Phd in IINNOVATION IN IMMUNO-MEDIATED AND HEMATOLOGICAL DISORDERS

Thesis title: Analysis of the mechanisms regulating human ILC2 activation and function

ILC2 represent one of the major lung-resident ILC populations under physiologic conditions in both human and mouse. In recent years, the number of studies investigating the role of ILC2s in lung cancer has increased. However, much of the knowledge we have on the role of ILC2 in pulmonary tumours comes from studies performed on mice. The few studies on ILC2 in the human setting are usually only descriptive and lack investigation of the molecular mechanisms. Therefore, the aim of my thesis was to understand how ILC2 response is regulated in the tumor microenvironment (TME) in the human setting. Initially, we analysed ex vivo malignant pleural effusions (mPE) from patients with lung tumors. mPE reproduces the composition of the TME and an important cellular component of this is represented by macrophages. We demonstrated that ILC2 were present in lung TME and also that they expressed PD1 and CTLA4. To investigate the molecular mechanisms that control ILC2 immune checkpoint expression and function in TME, we focused on ILC2-macrophages crosstalk and performed co-culture experiments in vitro between activated primary ILC2 and monocyte-derived-macrophages (MoM). We demonstrated that macrophages, by limiting ILC2 activation during co-culture, prevent ILC2 exhaustion, thus rendering ILC2 more responsive to tissue-derived signals. Moreover, macrophages differentially modulate the expression of PD1 and CTLA4 on ILC2 by distinct molecular mechanisms. In particular the binding between CTLA4 and its ligands, CD80 and CD86, is required to induce CTLA4 upregulation on ILC2. Our findings extend knowledge on the expression of immune checkpoints on human ILC2 in lung TME and on the regulation of ILC2 immune checkpoints, in particular CTLA4. Understanding the molecular mechanisms that regulate ILC2 immune response in the TME may help to better understand their contribution to antitumor immunity and improve the response to therapy.