Involvement of immune responses in the eradication of IL-1 alpha gene-transduced tumour cells: mechanisms of tumour rejection and immunotherapeutical implications.

We detected a strong correlation between the constitutive expression of IL-1 alpha and reduced tumorigenicity, using fibrosarcomas which produce the cytokine spontaneously (as an aberration of the transformation process) or upon 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 tumour regression of the IL-1 alpha producing fibroblastoid cell lines indicated that IL-1 alpha potentiates the development of tumour cell-specific CTLs, which are of importance for tumour eradication. It also appears that IL-1 alpha-induced enhanced helper T-cell activity provides auxiliary signals for the growth/development of CTLs. In addition, we observed a massive lymphocytic infiltrate in IL-1 alpha producing regressing tumours which ultimately replaces the tumour's mass. Non-adaptive effector cells, activated locally by IL-1 alpha expressing fibrosarcoma cells, were also shown to contribute, to some extent, 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, and by this anti-tumour immune responses were further potentiated. Mice, in which IL-1 alpha producing tumours regressed, developed systemic immunity and rejected a challenge with a non IL-1 producing violent tumour cell line. It appears that endogenous IL-1 alpha, being a strong inducer of cytokine production, operates a whole cytokine cascade (such as IL-6, CSFs and prostaglandins). However, studies using clonal populations have indicated that IL-1 alpha is essential for fibrosarcoma eradication, whereas the other cytokines possibly amplify and sustain its action. We assume that most naturally occurring tumours are not constitutive IL-1 alpha producers, as it would be disadvantageous for the tumour to express a cytokine which increases its immunogenicity. However, IL-1 non-producing fibrosarcomas can be induced easily to express IL-1 transiently, by treatment with cytokines/LPS, and upon the induction of the cytokine they shift from progressor to regressor tumours. We also obtained positive immunotherapeutical effects when treating mice bearing IL-1 non-producing fibrosarcomas with cells from the same line induced in vitro to express IL-1 alpha. The results may shed light on a novel parameter affecting tumour-host interactions, namely cytokine expression by the tumorous cells, and may provide the basis for new immunotherapy protocols for fibrosarcoma management.

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)

IL-1 and pro-inflammatory cytokines produced by primary and transformed fibroblasts abrogate the tumorigenic potential of fibrosarcomas.

In the present study we report on novel immunoregulatory functions lately attributed to fibroblasts, namely participation in cellular immune responses in connective tissues, by generation of pro-inflammatory cytokines and by presenting antigens to proliferating T cells. In order to execute immunoregulatory functions, the fibroblast has to be activated by signals abundant at inflammatory sites, i.e., cytokines and bacterial products. It was demonstrated that such immune-activated fibroblasts are able to generate a variety of cytokines such as interleukin-1 (IL-1), IL-6, colony stimulating factors (CSFs) as well as prostaglandins. The array of cytokines generated by immune-activated fibroblasts is determined by the stimulant and is controlled at multiple regulatory levels, such as transcription, translation, post-translational modifications, compartmentalization within the producing cell as well as the timing of expression. Some oncogene-transformed fibroblastoid cells lines were shown to constitutively generate IL-1 (and not IL-1 beta), as evidenced by the continuous expression of specific mRNA and biological activity of the cytokine, associated to the cell membrane or located in the cytosol. When these IL-2 producing cell lines were injected into mice, they failed to generate established tumors or regressed following initial growth, possibly due to mounting the host anti-tumor specific immune responses in which cytotoxic lymphocytes (CTLs) predominate. In contrast, IL-1 non-producing tumor cell lines induced progressive tumors which ultimately killed the animals. However, IL-1 non-producing fibroblastoid cell lines shifted from an in vivo progressive to a regressive phenotype, following immune activation of the malignant cells in vitro with cytokines/LPS. Similarly, primary immune-activated fibroblasts also induced tumor regression, mediated by anti-tumor specific immune responses, when the fibroblasts were injected into the vicinity of the tumor. Thus, the importance of activated stromal cells on tumor development was emphasized. This situation is relevant to the development of malignancies, as tumor growth is often accompanied by a local inflammatory response. Thus, the induction of IL-1 and other pro-inflammatory cytokines expression by the malignant cells or by stromal cells, in the vicinity of the tumor, might be efficient for tumor eradication. These findings should serve as a basis for development of novel immunotherapeutical strategies for the eradication of solid tumors.