Disabled infectious single cycle-herpes simplex virus (DISC-HSV) as a vector for immunogene therapy of cancer

Disabled infectious single cycle-herpes simplex viruses (DISC-HSV) have been shown to be safe for use in humans and may be considered efficacious as vectors for immunogene therapy in cancer. Preclinical studies show that DISC-HSV is an efficient delivery system for cytokine genes and antigens. DISC-HSV infects a high proportion of cells, resulting in rapid gene expression for at least 72 h. The DISC-HSV-mGM-CSF vector, when inoculated into tumors, induces tumor regression in a high percentage of animals, concomitant with establishing a cytotoxic T-cell response, which is MHC class I restricted and directed against peptides of known tumor antigens. The inherent properties of DISC-HSV makes it a suitable vector for consideration in human immunogene therapy trials.     

Suspension packaging cell lines for the simplified generation of T-cell receptor encoding retrovirus vector particles

The transfer of T-cell receptor (TCR) genes into primary human T-cells to endow their specificity toward virus-infected and tumor cells is becoming an interesting tool for immunotherapy. TCR-modified T cells are mainly generated by retrovirus-mediated gene transfer. To produce TCR-retrovirus particles, fibroblast packaging cell lines are the most common tool. We constructed two packaging cell lines based on the human suspension T-cell lymphoma line Deltabeta-Jurkat, which lacks endogenous TCRbeta-chains and is therefore unable to express CD3 complexes on the cell surface. After supply of gag-pol (murine leukemia virus (Mo-MLV)) and env (GALV or MLV-10A1) genes, a green fluorescent protein (GFP)-encoding retrovirus vector was transduced into both packaging cell clones, which then stably produced GFP-retroviruses with titers of up to 4 x 10(5) infectious particles (IP)/ml. After transfer of a TCRalpha/beta-encoding retrovirus vector, Deltabeta-Jurkat/GALV and Deltabeta-Jurkat/10A1 cells expressed CD3 molecules on the cell surface. CD3-high expressing packaging cells were enriched by fluorescence-activated cell sorter sorting. In these cells, the CD3 expression level directly correlated with the titer of vector particles. TCR-retroviruses efficiently transduced human T-cell lines and primary T cells. In conclusion, the method allowed the fast and easy generation of high virus titer supernatants for TCR gene transfer.     

Adeno-Associated Viral-Mediated Gene Transfer to Hepatoma: Thymidine Kinase/Interleukin 2 Is More Effective in Tumor Killing in Non-Ganciclovir (GCV)-Treated Than in GCV-Treated Animals

Interleukin 2 (IL-2) enhancement of herpes simplex virus-thymidine kinase (HSV-TK)/ganciclovir (GCV)-induced tumor killing was studied by cloning the human interleukin 2 gene into an HSV-TK-bearing adeno-associated viral (AAV) vector (TK/IL-2). The mouse hepatocellular carcinoma cell line Hepa 1-6 was used as a model in this study. We found that TK/IL-2-transduced Hepa 1-6 cells were more susceptible to ganciclovir treatment than tumor cells transduced with only TK in both nude mice and immunocompetent C57L/J mice. TK/IL-2-transduced tumors also showed shrinkage without GCV treatment. The tumor-killing effect of AAV-mediated TK/IL-2 gene transfer was further studied by inoculating animals with TK/IL-2- or TK-transduced tumor cells mixed with unmodified cells with or without GCV treatment. Although tumor growth in each group was inhibited, the best result was obtained from the TK/IL-2-transduced group without GCV treatment. In this group, 10% of the transduced tumor cells could eradicate the whole tumor in 50% of the animals tested as well as provide long-term protection against tumor cell rechallenge. When this group was treated with GCV, the antitumor effect of TK/IL-2 was reduced. We attribute this to the early ablation of transgene-bearing tumor cells by GCV treatment, which thus reduces the duration of IL-2 expression. We conclude that (i) TK/IL-2 plus GCV treatment generates a stronger tumor-killing effect than HSV-TK plus GCV and (ii) tumor killing of TK/IL-2 is more effective in non-GCV-treated animals than in GCV-treated animals.     

Retrovector encoding a green fluorescent protein-herpes simplex virus thymidine kinase fusion protein serves as a versatile suicide/reporter for cell and gene therapy applications

Expression vectors encoding herpes simplex virus thymidine kinase (HSVTK) have been extensively used in cell and gene therapy applications either as anticancer "suicide" or as "self-destruct" transgenes in adoptive immunotherapy applications. In both gene therapy applications, reliable detection of HSVTK transgene expression is required in genetically engineered cells. Direct fluorescent labeling of the HSVTK protein may be the remedy. We designed a retrovector encoding a chimeric GFP-HSVTK fusion protein that can serve as a bifunctional suicide and reporter transgene. The fusion gene was incorporated in a VSV G-pseudotyped retrovector (vGFPTKfus) and high-titer stable retroviral producer was generated ( approximately 3 x 10(6) retroparticles/ml). Tumor cell lines transduced at an MOI of 8 for 3 days led to >90% gene transfer efficiency. Southern blot analysis confirmed that unrearranged proviral genomes integrated in chromosomal DNA. Protein extract immunoblot with HSVTK antisera revealed the presence of a 70-kDa protein consistent with the predicted size of an HSVTK-GFP fusion protein. Fluorescence microscopy and FACS analysis revealed that GFPTKfus-mediated fluorescence was nuclear localized and was 30-fold greater than that observed in a bicistronic HSVTK-GFP vector. Growth of cell lines expressing vGFPTKfus was significantly suppressed in the presence of ganciclovir. The DA3 mouse mammary carcinoma cell line was transduced with vGFPTKfus and implanted in syngeneic BALB/c mice. Preestablished tumors completely regressed in seven of nine mice treated with ganciclovir. Normal human peripheral blood T lymphocytes were transduced with vGFPTKfus and nucleus-restricted green fluorescence was observed. Sorting of green fluorescent lymphocytes allowed for selection of engineered cells. In conclusion, we demonstrate the utility of vGFPTKfus as a suicide/reporter transgene in tumor cells in vitro and in vivo. Furthermore, its potential use as an analytical and therapeutic tool targeting human T lymphocytes is shown.     

Multifactorial optimization of gammaretroviral gene transfer into human T lymphocytes for clinical application

The ability to genetically modify human T cells to target tumor antigens through retroviral gene transfer constitutes a potentially powerful approach to cancer immunotherapy. However, low transduction efficiencies may hamper the efficacy of such therapeutic strategies in the clinical setting. Most commonly, gammaretroviral gene transfer into T cells is conducted through spinoculation, that is, centrifugation of retroviral particles and T cells on RetroNectin-coated non-tissue culture vessels. Here we present data investigating the impact of temperature, speed, and frequency of spinoculation on T cell transduction efficiencies. We found that all three variables independently impacted gene transfer, with increasing temperature, speed, and frequency of spinoculation all enhancing the transduction of T cells. These improved conditions were additive, with the greatest proportion of transduced T cells being generated at the highest tested temperature and speed, after daily spinoculation for 2 to 3 days. Under these conditions, enhanced gene transfer was observed in T cells derived from healthy donors, using research-grade vector stocks. Whereas both RetroNectin and spinoculation were critical to optimal gene transduction, preloading of gammaretroviral particles before spinoculation did not enhance gene transfer. Significantly, application of these enhanced transduction conditions to T cells derived from previously treated patients with chronic lymphocytic leukemia allowed for adequate gene transfer under both small-scale and large-scale clinically applicable conditions using either preclinical or current Good Manufacturing Practice-grade gammaretroviral vector stocks.     

Multidrug resistance 1 gene transfer can confer chemoprotection to human peripheral blood progenitor cells engrafted in immunodeficient mice.

Myelosuppression is the main side effect of cancer chemotherapy. An improved rate of retroviral vector-mediated gene transfer to hematopoietic stem cells, shown in more recent clinical trials, has created the basis to test the concept of myeloprotective gene therapy. We transplanted clinical-scale human peripheral blood progenitor cell grafts (n = 2) transduced with retroviral vector SF91m3, which contains the human multidrug resistance 1 gene (MDR1), into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Engrafted mice of one cohort were protected from paclitaxel toxicity (p < 0.05) and we noted a similar trend in the second cohort. In paclitaxel-treated mice that had received gene-transduced cells we found a significant increase in gene marking (p < 0.05 - p < 0.01) or P-glycoprotein expression (p < 0.01) compared with their chemotherapy-naive counterparts. This is the first report showing that cytostatic drug resistance gene therapy can mediate chemoprotection of human clinically relevant stem cell populations with marrow engraftment potential.     

Use of protamine to augment adenovirus-mediated cancer gene therapy.

Improving the therapeutic potential of adenoviral (Ad) suicide gene therapy has become an area of intense investigation since the inception of gene therapy strategies for cancer treatment. Poor efficiency of gene transfer to target tissues has become one of the most important limitations to Ad-based gene therapy. Since polycations have been shown to enhance adenovirus-mediated gene transfer in epithelial cells both in vitro and in vivo, we hypothesized that polycations could augment treatment efficacy in animals with established tumor. To address this hypothesis, protamine sulfate, a polycation already safely administered in humans, was complexed with a recombinant Ad (E1E3-deleted) vector containing the herpes simplex 1 thymidine kinase (HSVtk) suicide gene to treat cancer cell lines in vitro and in animals bearing intraperitoneal tumor. In the presence of 5 microg/ml protamine, the efficiency of gene transfer to a number of cancer cell lines normally resistant to adenovirus was significantly enhanced. Protamine's effect in vitro was found to be inversely proportional to the level of expression of the high affinity Ad binding site, coxsackievirus and adenovirus receptor (CAR), on the sur- face of the various cell lines tested. Ad.tk infected tumor cells were rendered 2.5- to three-fold more sensitive to 20 microM ganciclovir (GCV) in the presence of protamine. Protamine also augmented the in vivo transfer efficiency of the marker gene, LacZ (contained in an Ad vector), on the surface of tumors derived from an intraperitoneal mouse model. Quantitative imaging revealed 50% tumor surface transduced with LacZ when treatment was performed in the presence of 50 microg/ml protamine compared with 12% tumor surface in controls. However, experiments performed utilizing intraperitoneal administration of Ad.tk/GCV in the presence or absence of 50 microg/ml protamine demonstrated no significantly improved median survival in mice bearing established intraperitoneal tumors. Similarly, in Fischer rats bearing intrapleural tumor, no improvement in anti-tumor response was observed when Ad treatment was performed intrapleurally in the presence of protamine. Thus, although protamine induced an enhancement of Ad-mediated gene transfer in vitro and in vivo, its use as an adjunct to intracavitary Ad-based cancer gene therapy in vivo appears to be limited.     

靶向骨桥蛋白基因的RNA干扰对裸鼠肝癌影响的实验研究

目的检测骨桥蛋白（OPN）的核糖核酸（RNA）干扰技术对裸鼠肝癌的影响作用，探讨RNA干扰对肝癌基因治疗中的有效性和相关机制。方法体外化学合成骨桥蛋白序列特异性的短发夹RNA（shRNA）质粒载体，并导入肝癌细胞HepG2裸鼠皮下移植瘤，尾静脉注射OPN shRNA表达载体，观察其对肝癌生长的影响作用；酶联免疫吸附（ELISA）方法检测OPN在肿瘤组织中的蛋白浓度。结果全身系统性给予OPN shRNA后，空载体组、阴性shRNA组及OPN shRNA转染组肿瘤体积分别为235±5mm^3、222±24mm^3（P=0．2）、98±24mm^3（P〈0．05）；瘤组织中OPN浓度在空载体组、阴性shRNA组及OPN shRNA转染组分别为498±8pg／mg、382±98pg／mg和122±56pg／mg（P〈0．05）。结论OPN的RNA干扰明显抑制了肿瘤的生长，有望通过RNA干扰技术实现肝癌的基因治疗。     

T Cells Targeting Carcinoembryonic Antigen Can Mediate Regression of Metastatic Colorectal Cancer but Induce Severe Transient Colitis

Autologous T lymphocytes genetically engineered to express a murine T cell receptor (TCR) against human carcinoembryonic antigen (CEA) were administered to three patients with metastatic colorectal cancer refractory to standard treatments. All patients experienced profound decreases in serum CEA levels (74–99%), and one patient had an objective regression of cancer metastatic to the lung and liver. However, a severe transient inflammatory colitis that represented a dose limiting toxicity was induced in all three patients. This report represents the first example of objective regression of metastatic colorectal cancer mediated by adoptive T cell transfer and illustrates the successful use of a TCR, raised in human leukocyte antigen (HLA) transgenic mice, against a human tumor associated antigen. It also emphasizes the destructive power of small numbers of highly avid T cells and the limitations of using CEA as a target for cancer immunotherapy.     

Induction of ErbB-2/neu-specific protective and therapeutic antitumor immunity using genetically modified dendritic cells: enhanced efficacy by cotransduction of gene encoding IL-12

Overexpression of ErbB-2/neu occurs in 20-30% of patients with breast cancer and indicates a poor prognosis. The presence of a detectable immune response to ErbB-2/neu in some patients suggests that this oncogene may be a useful target for vaccine therapy. We evaluated whether genetic immunization using dendritic cells (DC) transduced ex vivo with an adenovirus expressing the ErbB-2/neu gene (AdNeuTK) could induce protective and therapeutic immunity against a breast tumor cell line overexpressing ErbB-2/neu. Subcutaneous (s.c.) immunization with the DC vaccine elicited protective immunity in an average of 60% of animals. CTL analysis demonstrated specific cytotoxic activity against breast tumor cells, as well as syngeneic fibroblasts transduced with AdNeuTK. In vivo depletion studies demonstrated both CD4+ and CD8+ T cells were required. In a therapeutic setting, immunization with the DC vaccines could cure mice with pre-established tumors and efficacy was further enhanced by cotransducing DCs with a vector expressing murine IL-12 (AdmIL-12). These studies support DC vaccines as a therapeutic strategy for human breast cancer, while emphasizing the importance of optimizing an immune response by combining tumor antigen presentation with immunostimulatory cytokines.     

Retroviral transduction of human peripheral blood lymphocytes with Bcl-X(L) promotes in vitro lymphocyte survival in pro-apoptotic conditions

The prolonged in vivo survival of genetically modified effector cells is crucial to the success of any (gene-modified) adoptive cellular immunotherapy approach. In cancer clinical trials to date, however, the detection of surviving circulating gene-modified T cells has required highly sensitive techniques. In vitro studies of T cell co-stimulation have shown that up-regulation of the anti-apoptosis gene Bcl-X(L) by ligation of CD28 promotes T cell survival, but not proliferation. Here we have investigated the ability to modulate resistance to apoptosis and improve cell survival by transducing human peripheral blood lymphocytes using a retroviral vector that expresses Bcl-X(L). We show that Jurkat cells transduced with Bcl-X(L) retrovirus were partially resistant to Fas (CD95) antibody-induced apoptosis. Subsequent in vitro assays with transduced primary human lymphocytes demonstrates that over-expression of Bcl-X(L) promotes the survival of lymphocytes cultured in the absence of interleukin-2. Activation-induced apoptosis with anti-CD3(epsilon) antibody, OKT3 is also modulated. Furthermore, Bcl-X(L) over-expression in human lymphocytes delays the onset of apoptosis induced by long-term co-culture with tumour cell lines. Despite this improved in vitro survival, in a preliminary experiment to assess safety, no signs of malignancy or autoimmunity were observed in NOD/SCID mice injected with Bcl-X(L) transduced lymphocytes. These results indicate that expression of Bcl-X(L) in lymphocyte therapy either alone or in conjunction with an additional therapeutic gene could enhance persistence of cells in vivo thereby potentially improving the clinical outcome of adoptive cellular therapy.     

Dendritic cells transduced with HSV-1 amplicons expressing prostate-specific antigen generate antitumor immunity in mice

There is currently much interest in generating cytotoxic T lymphocyte (CTL) responses against tumor antigens as a therapy for cancer. This work describes a novel gene transfer technique utilizing dendritic cells (DCs), an extremely potent form of antigen-presenting cell (APC), and herpes simplex virus-1 (HSV-1) amplicons. HSV-1 amplicons are plasmid-based viral vectors that are packaged into HSV-1 capsids, but lack viral coding sequences. Amplicon vectors have been constructed that encode the model tumor antigen ovalbumin (HSV-OVA) and human prostate-specific antigen (HSV-PSA), a protein that is expressed specifically in prostate epithelium and prostate carcinoma cells. These amplicons were packaged using a helper virus-free system that produces vector stocks that are devoid of contaminating cytotoxic helper virus. Transduction of DCs with HSV-OVA or HSV-PSA and co-culture with CTL hybridomas results in specific activation, indicating that transduced DCs express these transgenes and process the tumor antigens for class I MHC presentation to CTL. Mice immunized with HSV-PSA-transduced DCs generate a specific CTL response that can be detected in vitro by a (51)Cr-release assay and are protected from challenge with tumors that express PSA. These results indicate that DCs transduced with HSV-1 amplicon vectors may provide a tool for investigation of the biology of CTL activation by DCs and a new modality for immunotherapy of cancer.     

Pre-clinical evaluation of an in vitro selection protocol for the enrichment of transduced CD34+ cell-derived human dendritic cells

The efficient genetic modification of CD34+ cell-derived dendritic cells (DC) will provide a significant advancement towards the development of immunotherapy protocols for cancer, autoimmune disorders and infectious diseases. Recent reports have described the transduction of CD34+ cells via retrovirus- and lentivirus-based gene transfer vectors and subsequent differentiation into functional DC. Since there is significant apprehension regarding the clinical uses of HIV-based vectors, in this report, we compare a murine leukemia virus (MLV)- and a human immunodeficiency virus (HIV)-based bicistronic vector for gene transfer into human CD34+ cells and subsequent differentiation into mature DC. Each vector expressed both EGFP and the dominant selectable marker DHFR(L22Y) allowing for the enrichment of marked cells in the presence of the antifolate drug trimetrexate (TMTX). Both MLV-based and HIV-based vectors efficiently transduced cytokine mobilized human peripheral blood CD34+ cells. However, in vitro expansion and differentiation in the presence of GM-CSF, TNF-alpha, Flt-3L, SCF and IL-4 resulted in a reduction in the percentage of DC expressing the transgene. Selection with TMTX during differentiation increased the percentage of marked DC, resulting in up to 79% (MLV vector) and up to 94% (lentivirus-vector) transduced cells expressing EGFP without loss of DC phenotype. Thus, MLV-based vectors and in vitro selection of transduced human DC show great promise for immunotherapy protocols.     

Combined anti-CD40 conditioning and well-timed immunization prolongs CD8+ T cell accumulation and control of established brain tumors

Adoptive cell transfer has been shown to significantly reduce established tumors in both experimental models and cancer patients. Owing to the tolerogenic nature of cancer, approaches that lead to durable maintenance of functional T cells in tumor-bearing hosts are needed to maximize tumor regression. In this study, we investigated strategies to augment CD8+ T-cell (T-CD8)-mediated adoptive immunotherapy of mice bearing advanced-stage autochthonous brain tumors by targeting a weakly immunogenic epitope. We found that immunization enhanced the accumulation of adoptively transferred T-CD8 at the tumor site, but that the timing of immunization was critical for optimal T cell expansion. A more rapid accumulation of T-CD8 was achieved when mice were conditioned with agonist anti-CD40 antibody before adoptive transfer due to increased T cell activation against the endogenous tumor antigen. Both approaches led to an increase in the lifespan of SV11 mice due to decreased tumor progression. However, tumor-specific T-CD8 did not persist long term at the tumor site after administration of either regimen. Importantly, the combination of anti-CD40 conditioning followed by optimally timed immunization synergistically promoted long-term maintenance of T-CD8 in the brain and dramatically enhanced survival. A second round of combination immunotherapy resulted in a further increase in survival, suggesting long-term tumor sensitivity to CD8+ T-cell-based immunotherapy. These results demonstrate that even a weak antigen can be effectively targeted for control of established tumors using a combined adoptive transfer plus immune modulation approach and suggest that similar strategies may translate to clinical practice.     

Gene transfer to repopulating human CD34+ cells using amphotropic-, GALV-, or RD114-pseudotyped HIV-1-based vectors from stable producer cells.

A novel, stable human immunodeficiency virus type 1 vector packaging system, STAR, was tested for its ability to transduce human cord blood CD34+ progenitor cells assayed both in vitro and after transplantation into NOD/SCID mice. Vectors pseudotyped with three different gammaretrovirus envelopes were used: the amphotropic MLV envelope (MLV-A), a modified gibbon ape leukemia virus envelope (GALV+), and a modified feline endogenous virus RD114 envelope (RDpro). Gene transfer to freshly thawed CD34+ cells in the absence of cytokines was very low. Addition of cytokines increased gene transfer efficiency significantly and this was further augmented if the cells were prestimulated for 24 h. Concentration of the vectors (15-fold) by low-speed centrifugation increased gene transfer to CD34+ cells in vitro even further. More than 90% of cells were transduced with a single exposure to the RDpro vector as determined by GFP expression using flow cytometry. The two other pseudotypes transduced approximately 65-70% of the cells under the same conditions. Transplantation of CD34+ cells prestimulated for 24 h and then transduced with a single exposure to concentrated vector revealed that the RDpro vector transduced 55.1% of NOD/SCID repopulating human cells, which was significantly higher than the MLV-A (12.6%)- or GALV+ (25.1%)-pseudotyped vectors.     

Cellular immunotherapy for malignant gliomas

ABSTRACT

Introduction: Cancer immunotherapy has made much progress in recent years. Clinical trials evaluating a variety of immunotherapeutic approaches are underway in patients with malignant gliomas. Thanks to recent advancements in cell engineering technologies, infusion of ex vivo prepared immune cells have emerged as promising strategies of cancer immunotherapy.

Areas covered: Herein, the authors review recent and current studies using cellular immunotherapies for malignant gliomas. Specifically, they cover the following areas: a) cellular vaccine approaches using tumor cell-based or dendritic cell (DC)-based vaccines, and b) adoptive cell transfer (ACT) approaches, including lymphokine-activated killer (LAK) cells, γδ T cells, tumor-infiltrating lymphocytes (TIL), chimeric antigen receptor (CAR)-T cells and T-cell receptor (TCR) transduced T cells.

Expert opinion: While some of the recent studies have shown promising results, the ultimate success of cellular immunotherapy in brain tumor patients would require improvements in the following areas: 1) feasibility in producing cellular therapeutics; 2) identification and characterization of targetable antigens given the paucity and heterogeneity of tumor specific antigens; 3) the development of strategies to promote effector T-cell trafficking; 4) overcoming local and systemic immune suppression, and 5) proper interpretation of imaging data for brain tumor patients receiving immunotherapy.     

AAV-encoded expression of TRAIL in experimental human colorectal cancer leads to tumor regression

Gene transfer vectors based on the adeno-associated virus (AAV) are used for various experimental and clinical therapeutic approaches. In the present study, we demonstrate the utility of rAAV as a tumoricidal agent in human colorectal cancer. We constructed an rAAV vector that expresses tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) and used it to transduce human colorectal cancer cells. TRAIL belongs to the TNF superfamily of cytokines that are involved in various immune responses and apoptotic processes. It has been shown to induce cell death specifically in cancer cells. Transduction with AAV.TRAIL gave rise to rapid expression of TRAIL, followed by induction of apoptosis, which could be inhibited by the caspase inhibitor z-VAD.fmk, in several human colon cancer cell lines. The apoptotic mechanism included activation of caspase-3, as well as cytochrome c release from mitochondria. The outgrowth of human colorectal tumors grown in mice was completely blocked by transduction with AAV.TRAIL in vitro, while in vivo transduction significantly inhibited the growth of established tumors. AAV vectors could provide a safe method of gene delivery and offer a novel method of using TRAIL as a therapeutic protein.     

Importance of cyclophosphamide-induced bystander effect on T cells for a successful tumor eradication in response to adoptive immunotherapy in mice.

Cyclophosphamide (CTX) increases the antitumor effectiveness of adoptive immunotherapy in mice, and combined immunotherapy regimens are now used in some clinical trials. However, the mechanisms underlying the synergistic antitumor responses are still unclear. The purpose of this study was (a) to evaluate the antitumor response to CTX and adoptive immunotherapy in mice bearing four different syngeneic tumors (two responsive in vivo to CTX and two resistant); and (b) to define the mechanism(s) of the CTX-immunotherapy synergism. Tumor-bearing DBA/2 mice were treated with a single injection of CTX followed by an intravenous infusion of tumor-immune spleen cells. In all the four tumor models, a single CTX injection resulted in an impressive antitumor response to the subsequent injection of spleen cells from mice immunized with homologous tumor cells independently of the in vivo response to CTX alone. Detailed analysis of the antitumor mechanisms in mice transplanted with metastatic Friend leukemia cells revealed that (a) the effectiveness of this combined therapy was dependent neither on the CTX-induced reduction of tumor burden nor on CTX-induced inhibition of some putative tumor-induced suppressor cells; (b) the CTX/immune cells' regimen strongly protected the mice from subsequent injection of FLC, provided the animals were also preinoculated with inactivated homologous tumor together with the immune spleen cells; (c) CD4(+) T immune lymphocytes were the major cell type responsible for the antitumor activity; (d) the combined therapy was ineffective in mice treated with antiasialo-GM1 or anti-IFN-alpha/beta antibodies; (e) spleen and/ or bone marrow cells from CTX-treated mice produced soluble factors that assisted in proliferation of the spleen cells. Altogether, these results indicate that CTX acts via bystander effects, possibly through production of T cell growth factors occurring during the rebound events after drug administration, which may sustain the proliferation, survival, and activity of the transferred immune T lymphocytes. Thus, our findings indicate the need for reappraisal of the mechanisms underlying the synergistic effects of CTX and adoptive immunotherapy, and may provide new insights into the definition of new and more effective strategies with chemotherapy and adoptive immunotherapy for cancer patients.     

Adenoviral gene transfer of interleukin 12 into tumors synergizes with adoptive T cell therapy both at the induction and effector level

Tumors infected with a recombinant defective adenovirus expressing interleukin 12 (IL-12) undergo regression, associated with a cytotoxic T lymphocyte (CTL)-mediated antitumor immune response. In the present study we generated anti-CT26 CTLs by short-term coculture of CT26 cells and lymph node cells obtained from mice harboring subcutaneous CT26 tumors injected with an adenoviral vector expressing IL-12 (AdCMVIL-12), control adenovirus (AdCMVlacZ), or saline. Regression of small intrahepatic CT26 tumors in unrelated syngeneic animals was achieved with CTLs derived from mice whose subcutaneous tumors had been injected with AdCMVIL-12 but not with CTLs from the other two control groups. The necessary and sufficient effector cell population for adoptive transfer consisted of CD8+ T cells that showed anti-CT26 specificity partly directed against the AH1 epitope presented by H-2Ld. Interestingly, treatment of a subcutaneous tumor nodule with AdCMVIL-12, combined with intravenous adoptive T cell therapy with short-term CTL cultures, had a marked synergistic effect against large, concomitant live tumors. Expression of IL-12 in the liver in the vicinity of the hepatic tumor nodules, owing to spillover of the vector into the systemic circulation, appeared to be involved in the increased in vivo antitumor activity of injected CTLs. In addition, adoptive T cell therapy improved the outcome of tumor nodules transduced with suboptimal doses of AdCMVIL-12. Our data provide evidence of a strong synergy between gene transfer of IL-12 and adoptive T cell therapy. This synergy operates both at the induction and effector phases of the CTL response, thus providing a rationale for combined therapeutic strategies for human malignancies.