Tumor-associated macrophages (TAMs) play critical roles in tumor progression but are also capable of contributing to antitumor immunity. Recent studies have revealed an unprecedented heterogeneity among TAMs in both human cancer and experimental models. Nevertheless, we still understand little about the contribution of different TAM subsets to tumor progression. Here, we demonstrate that CD163-expressing TAMs specifically maintain immune suppression in an experimental model of melanoma that is resistant to anti–PD-1 checkpoint therapy. Specific depletion of the CD163+ macrophages results in a massive infiltration of activated T cells and tumor regression. Importantly, the infiltration of cytotoxic T cells was accompanied by the mobilization of inflammatory monocytes that significantly contributed to tumor regression. Thus, the specific targeting of CD163+ TAMs reeducates the tumor immune microenvironment and promotes both myeloid and T cell–mediated antitumor immunity, illustrating the importance of selective targeting of tumor-associated myeloid cells in a therapeutic context.

Reliable measurement of cellular cytotoxicity is essential for the characterization of immune responses and for the monitoring of antibody treatment efficacy. Until now, the standard Cr-release assay has remained the sole sensitive assay that measures cellular cytotoxicity. Alternative non-radioactive assays have been developed but they do not provide accurate measurement of target cell cytotoxicity. The cost and hazard of handling radioactivity are strong incentives to find alternative solutions to Cr. We took advantage of the recent development of cell-imaging multimode readers to develop a novel non-radioactive and real-time cytotoxic assay that demonstrates good reproducibility and sensitivity. The extent of target-cell cytotoxicity is monitored over time by imaging and quantifying live fluorescent target cells in 96-well plates. We have developed classical natural killer cell assays in the presence or absence of blocking antibodies and antibody-dependent cell-mediated cytotoxicity. We show that in these assays, cell killing occurs within the first 2 hr with half maximum killing reached after 30 min. This technology has numerous applications such as natural killer and T-cell cytotoxicity assays and can be extended to cell survival and apoptosis measurement assays.

This unit describes the monitoring and quantification of cellular cytotoxicity using a non-radioactive and real-time cytotoxic assay. The extent of target-cell lysis is monitored over time by imaging and quantifying live fluorescent target cells using a cell-imaging multimode reader. This assay is performed in a 96 well plate in optimized culture conditions at 37°C in the presence of 5% CO . The basic protocol describes natural killer cell-mediated cytotoxic assay that can be adapted to include antibodies blocking inhibitory NK receptors or triggering antibody-dependent cell-mediated cytotoxicity (ADCC). The assay is also suitable for antigen specific T-cell cytotoxic assays. Until now, the standard chromium 51 ( Cr)-release assay has remained the sole sensitive assay but its major drawbacks include cost and hazard of handling radioactivity. The real-time cytotoxic assay is therefore an effective alternative providing a robust and sensitive assay that accurately monitors lysis of target cells over time. © 2017 by John Wiley & Sons, Inc.

Reliable measurement of cellular cytotoxicity is essential for the characterization of immune responses and for the monitoring of antibody treatment efficacy. Until now, the standard chromium 51Cr-release assay has remained the sole sensitive assay that measures cellular cytotoxicity. Alternative non-radioactive assays have been developed but they do not provide accurate measurement of target cell cytotoxicity. The cost and hazard of handling radioactivity are strong incentive to find alternative solutions to 51Cr. We took advantage of the recent development of cell-imaging multimode readers to develop a novel non-radioactive and real-time cytotoxic assay that demonstrates good reproducibility and sensitivity. The extent of target-cell cytotoxicity is monitored over time by imaging and quantifying live fluorescent target cells in 96-well plates using the cell-imaging multimode reader Cytation™ 5 from Biotek. We have developed classical NK cell assays in the presence or absence of blocking antibodies and antibody-dependent cell-mediated cytotoxicity (ADCC). We show that in these assays, cell killing occurs within the first two hours with a half maximum killing reached after 30 minutes. This technology has numerous applications such as NK and T cell cytotoxicity assays and can be extended to cell survival and apoptosis measurement assays.