Name: studying the effects of tumor-secreted paracrine ligands on macrophage activation using co-culture with permeable membrane supports
Uploaded: 2019-11-28T13:30:00
Description: Watch this Scientific Journal Video about Studying the Effects of Tumor-Secreted Paracrine Ligands on Macrophage Activation using Co-Culture with Permeable Membrane Supports at JoVE.com

Eric Ubil was funded, in part, by the American Cancer Society Postdoctoral Fellowship (128770-PF-15-216-01-LIB). The work was supported by a grant from the NIH (R01-CA205398) and a Breast Cancer Research Foundation award (BCRF-18-041) to HSE.

All procedures related to the harvest and use of murine peritoneal macrophages were conducted at the University of North Carolina at Chapel Hill (UNC) and were approved by the UNC Institutional Animal Care and Use Committee (IACUC).
1. Macrophage culture
NOTE: This procedure can utilize primary peritoneal macrophages (described in detail below), bone marrow-derived macrophages, or macrophage cell lines such as J774 (ATCC) or RAW264 (ATCC).
<ol>
	<li>Harvest perito...

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The co-culture assay presented here is a modification of previously established assays that allows for the study of tumor-secreted factors on immune cell activation. While cell-cell contact is known to induce changes in immune activity, the ability of tumor-secreted ligands to modulate immune activation is less well understood. We describe a method which, unlike direct co-culture, can be used to interrogate how tumor-derived secreted factors impact immune cell activation without the confounding nature of contact-mediated...

Recent studies have focused on the ability of cancer cells to avoid detection by immune cells, suppress local immune activation, or to produce a tolerogenic tumor-permissive milieu in the tumor microenvironment. Two broad classes of tumor and immune cell interactions have been described that facilitate these effects: contact-mediated interactions or tumor-secreted ligands. One of the most well-studied and clinically tractable mechanisms of contact-mediated immune inhibition utilized by tumors is the expression of PD-L1, which interacts with PD-1 on T cells to inhibit their activation and function1,2. In response to interferon-gamma (IFN&#947;), which is expressed by a number of activated immune cells, tumor cells can increase expression of PD-L1 to induce exhaustion of PD-1&#8211;expressing activated T cells, thereby preventing them from effectively eradicating tumor cells3. The use of antibodies to block the interaction between PD-L1 and PD-1 is currently used to treat multiple cancer types in humans4. In light of this clinical success and others, the identification and targeting of tumor-derived immunosuppressive mechanisms has received increasing attention.
Beyond suppression of adaptive immunity, tumors are also known to secrete factors that suppress the pro-inflammatory responses of innate immune cells. Tumor-derived or tumor-induced secretions, including IL-6, IL-10, VEGF, IL-23, and colony stimulating factor (CSF-1), have been shown to inhibit antitumor responses of natural killer (NK) cells, granulocytes, and dendritic cells in the tumor microenvironment5,6,7. Tumor cells can also secrete factors that skew the recruitment and differentiation of myeloid-derived cells in the tumor microenvironment to promote suppression of T cell activation8,9.
One type of innate immune cell that has a profound effect on tumor progression is the macrophage. For many years, the presence of tumor-associated macrophages (TAMs) has been used as a negative prognostic of patient survival10. The concept that immunosuppressive TAMs dampen immune cell-mediated clearance of tumors was introduced more than 40 years ago11. More recently, it has been shown that the macrophage pro-inflammatory response can be downregulated while a pro-tumor phenotype can be induced in the tumor microenvironment. These immunosuppressive macrophages can contribute to a tolerogenic response, driving tumor progression and resistance to chemo- and immunotherapy12. Given that macrophages are often one of the most abundant leukocytes with the tumor, restoration of their tumor-specific immune activity represents a potential target for anticancer therapeutics13.
While contact-mediated interactions between tumor cells and macrophages can be modeled through direct coculture, the use of permeable membrane supports can elucidate which tumor-secreted factors are immunomodulatory without the potentially confounding influence of tumor-immune cell-cell contact. Using somewhat similar methods, others have demonstrated the potential of identifying secreted factors in microglia/neuronal interactions14 as well as tumor cells with mesothelial cells15. We have also successfully used this co-culture technique to characterize the role of a tumor-secreted protein, Pros1, as a suppressor of pro-inflammatory gene expression after the stimulation of peritoneal macrophages with LPS and interferon-gamma16. Here we describe a straightforward methodology that can be used to interrogate how tumor-secreted factors can affect macrophage activation.

<table border="0" cellpadding="0" cellspacing="0" style="width:1419px;" width="1418">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:444px;">B16-F10</td>
			<td style="width:244px;">ATCC</td>
			<td style="width:344px;">ATCC CRL-6475</td>
			<td style="width:387px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">cDNA synthesis kit</td>
			<td>Promega</td>
			<td>A3500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DMEM/F12 media</td>
			<td>ThermoFisher Scientific- Gibco</td>
			<td>11320033</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fetal Bovine Serum</td>
			<td>Millipore</td>
			<td>TMS-013-B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">J774A.1</td>
			<td>ATCC</td>
			<td>ATCC TIB-67</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lipopolysaccharides from Escherichia coli O111:B4</td>
			<td>Sigma-Aldrich</td>
			<td>L5293-2ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Murine M-CSF</td>
			<td>Prospec</td>
			<td>CYT-439</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td>ThermoFisher Scientific- Gibco</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pros1 ELISA</td>
			<td>MyBioSource</td>
			<td>MBS2886720</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RAW264.7</td>
			<td>ATCC</td>
			<td>ATCC TIB-71</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Recombinant Mouse IFN&#947;</td>
			<td>BioLegend</td>
			<td>575302</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sensimix SYBR Low-ROX kit</td>
			<td>Bioline</td>
			<td>QT625-05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transwell permeable supports</td>
			<td>Fisher Scientific</td>
			<td>07-200-170</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trypsin-EDTA</td>
			<td>ThermoFisher Scientific- Gibco</td>
			<td>25200056</td>
			<td></td>
		</tr>
	</tbody>
</table>

studying the effects of tumor-secreted paracrine ligands on macrophage activation using co-culture with permeable membrane supports

Tumor-derived paracrine signaling is an overlooked component of local immunosuppression and can lead to a permissive environment for continued cancer growth and metastasis. Paracrine signals can involve cell-cell contact between different cell types, such as PD-L1 expressed on the surface of tumors interacting directly with PD-1 on the surface of T cells, or the secretion of ligands by a tumor cell to affect an immune cell. Here we describe a co-culture method to interrogate the effects of tumor-secreted ligands on immune cell (macrophage) activation. This straightforward procedure utilizes commercially available 0.4 &#181;m polycarbonate membrane permeable supports and standard tissue culture plates. In the process described, macrophages are cultured in the upper chamber and tumor cells in the lower chamber. The presence of the 0.4 &#181;m barrier allows for the study of intercellular signaling without the confounding variable of physical contact, because the two cell types share the same medium and exposure to paracrine ligands. This approach can be combined with others, such as genetic alterations of the macrophage (e.g., isolation from genetic knock-out mice) or tumor (e.g., CRISPR-mediated alterations) to study the role of specific secreted factors and receptors. The approach also lends itself to standard molecular biological analyses such as quantitative reverse transcription polymerase chain reaction (qRT-PCR) or Western blot analysis, without the need for flow sorting to separate the two cell populations. Enzyme-linked immunosorbent assays (ELISAs) can similarly be utilized to measure secreted ligands to better understand the dynamic interaction of cell signaling in the multiple cell type context. Duration of co-culture can also be varied for the study of temporally regulated events. This co-culture method is a robust tool that facilitates the study of tumor-secreted signals in the immune context.

To determine the effect of tumor-secreted ligands on macrophage polarization, the procedure described was utilized. Peritoneal macrophages cultured in the absence of tumor cells were used as negative (untreated = far left) and positive (IFN&#947; and LPS stimulated = 2nd from left) controls (Figure 2A). Alternatively, peritoneal macrophages were co-cultured with B16F10 melanoma tumor cells (ATCC) (Figure 1A). Immediately after plating, cells were eith...

Watch this Scientific Journal Video about Studying the Effects of Tumor-Secreted Paracrine Ligands on Macrophage Activation using Co-Culture with Permeable Membrane Supports at JoVE.com

Studying the Effects of Tumor-Secreted Paracrine Ligands on Macrophage Activation using Co-Culture with Permeable Membrane Supports

Here, we present a method using permeable membrane supports to facilitate the study of non-contact paracrine signaling used by tumor cells to suppress the immune response. The system is amenable to studying the role of tumor-secreted factors in dampening macrophage activation.

Tumor-derived paracrine signaling is an overlooked component of local immunosuppression and can lead to a permissive environment for continued cancer ...

This Transwell co-culture method is used to study paracrine signaling used by tumor cells to suppress the immune response. This method can be used to discover novel secreted ligands, as well as the mechanistic underpinnings of their immune suppressive effects. We have previously used this method to show how tumor-secreted factors can dampen macrophage pro-inflammatory gene transcription.We believe this tool has wide-ranging implications in the study of tumor-derived immune suppression. One of the main advantages of this technique is that it can be used to study paracrine signaling between tumor cells and immune cells without the potentially confounding variable of cell-to-cell contact. This platform is also amenable to a variety of molecular biological techniques for downstream analysis.After harvesting peritoneal macrophages, plate them directly into the upper chambers of a 0.4 micrometer polyester membrane insert co-culture six-well plate. Then added supplemented DMEM to the well such that the top chamber contains one milliliter and the bottom chamber contains 1.5 milliliters. Incubate for three days at 37 degrees Celsius with 5%carbon dioxide.First, culture commercially available tumor cells in their respective medium, following ATCC recommended tissue culture methods. Next, wash the adherent tumor cells once with PBS. Add 0.05%trypsin in EDTA and incubate at 37 degrees Celsius until the cells detach.Then re-suspend the cells in media containing FBS. Use a hemocytometer or cell counter to quantitate the total number of cells and centrifuge at 220 times G for five minutes to pellet. During centrifugation, aspirate the medium from the upper and lower chambers of the macrophage containing permeable membrane support plates and replace with fresh medium.For the lower chambers where tumor cells will be plated, fill with one milliliter of medium instead of 1.5 milliliters to leave sufficient volume for cell addition. When the centrifugation is complete, aspirate the medium from the pelleted tumor cells and re-suspend the cells in supplemented DMEM at a concentration of 300, 000 cells per milliliter. Add 0.5 milliliters of this cell suspension to the lower chamber of the desired wells.To induce macrophage pro-inflammatory gene expression, treat singly or co-cultured macrophages by adding interferon gamma at a concentration of 100 nanograms per milliliter and LPS at a concentration of 50 nanograms per milliliter. Vary the duration of treatment times in culture as needed. Macrophage activation occurs within two hours, and some tumor-mediated suppression occurs by eight hours.Co-culture for 24 hours yields robust and consistent tumor-derived suppression. As a negative control, culture macrophages singly and leave untreated. As a positive control, treat singly-cultured macrophages with interferon gamma and LPS at the same concentrations used for the samples.After the desired incubation time has elapsed, isolate the cell lysate or condition culture medium as desired depending on testing needs. To isolate the cell lysate for quantitative polymerase chain reaction analysis, aspirate the medium from both chambers of the well and wash once with two milliliters of PBS. Apply RNA lysis buffer to the top chamber containing the macrophages.After this, gently scrape the membrane to release the cell lysate and transfer it to a collection tube for further processing according to the RNA isolation kit manufacturer's protocol. The co-culture method described here involves the culture of macrophages and tumor cells without physical contact. Peritoneal macrophages cultured in the absence of tumor cells are used as negative and positive controls.Peritoneal macrophages co-cultured in the presence of B16F10 tumor cells but without activating stimuli do not increase expression of pro-inflammatory associated genes. This implies that tumor-secreted ligands are either not sufficient to induce pro-inflammatory gene expression by themselves, or if there is immune activation by tumor secretions, paracrine ligands are sufficient to suppress it to its native levels. This co-culture method illustrates that when macrophages polarized by interferon gamma and LPS are cultured in the presence of tumor cells, suppression of inflammation-associated gene expression was reduced by as much as 60%A comparable level of macrophage pro-inflammatory gene suppression is observed when the murine macrophage cell line J774 is substituted for peritoneal macrophages.Previous work has identified protein S as a tumor-secreted factor that can inhibit macrophage activation, so the permeable membrane support co-culture model is used in conjunction with a lysA to assay the concentration of protein S in conditioned media after 24 hours. In conditioned media from interferon gamma and LPS-treated B16F10 melanoma cells, protein S is expressed in a concentration of approximately 475 nanograms per milliliter. Peritoneal macrophages treated in the same conditions expressed protein S at approximately 61 nanograms per milliliter.Interestingly, when co-cultured, the concentration of protein S in the interferon gamma and the LPS-treated well was approximately 86 nanograms per milliliter. This suggests that either macrophages ingest tumor-secreted protein S or that the amount of protein S secreted by B16F10 cells is substantially decreased when in the presence of macrophages. These results highlight profound changes of macrophage activation and paracrine signaling when macrophages are co-cultured with tumor cells.The Transwell co-culture method can answer a variety of questions pertaining to paracrine signaling. Western blot analysis could be conducted to determine how tumor-secreted proteins alter various signaling pathways in macrophages.

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