Cyclophosphamide Induces the Development of Early Myeloid Cells Suppressing Tumor Cell Growth by a Nitric Oxide-Dependent Mechanism

Abstract

Adoptive immunotherapy with cyclophosphamide (Cy) increases the host resistance against tumor growth. The precise mechanism(s) by which this therapy enhances tumor suppression is unclear. Cy induces the development of early myeloid cells that may be strongly antiproliferative through NO production. These cells are similar to the natural suppressor cells found in normal bone marrow with a potential antitumor effect. Here we have addressed whether the development of NO-producing cells may be involved in this tumor resistance in Cy-treated mice. The results show a synergism between Cy treatment and tumor-specific lymphocytes transferred systemically (i.v.) or locally (Winn’s assay) that results in a strong tumor suppression. Inhibition of NO production by NG-monomethyl-l-arginine at the site of tumor inoculation results in a loss of the protection achieved by the combined therapy. Cy-treated mice develop splenic early myeloid (CD11b, Gr-1, CD31 (ER-MP12), ER-MP20, ER-MP54) cells producing large amounts of NO upon T cell-derived signals (IFN-γ plus CD40 ligation) able to inhibit tumor cell growth in vitro. Early myeloid cells (ER-MP54+) and cells expressing inducible NO synthase are increased at the site of tumor challenge in mice treated with the combined therapy, but not in those treated with Cy or immune cell transfer alone. Thus, Cy induces the expansion of early myeloid cells, inhibiting tumor cell growth by a mechanism involving NO. Both the recruitment and the activation of these myeloid cells at the site of tumor challenge appear to be dependent on the presence of tumor-specific lymphocytes.

Immune-based mechanisms of cytotoxic chemotherapy: implications for the design of novel and rationale-based combined treatments against cancer

“…83,84 Recently, low-dose CTX treatment of mice spontaneously developing melanomas led to an accumulation of inflammatory mediators, such as GM-CSF, IL-1b, IL-5, IL-10, IFN-g and TNF-a, in skin tumors and metastatic LNs, inducing accumulation and activation of MDSCs that abrogated CTX antitumor effects. 85 Other reports, however, show that CTX induces early myeloid effector cells that may inhibit tumor cell growth through nitric oxide (NO) release, 86 and that metronomic CTX plus gemcitabine mitigates Treg-and MDSC-mediated immunosuppression and elicits antitumor immunity in vivo. 87 Among taxanes, paclitaxel specifically impairs viability and cytokine production in FOXP3 þ Treg cells, but not in FOXP3 À CD4 effector cells.…”

IMA901: A multi-peptide cancer vaccine for treatment of renal cell cancer

“…There is evidence from a number of pre-clinical and clinical studies that lowdose cyclophosphamide (CY) administered prior to vaccination is of benefit to cancer patients most likely through inhibition of Tregs and subsequently enhanced immune responses and/or clinical response to vaccination. [45][46][47][48][49][50][51] In addition, positive immunomodulatory effects of CY on dendritic cells [52][53][54][55] , other antigen presenting cells 52 , tumor infiltrating cells 53,55,56 and MDSCs 52,57,58 have been shown in in vitro experiments as well as in animal models.…”

IL-12 immunotherapy of minimal residual disease in murine models of HPV16-associated tumours: induction of immune responses, cytokine production and kinetics of immune cell subsets

“…Early results suggested that cyclophosphamide is an inhibitor of suppressor T cells induced in tumour bearers (14). Further studies have showed that cyclophosphamide induces development of spleen early myeloid cells (15). Recently (16), it has been demonstrated that these myeloid suppressor Gr1 + /CD11b + cells accumulate in the spleens of tumour-bearing animals and contribute to immunosupression in tumour bearers.…”