Anti-tumor activity of cytotoxic T lymphocytes elicited with recombinant and synthetic forms of a model tumor-associated antigen

Stimulation of an anti-tumor immune response with "chromatin-damaging" therapy

Curaxins are small molecules that bind genomic DNA and interfere with DNA-histone interactions leading to the loss of histones and decondensation of chromatin. We named this phenomenon 'chromatin damage'. Curaxins demonstrated anti-cancer activity in multiple pre-clinical tumor models. Here, we present data which reveals, for the first time, a role for the immune system in the anti-cancer effects of curaxins. Using the lead curaxin, CBL0137, we observed elevated expression of several group of genes in CBL0137-treated tumor cells including interferon sensitive genes, MHC molecules, some embryo-specific antigens suggesting that CBL0137 increases tumor cell immunogenicity and improves recognition of tumor cells by the immune system. In support of this, we found that the anti-tumor activity of CBL0137 was reduced in immune deficient SCID mice when compared to immune competent mice. Anti-tumor activity of CBL0137 was abrogated in CD8+ T cell depleted mice but only partially lost when natural killer or CD4+ T cells were depleted. Further support for a key role for the immune system in the anti-tumor activity of CBL0137 is evidenced by an increased antigen-specific effector CD8+ T cell and NK cell response, and an increased ratio of effector T cells to Tregs in the tumor and spleen. CBL0137 also elevated the number of CXCR3-expressing CTLs in the tumor and the level of interferon-γ-inducible protein 10 (IP-10) in serum, suggesting IP-10/CXCR3 controls CBL0137-elicited recruitment of effector CTLs to tumors. Our collective data underscores a previously unrecognized role for both innate and adaptive immunity in the anti-tumor activity of curaxins.

Administration of DNA Encoding the Interleukin-27 Gene Augments Antitumour Responses through Non-adaptive Immunity

DNA-mediated immunization of a tumour antigen is a possible immunotherapy for cancer, and interleukin (IL)-27 has diverse functions in adaptive immunity. In this study, we examined whether IL-27 DNA administration enhanced antitumour effects in mice vaccinated with DNA encoding a putative tumour antigen, β-galactosidase (β-gal). An intramuscular injection of cardiotoxin before DNA administration facilitated the exogenous gene expression. In mice received β-gal and IL-27 DNA, growth of β-gal-positive P815 tumours was retarded and survival of the mice was prolonged. Development of β-gal-positive Colon 26 tumours was suppressed by vaccination of β-gal DNA and further inhibited by additional IL-27 DNA administration or IL-12 family cytokines. Nevertheless, a population of β-gal-specific CD8(+) T cells did not increase, and production of anti-β-gal antibody was not enhanced by IL-27 DNA administration. Spleen cells from mice bearing IL-27-expressing Colon 26 tumours showed greater YAC-1-targeted cytotoxicity although CD3(-)/DX5(+) natural killer (NK) cell numbers remained unchanged. Recombinant IL-27 enhanced YAC-1-targeted cytotoxicity of IL-2-primed splenic NK cells and augmented a phosphorylation of signal transducer and activator of transcription 3 and an expression of perforin. These data collectively indicate that IL-27 DNA administration activates NK cells and augments vaccination effects of DNA encoding a tumour antigen through non-adaptive immune responses.

Fas ligand DNA enhances a vaccination effect by coadministered DNA encoding a tumor antigen through augmenting production of antibody against the tumor antigen

Interaction of Fas and Fas ligand (FasL) plays an important role in the regulation of immune responses by inducing apoptosis of activated cells; however, a possible role of FasL in DNA vaccination has not been well understood. We examined whether administration of DNA encoding FasL gene enhanced antitumor effects in mice that were vaccinated with DNA expressing a putative tumor antigen gene, β-galactosidase (β-gal). Growth of β-gal-positive Colon 26 tumors was retarded in the syngeneic mice immunized with β-gal and FasL DNA compared with those vaccinated with β-gal or FasL DNA. We did not detect increased numbers of β-gal-specific CD8(+) T cells in lymph node of mice that received combination of β-gal and FasL DNA, but amounts of anti-β-gal antibody increased with the combination but not with β-gal or FasL DNA injection alone. Subtype analysis of anti-β-gal antibody produced by the combination of β-gal and FasL DNA or β-gal DNA injection showed that IgG2a amounts were greater in mice injected with both DNA than those with β-gal DNA alone, but IgG2b amounts were lower in both DNA-injected than β-gal DNA-injected mice. These data suggest that FasL is involved in boosting humoral immunity against a gene product encoded by coinjected DNA and enhances the vaccination effects.

HDL mimetics inhibit tumor development in both induced and spontaneous mouse models of colon cancer

Recent studies suggest that high-density lipoprotein (HDL) levels are inversely related to colon cancer risk. HDL mimetics constructed from a number of peptides and proteins with varying structures possess anti-inflammatory and antioxidant properties reminiscent of HDL. In this article, we examined whether HDL mimetics, L-4F (an apolipoprotein A-I mimetic peptide) and G* (an apolipoprotein J mimetic peptide) affect tumor growth and development in mouse models of colon cancer. HDL mimetics reduced viability and proliferation of CT26 cells, a mouse colon adenocarcinoma cell line, and decreased CT26 cell-mediated tumor burden in BALB/c mice when administered subcutaneously or orally. Plasma levels of lysophosphatidic acid (LPA), a serum biomarker for colon cancer, were significantly reduced in mice that received HDL mimetics, suggesting that binding and removal of proinflammatory lipids is a potential mechanism for the inhibition of tumor development by HDL mimetics. Furthermore, L-4F significantly reduced size and number of polyps in APC(min/+) mice, a mouse model for human familial adenomatous polyposis, suggesting that HDL mimetics are effective in inhibiting the development of both induced and spontaneous cancers of the colon. Our results, for the first time, identify HDL mimetics as a novel therapeutic strategy for the treatment of colon cancer.

Photodynamic therapy of tumors can lead to development of systemic antigen-specific immune response

Background

The mechanism by which the immune system can effectively recognize and destroy tumors is dependent on recognition of tumor antigens. The molecular identity of a number of these antigens has recently been identified and several immunotherapies have explored them as targets. Photodynamic therapy (PDT) is an anti-cancer modality that uses a non-toxic photosensitizer and visible light to produce cytotoxic reactive oxygen species that destroy tumors. PDT has been shown to lead to local destruction of tumors as well as to induction of anti-tumor immune response.

Methodology/Principal Findings

We used a pair of equally lethal BALB/c colon adenocarcinomas, CT26 wild-type (CT26WT) and CT26.CL25 that expressed a tumor antigen, β-galactosidase (β-gal), and we treated them with vascular PDT. All mice bearing antigen-positive, but not antigen-negative tumors were cured and resistant to rechallenge. T lymphocytes isolated from cured mice were able to specifically lyse antigen positive cells and recognize the epitope derived from beta-galactosidase antigen. PDT was capable of destroying distant, untreated, established, antigen-expressing tumors in 70% of the mice. The remaining 30% escaped destruction due to loss of expression of tumor antigen. The PDT anti-tumor effects were completely abrogated in the absence of the adaptive immune response.

Conclusion

Understanding the role of antigen-expression in PDT immune response may allow application of PDT in metastatic as well as localized disease. To the best of our knowledge, this is the first time that PDT has been shown to lead to systemic, antigen- specific anti-tumor immunity.

IL-17 is a potent synergistic factor with GM-CSF in mice in stimulating myelopoiesis, dendritic cell expansion, proliferation, and functional enhancement

OBJECTIVE

Interleukin (IL)-17, which now defines the Th(17) immune response, is a critical cytokine expressed and required for stress granulopoiesis during microbial invasion. Dendritic cells (DC) can instigate this response by inducing IL-17 expression in CD4(+) T cells. Besides IL-17, microbial invasion also stimulates production of the DC growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF). The objective was the in vitro and in vivo investigation of IL-17 on DC proliferation and function in mice.

MATERIALS AND METHODS

Murine IL-17 (mIL-7) or murine GM-CSF (mGM-CSF), or both, was expressed in C57BL6 mice using adenoviral technology to assess hematopoietic and DC changes. The E-22 tymoma tumor cell line using a previously described vaccinia virus ovalbumin/LacZ murine tumor model was employed to study effects on tumor rejection.

RESULTS

The combination of mIL-17 and mGM-CSF increased peripheral neutrophila by 28-fold and splenic colonies by 11- and 14-fold over each individual factor in mice, respectively. The effect of mIL-17 by itself on murine DCs in vitro and in vivo was minimal; however, the combination greatly enhanced the stimulating effects of mGM-CSF, increasing the total numbers of CD14b/c(+) spleen DC by fourfold, as well as their function measured by enhanced endocytosis. Mixed lymphocyte reactions using mIL-17/mGM-CSF cultured DCs stimulator cells enhanced lymphocyte responses by twofold over mGM-CSF alone. Vaccination against LacZ in the C57BL6 E22 syngenic thymoma tumor model effectively delayed tumor growth in animals pretreated with the mIL-17/mGM-CSF combination prior to vaccination.

CONCLUSIONS

mIL-17 effectively synergizes with mGM-CSF in stimulating granulopoiesis and DC expansion, as well as in functional enhancement of DCs.

A green fluorescent protein-expressing murine tumour but not its wild-type counterpart is cured by photodynamic therapy

The ideal cancer treatment should both destroy the primary tumour and at the same time educate the immune system to recognise the tumour as foreign so that distant metastases will also be eradicated. Photodynamic therapy (PDT) involves the i.v. administration of photosensitisers followed by illumination of the tumour with red light producing reactive oxygen species that eventually cause vascular shutdown and tumour cell death by apoptosis and necrosis. Anti-tumour immunity is stimulated after PDT due to the acute inflammatory response, generation of tumour-specific antigens, and induction of heat-shock proteins. Green fluorescent protein (GFP) is used as an optical reporter to noninvasively image the progression of mouse tumours, and in addition, may act as a foreign (jellyfish) antigen. We asked whether GFP-expressing tumours could be used to monitor the response of tumour-bearing mice to PDT, and whether the tumour response differed when a nonimmunogenic tumour cell line was transduced with GFP. We injected RIF-1 or RIF-1 EGFP (stably transduced with a retroviral vector) cells in the leg of C3H/HeN mice and both the cells and tumour grew equally well. We used PDT with benzoporphyrin derivative and a short drug-light interval. There were complete cures and 100% mouse survival of RIF-1 EGFP while RIF-1 wild-type tumours all recurred. Cured mice were resistant to rechallenge with RIF-1 EGFP cells and a rechallenge with wild-type RIF-1 cells grew significantly slower. There was also slower RIF-1 EGFP rechallenge growth but no rejection when RIF-1 EGFP tumours were surgically removed. There was a low rate of PDT cure of tumours when RIF-1 cells were transduced with an empty retroviral vector. The presence of antibodies against EGFP in mouse serum suggests EGFP can act as a foreign antigen and PDT can then stimulate a long-term memory immune response.

Toward Personalized Immunotherapy for Non-Hodgkin Lymphoma

The idiotypic determinants of B-cell lymphomas, formed by cell-specific rearrangement of the immunoglobulin genes, are unique and are therefore a suitable target against which to direct immunotherapy. Recent advances in our understanding of the fundamental mechanisms behind an effective immune response, coupled with advances in genetic engineering techniques, have led to a renewed interest in immunotherapy. Early clinical studies have confirmed the immunogenicity of the idiotypic antigen in patients with lymphoma. This review discusses the different methods of idiotypic vaccination currently under investigation in the clinic, including protein, genetic, and cellular vaccines. Protein vaccines are the most clinically advanced, with phase III trials of idiotypic protein linked to GM-CSF currently underway. DNA vaccines are easier to produce but to date only appear to be weakly immunogenic in man. Dendritic cell vaccines have shown promise but their use may be limited by the complexity of this approach. This review also highlights other approaches not yet in the clinic but that have shown promise in the laboratory, such as viral vaccines and T-cell therapy.

Antigen-specific tumor vaccine efficacy in vivo against prostate cancer with low class I MHC requires competent class II MHC

BACKGROUND

Cancers can escape immune recognition by means of evading class I major histocompatibility complex (MHC) -mediated recognition by cytotoxic T lymphocytes. However, immunization strategies targeting defined tumor-associated antigens have not been extensively characterized in murine prostate cancer models. Therefore, we evaluated antigen-specific, antitumor immunity after antigen-encoding vaccinia immunization against mouse prostate cancer cells expressing a model tumor-associated antigen (beta-galactosidase) and exhibiting partially deficient class I MHC.

METHODS AND RESULTS

Low class I MHC expression in beta-galactosidase-expressing D7RM-1 prostate cancer cells was shown by fluorescence activated cell sorting, and deficient class I MHC-mediated antigen presentation was shown in resistance of D7RM-1 to cytolysis by beta-galactosidase-specific cytotoxic T lymphocytes (CTL). Despite partially deficient class I MHC presenting function, immunization with vaccinia encoding beta-galactosidase conferred antigen-specific protection against D7RM-1 cancer. Antigen-specific immunity was recapitulated in beta(2)m knockout mice (with deficient class I MHC and CTL function), confirming that class I MHC antigen presentation was not required for immunity against tumor partially deficient in class I MHC. Conversely, antigen-specific antitumor immunity was abrogated in A(b)beta knockout mice (with deficient class II MHC and helper T cell function), demonstrating a requirement for functional class II MHC. Resistant tumors from the otherwise effectively immunized beta(2)m knockout mice (among which tumor progression had been reduced or delayed) showed reduced target antigen expression, corroborating antigen-specificity (and showing an alternative immune escape mechanism), whereas antigen expression (like tumor growth) was unaffected among A(b)beta knockout mice.

CONCLUSION

Our results demonstrate that class I MHC-restricted antigen presentation and CTL activity is neither necessary nor sufficient for antigen-encoding vaccinia immunization to induce protective immunity against class I MHC-low tumors, whereas host class II MHC-mediated antigen presentation facilitates antigen-specific immunity against prostate cancer in vivo. Reduced expression of the target antigen developed rapidly in vivo as an immune escape mechanism for such cancers.

Regression of extensive pulmonary metastases in mice by adoptive transfer of antigen-specific CD8(+) CTL reactive against tumor cells expressing a naturally occurring rejection epitope

In this study, we developed a mouse model of adoptive immunotherapy reflecting immune recognition of syngeneic tumor cells naturally expressing an endogenous rejection Ag. Specifically, in a pulmonary metastases model, we examined the potency and maintenance of an antitumor CD8(+) CTL response in vivo, as well as its effectiveness against an "extensive" tumor burden. The approach taken was to first generate tumor-specific CTL from mice challenged with the CMS4 sarcoma coadministered with anti-CTLA4 mAb, which has been shown to facilitate the induction of Ag-specific T cell responses in vivo. An H-2L(d)-restricted nonamer peptide, derived from an endogenous murine leukemia provirus was identified as a CMS4-reactive CTL epitope based upon the following: CTL cross-recognition of another syngeneic tumor cell line (CT26 colon carcinoma) previously characterized to express that gene product; sensitization of Ag-negative lymphoblasts or P815 targets with the peptide; and by cold target inhibition assays. In vivo, the adoptive transfer of CMS4-reactive CTL (> or =1 x 10(6)) resulted in nearly the complete regression of 3-day established lung metastases. Furthermore, mice that rejected CMS4 following a single adoptive transfer of CTL displayed antitumor activity to a rechallenge 45 days later, not only in the lung, but also at a s.c. distal site. Lastly, the adoptive transfer of CTL to mice harboring extensive pulmonary metastases (> 150 nodules) led to a substantial reduction in tumor burden. Overall, these data suggest that the adoptive transfer of tumor-specific CTL may have therapeutic potential for malignancies that proliferate in or metastasize to the lung.

Soluble tumor necrosis factor receptor type I enhances tumor development and persistence in vivo

Secretion of human soluble tumor necrosis factor receptor type I (sTNFRI) by the mouse fibrosarcoma cell line, L929, previously has been demonstrated to confer resistance to in vitro lysis by TNF and to LAK- and CTL-mediated cytolysis. These findings suggest that, in vivo, sTNFRI contributes to tumor survival by inhibiting these immunologic mechanisms. To evaluate this hypothesis, we compared the growth of sTNFRI-secreting L929 cells with that of the unmodified parental fibrosarcoma in an in vivo mouse transplantation model. Secretion of sTNFRI by L929 cells markedly enhanced their tumorigenicity and persistence in syngeneic recipients. This benefit was abrogated by sTNFRI-neutralizing antibodies induced by immunization prior to tumor challenge. These data demonstrate that sTNFRI directly influences tumor formation and persistence in vivo and suggest the selective removal and/or inactivation of sTNFRI as a promising new avenue for cancer immunotherapy.

Are natural antibodies involved in tumour defence?

Natural antibodies (NAb) are found in the serum of healthy individuals. These antibodies are produced without any apparent specific antigenic stimulation. They are one part of the circulating immunoglobulins and are found in virtually all vertebrate species. NAb react to various self- and non-self antigens. A protective function in different infection models could be demonstrated. Several groups have reported the ability of NAb to bind to tumour cells. Their possible role in tumour defence is documented in mice. The present status of attempts to characterise the role of NAb in tumour defence is discussed, particularly as regards the human immune system. This paper focuses on antibody cell interactions and discusses the genetic background of the Nab-producing B-cells.

Cancer therapy: new concepts on active immunization

There is increasing evidence that tumors express putative target molecules for a therapeutic immune reaction. Yet, tumor cells lack the prerequisites for appropriate antigen presentation and--hence--the immune system does not respond. This difficulty can probably be circumvented when tumor antigens are processed by conventional antigen presenting cells. Thus, the identification of immunogenic tumor-associated antigens may allow new modes of vaccination with the hope of adding a fourth and hopefully powerful weapon to surgery, radiation and chemotherapy in the fight against cancer.

Apoptotic Death of CD8+ T Lymphocytes After Immunization: Induction of a Suppressive Population of Mac-1+/Gr-1+ Cells

Following an infection or immunization, a primary CD8+ T cell response generally rises then falls rapidly before giving rise to a “memory” response. When we immunized mice with recombinant viral immunogens optimized to enhance the lytic capability of CD8+ T cells, we measured a profound depression in Ag-specific effector function after early restimulation. Indeed, a “mirror image” cytolytic capability was observed: the most powerful immunogens, as measured by cytolytic capacity 6 days after immunization, elicited the weakest secondary immune response when evaluated following an additional 6 days after restimulation. To understand the mechanism of this suppression, we examined the fate of splenocytes immunized with a vaccinia virus encoding Ag and IL-2 then restimulated ex vivo. We found that these splenocytes underwent an apoptotic cell death, upon early restimulation, that was not dependent on the engagement of the FasR (CD95). Unlike previously described mechanisms of “propriocidal cell death” and “clonal exhaustion,” the cell death we observed was not an inherent property of the CD8+ T cells but rather was due to a population of splenocytes that stained positive for both the Mac-1 and Gr-1 surface markers. Deletion of these cells in vitro or in vivo completely abrogated the observed suppression of cytolytic reactivity of Ag-specific CD8+ T cells. These observations could account for the apparent absence of Ag-specific immune responses after some current vaccination regimens employing powerful immunogens. Finally, our results may shed new light on a mechanism for the suppression of CD8+ T cell responses and its effect on vaccine efficacy and on immune memory.

Apoptotic death of CD8+ T lymphocytes after immunization: induction of a suppressive population of Mac-1+/Gr-1+ cells

Following an infection or immunization, a primary CD8+ T cell response generally rises then falls rapidly before giving rise to a "memory" response. When we immunized mice with recombinant viral immunogens optimized to enhance the lytic capability of CD8+ T cells, we measured a profound depression in Ag-specific effector function after early restimulation. Indeed, a "mirror image" cytolytic capability was observed: the most powerful immunogens, as measured by cytolytic capacity 6 days after immunization, elicited the weakest secondary immune response when evaluated following an additional 6 days after restimulation. To understand the mechanism of this suppression, we examined the fate of splenocytes immunized with a vaccinia virus encoding Ag and IL-2 then restimulated ex vivo. We found that these splenocytes underwent an apoptotic cell death, upon early restimulation, that was not dependent on the engagement of the FasR (CD95). Unlike previously described mechanisms of "propriocidal cell death" and "clonal exhaustion," the cell death we observed was not an inherent property of the CD8+ T cells but rather was due to a population of splenocytes that stained positive for both the Mac-1 and Gr-1 surface markers. Deletion of these cells in vitro or in vivo completely abrogated the observed suppression of cytolytic reactivity of Ag-specific CD8+ T cells. These observations could account for the apparent absence of Ag-specific immune responses after some current vaccination regimens employing powerful immunogens. Finally, our results may shed new light on a mechanism for the suppression of CD8+ T cell responses and its effect on vaccine efficacy and on immune memory.

Use of cellular and cytokine adjuvants in the immunotherapy of cancer

Cellular and cytokine adjuvants, often immune effector cells and soluble factors, respectively, are supplemental and/or follow-up treatments of human origin for cancer patients who have unsatisfactory clinical responses to conventional chemotherapy, radiotherapy, and surgery. Since many human studies with these reagents are in their infancy, extensive data collection is only now being performed to determine which strategy provides the greatest therapeutic benefit. Research published in the literature since the genesis of this approach to cancer treatment is summarized in this report. Methodologies attempting to generate anticancer responses by provoking or enhancing the patient's own immune system are new compared with the other standard types of cancer treatment. Although a few encouraging human studies can be discussed, many of the most promising techniques are only now being transferred from the laboratory to the clinic. The administration of immune effector cells in combination with immunomodulators, such as interferons or interleukins, often enhances clinical outcome. The literature cited in this report indicate that immune-cell- and cytokine-based therapies hold promise in our attempts to improve the quality and duration of life in those with cancer. With each report reaching the literature, more effective clinical trials are being designed and implemented.

Dendritic cells retrovirally transduced with a model antigen gene are therapeutically effective against established pulmonary metastases

Dendritic cells (DCs) are bone marrow-derived leukocytes that function as potent antigen presenting cells capable of initiating T cell-dependent responses from quiescent lymphocytes. DC pulsed with tumor-associated antigen (TAA) peptide or protein have recently been demonstrated to elicit antigen-specific protective antitumor immunity in a number of murine models. Transduction of DCs with TAA genes may allow stable, prolonged antigen expression as well as the potential for presentation of multiple, or unidentified, epitopes in association with major histocompatibility complex class I and/or class II molecules. To evaluate the potential efficacy of retrovirally transduced DCs, bone marrow cells harvested from BALB/c mice were transduced with either a model antigen gene encoding beta-galactosidase (beta-gal) or a control gene encoding rat HER-2/neu (Neu) by coculture with irradiated ecotropic retroviral producer lines. Bone marrow cells were differentiated into DC in vitro using granulocyte/macrophage colony-stimulating factor and interleukin-4. After 7 d in culture, cells were 45-78% double positive for DC phenotypic cell surface markers by FACS(R) analysis, and DC transduced with beta-gal were 41-72% positive for beta-gal expression by X-gal staining. In addition, coculture of beta-gal transduced DC with a beta-gal-specific T cell line (CTLx) resulted in the production of large amounts of interferon-gamma, demonstrating that transduced DCs could process and present endogenously expressed beta-gal. DC transduced with beta-gal and control rat HER-2/neu were then used to treat 3-d lung metastases in mice bearing an experimental murine tumor CT26.CL25, expressing the model antigen, beta-gal. Treatment with beta-gal-transduced DC significantly reduced the number of pulmonary metastatic nodules compared with treatment with Hank's balanced salt solution or DCs transduced with rat HER-2/neu. In addition, immunization with beta-gal-transduced DCs resulted in the generation of antigen-specific cytotoxic T lymphocytes (CTLs), which were significantly more reactive against relevant tumor targets than CTLs generated from mice immunized with DCs pulsed with the Ld-restricted beta-gal peptide. The results observed in this rapidly lethal tumor model suggest that DCs transduced with TAA may be a useful treatment modality in tumor immunotherapy.

Highly attenuated modified vaccinia virus Ankara (MVA) as an effective recombinant vector: a murine tumor model

Modified vaccinia virus Ankara (MVA), a highly attenuated strain of vaccinia virus (VV) that is unable to replicate in most mammalian cells, was evaluated as an expression vector for a model tumor associated antigen (TAA) and as a potential anti-cancer vaccine. We employed an experimental murine model in which an adenocarcinoma tumor line, CT26.CL25, was stably transfected with a model TAA, beta-galactosidase (beta-gal). Mice injected intramuscularly with a recombinant MVA (rMVA) expressing beta-gal (MVA-LZ), were protected from a lethal intravenous (i.v.) challenge with CT26.CL25. In addition, splenocytes from mice primed with MVA-LZ were therapeutically effective upon adoptive transfer to mice bearing pulmonary metastases of the CT26.CL25 tumor established 3 days earlier. Most importantly, i.v. inoculation with MVA-LZ resulted in significantly prolonged survival of mice bearing three day old pulmonary metastases. This prolonged survival compared favorably to mice treated with a replication competent recombinant VV expressing beta-gal. These findings indicate that rMVA is an efficacious alternative to the more commonly used replication competent VV for the development of new recombinant anti-cancer vaccines.

The new vaccines: building viruses that elicit antitumor immunity

Whereas cancer cells are poor immunogens, some viruses are capable of eliciting powerful and lifelong immunity. Recombinant viruses and plasmid DNA encoding tumor-associated antigens can elicit powerful and specific immune responses that can be enhanced by the use of cytokines and costimulatory molecules. These immune responses have destroyed growing tumor cells in experimental animal models. For the first time, immunotherapeutic strategies that employ recombinant viruses are being tested in clinical trials with cancer patients.