Myeloid-derived suppressor cells (MDSCs) in patients with solid tumors: considerations for granulocyte colony-stimulating factor treatment

Abstract

Myeloid-derived suppressor cells (MDSCs) have been shown to contribute to tumor escape from host immune surveillance and to cancer progression by production of tumor-promoting soluble factors. Granulocyte colony-stimulating factor (G-CSF) is a principle cytokine controlling granulocyte number. Recombinant human G-CSF (rhG-CSF) has become the main therapeutic agent for the treatment of neutropenia and prophylaxis of febrile neutropenia in cancer patients. However, we show here that rhG-CSF triggers accumulation of granulocytic and monocytic subsets. Consequently, we discuss the pharmacological use of granulopoiesis stimulating factors not only in the context of febrile neutropenia but also from the perspective of MDSC-dependent and MDSC-independent mechanisms of immunosuppression and cancer angiogenesis.

Keywords: CITIM 2017; Cancer; Granulocyte colony-stimulating factor; Myeloid-derived suppressor cells; Prophylaxis of febrile neutropenia.

Fig. 1

Summary of MDSC nature and their immunosuppressive and tumor-promoting actions. a Acute-phase conditions, such as chronic infection, sepsis or cancer lead to normal and abnormal/emergency myelopoiesis that is controlled by the production of granulocytic or monocytic growth factors (GM-CSF, G-CSF and M-CSF) leading to the production of mature and immature myeloid cells from precursors in the bone marrow (BM). MDSCs may act in secondary lymphoid organs (SLO) by various immunosuppressive mechanisms (e.g., by the production of IDO, NOS, arginase, IL-10 or TGFβ) that stimulate Treg expansion and inhibit cytotoxic T cell and NK cell function or dendritic cell differentiation and maturation. Upon entering tumor tissue, M-MDSCs rapidly differentiate into tumor-associated M2 macrophages (TAM M2). Furthermore, MDSCs support tumor growth by production of pro-angiogenic factors or factors that promote metastatic spread (e.g., VEGF, bFGF, MMP-9). b To address the issue of strength of TLR4 activation on monocyte reprogramming, we examined dose-dependent change in M-MDSC proportion in monocytes upon 24 h stimulation of whole blood with LPS. Here, we show that low, but not high, endotoxin concentrations result in the increase of M-MDSC/CARS proportion in CD14⁺ cells. BM bone marrow, NOS nitric oxide synthase, SLO secondary lymphoid organ, tu tumor cell

Fig. 2

Inverse correlation between effector CD27⁻ cytotoxic CD8⁺ T cells and number of MDSCs in pediatric cancer patients. We perform immunomonitoring of circulating immune cells in high-risk pediatric cancer patients in the clinical trial evaluating anti-cancer vaccine based on dendritic cells loaded with autologous tumor lysate (EudraCT: 2014-003388-39). a Patients with low MDSC counts before DC vaccination have high proportions of effector CD27⁻ CD8⁺ T cells compared to patients with high MDSC counts. A low MDSC count was defined as ≤ 0.01 10⁹/L for CD33^hi PMN-MDSCs and ≤ 0.2 10⁹/L for M-MDSCs. b Case of early relapsing Burkitt lymphoma with PI3K-delta subunit germline mutation treated with long-term anti-cancer DC vaccination (29 doses) is shown. We observed opposing dynamics of CD27⁻ CD8⁺ effector T cells and CD33^hi PMN-MDSCs during the course of vaccination. The peak at dose 23 (depicted with an empty circle) overlaps with respiratory infection resolved by amoxicillin

Fig. 3

rhG-CSF triggers ‘emergency’ myelopoiesis and the accumulation of granulocytic and monocytic MDSCs in carcinoma patients. a Typical morphological changes in myeloid cells after rhG-CSF administration are shown. rhG-CSF caused release of immature granulocytes (IG) in peripheral blood: myeloblasts (i), promyelocytes (ii). Dysplastic changes with nucleo-cytoplasmic maturation asynchrony are apparent in IG (iii). Neutrophilic granulocytes have hyposegmented nuclei, contain Döhle bodies (arrows) (iv–vi), are hypergranulated (iv), less typically hypogranulated (vi) and/or show nucleo-cytoplasmic asynchrony (v). Monocytes of younger morphology have basophilic cytoplasm and lack vacuolization (vii). WBC differential count from blood smear was: band neutrophils: 15.7%, segmented neutrophils: 29.8%, eosinophils: 1.7%, basophils: 0.0%, lymphocytes: 8.3%, monocytes: 14.0%, promyelocytes: 4.1%, myelocytes: 13.2%, metamyelocytes: 11.6%, blasts: 1.7%. b, c Dynamics of circulating MDSC subsets after rhG-CSF administration. Numbers of circulating b M-MDSCs and c CD33^hi PMN-MDSCs were examined in breast carcinoma patients before and 2–7 days after rhG-CSF (filgrastim) administration. d Effect of rhG-CSF on MDSC level ex vivo in peripheral blood samples of cancer patients. Whole blood specimens were incubated (37 °C, 5% CO₂) with raising concentrations of rhG-CSF (filgrastim) (0–10,000 ng/mL) for 17 up to 20 h. Case 1—metastatic brain lesion of Grawitz tumor with bronchopneumonia under corticotherapy (CRP = 15 mg/L, increased IG in peripheral blood: 11%), case 2—inoperable cholangiocarcinoma treated with gemcitabine (CRP = 0.8 mg/L), case 3—colorectal cancer 1 day after surgery (sigmoid colectomy, CRP = N/A). Concentration of rhG-CSF of 10 ng/mL, that is reached in patients receiving filgrastim for neutropenia, led in all cases to accumulation of M-MDSCs as well as CD33 PMN-MDSCs ex vivo compared to baseline level. IG immature granulocyte

Fig. 4

Mechanisms of rhG-CSF immunosuppressive and tumor-promoting actions. rhG-CSF stimulates production of mature and immature myeloid cells (1), release of immature PMN-MDSCs and peripheral reprogramming of mature myeloid cells into M-MDSCs and mature PMN-MDSCs (2). In turn, rhG-CSF may contribute to MDSC-dependent cancer angiogenesis and metastasis (3), may directly stimulate the proliferation of tumor cells (tu) through their G-CSF receptors (4) and may contribute to a hypercoagulable state implicated in cancer progression (5). Finally, rhG-CSF inhibits T-cell function in MDSC-dependent and partially MDSC-independent manners and promotes Treg (6). BM bone marrow, SLO secondary lymphoid organ, tu tumor cell, PLT platelets