the CTL response raised in HLA-A*0201/Kb (A2/Kb) transgenic mice against the viral antigen, hepatitis B virus polymerase (HBV pol). From a pool of 26 nonamer peptides containing the HLA-A*0201-binding motif, we selected A2-binding peptides, immunized A2/Kb animals, and tested the CTL raised against the peptide for recognition of HBV pol transfectants. Of nine immunogenic CTL epitopes, only four were recognized on HBV pol transfectants, whereas the other five were cryptic. Characterization of the peptide-specific CTL lines indicated that crypticity may result from either poor processing or low T cell receptor (TCR) avidity. To identify the immunodominant epitopes, we determined the CTL specificities induced in A2/Kb animals in response to priming with HBV pol cDNA. We obtained a response against three epitopes that were contained with the set of four epitopes recognized by peptide-specific CTL on HBV pol transfectants. Comparative analysis of cDNA priming and peptide priming revealed, therefore, the presence of a subdominant epitope. We conclude that for the HBV pol antigen, the repertoire of CTL specificities is shaped by major histocompatibility complex class I peptide binding capacity, antigen processing, and TCR availability.

Two distinct HLA-A*0101-specific submotifs illustrate alternative peptide binding modes

Previous studies have defined two different peptide binding motifs specific for HLA-A*0101. These motifs are characterized by the presence of tyrosine (Y) at the C-termini of 9-mer and 10-mer peptides, and either a small polar or hydrophobic (S, T, M) residue in position 2, or a negatively charged (D or E) residue in position 3. In this study, the structural requirements for peptide binding to A*0101 have been further analyzed by examining the binding capacity of large sets of peptides corresponding to naturally occurring sequences which bore one or the other of these two A*0101-specific motifs. By correlating the presence of specific residue types at each position along the peptide sequence with increased (or decreased) binding affinity, the prominent influence of secondary anchor residues was revealed. In most cases, the two anchors in positions 2 and 3 appear to act synergistically. With the exception of the DE3 submotif in 9-mer peptides, a positive role for aromatic residues in position 1 and the center of the peptide (positions 4 or 5 of 9- or 10-mer peptides, respectively), and proline at C-3, were also consistently detected. However, secondary anchor residues also appear to differ significantly between the two different submotifs, demonstrating that A*0101 can utilize alternative modes in binding its peptide ligands. According to these analyses, specific refined submotifs were also established, and their merit verified by independent sets of potential A*0101 binding peptides. Besides providing useful insight into the nature of the interaction of the A*0101 allele with its peptide ligands, such refined motifs should also facilitate accurate prediction of potential A*0101-restricted peptide epitopes.

Immunodominance analysis of CTL responses to influenza PR8 virus reveals two new dominant and subdominant Kb-restricted epitopes

In the present study, a systematic analysis of the influenza (Flu) PR8 determinants recognized by H-2b mice was undertaken. A single Db-restricted immunodominant epitope (NP(366)) was previously known in this system. Twenty-three different Flu PR8-derived peptides that bound either Kb or Db molecules in vitro were identified. Sixteen were immunogenic following peptide immunization of C57BL/6 mice, yet CTL induced by peptide immunization recognized PR8-infected target cells only in the case of the NP(366) and NS2(114) epitopes. Similarly, CTL responses following whole-PR8 virus immunization were detected only for the same two determinants. CTL recognizing these dominant epitopes had high avidity for peptide-pulsed target cells, with 5 to 200 pM of peptide required for 30% specific lysis. In contrast, most (80%) of the remaining epitopes were recognized with lower avidity (30% effective concentration in the range of 0.4-50 nM). Repeated in vitro stimulation of primary CTL cultures revealed one additional Kb-restricted epitope (M1(128)). This peptide bound Kb with high affinity (4.6 nM) and induced CTL that effectively recognized PR8-infected cells. These results suggest that 1) this epitope is produced by natural processing in relatively high amounts and 2) low precursor frequency might be related to the subdominant status of the M1(128) epitope. Taken together, these results illustrate the crucial contributions of MHC-binding capacity, and T cell repertoire availability, to the shaping of the repertoire of CTL specificities for Flu Ag virus.

Analysis of cytotoxic T cell responses to dominant and subdominant epitopes during acute and chronic lymphocytic choriomeningitis virus infection

The cytotoxic T cell response against lymphocytic choriomeningitis virus (LCMV) in BALB/c (H-2d) mice is predominantly directed against a single immunodominant Ld-restricted epitope in the viral nucleoprotein (NP118-126). Here we report that the immunodominance of this peptide can be in part attributed to its very high affinity for Ld class I molecules. By employing motif searches and sensitive MHC class I binding assays, we also identified 5 Kd-binding peptides in the viral nucleoprotein and glycoprotein among 16 Kd motif-fitting peptides. The nucleoprotein and glycoprotein sequences also contained 18 Dd motif-fitting peptides, three of which bound Dd with weak affinity. Two of the Kd-binding peptides, residues 99-108 and residues 283-291 from the viral glycoprotein, are subdominant epitopes. Although these peptides did not sensitize target cells for direct ex vivo killing by primary antiviral CTL, secondary responses against these peptides were readily detected in BALB/c mice after acute LCMV infection. BALB/c mice that had cleared a long-term LCMV infection showed more sustained CTL responses against these subdominant epitopes, suggesting that subdominant responses might play a role in clearance of chronic infections. One of the subdominant epitopes, GP283-291, conferred partial protection against persistent viral infection after peptide vaccination.

Immunodominance analysis of CTL responses to influenza PR8 virus reveals two new dominant and subdominant Kb-restricted epitopes

In the present study, a systematic analysis of the influenza (Flu) PR8 determinants recognized by H-2b mice was undertaken. A single Db-restricted immunodominant epitope (NP(366)) was previously known in this system. Twenty-three different Flu PR8-derived peptides that bound either Kb or Db molecules in vitro were identified. Sixteen were immunogenic following peptide immunization of C57BL/6 mice, yet CTL induced by peptide immunization recognized PR8-infected target cells only in the case of the NP(366) and NS2(114) epitopes. Similarly, CTL responses following whole-PR8 virus immunization were detected only for the same two determinants. CTL recognizing these dominant epitopes had high avidity for peptide-pulsed target cells, with 5 to 200 pM of peptide required for 30% specific lysis. In contrast, most (80%) of the remaining epitopes were recognized with lower avidity (30% effective concentration in the range of 0.4-50 nM). Repeated in vitro stimulation of primary CTL cultures revealed one additional Kb-restricted epitope (M1(128)). This peptide bound Kb with high affinity (4.6 nM) and induced CTL that effectively recognized PR8-infected cells. These results suggest that 1) this epitope is produced by natural processing in relatively high amounts and 2) low precursor frequency might be related to the subdominant status of the M1(128) epitope. Taken together, these results illustrate the crucial contributions of MHC-binding capacity, and T cell repertoire availability, to the shaping of the repertoire of CTL specificities for Flu Ag virus.

Analysis of cytotoxic T cell responses to dominant and subdominant epitopes during acute and chronic lymphocytic choriomeningitis virus infection

The cytotoxic T cell response against lymphocytic choriomeningitis virus (LCMV) in BALB/c (H-2d) mice is predominantly directed against a single immunodominant Ld-restricted epitope in the viral nucleoprotein (NP118-126). Here we report that the immunodominance of this peptide can be in part attributed to its very high affinity for Ld class I molecules. By employing motif searches and sensitive MHC class I binding assays, we also identified 5 Kd-binding peptides in the viral nucleoprotein and glycoprotein among 16 Kd motif-fitting peptides. The nucleoprotein and glycoprotein sequences also contained 18 Dd motif-fitting peptides, three of which bound Dd with weak affinity. Two of the Kd-binding peptides, residues 99-108 and residues 283-291 from the viral glycoprotein, are subdominant epitopes. Although these peptides did not sensitize target cells for direct ex vivo killing by primary antiviral CTL, secondary responses against these peptides were readily detected in BALB/c mice after acute LCMV infection. BALB/c mice that had cleared a long-term LCMV infection showed more sustained CTL responses against these subdominant epitopes, suggesting that subdominant responses might play a role in clearance of chronic infections. One of the subdominant epitopes, GP283-291, conferred partial protection against persistent viral infection after peptide vaccination.

Specificity and degeneracy in peptide binding to HLA-B7-like class I molecules

The HLA-B7-like binding supertype includes several different HLA-B molecules. Herein, the primary and secondary anchor specificities of the five most common HLA-B7-like molecules (B*0702, B*3501, B51, B*5301, and B*5401) were defined by the use of molecular binding assays, analogue peptides, and large sets of peptides corresponding to naturally occurring sequences. All five B7-like molecules analyzed preferentially bound 9-mers, with a stringent requirement for proline in position 2, while a variety of hydrophobic or aromatic residues were well tolerated at the C-terminal anchor position. Although most peptides bound in an allele-specific fashion, approximately 20% of the binders identified were degenerate and bound at least three of the five B7-like molecules analyzed with affinities of 500 nM or less. It was also noted that, in general, peptides that bind with high affinity to any given one B7-like molecule were also most frequently capable of degenerate binding. Prominent roles for secondary anchors in positions 1 and 3 were observed for most B7-like molecules, and secondary anchor motifs were utilized to derive an HLA-B7-like supermotif. The validity of this B7-like supermotif was tested by a blind prediction set. Finally, the B7-like supermotif was utilized to derive a general strategy for rationally engineering peptide analogues of naturally occurring sequences with greatly increased binding affinity and degeneracy. Such engineered supermotif binding peptides may be of significant utility in the development of peptide-based vaccines against chronic viral diseases and cancer.

Specificity and degeneracy in peptide binding to HLA-B7-like class I molecules

The HLA-B7-like binding supertype includes several different HLA-B molecules. Herein, the primary and secondary anchor specificities of the five most common HLA-B7-like molecules (B*0702, B*3501, B51, B*5301, and B*5401) were defined by the use of molecular binding assays, analogue peptides, and large sets of peptides corresponding to naturally occurring sequences. All five B7-like molecules analyzed preferentially bound 9-mers, with a stringent requirement for proline in position 2, while a variety of hydrophobic or aromatic residues were well tolerated at the C-terminal anchor position. Although most peptides bound in an allele-specific fashion, approximately 20% of the binders identified were degenerate and bound at least three of the five B7-like molecules analyzed with affinities of 500 nM or less. It was also noted that, in general, peptides that bind with high affinity to any given one B7-like molecule were also most frequently capable of degenerate binding. Prominent roles for secondary anchors in positions 1 and 3 were observed for most B7-like molecules, and secondary anchor motifs were utilized to derive an HLA-B7-like supermotif. The validity of this B7-like supermotif was tested by a blind prediction set. Finally, the B7-like supermotif was utilized to derive a general strategy for rationally engineering peptide analogues of naturally occurring sequences with greatly increased binding affinity and degeneracy. Such engineered supermotif binding peptides may be of significant utility in the development of peptide-based vaccines against chronic viral diseases and cancer.

Identification of A2-restricted hepatitis C virus-specific cytotoxic T lymphocyte epitopes from conserved regions of the viral genome

We have focused on conserved regions of the hepatitis C Virus (HCV) genome to identify viral peptides that contain HLA class I binding motifs and bind with high affinity to the corresponding purified HLA molecules. Accordingly, we have identified 31 candidate epitopes in the HCV that have the potential to be recognized by either HLA-A1, A2.1-, A3, A11- or A24-restricted cytotoxic T lymphocytes (CTL). Twelve conserved peptides that bind HLA-A2.1 with high or intermediate affinity were tested for immunogenicity in vitro in human primary CTL cultures and in vivo by direct immunization of HLA-A2.1/Kb transgenic mice. Six HLA-A2.1-restricted CTL epitopes were immunogenic in both systems. At least three of these peptide epitopes were endogenously processed and presented for CTL recognition. Overall, these data illustrate the value of this approach for the development of virus-specific, peptide-based vaccines.

Definition of an HLA-A3-like supermotif demonstrates the overlapping peptide-binding repertoires of common HLA molecules

An HLA-A3-like supertype (minimally comprised of products from the HLA class I alleles A3, A11, A31, A*3301, and A*6801) has been defined on the basis of (a) structural similarities in the antigen-binding groove, (b) shared main anchor peptide-binding motifs, (c) the identification of peptides cross-reacting with most or all of these molecules, and (d) the definition of an A3-like supermotif that efficiently predicts highly cross-reactive peptides. Detailed secondary anchor maps for A3, A11, A31, A*3301, and A*6801 are also described. The biologic relevance of the A3-like supertype is indicated by the fact that high frequencies of the A3-like supertype alleles are conserved in all major ethnic groups. Because A3-like supertype alleles are found in most major HLA evolutionary lineages, possibly a reflection of common ancestry, the A3-like supermotif might in fact represent a primeval human HLA class I peptide-binding specificity. It is also possible that these phenomena might be related to optimal exploitation of the peptide specificity by human TAP molecules. The grouping of HLA alleles into supertypes on the basis of their overlapping peptide-binding repertoires represents an alternative to serologic or phylogenetic classification.

Differences and similarities in the A2.1-restricted cytotoxic T cell repertoire in humans and human leukocyte antigen-transgenic mice

HLA-A2.1-binding peptides (n = 38) were screened for immunogenicity with human peripheral blood mononuclear cells in cytotoxic T lymphocyte (CTL) induction experiments in vitro and with splenocytes from HLA-A2.1/Kb transgenic mice following immunization in vivo. These data were compiled and analyzed to determine the level of overlap between the A2.1-restricted CTL repertoire of A2.1/Kb-transgenic mice and A2.1+ humans. In both humans and mice, a major histocompatibility complex affinity threshold of approximately 500 nM appears to determine the capacity of a peptide to elicit a CTL response. Good concordance between the human data in vitro and mouse data in vivo was observed with 85% of the high-binding peptides, 58% of the intermediate binders, and 83% of the low/negative binders. Although some peptides immunogenic for mouse CTL but not for humans (and vice versa) could be identified, the data as a whole suggest an extensive overlap between T cell receptor repertoires of mouse and human CTL and support the use of HLA-transgenic mice for the identification of potential human CTL epitopes.

Prominent roles of secondary anchor residues in peptide binding to HLA-A24 human class I molecules

The binding capacity of large sets of peptides corresponding to naturally occurring sequences and carrying previously defined A24-specific motifs was analyzed. It was found that only a minority (9-25%) of the motif-carrying peptides bound the relevant HLA-A molecule with good affinity (IC 50% < or = 50 nM), while the majority of them bound only weakly or not at all (IC 50% > or = 500 nM). By correlating the presence of specific residue types at each position along the peptide sequence with average binding affinity, the prominent influence of specific secondary interactions (secondary anchor residues) was revealed. Moreover, secondary interactions appeared to be size-dependent in that the specific effects detected differed in 9-mer and 10-mer peptide sets. Based on these observations, A24-specific refined motifs were also established for both 9-mer and 10-mer ligands, and their merit was verified by testing the binding capacity of independent sets of synthetic peptides. Such refined motifs should facilitate accurate prediction of potential A24-restricted peptide epitopes. It was also noted that certain crucial secondary interactions appear to be remarkably similar in the case of A24 and other HLA-A molecules previously analyzed (A*0201, A3, A11, and others). This may reflect contributions to binding affinity of relatively invariant residues located within the polymorphic pockets of the HLA binding groove.

Prominent roles of secondary anchor residues in peptide binding to HLA-A24 human class I molecules

The binding capacity of large sets of peptides corresponding to naturally occurring sequences and carrying previously defined A24-specific motifs was analyzed. It was found that only a minority (9-25%) of the motif-carrying peptides bound the relevant HLA-A molecule with good affinity (IC 50% &lt; or = 50 nM), while the majority of them bound only weakly or not at all (IC 50% &gt; or = 500 nM). By correlating the presence of specific residue types at each position along the peptide sequence with average binding affinity, the prominent influence of specific secondary interactions (secondary anchor residues) was revealed. Moreover, secondary interactions appeared to be size-dependent in that the specific effects detected differed in 9-mer and 10-mer peptide sets. Based on these observations, A24-specific refined motifs were also established for both 9-mer and 10-mer ligands, and their merit was verified by testing the binding capacity of independent sets of synthetic peptides. Such refined motifs should facilitate accurate prediction of potential A24-restricted peptide epitopes. It was also noted that certain crucial secondary interactions appear to be remarkably similar in the case of A24 and other HLA-A molecules previously analyzed (A*0201, A3, A11, and others). This may reflect contributions to binding affinity of relatively invariant residues located within the polymorphic pockets of the HLA binding groove.

In vitro induction of primary, antigen-specific CTL from human peripheral blood mononuclear cells stimulated with synthetic peptides

A protocol for in vitro induction of primary, antigen-specific CTL from human peripheral blood mononuclear cells (PBMCs) was developed. Antigen presenting cells (APCs) consisted of Staphylococcus aureus Cowan-I (SAC-I) activated PBMCs treated with a citrate-phosphate buffer at pH 3 to release endogenous peptides bound to surface MHC. This treatment resulted in transient expression of empty class I molecules which could be subsequently stabilized with peptide and beta 2-microglobulin (beta 2m). SAC-I activated PBMCs from HLA-A2.1 normal donors loaded with HBV core 18-27 peptide following acid treatment were used to stimulate PBMCs depleted of CD4+ T cells, in the presence of recombinant interleukin-7 (rIL-7). After 12 days, cells were restimulated with autologous, peptide-pulsed, adherent cells and tested for CTL activity 7 days later. In 23 independent experiments from 13 different HLA-A2.1 donors, this protocol resulted in induction of primary CTL more than 90% of the time. As indicated by both the frequency and magnitude of the response against peptide-sensitized target cells, SAC-I activated PBMCs treated with acid were the most efficient stimulator APC. Thirteen per cent of the cultures generated were capable of lysing target cells transfected with the HBV core antigen and, in general, these CTL cultures exhibited high avidity for the HBV core peptide. This protocol is generally applicable to different antigens and class I alleles, and thus, may be utilized to screen large numbers of peptides to identify human CTL epitopes.

The relationship between class I binding affinity and immunogenicity of potential cytotoxic T cell epitopes

The relationship between binding affinity for HLA class I molecules and immunogenicity of discrete peptide epitopes has been analyzed in two different experimental approaches. In the first approach, the immunogenicity of potential epitopes ranging in MHC binding affinity over a 10,000-fold range was analyzed in HLA-A*0201 transgenic mice. In the second approach, the antigenicity of approximately 100 different hepatitis B virus (HBV)-derived potential epitopes, all carrying A*0201 binding motifs, was assessed by using PBL of acute hepatitis patients. In both cases, it was found that an affinity threshold of approximately 500 nM (preferably 50 nM or less) apparently determines the capacity of a peptide epitope to elicit a CTL response. These data correlate well with class I binding affinity measurements of either naturally processed peptides or previously described T cell epitopes. Taken together, these data have important implications for the selection of epitopes for peptide-based vaccines, and also formally demonstrate the crucial role of determinant selection in the shaping of T cell responses. Because in most (but not all) cases, high affinity peptides seem to be immunogenic, our data also suggest that holes in the functional T cell repertoire, if they exist, may be relatively rare.

The relationship between class I binding affinity and immunogenicity of potential cytotoxic T cell epitopes

The relationship between binding affinity for HLA class I molecules and immunogenicity of discrete peptide epitopes has been analyzed in two different experimental approaches. In the first approach, the immunogenicity of potential epitopes ranging in MHC binding affinity over a 10,000-fold range was analyzed in HLA-A*0201 transgenic mice. In the second approach, the antigenicity of approximately 100 different hepatitis B virus (HBV)-derived potential epitopes, all carrying A*0201 binding motifs, was assessed by using PBL of acute hepatitis patients. In both cases, it was found that an affinity threshold of approximately 500 nM (preferably 50 nM or less) apparently determines the capacity of a peptide epitope to elicit a CTL response. These data correlate well with class I binding affinity measurements of either naturally processed peptides or previously described T cell epitopes. Taken together, these data have important implications for the selection of epitopes for peptide-based vaccines, and also formally demonstrate the crucial role of determinant selection in the shaping of T cell responses. Because in most (but not all) cases, high affinity peptides seem to be immunogenic, our data also suggest that holes in the functional T cell repertoire, if they exist, may be relatively rare.

Induction of anti-tumor cytotoxic T lymphocytes in normal humans using primary cultures and synthetic peptide epitopes

Cytotoxic T lymphocytes (CTLs) recognize peptide antigens associated with cell surface major histocompatibility complex (MHC) molecules. The identification of tumor cell-derived peptides capable of eliciting anti-tumor CTL responses would enable the design of antigen-specific immunotherapies. Our strategy to identify such potentially therapeutic peptides relies on selecting high-affinity MHC binders from known tumor-associated antigens. These peptides are subsequently tested for their ability to induce CTLs capable of killing tumor cells. With this strategy, we have identified a nine-residue epitope, derived from the product of the tumor-associated gene MAGE-3, which has the capacity to induce in vitro CTLs that kill melanoma and other tumor cell lines. These results show the primary in vitro induction of tumor-specific human CTLs and illustrate the feasibility of ex vivo antigen-specific approaches to the immunological therapy of cancer.

Analysis of the HLA-restricted influenza-specific cytotoxic T lymphocyte response in transgenic mice carrying a chimeric human-mouse class I major histocompatibility complex

Transgenic murine lines have been constructed that express a chimeric class I molecule composed of the alpha 1 and alpha 2 domains of HLA-A2.1 and the alpha 3, transmembrane, and cytoplasmic domains of H-2Kb. Upon immunization with influenza virus, transgenic mice developed a strong A2.1Kb-restricted cytotoxic T lymphocyte (CTL) response specific for the same matrix protein epitope that serves as the dominant A2.1-restricted determinant in the equivalent human response. Fine specificity analysis of CTL clones using truncated peptides revealed strong similarity between the response repertoire of transgenic mice and that previously reported using influenza-specific A2.1-restricted CTL clones from humans. This suggests that even when considering T cell responses by different species, the alpha 1 and alpha 2 domains of the restriction element play a dominant role in determining the CTL specific repertoire. Thus, substituting the alpha 3 domain of A2.1 with a murine counterpart has permitted development of a transgenic strain that should serve as an excellent model system in studies of HLA-restricted responses.

cDNA cloning and immunological characterization of the rye grass allergen Lol p I

The complete amino acid sequence of two "isoallergenic" forms of Lol p I, the major rye grass (Lolium perenne) pollen allergen, was deduced from cDNA sequence analysis. cDNA clones isolated from a Lolium perenne pollen library contained an open reading frame coding for a 240-amino acid protein. Comparison of the nucleotide and deduced amino acid sequence of two of these clones revealed four changes at the amino acid level and numerous nucleotide differences. Both clones contained one possible asparagine-linked glycosylation site. Northern blot analysis shows one RNA species of 1.2 kilobases. Based on the complete amino acid sequence of Lol p I, overlapping peptides covering the entire molecule were synthesized. Utilizing these peptides we have identified a determinant within the Lol p I molecule that is recognized by human leukocyte antigen class II-restricted T cells obtained from persons allergic to rye grass pollen.

Characterization of the specificity of peptide binding to four DR haplotypes

This study describes the establishment of a peptide-binding assay for purified, detergent-solubilized DR molecules. For each of the DR specificities and peptides studied, a unique pattern of interaction was observed. Excellent correlation was detected between the DR1-, 2-, 5-, and 52a-binding capacities and the known DR restrictions of a panel of synthetic peptides. This supports the immunologic relevance of the binding assay, and emphasizes the importance of determinant selection in defining the immune response of individuals. We have also examined the capacity of a panel of DR-restricted peptides to compete with one another for binding to DR1. The results obtained are compatible with a single peptide-binding site on DR molecules. The peptide-binding capacity of the four different DR types (DR1, DR2, DR5, and DR52a) has been further examined by testing a collection of 133 different peptides. This collection is unbiased with respect to previously known DR binding and restrictions, and includes peptides of eukaryotic, bacterial, and viral origins. It was found that: 1) approximately 15 to 35% of the peptides tested bound any given DR type; 2) DR-binding capacities appeared to correlate with each other, suggesting that different alleles of the DR isotype may recognize related structures on an Ag molecule; and 3) despite the statistical correlation between binding capacity of different DR types, approximately 50% of the peptides that were positive binders still were specific in that they could bind only one of the four DR molecules tested. Degenerate binding (i.e., binding to most or all the DR molecules tested) was detected in only a minority of the cases analyzed (approximately 25%).

Characterization of the specificity of peptide binding to four DR haplotypes

This study describes the establishment of a peptide-binding assay for purified, detergent-solubilized DR molecules. For each of the DR specificities and peptides studied, a unique pattern of interaction was observed. Excellent correlation was detected between the DR1-, 2-, 5-, and 52a-binding capacities and the known DR restrictions of a panel of synthetic peptides. This supports the immunologic relevance of the binding assay, and emphasizes the importance of determinant selection in defining the immune response of individuals. We have also examined the capacity of a panel of DR-restricted peptides to compete with one another for binding to DR1. The results obtained are compatible with a single peptide-binding site on DR molecules. The peptide-binding capacity of the four different DR types (DR1, DR2, DR5, and DR52a) has been further examined by testing a collection of 133 different peptides. This collection is unbiased with respect to previously known DR binding and restrictions, and includes peptides of eukaryotic, bacterial, and viral origins. It was found that: 1) approximately 15 to 35% of the peptides tested bound any given DR type; 2) DR-binding capacities appeared to correlate with each other, suggesting that different alleles of the DR isotype may recognize related structures on an Ag molecule; and 3) despite the statistical correlation between binding capacity of different DR types, approximately 50% of the peptides that were positive binders still were specific in that they could bind only one of the four DR molecules tested. Degenerate binding (i.e., binding to most or all the DR molecules tested) was detected in only a minority of the cases analyzed (approximately 25%).

Induction of class I MHC-restricted, peptide-specific cytolytic T lymphocytes by peptide priming in vivo

The present study investigated the possibility that protein Ag fragments in the form of peptides could serve as the priming Ag in the generation of a MHC class I-restricted immune response. Trypsin-digested chicken ovalbumin (OVA-TD) fragments were used as the model Ag. The results demonstrate the peptides within OVA-TD, when injected into C57BL/6 mice, could prime T cells which lysed H-2b Ia-EL4 target cells in an OVA-TD-specific manner. In contrast to priming with OVA-TD, immunization of mice with intact OVA did not lead to generation of CTL against OVA-TD or OVA. Furthermore, target cells sensitized with intact OVA failed to be recognized by OVA-peptide-specific CTL indicating that the target cells serving as APC were unable to generate the relevant peptide determinants recognized by the T cells. These results support the idea that the processing pathway within APC for class I-restricted T cells may differ from that used for class II-restricted T cells. Using OVA-TD-specific CTL clones (phenotypically Thy 1+, CD8+, CD4-, Pgp-1+) isolated from primed animals to screen OVA-TD fractions separated by HPLC, two T cell peptide determinants were identified corresponding to OVA sequences 111-122 and 370-381. Both determinants were recognized by CTL clones in the context of the H-2Db molecule.

Induction of class I MHC-restricted, peptide-specific cytolytic T lymphocytes by peptide priming in vivo

The present study investigated the possibility that protein Ag fragments in the form of peptides could serve as the priming Ag in the generation of a MHC class I-restricted immune response. Trypsin-digested chicken ovalbumin (OVA-TD) fragments were used as the model Ag. The results demonstrate the peptides within OVA-TD, when injected into C57BL/6 mice, could prime T cells which lysed H-2b Ia-EL4 target cells in an OVA-TD-specific manner. In contrast to priming with OVA-TD, immunization of mice with intact OVA did not lead to generation of CTL against OVA-TD or OVA. Furthermore, target cells sensitized with intact OVA failed to be recognized by OVA-peptide-specific CTL indicating that the target cells serving as APC were unable to generate the relevant peptide determinants recognized by the T cells. These results support the idea that the processing pathway within APC for class I-restricted T cells may differ from that used for class II-restricted T cells. Using OVA-TD-specific CTL clones (phenotypically Thy 1+, CD8+, CD4-, Pgp-1+) isolated from primed animals to screen OVA-TD fractions separated by HPLC, two T cell peptide determinants were identified corresponding to OVA sequences 111-122 and 370-381. Both determinants were recognized by CTL clones in the context of the H-2Db molecule.

The role of dendritic cells as stimulators of minor lymphocyte-stimulating locus-specific T cell responses in the mouse. I. Differential capacity of dendritic cells to stimulate minor lymphocyte-stimulating locus-reactive T cell hybridomas and the primary anti-minor lymphocyte-stimulating locus mixed lymphocyte reaction

The response of T cells to minor lymphocyte-stimulating locus (Mls) determinants remains poorly understood with respect to the antigenic determinants responsible for T cell stimulation and the types of APC capable of stimulating the response. In this report, we demonstrate that highly purified dendritic cells (DC) as well as B cells have the capacity to stimulate Mls-specific responses. Unseparated spleen cells, purified DC, resting B cells, and activated B cells were compared for their capacity to stimulate several Mls-reactive T cell hybridomas. Whereas the entire panel of Mls-reactive T cell hybridomas was stimulated strongly by unseparated spleen cells and activated B cells, the hybridomas responded only weakly to purified DC or resting B cells. Activation of resting B cells with either B cell stimulatory factor-1 (1 day pre-treatment) or LPS/dextran (2 or 3 day pre-treatment) greatly augmented their Mls-stimulatory capacity. In contrast, the Mls-stimulatory capacity of DC was not augmented by a 1-day pre-treatment with either B cell stimulatory factor-1 or supernatant from the DC-induced primary anti-Mls-MLR. In the primary anti-Mls-MLR, both purified DC and LPS/dextran-stimulated B blasts were found to elicit vigorous T cell proliferative responses. Much weaker responses were elicited by unseparated spleen cells. The stimulation of the primary anti-Mls-MLR by purified DC was further confirmed by producing Mls-specific T cell clones which were preferentially stimulated by DC. Autologous (Mlsb) DC were found to markedly enhance the primary anti-Mls-MLR response to small numbers of Mlsa B blasts. Thus, DC possess other "accessory cell" properties that augment the primary anti-Mls-MLR despite the predicted low level of Mls determinant expression on DC based on the results obtained with Mls-reactive hybridomas. Possible accessory cell properties of DC relevant to this phenomenon are discussed.

The role of dendritic cells as stimulators of minor lymphocyte-stimulating locus-specific T cell responses in the mouse. I. Differential capacity of dendritic cells to stimulate minor lymphocyte-stimulating locus-reactive T cell hybridomas and the primary anti-minor lymphocyte-stimulating locus mixed lymphocyte reaction

The response of T cells to minor lymphocyte-stimulating locus (Mls) determinants remains poorly understood with respect to the antigenic determinants responsible for T cell stimulation and the types of APC capable of stimulating the response. In this report, we demonstrate that highly purified dendritic cells (DC) as well as B cells have the capacity to stimulate Mls-specific responses. Unseparated spleen cells, purified DC, resting B cells, and activated B cells were compared for their capacity to stimulate several Mls-reactive T cell hybridomas. Whereas the entire panel of Mls-reactive T cell hybridomas was stimulated strongly by unseparated spleen cells and activated B cells, the hybridomas responded only weakly to purified DC or resting B cells. Activation of resting B cells with either B cell stimulatory factor-1 (1 day pre-treatment) or LPS/dextran (2 or 3 day pre-treatment) greatly augmented their Mls-stimulatory capacity. In contrast, the Mls-stimulatory capacity of DC was not augmented by a 1-day pre-treatment with either B cell stimulatory factor-1 or supernatant from the DC-induced primary anti-Mls-MLR. In the primary anti-Mls-MLR, both purified DC and LPS/dextran-stimulated B blasts were found to elicit vigorous T cell proliferative responses. Much weaker responses were elicited by unseparated spleen cells. The stimulation of the primary anti-Mls-MLR by purified DC was further confirmed by producing Mls-specific T cell clones which were preferentially stimulated by DC. Autologous (Mlsb) DC were found to markedly enhance the primary anti-Mls-MLR response to small numbers of Mlsa B blasts. Thus, DC possess other "accessory cell" properties that augment the primary anti-Mls-MLR despite the predicted low level of Mls determinant expression on DC based on the results obtained with Mls-reactive hybridomas. Possible accessory cell properties of DC relevant to this phenomenon are discussed.

Studies on the capacity of B cells as well as T cells to serve as accessory cells for the activation of herpes simplex virus-specific cytolytic T cells

Experiments were conducted in an effort to determine the ability of B and T lymphocytes to serve as APC for the activation of HSV-primed splenic T cells to become class I-restricted, HSV-specific CTL. The results showed that both freshly isolated splenic B cells as well as LPS and dextran sulfate (L/D)-activated B cells were effective at stimulating the generation of CTL during a 5-day in vitro culture. There was no requirement for the addition of exogenous IL-2 to the culture and, since murine B cells do not appear to express either membrane or secreted IL-1, this lymphokine appears to either not be required for the activation of virus-specific CTL or to be provided by the T cells themselves. When normal B cells were separated into fractions enriched for resting vs activated cells and then tested for their ability to stimulate the generation of HSV-specific CTL, it was found that while the activated B cells were quite effective at stimulating the generation of CTL, resting B cells were ineffective at carrying out this function. In contrast to normal B cells, normal T cells were unable to act as APC. However, Con A-activated T lymphoblasts were equivalent to L/D B cells in their ability to mediate the generation of CTL activity. L/D B cells that had been pulsed with HSV and then incubated at 37 degrees C for greater than 1 h could be fixed with paraformaldehyde and were still able to function as APC. The finding that L/D B cells, that had been fixed at 1 h or less after exposure to HSV, were unable to function as APC suggested that either active Ag "processing" steps may be required for the presentation of Ag in the context of class I molecules or that there is a requirement for the synthesis of viral protein Ag before presentation.