High-Dose Granulocyte-Macrophage Colony-Stimulating Factor-Producing Vaccines Impair the Immune Response through the Recruitment of Myeloid Suppressor Cells

Abstract

Tumor vaccines have shown promise in early clinical trials. Among them, tumor cells genetically engineered to secrete biologically active granulocyte-macrophage colony-stimulating factor (GM-CSF) can generate a systemic antitumor immune response. Although the minimal required GM-CSF dose produced by modified tumor cells to achieve a measurable antitumor effect is well known, no data examined whether an upper therapeutic limit may exist for this vaccination strategy. Because recent data demonstrate an immunosuppressive effect of GM-CSF produced by growing tumors, we thus sought to determine whether high GM-CSF doses administered in a vaccine formulation could impair antitumor immunity. Using a vaccine strategy involving a GM-CSF-producing bystander cell line (B78H1-GM) admixed with autologous tumor, we assessed the impact of varying doses of GM-CSF while maintaining a constant antigen dose. Our results defined a threshold above which a GM-CSF-based vaccine not only lost its efficacy, but more importantly for its clinical implications resulted in substantial immunosuppression in vivo. Above this threshold, GM-CSF induced Gr1؉ /CD11b ؉ myeloid suppressor cells that substantially impaired antigen-specific T-cell responses and adversely affected antitumor immune responses in vivo. The dual effects of GM-CSF are mediated by the systemic and not local concentration of this cytokine. Myeloid suppressor cell-induced immunosuppression is mediated by nitric oxide production via inducible nitric oxide synthase (iNOS) because the specific iNOS inhibitor, L-NMMA, restored antigenspecific T-cell responsiveness in vitro. Taken together, our data demonstrated the negative impact of supra-therapeutic vaccine doses of GM-CSF and underscored the importance of identifying these critical variables in an effort to increase the therapeutic efficacy of tumor vaccines.

Phase 1/2 trial of autologous tumor mixed with an allogeneic GVAX® vaccine in advanced-stage non-small-cell lung cancer

“…Such immunosuppression has been demonstrated in animal studies using high GM-CSF-secreting cellular vaccines. 21 However, the serum GM-CSF levels measured in patients in this study were consistently below the levels associated with immunosuppression in animals (4250 pg/ml) and, generally, were in the range associated with a therapeutic vaccine effect (p40 pg/ml), making this explanation unlikely.…”

The Multifaceted Roles Neutrophils Play in the Tumor Microenvironment

“…While physiological concentrations of GM-CSF are required for normal myelopoiesis, chronic administration of GM-CSF resulted in the generation of immune suppressive Gr-1 + CD11b + cells in mice [184]. Experimental tumors overexpressing GM-CSF induced a systemic increase of immature myeloid cells, which was associated with suppression of T cell immune responses [184][185][186]. However, irradiated cancer cells engineered to secrete GM-CSF elicited potent anti-tumor immune responses in various animal tumor models [187].…”

Toll like receptor 7 expressed by malignant cells promotes tumor progression and metastasis through the recruitment of myeloid derived suppressor cells

“…We found that stimulation of TLR7 expressed by adenocarcinoma cells modulated the immune infiltrate, leading to a significant expansion in MDSCs, associated with an increased secretion of CCL2 and GM-CSF in the tumor microenvironment. Both these cytokines are known to play a key role in the recruitment of MDSCs 38,41,42 . Indeed, the absence of CCL2 production by cancer cells considerably reduces the recruitment of MDSCs into tumors 42 .…”