Enhancement of cytotoxic T lymphocyte growth from spleens of P815-tumor-bearing host mice with mafosfamide

Myeloid progenitor cells mediate immune suppression in patients with head and neck cancers

Patients with squamous cell carcinomas of the head and neck (HNSCC) have profound defects in their immune defenses. We have shown that among the mechanisms that contribute to this immune dysfunction are immune inhibitory CD34+ progenitor cells, whose levels become elevated in the peripheral blood and within the tumor tissue. One goal of our studies is to overcome the immune inhibitory activities of tumor-induced CD34+ progenitor cells by stimulating their differentiation into cells, such as dendritic or monocytic cells, that can stimulate immune reactivity to autologous cancer. Results of in vitro analyses with CD34+ suppressor cells of HNSCC patients and of in vivo studies in animal tumor models have shown the capacity of tumor-induced CD34+ cells to differentiate into cells that phenotypically resemble monocytic or dendritic cells. Whether these cells can differentiate into dendritic cells in HNSCC patients is currently being tested. Less clear is whether the pathway by which the tumor-induced CD34+ cells differentiate will result in cells having the full capacity to function as potent stimulators of immune reactivity to autologous tumor.

Mechanisms of immune suppression in patients with head and neck cancer: influence on the immune infiltrate of the cancer

Freshly excised human head and neck cancers (219 primary cancers; 64 metastatic lymph node cancers) were analyzed for the immune inhibitory mediators released from the cancer tissues and the immune infiltrate within the tumor. Significant levels of the immune inhibitory mediators transforming growth factor-beta (TGF-beta), prostaglandin E2 (PGE2) and interleukin-10 (IL-10) were released from these cancers. Also released was granulocyte-macrophage colony-stimulating factor (GM-CSF), whose secretion was associated with an intratumoral presence of CD34+ cells. We have previously shown that CD34+ cells within human head and neck cancers are immune inhibitory granulocyte-macrophage progenitor cells. The presence of TGF-beta, PGE2 and IL-10 was associated with a reduced content of CD8+ T-cells within the cancers. The CD4+ cell content appeared to be less affected by these immune inhibitory mediators. Instead, parameters indicative of CD4+ cell function (p55 IL-2 receptor expression, release of IL-2 and IFN-gamma) were diminished in cancers that released higher levels of TGF-beta, IL-10 and GM-CSF and had a higher CD34+ cell content. Furthermore, metastatic cancers released higher levels of the soluble immune inhibitory mediators and lower levels of IFN-gamma and IL-2 than did primary cancers, although CD34+ cells were similarly present in both primary and metastatic cancers. Our results show that human head and neck cancers have a multiplicity of non-mutually exclusive mechanisms of immune suppression that are most prominently associated with reduced CD8+ cell influx and reduced influx and altered function of intratumoral CD4+ cells.

Vitamin D3 treatment of tumor bearers can stimulate immune competence and reduce tumor growth when treatment coincides with a heightened presence of natural suppressor cells

By secreting granulocyte-macrophage colony-stimulating factor (GM-CSF), Lewis lung carcinoma tumors induce immune suppressive granulocyte-macrophage progenitor cells. Treating mice having established tumors and high levels of suppressor activity with vitamin D3 eliminated suppressor activity, increased anti-tumor immunity, induced an immune stimulatory cell population, and reduced tumor growth. When instead, the vitamin D3 treatment was initiated earlier, when implanted tumors first became detectable and when natural suppressor activity was less prominent, the treatment had no effect. Thus, vitamin D3 treatment can stimulate the immune competence of tumor bearers when treatment is targeted to coincide with a heightened presence of GM-CSF-induced suppressor cells.

Treating tumor-bearing mice with vitamin D3 diminishes tumor-induced myelopoiesis and associated immunosuppression, and reduces tumor metastasis and recurrence

Metastatic Lewis lung carcinoma (LLC-LN7) tumors that secrete granulocyte/macrophage-colony-stimulating factor (GM-CSF) stimulate myelopoiesis and induce bone marrow-derived immunosuppressor cells that are homologous to granulocyte/macrophage progenitor cells. In vitro treatment of the LLC-LN7 cells with 1 alpha,25-dihydroxyvitamin D3 reduced tumor cell production of suppressor-inducing activity, although suppressor-inducing activity could be restored by reconstituting the tumor supernatants with recombinant GM-CSF. Treatment of mice having LLC-LN7 tumors with vitamin D3 reduced tumor production of GM-CSF and the frequency of myeloid progenitor cells. This was associated with a reduction in immunosuppressor activity and an increase in T cell function. Vitamin D3 treatment of mice having palpable tumors transiently retarded tumor growth, but caused a prominent reduction in tumor metastasis. Treating mice with vitamin D3 after tumor excision resulted in a reduction in the tumor-induced myelopoietic stimulation and associated immunosuppressive activity, and enhanced T cell function. These mice had a markedly reduced incidence of tumor recurrence. The results of this study suggest that vitamin D3 treatment of mice with GM-CSF-secreting tumors can interrupt the myelopoiesis-associated immunosuppressor cascade and, in turn, reduce tumor metastasis and recurrence.

Eicosanoids and the immunology of cancer

Studies in both cancer patients and in animal tumor models have shown that immune defenses can mediate destruction of tumor, but these defenses are often functioning at a suppressed or suboptimal level. Frequently, prostaglandins, mainly PGE2, have been implicated in this tumor-associated subversion of immune function, with immune reactivities to tumor typically being enhanced by prostaglandin synthesis inhibitor. Both the tumor and tumor-induced host immune suppressive macrophages have the capacity to suppress immune functions through their production of PGE2. Although the inhibitory functions have been more widely studied, recent evaluations of the effects of PGE2 have led to the surprising realization that not all of the PGE2's effects are inhibitory to immune function. Summarized below are some of the well characterized inhibitory effects of PGE2, as well as the lesser studied stimulatory effects of PGE2 toward the effector cells that are considered to be important in the immune defense against cancer.

Ability of low-dose cyclophosphamide to overcome metastasis-induced immunosuppression

BACKGROUND

Lymphocytes obtained from tumor-draining lymph nodes (DLN) can have potent in vivo antitumor activity after in vitro activation with bryostatin 1 and ionomycin. However, the presence of visceral metastases in the donor can inhibit the effectiveness of such lymphocytes. In the present study, we tested the ability of low-dose cyclophosphamide to overcome metastasis-induced immunosuppression in a murine model.

METHODS

Mice were injected with MCA-105 sarcoma cells in the footpad alone or in the footpad and the tail vein to establish lung metastases. Cyclophosphamide was given i.p. 1 day before harvesting the draining popliteal lymph nodes. For all donor groups, DLN cells were activated with 5 nM bryostatin 1 and 1 microM ionomycin and cultured for 7 days in 20 U/ml IL-2. Activated DLN cells were then adoptively transferred to syngeneic mice with 3-day lung metastases.

RESULTS

The adoptive transfer of DLN cells from mice with footpad tumors only significantly reduced the number of lung metastases compared to untreated mice. However, activated DLN cells obtained from mice with both footpad and lung tumors were significantly less effective. Treatment of similar donor mice with 10 mg/kg cyclophosphamide significantly improved the anti-tumor activity of adoptively transferred cells. This dose of cyclophosphamide did not reduce the number of cells obtained from each lymph node or the expansion of cell numbers in vitro.

CONCLUSIONS

These results suggest that the administration of low-dose cyclophosphamide prior to harvesting DLN cells may improve the success of adoptive immunotherapy in cancer patients.

Increasing infiltration and activation of CD8+ tumor-infiltrating lymphocytes after eliminating immune suppressive granulocyte/macrophage progenitor cells with low doses of interferon gamma plus tumor necrosis factor alpha

By secreting granulocyte/macrophage colony-stimulating factor (GM-CSF), metastatic Lewis lung carcinoma (LLC-LN7) tumors induce the appearance of myelopoiesis-associated immune-suppressor cells that resemble granulocytic-macrophage (GM) progenitor cells. The presence of these GM-suppressor cells in mice bearing LLC-LN7 tumors was associated with a reduced capacity of splenic T cells to proliferate in response to interleukin-2 (IL-2). Administration of low doses of 100 U interferon gamma (IFN gamma) plus 10 U tumor necrosis factor alpha (TNF alpha) to the tumor bearers, a combination treatment that we previously showed to diminish the presence of GM-suppressor cells synergistically, restored proliferative responsiveness of the splenic T cells to IL-2. These LLC-LN7-bearing mice were also examined for whether cells that phenotypically resemble GM-progenitor cells (ER-MP12+ cells) infiltrate the tumor mass. ER-MP12+ cells composed approximately 10% of the cells isolated from dissociated tumors of mice that had been treated with placebo or with either IFN gamma or TNF alpha alone, but IFN gamma/TNF alpha therapy markedly reduced the number of tumor-infiltrating ER-MP12+ suppressor cells. The IFN gamma/TNF alpha treatment to eliminate GM-suppressor cells and restore T cell responsiveness to IL-2 was next coupled with low dose IL-2 therapy (100 U twice daily). Addition of IL-2 to the treatment regimen did not significantly influence the effectiveness of the IFN gamma/TNF alpha treatment in eliminating GM-suppressor cells from the LLC-LN7 tumor mass. However, inclusion of IL-2 with the IFN gamma/TNF alpha treatment regimen enhanced the CD8+, but not the CD4+, cell content within the tumor, and diminished the number of metastatic lung nodules within the mice. When these tumors were excised, dissociated, and bulk-cultured with a low dose of IL-2, an increased level of cytotoxic T lymphocyte (CTL) activity was generated in the TIL cultures from mice that had received IFN gamma/TNF alpha plus IL-2 treatments. A lesser but detectable level of CTL activity was generated in TIL cultures from mice that were treated with only IFN gamma/TNF alpha, while no CTL activity was generated in tumor cultures from mice receiving only placebo or low-dose IL-2. These results suggest the effectiveness of IFN gamma plus TNF alpha therapy in restoring IL-2 responsiveness in mice bearing GM-suppressor cell-inducing tumors and at enhancing both the intratumoral CD8+ cell content and the generation of CTL activity in bulk cultures of these tumors.