Transduction of human melanoma cells with interleukin-2 gene reduces tumorigenicity and enhances host antitumor immunity: a nude mouse model

A new dawn for eosinophils in the tumour microenvironment

Eosinophils are evolutionarily conserved, pleotropic cells that display key effector functions in allergic diseases, such as asthma. Nonetheless, eosinophils infiltrate multiple tumours and are equipped to regulate tumour progression either directly by interacting with tumour cells or indirectly by shaping the tumour microenvironment (TME). Eosinophils can readily respond to diverse stimuli and are capable of synthesizing and secreting a large range of molecules, including unique granule proteins that can potentially kill tumour cells. Alternatively, they can secrete pro-angiogenic and matrix-remodelling soluble mediators that could promote tumour growth. Herein, we aim to comprehensively outline basic eosinophil biology that is directly related to their activity in the TME. We discuss the mechanisms of eosinophil homing to the TME and examine their diverse pro-tumorigenic and antitumorigenic functions. Finally, we present emerging data regarding eosinophils as predictive biomarkers and effector cells in immunotherapy, especially in response to immune checkpoint blockade therapy, and highlight outstanding questions for future basic and clinical cancer research.

Modulation of T-cell activation by malignant melanoma initiating cells

Highly immunogenic cancers such as malignant melanoma are capable of inexorable tumor growth despite the presence of antitumor immunity. Thus, only a restricted minority of tumorigenic malignant cells may possess the phenotypic and functional characteristics needed to modulate tumor-directed immune activation. Here we provide evidence supporting this hypothesis. Tumorigenic ABCB5(+) malignant melanoma initiating cells (MMICs) possessed the capacity to preferentially inhibit IL-2-dependent T-cell activation and to support, in a B7.2-dependent manner, induction of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs). Compared with melanoma bulk cell populations, ABCB5(+) MMICs displayed lower levels of MHC class I, aberrant positivity for MHC class II, and lower expression levels of the melanoma-associated antigens MART-1, ML-IAP, NY-ESO-1, and MAGE-A. Additionally, these tumorigenic ABCB5(+) subpopulations preferentially expressed the costimulatory molecules B7.2 and PD-1, both in established melanoma xenografts and in clinical tumor specimens. In immune activation assays, MMICs inhibited mitogen-dependent human peripheral blood mononuclear cell (PBMC) proliferation and IL-2 production more efficiently than ABCB5(-) melanoma cell populations. Moreover, coculture with ABCB5(+) MMICs increased the abundance of Tregs, in a B7.2 signaling-dependent manner, along with IL-10 production by mitogen-activated PBMCs. Consistent with these findings, MMICs also preferentially inhibited IL-2 production and induced IL-10 secretion by cocultured patient-derived, syngeneic PBMCs. Our findings identify novel T-cell modulatory functions of ABCB5(+) melanoma subpopulations and suggest specific roles for these MMICs in the evasion of antitumor immunity and in cancer immunotherapeutic resistance.

Antitumor immunity and cancer stem cells

Self-renewing cancer stem cells (CSC) capable of spawning more differentiated tumor cell progeny are required for tumorigenesis and neoplastic progression of leukemias and several solid cancers. The mechanisms by which CSC cause tumor initiation and growth are currently unknown. Recent findings that suggest a negative correlation between degrees of host immunocompetence and rates of cancer development raise the possibility that only a restricted minority of malignant cells, namely CSC, may possess the phenotypic and functional characteristics to evade host antitumor immunity. In human malignant melanoma, a highly immunogenic cancer, we recently identified malignant melanoma initiating cells (MMIC), a novel type of CSC, based on selective expression of the chemoresistance mediator ABCB5. Here we present evidence of a relative immune privilege of ABCB5(+) MMIC, suggesting refractoriness to current immunotherapeutic treatment strategies. We discuss our findings in the context of established immunomodulatory functions of physiologic stem cells and in relation to mechanisms responsible for the downregulation of immune responses against tumors. We propose that the MMIC subset might be responsible for melanoma immune evasion and that immunomodulation might represent one mechanism by which CSC advance tumorigenic growth and resistance to immunotherapy. Accordingly, the possibility of an MMIC-driven tumor escape from immune-mediated rejection has important implications for current melanoma immunotherapy.

Therapeutic efficiency of IL-2 gene transduced tumor vaccine for head and neck carcinoma

Transduction of the human interleukin-2 (IL-2) gene into tumor cells was carried out in order to develop a new immunotherapy for advanced head and neck carcinomas with a poor outcome. We transduced the IL-2 gene into KB cells, a head and neck squamous cell carcinoma cell line, using a defective herpes simplex viral (HSV) amplicon vector as a gene transfer vehicle. A high level of IL-2 was secreted by IL-2 gene-transduced KB cells (KB/IL-2). The IL-2 producibility of irradiated KB/IL-2 cells was almost the same as that of non-irradiated cells. In the tumor establishment model in nude mice, IL-2 and interferon-gamma (IFN-gamma) at high concentrations were detected in the sera of mice transplanted with KB/IL-2 cells. The spleen cells of nude mice transplanted with KB/IL-2 cells exhibited high cytotoxic activity compared to those from mice transplanted with KB cells and from untreated mice. Three of five mice transplanted with KB/IL-2 cells rejected tumors. In the treatment of established tumors, therapeutic effects due to irradiated KB/IL-2 were dose-dependent. The suppressive effects on tumor growth were blocked by anti-asialo GM1, anti-human IL-2 and anti-IFN-gamma antibodies. Immunohistochemical observation revealed the presence of asialo GM1(+) cells among the KB/IL-2 cells in tumors transplanted into nude mice.

MCA106 fibrosarcoma cells transduced with granulocyte/macrophage colony-stimulating factor are not superior to the wild-type cells in suppressing the growth of hepatic metastases

BACKGROUND AND OBJECTIVES

Vaccination with cytokine gene-modified tumor cells augments the immune response against established tumors and protects against tumor challenges. In this study, we investigated the vaccine potential of GM-CSF-transduced MCA106 fibrosarcoma (MCA-GMCSF) cells in the C57BL/6 (B6) murine hepatic metastasis model.

METHODS

Experimental mice received one to three weekly vaccines (subcutaneous/intramuscular, s.c./i.m.) of irradiated, parental, or GM-CSF-transduced MCA106 tumor cells. One week after the last immunization, hepatic metastases were established through the intrasplenic injection of live MCA106 parental (MCA106P) tumor cells. The animals were then sacrificed 3-4 weeks after surgery for evaluation of hepatic tumor burden.

RESULTS

Based on in vivo experiments, both GM-CSF-modified and parental MCA106 tumor cell vaccines induced strong protection against hepatic tumor growth with grossly visible tumors rarely identified. This protection was evident even at a single vaccine dose of as low as 1x10(5) irradiated cells. Unimmunized control mice, on the other hand, consistently developed substantial hepatic tumors. Cytotoxicity assays on splenocytes (cultured in vitro for 4-5 days) showed that both groups of vaccinated mice developed strong tumor-specific cytotoxic T-lymphocyte (CTL) responses. Immunohistochemical analysis of injection sites showed infiltration of dendritic cells (DCs) and macrophages into subcutaneously injected MCA-GMCSF cells. Mostly macrophages, however, were seen at the injection site of MCA106P cells. Furthermore, the MCA106P cells expressed high levels of MHC class I antigens and the level of expression was not significantly altered by transduction with the GM-CSF gene. The high expression of MHC class I antigens probably contributed to the strong immunogenicity of the MCA106P cell vaccine.

CONCLUSIONS

This study demonstrates that MCA106 parental cells are as effective as the GM-CSF-transduced cells in suppressing the growth of hepatic metastases. The cellular immune responses induced by these two vaccines, however, are probably mediated by different subsets of host effector cells. These results have important implications for the use of GM-CSF-transduced cell vaccines in the immunotherapy of tumors that have the propensity to metastasize through the lymphatic channels and the circulatory system.

Human dendritic cells, pulsed with either melanoma tumor cell lysates or the gp100 peptide(280-288), induce pairs of T-cell cultures with similar phenotype and lytic activity

Dendritic cells (DCs) pulsed with unfractionated tumor cell lysates or defined tumor peptides provide potent vaccines which elicit strong antitumor immunity. In this study, we generated DCs from the 2-h adherent progenitor cells obtained from the peripheral blood of melanoma patients. These DCs were able to capture biotinylated melanoma tumor cell lysates. We examined the efficacy of immunogens composed of DCs loaded either with the melanoma peptide gp100 [amino acids 280-288 (DC/gp100)] or with lysates from melanoma tumor cells (DC/lysates) in inducing cytotoxic T-cells from autologous PBLs of HLA-A2 melanoma patients. After four to five weekly stimulations of bulk PBLs with DC/gp100 or DC/lysates, the cultures were enriched with CD3+ T-cells and exhibited one of three phenotypic and functional patterns: (1) Predominant expression of CD8+ and MHC class I-restricted CTLs which displayed strong lytic activity against melanoma cells and T2 cells loaded with the gp100 peptide, (2) mixed CD4+/CD8+ phenotype and weak lytic activity, or (3) nonlytic and predominantly CD4+ cultures. Interestingly, T-cell cultures from each patient exhibited similar phenotypes and lytic activities whether the stimulant was DC/gp100 or DC/cell lysates. Our study demonstrates that DCs pulsed with soluble melanoma peptides or cell lysates are capable of inducing CD8+ CTLs from autologous PBLs of some, but not all, melanoma patients. The function and phenotype of the generated T-cell cultures are governed by DCs since both antigens (the gp100 peptide and melanoma lysates), when presented by a given DC preparation, induced similar T-cell cultures. In summary, it may be difficult to predict the nature of the cellular responses elicited by DC/tumor antigen vaccines from patient to patient.

Conditionally replicative adenoviruses for cancer therapy

The delineation of the genetic etiology of cancer makes gene therapy a rational approach for the molecular treatment of cancer. Many gene delivery systems have been developed, with viral vectors being the most effective. Underlying cancer gene therapy protocols is the recognition that quantitative tumor transduction cannot be achieved with the vector systems available at the present time. One way to overcome this problem could be to amplify the transduction efficiency through the use of vectors capable of replicating specifically in tumor cells. We are currently developing an adenoviral vector in which viral replication will be restricted to the target tumor cells by limiting the expression of viral genes essential for the virus replication only to the tumor cells of interest.

A Phase I clinical trial of immunotherapy with interferon-gamma gene-modified autologous melanoma cells: monitoring the humoral immune response

BACKGROUND

Tumor cells transduced with cytokine genes provide immunogenic vaccines for cancer immunotherapy.

METHODS

A Phase I clinical trial was conducted for the specific active immunization of melanoma patients with interferon-gamma (IFN-gamma) gene-modified autologous melanoma tumor cells. Short term melanoma cultures were transduced retrovirally with the gene for human IFN-gamma. The genetically modified melanoma cells secreted biologically active IFN-gamma and showed enhanced expression of major histocompatibility complex class I and class II surface antigens. These cells were inactivated by irradiation (50 gray) and were cryopreserved for the vaccine. Twenty melanoma patients were enrolled in this clinical trial. The immunizations were administered in escalating doses once every 2 weeks for 3 months. The first and second injections consisted of 2 million cells, followed by 6 million for the third and fourth injections, and then 18 million for the fifth and sixth injections. The humoral immune responses of the patients were assessed by enzyme-linked immunoadsorbent assay, radioimmunoassay, and radioimmunoprecipitation.

RESULTS

Thirteen of the 20 patients completed the immunization protocol. Eight of these 13 patients showed a humoral immunoglobulin (Ig)G response against autologous and allogeneic melanoma cells. The other five patients either had no detectable antimelanoma antibodies or showed a weak IgG response that did not rise significantly above the preimmune level. All the sera contained low or undetectable levels of antimelanoma IgM antibodies. The IgG response increased progressively in titer during the course of immunization. The positive sera showed preferentially strong binding to melanoma cell lines and some cross-reactivity to nonmelanoma tumors. A 75-80 kD antigen on melanoma cells was immunoprecipitated by postimmune sera of 3 of the responding patients. Preimmune sera from these three patients and sera from other patients immunized with a standard nontransduced melanoma cell vaccine failed to precipitate this antigen. Two patients with significant increases in serum IgG had clinical tumor regression, and two additional patients with low serum IgG response had transient shrinkage of nodular disease during therapy.

CONCLUSIONS

These data suggest that gene therapy with IFN-gamma-transduced melanoma cells is safe and worthy of further investigation in patients with less advanced stage malignant melanoma. The ability to monitor changes in the humoral responses of the immunized patients has been demonstrated.

Human gastric carcinoma transduced with the IL-2 gene: increased sensitivity to immune effector cells in vitro and in vivo

We transduced a human gastric carcinoma cell line, HR, with the interleukin 2 (IL-2) gene. Stable HR transfectants secreted nanogram quantities of biologically active IL-2 and had significantly increased expression of IL-2 mRNA relative to that in parental cells. Expression of intracellular IL-2 protein was not quantitatively different in the parental and IL-2 gene-transduced cells, although the former did not secrete IL-2. Surface expression of IL-2 receptors was comparable in the parental and transduced cells at the mRNA or protein levels. Nevertheless, in vitro proliferation of IL-2 gene-transduced HR cells was significantly more rapid than that of parental cells. Both parental and IL-2 gene-transduced HR cells were equally sensitive to lysis by IL-2-activated natural killer (A-NK) cells, as measured in 4 hr 51Cr-release assasys or to apoptosis induced by NK or A-NK cells, assessed in 1 hr 3H-TdR-release assays. In 24 hr MTT assays, however, the IL-2 gene-transduced cells were significantly more sensitive to these effector cells than were parental cells. Upon intrasplenic injection of 5 x 10(6) parental or transduced HR cells into nude mice, liver metastases developed. Metastases of parental HR cells killed the animals in 24 days. In contrast, metastases of the IL-2 gene-transduced HR cells became necrotic by day 14 and were found to be surrounded by murine NK cells and macrophages. Survival of nude mice injected with IL-2 gene-transduced HR cells was significantly prolonged (>50 days) relative to that of mice injected with parental HR. Thus, IL-2 gene-transduced HR cells produced sufficient amounts of functional IL-2 in vivo to be able to recruit to the tumor site and support functions of endogenous cytotoxic immune effector cells, which were responsible for regression of hepatic metastases and significant improvement of survival in these mice.

Analysis of IL-2 receptor expression and of the biological effects of IL-2 gene transfection in small-cell lung cancer

We have analysed the expression of interleukin-2 receptor (IL-2R) on a panel of small-cell lung cancer (SCLC) cell lines. None of the 11 SCLC cell lines studied expressed detectable surface IL-2R alpha or beta chains by indirect immunofluorescence. Reverse transcriptase-polymerase chain reaction (RT-PCR) analyses indicated that only one out of 11 cell lines expressed detectable IL-2R beta mRNA while two expressed a weak positivity for IL-2R gamma. Five SCLC cell lines were transfected with the plasmid vector RSV.5 neo containing IL-2 cDNA coding sequence. Stable transfectants secreted biologically active IL-2 (ranging from 25 to 100 U ml-1 in the culture supernatant). IL-2 transfection did not produce significant modifications in the expression of surface molecules such as IL-2R alpha and beta chains, intercellular adhesion molecule-1 (ICAM-1), CD44, HLA class I and II or in IL-2R beta or gamma mRNA. More importantly, IL-2-transfected N592 and NCI H69 cell lines completely lost their tumorigenic potential in nude mice after subcutaneous injection, whereas experimental controls transfected with RSV.5 neo vector only, displayed an in vivo growth pattern identical to that of untransfected cells. In addition, in the N592 model, IL-2-producing N592 inhibited the growth of wild-type N592 injected at the same site, while injection of parental cells on the opposite side did not significantly affect the growth of wild-type tumour cells. Histopathological analysis of the rejection process of IL-2-transfected cells demonstrated the presence of MAC-1+, MAC-3+ macrophages and of RB68C5+ granulocytes, whereas T cells were undetectable and NK cells were scarcely represented. In addition, a reduction of the tumour blood vessels was observed. The possible relevance of these data for the development of vaccination strategies using cytokine-engineered tumour cells in SCLC is discussed.

Cytokines in animal models of cancer

Cytokines are a complex family of mediators that play a wide role in development, immunity, inflammation and tissue repair. Their use in therapy is still in its infancy and animal models have a key role to play in optimizing doses and schedules. Whilst xenogeneic and syngeneic transplantable systems have traditionally been used to look at the effects of cytokines in tumour models, oncogene transgenic mice prone to develop cancer, may now have a role to play. Moreover, gene therapy has allowed the investigation of ectopically expressed high and continuous levels of cytokines. We will attempt to review the literature on the effect of cytokines and their combinations in these models of cancer.

Cytokine gene-modified vaccines in the therapy of cancer

Therapeutic strategies based on the insertion of cytokine genes into the genome of tumour cells, followed by vaccination with the resulting genetically modified, cytokine-producing cells, represent a new potential prospect for treatment of cancer patients. In this review, the concept of cytokine gene-modified cancer vaccines is discussed; the discussion is focused on the rationale, characterization, progress in the development, preclinical testing, and first clinical trials. An effort is made to analyse and integrate the results obtained in different experimental model systems in order to determine the needed approaches and directions for further research.