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c-Kit-dependent Tissue Resident Macrophage Progenitors drive cancer progression

Paulina Pathria
Appointment Period: 2018-2019, Grant Year: [33]

Paulina Pathria

Macrophages can switch between pro- and anti-inflammatory states to defend and repair damaged tissues. Pro-inflammatory myeloid cells stimulate cytotoxic T cells, while anti-inflammatory myeloid cells express anti-inflammatory cytokines that limit anti-tumor T cell responses and consequently promote cancer progression (1). The Varner lab found that a single myeloid cell kinase, PI(3)Kinase gamma controls this switch between immune stimulation and suppression during inflammation and cancer (2). Inhibition of PI(3)Kinase gamma repolarizes macrophages and activates cytotoxic CD8 T cells, leading to significant reduction or complete regression of tumor growth of implanted HPV+ and HPV- head and neck squamous cell carcinoma (HNSCC), lung carcinoma (LLC) and breast carcinoma (PyMT) tumors (2), and inhibition of spontaneous and orthotopic pancreatic ductal adenocarcinoma (PDAC) as well as PDAC metastasis (3).

It has been long established that macrophages originate from hematopoietic stem cells in the bone marrow that gives rise to a common myeloid progenitor, and subsequently, to monocytes and /macrophages; bone marrow-derived monocytes traffick to tumors, where they become bone marrow derived macrophages (BMDMs) that contribute to tumor immune suppression and tumor progression (4). In recent years, however, a tissue resident macrophage population (TRM) was discovered (5). These Cx3CR1+ cells originate during embryonic development either from erythro-myeloid progenitors in the yolk sac (microglia) or the fetal liver (peripheral tissues) and colonize the embryo at the onset of organogenesis (5-7). This population of macrophages self-maintain in adult tissues throughout life, independently of bone marrow derived hematopoietic stem cells (6-8).

To determine the role of myeloid cell trafficking pathways in tumor progression, I am evaluating the mechanisms regulating myeloid cell accumulation in tumors using mouse models of lung, breast, and HNSCC by comparing myeloid cell populations in WT, PI3Kg-/-, Cx3CR1GFP/GFP and CCR2RFP/RFP mice. I have determined that two macrophage populations accumulate in all tumors: Bone Marrow Derived Macrophages (BMDM) and Tissue Resident Macrophages (TRM). My studies show that while BMDM accumulate by trafficking from BM, TRMs do not. To identify novel biomarkers and differences in the expression profiles of BMDMs and TRMs, I performed RNA sequencing on both populations of macrophages sorted from murine tumors via flow cytometry. These analyses revealed that TRMs are highly proliferative and immune suppressive whereas BMDM are less proliferative and immune suppressive but more pro-angiogenic. Based on the identified expression signatures, I am working with bioinformatics experts in the Moores Cancer Center to identify the presence and significance of TRM and BMDM gene expression signatures in human TCGA databases.

To determine how TRM accumulate in tumors, I have examined whether these cells accumulate by proliferation from progenitor cells in tissues. I sorted TRM from tumors and examining properties and mechanisms of proliferation in vitro and in vivo. To investigate if TRMs and/or BMDMs could have progenitor properties and form colonies in vitro, I plated sorted TAMs in stem cell media containing methylcellulose, SCF, IL-3, IL-6, EPO, and serum, and observed colony forming potential and expression of biomarkers of myeloid progenitors on outgrowing colonies. To identify the factors driving the development of tumor-associated macrophage (TAM)-derived progenitor colonies, I am testing the roles of individual cytokines present in stem cell medium (SCF, IL-3, IL-6) or present in tumor cell conditioned medium in promoting development of progenitor-like colonies. Importantly, the receptor for SCF, c-Kit, regulates myeloid progenitor development (9); 1-3% of TRMs and BMDMs are c-Kit+, and the c-Kit ligand SCF (Stem Cell Factor) is expressed by most tumor cells, including HNSCC. Thus, I am evaluating the dependence of macrophage colony formation on c-Kit and SCF function. To examine the role of macrophage progenitors in vivo, I will perform lineage-tracing studies and test tumor growth in mice expressing mutant c-Kit and in mice treated with c-Kit inhibitors. Together, these studies will evaluate novel mechanisms regulating immune suppressive macrophage accumulation and function in the tumor microenvironment.

References:

  1. Sica A., Mantovani A. Macrophage plasticity and polarization: in vivo veritas. J. Clin. Invest. 122, 787-795 (2012).
  2. Kaneda M.M., Messer K.M., Ralainirina N., et al. PI3Kg is a molecular switch that controls immune suppression. Nature 539, 437-442 (2016).
  3. Kaneda M.M., Capello P., Nguyen A.V., et al. Macrophage PI3Kg drives pancreatic ductal adenocarcinoma progression. Cancer Discov. 6, 870-885 (2016).
  4. Schmid M.C., Avraamides C.J., Dippold H.C., et al. Receptor tyrosine kinases and TLR/IL1Rs unexpectedly activate myeloid cell PI3Kg, a single convergent point promoting tumor inflammation and progression. Cancer Cell 19, 715-727 (2011).
  5. Schulz C.,  Gomez Perdogiero E., Chorro L., et al. A lineage of myeloid cells independent of Myb and hematopoietic stem cells. Science 336, 86-90 (2012).
  6. Gomez Perdogiero E., Klappenroth K., Schulz C., et al. Tissue-Resident macrophages originate from yolk sac-derived erythro-myeloid progenitors. Nature 518, 547-551 (2015).
  7. Mass E., Ballesteros I., Farlik M., Specification of tissue-resident macrophages during organogenesis. Science 353, aaf4238 (2016).
  8. Zhu Y., Herndon J. M., Soika D.K., et al. Tissue-resident macrophages in pancreatic ductal adenocarcinoma originate from embryonic hematopoiesis and promote tumor progression. Immunity 47, 323-338 (2017).
  9. Masson K. and Roennstrand L. Oncogenic signaling from the hematopoietic growth factors c-kit and Flt3. Cell Signal. 21, 1717-1726 (2009).

PUBLICATIONS (resulting from this training):  

Trainee recently appointed to grant: publications are still in progress.