Human tumour antigens recognized by T-cells: perspectives for new cancer vaccines

Antitumor activity of liposomal ErbB2/HER2 epitope peptide-based vaccine constructs incorporating TLR agonists and mannose receptor targeting

Synthetic and molecularly defined constructs containing the minimal components to mimic and amplify the physiological immune response are able to induce an efficient cytotoxic response. In the current study this approach was applied to the development of highly versatile liposomal constructs to co-deliver peptide epitopes in combination with TLR agonists in order to induce a specific anti-tumor cellular immune response against ErbB2 protein-expressing tumor cells. Liposomes containing ErbB2 p63-71 cytotoxic T lymphocyte (CTL) and HA307-319 T- helper (Th) peptide epitopes associated to innovative synthetic TLR2/1 (Pam(3)CAG) or TLR2/6 agonists (Pam(2)CAG and Pam(2)CGD), were injected in mice bearing ErbB2 protein-expressing tumor cells. Mannosylated ligands were also incorporated into the constructs to target antigen-presenting cells. We showed that the TLR2/6 agonists were more efficient than the TLR2/1 agonists for the eradication of tumors expressing ErbB2 protein. Furthermore, mannose-targeted liposomes displayed higher therapeutic efficiency against tumor allowing treatment with decreased quantities of both TLR ligands and peptide epitopes. Our results validated that antigen-associated mannosylated liposomes combined with efficient TLR ligands are effective vectors for vaccination against tumor. In this study we developed useful tools to evaluate the vaccination efficiency of various adjuvants and/or targeting molecules and their potential synergy.

Chemokine expression in melanoma metastases associated with CD8+ T-cell recruitment

Despite the frequent detection of circulating tumor antigen-specific T cells, either spontaneously or following active immunization or adoptive transfer, immune-mediated cancer regression occurs only in the minority of patients. One theoretical rate-limiting step is whether effector T cells successfully migrate into metastatic tumor sites. Affymetrix gene expression profiling done on a series of metastatic melanoma biopsies revealed a major segregation of samples based on the presence or absence of T-cell-associated transcripts. The presence of lymphocytes correlated with the expression of defined chemokine genes. A subset of six chemokines (CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10) was confirmed by protein array and/or quantitative reverse transcription-PCR to be preferentially expressed in tumors that contained T cells. Corresponding chemokine receptors were found to be up-regulated on human CD8(+) effector T cells, and transwell migration assays confirmed the ability of each of these chemokines to promote migration of CD8(+) effector cells in vitro. Screening by chemokine protein array identified a subset of melanoma cell lines that produced a similar broad array of chemokines. These melanoma cells more effectively recruited human CD8(+) effector T cells when implanted as xenografts in nonobese diabetic/severe combined immunodeficient mice in vivo. Chemokine blockade with specific antibodies inhibited migration of CD8(+) T cells. Our results suggest that lack of critical chemokines in a subset of melanoma metastases may limit the migration of activated T cells, which in turn could limit the effectiveness of antitumor immunity.

Bone marrow-derived mesenchymal stem cells for treatment of heart failure: is it all paracrine actions and immunomodulation?

Despite significant advances in medical and surgical management of heart failure, mostly of ischaemic origin, the mortality and morbidity associated with it continue to be high. Pluripotent stem cells are being evaluated for treatment of heart failure. Bone marrow-derived mesenchymal stem cells (MSCs) have been extensively studied. Emerging evidence suggests that locally delivered MSCs can lead to an improvement in ventricular function, but the cellular and molecular mechanisms involved remain unclear. Myocardial regeneration, as proposed by many researchers as the underlying mechanism, has failed to convince the scientific community. Recently some authors have ascribed improvement in ventricular function to paracrine actions of MSCs.A lot has been written about the host immune response triggered by embryonic stem cells and the consequent need for immunosuppression. Not enough work has been done on immune interactions involving allogeneic bone marrow cells. Full potential of stem cell therapy can be realised only when we are able to use allogeneic cells. The potential use of MSCs in cellular therapy has recently prompted researchers to look into their interaction with the host immune response. MSCs have immunomodulatory properties. They cause suppression of proliferation of alloreactive T cells in a dose-dependent manner.Tissue injury causes inflammation and release of several chemokines, cytokines and growth factors. They can cause recruitment of bone marrow-derived MSCs to the injured area. We review the literature on paracrine actions and immune interactions of allogeneic MSCs.

Cancer-testis antigens: expression and correlation with survival in human urothelial carcinoma

PURPOSE

Vaccination against human cancer is a promising therapeutic approach but the optimal antigen or antigens remain undefined. Cancer-testis antigens (CTA), a family of tumor-associated antigens, have both potent immunogenicity and restricted expression patterns in normal adult tissues, highly desirable characteristics for targets of anticancer vaccines. These antigens were evaluated for both the degree of expression and prognostic value in cancer of the urothelium.

EXPERIMENTAL DESIGN

The expression patterns of nine CTAs (NY-ESO-1, LAGE-1, MAGE-A1, MAGE-A3, MAGE-A4, MAGE-A10, CT7, CT10, and GAGE) were examined by immunohistochemistry and reverse transcription-PCR in a panel of high-grade urothelial carcinomas of the urinary bladder. Also assessed were correlations between the expression of CTAs by immunohistochemistry and both disease-free and overall survival.

RESULTS

At least one CTA was expressed in 77% of samples and 61% of these tumors expressed more than one CTA. Additionally, patients with CT10-positive tumors had an improved disease-free survival (P=0.008) and overall survival (P=0.037) compared with patients with CT10-negative tumors.

CONCLUSIONS

These findings establish CTAs as potential prognostic markers and as target candidates for vaccine development for patients with urothelial carcinoma.

Non-classical HLA-G antigen and its role in the cancer progression

Various changes take place during the progression of cancer, some of which are favorable for tumor development and may help to escape the immunosurvillance. These include changes in the microenvironment around the developing tumor, which could be produced in response to phenotypic alterations or could modulate the expression of certain markers of tumor development. One such newly discovered molecule is HLA-G, which has been found to have immunosuppressive and immunomodulatory roles in the cancer development. The regulatory sequences, as seen, may be induced by various factors that may be present in tumor microenvironment. A recent study has investigated the antigen -G as a marker of susceptibility to chemotherapy. Further, its expression on tumors and how it can be exploited for diagnosis and therapy is discussed in this article.

Mesenchymal stem cells avoid allogeneic rejection

Adult bone marrow derived mesenchymal stem cells offer the potential to open a new frontier in medicine. Regenerative medicine aims to replace effete cells in a broad range of conditions associated with damaged cartilage, bone, muscle, tendon and ligament. However the normal process of immune rejection of mismatched allogeneic tissue would appear to prevent the realisation of such ambitions. In fact mesenchymal stem cells avoid allogeneic rejection in humans and in animal models. These finding are supported by in vitro co-culture studies. Three broad mechanisms contribute to this effect. Firstly, mesenchymal stem cells are hypoimmunogenic, often lacking MHC-II and costimulatory molecule expression. Secondly, these stem cells prevent T cell responses indirectly through modulation of dendritic cells and directly by disrupting NK as well as CD8+ and CD4+ T cell function. Thirdly, mesenchymal stem cells induce a suppressive local microenvironment through the production of prostaglandins and interleukin-10 as well as by the expression of indoleamine 2,3,-dioxygenase, which depletes the local milieu of tryptophan. Comparison is made to maternal tolerance of the fetal allograft, and contrasted with the immune evasion mechanisms of tumor cells. Mesenchymal stem cells are a highly regulated self-renewing population of cells with potent mechanisms to avoid allogeneic rejection.

Mass-spectrometric evaluation of HLA-A*0201-associated peptides identifies dominant naturally processed forms of CTL epitopes from MART-1 and gp100

Melanoma-reactive human cytotoxic T lymphocytes (CTLs) mediate tumor regression in vivo through specific recognition of MHC-associated peptide epitopes, many of which are encoded by the melanocytic tissue differentiation proteins gp100/Pme117 and MART-1/Melan-A. Vaccines using these peptides may induce protective or therapeutic immunity against melanoma. Rational design of such approaches is aided by a clear understanding of the identity of these antigenic peptides; however, most CTL epitopes described to date were identified indirectly. Especially where these peptides may be used in human clinical trials for the treatment or prevention of cancer, there is substantial need for direct evaluation of HLA-A*0201-associated peptides from MART-1 and gp100 that are naturally processed and presented. To that end, we have isolated peptides directly from HLA-A*0201 molecules of human melanoma cells and have determined that naturally processed epitopes for HLA-A*0201-restricted, melanoma-reactive CTLs include the nonamers MART-1(27-35) (AAGIGILTV), gp100(154-162) (KTWGQYWQV), gp100(209-217) (ITDQVPFSV) and gp100(280-288) (YLEPGPVTA) and the decamer gp100(476-485) (VLYRYGSFSV). Among these, the one that appears to be most abundant at the cell surface is gp100(154-162) (KTWGQYWQV). The others are among the less abundant peptides. HLA-A*0201-restricted CTLs from one melanoma patient who has survived metastatic disease recognized MART-1(27-35) (AAGIGILTV), gp100(280-288) (YLEPGPVTA) and gp100(154-162) (KTWGQYWQV) and were cross-reactive on longer peptides that contained these nonamer sequences. These peptides, identified by both an indirect genetic approach and by a direct peptide approach, can be used for tumor vaccine strategies with confidence that they are identical to the naturally processed peptide epitopes presented at the surface of melanoma cells in association with HLA-A*0201 molecules.

Immunotherapeutic approaches to sarcoma

In the last decade, the most important factor in the rekindled interest in immune therapy for cancer is the development of new methods to identify tumor antigens that can be recognized by T-cells and other immune effectors. In addition, greater knowledge about tolerance and mechanisms of tumor cell evasion from immune effectors has made the prospect of developing clinically effective immune therapies for cancer seem promising. Research in immune therapies for sarcoma has been limited, mainly because of the previous lack of defined tumor antigens in this disease and the low prevalence of sarcoma in the general population. We will review the fundamental concepts of tumor immunobiology, both cellular and humoral, and highlight the new, powerful methods for identifying novel tumor antigens. Further, we will focus on the unique situation presented by sarcoma as the only solid tumor in which many cytogenetic abnormalities have been characterized which encode for unique, tumor-specific fusion proteins that are ideal targets for immune-based therapy. We will review the specifics of vaccine therapy approach to this disease, with emphasis on strategies to improve the immunogenicity of newly defined tumor antigens in sarcoma.

Approaches to new vaccines

The explosive technological advances in the fields of immunology and molecular biology in the last 5 years had an enormous impact on the identification of candidate vaccines against diseases, which until a few years ago seemed uncontrollable. Increased knowledge of the immune system has helped to define the mechanisms that underlie successful immunization and is now being exploited to develop improved versions of existing vaccines and new vaccines against emerging pathogens, tumors, or autoimmune diseases. An understanding of the mechanisms of action of novel adjuvants and the development of new vector and delivery systems will have a major impact on vaccine strategies. The use of DNA encoding antigens from pathogenic viruses, bacteria, and parasites as vaccines is a new approach that is receiving considerable attention. This and other innovative approaches, including vaccine production in plants, are appraised in this review. The successful eradication of smallpox and the imminent eradication of poliomyelitis by worldwide immunization campaigns provide positive examples of how the vaccine-mediated approach can lead to disease elimination; with the advent of new vaccines and improved delivery systems, there is no scientific reason why these successes cannot be repeated.

Pulsing of dendritic cells with cell lysates from either B16 melanoma or MCA-106 fibrosarcoma yields equally effective vaccines against B16 tumors in mice

BACKGROUND AND OBJECTIVES

Dendritic cells (DC) pulsed in vitro with a variety of antigens have proved effective in producing specific antitumor effects in vivo. Experimental evidence from other laboratories has confirmed that shared antigens can be encountered in histologically distinct tumors. In our experiments, we set out to evaluate the immunotherapeutic potential of vaccines consisting of DC pulsed with MCA-106 fibrosarcoma or B16 melanoma cell lysates and to determine whether a cross-reactivity exists between the two tumors.

METHODS

DC were prepared from the bone marrow of C57BL/6 (B6) mice by culturing progenitor cells in murine granulocyte-macrophage colony-stimulating factor (GM-CSF). They were separated into three equal groups and were either pulsed with B16 melanoma cell lysates (BDC), pulsed with tumor extract from the syngeneic fibrosarcoma MCA-106 (MDC), or left unpulsed (UDC). DC were then used to immunize three groups of mice, with all mice receiving two weekly intravenous (IV) doses of 1 x 10(6) DC from their respective preparations on days -14 and -7. A fourth group of control mice were left untreated. On day 0, all mice were challenged with subcutaneous injections of 1 x 10(5) B16 and 1 x 10(5) MCA tumor cells, administered in the left and right thighs, respectively. After the inoculations, the mice were monitored closely with respect to tumor growth and survival.

RESULTS

The MDC mice developed specific cellular immunity directed against not only MCA-106 tumor cells, but also against B16 melanoma, as measured through chromium-release assays of splenocyte preparations, while remaining ineffective at killing both L929 fibroblasts and CT26 tumor cells. By day 30 after tumor inoculations, control mice manifested the largest B16 tumor volumes at a mean of 2185 mm3, followed by the UDC, MDC, and BDC groups at 92 mm3 (P=0.00008), 3 mm3 (P=0.000002), and 2 mm3 (P=0.00004), respectively. The survival data mirrored this pattern, with control animals displaying the shortest mean survival time (37.1+/-4.0 days), followed by UDC (44.8+/-6.6), MDC (56.2 +/-14.7), and BDC (56.4+/-18.3) animals. No significant differences were noted between MCA-106 and B16 cell lysate-pulsed DC vaccines with respect to their abilities to inhibit B16 tumor growth and to prolong survival. These findings were confirmed using a B16 pulmonary metastasis model. Likewise, vaccination with interferon-gamma gene-modified MCA-106 tumor cells was shown to be effective at protecting against a subsequent subcutaneous B16 tumor challenge in 3 of 4 mice observed.

CONCLUSIONS

These results demonstrate that immunization with antigen-pulsed DC confers cellular immunity, retards tumor growth, and prolongs the survival of tumor-challenged mice. The ability of MCA-106 cell lysate-pulsed DC vaccines to inhibit the growth of subcutaneous B16 tumors also suggests the presence of shared tumor-associated antigens between these two histologically distinct tumors.

Blockade of metastasis formation by CD44-receptor globulin

CD44 standard as well as variant isoforms have been frequently reported to be involved in the process of metastasis formation. Whereas in the rat system, but also in some human tumours, the variant exon v6 is of importance in the lymphatic spread of carcinomas, in human malignant melanoma CD44s and, possibly, CD44v10 appear to facilitate local invasion and haematogenous spread. This has been tested in the B16F10 murine melanoma model by treating B16F10-bearing C57BL/6 mice either with a CD44s-/ CD44v10-specific antibody, or with receptor globulins (Rg) containing the extracellular part of CD44s or CD44v10 linked to the constant region of the immunoglobulin kappa light chain. Prior characterization of the CD44s and CD44v10 Rg had shown that both Rgs bound to components of the extracellular matrix, CD44s in particular to hyaluronic acid. Immunohistological screening of organ sections from adult C57BL/6 mice revealed additional evidence for both Rgs binding to elements of the extracellular matrix, particularly in bone marrow, intestine and lung. In the absence of any further treatment, the CD44s Rg reduced the number of lung colonies by 70%, while application of the CD44v10 Rg resulted in 60% reduction. CD44-specific antibodies were equally efficient with regard to B16F10 settlement in the lung. However, only the CD44 Rgs prevented spread and settlement of melanoma cells in distant organs. The finding confirms the involvement of both CD44s and CD44v10 in melanoma progression, and is suggestive for the use of Rgs as therapeutic reagents.

Management of cutaneous melanoma M0: state of the art and trends

This article reviews the epidemiology, diagnosis and treatment of cutaneous melanoma, including the most recent developments. The combination of positive family history, fair complexion, number of nevi, exposure to sun and/or chromosomal alterations seem to be implicated in the pathogenesis of cutaneous melanoma. Melanomas can be classified according to their growth patterns, and tumour microstaging is of straightforward predictive value for survival and risk of metastasis, although new factors are also being investigated. As yet, surgical excision is the only effective treatment available for primary tumours, resection margins varying according to tumour thickness. Elective node dissection is, however, no longer advocated for melanomas thinner than 1.5 mm, and there is disagreement as to its role for thicker lesions. In contrast, selective node dissection at the time of definitive surgery is becoming more widely accepted, with regional node dissection being restricted to positive cases. Therapeutic dissection is required for lymph node involvement, the most common pattern of recurrence from melanoma, which affects nearly 30% of all patients. Complete remission rates from isolated limb perfusion, which has been employed in patients with multiple recurrences or in-transit metastases, range from 40 to 90%, depending on drugs and techniques used in different series; the best responses so far have been obtained with tumour necrosis factor in combination with melphalan. Patients with thick lesions (> 4 mm) or lymph node metastases have a high risk of micrometastases that would warrant adjuvant therapy. The only agent found to affect survival is interferon alpha-2.

Tumor antigens and tumor vaccines: peptides as immunogens

Tumor antigens recognized by human cytotoxic T lymphocytes (CTL) have been identified for multiple types of solid tumors. These include both shared and unique antigens. Unique antigens are those expressed uniquely by one patient's tumor, and shared antigens are those present on tumor cells from many different patients. Many of the shared antigens are derived from tissue-specific differentiation antigens, oncogenes, or a set of antigens expressed only in tumors or in testis. In addition to advances in understanding tumor antigens that stimulate CTL and T-helper cell responses, there have been advances in understanding immunity in general, including the characterization of cytokines, the recognition of the dendritic cell as an optimal antigen-presenting cell (APC), and the characterization of costimulatory molecules as critical components of antigen presentation. Together, these developments have breathed new life into tumor immunology, and they promise to lead to a new generation of peptide- and cell-based tumor vaccines.