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Vaccines consisting of synthetic peptides representing cytotoxic T-lymphocyte (CTL) epitopes have long been considered as a simple and cost-effective approach to treat cancer. However, the efficacy of these vaccines in the clinic in patients with measurable disease remains questionable. We believe that the poor performance of peptide vaccines is due to their inability to generate sufficiently large CTL responses that are required to have a positive impact against established tumors. Peptide vaccines to elicit CTLs in the clinic have routinely been administered in the same manner as vaccines designed to induce antibody responses: injected subcutaneously and in many instances using Freund's adjuvant. We report here that peptide vaccines and poly-ICLC adjuvant administered via the unconventional intravenous route of immunization generate substantially higher CTL responses as compared to conventional subcutaneous injections, resulting in more successful antitumor effects in mice. Furthermore, amphiphilic antigen constructs such as palmitoylated peptides were shown to be better immunogens than long peptide constructs, which now are in vogue in the clinic. The present findings if translated into the clinical setting could help dissipate the wide-spread skepticism of whether peptide vaccines will ever work to treat cancer. [ABSTRACT FROM AUTHOR]

Cytotoxic T lymphocytes (CTLs) are effective components of the immune system capable of destroying tumor cells. Generation of CTLs using peptide vaccines is a practical approach to treat cancer. We have previously described a peptide vaccination strategy that generates vast numbers of endogenous tumor-reactive CTLs after two sequential immunizations (prime-boost) using poly-ICLC adjuvant, which stimulates endosomal toll-like receptor 3 (TLR3) and cytoplasmic melanoma differentiation antigen 5 (MDA5). Dendritic cells (DCs) play an important role not only in antigen presentation but are critical in generating costimulatory cytokines that promote CTL expansion. Poly-ICLC was shown to be more effective than poly-IC in generating type-I interferon (IFN-I) in various DC subsets, through its enhanced ability to escape the endosomal compartment and stimulate MDA5. In our system, IFN-I did not directly function as a T cell costimulatory cytokine, but enhanced CTL expansion through the induction of IL15. With palmitoylated peptide vaccines, CD8α+ DCs were essential for peptide crosspresentation. For vaccine boosts, non-professional antigen-presenting cells were able to present minimal epitope peptides, but DCs were still required for CTL expansions through the production of IFN-I mediated by poly-ICLC. Overall, these results clarify the roles of DCs, TLR3, MDA5, IFN-I and IL15 in the generation of vast and effective antitumor CTL responses using peptide and poly-IC vaccines. [ABSTRACT FROM AUTHOR]

The design of efficacious and cost-effective therapeutic vaccines against cancer remains both a research priority and a challenge. For more than a decade, our laboratory has been involved in the development of synthetic peptide-based anti-cancer therapeutic vaccines. We first dedicated our efforts in the identification and validation of peptide epitopes for both CD8 and CD4 T cells from tumor-associated antigens (TAAs). Because of suboptimal immune responses and lack of therapeutic benefit of peptide vaccines containing these epitopes, we have focused our recent efforts in optimizing peptide vaccinations in mouse tumor models using numerous TAA epitopes. In this focused research review, we describe how after taking lessons from the immune system's way of dealing with acute viral infections, we have designed peptide vaccination strategies capable of generating very high numbers of therapeutically effective CD8 T cells. We also discuss some of the remaining challenges to translate these findings into the clinical setting. [ABSTRACT FROM AUTHOR]

Background: The impacts of patient age and gender on immune response (IR) and clinical outcome after cancer vaccines are not known. We hypothesized younger and female patients would have higher IR rates and better survival. Methods: Patients with resected stage IIB-IV melanoma in three clinical trials (Mel43, Mel44, Mel48) were vaccinated with 12 melanoma-associated peptides restricted by class I MHC. The cumulative incidence rate of CD8 T cell responses (direct interferon-gamma ELIspot assay) by week 7 was compared by age and gender. Overall survival (OS) and disease-free survival (DFS) landmark analyses were compared by Kaplan-Meier estimates and in multivariate analyses. Results: T cell responses were evaluated in 327 patients and detected in 50 % of males and 48 % of females, with no difference in IR by gender or menopausal status. Males had trends toward longer DFS ( p = 0.12) and OS ( p = 0.09). Cumulative incidence of IR was higher in patients <64 years of age versus older patients ( p = 0.03). OS and DFS were similar by age group ( p > 0.50). In multivariate modeling, younger age was associated with better IR (OR 0.40, p value 0.003), without an impact of age or gender on clinical outcomes. Conclusion: These data support the hypothesis that older patients are less likely to develop T cell responses to a cancer vaccine. Nonetheless, significant proportions of older patients mount immune responses with comparable survival outcomes. Thus, these data support including older patients in cancer vaccine trials, but suggest value in stratifying patients by age 64 years. [ABSTRACT FROM AUTHOR]

Therapeutic vaccines to induce anti-tumor CD8 T cells have been used in clinical trials for advanced melanoma patients, but the clinical response rate and overall survival time have not improved much. We believe that these dismal outcomes are caused by inadequate number of antigen-specific CD8 T cells generated by most vaccines. In contrast, huge CD8 T cell responses readily occur during acute viral infections. High levels of type-I interferon (IFN-I) are produced during these infections, and this cytokine not only exhibits anti-viral activity but also promotes CD8 T cell responses. The studies described here were performed to determine whether promoting the production of IFN-I could enhance the potency of a peptide vaccine. We report that cyclic diguanylate monophosphate (c-di-GMP), which activates the stimulator of interferon genes, potentiated the immunogenicity and anti-tumor effects of a peptide vaccine against mouse B16 melanoma. The synergistic effects of c-di-GMP required co-administration of costimulatory anti-CD40 antibody, the adjuvant poly-IC, and were mediated in part by IFN-I. These findings demonstrate that peptides representing CD8 T cell epitopes can be effective inducers of large CD8 T cell responses in vaccination strategies that mimic acute viral infections. [ABSTRACT FROM AUTHOR]

Immunization with a combination melanoma helper peptide (6MHP) vaccine has been shown to induce CD4 T cell responses, which are associated with patient survival. In the present study, we define the relative immunogenicity and HLA allele promiscuity of individual helper peptides and identify helper peptide-mediated augmentation of specific CD8 T cell responses. Thirty-seven participants with stage IIIB-IV melanoma were vaccinated with 6MHP in incomplete Freund's adjuvant. The 6MHP vaccine is comprised of 6 peptides representing melanocytic differentiation proteins gp100, tyrosinase, Melan-A/MART-1, and cancer testis antigens from the MAGE family. CD4 and CD8 T cell responses were assessed in peripheral blood and in sentinel immunized nodes (SIN) by thymidine uptake after exposure to helper peptides and by direct interferon-γ ELIspot assay against 14 MHC class I-restricted peptides. Vaccine-induced CD4 T cell responses to individual epitopes were detected in the SIN of 63 % (22/35) and in the peripheral blood of 38 % (14/37) of participants for an overall response rate of 65 % (24/37). The most frequently immunogenic peptides were MAGE-A3 (49 %) and tyrosinase (32 %). Responses were not limited to HLA restrictions originally described. Vaccine-associated CD8 T cell responses against class I-restricted peptides were observed in 45 % (5/11) of evaluable participants. The 6MHP vaccine induces both CD4 and CD8 T cell responses against melanoma antigens. CD4 T cell responses were detected beyond reported HLA-DR restrictions. Induction of CD8 T cell responses suggests epitope spreading and systemic activity mediated at the tumor site. [ABSTRACT FROM AUTHOR]

Therapeutic vaccines for the treatment of cancer are an attractive alternative to some of the conventional therapies that are currently used. More importantly, vaccines could be very useful to prevent recurrences when applied after primary therapy. Unfortunately, most therapeutic vaccines for cancer have performed poorly due to the low level of immune responses that they induce. Previous work done in our laboratory in cancer mouse models demonstrated that vaccines consisting of synthetic peptides representing minimal CD8 T-cell epitopes administered i.v. mixed with poly-IC and anti-CD40 antibodies (TriVax) were capable of inducing massive T cell responses similar to those found during acute infections. We now report that some peptides are capable of inducing similarly large T cell responses after vaccination with poly-IC alone (BiVax). The results show that amphiphilic peptides are more likely to function as strong immunogens in BiVax and that systemic immunizations (i.v. or i.m.) were more effective than local (s.c.) vaccine administration. The immune responses induced by BiVax were found to be effective against established tumors in two mouse cancer models. The roles of various immune-related pathways such as type-I IFN, CD40 costimulation, CD4 T cells, TLRs and the MDA5 RNA helicase were examined. The present findings could facilitate the development of simple and effective subunit vaccines for diseases where CD8 T cells provide a therapeutic benefit. [ABSTRACT FROM AUTHOR]

A major goal of immunotherapy for cancer is the activation of T cell responses against tumor-associated antigens (TAAs). One important strategy for improving antitumor immunity is vaccination with peptide variants of TAAs. Understanding the mechanisms underlying the expansion of T cells that respond to the native tumor antigen is an important step in developing effective peptide-variant vaccines. Using an immunogenic mouse colon cancer model, we compare the binding properties and the TCR genes expressed by T cells elicited by peptide variants that elicit variable antitumor immunity directly ex vivo. The steady-state affinity of the natural tumor antigen for the T cells responding to effective peptide vaccines was higher relative to ineffective peptides, consistent with their improved function. Ex vivo analysis showed that T cells responding to the effective peptides expressed a CDR3β motif, which was also shared by T cells responding to the natural antigen and not those responding to the less effective peptide vaccines. Importantly, these data demonstrate that peptide vaccines can expand T cells that naturally respond to tumor antigens, resulting in more effective antitumor immunity. Future immunotherapies may require similar stringent analysis of the responding T cells to select optimal peptides as vaccine candidates. [ABSTRACT FROM AUTHOR]

Background: Therapeutic vaccines for cancer are an attractive alternative to conventional therapies, since the later result in serious adverse effects and in most cases are not effective against advanced disease. Human papillomavirus (HPV) is responsible for several malignancies such as cervical carcinoma. Vaccines targeting oncogenic viral proteins like HPV16-E6 and HPV16-E7 are ideal candidates to elicit strong immune responses without generating autoimmunity because: (1) these products are not expressed in normal cells and (2) their expression is required to maintain the malignant phenotype. Our group has developed peptide vaccination strategy called TriVax, which is effective in generating vast numbers of antigen-specific T cells in mice capable of persisting for long time periods. Materials and methods: We have used two HPV-induced mouse cancer models (TC-1 and C3.43) to evaluate the immunogenicity and therapeutic efficacy of TriVax prepared with the immunodominant CD8 T-cell epitope HPV16-E7, mixed with poly-IC adjuvant and costimulatory anti-CD40 antibodies. Results: TriVax using HPV16-E7 induced large and persistent T-cell responses that were therapeutically effective against established HPV16-E7 expressing tumors. In most cases, TriVax was successful in attaining complete rejections of 6-11-day established tumors. In addition, TriVax induced long-term immunological memory, which prevented tumor recurrences. The anti-tumor effects of TriVax were independent of NK and CD4 T cells and, surprisingly, did not rely to a great extent on type-I or type-II interferon. Conclusions: These findings indicate that the TriVax strategy is an appealing immunotherapeutic approach for the treatment of established viral-induced tumors. We believe that these studies may help to launch more effective and less invasive therapeutic vaccines for HPV-mediated malignancies. [ABSTRACT FROM AUTHOR]

Disrupting tumor-mediated mechanisms suppressing host immunity represents a novel approach to tumor immunotherapy. Depletion of regulatory T cells (Tregs) increases endogenous anti-tumor immunity and the efficacy of active immunotherapy in experimental tumor models. HLA-A2.1/HLA-DR1 (A2.1/DR1) × BALB- neuT ( neuT) triple transgenic mice represent an improvement over neuT mice for evaluating vaccination regimens to overcome tolerance against HER-2/ neu. We questioned whether depletion of Tregs with Denileukin diftitox (Ontak) enhances the efficacy of a therapeutic vaccine consisting of HER-2(85-94) (p85) CTL and HER-2(776-790) (p776) Th peptides against the growth of TUBO.A2 transplantable tumor in male A2.1/DR1 × neuT Tg mice. While the therapeutic vaccine primed the tumor-reactive CD8 CTLs and CD4 effector T lymphocytes (Teffs) compartment, inducing activation, tumor infiltration, and tumor rejection or delay in tumor growth, treatment with Ontak 1 day prior to vaccination resulted in enhanced CD4 and CD8 T-cell-mediated vaccine-specific immune responses in the periphery. This was closely associated with greater infiltration and a striking change in the intratumor balance of Tregs and vaccine-specific CTLs/Teffs that directly correlated with markedly enhanced antitumor activity. The data suggest that Tregs control both CD4 and CD8 T-cell activity within the tumor, emphasize the importance of the intratumor ratio of vaccine-specific lymphocytes to Tregs, and demonstrate significant inversion of this ratio and correlation with tumor rejection during Ontak/vaccine immunotherapy. [ABSTRACT FROM AUTHOR]

Our aim is to develop peptide vaccines that stimulate tumor antigen-specific T-lymphocyte responses against frequently detected cancers. We describe herein a novel HLA-A*0201-restricted epitope, encompassing amino acids 828–836 (residues QIAKGMSYL), which is naturally presented by various HER-2/ neu+ tumor cell lines. HER-2/ neu(828-836), [HER-2(9828)], possesses two anchor residues and stabilized HLA-A*0201 on T2 cells in a concentration-dependent Class I binding assay. This peptide was stable for 3.5 h in an off-kinetic assay. HER-2(9828) was found to be immunogenic in HLA-A*0201 transgenic (HHD) mice inducing peptide-specific and functionally potent CTL and long-lasting anti-tumor immunity. Most important, using HLA-A*0201 pentamer analysis we could detect increased ex vivo frequencies of CD8+ T-lymphocytes specifically recognizing HER-2(9828) in 8 out of 20 HLA-A*0201+ HER-2/ neu+ breast cancer patients. Moreover, HER-2(9828)-specific human CTL recognized the tumor cell line SKOV3.A2 as well as the primary RS.A2.1.DR1 tumor cell line both expressing HER-2/ neu and HLA-A*0201. Finally, therapeutic vaccination with HER-2(9828) in HHD mice was proven effective against established transplantable ALC.A2.1.HER tumors, inducing complete tumor regression in 50% of mice. Our data encourage further exploitation of HER-2(9828) as a promising candidate for peptide-based cancer vaccines. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests that despite the potency of cytotoxic anticancer agents, and the great specificity that can be achieved with immunotherapy, neither of these two types of treatment by itself has been sufficient to eradicate the disease. Still, the combination of these two different modalities holds enormous potential for eliciting therapeutic results. Indeed, certain chemotherapeutic agents have shown immunomodulatory activities, and several combined approaches have already been attempted. For instance, chemotherapy has been proven to enhance the efficacy of tumor cell vaccines, and to favor the activity of adoptively transferred tumor-specific T cells. A number of mechanisms have been proposed for the chemotherapy-triggered enhancement of immunotherapy response. Thus, chemotherapy may favor tumor cell death, and by that enhance tumor-antigen cross-presentation in vivo. Drug-induced myelosuppression may induce the production of cytokines favoring homeostatic proliferation, and/or ablate immunosuppression mechanisms. Furthermore, the recently reported synergy between monoclonal antibodies and chemotherapy or peptide vaccination is based upon the induction of endogenous humoral and cellular immune responses. This would suggest that monoclonal antibodies may not only provide passive immunotherapy but can also promote tumor-specific active immunity. This article will review several strategies in which immunotherapy can be exploited in preclinical and clinical studies in combination with other agents and therapeutic modalities that are quite unique when compared with “conventional” combination therapies (ie, treatments with chemotherapeutic drugs or chemotherapy and radiotherapy based protocols). The results from these studies may have significant implications for the development of new protocols based on combinatorial treatments including vaccines, chemotherapy and monoclonal antibodies, suggesting an exciting potential for therapeutic synergy with general applicability to various cancer types. Given the complicity of immune-based therapies and cancer pharmacology, it will be necessary to bring together cancer immunologists and clinicians, so as to provide a robust stimulus for realizing the successful management of cancer in the near future. [ABSTRACT FROM AUTHOR]

Previous studies in small groups of patients suggested that immunization of melanoma patients with peptide epitopes recognized by T cells could induce regression of melanoma. This approach was tested in 36 patients with stage IV melanoma. The (MHC class I-restricted) peptides were from gp100, MART-1, tyrosinase, and MAGE-3. The gp100 and MART-1 peptides had been modified to increase their immunogenicity. In half the patients (groups 3 and 4) the peptides were given in the adjuvant Montanide-ISA-720, and half the patients in both groups were given GM-CSF s.c. for 4 days following each injection. Treatment was well tolerated except for two severe erythematous responses to Montanide-ISA-720 and marked inflammatory responses at sites of GM-CSF administration in three patients. There were no objective clinical responses but stabilization of disease for periods from 3 to 12 months were seen in seven patients. Five of these were patients given the peptides in Montanide-ISA-720. Delayed-type hypersensitivity (DTH) skin test responses were also seen mainly in the patients given the peptides in Montanide-ISA-720. GM-CSF did not increase DTH responses in patients in the latter group but may have increased DTH responses in those not given peptides in Montanide-ISA-720. Inflammatory responses around s.c. metastases or regional lymph nodes were observed in two patients. These results suggest that the peptides are more effective when given in the adjuvant Montanide-ISA-720. Nevertheless, results from this study, together with those from a number of comparable studies, indicate that peptide vaccines are currently of minimal benefit to patients and support the need for ongoing development of new strategies in treatment of this disease. [ABSTRACT FROM AUTHOR]