Identification of helper T-cell epitopes that encompass or lie proximal to cytotoxic T-cell epitopes in the gp100 melanoma tumor antigen

The melanocyte-associated antigen gp100 constitutes one of the most attractive targets for T-cell-based immunotherapy against malignant melanoma. Although several MHC class I-restricted epitopes have been identified for CTLs, thus far, only one MHC class II T helper epitope (restricted by HLA-DR4) has been described in the literature. Using an algorithm to identify promiscuous helper T-cell epitopes, here we describe three additional MHC class II-restricted epitopes from gp100. Whereas one T helper epitope, gp100(175-189), was restricted by the HLA-DR53 and DQw6 alleles, the T-cell responses to two other epitopes, gp100(74-89) and gp100(576-590), were restricted by HLA-DR7. Most interestingly, the newly identified helper T lymphocyte epitopes encompass or lie proximal to previously described CTL epitopes for this tumor-associated antigen. Together with the previously described HLA-DR4-restricted epitope, these T helper epitopes offer coverage for the majority of the human population. Moreover, the use of peptide vaccines containing both CTLs and T helper epitopes could offer therapeutic advantages over current approaches that focus solely on eliciting antitumor CTL responses.

Existence of MHC class I-restricted alloreactive CD4+ T cells reacting with peptide transporter-deficient cells

It is generally accepted that as the result of positive thymic selection, CD8-expressing T cells recognize peptide antigens presented in the context of MHC class I molecules and CD4-expressing T cells interact with peptide antigens presented by MHC class II molecules. Here we report the generation of TCRalpha/beta(+), CD3(+), CD4(+), CD8(-), MHC class I-restricted alloreactive T-cell clones which were induced using peripheral blood mononuclear cells from healthy individuals following in vitro stimulation with transporter associated with antigen processing (TAP)-deficient cell lines T2. The CD4(+) T-cell clones showed an HLA-A2.1-specific proliferative response against T2 cells which was inhibited by anti-CD3 and anti-CD4 monoclonal antibodies. These results suggest that interaction of the TCR with peptide-bound HLA class I molecules contributes to antigen-specific activation of these co-receptor-mismatched T-cell clones. Antigen recognition by alloreactive MHC class I-restricted CD4(+) T cells was inhibited by removing peptides bound to HLA molecules on T2 cells suggesting that the alloreactive CD4(+) T cells recognize peptides that bind in a TAP-independent manner to HLA-A2 molecules. The existence of such MHC class I-restricted CD4(+) T cells which can recognize HLA-A2 molecules in the absence of TAP function may provide a basis for the development of immunotherapy against TAP-deficient tumor variants which would be tolerant to immunosurveillance by conventional MHC class I-restricted cytotoxic lymphocytes.

Identification of new epitopes from four different tumor-associated antigens: recognition of naturally processed epitopes correlates with HLA-A*0201-binding affinity

Forty-two wild-type and analogue peptides derived from p53, carcinoembryonic Ag, Her2/neu, and MAGE2/3 were screened for their capacity to induce CTLs, in vitro, capable of recognizing tumor target lines. All the peptides bound HLA-A*0201 and two or more additional A2 supertype alleles with an IC(50) of 500 nM or less. A total of 20 of 22 wild-type and 9 of 12 single amino acid substitution analogues were found to be immunogenic in primary in vitro CTL induction assays, using normal PBMCs and GM-CSF/IL-4-induced dendritic cells. These results suggest that peripheral T cell tolerance does not prevent, in this system, induction of CTL responses against tumor-associated Ag peptides, and confirm that an HLA class I affinity of 500 nM or less is associated with CTL epitope immunogenicity. CTLs generated by 13 of 20 of the wild-type epitopes, 6 of 9 of the single, and 2 of 5 of the double substitution analogues tested recognized epitopes generated by endogenous processing of tumor-associated Ags and expressed by HLA-matched cancer cell lines. Further analysis revealed that recognition of naturally processed Ag was correlated with high HLA-A2.1-binding affinity (IC(50) = 200 nM or less; p = 0.008), suggesting that high binding affinity epitopes are frequently generated and can be recognized as a result of natural Ag processing. These results have implications for the development of cancer vaccines, in particular, and for the process of epitope selection in general.

TAP-independent presentation of CTL epitopes by Trojan antigens

The majority of CTL epitopes are derived from intracellular proteins that are degraded in the cytoplasm by proteasomes into peptides that are transported into the endoplasmic reticulum by the TAP complex. These peptides can be further processed into the optimal size (8-10 residues) for binding with nascent MHC class I molecules, generating complexes that are exported to the cell surface. Proteins or peptides containing CTL epitopes can be introduced into the cytoplasm of APCs by linking them to membrane-translocating Trojan carriers allowing their incorporation into the MHC class I Ag-processing pathway. The present findings suggest that these "Trojan" Ags can be transported into the endoplasmic reticulum in a TAP-independent way where they are processed and trimmed into CTL epitopes. Furthermore, processing of Trojan Ags can also occur in the trans-Golgi compartment, with the participation of the endopeptidase furin and possibly with the additional participation of a carboxypeptidase. We believe that these findings will be of value for the design of CTL-inducing vaccines for the treatment or prevention of infectious and malignant diseases.

Tumor-reactive T helper lymphocytes recognize a promiscuous MAGE-A3 epitope presented by various major histocompatibility complex class II alleles

The development of effective T cell-based immunotherapy for cancer requires the identification of antigens capable of inducing both CTL and T helper immune responses. Although CTLs will participate in the antitumor response mainly by exerting their lytic activity on the tumor cells, helper T lymphocytes will be critical for the induction and maintenance of the CTLs. Thus, effective subunit therapeutic vaccines should include both CTL and T helper epitopes from antigens expressed on the tumor cells. The product of the MAGE-A3 gene is an attractive candidate for tumor immunotherapy because it is expressed in the majority of melanomas and in a great proportion of other solid tumors. Although numerous CTL epitopes for the MAGE-A3 antigen have been reported, only a few have been described for helper T cells. Here we show that a synthetic peptide derived from the MAGE-A3 sequence (MAGE-A3(146-160)) was effective in inducing in vitro T helper responses in the context of HLA-DR4 and HLA-DR7 alleles. Most significantly, the peptide-reactive helper T lymphocytes were capable of recognizing various forms of MAGE-A3 antigen (tumor cell lysates, dead/apoptotic tumor cells, or recombinant MAGE-A3 protein), indicating that the T-cell epitope represented by peptide MAGE-A3(146-160) is naturally processed by antigen-presenting cells. These studies are relevant for the design of multi-epitope vaccines for treating MAGE-A3-expressing tumors through the simultaneous stimulation of CTL and T helper lymphocytes.

Avoiding Tolerance Against Prostatic Antigens With Subdominant Peptide Epitopes

SUMMARY: A potential novel therapy for prostate cancer is the induction of immune responses to normal prostate-associated antigens (PAA). One approach is to use synthetic peptides from PAA to educate T cells as a means of developing a defined and specific immunotherapy for prostate cancer. A likely major hurdle when using normal PAA for this type of therapy is the tolerance that the immune system may already have for PAA. To evaluate mechanisms for overcoming tolerance, the authors assessed the level of tolerance to SV40T antigen in a transgenic mouse. The SV40T antigen is selectively expressed in the prostates of mice from the transgenic adenocarcinoma mouse prostate (TRAMP) model. The authors have shown that TRAMP mice are tolerant to a dominant cytotoxic T-lymphocyte (CTL) epitope from the SV40T antigen compared with nontransgenic littermates. The tolerance was exhibited as early as 4 weeks and as late as 24 weeks. The use of multiple injections of an oligonucleotide that contains an unmethylated CpG induced high levels of hematopoiesis but did not overcome the tolerance. Injection of an antibody to activate CD40 increased the CTL response in normal mice but also did not overcome tolerance. However, tolerance in the TRAMP mice was avoided when an epitope that had previously been characterized as a subdominant epitope was administered. The authors are investigating the potential of subdominant epitopes to induce prostatitis and antitumor responses. The results of this work should facilitate the development of immune-based therapies for prostate cancer.

Antimicrobial activity of MHC class I-restricted CD8+ T cells in human tuberculosis

Studies of mouse models of tuberculosis (TB) infection have indicated a central role for MHC class I-restricted CD8+ T cells in protective immunity. To define antigens and epitopes of Mycobacterium tuberculosis (MTB) proteins that are presented by infected cells to CD8+ T cells, we screened 40 MTB proteins for HLA class I A*0201-binding motifs. Peptides that bound with high affinity to purified HLA molecules were subsequently analyzed for recognition by CD8+ cytotoxic T lymphocytes. We identified three epitopes recognized by CD8+ T cells from patients recovering from TB infection. Those three epitopes were derived from three different antigens: thymidylate synthase (ThyA(30-38)), RNA polymerase beta-subunit (RpoB(127-135)), and a putative phosphate transport system permease protein A-1 (PstA1(75-83)). In addition, CD8+ T cell lines specific for three peptides (ThyA(30-38), PstA1(75-83), and 85B(15-23)) were generated from peripheral blood mononuclear cells of normal HLA-A*0201 donors. These CD8+ T cell lines specifically recognized MTB-infected macrophages, as demonstrated by production of IFN-gamma and lysis of the infected target cells. Finally, CD8+ cytotoxic T lymphocytes reduced the viability of the intracellular MTB, providing evidence that CD8+ T cell recognition of MHC class I-restricted epitopes of these MTB antigens can contribute to effective immunity against the pathogen.

Identification of HLA-A*03, A*11 and B*07-restricted melanoma-associated peptides that are immunogenic in vivo by vaccine-induced immune response (VIIR) analysis

With the discovery of increasing numbers of tumor antigens, there is a need to rapidly determine whether these antigens and the individual peptides they express are able to stimulate immune responses in vivo and thus, can be used to construct cancer vaccines. In this study we used the method of vaccine-induced immune response (VIIR) analysis to identify multiple immunogenic peptide epitopes derived from several melanoma associated antigens and presented by HLA-A*03, A*11 and B*07. Thirty-one patients with melanoma were immunized to a polyvalent vaccine containing multiple antigens, including MAGE-3, Melan A/MART-1, gp100 and tyrosinase. Their peripheral blood was tested for peptide-specific, vaccine-induced CD8+ T cell responses before and after immunization using an enzyme-linked immune spot (ELISPOT) assay with panels of peptides restricted by these three alleles. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*03, A*11 or B*07. Overall, 60% of the 20 peptides studied were recognized by at least one patient and 50% of the patients showed a vaccine-induced CD8+ T cell response to at least one peptide that matched their HLA specificity. We conclude that VIIR analysis is an effective strategy to directly identify immunogenic peptides that are good candidates for vaccine construction.

Use of two predictive algorithms of the world wide web for the identification of tumor-reactive T-cell epitopes

Tumor cells can be effectively recognized and eliminated by CTLs. One approach for the development of CTL-based cancer immunotherapy for solid tumors requires the use of the appropriate immunogenic peptide epitopes that are derived from defined tumor-associated antigens. Because CTL peptide epitopes are restricted to specific MHC alleles, to design immune therapies for the general population it is necessary to identify epitopes for the most commonly found human MHC alleles. The identification of such epitopes has been based on MHC-peptide-binding assays that are costly and labor-intensive. We report here the use of two computer-based prediction algorithms, which are readily available in the public domain (Internet), to identify HL4-B7-restricted CTL epitopes for carcinoembryonic antigen (CEA). These algorithms identified three candidate peptides that we studied for their capacity to induce CTL responses in vitro using lymphocytes from HLA-B7+ normal blood donors. The results show that one of these peptides, CEA9(632) (IPQQHTQVL) was efficient in the induction of primary CTL responses when dendritic cells were used as antigen-presenting cells. These CTLs were efficient in killing tumor cells that express HLA-B7 and produce CEA. The identification of this HLA-B7-restricted CTL epitope will be useful for the design of ethnically unbiased, widely applicable immunotherapies for common solid epithelial tumors expressing CEA. Moreover, our strategy of identifying MHC class I-restricted CTL epitopes without the need of peptide/HLA-binding assays provides a convenient and cost-saving alternative approach to previous methods.

Defining promiscuous MHC class II helper T-cell epitopes for the HER2/neu tumor antigen

It is accepted that both helper and CTLs play a critical role in immune antitumor responses. Thus, the design of effective immune-based therapies for cancer relies in the identification of relevant tumor-associated antigens (TAAs) capable of eliciting strong helper and cytotoxic T-cell responses against tumor cells. The product of the HER2/neu oncogene is considered as a prototype TAA, because it is found overexpressed in a large variety of malignancies, whereas normal cells only produce low levels of this product. Several cytotoxic T-cell epitopes for HER2/neu have been identified that enable the design of peptide-based therapeutic vaccines for tumors expressing this TAA. Nevertheless, it is expected that inclusion of peptide epitopes capable of eliciting HER2/neu-specific T helper responses into these vaccines may enhance their effectiveness in the clinic. We describe here a strategy to identify helper T-cell epitopes for HER2/neu that focuses on peptides predicted to bind to numerous histocompatibility alleles (promiscuous epitopes), which would encourage their use in therapeutic vaccines for the general cancer patient population. Following this approach, we successfully identified several peptides that elicited T helper (CD4+) proliferative responses to peptides derived from HER2/neu. Most of the T-cell responses appeared to reflect a low affinity for antigen, which could be the result of immune tolerance because HER2/neu is expressed in low levels in normal cells and possibly including lymphocytes and monocytes. Interestingly, one of these peptides, HER2(883), was recognized by T cells in the context of either HLA-DR1, HLA-DR4, HLA-DR52, and HLA-DR53, indicating a high degree of histocompatibility promiscuity. Furthermore, T cells that reacted with peptide HER2(883) could also recognize antigen-presenting cells that process HER2/neu recombinant protein. These results may be relevant for the design of more effective therapeutic vaccines for tumors expressing the HER2/neu oncogene product.

Tumor prevention and antitumor immunity with heat shock protein 70 induced by 15-deoxy-delta12,14-prostaglandin J2 in transgenic adenocarcinoma of mouse prostate cells

The biological modifier delta12-prostaglandin J2 and related prostaglandins have been reported to have significant growth-inhibitory activity with induction of heat shock proteins (Hsps). Tumor-derived Hsps have been shown previously to elicit specific immunity to tumors from which they are isolated. In this study, 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2)-induced Hsp70 was purified from transgenic adenocarcinoma mouse prostate cells (TRAMP-C2). It was then tested for its ability to activate specific CTLs and induce protective immunity against prostate cancer in C57BL/6 mice. Treatment of cells with 8.0 microM 15d-PGJ2 for 24 h caused significant induction of Hsp70 expression. The yield of Hsp70 purified from 15d-PGJ2-treated cells was 4-5-fold higher when compared with untreated TRAMP-C2 cells. Vaccination of mice with Hsps isolated from TRAMP-C2 cells elicited tumor-specific CTLs and prevented the growth of TRAMP-C2 tumors. These results indicate that the induced heat shock proteins may have promising applications for antitumor, T-cell immunotherapy. In particular, these findings have important implications for the development of novel anticancer therapies aimed at promoting an immune response to prostate tumors.

Repeated administration of cytosine-phosphorothiolated guanine-containing oligonucleotides together with peptide/protein immunization results in enhanced CTL responses with anti-tumor activity

The development of therapeutic anti-cancer vaccines designed to elicit CTL responses with anti-tumor activity has become a reality thanks to the identification of several tumor-associated Ags and their corresponding peptide T cell epitopes. However, peptide-based vaccines, in general, fail to elicit sufficiently strong CTL responses capable of producing therapeutic anti-tumor effects (i.e., prolongation of survival, tumor reduction). Here we report that repeated administration of synthetic oligonucleotides containing foreign cytosine-phosphorothiolated guanine (CpG) motifs increased 10- to 100-fold the CTL response to immunization with various synthetic peptides corresponding to well-known T cell epitopes. Moreover, repeated CpG administration allowed the induction of CTL to soluble protein even in the absence of additional adjuvant. Our results indicate that the potentiating effect of CpG in CTL responses required the participation of Th lymphocytes. Repeated CpG administration resulted in overt splenomegaly and lymphadenopathy with a significant increase in the numbers of CTL precursors and dendritic cells. Protein vaccination in combination with repeated CpG therapy was effective in delaying tumor cell growth and extending survival in mice bearing melanoma tumors. These findings support the contention that repeated administration of CpG-oligonucleotides enhances the effect of peptide and protein vaccines leading to potent anti-tumor responses, presumably through the induction of Th1 and dendritic cells, which are essential for optimal CTL responses. The immunostimulatory properties of CpG motifs may be key in inducing a consistent long term immunity to tumor-associated Ags when using peptides or proteins as T cell-inducing vaccines.

Detection of T helper responses, but not of human papillomavirus-specific cytotoxic T lymphocyte responses, after peptide vaccination of patients with cervical carcinoma

Human papillomavirus type 16 (HPV16)-encoded E7 oncoprotein is constitutively expressed in cervical carcinoma cells and is required for cellular transformation to be maintained. The E7 protein, therefore, forms an attractive target for T-cell-mediated immune intervention to prevent or treat HPV16+ tumors. The authors performed a peptide-based phase I/II vaccination trial to induce anti-tumor immune responses in patients with recurrent or residual cervical carcinoma. Fifteen HLA-A*0201+ patients with HPV16+ cervical carcinoma received vaccinations with synthetic peptides representing 2 HPV16 E7-encoded, HLA-A*0201-restricted cytotoxic T lymphocyte epitopes and a pan-HLA-DR-binding T-helper epitope, PADRE, in adjuvant. No signs of toxicity were observed. Two patients had stable disease for more than 1 year after vaccination, 3 patients died of the disease during or shortly after the vaccination period, and 10 patients maintained progressive cervical carcinoma. Specific immune responses directed against the vaccine components were analyzed in peripheral blood samples. No cytotoxic T lymphocyte responses against the HPV16 E7 peptides were detectable. After vaccination, strong PADRE helper peptide-specific proliferation was detected in 4 of 12 patients. In conclusion, peptide vaccination with 2 HPV16 E7 cytotoxic T lymphocyte epitopes and a universal T helper epitope is well tolerated by patients with advanced cervical carcinoma. Despite a reduction of in vitro cytolytic or proliferative recall responses to some, but not all, conventional antigens in this patient group, peptide-specific proliferative responses were induced in 4 patients. Based on the current study, it is now feasible to perform peptide vaccination in earlier stages of HPV16-induced cervical disease.

A phase I trial of an HLA-A1 restricted MAGE-3 epitope peptide with incomplete Freund's adjuvant in patients with resected high-risk melanoma

Cytolytic and helper T cells recognize small peptide fragments of protein antigens that are intracellularly processed and delivered to the cell surface in conjunction with HLA molecules. In mice, peptide vaccines can protect against lethal virus infections and tumor challenges. To test whether epitope peptides derived from a human tumor antigen can induce immune responses in patients, a vaccine was prepared consisting of an HLA-A1-restricted epitope of the antigen MAGE-3 mixed with a pan-class II epitope peptide PADRE and emulsified with incomplete Freund's adjuvant. Eighteen patients with resected stages III and IV melanoma at high risk for relapse were vaccinated subcutaneously with increasing doses of the MAGE-3 vaccine ranging from 100 to 2,000 micrograms per injection four times, each 4 weeks apart. The purpose of the phase I trial was to assess the toxicity, tolerability, and immune responses to the vaccine. The vaccine was not toxic, with only one case of grade III lethargy, and most patients complaining of grade I or II local pain, swelling, and tenderness at the injection sites. Peripheral blood mononuclear cells (PBMC) were collected from most patients prior to and after vaccination and used for assessment of global levels of immunity prevaccination, and to measure immune responses to the MAGE-3 and PADRE peptides prior to and after vaccination. Significant defects in global immunity shown by anergy to DTH skin testing in 7 of 16 patients and decreased proliferation to PHA (phytohemagglutinin) and CASTA, a Candida albicans protein extract, were observed. Seven of nine patients showed an increased response to PADRE after restimulation in vitro. Five of 14 patients at doses from 100 to 2,000 micrograms demonstrated an immune response to MAGE-3 by cytolysis of MAGE-3-specific target cells. Release of gamma interferon by T cells from 8 patients at the 100, 1,000, or 2,000 micrograms dose was measured after vaccination, and only two of eight patients showed an increase indicating augmented antigen-specific immunity. These data suggest that immune responses can be detected against PADRE and MAGE-3 in vaccinated melanoma patients, albeit with a low frequency of effector cells.

Identification of a MAGE-2-encoded human leukocyte antigen-A24-binding synthetic peptide that induces specific antitumor cytotoxic T lymphocytes

Because MAGE-2 gene is expressed in a wide variety of malignant tumors and HLA-A24 is the most common allele in the Japanese population and is also frequently present in Caucasians, the identification of MAGE-2-encoded peptide presented by HLA-A24 is, therefore, considered to be important in order to develop specific immunotherapy for malignant tumors using peptides as a vaccine. By using a MHC-binding assay, eight peptides derived from MAGE-2 were found to bind with sufficient affinity to the HLA-A24 molecule. When the induction of specific cytotoxic T lymphocytes (CTLs) was examined using a simplified method, the highest human lymphocyte antigen (HLA) binder (EYLQLVFGI) in these peptides was able to elicit CTLs from unseparated peripheral blood mononuclear cells in HLA-A24 healthy donors by stimulation with freshly isolated, peptide-pulsed peripheral blood mononuclear cells as antigen-presenting cells and also by using interleukin 7 and keyhole-limpet hemocyanin in a primary culture. The induced CTL could, thus, lyse HLA-A24 tumor cells expressing MAGE-2, as well as the peptide-pulsed target cells, with antigen specificity in a HLA class I-restricted manner. The identification of this peptide may, thus, be of therapeutic value in peptide-based vaccines for the treatment of several types of malignant tumors expressing MAGE-2.

Identification of new HER2/neu-derived peptide epitopes that can elicit specific CTL against autologous and allogeneic carcinomas and melanomas

Twenty-two new HLA-A2.1-binding peptides derived from the protooncogene HER2/neu were identified and analyzed for their capacity to elicit peptide and tumor-specific CTL responses. We used peptide-pulsed autologous DC from the ascites of patients with ovarian carcinomas to induce CTL. Of the 22 tested new HER2/neu-derived epitopes that could bind HLA-A2 with high (IC50 < 50 nM) or intermediate (50 nM < IC50 < 500 nM) affinity, we report the recognition by CTL of at least four novel epitopes, including HER2(9435), HER2(9665), HER2(9689), and HER2(10952), and confirm that of the known HER2 (9369) epitope. These epitopes were able to elicit CTL that specifically killed peptide-sensitized target cells and, most importantly, a HER2/neu-transfected cell line and the autologous tumor cells. We also confirm that HER2/neu is overexpressed in several melanoma lines, and as a new finding, report that some of these lines are sensitive to CTL induced by the HER2 (9369), HER2(9435), and HER2(9689) epitopes. Finally, CTL clones specific for HER2 (9369), HER2(9435), and HER2(9689) epitopes were isolated from tumor-specific CTL lines, further demonstrating the immunodominance of these epitopes. These findings broaden the potential application of HER2/neu-based immunotherapy.

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.

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-γ 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-γ 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.

Identification of HLA-A24 epitope peptides of carcinoembryonic antigen which induce tumor-reactive cytotoxic T lymphocyte

Carcinoembryonic antigen (CEA), which is expressed in several cancer types, is a potential target for specific immunotherapy. HLA-A24 is the most frequent allele among Japanese and is also frequently present in Asians and Caucasians. We tested CEA-encoded HLA-A24 binding peptides for their capacity to elicit anti-tumor cytotoxic T lymphocytes (CTL) in vitro. For this purpose, we used CD8+ T lymphocytes from peripheral blood mononuclear cells (PBMC) of a healthy donor and autologous peptide-pulsed dendritic cells as antigen-presenting cells. This approach enabled us to identify 2 peptides, QYSWFVNGTF and TYACFVSNL, which were capable of eliciting CTL lines that lysed tumor cells expressing HLA-A24 and CEA. The cytotoxicity to tumor cells by the CTL lines was antigen-specific since it was inhibited by peptide-pulsed cold target cells as well as by anti-class I major histocompatibility complex (MHC) and anti-CD3 monoclonal antibodies (MAbs). The antigen specificity of the 2 CTL lines was examined using several tumor cell lines of various origins and for their peptide-dose responses. The identification of these novel CEA epitopes for CTL offers the opportunity to design and develop epitope-based immunotherapeutic approaches for treating HLA-A24+ patients with tumors that express CEA.

Identification of HLA-A3-restricted cytotoxic T lymphocyte epitopes from carcinoembryonic antigen and HER-2/neu by primary in vitro immunization with peptide-pulsed dendritic cells

The human carcinoembryonic antigen (CEA) and HER-2/neu are potential target antigens for CTL specific immunotherapy for common malignancies such as breast, lung, colon, and gastric carcinomas. Several CTL epitopes restricted by HLA-A2, the most common human histocompatibility molecule, have been previously reported. However, to develop CTL-based immunotherapies for the general population, it is necessary to identify epitopes restricted by other common histocompatibility alleles. Here, we describe two HLA-A3-restricted CTL epitopes from the CEA and HER-2/neu antigens. HLA-A3 binding synthetic peptides from CEA and HER-2/neu were tested for immunogenicity by in vitro primary CTL induction protocol using peripheral blood mononuclear cells from normal healthy volunteers. One peptide from CEA (CEA[9(61)]: HLFGYSWYK) and one peptide from HER-2/neu (HER2[9(754)]: VLRENTSPK) were shown to induce CTL that was capable of killing a tumor cell line expressing HLA-A3 and the corresponding tumor-associated antigen. Additional MHC binding studies with the most common HLA molecules belonging to the HLA-A3 superfamily (HLA-A*1101, -A*3101, -A*3301, and -A*6801), demonstrated that CEA[9(61)] binds five of five A3 supertype molecules with high affinity, and the HER2[9(754)] epitope was able to bind to four of the same five alleles. These results indicate that these two new CTL epitopes should be immunogenic in individuals expressing either HLA-A3, or other members of the HLA-A3 superfamily.

Identification of HLA-A24 epitope peptides of carcinoembryonic antigen which induce tumor-reactive cytotoxic T lymphocyte

Carcinoembryonic antigen (CEA), which is expressed in several cancer types, is a potential target for specific immunotherapy. HLA-A24 is the most frequent allele among Japanese and is also frequently present in Asians and Caucasians. We tested CEA-encoded HLA-A24 binding peptides for their capacity to elicit anti-tumor cytotoxic T lymphocytes (CTL) in vitro. For this purpose, we used CD8+ T lymphocytes from peripheral blood mononuclear cells (PBMC) of a healthy donor and autologous peptide-pulsed dendritic cells as antigen-presenting cells. This approach enabled us to identify 2 peptides, QYSWFVNGTF and TYACFVSNL, which were capable of eliciting CTL lines that lysed tumor cells expressing HLA-A24 and CEA. The cytotoxicity to tumor cells by the CTL lines was antigen-specific since it was inhibited by peptide-pulsed cold target cells as well as by anti-class I major histocompatibility complex (MHC) and anti-CD3 monoclonal antibodies (MAbs). The antigen specificity of the 2 CTL lines was examined using several tumor cell lines of various origins and for their peptide-dose responses. The identification of these novel CEA epitopes for CTL offers the opportunity to design and develop epitope-based immunotherapeutic approaches for treating HLA-A24+ patients with tumors that express CEA.

Role of preimmunization virus sequences in cellular immunity in HIV-infected patients during HIV type 1 MN recombinant gp160 immunization

The effect of patient preimmunization virus sequences on CTL responses during gp160 immunization were studied. Ten HLA-A2+, HIV+ asymptomatic patients with CD4+ T cells >500/mm3 were given two courses of HIV-1 MN rgp160 vaccine over a 2-year period. Envelope epitope-specific CTL responses, using PBMCs, were measured against peptide-coated autologous B lymphoblastoid cell lines. Optimum CTL epitopes were determined by HLA-A2-binding affinity of 9- to 10-mer peptides containing the HLA-A2.1-binding motif. Ten of the high- or intermediate-binding peptides were conserved among >50% of reported clade B HIV strains. These peptide-specific CTL activities and the patient virus sequences in peptide-coding regions were monitored. Six patients showed envelope peptide-specific CTL responses, which correlated with the presence of whole envelope antigen-specific CTL responses. Five of these patients, who showed responses to epitopes in the gp41 region (aa 814-824), had preimmunization virus similar to the vaccine sequence in this region. Three patients who did not show these epitope-specific responses had initially different sequences in the HIV gene encoding that region. The epitope-specific CTL responses appear to reflect recall responses, as only patients infected with virus containing the vaccine sequence developed them and they could be recalled with a second set of vaccine injections. This appears to be reminiscent of the concept of T cell "original antigenic sin." This vaccine was also immunogenic as measured by gp160-specific lymphocyte-proliferative responses. However, increased immune responses did not impact the HIV load or CTL epitope sequences during therapy.

HLA-independent heterogeneity of CD8+ T cell responses to MAGE-3, Melan-A/MART-1, gp100, tyrosinase, MC1R, and TRP-2 in vaccine-treated melanoma patients

An important element in melanoma vaccine construction is to identify peptides from melanoma-associated Ags that have immunogenic potential in humans and are recognized by CD8+ T cells in vivo. To identify such peptides, we evaluated HLA-A*02+ melanoma patients immunized to a polyvalent vaccine containing multiple Ags, including MAGE-3, Melan-A/MART-1, gp100, tyrosinase, melanocortin receptor (MC1R), and dopachrome tautomerase (TRP-2). Using a filter spot assay, we measured peripheral blood CD8+ T cell responses, before and after immunization, to a panel of 45 HLA-A*0201-restricted peptides derived from these Ags. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*0201. Vaccine treatment induced peptide-specific CD8+ T cell responses to 22 (47.8%) of the peptides. The most striking finding was the HLA-independent heterogeneity of responses to both peptides and Ags. All responding patients reacted to different combination of peptides and Ags even though the responding patients were all A*0201+ and the peptides were all A*0201-restricted. From 9 to 27% of patients developed a CD8+ T cell response to at least one peptide from each Ag, but no more than 3 (14%) reacted to the same peptide from the same Ag. This heterogeneity of responses to individual peptides and Ags in patients with the same haplotype points to the need to construct vaccines of multiple peptides or Ags to maximize the proportion of responding patients.

HLA-Independent Heterogeneity of CD8+ T Cell Responses to MAGE-3, Melan-A/MART-1, gp100, Tyrosinase, MC1R, and TRP-2 in Vaccine-Treated Melanoma Patients

An important element in melanoma vaccine construction is to identify peptides from melanoma-associated Ags that have immunogenic potential in humans and are recognized by CD8+ T cells in vivo. To identify such peptides, we evaluated HLA-A*02+ melanoma patients immunized to a polyvalent vaccine containing multiple Ags, including MAGE-3, Melan-A/MART-1, gp100, tyrosinase, melanocortin receptor (MC1R), and dopachrome tautomerase (TRP-2). Using a filter spot assay, we measured peripheral blood CD8+ T cell responses, before and after immunization, to a panel of 45 HLA-A*0201-restricted peptides derived from these Ags. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*0201. Vaccine treatment induced peptide-specific CD8+ T cell responses to 22 (47.8%) of the peptides. The most striking finding was the HLA-independent heterogeneity of responses to both peptides and Ags. All responding patients reacted to different combination of peptides and Ags even though the responding patients were all A*0201+ and the peptides were all A*0201-restricted. From 9 to 27% of patients developed a CD8+ T cell response to at least one peptide from each Ag, but no more than 3 (14%) reacted to the same peptide from the same Ag. This heterogeneity of responses to individual peptides and Ags in patients with the same haplotype points to the need to construct vaccines of multiple peptides or Ags to maximize the proportion of responding patients.

Identification of gp100-derived, melanoma-specific cytotoxic T-lymphocyte epitopes restricted by HLA-A3 supertype molecules by primary in vitro immunization with peptide-pulsed dendritic cells

The human melanocyte lineage-specific antigen gp100 contains several epitopes recognized by cytotoxic T lymphocytes (CTL). However, most of the epitopes reported to date are HLA-A2.1-restricted. Despite the high frequency of HLA-A2.1 in melanoma patients, effective population coverage requires the identification of epitopes restricted by other frequent HLA alleles. Herein, HLA-A3 binding, gp100-derived synthetic peptides were tested for their capacity to elicit anti-melanoma CTL in vitro using CD8+ T cells from healthy donors as responders and peptide-pulsed autologous dendritic cells as antigen-presenting cells. Of 7 peptides tested, 2 (gp100[9(87)] and gp100[10(86)]) induced CTLs that killed melanoma cell lines expressing HLA-A3 and gp100. Additional MHC-binding studies to various HLA molecules belonging to the HLA-A3 superfamily (HLA-A*1101, -A*3101, -A*3301 and -A*6801) were performed to determine whether these CTL epitopes could further increase potential population coverage. Further experiments indicated that the peptide gp100[9(87)], which bound to HLA-A11 with high affinity, was capable of inducing specific CTLs that killed melanoma cells expressing gp100 and HLA-A11 molecules. Our results indicate that the gp100[9(87)] peptide corresponds to a CTL epitope which may be restricted by either the HLA-A3 or HLA-A11 allele, emphasizing its utility for the design and development of epitope-based therapies for melanoma.

Identification of HER2/neu-derived peptide epitopes recognized by gastric cancer-specific cytotoxic T lymphocytes

We have derived HLA-A2.1-restricted, gastric cancer-specific cytotoxic T lymphocyte (CTL) lines by repetitive in vitro stimulation of tumor-associated lymphocytes (TAL) with autologous tumor cells. The HER2/neu specificity of these gastric cancer-specific CTLs was demonstrated using HER2/neu-transfected cell lines and HER2/neu-expressing tumors, and with a set of HER2/neu-derived peptide epitopes. Gastric cancer-specific CTLs specifically lysed autologous and allogeneic HLA-A2.1+, HER2/neu+ gastric cancer cells, HER2/neu-transfected C1R/A2 cell lines (HLA-A2.1+, HER2+) and HLA-A2.1-transfected SW626 tumor cell lines (HLA-A2.1+, HER2+). This recognition could be inhibited by anti-HLA-A2 antibody or by cold target HER2/neu-transfected C1R/A2 cells. Our results demonstrate that the HER2/neu-encoded HLA-A2.1-associated epitopes recognized by CTLs are presented as naturally processed peptides on gastric cancer lines. Furthermore, 3 of 19 tested HER2/neu-derived peptide epitopes [HER2(9(106)), HER2(9(369)), HER2(9(689))], which all bound HLA-A2.1 with high (IC50 < 50 nM) affinity, were able to sensitize HLA-A2+ C1R/A2 cells to be recognized by the gastric cancer-specific CTLs, demonstrating the immunodominance of these epitopes. In conclusion, our findings implicate HER2/neu-derived epitopes as potential candidates for novel immunotherapy and vaccine strategies against gastric cancer.

Identification of HER2/neu-derived peptide epitopes recognized by gastric cancer-specific cytotoxic T lymphocytes

We have derived HLA-A2.1-restricted, gastric cancer-specific cytotoxic T lymphocyte (CTL) lines by repetitive in vitro stimulation of tumor-associated lymphocytes (TAL) with autologous tumor cells. The HER2/neu specificity of these gastric cancer-specific CTLs was demonstrated using HER2/neu-transfected cell lines and HER2/neu-expressing tumors, and with a set of HER2/neu-derived peptide epitopes. Gastric cancer-specific CTLs specifically lysed autologous and allogeneic HLA-A2.1+, HER2/neu+ gastric cancer cells, HER2/neu-transfected C1R/A2 cell lines (HLA-A2.1+, HER2+) and HLA-A2.1-transfected SW626 tumor cell lines (HLA-A2.1+, HER2+). This recognition could be inhibited by anti-HLA-A2 antibody or by cold target HER2/neu-transfected C1R/A2 cells. Our results demonstrate that the HER2/neu-encoded HLA-A2.1-associated epitopes recognized by CTLs are presented as naturally processed peptides on gastric cancer lines. Furthermore, 3 of 19 tested HER2/neu-derived peptide epitopes [HER2(9(106)), HER2(9(369)), HER2(9(689))], which all bound HLA-A2.1 with high (IC50 < 50 nM) affinity, were able to sensitize HLA-A2+ C1R/A2 cells to be recognized by the gastric cancer-specific CTLs, demonstrating the immunodominance of these epitopes. In conclusion, our findings implicate HER2/neu-derived epitopes as potential candidates for novel immunotherapy and vaccine strategies against gastric cancer.

Cell-mediated immunological responses in cervical and vaginal cancer patients immunized with a lipidated epitope of human papillomavirus type 16 E7

Human papillomavirus (HPV) infection has been causally associated with cervical cancer. We tested the effectiveness of an HLA-A*0201-restricted, HPV-16 E7 lipopeptide vaccine in eliciting cellular immune responses in vivo in women with refractory cervical cancer. In a nonrandomized Phase I clinical trial, 12 women expressing the HLA-A2 allele with refractory cervical or vaginal cancer were vaccinated with four E786-93 lipopeptide inoculations at 3-week intervals. HLA-A2 subtyping was also performed, and HPV typing was assessed on tumor specimens. Induction of epitope-specific CD8+ T-lymphocyte (CTL) responses was analyzed using peripheral blood leukapheresis specimens obtained before and after vaccination. CTL specificity was measured by IFN-gamma release assay using HLA-A*0201 matched target cells. Clinical responses were assessed by physical examination and radiographic images. All HLA-A*0201 patients were able to mount a cellular immune response to a control peptide. E786-93-specific CTLs were elicited in 4 of 10 evaluable HLA-A*0201 subjects before vaccination, 5 of 7 evaluable HLA-A*0201 patients after two vaccinations, and 2 of 3 evaluable HLA-A*0201 cultures after all four inoculations. Two of three evaluable patients' CTLs converted from unreactive to reactive after administration of all four inoculations. There were no clinical responses or treatment toxicities. The ability to generate specific cellular immune responses is retained in patients with advanced cervical cancer. Vaccination with a lipidated HPV peptide epitope appears capable of safely augmenting CTL reactivity. Although enhancements of cellular immune responses are needed to achieve therapeutic utility in advanced cervical cancer, this approach might prove useful in treating preinvasive disease.

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.

In vitro immunization and expansion of antigen-specific cytotoxic T lymphocytes for adoptive immunotherapy using peptide-pulsed dendritic cells

The design of an effective procedure to sensitize and expand antigen-specific cytotoxic T lymphocytes (CTL) in vitro is essential for the development of effective adoptive cellular immunotherapy protocols for cancer. We have analyzed the capacity of tissue culture-derived dendritic cells (DC) to present specific peptide epitopes to CTL precursors. Our results demonstrate that peptide-pulsed DC were efficient in generating CTL responses specific for various viral and tumor epitopes. Furthermore, IL-7 and IL-10 potentiated the ability of the peptide-pulsed DC to trigger antigen-specific CTL responses. The CTL generated using this procedure efficiently recognized the naturally processed antigens and could be expanded approximately 100- to 1000-fold in tissue culture in 10 to 15 days without a loss of activity and specificity. The results and procedures described herein may facilitate the development of effective CTL-based adoptive immunotherapy for chronic viral diseases and cancer.

Specific T cell recognition of peptides derived from prostate-specific antigen in patients with prostate cancer

OBJECTIVES

To determine if proteins known to be expressed by both benign and malignant prostate epithelium can be recognized by T cells from patients with prostate cancer. We examined 7 HLA-A2 patients with prostate cancer for evidence of T cell reactivity with prostate-specific antigen (PSA).

METHODS

Four peptides derived from PSA were chemically synthesized and shown to bind to HLA-A2. As a control, we also examined the immunogenic influenza matrix peptide Flu58-66 that binds to HLA-A2. These peptides were used to stimulate peripheral blood lymphocytes by in vitro stimulation.

RESULTS

In 1 patient, specific recognition of peptide PSA141-150 was observed. The remaining 6 patients had no reactivity with any PSA-derived peptide. The T cell line with specific recognition of peptide PSA141-150 failed to recognize an autologous B cell blast line expressing endogenous PSA following infection with a recombinant PSA vaccinia virus construct. Three of the 7 patients demonstrated specific reactivity with Flu58-66.

CONCLUSIONS

We found specific recognition of one PSA-derived peptide in 1 patient of 7 with prostate cancer. The peptide-specific lymphocyte cell line did not recognize endogenous PSA, suggesting that the peptide may not be produced by prostate cancer cells producing PSA. Specific recognition of PSA peptides was not common in our patients with prostate cancer. Whether such activity can be induced by vaccination strategies or can be therapeutic in men with established prostate cancer remains to be demonstrated.

The multi-epitope approach for immunotherapy for cancer: identification of several CTL epitopes from various tumor-associated antigens expressed on solid epithelial tumors

One approach to development of specific cancer immunotherapy relies on the induction of cytotoxic T lymphocytes (CTL) specific for tumor-associated antigens (TAA). Induction of TAA-specific CTL could be used towards the eradication of established tumors, or to prevent their dissemination or recurrence after primary treatment. The present study identifies a set of CTL epitopes from TAA frequently found on solid epithelial tumors such as breast, lung and gastro-intestinal tumors. Specifically, HLA-A2.1 binding peptides from the MAGE2, MAGE3, HER-2/neu and CEA antigens were tested for their capacity to elicit in vitro anti-tumor CTL using lymphocytes from normal volunteers and autologous dendritic cells as antigen-presenting cells. A total of 6 new epitopes (MAGE2[10(157)], MAGE3[9(112)], CEA[9(691)], CEA[9(24)], HER2[9(435)] and HER2[9(5)]) were identified which were capable of specifically recognizing tumor cell lines lines expressing HLA-A2.1 and the corresponding TAA. In one case (CEA[9(24)]), induction of vigorous anti-tumor CTL responses required epitope engineering to increase HLA-A2.1 binding affinity. Finally, most of the newly identified epitopes (5 out of 6) were found to be highly crossreactive with other common HLA alleles of the A2 supertype (A2.2, A2.3, A2.6 and A6802), thus demonstrating their potential in providing broad and non-ethnically biased population coverage. The results are discussed in the context of the development of multi-epitope-based therapies with broad applicability for patients suffering from commonly found tumors.

Synthetic antigenic peptides as a new strategy for immunotherapy of cancer

Antigens presented by class I of the major histocompatibility complex (MHC) are recognised by the T cell receptor of CD8+ cytolytic effector cells (CTLs), while class II molecules present antigens to CD4+ helper T cells. For both class I and class II molecules, structure and function are linked through the binding of peptides. Consensus or individual sequences have been obtained for naturally processed peptides bound to a variety of class I and class II molecules, revealing the general features of peptides associated with MHC molecules. The interactions between peptides and MHC molecules have been more clearly defined by the characterization of the three dimensional structure of several different MHC molecules. CTLs have been implicated in immune responses against tumors and it is now well documented that some human tumors express specific antigens, which are recognised by CTLs and could potentially be used in immunotherapy protocols. The use of antigenic peptides to elicit a specific and effective CTL response in vivo offers several advantages over the use of other antigenic moieties. Emerging strategies for the safe and effective administration of peptides to humans may lead to their use in the immunological prevention and treatment of cancer.

Induction of antitumor cytotoxic T lymphocytes with a MAGE-3-encoded synthetic peptide presented by human leukocytes antigen-A24

For the development of immunotherapy using MAGE peptides, the identification of additional tumor antigens is required. Because HLA-A24 is the most common allele in Japanese and is also frequently present in Caucasians, MAGE-3-encoded synthetic peptides with binding affinity for HLA-A24 were thus tested for the induction of specific CTLs from the peripheral blood mononuclear cells (PBMCs) of HLA-A24 healthy donors using a simplified method. By using a peptide with a sequence of IMPKAGLLI (amino acid position in MAGE-3 195-203), the CTL responses could thus be induced from unseparated PBMCs by stimulation with freshly isolated, peptide-pulsed PBMCs as antigen-presenting cells (APCs) and by also using interleukin 7 and keyhole limpet hemocyanin for a primary culture. The induced CTLs could lyse HLA-A24 carcinoma cells expressing MAGE-3, as well as the peptide-pulsed target cells, in an HLA class-I restricted manner. The identification of the MAGE-3/HLA-A24 peptide, IMPKAGLLI, may thus potentially offer the opportunities to design peptide-based immunotherapeutic approaches that might prove to be effective in treating patients with MAGE-3-positive malignant tumors.

Synthetic peptides derived from the melanocyte-stimulating hormone receptor MC1R can stimulate HLA-A2-restricted cytotoxic T lymphocytes that recognize naturally processed peptides on human melanoma cells

Human melanoma-specific HLA-A2 restricted CTLs have recently been shown to recognize antigens expressed by melanoma lines and normal melanocytes, including Melan-A/Mart-1, gp100, gp75, and tyrosinase. Herein, we define HLA-A2-restricted CTL epitopes from a recently cloned melanocortin 1 receptor (MC1R), which belongs to a new subfamily of the G-protein-coupled receptors expressed on melanomas and melanocytes. Thirty-one MC1R-derived peptides were selected on the basis of HLA-A2-specific motifs and tested for their HLA-A2 binding capacity. Of a group of 12 high or intermediate HLA-A2 binding peptides, three nonamers, MC1R244 (TILLGIFFL), MC1R283 (FLALIICNA), and MC1R291 (AIIDPLIYA), were found to induce peptide-specific CTLs from peripheral blood mononuclear cells of healthy HLA-A2+ donors after repeated in vitro stimulation with peptide-pulsed antigen-presenting cells. The CTLs raised against these three HLA-A2+-restricted peptides could recognize naturally processed peptides from HLA-A2+ melanomas and from Cos7 cells cotransfected with MC1R and HLA-A2. CTLs induced by the MC1R291 peptide (but not induced or induced only to a very low extent by the other two MCR1 peptide epitopes) showed cross-reactions with two other members of the melanocortin receptor family, which are more broadly expressed on other tissues. Taken together, our findings have implications in relation both to autoimmunity and immunotherapy of malignant melanomas.

Identification of subdominant CTL epitopes of the GP100 melanoma-associated tumor antigen by primary in vitro immunization with peptide-pulsed dendritic cells

The gp100 melanoma-associated tumor Ag was selected as a model system to study the diversity of human antitumor cytotoxic T cell responses. First, peptides corresponding to dominant gp100 HLA-A2.1-restricted CTL epitopes were tested using lymphocytes from normal volunteers and an in vitro priming protocol that uses peptide-pulsed dendritic cells as APCs and IL-7 and IL-10 as immune-enhancing cytokines. High CTL activity toward both peptide-pulsed target cells and gp100+ melanoma cells was obtained with four out of five peptides tested. Second, HLA-A2.1-binding peptides from gp100 that do not appear to represent CTL epitopes in melanoma patients were also tested for their capacity to induce CTL using the in vitro priming protocol. Three of six peptides tested induced CTL in lymphocytes from normal volunteers. One of these peptides was also immunogenic for lymphocytes derived from a melanoma patient in remission. Because these three CTL epitopes were not recognized in the natural immune response in melanoma patients but do appear as immunogens when peptides are used to induce the T cell response, they may be considered as typical "subdominant" epitopes. The results are discussed in the context of the usefulness of this approach to detail the immunologic potential of a given tumor-associated Ag and its relevance for the design of effective immune-based therapies.

Identification of subdominant CTL epitopes of the GP100 melanoma-associated tumor antigen by primary in vitro immunization with peptide-pulsed dendritic cells

The gp100 melanoma-associated tumor Ag was selected as a model system to study the diversity of human antitumor cytotoxic T cell responses. First, peptides corresponding to dominant gp100 HLA-A2.1-restricted CTL epitopes were tested using lymphocytes from normal volunteers and an in vitro priming protocol that uses peptide-pulsed dendritic cells as APCs and IL-7 and IL-10 as immune-enhancing cytokines. High CTL activity toward both peptide-pulsed target cells and gp100+ melanoma cells was obtained with four out of five peptides tested. Second, HLA-A2.1-binding peptides from gp100 that do not appear to represent CTL epitopes in melanoma patients were also tested for their capacity to induce CTL using the in vitro priming protocol. Three of six peptides tested induced CTL in lymphocytes from normal volunteers. One of these peptides was also immunogenic for lymphocytes derived from a melanoma patient in remission. Because these three CTL epitopes were not recognized in the natural immune response in melanoma patients but do appear as immunogens when peptides are used to induce the T cell response, they may be considered as typical "subdominant" epitopes. The results are discussed in the context of the usefulness of this approach to detail the immunologic potential of a given tumor-associated Ag and its relevance for the design of effective immune-based therapies.

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.

Generation of tumor-specific cytolytic T lymphocytes from peripheral blood of cervical cancer patients by in vitro stimulation with a synthetic human papillomavirus type 16 E7 epitope

OBJECTIVE

Approximately 90% of squamous carcinomas of the cervix harbor the human papillomavirus and type 16 has been detected in nearly 50% of cases. Recent studies in mice have shown that the human papillomavirus type 16 E7 oncoprotein contains peptide epitopes that are processed and presented in association with a major histocompatibility antigen for recognition by cytolytic T lymphocytes. We investigated whether an epitope from human papillomavirus type 16 E7 could be used to generate specific human cytolytic T lymphocytes in patients with cervical carcinoma.

STUDY DESIGN

After radiation therapy, three patients with antigen HLA-A2 and with locally advanced cervical cancer underwent leukapheresis. Epitope-specific cytolytic T lymphocytes were generated from the peripheral blood mononuclear cells by in vitro stimulation with autologous peripheral blood mononuclear cells pulsed with a human papillomavirus type 16 E7, HLA-A2-restricted, synthetic peptide, E7(11-20) (YMLDLQPETT).

RESULTS

In two patients cytolytic T lymphocytes were capable of E7(11-20)-specific, HLA-A2-restricted cytolysis of the peptide-pulsed, HLA-matched, T2 target cell line. Cytolytic T lymphocytes from one of these patients also demonstrated specific cytolysis against the HLA-A2+, HPV-16+ CaSki cervical cancer cell line but did not lyse either HLA-A2+, HPV-16- MS-751 cells or HLA-A2-, HPV-16- HT-3 cells.

CONCLUSIONS

These experiments demonstrate that novel cytolytic T lymphocytes that recognize a human papillomavirus type 16 E7 epitope can be generated by using the peripheral blood mononuclear cells from irradiated patients with cervical cancer. In addition, because CaSki cells were specifically lysed by the cytolytic T lymphocytes, these data indicate that the peptide E7(11-20) is endogenously processed and presented on the cell surface of the CaSki cells. The demonstration of epitope-specific lysis of cytolytic T lymphocytes of HPV-16+ cervical cancer cells supports further efforts to develop human papillomavirus peptide-based vaccines or antigen-specific adoptive immunotherapy for the prevention and treatment of cervical carcinoma.

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.

Substitutions in the HLA-DR alpha chain differentially affect DR7-restricted T-cell recognition of rabies virus antigen

To investigate the functional roles of DR alpha residues in T-cell recognition, 20 mutants of the DR alpha chain were constructed by site-directed mutagenesis. These DR alpha mutants were expressed with WT DR(beta 1*0701) on mouse L cells and used as APC for four DR7-restricted T-cell clones specific for rabies virus antigens. The results indicate that the DR alpha residues are differentially involved in recognition of rabies virus antigen by different T-cell clones. Mutations in the floor of the antigen-binding groove (positions 9, 11, 22, and 24), on the alpha-helix (47, 55, 65, 66, and 72), and surprisingly on the outer loop (15, 18, and 19), abrogated recognition by at least one T-cell clone. Most of these residues appear to be involved in either peptide or TCR contact, based on the DR1 crystal structure. The involvement in T-cell recognition of DR alpha residues located in the outer loop outside the binding groove suggests that these residues may directly contact TCR, or indirectly contribute to the conformation of peptide sitting in the groove.

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.

Occasional memory cytotoxic T-cell responses of patients with human papillomavirus type 16-positive cervical lesions against a human leukocyte antigen-A *0201-restricted E7-encoded epitope

Most cervical carcinoma (Cxca) cells constitutively express human papillomavirus type 16 (HPV16) E6 and E7 oncoproteins. These proteins are, therefore, attractive targets for T cell-based immunotherapy. Previously, we identified HVP16 E7-encoded CTL epitopes. In patients with cervical intraepithelial neoplasia or Cxca, little is known concerning T-cell activity against viruses in general and against HPV16 in particular. Here, we have screened the blood of 10 healthy donor controls and of 22 patients with HPV16+ cervical lesions for the presence of CTLs directed against HPV16 E7- and control influenza virus matrix-derived epitopes presented by HLA-A *0201. We detected influenza virus-specific CTLs in all donors and in the majority of patients, indicating that most patients have functioning T-cell responses despite their lesions or therapeutic interventions. Moreover, we show that patients with HPV16+ lesions occasionally have memory CTLs against a HPV16 E7-encoded epitope (sequence YMLD-LQPETT), providing evidence for natural CTL immunity against HPV16 in patients with cervical lesions. Combined, these findings raise possibilities for vaccination with HPV16 E7-encoded peptides to induce or augment CTL responses for treatment or prevention of Cxca.

Epitope selection and development of peptide based vaccines to treat cancer

Cytotoxic T lymphocytes recognize peptides that associate with class I major histocompatibility complex molecules. Since cytotoxic T cells have the capacity to recognize and destroy tumor cells, identification of epitopes recognized by these cells in tumor-associated antigens would allow the production of compounds for the treatment of cancer. Here we review some of the approaches being explored to identify tumor-associated antigens and to develop peptide-based vaccines that induce cytotoxic T lymphocytes against specific tumors.

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.

Patients with chronic hepatitis C have circulating cytotoxic T cells which recognize hepatitis C virus-encoded peptides binding to HLA-A2.1 molecules

Antiviral cytotoxic T lymphocytes (CTL) may play a role in clearance of hepatitis C virus (HCV)-infected cells and thereby cause hepatocellular injury during acute and chronic HCV infection. The aim of this study was to identify HLA-A2.1-restricted HCV T-cell epitopes and to evaluate whether anti-HCV-specific CTL are present during chronic hepatitis C. Peripheral blood mononuclear cells from four HLA-A2-positive patients with chronic hepatitis C and from two individuals after recovery from HCV infection were tested against a panel of HCV-encoded peptides derived from different regions of the genome, including some peptides containing HLA-A2.1 binding motifs. HLA-A2-negative patients with chronic hepatitis C as well as healthy HLA-A2-positive (anti-HCV-negative) donors served as controls. Peripheral blood mononuclear cells stimulated repeatedly with several HCV-encoded peptides (three in core, one in NS4B, and one in NS5B) yielded cytolytic responses. All four HLA-A2-positive patients with active infection had CTL specific for at least one of the identified epitopes, whereas two patients who had recovered from HCV infection had almost no CTL responses. Monoclonal antibody blocking experiments performed for two epitopes demonstrated a class I- and HLA-A2-restricted CTL response. CTL epitopes could partially be predicted by HLA-A2 binding motifs and more reliably by quantitative HLA-A2.1 molecule binding assays. Most of the identified epitopes could also be produced via the endogenous pathway. Specific CTL against multiple, mostly highly conserved epitopes of HCV were detected during chronic HCV infection. This finding may be important for further investigations of the immunopathogenesis of HCV, the development of potential therapies against HCV on the basis of induction or enhancement of cellular immunity, and the design of vaccines.

Analysis of MHC-specific peptide motifs. Applications in immunotherapy

The structural features which underlie peptide binding to MHC molecules permit the binding of a diverse array of peptides. Polymorphic residues of class I, and to a lesser extent, class II molecules, determine the peptide selectivities associated with various allomorphs. The motifs which are described here and elsewhere in the literature mainly reflect peptide features which contribute to high affinity binding. While high affinity MHC binding is not an absolute prerequisite for the immunologic relevance of a peptide, motifs provide general guidelines for eliciting and characterizing cellular responses to epitopes presented by a given MHC allomorph or group of related allomorphs. The utility of motifs is underscored by emerging developments in the clinical application of peptides to elicit specific and effective cellular responses.