Immunological memory induced by genetically transduced tumor cells

Overview of Tumor Cell–Based Vaccines

Whole-cell tumor vaccines have been investigated for more than 20 years for their efficacy in both preclinical models and in clinical trials in humans. There are clear advantages of whole-cell/polyepitope vaccination over those types of immunotherapy that target specific epitopes. Multiple and unknown antigens may be targeted to both the innate and adaptive immune system, and this may be further augmented by genetic modification of the vaccine cells to provide cytokines and costimulation. In this review, we give an overview of the field including the preclinical and clinical advances using unmodified and modified tumor-cell vaccines.

Interferon-gamma reverses the immunosuppressive and protumoral properties and prevents the generation of human tumor-associated macrophages

Tumor-associated macrophages (TAM) are M2d-polarized cells (IL-10(high), IL-12(low), ILT3(high), CD86(low)) that accumulate in tumor microenvironment. TAM inhibit antitumor T lymphocyte generation and function, contribute to tumor tolerance and are trophic for tumors. In this study, we investigated whether some immunological factors may reverse TAM immunosuppressive properties. Among 32 cytokines, we have identified IFNgamma on its ability to switch immunosuppressive TAM into immunostimulatory cells. Upon IFNgamma exposure, TAM purified from ovarian cancer ascites recover a M1 phenotype (IL-10(low), IL-12(high)), express high levels of CD86 and low levels of ILT3, enhance the proliferation of CD4(+) T lymphocytes and potentiate the cytotoxic properties of a MelanA-specific CD8(+) T cell clone. IFNgamma-treated TAM also secreted reduced levels of mediators promoting suppressive T cell accumulation (CCL18) and trophic for tumors (VEGF and MMP9). As TAM derive from the local differentiation of peripheral blood monocytes, we investigated whether IFNgamma may also affect TAM generation. In the presence of ovarian ascites, IFNgamma skewed monocyte differentiation from TAM-like cells to M1-polarized immunostimulatory macrophages. Together, these data show that IFNgamma overcomes TAM-induced immunosuppression by preventing TAM generation and functions. These data highlight that IFNgamma used locally at the tumor site could potentiate the efficacy of antitumor immunotherapies based on the generation of effector T cells.

Human cancer gene therapy with cytokine gene-modified cells

Cytokines can impede tumour growth and activate innate and adaptive immune responses, leading to elimination of cancer cells. For many years, it was believed that systemic administration of recombinant cytokines might become a standard treatment of different cancer types. However, due to a high toxicity of therapeutic doses and a low efficacy, even in combination with chemotherapy, this strategy is generally not accepted. On the other hand, cancer gene therapy approaches utilising cells modified with cytokine genes seem to represent a novel promising approach. For the last decade, numerous Phase I and II clinical trials evaluating different therapies based on cytokine gene-modified cells have been carried out. In the early studies, several strategies have been shown to improve clinical outcomes and induce strong antitumour immune responses. Recently, a few prospective, randomised, Phase III clinical trials have been initiated in order to finally determine the efficacy of particular cancer immunogene therapy strategies. This article reviews the present status and perspectives of clinical trials of cancer immunotherapies utilising cytokine gene-modified cells.

Spontaneous regression of neoplasms: new possibilities for immunotherapy

In mammalian cells, neoplastic transformation is directly associated with the expression of oncogenes, loss or simple inactivation of the function of tumour suppressor genes and the production of certain growth factors. Genes for suppression of the development of the neoplastic cellular immunophenotype, as well as inhibitory growth factors, have regulatory functions within the normal processes of cell division and differentiation. Telomerase (a ribonucleoprotein polymerase) activation is frequently detected in various neoplasms. Telomerase activation is regarded as essential for cell immortalisation and its inhibition may result in spontaneous regression of neoplasms. This phenomenon of neoplasms occurs when the malignant tissue mass partially or completely disappears without any treatment or as a result of a therapy considered inadequate to influence systemic neoplastic growth. This definition makes it clear that the term 'spontaneous regression' applies to neoplasms in which the overall malignant disease is not necessarily cured and to cases where the regression may not be complete or permanent. A number of possible mechanisms of spontaneous regression are reviewed, with the understanding that no single mechanism can completely account for this phenomenon. The application of the newest immunological, molecular biological and genetic insights for more individualised and adequate antineoplastic immunotherapy (alternative biotherapy) is also discussed.

Tumor cells cotransduced with B7.1 and gamma-IFN induce effective rejection of established parental tumor

Genetic modification of tumor cells with the gene for the B7.1 or with the genes for cytokines results in increased tumor cell immunogenicity. In the work reported here, immunization of naive animals with either B7.1 or gamma-IFN gene-modified MCA106 tumor cells effectively protects the host from subsequent challenge with parental tumor. The same treatment fails to induce regression of established tumors, although tumor-specific CTL are generated in the tumor-bearing animals. In contrast, a large tumor burden of the MCA106 fibrosarcoma can be successfully eliminated by treatment with MCA106 tumor cells cotransduced with the B7.1 and gamma-IFN genes. Antitumor immunity induced by the cotransductants is primarily dependent on CD8+ T cells and partly on CD4+ T cells and NK cells, and the enhanced therapeutic effect may be attributed to the in vivo increase of CTL precursors following treatment. The gamma-IFN and B7.1 genes must be expressed on the same tumor cell for optimal therapeutic effect. Our results suggest that tumor vaccines with a potent immunoprotective effect do not necessarily have therapeutic potential and that weakly immunogenic tumors may be rendered highly immunogenic by cotransfection with the genes for B7.1 and gamma-IFN.

Pulsing of dendritic cells with cell lysates from either B16 melanoma or MCA-106 fibrosarcoma yields equally effective vaccines against B16 tumors in mice

BACKGROUND AND OBJECTIVES

Dendritic cells (DC) pulsed in vitro with a variety of antigens have proved effective in producing specific antitumor effects in vivo. Experimental evidence from other laboratories has confirmed that shared antigens can be encountered in histologically distinct tumors. In our experiments, we set out to evaluate the immunotherapeutic potential of vaccines consisting of DC pulsed with MCA-106 fibrosarcoma or B16 melanoma cell lysates and to determine whether a cross-reactivity exists between the two tumors.

METHODS

DC were prepared from the bone marrow of C57BL/6 (B6) mice by culturing progenitor cells in murine granulocyte-macrophage colony-stimulating factor (GM-CSF). They were separated into three equal groups and were either pulsed with B16 melanoma cell lysates (BDC), pulsed with tumor extract from the syngeneic fibrosarcoma MCA-106 (MDC), or left unpulsed (UDC). DC were then used to immunize three groups of mice, with all mice receiving two weekly intravenous (IV) doses of 1 x 10(6) DC from their respective preparations on days -14 and -7. A fourth group of control mice were left untreated. On day 0, all mice were challenged with subcutaneous injections of 1 x 10(5) B16 and 1 x 10(5) MCA tumor cells, administered in the left and right thighs, respectively. After the inoculations, the mice were monitored closely with respect to tumor growth and survival.

RESULTS

The MDC mice developed specific cellular immunity directed against not only MCA-106 tumor cells, but also against B16 melanoma, as measured through chromium-release assays of splenocyte preparations, while remaining ineffective at killing both L929 fibroblasts and CT26 tumor cells. By day 30 after tumor inoculations, control mice manifested the largest B16 tumor volumes at a mean of 2185 mm3, followed by the UDC, MDC, and BDC groups at 92 mm3 (P=0.00008), 3 mm3 (P=0.000002), and 2 mm3 (P=0.00004), respectively. The survival data mirrored this pattern, with control animals displaying the shortest mean survival time (37.1+/-4.0 days), followed by UDC (44.8+/-6.6), MDC (56.2 +/-14.7), and BDC (56.4+/-18.3) animals. No significant differences were noted between MCA-106 and B16 cell lysate-pulsed DC vaccines with respect to their abilities to inhibit B16 tumor growth and to prolong survival. These findings were confirmed using a B16 pulmonary metastasis model. Likewise, vaccination with interferon-gamma gene-modified MCA-106 tumor cells was shown to be effective at protecting against a subsequent subcutaneous B16 tumor challenge in 3 of 4 mice observed.

CONCLUSIONS

These results demonstrate that immunization with antigen-pulsed DC confers cellular immunity, retards tumor growth, and prolongs the survival of tumor-challenged mice. The ability of MCA-106 cell lysate-pulsed DC vaccines to inhibit the growth of subcutaneous B16 tumors also suggests the presence of shared tumor-associated antigens between these two histologically distinct tumors.

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.