Identification of an HLA-A*0201 cytotoxic T lymphocyte epitope specific to the endothelial antigen Tie-2

Vaccination approach to anti-angiogenic treatment of cancer

Improvement of patient survival by anti-angiogenic therapy has proven limited. A vaccination approach inducing an immune response against the tumor vasculature combines the benefits of immunotherapy and anti-angiogenesis, and may overcome the limitations of current anti-angiogenic drugs. Strategies to use whole endothelial cell vaccines and DNA- or protein vaccines against key players in the VEGF signaling axis, as well as specific markers of tumor endothelial cells, have been tested in preclinical studies. Current clinical trials are now testing the promise of this specific anti-cancer vaccination approach. This review will highlight the state-of-the-art in this exciting field of cancer research.

Vaccines targeting the neovasculature of tumors

Angiogenesis has a critical role in physiologic and disease processes. For the growth of tumors, angiogenesis must occur to carry sufficient nutrients to the tumor. In addition to growth, development of new blood vessels is necessary for invasion and metastases of the tumor. A number of strategies have been developed to inhibit tumor angiogenesis and further understanding of the interplay between tumors and angiogenesis should allow new approaches and advances in angiogenic therapy. One such promising angiogenic approach is to target and inhibit angiogenesis with vaccines. This review will discuss recent advances and future prospects in vaccines targeting aberrant angiogenesis of tumors. The strategies utilized by investigators have included whole endothelial cell vaccines as well as vaccines with defined targets on endothelial cells and pericytes of the developing tumor endothelium. To date, several promising anti-angiogenic vaccine strategies have demonstrated marked inhibition of tumor growth in pre-clinical trials with some showing no observed interference with physiologic angiogenic processes such as wound healing and fertility.

CD8+ T-cell responses against hemoglobin-beta prevent solid tumor growth

Bone marrow-derived dendritic cells engineered using recombinant adenovirus to secrete high levels of IL-12p70 dramatically inhibited the growth of established CMS4 sarcomas in BALB/c mice after intratumoral administration. An analysis of splenic CD8(+) T cells in regressor mice revealed a strong, complex reactivity pattern against high-performance liquid chromatography (HPLC)-resolved peptides isolated by acid elution from single-cell suspensions of surgically resected CMS4 lesions. Mass spectrometry analyses defined two major overlapping peptide species that derive from the murine hemoglobin-beta (HBB) protein within the most stimulatory HPLC fractions. Although cultured CMS4 tumor cells failed to express HBB mRNA based on reverse transcription-PCR analyses, prophylactic vaccination of BALB/c mice with vaccines containing HBB peptides promoted specific CD8(+) T-cell responses that protected mice against a subsequent challenge with CMS4 or unrelated syngeneic (HBB(neg)) tumors of divergent histology (sarcoma, carcinomas of the breast or colon). In situ imaging suggested that vaccines limit or destabilize tumor-associated vascular structures, potentially by promoting immunity against HBB+ vascular pericytes. Importantly, there were no untoward effects of vaccination with the HBB peptide on peripheral RBC numbers, RBC hemoglobin content, or vascular structures in the brain or eye.

HLA class I transgenic mice: development, utilisation and improvement

Classical major histocompatibility complex (MHC) class I antigens are trimeric molecules found on the surface of nucleated cells in all jawed vertebrates. MHC I are recognised by two families of receptors: clonotypic T cell receptors expressed on the surface of CD8+ cytotoxic T lymphocytes (CTLs), and monomorphic receptors expressed by both natural killer cells and CTLs. The production of MHC I molecules within the cells is a sequential process performed with the help of interacting proteins: proteases, chaperones, transporters and so on. Although largely homologous in their structure, organisation and function, the human and mouse MHC I antigen processing and presentation machineries show fine differences. Transgenesis and 'knockout' or 'knock-in' technologies permit the addition of relevant human genes or the replacement of mouse genes by their human orthologues in order to produce immunologically humanised mice. Such experimental animals are especially relevant for the comparative evaluation of immunotherapies and for the characterisation of MHC I peptide epitopes. This review presents the similarities and differences between mouse and human MHC I antigen processing machinery, and describes the development and utilisation of improving mouse models of human cytotoxic T cell immunity.

The use of reverse immunology to identify HLA-A2 binding epitopes in Tie-2

A potential target for a cancer vaccine would be receptors, such as Tie-2 which are over expressed on tumour endothelium. Using computer aided motif predictions for possible HLA class I epitopes, we have identified peptides from Tie-2 that should bind with a range of affinities to HLA-A*0201. No direct correlation between predicted values and actual binding affinities was observed. Although, the programs did produce a number of false positives, two epitopes were predicted that bound with relatively high affinity when compared with an influenza peptide. We have previously identified a Tie-2 epitope and shown that it was only immunogenic when we substituted preferred amino acids at key anchor residues to increase binding affinity. In this study we used a similar approach to generate modified epitopes. When HLA-A2 transgenic mice were immunised with peptides, CTL killing of the target cells was only achieved when the wild type epitope was presented at moderate levels. Moreover, the efficiency of immunisation was increased when we linked CD4 epitopes to CD8 epitopes. Caution should therefore be employed in the use of both reverse immunology and anchor modification of CTL epitopes in the identification of CTL epitopes for cancer vaccines.

Complement decay accelerating factor (DAF)/CD55 in cancer

The complement system is a powerful innate mechanism involved in protection of the host against pathogens. It also has a role in the clearance of apoptotic cells and has been implicated in a range of pathologies including autoimmunity and graft rejection. The control of complement is mediated through the complement regulatory proteins (CRPs). These are present on most cells and protect normal cells from complement-mediated attack during innate activation. However, in a range of pathologies and cancer, these molecules are up or down regulated, sometimes secreted and even lost. We will review the expression of CRPs in cancer, focussing on CD55 and highlight other roles of the CRPs and their involvement in leukocyte function. We will also provide some data providing a potential mechanism by which soluble CD55 can inhibit T-cell function and discuss some of the implications of this data.

Development of cancer vaccines to activate cytotoxic T lymphocytes

Cancer vaccines have been shown to stimulate cytotoxic T lymphocyte (CTL) responses in a variety of cancer patients. However, the response is often of low frequency and moderate avidity, and does not result in objective clinical responses. This is related to the target antigens, which are usually over-expressed self-antigens that elicit tolerogenic and regulatory immune responses, resulting in deletion or inactivation of high-avidity T cells. Although moderate-avidity T cells can be efficient killers, tumours are often poor targets as they express a variety of molecules to protect them from cell-mediated immunity. Adoptive transfer of large numbers of high-avidity T cells has been shown to induce regression of bulky disease, proving that immune responses can effectively eradicate tumours. New approaches that target activated dendritic cells in vivo, resulting in cross-presentation of CTL epitopes and release of cytokines that suppress regulatory T cells, have resulted in the production of T cells with sufficient avidity to kill tumour target cells. These approaches in combination with regimes, such as cytokine therapy, chemotherapy or radiotherapy, that modulate effector costimulatory expression on tumour targets may result in more effective second-generation cancer vaccines.

Vaccines targeting tumour angiogenesis--a novel strategy for cancer immunotherapy

AIMS

To review the concept of tumour angiogenesis and anti-angiogenic therapy, limitations of recently used anti-angiogenic therapeutics; provide an up-to-date overview of the growing number of reports on vaccines targeting tumour angiogenesis; and finally discuss potential complications and future directions in the development of more potent and specific vaccines.

METHODS

A literature search was carried out from PubMed for indexed articles. The most important articles were analysed and discussed.

FINDINGS

The search yielded a large number of important indexed published articles that were reviewed, screened and tracked for other relevant publications. The most relevant articles, including those previously published by authors, were analysed and discussed.

CONCLUSIONS

Recently, different vaccine strategies have been reported to inhibit tumour growth and metastasis by induction of specific cellular and/or humoral immunity against angiogenesis-associated antigens in pre-clinical models, suggesting effective combination of anti-angiogenesis and cancer immunotherapy. Evaluation of tumour endothelial cells and clinical phase I study of the vaccines are recently ongoing, and should give us better insight into the possibilities of this novel strategy for cancer immunotherapy.