Gain and loss of function approaches to study immune cell development and function : CTCF - a key player in dendritic cell biology?

Abstract

Dendritic cells (DCs) are the most potent antigen-presenting cells and as key players in the control of adaptive immune responses, they are involved in the balance of immunity versus tolerance. A better understanding of the molecular mechanisms underlying DC differentiation and maturation may therefore also help to develop strategies for the treatment of autoimmune diseases, cancer or chronic infections.<br />To identify genes that regulate the maturation of human monocyte-derived DCs, expression profiling approaches using 18k human EST DNA arrays were performed. To validate the functional relevance of identified differentially expressed genes, an in vivo murine screening model was developed by adapting existing protocols for retroviral-mediated gene transduction of hematopoietic stem cells followed by bone marrow (BM) transplantation.<br />Gain of function approaches with more than 15 candidate genes led to the identification of the zinc finger transcription factor CTCF as negative regulator of DC development and function. CTCF expression is down-regulated during DC differentiation. Forced expression of CTCF caused increased apoptosis and reduced proliferation of differentiating BM-derived DCs, resulting in dramatically reduced numbers of immature DCs. Those BM-DCs that developed displayed also defects upon LPS-induced maturation, indicated by impaired up-regulation of MHC class II and of costimulatory molecules, and therefore CTCF-transduced DCs had a reduced T cell stimulatory capacity.<br />The results obtained during my PhD thesis give new perspectives in the molecular mechanisms underlying DC differentiation and maturation and suggest that CTCF acts as a key player involved in the generation of DC subsets.