Lymphokine gene therapy for cancer

In vivoanti-tumour activity of recombinant MVM parvoviral vectors carrying the human interleukin-2 cDNA

BACKGROUND

The natural oncotropism and oncotoxicity of vectors derived from the autonomous parvovirus, minute virus of mice (prototype strain) [MVM(p)], combined with the immunotherapeutic properties of cytokine transgenes, make them interesting candidates for cancer gene therapy.

METHODS

The in vivo anti-tumour activity of a recombinant parvoviral vector, MVM-IL2, was evaluated in a syngeneic mouse melanoma model that is relatively resistant in vitro to the intrinsic cytotoxicity of wild-type MVM(p).

RESULTS

In vitro infection of the K1735 melanoma cells prior to their injection resulted in loss of tumorigenicity in 70% of mice (7/10). Tumour-free mice were protected against a challenge with non-infected parental cells. In addition, MVM-IL2-infected tumour cells induced an anti-tumour activity on parental cells injected at a distant location. These non-infected tumour cells were injected either at the same time or 7 days before the injection of MVM-IL2-infected cells. In the latter setting, which mimics a therapeutic model for small tumours, 4/10 mice were still tumour-free after 4 months.

CONCLUSIONS

Our results show that (i) the MVM-IL2 parvoviral vector efficiently transduces tumour cells; and (ii) the low multiplicity of infection (MOI = 1) used in our experiments was sufficient to elicit an anti-tumour effect on distant cells, which supports further studies on this vector as a new tool for cancer gene therapy.

A novel MVMp-based vector system specifically designed to reduce the risk of replication-competent virus generation by homologous recombination

Recent work highlights the potential usefulness of MVM-based vectors as selective vehicles for cancer gene therapy (Dupont et al, Gene Therapy, 2000; 7: 790-796). To implement this strategy, however, it is necessary to develop optimized methods for producing high-titer, helper-free parvovirus stocks. Recombinants of MVMp (rMVMp) are currently generated by transiently co-transfecting permissive cell lines with a plasmid carrying the vector genome and a helper plasmid expressing the capsid genes (replaced with a foreign gene in the vector genome). The resulting stocks, however, are always heavily contaminated with replication-competent viruses (RCV), which precludes their use in vivo and particularly in gene therapy. In the present work we have developed a second-generation MVMp-based vector system specifically designed to reduce the probability of RCV generation by homologous recombination. We have constructed a new MVMp-based vector and a new helper genome with minimal sequence overlap and have used the degeneracy of the genetic code to further decrease vector-helper homology. In this system, the left homologous region was almost completely eliminated and the right sequence overlap was reduced to 74 nt with only 61% homology. We were thus able to substantially reduce ( approximately 200 x), but not completely eliminate, generation of contaminating viruses in medium-scale rMVMp preparations. Since the remaining sequence homology between the new vector and helper genomes is weak, our results suggest that contaminating viruses in this system are generated by nonhomologous recombination. It is important to note, unlike the autonomously replicating helper viruses produced from the first-generation vector/helper genomes, the contaminating viruses arising from the new packaging system cannot initiate secondary infection rounds (so they are not 'replication-competent viruses'). Our findings have important implications for the design of new MVMp-based vectors and for the construction of trans-complementing packaging cell lines.

Cloning and sequencing of defective particles derived from the autonomous parvovirus minute virus of mice for the construction of vectors with minimal cis-acting sequences

The production of wild-type-free stocks of recombinant parvovirus minute virus of mice [MVM(p)] is difficult due to the presence of homologous sequences in vector and helper genomes that cannot easily be eliminated from the overlapping coding sequences. We have therefore cloned and sequenced spontaneously occurring defective particles of MVM(p) with very small genomes to identify the minimal cis-acting sequences required for DNA amplification and virus production. One of them has lost all capsid-coding sequences but is still able to replicate in permissive cells when nonstructural proteins are provided in trans by a helper plasmid. Vectors derived from this particle produce stocks with no detectable wild-type MVM after cotransfection with new, matched, helper plasmids that present no homology downstream from the transgene.

Tumor-selective gene transduction and cell killing with an oncotropic autonomous parvovirus-based vector

A recombinant MVMp of the fibrotropic strain of minute virus of mice (MVMp) expressing the chloramphenicol acetyltransferase reporter gene was used to infect a series of biologically relevant cultured cells, normal or tumor-derived, including normal melanocytes versus melanoma cells, normal mammary epithelial cells versus breast adenocarcinoma cells, and normal neurons or astrocytes versus glioma cells. As a reference cell system we used normal human fibroblasts versus the SV40-transformed fibroblast cell line NB324K. After infection, we observed good expression of the reporter gene in the different tumor cell types, but only poor expression if any in the corresponding normal cells. We also constructed a recombinant MVMp expressing the green fluorescent protein reporter gene and assessed by flow cytometry the efficiency of gene transduction into the different target cells. At a multiplicity of infection of 30, we observed substantial transduction of the gene into most of the tumor cell types tested, but only marginal transduction into normal cells under the same experimental conditions. Finally, we demonstrated that a recombinant MVMp expressing the herpes simplex virus thymidine kinase gene can, in vitro, cause efficient killing of most tumor cell types in the presence of ganciclovir, whilst affecting normal proliferating cells only marginally if at all. However, in the same experimental condition, breast tumor cells appeared to be resistant to GCV-mediated cytotoxicity, possibly because these cells are not susceptible to the bystander effect. Our data suggest that MVMp-based vectors could prove useful as selective vehicles for anticancer gene therapy, particularly for in vivo delivery of cytotoxic effector genes into tumor cells.

cis requirements for the efficient production of recombinant DNA vectors based on autonomous parvoviruses

The replication of viral genomes and the production of recombinant viral vectors from infectious molecular clones of parvoviruses MVMp and H1 were greatly improved by the introduction of a consensus NS-1 nick site at the junction between the left-hand viral terminus and the plasmid DNA. Progressive deletions of up to 1600 bp in the region encoding the structural genes as well as insertions of foreign DNA in replacement of those sequences did not appreciably affect the replication ability of the recombinant H1 virus genomes. In contrast, the incorporation of these genomes into recombinant particles appeared to depend on in cis-provided structural gene sequences. Indeed, the production of H1 viral vectors by cotransfection of recombinant clones and helper plasmids providing the structural proteins (VPs) in trans, drastically decreased when more than 800 bp was removed from the VP transcription unit. Furthermore, titers of viral vectors, in which most of the VP-coding region was replaced by an equivalent-length sequence consisting of reporter cDNA and stuffer DNA, were reduced more than 50 times in comparison with recombinant vectors in which stuffer DNA was not substituted for the residual VP sequence. In addition, viral vector production was restricted by the overall size of the genome, with a mere 6% increase in DNA length leading to an approximately 10 times lower encapsidation yield. Under conditions fulfilling the above-mentioned requirements for efficient packaging, titers of virus vectors from improved recombinant molecular DNA clones amounted to 5 x 10(7) infectious units per milliliter of crude extract. These titers should allow the assessment of the therapeutic effect of recombinant parvoviruses expressing small transgenes in laboratory animals.

Influence of sequence and size of DNA on packaging efficiency of parvovirus MVM-based vectors

We have derived a vector from the autonomous parvovirus MVM(p), which expresses human IL-2 specifically in transformed cells (Russell et al., J. Virol 1992;66:2821-2828). Testing the therapeutic potential of these vectors in vivo requires high-titer stocks. Stocks with a titer of 10(9) can be obtained after concentration and purification (Avalosse et al., J. Virol. Methods 1996;62:179-183), but this method requires large culture volumes and cannot easily be scaled up. We wanted to increase the production of recombinant virus at the initial transfection step. Poor vector titers could be due to inadequate genome amplification or to inefficient packaging. Here we show that intracellular amplification of MVM vector genomes is not the limiting factor for vector production. Several vector genomes of different size and/or structure were amplified to an equal extent. Their amplification was also equivalent to that of a cotransfected wild-type genome. We did not observe any interference between vector and wild-type genomes at the level of DNA amplification. Despite equivalent genome amplification, vector titers varied greatly between the different genomes, presumably owing to differences in packaging efficiency. Genomes with a size close to 100% that of wild type were packaged most efficiently with loss of efficiency at lower and higher sizes. However, certain genomes of identical size showed different packaging efficiencies, illustrating the importance of the DNA sequence, and probably its structure.

An IgG3-IL-2 fusion protein recognizing a murine B cell lymphoma exhibits effective tumor imaging and antitumor activity

Antibody (Ab)-based tumor therapeutics use the tumor-binding specificity of the Ab to target Fc functions or associated molecules to the site of the tumor. We have used an Ab-interleukin-2 (IL-2) fusion protein to deliver IL-2 to a murine B cell lymphoma (38C13). This anti-Id IgG3-CH3-IL-2, which recognizes the idiotype present on the surface of the lymphoma has a half-life in mice approximately 17-fold longer than the half-life reported for IL-2. Gamma camera studies showed that anti-Id IgG3-CH3-IL-2 localizes at the site of a subcutaneous tumor in mice. The anti-Id IgG3-CH3-IL-2 also shows enhanced antitumor activity compared with the combination of Ab and IL-2 administered together. However, the mechanism of antitumor activity appears to depend on the dose and the treatment schedule used. A single dose of fusion protein prevented tumor in only 50% of the animals, although all the survivors showed some evidence of immunologic memory. Although multiple doses are more effective in preventing tumor growth (87% survivors), they are ineffective in generating protective immunologic memory. Our results suggest that Ab-IL-2 fusion proteins will be useful in the diagnosis and treatment of human B cell lymphomas and other related malignancies.

Delivery of anticancer drugs via isolated hepatic perfusion: a promising strategy in the treatment of irresectable liver metastases?

The prognosis of patients with irresectable liver metastases derived from colorectal cancer is invariably poor; unfortunately, these tumours show only minor responses to conventional anticancer agents. The best responses have been obtained by fluoropyrimidines delivered as continuous infusion into the hepatic artery (HAI): their rapid uptake and detoxification by liver cells results in relatively low systemic drugs levels. This approach increases mean survival duration from 17 to 26 months and, in few patients, causes "down-staging" that may result in resectability. To improve opportunities for chemotherapy, the technique of 1-hour recirculating perfusion of the vascularly isolated liver (isolated hepatic perfusion, IHP) was developed. If leakage to the systemic circulation is negligible-and the compounds used do not readily cause hepatotoxicity-IHP allows usage of drug doses that would be fatal if delivered systemically. Because alkylating agents generally have steep dose-response curves, mitomycin C (MMC) and melphalan (L-PAM) entered phase I/II studies on IHP. Using these drugs, IHP was performed in principle as a single procedure in 60 otherwise untreated patients at our institution. However, despite preliminary data that indicate impressive clinical responses are obtained, improvement over HAI will probably be minor. Because IHP is a complicated way of drug delivery, one could argue that its use is justified only when it has the potential to kill all tumour cells in the liver. We critically discuss the possibilities of IHP and/or the use of gene therapy in an IHP setting.

Method for concentrating and purifying recombinant autonomous parvovirus vectors designed for tumour-cell-targeted gene therapy

Recent work has highlighted the use of parvoviruses as potential vectors for tumour-cell-targeted gene therapy. The oncotropic properties of the prototype strain of minute virus of mice (MVMp) suggest that this virus might be a useful vehicle for introducing selectively therapeutic genes, e.g. lymphokine or suicide genes, into tumour cells and preferentially expressing them. But the low titre of recombinant virus stocks (10(5)-10(6) infectious units per ml) and their high level of contamination by cell proteins make it practically impossible to evaluate their efficacy in in vivo systems. A technique is described for producing cellular contaminant-free stocks of recombinant virus particles, with titres up to 5 x 10(8) IU/ml.

Induction of cellular immunity in chimpanzees to human tumor-associated antigen mucin by vaccination with MUC-1 cDNA-transfected Epstein-Barr virus-immortalized autologous B cells

Aberrant glycosylation of the mucin molecule (encoded by the gene MUC-1) on human epithelial cell tumors leads to the exposure of tumor-associated epitopes recognized by patients' antibodies and cytotoxic T cells. Consequently, these epitopes could be considered targets for immunotherapy. We designed a cellular vaccine, employing, instead of tumor cells, autologous Epstein-Barr virus (EBV)-immortalized B cells as carriers of tumor-associated mucin, to take advantage of their costimulatory molecules for T-cell activation. The vaccine was tested in chimpanzees because of the identity of the human and chimpanzee MUC-1 tandem repeat sequence. EBV-immortalized B cells derived from two chimpanzees were transfected with MUC-1 cDNA, treated with glycosylation inhibitor phenyl-N-acetyl-alpha-D-galactosaminide to expose tumor-associated epitopes, irradiated, and injected subcutaneously four times at 3-week intervals. One vaccine preparation also contained cells transduced with the interleukin 2 (IL-2) cDNA and producing low levels of IL-2. Already after the first injection we found in the peripheral blood measurable frequency of cytotoxic T-cell precursors specific for underglycosylated mucin. The highest frequency observed was after the last boost, in the lymph node draining the vaccination site. Delayed-type hypersensitivity reaction to the injected immunogens was also induced, whereas no appearance of mucin-specific antibodies was seen. Long-term observation of the animals yielded no signs of adverse effects of this immunization. Autologous antigen-presenting cells, like EBV-immortalized B cells, expressing tumor-associated antigens are potentially useful immunogens for induction of cellular anti-tumor responses in vivo.

Prevention of murine breast cancer by vaccination with tumor cells modified by cytokine-producing recombinant vaccinia viruses

BACKGROUND

Cancer gene therapy expressing specific levels of multiple genes has not been adequately tested. This study investigates the antitumor effects of recombinant vaccinia viruses (recVVs) that express predictable levels of single and multiple cytokines in a passive immunization murine breast cancer (C3HBA) model.

METHODS

Seventeen recVVs encoding different cytokine combinations under weak and strong VV promoters were constructed. Cytokine production was measured in vitro by enzyme-linked immunosorbent assay. Mice were immunized with infected C3HBA cells and rechallenged 10 days later with 10(6) parental tumor cells. Controls were treated with saline or recVVs not expressing cytokines. Tumors were measured for 24 days. Data were analyzed using Fisher's exact test and the Breslow-Gehan-Wilcoxon test.

RESULTS

recVVs encoding multiple cytokines induced secretion of each cytokine at predictable levels corresponding to VV promoter strength. Ten of 10 controls developed tumors by day 11 after rechallenge. recVVs producing large but not small amounts of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) alone resulted in complete protection in all immunized mice (p = 0.0003) for 24 days and disease-free survival (DFS) was significantly prolonged versus controls (p < 0.001). GM-CSF under a weak promoter was also effective in combination with human interleukin-1 beta (hIL-1 beta; p = 0.0220; DFS, p = 0.031) or interferon-gamma (IFN-gamma; p = 0.0037; DFS, p = 0.003). Effectiveness of hIL-1 beta and IFN-gamma vaccines depended on cytokine combinations and not the amount of cytokine produced. IL-2 or tumor necrosis factor-alpha vaccines had no significant antitumor effect.

CONCLUSIONS

(a) recVVs can simultaneously express controllable levels of two cytokines; (b) tumor cells modified by recVVs generate systemic antitumor immunity; and (c) strength of immunity appears to be related to the amounts and specific cytokine(s) produced.

Construction and expression in tumor cells of a recombinant vaccinia virus encoding human interleukin-1 beta

BACKGROUND

Human interleukin-1 beta (hIL-1 beta) injected intratumorally has demonstrated growth inhibition of transplanted subcutaneous tumors in mice, regression of metastatic lesions, resistance to tumor rechallenge, and increased survival. Vaccinia virus (VV) can be genetically engineered to produce cytokines and may be an effective vector for gene therapy of cancer. This study was designed to (a) construct a VV expressing hIL-1 beta, (b) assess tumor cell infection in vitro with this construct, (c) measure hIL-1 beta production, and (d) assess the bioactivity of the secreted cytokine.

METHODS

The hIL-1 beta gene was amplified from a plasmid clone using polymerase chain reaction (PCR) and then cloned into a homologous recombination (HR) and expression vector, which was used to insert the hIL-1 beta gene into the VV genome. Selection of the recombinant VV (vMJ601hIL-1 beta) was based on inactivation of viral TK and expression of beta-galactosidase. vMJ601hIL-1 beta infectivity and cytokine production was assessed by infecting tumor cell lines and analyzing culture supernatants for hIL-1 beta. Bioactivity of the hIL-1 beta produced was demonstrated using an IL-1 dependent T helper cell line.

RESULTS

The hIL-1 beta gene was successfully cloned into the VV genome by HR, which was confirmed by PCR. vMJ601hIL-1 beta efficiently infected tumor cells, as shown by increased hIL-1 beta secretion (0 to > 500 ng/ml) and morphologic evidence of viral cytopathic effect. vMJ601hIL-1 beta-infected cells secreted large amounts of hIL-1 beta (mean 772 ng/10(6) cells/24 h). The secreted hIL-1 beta was bioactive (mean bioactivity 6.8 x 10(8) U/mg of hIL-1 beta).

CONCLUSIONS

(a) hIL-1 beta can be cloned into VV, (b) vMJ601hIL-1 beta retains its infectivity, (c) a large amount of hIL-1 beta is secreted, and (d) the secreted hIL-1 beta is bioactive. Recombinant VV may allow in situ cytokine gene delivery and expression in established tumors.

Expression of interleukin 10 in human melanoma

The expression of interleukin 10 (IL-10) mRNA in human malignant melanoma was investigated by reverse transcriptase polymerase chain reaction analysis. Selective expression of IL-10 mRNA in tissues of primary melanomas and melanoma metastases was found in comparison with normal skin. In addition, strong expression of IL-10 mRNA and of biologically active IL-10 was detected in 3 out of 13 melanoma cell lines. Normal melanocytes consistently expressed low levels of IL-10 mRNA but did not produce detectable IL-10 protein, nor did keratinocytes or fibroblasts. The production of biologically active IL-10 by melanoma cell lines suggests that IL-10 mRNA in melanoma lesions may derive at least in part from the tumour cells themselves. Tumour-infiltrating cells, however, could also be a source of IL-10 in melanoma tissues. The presence of IL-10 in melanoma lesions may contribute to the postulated 'paralysis' of an anti-melanoma immune response.

Persistence of dormant tumor cells in the bone marrow of tumor cell-vaccinated mice correlates with long-term immunological protection

Live proliferation-competent and irradiated proliferation-incompetent L5178 murine lymphoma cells (Eb cell line) were compared for their potency to induce systemic anti-tumor immunity in syngeneic DBA/2 mice. The tumorigenic potential in vivo of live Eb cells was suppressed through local secretion of interleukin 4 (IL4) or alternatively by injection of parental cells at a site refractory to tumor growth. Inoculation of nontumorigenic doses of live Eb or Eb-IL4 cells led to long-lasting specific and systemic T-cell-mediated antitumor response requiring both CD4+ and CD8+ T lymphocytes. Irradiated cells offered only limited short-term protection, which could be marginally improved by IL4. The more effective protection offered by vaccination with live tumor cells correlated with rapid migration and persistence of tumor cells in the bone marrow of host animals after tumor cell inoculation. In contrast, irradiated Eb-lacZ cells had a short persistence. Tumor cells recovered from the bone marrow of host animals injected with live Eb-IL4 cells still expressed IL4. These observations indicate that in the course of vaccination with live Eb or Eb-IL4 cells, a fraction of these cells escaped destruction by host mechanisms and persisted in a dormant state in the bone marrow for long periods of time. Persistence of dormant tumor in the bone marrow correlated with the duration of anti-tumor immunity.

In vivo delivery of interleukin-4 by a recombinant vaccinia virus prevents tumor development in mice

To study the immunotherapeutic potential of interleukin-4 (IL-4) delivered in vivo via a recombinant vaccinia virus, a thymidine kinase-negative (TK-) vaccinia virus that expressed the murine IL-4 gene (VV1/IL-4) was constructed. When mice were inoculated with 10(7) plaque-forming units (pfu) of VV1/IL-4 subcutaneously (s.c.), 10(5) pfu/cm2 were found in skin, and smaller numbers in liver and kidney between 1 and 7 days after infection; few viral pfu were found in spleen and lung, or in any organ after intravenous infection. This suggested that recombinant vaccinia viruses might be most efficient at delivery of cytokine genes to the skin. Because IL-4 has recently been found to have potent anti-tumor activity, the effect of recombinant virus infection on the development of s.c. tumors was studied. A single s.c. inoculation with VV1/IL-4 delayed the development of NCTC 2472 tumors, but when VV1/IL-4 was inoculated s.c. weekly for 8 weeks, tumor development was completely prevented in 93% of mice. Similarly, the development of M-3 melanoma tumors was also prevented by weekly s.c. inoculations of VV1/IL-4. About 40% of mice treated with control VV2/beta gal by the same regimen also failed to develop tumors. Weekly virus treatment did not prevent NCTC 2472 tumor development in athymic nu/nu mice, suggesting that mature T cells are required for expression of VV1/IL-4 induced antitumor activity. Thus, recombinant vaccinia viruses may be especially well suited for convenient therapeutic delivery of immunomodulator genes to skin-related sites.

Direct in vivo gene transfer and expression in malignant cells using adenovirus vectors

To evaluate the ability of replication-deficient, recombinant adenovirus vectors to transfer genes to human tumor cells in vivo, adenovirus vectors containing the Escherichia coli lacZ (Ad.RSV beta gal) gene (coding for beta-galactosidase; used as a cell marker for gene transfer) or the human alpha 1-antitrypsin (Ad-alpha 1AT) cDNA (used as an example of a secreted protein) were administered intraperitoneally to nude mice with human malignant mesothelioma cell (H-MESO-1) malignant ascites. Preliminary in vitro studies showed that both vectors effectively transferred genes to H-MESO-1 cells. Tumor cells recovered from ascites of animals intraperitoneally administered a control adenovirus revealed no evidence of beta-galactosidase (beta-gal) activity 3 or 14 days later. In contrast, beta-gal activity was detected at the same time points in tumor cells from animals receiving intraperitoneal Ad.RSV beta gal. Flow cytometric quantification of beta-gal activity in recovered cells showed < 3% beta-gal-positive cells in animals administered control virus, but in animals administered intraperitoneal Ad.RSV beta gal there was a mean of 71 +/- 18% positive cells at 3 days and 56 +/- 27% at 14 days. Human alpha 1AT was not detected by enzyme-linked immunosorbent assay (ELISA) in ascites of animals receiving a control virus; however, in ascites of animals administered Ad-alpha 1AT, 21,000 +/- 3,800 ng/ml of human alpha 1AT was detected at 3 days and 4,900 +/- 1,700 ng/ml at 14 days. These data demonstrate that replication-deficient recombinant adenovirus vectors can be used to transfer genes to malignant cells in vivo and suggest a new strategy for genetic modification for antitumor therapy.

Use of an autonomous parvovirus vector for selective transfer of a foreign gene into transformed human cells of different tissue origins and its expression therein

In this work, we report the transduction of a chloramphenicol acetyltransferase (CAT) reporter gene into a variety of normal and transformed human cells of various tissue origins. The vector used was MVM/P38cat, a recombinant of the prototype strain of the autonomous parvovirus minute virus of mice (MVMp). The CAT gene was inserted into the capsid-encoding region of the infectious molecular clone of MVMp genome, under the control of the MVM P38 promoter. When used to transfect permissive cells, the MVM/P38cat DNA was efficiently replicated and expressed the foreign CAT gene at high levels. By cotransfecting with a helper plasmid expressing the capsid proteins, it was possible to produce mixed virus stocks containing MVM/P38cat infectious particles and variable amounts of recombinant MVM. MVM/P38cat viral particles were successfully used to transfer the CAT gene and to express it in a variety of human cells. Both viral DNA replication and P38-driven CAT expression were achieved in fibroblasts, epithelial cells, T lymphocytes, and macrophages in a transformation-dependent way, but with an efficiency depending on the cell type. In transformed B lymphocytes, however, the vector was not replicated, nor did it express the CAT gene.

Cytokine gene transfer in the therapy of malignancy

Failure to eradicate tumour may be due to insufficient activation of host effector cells. Attempts to enhance such effector function by administration of high doses of cytokines systemically has produced little therapeutic benefit and considerable toxicity. An alternative approach is to provide cytokines locally at sites of tumour deposits. One method for achieving this is to transduce cytokine genes into TIL cells which will then home to sites of tumour. An alternative strategy is to transduce cytokine genes into tumour cells to enhance haematopoietic and immune system defence against tumour. In murine models transfection of tumour cells with cytokine genes has resulted in eradication of local tumour in models using several tumour types and several cytokines. The mechanism by which anti-tumour activity is produced varies with the transduced cytokine and the haematopoietic and immune effector cells recruited. Mechanisms include generation of CTLs which specifically recognize tumour cells, enhancement of antigen presentation, and recruitment of non-specific cytotoxic cells such as eosinophils and neutrophils. With some combinations systemic immunity is induced so the animal is resistant to rechallenge at a distant site with non-transduced parental tumour and the transduced tumour has acted like a vaccine. Both these strategies are currently being evaluated in phase I trials in human tumours.

Cytokine-induced tumor immunogenicity: endogenous interleukin-1 alpha expressed by fibrosarcoma cells confers reduced tumorigenicity

A direct correlation between the constitutive expression of IL-1 alpha and reduced tumorigenicity of fibrosarcomas was observed. This was established in fibrosarcoma cell lines which produce IL-1 alpha 'spontaneously', possibly as an aberration of oncogene-mediated transformation or upon IL-1 alpha gene transfer. In fibroblasts intracellular or membrane-associated IL-1 alpha is expressed, whereas the secreted form of the cytokine (IL-1 beta) is absent. Studies on the mechanisms of tumor regression of the IL-1 alpha-positive fibroblastoid cell lines indicated that IL-1 alpha potentiates the development of tumor cell-specific CTLs, which are of importance for tumor eradication. Thus, IL-1 alpha induces enhanced helper T cell activity which provides auxiliary signals for the growth/development of CTLs. Non-adaptive effector cells, activated locally by IL-1 alpha-expressing fibrosarcoma cells, also contribute to the eradication of IL-1 alpha-expressing fibrosarcomas. Local IL-1 alpha expression potentiated antigen presentation, by the malignant fibroblasts as well as by tissue-resident antigen-presenting cells, thus further potentiating anti-tumor immune responses. Mice, in which IL-1 alpha-producing tumors were regressed, developed an immune memory and rejected a challenge with an IL-1 non-producing violent tumor cell line. Endogenous IL-1 alpha activates a cytokine cascade (i.e., IL-6, CSF), produced by the malignant cells and possibly also by stromal cells. However, IL-1 alpha expression is essential for fibrosarcoma eradication, while other cytokines possibly amplify and sustain its action.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of lung squamous cell carcinoma-derived T-cell suppressive factor

BACKGROUND

The immunosuppressive state of a tumor-bearing patient is possibly mediated by tumor-derived factor. In this study, the authors characterized lung squamous cell carcinoma-derived immunosuppressive factor (LSCF).

METHODS

The immunosuppressive activity of QG56 (a lung squamous carcinoma cell line)-derived LSCF was evaluated by the effect of culture supernatant of QG56 on anti-CD3 monoclonal antibody-induced T-cell, response such as proliferation (3H-thymidine uptake), cytotoxicity (51Cr-releasing assay), and expression of cytokine mRNA (polymerase chain reaction). The LSCF was partially purified with an ion-exchange high-performance liquid chromatography (HPLC) and a gel-filtration HPLC.

RESULTS

The LSCF inhibited proliferation, cytotoxicity, and expression of cytokine mRNA of T-cells in a dose-dependent manner. It has a molecular weight of approximately 22 kd, and was sensitive to proteinase K, heating at 60 degrees C, and resistant to treatment with trypsin and pH 3 and 9. These properties appear to be similar to those of transforming growth factor-beta (TGF-beta). However, the activity of the LSCF was not abrogated by anti-TGF-beta sera, and the LSCF did not suppress the proliferation of TGF-beta-sensitive mink lung cells (Mv1Lu).

CONCLUSIONS

These data suggest that LSCF may be a novel tumor-derived immunosuppressive protein factor.

Interferon-gamma-producing tumor induces host tumor-specific T cell responses

We investigated the mechanism of host immune responses against two interferon-gamma (IFN-gamma) gene-transduced tumors, plasmacytoma MOPC104E(Mu gamma) and mammary cancer SC115(K gamma), which originally had weak immunogenicity. Both IFN-gamma-producing tumor cells had reduced tumorigenicity and were rejected by syngeneic mice. The rejection was completely blocked by in vivo treatment with anti-CD8 or anti-IFN-gamma monoclonal antibodies. While anti-CD4 monoclonal antibody also blocked the rejection of SC115(K gamma), it enhanced the initial tumor growth of MOPC104E(Mu gamma). Specific protection against subsequent challenge with the respective parental tumor cells was demonstrated in mice which rejected the IFN-gamma-producing tumor cells. Cultured lymphocytes derived from immunized mouse spleens had cytotoxic T cell activity against parental tumor cells, as well as against cells that produced IFN-gamma. These findings indicate that the antitumor effects are mediated by cytotoxic T cells and, partly, by helper T cells, and that locally secreted IFN-gamma plays an important role in generating these effector cells.

Immunotherapy of malignancy by in vivo gene transfer into tumors

The immune system confers protection against a variety of pathogens and contributes to the surveillance and destruction of neoplastic cells. Several cell types participate in the recognition and lysis of tumors, and appropriate immune stimulation provides therapeutic effects in malignancy. Foreign major histocompatibility complex (MHC) proteins also serve as a potent stimulus to the immune system. In this report, a foreign MHC gene was introduced directly into malignant tumors in vivo in an effort to stimulate tumor rejection. In contrast to previous attempts to induce tumor immunity by cell-mediated gene transfer, the recombinant gene was introduced directly into tumors in vivo. Expression of the murine class I H-2Ks gene within the CT26 mouse colon adenocarcinoma (H-2Kd) or the MCA 106 fibrosarcoma (H-2Kb) induced a cytotoxic T-cell response to H-2Ks and, more importantly, to other antigens present on unmodified tumor cells. This immune response attenuated tumor growth and caused complete tumor regression in many cases. Direct gene transfer in vivo can therefore induce cell-mediated immunity against specific gene products, which provides an immunotherapeutic effect for malignancy, and potentially can be applied to the treatment of cancer and infectious diseases in man.

Gene transfer therapy in cancer

Gene transfer techniques have now achieved clinical realization in the wake of recent advances in recombinant DNA technology, together with increased understanding of the molecular biology and immunology of cancer. These novel treatments, and their applications and limitations merit intensive study.

Retroviral vectors displaying functional antibody fragments

We have made retrovirus particles displaying a functional antibody fragment. We fused the gene encoding an antibody fragment directed against a hapten with that encoding the viral envelope protein (Pr80env) of the ecotropic Moloney murine leukemia virus. The fusion gene was co-expressed in ecotropic retroviral packaging cells with a retroviral plasmid carrying the neomycin phosphotransferase gene (neo), and retroviral particles with specific hapten binding activities were recovered. Furthermore the hapten-binding particles were able to transfer the neo gene and the antibody-envelope fusion gene to mouse fibroblasts. In principle, the display of antibody fragments on the surface of recombinant retroviral particles could be used to target virus to cells for gene delivery, or to retain the virus in target tissues.

Reduced tumorigenicity of fibrosarcomas which constitutively generate IL-1 alpha either spontaneously or following IL-1 alpha gene transfer

Interleukin-1 (IL-1) is a major immunoregulatory/proinflammatory cytokine which also affects fibroblast proliferation and function and therefore it was of interest to investigate whether its constitutive expression influences the in vivo tumorigenic potential of transformed fibroblastoid cell lines. Here we report on a strong correlation between the constitutive expression of IL-1 alpha and reduced tumorigenicity, using various series of oncogene-transformed NIH/3T3-derived cell lines which produce the cytokine spontaneously or upon gene transfer, following transfection with the IL-1 alpha cDNA. Reduced tumorigenicity of the constitutive IL-1 alpha producing cell lines was manifested either by inability to grow in animals or by regressions of initially growing tumors, within 2 to 3 weeks from cell inoculation. In contrast, mice inoculated with non-IL-1-producing cell lines developed progressive tumors which ultimately killed the animals. Clones obtained from a non-IL-1-producing met-transformed cell line shifted from a progressive to a regressive phenotype, following transfection with an IL-1 alpha-encoding gene, inserted into an appropriate expression vector, resulting in constitutive expression of the cytokine. The effects of constitutive IL-1 expression on tumor development were observed both in histocompatible (NFS/N) and partially allogeneic (BALB/c) mice; however, they were more pronounced in the allogeneic environment. Fibrosarcomas which are non-IL-1 producers induced progressive tumors in both strains of mice at the same growth rate. The differences between the growth characteristics of the fibrosarcomas in histocompatible vs. partially allogenic mice suggest that IL-1 exerts adjuvant-like effects which increase the immunogenicity of tumor-cell antigens, and they also argue against the possibility that an IL-1-mediated local non-specific inflammatory response is the major effector mechanism of tumor rejection. Indeed, in subsequent studies we shall report on the importance of specific cellular immune responses, especially cytotoxic T lymphocytes (CTLs), in the eradication of constitutive IL-1-producing fibrosarcomas. Thus, our findings may serve as the basis for novel immunotherapy strategies aimed at the induction of IL-1 expression by cells comprising the neoplasm or alternatively by local application of the cytokine in the vicinity of the tumor.

Transformation-dependent expression of interleukin genes delivered by a recombinant parvovirus

The prototype strain of minute virus of mice [MVM(p)] is an autonomous parvovirus with a tropism for cells expressing a neoplastically transformed phenotype. To generate gene transfer vectors for tumor-specific gene expression, human interleukin-2 (IL-2) and murine interleukin-4 (IL-4) genes were cloned under the control of the p38 late promoter of MVM(p). Upon transfection into permissive cells, the recombinant MVMIL2 or MVMIL4 DNA was excised, amplified, and, in the presence of a helper plasmid, packaged into recombinant viral particles. The recombinant viruses were able to transfer fully functional IL-2 and IL-4 genes to permissive target cells and retained the oncotropic host range properties of the parental virus. Following infection with MVMIL2, nontransformed fibroblasts of rodent (FR3T3) or human (MRC-5) origin produced minimal IL-2 compared with the high levels of IL-2 production observed in their transformed derivatives (FREJ4 and MRC-5V1).

Chemo-immunotherapy of murine solid tumors: enhanced therapeutic effects by interleukin-2 combined with interferon alpha and the role of specific T cells

The aim of the present study has been to assess the therapeutic efficacy of various cytokines, singly or in combination, with and without chemotherapy (cyclophosphamide, Cy), in mice carrying advanced, weakly immunogenic tumors (MCA-105 sarcoma, M109 carcinoma). Treatment of animals with i.p. growths or experimental pulmonary metastases began 8-18 days after i.p. or i.v. tumor cell inoculation respectively. None of the cytokines tested [interleukin-2 (IL-2), interferon alpha (IFN alpha), tumor necrosis factor alpha (TNF alpha) and macrophage-colony-stimulating factor (M-CSF)] nor Cy had by itself a significant curative effect. A synergistic therapeutic effect was obtained with IL-2 or IFN alpha (but not with TNF alpha or M-CSF) in combination with Cy. The most efficacious regimen (65%-90% cure of mice carrying i.p. tumors) was the combination of Cy+IL-2+IFN alpha. Preliminary experiments suggested that sequential administration of these cytokines might be more beneficial than concurrent administration. Following successful immunotherapy, long-term (3-6 months) survivors showed a tumor-specific resistance to a second tumor challenge and their spleen contained an increased number of specific antitumor cytotoxic T lymphocyte precursors (5- to 20-fold, compared to control mice). In vitro and in vivo cell-depletion experiments using monoclonal antibodies revealed that T cells (primarily CD8), but not NK cells, are crucial for the therapeutic effects. This study indicates that a potent specific antitumor T cell immunity can be elicited against advanced weakly immunogenic tumors by combining chemotherapy (Cy) with IL-2 and IFN alpha.

An analysis of T-cell-receptor variable-region genes in tumor-infiltrating lymphocytes within malignant tumors

Expression of T-cell-receptor (TCR) V alpha and V beta genes in tumor-infiltrating lymphocytes (TILs) of 29 patients, 15 melanomas and 14 malignant glial tumors (glioma and medulloblastoma), was investigated. The identification and propagation of T cells with anti-tumor reactivity is crucial to the understanding of the human immune response to tumors, which may possibly be useful in the successful implementation of adoptive immunotherapy against cancer. Despite clinical evidence that a more favorable prognosis is associated with the degree of lymphocyte infiltration within a tumor, the actual role of TIL remains uncertain. In order to address this question, we examined the diversity of the RNA transcripts of TCR genes in TILs within 29 specimens obtained at surgery. Using the polymerase-chain-reaction (PCR) method and primers for 18 different human TCR V alpha and 21 V beta families to analyze TCR V-(D)-J-C gene rearrangements, we detected a limited expression of TCR variable-region V alpha genes of TILs. TCR V beta gene rearrangements were more diverse than those for V alpha. In addition to restricted usage of TCR V alpha genes, preferential expression of V alpha 7 genes was found in 20 out of 29 cases (69%). Predominant usage of V alpha 7 genes was more remarkable in melanoma TILs (14/15) than in glial tumor TILs (6/14). These findings were also confirmed by Southern blot analysis with oligonucleotide probes for the constant (C) region of TCR alpha and beta chains. We suspect that some specific T-cell populations may be directed to antigenic determinants in melanoma cells.

Cytokines and cancer: experimental systems

The transfer of certain cytokine genes into cancer cells can provide very powerful suppression of tumor growth in the absence of any toxic side effects. Some of these cytokines, such as interleukin-4, granulocyte colony-stimulating factor and tumor necrosis factor, can mediate powerful immune suppression even in T-cell-deficient animals and appear to be effective for poorly or non-antigenic tumors. However, approaches must be found to induce or deliver cytokines locally at the tumor site.

Cellular and humoral immune responses against cancer: implications for cancer vaccines

The key issue in tumor immunology is to identify antigens as target structures for a cancer-selective immunological attack in the tumor-bearing host, resulting in tumor rejection. There is a growing detailed understanding of structural and regulatory gene alterations giving rise to candidate rejection antigens and peptides in tumor cells. As well as reviewing the development of new adjuvant and recombinant vector systems, new approaches are suggested for the construction of cancer vaccines.

A new method of gene transfer into hematopoietic progenitors using liquid culture with interleukin-3 and interleukin-6

The technique of gene transfer into hematopoietic cells is expected to offer a new form of therapeutics. As a result of studies on a gene-delivery system using granulocyte-macrophage colony-forming units (CFU-GM), a type of hematopoietic progenitor, we have established a technique for efficient gene transfer into CFU-GM. DGL, a retrovirus vector containing the SV40 promoter and the neomycin resistance gene, was constructed and found to transfer genes effectively into murine CFU-GM, which subsequently expressed the neomycin resistance gene. After gene transfer of murine non-adherent bone marrow cells precultured in liquid culture with recombinant murine IL-3 (rmIL-3) and recombinant human IL-6 (rhIL-6) for 6 days, gene transferred CFU-GM in bone marrow cells were able to proliferate 5-10-fold and the ratio of gene transferred CFU-GM to total CFU-GM reached 70-100% from less than 1% in the liquid culture with rmIL-3, rhIL-6 and neomycin for 6 days. Using this protocol, we have been able to obtain large amounts of highly concentrated gene-transferred CFU-GM for fundamental research on CFU-GM gene-delivery systems.

Lymphokines and the immune response: the central role of interleukin-2

A number of recent and past reports on the in vitro and in vivo roles of interleukin-2, interleukin-4, interferon-gamma and tumor necrosis factor-beta suggest that interleukin-2 plays a general role in the immune response. The other three lymphokines often play directive roles that determine the kind of response that occurs.

Tumor suppression after tumor cell-targeted tumor necrosis factor alpha gene transfer

The tumor necrosis factor alpha (TNF-alpha) gene was introduced by retroviral gene transfer into the TNF-alpha-insensitive tumor cell line J558L. Production of 40 pg/ml TNF-alpha by clone J2T12 consistently did not change the growth rate in vitro, but drastically suppressed tumor growth when injected into syngeneic BALB/c mice. Within 2 wk, 90% of the mice inoculated with J558L cells developed a tumor, but none of the mice injected with J2T12 did so. Within the observation period (greater than 3 mo), 60% of the mice inoculated with J2T12 did not develop a tumor. In the other 40% of the mice, tumor manifestation was significantly delayed. Mice injected simultaneously with J2T12 cells and an anti-TNF-alpha monoclonal antibody developed tumors similar to parental J558L cells. Similarly, the tumor-suppressive effects of TNF-alpha were abolished, e.g., by injection of an anti-type 3 complement receptor (CR3) monoclonal antibody that is known to prevent migration of inflammatory cells. These results and the observation of tumor-infiltrating macrophages suggest that lack of tumorigenicity of J2T12 cells is due to the TNF-alpha secretion by the tumor cells and that TNF-alpha acts indirectly by a mechanism that involves chemotactic recruitment and activation of cells, predominantly of macrophages. In contrast, the tumor growth was not affected when, instead of TNF-alpha, interleukin 6 was expressed by J558L cells. Together, our results support the concept of tumor cell-targeted cytokine gene transfer as a tool for cancer treatment, and particularly demonstrate that extremely low doses of TNF-alpha produced by tumor cells are sufficient to inhibit tumor growth without detectable side effects.

Decreased tumorigenicity of a transplantable rat sarcoma following transfer and expression of an IL-2 cDNA

The notion that tumour-cell-derived IL-2 might lead to paracrine stimulation of the host anti-tumour response was tested in a transplantable rat sarcoma model. Three HSNLV clones induced to secrete different amounts of human IL-2 following retroviral gene transfer showed reduced tumorigenicity and metastatic potential in athymic (nu/nu) and immunocompetent syngeneic rats which was directly related to the level of IL-2 secretion. In contrast, the tumorigenicity of HSNLV clones secreting a biologically inactive form of IL-2 (IL-2Lys20) was unaltered. T-lymphocyte-mediated rejection of ZipI, the highest IL-2 producer, was demonstrated histologically in hooded rats and infiltrating mononuclear cells were also observed in ZipI tumours growing in athymic rats. Tumours derived from IL-2-secreting HSNLV showed reduced or absent IL-2 secretion in immunocompetent rats, sometimes with associated loss of the IL-2 provirus, but continued to secrete IL-2 in nude rats. The host response to Moloney-helper-virus-infected HSNLV was also examined and the results represent a cautionary note to those undertaking experiments of a similar nature.