Immune phenomena involved in the in vivo regression of fibrosarcoma cells expressing cell-associated IL-1alpha.

Constitutive expression of cell-associated, but not secreted, interleukin-1alpha (IL-1alpha) by oncogene-transformed fibrosarcoma cells induced regressing tumors in mice, a phenomenon that was abrogated by the IL-1 inhibitor, the IL-1 receptor antagonist (IL-1Ra). On the contrary, non-IL-1alpha-expressing tumor cells induce progressive tumors in mice. In vivo and ex vivo experiments have shown that regression of IL-1alpha-positive fibrosarcoma cells depends on CD8(+) T cells, which can also be activated in CD4(+) T cell-depleted mice, with some contribution of natural killer cells. In spleens of mice bearing the non-IL-1alpha-expressing fibrosarcoma cells, some early and transient manifestations of antitumor-specific immunity, such as activation of specific proliferating T cells, are evident; however, no development of cytolytic T lymphocytes or other antitumor protective cells could be detected. In spleens of mice bearing the non-IL-1alpha-expressing fibrosarcoma cells, the development of early tumor-mediated suppression was observed, and in spleens of mice injected with IL-1alpha-positive fibrosarcoma cells, protective immunity developed in parallel to tumor regression. Treatment of mice bearing violent fibrosarcoma tumors with syngeneic-inactivated, IL-1alpha-positive fibrosarcoma cells, at a critical interval after injection of the malignant cells (Days 5-12), induced tumor regression, possibly by potentiating and amplifying transient antitumor cell immune responses or by ablation of tumor-mediated suppression. Membrane-associated IL-1alpha may thus serve as an adhesion molecule, which allows efficient cell-to-cell interactions between the malignant and immune effector cells that bear IL-1Rs and function as a focused cytokine with adjuvant activities at nontoxic, low levels of expression. Our results also point to the potential of using antitumor immunotherapeutic approaches using cell-associated IL-1alpha.

Effects of micro-environment- and malignant cell-derived interleukin-1 in carcinogenesis, tumour invasiveness and tumour-host interactions.

Interleukin-1 (IL-1) comprises a family of closely related genes; the two major agonistic proteins, IL-1alpha and IL-1beta, are pleiotropic and affect mainly inflammation, immunity and haemopoiesis. IL-1beta is active solely in its secreted form, whereas IL-1alpha is active mainly as an intracellular precursor. IL-1 is abundant at tumour sites, where it may affect the process of carcinogenesis, tumour growth and invasiveness and the patterns of tumour-host interactions. Here, we review the effects of micro-environment- and tumour cell-derived IL-1 on malignant processes in experimental tumour models. We propose that membrane-associated IL-1alpha expressed on malignant cells stimulates anti-tumour immunity, while secretable IL-1beta derived from the micro-environment or the malignant cells, activates inflammation that promotes invasiveness and induces tumour-mediated suppression. Inhibition of the function of IL-1 by the inhibitor of IL-1, interleukin-1 receptor antagonist (IL-1Ra), reduces tumour invasiveness and alleviates tumour-mediated suppression, pointing to its feasible use in cancer therapy. Differential manipulation of IL-1alpha and IL-1beta in malignant cells or in the tumour's micro-environment may open new possibilities for using IL-1 in cancer immunotherapy.

CD11b+/Gr-1+ immature myeloid cells mediate suppression of T cells in mice bearing tumors of IL-1beta-secreting cells.

Tumor cells secreting IL-1beta are invasive and metastatic, more than the parental line or control mock-transfected cells, and concomitantly induce in mice general immune suppression of T cell responses. Suppression strongly correlates with accumulation in the peripheral blood and spleen of CD11b+/Gr-1+ immature myeloid cells and hematological alterations, such as splenomegaly, leukocytosis, and anemia. Resection of large tumors of IL-1beta-secreting cells restored immune reactivity and hematological alterations within 7-10 days. Treatment of tumor-bearing mice with the physiological inhibitor of IL-1, the IL-1R antagonist, reduced tumor growth and attenuated the hematological alterations. Depletion of CD11b+/Gr-1+ immature myeloid cells from splenocytes of tumor-bearing mice abrogated suppression. Despite tumor-mediated suppression, resection of large tumors of IL-1beta-secreting cells, followed by a challenge with the wild-type parental cells, induced resistance in mice; protection was not observed in mice bearing tumors of mock-transfected fibrosarcoma cells. Altogether, we show in this study that tumor-derived IL-1beta, in addition to its proinflammatory effects on tumor invasiveness, induces in the host hematological alterations and tumor-mediated suppression. Furthermore, the antitumor effectiveness of the IL-1R antagonist was also shown to encompass restoration of hematological alterations, in addition to its favorable effects on tumor invasiveness and angiogenesis that have previously been described by us.

Self HSP60 peptide serves as an immunogenic carrier for a CTL epitope against persistence of murine cytomegalovirus in the salivary gland.

Murine cytomegalovirus (MCMV) infection is associated with persistence of virus in the salivary glands, despite relatively rapid clearance of virus from the spleen. An effective immunization against MCMV should prevent such viral persistence. We previously reported that a peptide (p458) from the sequence of the 60 kDa heat shock protein (HSP60) molecule in a conjugate vaccine can provide T cell help for the induction of protecting antibody against bacterial capsular polysaccharides. We now report that the p458 peptide as a carrier peptide can also enhance the immunogenicity of a dominant CTL epitope of the MCMV pp89 antigen-89pep. We synthesized a linear combined peptide: chimeric p458-89pep. We immunized young BALB/c mice and challenged them with MCMV. We found that the p458-89pep chimeric peptide was more effective than the 89pep in inducing 89pep-specific IFN(gamma) secretion and specific CTL activity. Moreover, the p458-89pep chimeric peptide induced sustained IFN(gamma) secretion in the salivary gland specific to 89pep and only this immunization was associated with clearance of virus from the salivary gland. These results suggest that a peptide epitope of HSP60 may be advantageous as a T cell carrier peptide in the induction of specific T cell immunity against infectious agents.

Differential effects of IL-1 alpha and IL-1 beta on tumorigenicity patterns and invasiveness.

In this study, we show that distinct compartmentalization patterns of the IL-1 molecules (IL-1alpha and IL-1beta), in the milieu of tumor cells that produce them, differentially affect the malignant process. Active forms of IL-1, namely precursor IL-1alpha (pIL-1alpha), mature IL-1beta (mIL-1beta), and mIL-1beta fused to a signal sequence (ssIL-1beta), were transfected into an established fibrosarcoma cell line, and tumorigenicity and antitumor immunity were assessed. Cell lines transfected with pIL-1alpha, which expresses IL-1alpha on the membrane, fail to develop local tumors and activate antitumor effector mechanisms, such as CTLs, NK cells, and high levels of IFN-gamma production. Cells transfected with secretable IL-1beta (mIL-1beta and ssIL-1beta) were more aggressive than wild-type and mock-transfected tumor cells; ssIL-1beta transfectants even exhibited metastatic tumors in the lungs of mice after i.v. inoculation (experimental metastasis). In IL-1beta tumors, increased vascularity patterns were observed. No detectable antitumor effector mechanisms were observed in spleens of mice injected with IL-1beta transfectants, mock-transfected or wild-type fibrosarcoma cells. Moreover, in spleens of mice injected with IL-1beta transfectants, suppression of polyclonal mitogenic responses (proliferation, IFN-gamma and IL-2 production) to Con A was observed, suggesting the development of general anergy. Histologically, infiltrating mononuclear cells penetrating the tumor were seen at pIL-1alpha tumor sites, whereas in mIL-1beta and ssIL-1beta tumor sites such infiltrating cells do not penetrate inside the tumor. This is, to our knowledge, the first report on differential, nonredundant, in vivo effects of IL-1alpha and IL-1beta in malignant processes; IL-1alpha reduces tumorigenicity by inducing antitumor immunity, whereas IL-1beta promotes invasiveness, including tumor angiogenesis, and also induces immune suppression in the host.