Cancer immunotherapy is a growing field. GM-CSF, a potent cytokine promoting the differentiation of myeloid cells, can also be used as an immunostimulatory adjuvant to elicit antitumor immunity. Additionally, GM-CSF is essential for the differentiation of dendritic cells, which are responsible for processing and presenting tumor antigens for the priming of antitumor cytotoxic T lymphocytes. Some strategies have been developed for GM-CSF-based cancer immunotherapy in clinical practice: GM-CSF monotherapy, GM-CSF-secreting cancer cell vaccines, GM-CSF-fused tumor-associated antigen protein-based vaccines, GM-CSF-based DNA vaccines and GM-CSF combination therapy. GM-CSF also contributes to the regulation of immunosuppression in the tumor microenvironment. This review provides recommendations regarding GM-CSF-based cancer immunotherapy.

A phase 1 study was conducted to assess the safety and immunologic response induced by direct injection of autologous immature dendritic cells (DCs) into tumor under radiotherapy in advanced hepatoma patients. Patients with advanced/metastatic stage hepatoma not suitable for surgery or transarterial embolization were enrolled. Groups of patients received two vaccinations. Each vaccination consisted of intratumoral injections of autologous immature DCs in four dose cohorts of 5 × 106, 1.5 × 107, 3 × 107, and 5 × 107 cells 2 days after a single fraction of conformal radiotherapy of 8 Gy. The second vaccination was performed 3 weeks later. Of the 14 patients entered, 12 completed two cycles of vaccination. The treatment was well tolerated at any of the dose levels. Six patients had mild transient fever (grade 1-2) with chill reactions, three patients developed grade 1 fatigue, and one patient developed mild myalgia and arthralgia after DC injections. There was no evidence of clinically manifested autoimmune disease. There were two partial responses and four minor responses. A decrease in the alpha-fetoprotein (AFP) level of more than 50% was found in three patients. Ten patients had completed immunologic response evaluation 2 weeks after the second cycle of vaccination. The AFP-specific immune response was evident in eight patients examined by cytokine release assay and in seven patients by ELISPOT assay. Six patients showed an increased NK cell cytotoxic activity after vaccination. These data suggest that the combination of intratumoral injection of DCs and conformal radiotherapy is safe and can induce tumor-specific and innate immunity.

Cross-talk between TGF-β and IL-6 has been shown to direct the differentiation of CD4⁺ cells into special IL-17-secreting cells, which are termed Th17 cells. In this study, we demonstrated that TGF-β and IL-6 could stimulate CD8⁺ cells to differentiate into noncytotoxic, IL-17-producing cells in MLC. These IL-17-producing CD8⁺ cells exhibit a unique granzyme B⁻IFN-γ⁻IL-10⁻ phenotype. The mRNA level of Th2/T cytotoxic 2 (Tc2) transcription factors GATA3 and Th1/Tc1 transcription factors T-box expressed in T cell (T-bet) as well as its target H2·O-like homeobox (Hlx) is decreased in CD8⁺ cells from TGF-β- and IL-6-treated MLC. In addition, these CD8⁺ cells display a marked up-regulation of retinoic acid-related orphan receptor-γt, a key IL-17 transcription factor. These results demonstrate that the existence of an IL-17-producing CD8⁺ subset belongs to neither the Tc1 nor the Tc2 subset and can be categorized as a T noncytotoxic 17 (Tnc17) subset.

Mesenchymal stem/stromal cells (MSCs) are promising potential candidates for the treatment of immunological diseases because of their immunosuppressive functions. However, the molecular mechanisms that mediate MSCs’ immunosuppressive activity remain elusive. In this article, we report for the first time, to our knowledge, that secreted growth-regulated oncogene (GRO) chemokines, specifically GRO-γ, in human MSC-conditioned media have an effect on the differentiation and the function of human monocyte-derived dendritic cells. The monocyte-derived dendritic cells were driven toward a myeloid-derived suppressor cell (MDSC)–like phenotype by the GRO chemokines. GRO-γ–treated MDSCs had a tolerogenic phenotype that was characterized by an increase in the secretion of IL-10 and IL-4, and a reduction in the production of IL-12 and IFN-γ. We have also shown that the mRNA expression levels of the arginase-1 and inducible NO synthase genes, which characterize MDSCs, were upregulated by GRO-γ–primed mouse bone marrow cells. In addition, the ability of GRO-γ–treated bone marrow–derived dendritic cells to stimulate the OVA-specific CD8⁺ T (OT-1) cell proliferation and the cytokine production of IFN-γ and TNF-α were significantly decreased in vivo. Our findings allow a greater understanding of how MDSCs can be generated and offer new perspectives to exploit the potential of MDSCs for alternative approaches to treat chronic inflammation and autoimmunity, as well as for the prevention of transplant rejection.