RIKEN IMS AnnualReport 2020

11/98

AB5+10,000 cells per 25 l drop of culture media on a lidGroup 2 innate lymphoid cells (ILC2s) are abundant 7 days incubation with change of medium every 3rdday Transfer to an appropriate plate for experiments of interest5 ml of PBS in a culture platein non-lymphoid tissues, including skin, where they mediate allergic reactions and protect against infection by parasitic worms (helminths). When epithelial cells contact a helminth, they release interleukin 33 (IL-33), which trig-gers ILC2s to mass-produce IL-5 and promote inflamma-tion via eosinophils to prevent infection.ILC2s use similar tactics to suppress the growth of epi-thelial solid tumors. However, in solid tumors, ILC2s com-prise only a small proportion of the immune cells present. This situation suggests that cancer cells evade surveillance and attenuation by ILC2s.To understand how cancer cells are able to slip past ILC2s, Marek Wagner, a cancer biologist and a member of Koyasu’s research team, examined the relationship between ILC2s and the environment of melanoma tumors. First, he confirmed that injecting mice with IL-33 causes eosino-phils to infiltrate melanomas and thus suppresses their growth. Wagner also realized that the more malignant the cancer, the lower the ILC2 levels in the tissues around the melanomas.Next, Koyasu and Wagner devised an ingenious system (Figure, A) to investigate how cancer cells suppress ILC2 function and survival. To address this question, the re-searchers considered two features of carbohydrate metabo-lism in cancer cells: high levels of glucose transporters and lactate dehydrogenase (LDHA) during proliferation, and the metabolism of glucose into lactate, which causes lactate to accumulate around the cancer and acidify its microenvi-ronment.To test whether lactate accumulation reduces ILC2 activity in vivo, the team used RNA interference and gen-erated malignant cells expressing low levels of LDHA. As expected, ILC2s and eosinophils infiltrated cancer tissues and suppressed the growth of these low-LDHA-expressing cells more than typical cancer cells (Figure, B).Finally, to corroborate their findings in humans, the team analyzed gene expression data from melanoma pa-tients. As in mice, both IL-33 and eosinophil levels were elevated in humans with malignant melanomas; patient survival rates were high for cases with high ILC2 activity; and ILC2 and eosinophil levels were inversely related to lactate production. However, when the researchers then looked at lung cancers or pancreatic cancers, survival rates were unrelated to IL-33 and eosinophil levels.Overall, the team’s results suggest that the growth of melanoma tumors depends on the balance between the mutually suppressive activities of ILC2s and cancer cells. They also underscore the view that ILC2 function depends on numerous factors, including the tissue environment and type of cancer. Why? As Dr. Koyasu puts it, “ILCs are gen-erally tissue-resident cells. It may be that they change their character depending on the tools a tissue has to maintain its structure and repel invaders.”Figure: A novel spheroid culture revealed how certain cancer cells suppress ILC2sA. The underside of the lid of a petri dish was dotted with droplets of culture medium, onto which melanoma cells were plated. The lid was then placed on a culture plate containing phosphate-buffered saline (PBS) to prevent the droplets from drying out. The photo represents mela-noma spheroids on day 7.B. Activation of ILC2s by interleukin 33 (IL-33) induces the release of cytokines such as interleukin 5 (IL-5), which in turn induces eosinophils to release cytotoxic proteins such as major basic protein (MBP). Co-culture experiments with ILC2 revealed that certain cancer cells, such as those in malignant melanomas, counter this assault via the IL-33-ILC2–eosinophil axis by producing lactic acid, which suppresses ILC2 function. Abbreviation: LDHA, lactic acid dehydrogenase.Original paper and reference:Wagner M, Ealey KN, Tetsu H, Kiniwa T, Motomura Y, Moro K, Koyasu S. Tumour-derived lactic acid contributes to the paucity of intratu-moural ILC2s. Cell Rep 30, 2743-2757 (2020)https://doi.org/10.1016/j.celrep.2020.01.103Wagner M, Koyasu S. A 3D Skin melanoma spheroid-based model to assess tumor-immune cell interactions. Bio Protoc 10, e3839 (2020)https://doi.org/10.21769/BioProtoc.3839Shigeo KoyasuLearning how cancer cells evade group 2 innate lymphoid cells