Generation of cytotoxic T-cell responses with synthetic melanoma-associated peptides in vivo: implications for tumor vaccines with melanoma-associated antigens

Therapeutic vaccination targeting CD40 and TLR3 controls melanoma growth through existing intratumoral CD8 T cells without new T cell infiltration

Dendritic cells are potently activated by the synergistic action of CD40 stimulation in conjunction with signaling through toll like receptors, subsequently priming T cells. Cancer vaccines targeting the activation of dendritic cells in this manner show promise in murine models and are being developed for human patients. While the efficacy of vaccines based on CD40 and toll like receptor stimulation has been established, further investigation is needed to understand the mechanism of tumor control and how vaccination alters tumor infiltrating immune cells. In this study we vaccinated mice bearing established murine melanoma tumors with agonistic anti-CD40, polyI:C, and tumor antigen. Vaccination led to increased intratumoral T cell numbers and delayed tumor growth, yet did not require trafficking of T cells from the periphery. Pre-existing intratumoral T cells exhibited an acute burst in proliferation but became less functional in response to vaccination. However, the increased intratumoral T cell numbers yielded increased numbers of effector T cells per tumor. Together, our data indicate that the existing T cell response and intratumoral dendritic cells are critical for vaccination efficacy. It also suggests that circulating T cells responding to vaccination may not be an appropriate biomarker for vaccine efficacy.

A multi-antigen vaccine in combination with an immunotoxin targeting tumor-associated fibroblast for treating murine melanoma

A therapeutically effective cancer vaccine must generate potent antitumor immune responses and be able to overcome tolerance mechanisms mediated by the progressing tumor itself. Previous studies showed that glycoprotein 100 (gp100), tyrosinase-related protein 1 (TRP1), and tyrosinase-related protein 2 (TRP2) are promising immunogens for melanoma immunotherapy. In this study, we administered these three melanoma-associated antigens via lentiviral vectors (termed LV-3Ag) and found that this multi-antigen vaccine strategy markedly increased functional T-cell infiltration into tumors and generated protective and therapeutic antitumor immunity. We also engineered a novel immunotoxin, αFAP-PE38, capable of targeting fibroblast activation protein (FAP)-expressing fibroblasts within the tumor stroma. When combined with αFAP-PE38, LV-3Ag exhibited greatly enhanced antitumor effects on tumor growth in an established B16 melanoma model. The mechanism of action underlying this combination treatment likely modulates the immune suppressive tumor microenvironment and, consequently, activates cytotoxic CD8⁺ T cells capable of specifically recognizing and destroying tumor cells. Taken together, these results provide a strong rationale for combining an immunotoxin with cancer vaccines for the treatment of patients with advanced cancer.

Vitiligo-like depigmentation in patients with stage III-IV melanoma receiving immunotherapy and its association with survival: a systematic review and meta-analysis

PURPOSE

Vitiligo-like depigmentation in patients with melanoma may be associated with more favorable clinical outcome. We conducted a systematic review of patients with stage III to IV melanoma treated with immunotherapy to determine the cumulative incidence of vitiligo-like depigmentation and the prognostic value of vitiligo development on survival.

METHODS

We systemically searched and selected all studies on melanoma immunotherapy that reported on autoimmune toxicity and/or vitiligo between 1995 and 2013. Methodologic quality of each study was appraised using adapted criteria for systematic reviews in prognostic studies. Random-effect models were used to calculate summary estimates of the cumulative incidence of vitiligo-like depigmentation across studies. The prognostic value of vitiligo-like depigmentation on survival outcome was assessed using random-effects Cox regression survival analyses.

RESULTS

One hundred thirty-seven studies were identified comprising 139 treatment arms (11 general immune stimulation, 84 vaccine, 28 antibody-based, and 16 adoptive transfer) including a total of 5,737 patients. The overall cumulative incidence of vitiligo was 3.4% (95% CI, 2.5% to 4.5%). In 27 studies reporting individual patient data, vitiligo development was significantly associated with both progression-free-survival (hazard ratio [HR], 0.51; 95% CI, 0.32 to 0.82; P < .005) and overall survival (HR, 0.25; 95% CI, 0.10 to 0.61; P < .003), indicating that these patients have two to four times less risk of disease progression and death, respectively, compared with patients without vitiligo development.

CONCLUSION

Although vitiligo occurs only in a low percentage of patients with melanoma treated with immunotherapy, our findings suggest clear survival benefit in these patients. Awareness of vitiligo induction in patients with melanoma is important as an indicator of robust antimelanoma immunity and associated improved survival.

The use of signal peptide domains as vaccine candidates

Signal peptide (SP) domains have a common motif but also sequence specific features. This knowledge was mainly ignored by immunologists who considered SP as generic, short-lived, targeting sequences. Consequently, while SP-derived MHC class I, class II and HLA-E epitopes have been isolated, their use as antigen-specific vaccine candidates (VCs) was mostly neglected. Recently we demonstrated the rational of selecting entire SP domains as multi-epitope long peptide VCs based on their high T and B-cell epitope densities. This review summarizes preclinical and clinical results demonstrating the various advantages of human SP domain VCs derived from both bacterial and tumor antigens. Such vaccine design provides for a straightforward, yet unique immunotherapeutic means of generating robust, non-toxic, diversified, combined antigen-specific CD4+/CD8+ T/B-cell immunity, irrespective of patient HLA repertoire also in disease associated transporter-associated with antigen processing (TAP) deficiencies. Subsequent clinical trials will further assess the full potential of this approach.

Helper cell-independent antitumor activity of potent CD8+ T cell epitope peptide vaccines is dependent upon CD40L

Peptide vaccines derived from CD8⁺ T-cell epitopes have shown variable efficacy in cancer patients. Thus, some peptide vaccines are capable of activating CD8⁺ T-cell responses, even in the absence of CD4⁺ T-cell epitopes or dendritic cell (DC)-activating adjuvants. However, the mechanisms underlying the clinical activity of these potent peptides are poorly understood. Using CT26 and ovalbumin-expressing B16 murine allograft tumor models, we found that the antitumor effect of helper cell-independent CD8 T-cell peptide vaccines is inhibited by the blockade of CD40 ligand (CD40L) in vivo. Furthermore, in vitro stimulation with antigenic peptides of cells derived from immunized mice induced the expression of CD40L on the surface of CD8⁺ T cells and fostered DC maturation, an effect that was partially inhibited by CD40L-blocking antibodies. Interestingly, CD40L blockade also inhibited CD8⁺ T-cell responses, even in the presence of fully mature DCs, suggesting a role for CD40L not only in promoting DC maturation but also in mediating CD8⁺ T-cell co-stimulation. Importantly, these potent peptides share features with bona fide CD4 epitopes, since they foster responses against less immunogenic CD8⁺ T-cell epitopes in a CD40L-dependent manner. The analysis of peptides used for the vaccination of cancer patients in clinical trials showed that these peptides also induce the expression of CD40L on the surface of CD8⁺ T cells. Taken together, these results suggest that CD40L expression induced by potent CD8⁺ T-cell epitopes can activate antitumor CD8⁺ T-cell responses, potentially amplifying the immunological responses to less immunogenic CD8⁺ T-cell epitopes and bypassing the requirement for CD4⁺ helper T cells in vaccination protocols.

Granulocyte-Macrophage Colony Stimulating Factor: An Adjuvant for Cancer Vaccines

Granulocyte-macrophage colony stimulating factor (GM-CSF) enhances immune responses by inducing the proliferation, maturation, and migration of dendritic cells, and the expansion and differentiation of B and T lymphocytes. There is significant data in pre-clinical animal models demonstrating the adjuvant effects of GM-CSF in a variety of cancer vaccine approaches, including cellular vaccines, viral vaccines, peptide and protein vaccines, and DNA vaccines. GM-CSF is an attractive vaccine adjuvant because of its immune modulation effects and low toxicity profile. The results in animal models have been confirmed in pilot clinical trials and several clinical trials are currently ongoing.

Enhanced cytotoxicity and decreased CD8 dependence of human cancer-specific cytotoxic T lymphocytes after vaccination with low peptide dose

In mice, vaccination with high peptide doses generates higher frequencies of specific CD8+ T cells, but with lower avidity compared to vaccination with lower peptide doses. To investigate the impact of peptide dose on CD8+ T cell responses in humans, melanoma patients were vaccinated with 0.1 or 0.5 mg Melan-A/MART-1 peptide, mixed with CpG 7909 and Incomplete Freund's adjuvant. Neither the kinetics nor the amplitude of the Melan-A-specific CD8+ T cell responses differed between the two vaccination groups. Also, CD8+ T cell differentiation and cytokine production ex vivo were similar in the two groups. Interestingly, after low peptide dose vaccination, Melan-A-specific CD8+ T cells showed enhanced degranulation upon peptide stimulation, as assessed by CD107a upregulation and perforin release ex vivo. In accordance, CD8+ T cell clones derived from low peptide dose-vaccinated patients showed significantly increased degranulation and stronger cytotoxicity. In parallel, Melan-A-specific CD8+ T cells and clones from low peptide dose-vaccinated patients expressed lower CD8 levels, despite similar or even stronger binding to tetramers. Furthermore, CD8+ T cell clones from low peptide dose-vaccinated patients bound CD8 binding-deficient tetramers more efficiently, suggesting that they may express higher affinity TCRs. We conclude that low peptide dose vaccination generated CD8+ T cell responses with stronger cytotoxicity and lower CD8 dependence.

Antigen-specific versus antigen-nonspecific immunotherapeutic approaches for human melanoma: the need for integration for optimal efficacy?

Due to its immunogenecity and evidence of immune responses resulting in tumor regression, metastatic melanoma has been the target for numerous immunotherapeutic approaches. Unfortunately, based on the clinical outcomes, even the successful induction of tumor-specific responses does not correlate with efficacy. Immunotherapies can be divided into antigen-specific approaches, which seek to induce T cells specific to one or several known tumor associated antigens (TAA), or with antigen-nonspecific approaches, which generally activate T cells to become nonspecifically lytic effectors. Here the authors critically review the different immunotherapeutic approaches in melanoma.

Dendritic cell vaccination combined with CTLA4 blockade in patients with metastatic melanoma

PURPOSE

Tumor antigen-loaded dendritic cells (DC) are believed to activate antitumor immunity by stimulating T cells, and CTL-associated antigen 4 (CTLA4)-blocking antibodies should release a key negative regulatory pathway on T cells. The combination was tested in a phase I clinical trial in patients with advanced melanoma.

EXPERIMENTAL DESIGN

Autologous DC were pulsed with MART-1(26-35) peptide and administered with a dose escalation of the CTLA4-blocking antibody tremelimumab. Sixteen patients were accrued to five dose levels. Primary end points were safety and immune effects; clinical efficacy was a secondary end point.

RESULTS

Dose-limiting toxicities of grade 3 diarrhea and grade 2 hypophysitis developed in two of three patients receiving tremelimumab at 10 mg/kg monthly. Four patients had an objective tumor response, two partial responses and two complete responses, all melanoma free between 2 and 4 years after study initiation. There was no difference in immune monitoring results between patients with an objective tumor response and those without a response. Exploratory gene expression analysis suggested that immune-related gene signatures, in particular for B-cell function, may be important in predicting response.

CONCLUSION

The combination of MART-1 peptide-pulsed DC and tremelimumab results in objective and durable tumor responses at the higher range of the expected response rate with either agent alone.

Skin layer-specific Melan-A expression during progression of human cutaneous melanoma: implications for diagnostic applications of the marker

Melan-A is widely used in the diagnostics of human melanoma. The immunogenicity of this glycoprotein makes it a potential target in immunotherapy and several authors have suggested its potential as a prognostic factor. Up to now there has been no clear direct evidence of changes of Melan-A expression during the progression of melanoma. We have performed objective immunohistochemical assessment of the expression of Melan-A in benign naevi and melanomas at different stages of progression. Our results show a complex pattern of changes in the expression of Melan-A in melanomas depending on the location of melanoma cells within individual skin layers. The expression of the antigen during tumour progression significantly decreases for melanoma cells located in the granular/spinous layer (r=-0.94, P=0.02) and increases for the papillary layer (r=0.99, P=0.002) and reticular layer (r=0.89, P=0.04). It should also be emphasized that from the Clark II level of progression the melanomas can be detected with high sensitivity and specificity using a simple cut-off test based on the determination of Melan-A expression in tumour cells located within the papillary layer.

Results of the first phase I clinical trial of the novel II-key hybrid preventive HER-2/neu peptide (AE37) vaccine

PURPOSE

HER-2/neu is overexpressed in breast cancer and is the source of immunogenic peptides. CD4(+) T-helper peptides for HER-2/neu are being evaluated in vaccine trials. The addition of Ii-Key, a four-amino-acid LRMK modification, increases vaccine potency when compared with unmodified class II epitopes. We present the results of the first human phase I trial of the Ii-Key hybrid HER-2/neu peptide (AE37) vaccine in disease-free, node-negative breast cancer patients.

PATIENTS AND METHODS

The dose escalation trial included five dose groups, to determine safety and optimal dose of the hybrid peptide (100 microg, 500 microg, 1,000 microg) and granulocyte-macrophage colony-stimulating factor (GM-CSF; range, 0 to 250 microg). In the event of significant local toxicity, GM-CSF (or peptide in absence of GM-CSF) was reduced by 50%. Immunologic response was monitored by delayed-type hypersensitivity and [(3)H]thymidine proliferative assays for both the hybrid AE37 (LRMK-positive HER-2/neu:776-790) and AE36 (unmodified HER-2/neu:776-790).

RESULTS

All 15 patients completed the trial with no grade 3 to 5 toxicities. Dose reductions occurred in 47% of patients. In the second group (peptide, 500 microg; GM-CSF, 250 microg), all patients required dose reductions, prompting peptide-only inoculations in the third group. The vaccine induced dose-dependent immunologic responses in vitro and in vivo to AE37, as well as AE36.

CONCLUSION

The hybrid AE37 vaccine seems safe and well tolerated with minimal toxicity if properly dosed. AE37 is capable of eliciting HER-2/neu-specific immune responses, even without the use of an adjuvant. This trial represents the first human experience with the Ii-Key modification, and to our knowledge, AE37 is the first peptide vaccine to show potency in the absence of an immunoadjuvant.

Tumor escape mechanisms: potential role of soluble HLA antigens and NK cells activating ligands

The crucial role played by human leukocyte antigen (HLA) antigens and natural killer (NK)-cell-activating ligands in the interactions of malignant cells with components of the host's immune system has stimulated interest in the characterization of their expression by malignant cells. Convincing evidence generated by the immunohistochemical staining of surgically removed malignant lesions with monoclonal antibodies recognizing HLA antigens and NK-cell-activating ligands indicates that the surface expression of these molecules is frequently altered on malignant cells. These changes appear to have clinical significance because in some types of malignant disease they are associated with the histopathological characteristics of the lesions as well as with disease-free interval and survival. These associations have been suggested to reflect the effect of HLA antigen and NK-cell-activating ligand abnormalities on the interactions of tumor cells with antigen-specific cytotoxic T lymphocytes (CTL) and with NK cells. Nevertheless, there are examples in which disease progresses in the face of appropriate HLA antigen and/or NK-cell-activating ligand as well as tumor antigen expression by malignant cells and of functional antigen-specific CTL in the investigated patient. In such scenarios, it is likely that the tumor microenvironment is unfavorable for CTL and NK cell activity and contributes to tumor immune escape. Many distinct escape mechanisms have been shown to protect malignant cells from immune recognition and destruction in the tumor microenvironment. In this article, following the description of the structural and functional characteristics of soluble HLA antigens and NK-cell-activating ligands, we will review changes in their serum level in malignant disease and discuss their potential role in the escape mechanisms used by tumor cells to avoid recognition and destruction.

Skin reactions to human papillomavirus (HPV) 16 specific antigens intradermally injected in healthy subjects and patients with cervical neoplasia

We have tested the safety and feasibility of a synthetic long peptide-based HPV16-specific skin test to detect cellular immune responses to HPV16 E2, E6 and E7 in vivo. Women with cervical neoplasia (n = 11) and healthy individuals (n = 19) were intradermally challenged with 8 different pools of HPV16 E2, E6 and E7 peptides. The skin test was safe as the injections were perceived as mildly painful and no adverse events were observed. The majority of skin reactions appeared significantly earlier in HPV16+ patients (<8 days) than in healthy subjects (8-25 days). The development of late skin reactions in healthy subjects was associated with the appearance of circulating HPV16-specific T cells and the infiltration of both HPV16-specific CD4+ Th1/Th2 and CD8+ T cells into the skin. These data show that the intradermal injection of pools of HPV16 synthetic long peptides is safe and results in the migration of HPV16-specific T cells into the skin as well as in an increase in the number of circulating HPV16-specific T cells. The use of this test to measure HPV16-specific immunity is currently tested in a low resource setting for the measurement of spontaneously induced T-cell responses as well as in our HPV16 vaccination trials for the detection of vaccine-induced immunity.

GMP production of pDERMATT for vaccination against melanoma in a phase I clinical trial

For the treatment of melanoma DNA vaccines are a promising therapeutic approach. In our institute a plasmid encoding a melanoma-associated epitope (MART-1) and an immunostimulatory sequence (tetanus toxin fragment-c) termed pDERMATT was developed. In a phase I study the plasmid will be administered intradermally using a newly developed tattoo strategy to assess the toxicity and efficacy of inducing tumor-specific T-cell immunity. To facilitate this study a Good Manufacturing Practice (GMP)-compliant plasmid manufacturing process was set up and a pharmaceutical dosage form was developed. Each batch resulted in approximately 200mg plasmid DNA of a high purity >90% supercoiled DNA, an A260/280 ratio 1.80-1.95, undetectable or extremely low residual endotoxins, Escherichia coli host cell protein, RNA, and DNA. In the manufacturing process no animal derived enzymes like RNase or potentially harmful organic solvents are used. After sterile filtration the concentration of the plasmid solution is approximately 1.1mg/mL. For the scheduled phase I study a concentration of 5mg/mL is desired, and further concentration of the solution is achieved by lyophilisation. The formulation solution is composed of 1mg/mL pDERMATT and 20mg/mL sucrose in Water for Injections. Upon reconstitution with a five times smaller volume an isotonic sucrose solution containing 5mg/mL pDERMATT is obtained. Lyophilised pDERMATT is sterile with >90% supercoiled DNA, an A260-280 ratio 1.80-1.95, content 90-110% of labeled, and residual water content <2% (w/w). The product yields the predicted profile upon restriction-enzyme digestion, is highly immunogenic as confirmed in an in vivo mouse model, and stable for at least six months at 5 degrees C. We have not only developed a reproducible process to manufacture pharmaceutical grade plasmid DNA but also a stable dosage form for the use in clinical trials.

Unmodified self antigen triggers human CD8 T cells with stronger tumor reactivity than altered antigen

Human cancer vaccines are often prepared with altered "analog" or "heteroclitic" antigens that have been optimized for HLA class I binding, resulting in enhanced immunogenicity. Here, we take advantage of CpG oligodeoxynucleotides as powerful vaccine adjuvants and demonstrate the induction of high T cell frequencies in melanoma patients, despite the use of natural (unmodified) tumor antigenic peptide. Compared with vaccination with analog peptide, natural peptide induced T cell frequencies that were approximately twofold lower. However, T cells showed superior tumor reactivity because of (i) increased functional avidity for natural antigen and (ii) enhancement of T cell activation and effector function. Thus, novel vaccine formulations comprising potent immune stimulators may allow to circumvent the need for modified antigens and can induce highly functional T cells with precise antigen specificity.

Immunologic and clinical outcomes of a randomized phase II trial of two multipeptide vaccines for melanoma in the adjuvant setting

PURPOSE

Human melanoma cells express shared antigens recognized by CD8(+) T lymphocytes, the most common of which are melanocytic differentiation proteins and cancer-testis antigens. However, peptide vaccines for melanoma usually target only one or two MHC class I-associated peptide antigens. Because melanomas commonly evade immune recognition by selective antigen loss, optimization of melanoma vaccines may require development of more complex multipeptide vaccines.

EXPERIMENTAL DESIGN

In a prospective randomized clinical trial, we have evaluated the safety and immunogenicity of a vaccine containing a mixture of 12 peptides from melanocytic differentiation proteins and cancer-testis antigens, designed for human leukocyte antigen types that represent 80% of the melanoma patient population. This was compared with a four-peptide vaccine with only melanocytic differentiation peptides. Immune responses were assessed in peripheral blood and in vaccine-draining lymph nodes.

RESULTS

These data show that (a) the 12-peptide mixture is immunogenic in all treated patients; (b) immunogenicity of individual peptides is maintained despite competition with additional peptides for binding to MHC molecules; (c) a broader and more robust immune response is induced by vaccination with the more complex 12-peptide mixture; and (d) clinical outcome in this peptide vaccine trial correlates with immune responses measured in the peripheral blood lymphocytes.

CONCLUSIONS

These data support continued investigation of complex multipeptide vaccines for melanoma.

Less yin, more yang: confronting the barriers to cancer immunotherapy

Clinical trials involving T cell-based immunotherapy for the treatment of human cancer have shown limited degrees of success. In cancer vaccine trials conducted at multiple centers worldwide, immunization has often resulted in the robust elicitation of T cells that specifically recognize antigens expressed on the surface of tumor cells. However, to date, objective clinical responses resulting from these approaches have remained relatively rare. By contrast, adoptive transfer of laboratory-expanded T cells into patients has had more success, producing impressive clinical regressions in a subset of advanced metastatic melanoma patients. The failure of activated T cells to consistently induce clinical responses in many other patients has pushed us toward a deeper understanding of natural immunoregulatory mechanisms that are directly responsible for diminishing tumor-specific T-cell activation, migration, and effector function in vivo. Such immunosuppressive factors likely evolved to prevent autoimmunity, but are frequently co-opted by tumors to evade tumor-specific immune responses. With this knowledge, it now becomes imperative to develop specific clinical interventions capable of eliminating tumor-specific immunosuppression, with the goal of shifting the balance to favor effector T-cell function and tumor cell killing.

MHC-peptide-specific antibodies reveal inefficient presentation of an HLA-A*0201-restricted, Melan-A-derived peptide after active intracellular processing

MHC-peptide-specific Fab antibodies binding to HLA-A*0201 complexes presenting the wild-type EAAGIGILTV (EAA) or analogue Melan-A 10-mer ELAGIGILTV (ELA) peptide were generated to study efficacy of peptide processing and presentation. None of the selected Fab antibodies detected the naturally processed EAA/HLA-A*0201 complex on melanoma tumor cells, confirming the known low peptide number on the cell surface. To study the effect of peptide presentation and processing in more detail, genes coding for the A27L-mutated Melan-A protein or the processed ELA peptide were introduced into HLA-A*0201(+) B cells by infection with the respective recombinant vaccinia virus construct producing equimolar amounts of GFP-ubiquitin directly linked to the fragment of interest. Correlating GFP expression to actual numbers of peptide presented, 1100-2600 [corrected] ELA peptides had to be synthesized to be presented by a single MHC class I antigen-peptide complex. This number increased 10- to 20-fold when ELA peptide presentation from the A27L-mutated full length Melan-A protein was studied, since 16000-52000 [corrected] GFP molecules needed to be synthesized for the detection of one ELA peptide. Our results indicate that peptide processing rather than presentation is the rate-limiting step in our experimental setting and is much more ineffective for Melan-A than has been previously shown for other MHC class I-restricted epitopes.

New strategy for the identification of squamous carcinoma antigens that induce therapeutic immune responses in tumor-bearing mice

This study describes a new strategy for the identification of squamous carcinoma antigens tumor-associated antigens (TAA). The antigens were discovered by comparing microarrays of squamous carcinoma vaccines highly enriched for immunotherapeutic cells with non-enriched vaccines. The vaccines were prepared by transferring sheared genomic DNA fragments (25 kb) from KLN205 cells, a squamous carcinoma cell line (DBA/2 mouse origin (H-2(d)) into LM fibroblasts (C3H/He origin, H-2(k)). The transferred tumor DNA segments integrate spontaneously into the genome of the recipient cells, replicate as the cells divide and are expressed. As only a small proportion of the transfected cell population was expected to have incorporated DNA segments that included genes specifying TAA (the vast majority specify normal cellular constituents), a novel strategy was employed to enrich the vaccine for TAA-positive cells. Microarrays were used to compare genes expressed by enriched and non-enriched vaccines. Seventy-five genes were overexpressed in cells from the enriched vaccine. One, the gene for Cytochrome P450 (family 2, subfamily e, polypeptide 1) (Cyp2e1), was overexpressed in the enriched but not the non-enriched vaccine. A vaccine for squamous carcinoma was prepared by transfer of a 357 bp fragment of the gene for Cyp2e1 into the fibroblast cell line. Robust immunity, sufficient to result in indefinite survival, was induced in tumor-bearing mice immunized with cells transfected with this gene fragment.

New generation vaccine induces effective melanoma-specific CD8+ T cells in the circulation but not in the tumor site

Although increasing evidence suggests that CTL are important to fight the development of some cancers, the frequency of detectable tumor-specific T cells is low in cancer patients, and these cells have generally poor functional capacities, compared with virus-specific CD8(+) T cells. The generation with a vaccine of potent CTL responses against tumor Ags therefore remains a major challenge. In the present study, ex vivo analyses of Melan-A-specific CD8(+) T cells following vaccination with Melan-A peptide and CpG oligodeoxynucleotides revealed the successful induction in the circulation of effective melanoma-specific T cells, i.e., with phenotypic and functional characteristics similar to those of CTL specific for immunodominant viral Ags. Nonetheless, the eventual impact on tumor development in vaccinated melanoma donors remained limited. The comprehensive study of vaccinated patient metastasis shows that vaccine-driven tumor-infiltrating lymphocytes, although activated, still differed in functional capacities compared with blood counterparts. This coincided with a significant increase of FoxP3(+) regulatory T cell activity within the tumor. The consistent induction of effective tumor-specific CD8(+) T cells in the circulation with a vaccine represents a major achievement; however, clinical benefit may not be achieved unless the tumor environment can be altered to enable CD8(+) T cell efficacy.

Immunity to melanoma antigens: from self-tolerance to immunotherapy

The development of effective immune therapy for cancer is a central goal of immunologists in the 21st century. Our laboratories have been deeply involved in characterization of the immune response to melanoma and translation of laboratory discoveries into clinical trials. We have identified a cohort of peptide antigens presented by Major Histocompatibility Complex (MHC) molecules on melanoma cells and widely recognized by T cells from melanoma patients. These have been incorporated into peptide-based vaccines that induce CD8(+) and CD4(+) T-cell responses in 80-100% of patients. Major objective clinical tumor regressions have been observed in some patients, and overall survival in vaccinated patients exceeds expected stage-specific survival. New clinical trials will determine the value of combination of melanoma helper peptides (MHP) into multipeptide vaccines targeting CD8 cells. New trials will also evaluate new approaches to modulating the host-tumor relationship and will develop new combination therapies. Parallel investigations in murine models are elucidating the immunobiology of the melanoma-host relationship and addressing issues that are not feasible to approach in human trials. Based on the fact that the largest cohort of melanoma antigens are derived from normal proteins concerned with pigment production, we have evaluated the mechanisms of self-tolerance to tyrosinase (Tyr) and have determined how T cells in an environment of self-tolerance are impacted by immunization. Using peptide-pulsed dendritic cells as immunogens, we have also used the mouse model to establish strategies for quantitative and qualitative enhancement of antitumor immunity. This information creates opportunities for a new generation of therapeutic interventions using cancer vaccines.

Design of enhanced agonists through the use of a new virtual screening method: application to peptides that bind class I major histocompatibility complex (MHC) molecules

A new screening procedure is described that uses docking calculations to design enhanced agonist peptides that bind to major histocompatibility complex (MHC) class I receptors. The screening process proceeds via single mutations of one amino acid at the positions that directly interact with the MHC receptor. The energetic and structural effects of these mutations have been studied using fragments of the original ligand that vary in length. The results of these docking studies indicate that the mutant affinity ranking of long peptides can be practically reproduced with a screening approach performed using fragments of six residues. Fragments of four and five residues could mimic, in some cases, the structural arrangement of the side chains of the full-length peptide. We have compared the structural and energetic results of the docking calculations with experimental data using three unrelated ligand peptides that differ greatly in their affinity for the MHC complex. Analysis of the affinity of the fragments led to the identification of three important parameters in the construction of fragments that mimic the structural and energetic properties of the full-length ligand: the length of the fragment; its intermolecular energy; and the number and localization, internal or terminal, of the anchor residues. The results of this new peptide-design methodology have been applied to suggest new peptides derived from the MUC1-8 peptide that could be used as murine vaccines that trigger the immune response through the MHC class I protein H-2K(b).

Assessment of CD8 involvement in T cell clone avidity by direct measurement of HLA-A2/Mage3 complex density using a high-affinity TCR like monoclonal antibody

Peptide affinity for MHC molecules determines the number of MHC/peptide complexes stabilized at the cell surface in in vitro tests or in vaccination protocols. We isolated a high affinity monoclonal antibody specific for the HLA-A2/Mage3 complex that enables an equilibrium binding assay to be performed on T2 cell line loaded with a range of Mage3 peptides. Binding of Mage3 to the HLA-A2 molecule can be modeled by a standard receptor-ligand interaction characterized by an affinity constant. This model enables the measurement of the affinity of other immunogenic peptides for HLA-A2 by a competition test and the calculation of the density of complexes stabilized at the T2 cell surface for all peptide concentrations. Quantification of the HLA-A2/Mage3 complexes at target cell surfaces was used to estimate the number of complexes required to reach cytotoxicity ED50 of human T cell clones sorted from an unprimed repertoire. We confirm with this antibody the direct relationship between clone avidity and TCR affinity, and the moderate contribution of the CD8 co-receptor in the reinforcement of TCR-MHC/peptide contact. Nevertheless, CD8 plays a critical role in the amplification of the specific signal to establish an efficient T cell response at low specific complex densities found in physiological situations.

Production and characterization of amplified tumor-derived cRNA libraries to be used as vaccines against metastatic melanomas

Background

Anti-tumor vaccines targeting the entire tumor antigen repertoire represent an attractive immunotherapeutic approach. In the context of a phase I/II clinical trial, we vaccinated metastatic melanoma patients with autologous amplified tumor mRNA. In order to provide the large quantities of mRNA needed for each patient, the Stratagene Creator™ SMART™ cDNA library construction method was modified and applied to produce libraries derived from the tumors of 15 patients. The quality of those mRNA library vaccines was evaluated through sequencing and microarray analysis.

Results

Random analysis of bacterial clones of the library showed a rate of 95% of recombinant plasmids among which a minimum of 51% of the clones contained a full-Open Reading Frame. In addition, despite a biased amplification toward small abundant transcripts compared to large rare fragments, we could document a relatively conserved gene expression profile between the total RNA of the tumor of origin and the corresponding in vitro transcribed complementary RNA (cRNA). Finally, listing the 30 most abundant transcripts of patient MEL02's library, a large number of tumor associated antigens (TAAs) either patient specific or shared by several melanomas were found.

Conclusion

Our results show that unlimited amounts of cRNA representing tumor's transcriptome could be obtained and that this cRNA was a reliable source of a large variety of tumor antigens.

Phase I Study of a Plasmid DNA Vaccine Encoding MART-1 in Patients with Resected Melanoma at Risk for Relapse

Immunization with plasmid DNA represents an attractive method for increasing cellular immune responses against cancer antigens. The safety and immunologic response of a plasmid encoding the MART-1 melanocyte differentiation antigen was evaluated in 12 patients with resected melanoma at risk for relapse. As a control, patients were also administered a plasmid encoding hepatitis B surface antigen (HBsAg). After establishing immunologic activity of the vaccines in mice, groups of three to six HLA-A2-positive patients were enrolled into one of three cohorts in which they received intramuscular injections of the MART-1 plasmid into the right deltoid and the HBsAg plasmid into the left deltoid at doses of 0.1, 0.3, or 1.0 mg on days 1, 43, 85, and 127. Injections were well tolerated. Toxicity was limited to grade 1 pain and injection site tenderness. Systemic toxicity was not observed. Although baseline MART-1-specific lymphoproliferative and ELISPOT responses were evident, no patient manifested increases after injection of the MART-1 plasmid. Furthermore, changes in MART-1-specific precursors were not evident after immunization as assessed by an in vitro stimulation assay. No patients manifested a lymphoproliferative response to HBsAg antigen, and significant antibody responses to HBsAg were also not observed. Although injections were safe, the authors could not show significant immunologic responses to plasmid encoding MART-1 or HBsAg using the dose, schedule, and route of administration applied. This study underscores species differences in the ability to respond to plasmid immunogens.

Antigen-specific CD8+ T cells mediate a peptide-induced fatal syndrome

Peptide immunotherapy both activates and suppresses the T cell response against known peptide Ags. Although pretreatment with VP2(121-130) peptide inhibits the development of antiviral CTL specific for the immunodominant D(b):VP2(121-130) epitope expressed during acute Theiler's murine encephalomyelitis virus infection, i.v. injection of this same peptide or MHC tetramers containing the peptide during an ongoing antiviral CTL response results in a peptide-induced fatal syndrome (PIFS) within 48 h. Susceptibility to PIFS is dependent on peptide-specific CD8(+) T cells, varies among inbred strains of mice, and is not mediated by traditionally defined mechanisms of shock. Analyses using bone marrow chimeras and mutant mice demonstrate that susceptibility to PIFS is determined by the genotype of bone marrow-derived cells and requires the expression of perforin. Animals responding to peptide treatment with PIFS develop classical stress responses in the brain. These findings raise important considerations for the development of peptide therapies for active diseases to modify immune responses involving expanded populations of T cells. In summary, treatment with peptides or MHC-tetramers during a peptide-specific immune response can result in a fatal shock-like syndrome. Susceptibility to the syndrome is genetically determined, is mediated by CD8(+) T cells, and requires expression of perforin. These findings raise concerns about the use of peptides and MHC tetramers in therapeutic schemes.

Identification of Noncanonical Melanoma-Associated T Cell Epitopes for Cancer Immunotherapy

The identification of tumor-associated T cell epitopes has contributed significantly to the understanding of the interrelationship of tumor and immune system and is instrumental in the development of therapeutic vaccines for the treatment of cancer. Most of the known epitopes have been identified with prediction algorithms that compute the potential capacity of a peptide to bind to HLA class I molecules. However, naturally expressed T cell epitopes need not necessarily be strong HLA binders. To overcome this limitation of the available prediction algorithms we established a strategy for the identification of T cell epitopes that include suboptimal HLA binders. To this end, an artificial neural network was developed that predicts HLA-binding peptides in protein sequences by taking the entire sequence context into consideration rather than computing the sum of the contribution of the individual amino acids. Using this algorithm, we predicted seven HLA A*0201-restricted potential T cell epitopes from known melanoma-associated Ags that do not conform to the canonical anchor motif for this HLA molecule. All seven epitopes were validated as T cell epitopes and three as naturally processed by melanoma tumor cells. T cells for four of the new epitopes were found at elevated frequencies in the peripheral blood of melanoma patients. Modification of the peptides to the canonical sequence motifs led to improved HLA binding and to improved capacity to stimulate T cells.

Phase I/II study of immunotherapy with T-cell peptide epitopes in patients with stage IV melanoma

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.

Rapid and strong human CD8+ T cell responses to vaccination with peptide, IFA, and CpG oligodeoxynucleotide 7909

The induction of potent CD8+ T cell responses by vaccines to fight microbes or tumors remains a major challenge, as many candidates for human vaccines have proved to be poorly immunogenic. Deoxycytidyl-deoxyguanosin oligodeoxynucleotides (CpG ODNs) trigger Toll-like receptor 9, resulting in dendritic cell maturation that can enhance immunogenicity of peptide-based vaccines in mice. We tested whether a synthetic ODN, CpG 7909, could improve human tumor antigen-specific CD8+ T cell responses. Eight HLA-A2+ melanoma patients received 4 monthly vaccinations of low-dose CpG 7909 mixed with melanoma antigen A (Melan-A; identical to MART-1) analog peptide and incomplete Freund's adjuvant. All patients exhibited rapid and strong antigen-specific T cell responses: the frequency of Melan-A-specific T cells reached over 3% of circulating CD8+ T cells. This was one order of magnitude higher than the frequency seen in 8 control patients treated similarly but without CpG and 1-3 orders of magnitude higher than that seen in previous studies with synthetic vaccines. The enhanced T cell populations consisted primarily of effector memory cells, which in part secreted IFN- and expressed granzyme B and perforin ex vivo. In vitro, T cell clones recognized and killed melanoma cells in an antigen-specific manner. Thus, CpG 7909 is an efficient vaccine adjuvant that promotes strong antigen-specific CD8+ T cell responses in humans.

New dimensions in vaccinology: A new insight

The development of vaccines to prevent infectious diseases has been one of the most important contributions of biomedical sciences. Increasing understanding in biochemistry, molecular biology, molecular genetics and related fields have provided an opportunity for the development of new generation vaccines that are based on rational design approaches. This is possible because of proper understanding of the microbial-genetics, biochemistry, host-pathogen interaction and recent developments in molecular immunology. Another important improvement made in the quality of vaccine production is the incorporation of immunomodulators or adjuvants with modified delivery vehicles viz liposomes, Iscoms and microspheres apart from alum being used as a gold standard. This article reviews the art of vaccination from Jenner period to present day context highlighting all the developments made at each stage of the vaccine development. Various criteria have been discussed regarding the selection of epitopes that expand B & T cells, its linkage with other accessory cells of the immune system, means to overcome MHC linked immune unresponsiveness, enhanced antigen processing and presentations that specially induce either helper or cytotoxic or mucosal immune responses were critically discussed.

Dendritic cells strongly boost the antitumor activity of adoptively transferred T cells in vivo

Dendritic cells (DCs) have been well characterized for their ability to initiate cell-mediated immune responses by stimulating naive T cells. However, the use of DCs to stimulate antigen-activated T cells in vivo has not been investigated. In this study, we determined whether DC vaccination could improve the efficacy of activated, adoptively transferred T cells to induce an enhanced antitumor immune response. Mice bearing B16 melanoma tumors expressing the gp100 tumor antigen were treated with cultured, activated T cells transgenic for a T-cell receptor specifically recognizing gp100, with or without concurrent peptide-pulsed DC vaccination. In this model, antigen-specific DC vaccination induced cytokine production, enhanced proliferation, and increased tumor infiltration of adoptively transferred T cells. Furthermore, the combination of DC vaccination and adoptive T-cell transfer led to a more robust antitumor response than the use of each treatment individually. Collectively, these findings illuminate a new potential application for DCs in the in vivo stimulation of adoptively transferred T cells and may be a useful approach for the immunotherapy of cancer.

Evaluation of melanoma vaccines with molecularly defined antigens by ex vivo monitoring of tumor-specific T cells

Immunotherapy of melanoma is aimed to mobilize cytolytic CD8+ T cells playing a central role in protective immunity. Despite numerous clinical vaccine trials, only few patients exhibited strong antigen-specific T-cell activation, stressing the need to improve vaccine strategies. For a rational development, we propose to focus on molecularly defined vaccine components, and evaluate their immunogenicity with highly reproducible and standardized methods for ex vivo immune monitoring. Careful immunogenicity comparison of vaccine formulations in phase I/II studies allow to select optimized vaccines for subsequent clinical efficacy testing in large scale phase III trials.

Encapsulation into sterically stabilised liposomes enhances the immunogenicity of melanoma-associated Melan-A/MART-1 epitopes

Tumour-associated antigens (TAA)-specific vaccination requires highly immunogenic reagents capable of inducing cytotoxic T cells (CTL). Soluble peptides are currently used in clinical applications despite an acknowledged poor immunogenicity. Encapsulation into liposomes has been suggested to improve the immunogenicity of discrete antigen formulations. We comparatively evaluated the capacity of HLA-A2.1 restricted Melan-A/MART-1 epitopes in soluble form (S) or following inclusion into sterically stabilised liposomes (SSL) to be recognised by specific CTL, to stimulate their proliferation and to induce them in healthy donors' peripheral blood mononuclear cells (PBMC), as well as in melanoma-derived tumour-infiltrating lymphocytes (TIL). HLA-A2.1⁺, Melan-A/MART-1-NA-8 melanoma cells served as targets of specific CTL in 51Cr release assays upon pulsing by untreated or human plasma-treated soluble or SSL-encapsulated Melan-A/MART-1 27–35 (M27–35) or 26–35 (M26–35) epitopes. These reagents were also used to stimulate CTL proliferation, measured as 3H-thymidine incorporation, in the presence of immature dendritic cells (iDC), as antigen-presenting cells (APC). Induction of specific CTL upon stimulation with soluble or SSL-encapsulated peptides was attempted in healthy donors' PBMC or melanoma-derived TIL, and monitored by 51Cr release assays and tetramer staining. Na-8 cells pulsing with SSL M27–35 resulted in a five-fold more effective killing by specific CTL as compared with equal amounts of S M27–35. Encapsulation into SSL also provided a partial (50%) protection of M27–35 from plasma hydrolysis. No specific advantages regarding M26–35 were detectable in these assays. However, at low epitope concentrations (⩽100 ng ml⁻¹), SSL M26–35 was significantly more effective in inducing CTL proliferation than S M26–35, in the presence of iDC, as APC. Preincubation with iDC for 6 h virtually abolished the capacity of S M26–35 to stimulate specific CTL proliferation, but only partially affected that of SSL M26–35. Most importantly, SSL M26–35 was able to enhance the induction of specific CTL in healthy donors PBMC and in melanoma-derived TIL as compared to S M26–35. Taken together, our data indicate that encapsulation of TAA epitopes into SSL results in effective immunogenic formulations suitable for clinical use in active specific tumour immunotherapy.

Proteasomal Targeting and Minigene Repetition Improve Cell-Surface Presentation of a Transfected, Modified Melanoma Tumour Antigen

Melanoma antigen recognized by T cell 1 (MART-1) is regarded as a candidate peptide for vaccination against malignant melanoma, and it is of importance to develop strategies to improve the vaccine-elicited T-cell activation towards MART-1. T-cell activation is, among other determinants, dependent on the density of specific major histocompatibility complex-peptide complexes on the surface of the antigen-presenting cell. In this study, we explored the cell-surface presentation of a substituted MART-1 peptide encoded by transfected minigenes. We investigated the potential of proteasomal targeting compared to non-proteasomal targeting of the epitope to increase its cell-surface presentation. Furthermore, we explored the potential of incorporating multiple minigenes instead of one to increase cell-surface presentation. We show that both proteasomal targeting and repetition of the minigene increase cell-surface presentation of the epitope and propose both these approaches as potential strategies in DNA vaccines to increase MART-1-specific T-cell activation.

Induction of CAMEL/NY-ESO-ORF2-specific CD8+ T cells upon stimulation with dendritic cells infected with a modified Ad5 vector expressing a chimeric Ad5/35 fiber

Delivery of the full-length tumor antigen might be more successful in immunotherapy than single peptides and has the advantage that patients no longer need to be selected for their HLA type. In this study, we tested the in vitro induction of CAMEL/NY-ESO-ORF2-specific T cells by dendritic cells infected with an adenovirus (Ad) type 5 vector containing the fiber shaft and knob of human serotype Ad35 (Ad5F35 vector). Our data show induction of CD8(+) T cells specific for the known HLA-A(*)0201-binding CAMEL/NY-ESO-ORF2(1-11) epitope by DC infected with Ad5F35-CAMEL, but not by DC pulsed with the recombinant CAMEL protein. In one healthy donor, even CD8(+) T cells specific for a new HLA-B7-binding CAMEL/NY-ESO-ORF2(46-54) epitope were raised. In conclusion, the in vitro induction of CAMEL/NY-ESO-ORF2-specific CD8(+) T cells in healthy donors by DC infected with Ad5F35-CAMEL strongly supports further investigation of the Ad5F35 vector as a vehicle for gene transfer into DC for the generation of tumor antigen-specific CD8(+) T cell responses in vivo.

Antigen-specific immunotherapy and cancer vaccines

The specific activation of the immune system to control cancer growth in vivo has been a long-standing goal in cancer immunology and medical oncology. The identification of tumor-associated antigens has provided the basis for new concepts in antigen-specific immunotherapy. The first clinical trials on cancer vaccines were designed to evaluate the toxicity and objectively measurable immunologic effects in relation to clinical developments mostly in patients with metastatic disease. MHC class I- and II-restricted peptide epitopes, antigenic proteins, viral constructs, mini-genes and whole tumor cells have been used either alone or combined with different cytokines (i.e., IL-2, IL-12, GM-CSF), adjuvants (incomplete Freund's adjuvant, montanide, QS21) or with dendritic cells to induce specific immune responses in vivo. Standardized assay systems to evaluate the immunologic effects of cancer vaccines have been established. Clinical developments during and after vaccination were followed in relation to vaccine-induced immune responses. Prognostic tumor features, i.e., homogeneity of tumor antigen and MHC class I/II expression and intratumoral cellular infiltrates, have been identified that may help to select patients who are more likely to benefit from antigen-specific cancer vaccines in the future.

Vaccination with irradiated, autologous melanoma cells engineered to secrete granulocyte-macrophage colony-stimulating factor by adenoviral-mediated gene transfer augments antitumor immunity in patients with metastatic melanoma

PURPOSE

Vaccination with irradiated, autologous melanoma cells engineered to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF) by retroviral-mediated gene transfer generates potent antitumor immunity in patients with metastatic melanoma. Further clinical development of this immunization scheme requires simplification of vaccine manufacture. We conducted a phase I clinical trial testing the biologic activity of vaccination with irradiated, autologous melanoma cells engineered to secrete GM-CSF by adenoviral-mediated gene transfer.

PATIENTS AND METHODS

Excised metastases were processed to single cells, transduced with a replication-defective adenoviral vector encoding GM-CSF, irradiated, and cryopreserved. Individual vaccines were composed of 1 x 10(6), 4 x 10(6), or 1 x 10(7) tumor cells, depending on overall yield, and were injected intradermally and subcutaneously at weekly and biweekly intervals.

RESULTS

Vaccines were successfully manufactured for 34 (97%) of 35 patients. The average GM-CSF secretion was 745 ng/106 cells/24 hours. Toxicities were restricted to grade 1 to 2 local skin reactions. Eight patients were withdrawn early because of rapid disease progression. Vaccination elicited dense dendritic cell, macrophage, granulocyte, and lymphocyte infiltrates at injection sites in 19 of 26 assessable patients. Immunization stimulated the development of delayed-type hypersensitivity reactions to irradiated, dissociated, autologous, nontransduced tumor cells in 17 of 25 patients. Metastatic lesions that were resected after vaccination showed brisk or focal T-lymphocyte and plasma cell infiltrates with tumor necrosis in 10 of 16 patients. One complete, one partial, and one mixed response were noted. Ten patients (29%) are alive, with a minimum follow-up of 36 months; four of these patients have no evidence of disease.

CONCLUSION

Vaccination with irradiated, autologous melanoma cells engineered to secrete GM-CSF by adenoviral-mediated gene transfer augments antitumor immunity in patients with metastatic melanoma.

Generation of melanoma-specific cytotoxic T lymphocytes for allogeneic immunotherapy

To exploit alloreactive T-cell responses known as the graft-versus-tumor effect, allogeneic hematopoietic stem cell transplantation is being explored as experimental therapy in selected solid tumors, including metastatic melanoma. However, donor T-cell responses are often delayed and associated with severe graft-versus-host disease. Posttransplant adoptive immunotherapy using tumor-specific cytotoxic T lymphocytes (CTL) of donor origin might provide immediate graft-versus-tumor effects but not graft-versus-host disease. Therefore, the aim of the current study was to define in vitro conditions for the expansion of allogeneic major histocompatibility complex-matched CTLs targeting melanoma-associated antigens (MAA). The CTLs were generated from peripheral blood mononuclear cells (PBMCs) of HLA-A*0201+ healthy donors by repetitive stimulations with HLA-A*0201-restricted MAA-derived peptides. Melanoma reactivity, as determined by lysis of peptide-pulsed T2 cells and HLA-A2+/Ag+ melanoma cells, was detected using in vitro expanded CTL targeting MAA peptides AAGIGILTV(MT(27-35)), IMDQVPFSV(G(209-2M)), and YMDGTMSQV(T(368-376)). In contrast, FLWGPRALV(MAGE3(271)-(279)) and VLPDVFIRCV(GnT-V(nt38-67)) induced peptide-specific recognition of T2 target cells only, whereas ITDQVPFSV(G(209-217)), KTWGQYWQV(G9(154)), MLLAVLYCL(T(1-9)), and tumor lysate could not induce specific CTLs. Specific cytolytic activity was accompanied by interferon-gamma secretion. Peptide-pulsed dendritic cells were required only for the initial stimulation of CTLs and could be substituted by PBMCs during restimulations. The median expansion rate of CTL was five to six times, regardless of whether dendritic cells or PBMCs were used after the initial stimulation. The results delineate the conditions for effective ex vivo expansion of melanoma-specific CTLs from PBMCs of healthy donors to be used as an adjunct in allogeneic cell therapy of metastatic melanoma.

Universal tumor antigens as targets for immunotherapy

BACKGROUND

Clinically successful Ag-specific cancer immunotherapy depends on the identification of tumor-rejection Ags. Historically, tumor Ags have been identified by analyzing cancer patients' own T-cell or Ab responses.

METHODS

The unveiling of the human genome and optimized immunological analytical tools, particularly 'reverse immunology', have made it possible to screen any given protein for immunogenic epitopes. These advances enable the immunological characterization of universal tumor-associated gene products that mediate critical functions for tumor growth and development.

RESULTS

Four examples of candidate universal tumor Ags reviewed here include the telomerase reverse transcriptase (hTERT), the inhibitor of apoptosis survivin, the p53-interacting protein MDM2, and the cytochrome P450 isoform 1B1--each at various levels of preclinical and clinical development.

DISCUSSION

The cardinal feature of universal TAA is that they are expressed in (nearly) all tumors and in no normal tissues. They are directly involved in the malignant phenotype of the tumor. Certain peptides derived from such Ags are expressed on the tumor-cell surface, as evidenced by Ag-specific, MHC-restricted T-cell anti-tumor reactivity in vitro. It is hoped that these features imply a pre-existing, high-affinity T-cell pool that can be activated in vivo in patients, without immunoselection of variant tumor cells no longer expressing the Ag of choice.