Altogether, combined treatment with CD40 and CSF-1Ri more effectively suppressed tumor growth than either CD40 or CSF-1Ri alone

Altogether, combined treatment with CD40 and CSF-1Ri more effectively suppressed tumor growth than either CD40 or CSF-1Ri alone. Open in a separate window LUF6000 Figure 3. Effects of CSF-1Ri and CD40 agonist treatment alone or in combination on TAM subsets. TAMs to convert a cold into an inflamed tumor microenvironment capable of eliciting protective T cell responses. Introduction Melanoma is a challenging disease as it readily metastasizes, and chemotherapy does not improve survival (Flaherty et al., 2013). Inhibitors of mutant B-raf (vemurafenib and dabrafenib) improve survival compared with dacarbazine chemotherapy, and survival is further prolonged with the addition of mitogen-activated protein kinase kinase (MEK) inhibitor treatment (Flaherty et al., 2012; Hauschild et al., 2012). Responses to these targeted therapies, however, typically last less than a year and are limited to the subset of melanomas with mutations. After Food and Drug Administration approval, immune checkpoint inhibitors are now the frontline treatment for most patients with metastatic melanoma. Responses to CTLA-4 or PD-1 inhibitors are seen in up to 19 and 40% of melanoma patients, respectively (Larkin et al., 2015). The combination of the CTLA-4 and PD-1 inhibitors results in a higher response rate of 57.6%, with a median progression-free survival of 11.5 mo (Larkin et al., 2015). While these are major advances in cancer care, the current challenge is that not all patients respond, and many develop acquired resistance or must discontinue treatment as a result of adverse immune-associated toxicities. Multiple clinical trials of PD-1/PD-L1 inhibitors have shown that a lack of PD-L1 expression on tumor cells or in the tumor microenvironment (TME), including expression on myeloid cells, is associated with resistance to therapy (Larkin et al., 2015). Additionally, tumors displaying low levels of T cell infiltration, yet a relative abundance of tumor-associated macrophages (TAMs), tend to show reduced responsiveness to PD-1/PD-L1 inhibitors (Tumeh et al., 2014). Therefore, new approaches are sorely needed for patients who do not respond to antiCPD-1C or antiCCTLA-4Cbased regimens or who develop acquired resistance. TAMs, tumor-associated neutrophils (TANs), and myeloid-derived suppressor cells are pivotal in influencing the nature of the TME and can serve as both positive and negative mediators of tumor growth. TAMs can mediate direct antitumor cytotoxicity and the presentation of tumor-associated antigens. However, they can also foster tumor development by secreting growth factors such as insulin-like growth factor 1 (IGF1) and platelet-derived growth factor (PDGF), promoting angiogenesis via vascular endothelial growth factor, and favoring tumor dissemination by producing matrix-degrading enzymes (Pollard, 2004). TAMs are abundant in the melanoma TME and typically comprise 5C30% of immune cells in metastatic deposits (Hussein, 2006). TAMs and myeloid-derived suppressor cells can be associated with resistance to immune checkpoint inhibitors and suppress adaptive immune LUF6000 responses via a variety of mechanisms, including (but not limited to) TGF-, IL-10, ARG1, IDO, PGE2, and PD-L1 (Kryczek et al., 2006; Daz-Valds et al., 2011). There is compelling rationale based on prior studies that drugs aimed to reprogram and stimulate macrophages and dendritic cells (DCs), such as inhibitors of CSF-1, leukocyte immunoglobulin-like receptor subfamily B, CD200, Tyro-Axl-Mer receptors, or, conversely, agonists of CD40 and TLRs, offer promise for tumor suppression (Bhadra et al., 2011; Ugel et al., 2015; Woo et al., 2015). CSF-1 is a critical growth and maturation factor for monocytes, macrophages, and DCs, and deletion of CSF-1 or its receptor (CSF-1R) interrupts the development and maintenance of mononuclear phagocytes, particularly in tissues (Wynn et al., 2013). Indeed, inhibition of CSF-1R via genetic deletion, small molecule inhibitors (CSF-1Ri), or antibody blockade has demonstrated interesting therapeutic effects in multiple tumor models as well as LUF6000 in humans in tenosynovial giant cell tumors (Cassier et al., Rabbit polyclonal to smad7 2012; Ries et al., 2014). Blockade of CSF-1R has reduced TAM numbers in some studies (Mitchem et al., 2013; Xu et al., 2013), but not all (Pyonteck et al., 2013), and therefore, it is generally well-accepted that CSF-1R inhibition rewires TAM functionality to promote tumoricidal functions (Pyonteck et al., 2013). Another promising immunotherapy target on myeloid cells is agonistic CD40 mAbs, which are potent stimulators of DCs, macrophages, and B cells, even independently of T cells (Beatty et al., 2011; Li and Ravetch, 2011). When combined with chemotherapy, CD40 reversed the resistance of pancreatic tumors to PD-1 and CTLA-4 in a T cellCdependent manner (Beatty et al., 2011; Winograd et al., 2015). In the autochthonous mouse model used in this study, our group previously showed that CD40 agonist treatment slowed tumor growth independent of T cells and increased MHCI, MHCII, and CD86 expression by TAMs.

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