Developmental Immunology Group

Hugh Robson (Rob) MacDonald received a Ph.D. from the University of Toronto in 1972, working on cytotoxic T cells and continued these studies as a postdoctoral fellow with Jean-Charles Cerottini in Lausanne, Switzerland. After a brief stay in London, Canada, he returned to Switzerland in 1977 and joined the Lausanne Branch of the Ludwig Institute for Cancer Research, where he became Director in 2006. Since 2011 he is Interim Director of the Ludwig Center for Cancer Research of the University of Lausanne. Over the years, Dr MacDonald has contributed to many areas of T cell biology including development, lineage commitment, repertoire selection, tolerance and memory. At present, his research program is mainly focused on T and NKT cell development.

The main focus of our research is to study the development of conventional and unconventional T cells in the thymus. All T cells are derived from hematopoietic precursors that enter the thymus where they commit to the T cell lineage as a result of Notch signaling. Commited precursors then undergo T cell receptor rearrangement (TCR) and sequential cell fate specification events that give rise to the TCRαβ and TCRγδ lineages and (among TCRαβ cells) the MHC-restricted CD4 and CD8 conventional T cell lineages. In parallel unconventional subsets of TCRαβ cells such as  CDld-restricted NKT cells and CD8αα-expressing intestinal intraepithelial lymphocytes (IEL) develop from CD4+ CD8+ thymocyte precursors by an agonist selection process. Our laboratory investigates many aspects of this complex developmental program, largely relying on genetic approaches.

Notch signaling in T cell development

During the past decade our group has been studying the role of Notch signaling during T cell development in collaboration with Freddy Radtke (EPFL Lausanne). This collaboration has led to the identification of a critical requirement for interaction between Notch-1 on lymphoid precursors and Delta-like 4 (DL4) on thymic cortical epithelial cells (cTEC) in order to specify T cell fate in the thymus. To further define the mechanism of T cell fate specification we have recently generated novel monoclonal antibodies directed against Notch receptors and ligands (in collaboration with Michel Pierres, CIML, Marseille). Using these reagents we have established that Notch-1 is already expressed on bone marrow precursors of T lymphocytes and remains highly expressed during early (CD4- CD8-) stages of intrathymic T cell development. Notch-1 expression decreases sharply at the CD4+ CD8+ thymocyte stage and remains at low levels on mature CD4+ and CD8+ T cells. Staining of thymus sections with Notch-1 and Keratin 5 (a marker for the thymic medulla) reveals that Notch-1 high cells are restricted to the thymic cortex and highly enriched in the subcapsular zone (see Figure). These data confirm and extend other studies indicating that Notch signaling is largerly confined to early T cell progenitors in the outer thymic cortex.

Expression of Notch-1 (red) and Keratin 5 (green) in the adult mouse thymus.
Notch-1+ cells are concentrated in the subcapsular zone of the outer thymic cortex.

In related studies our novel monoclonal antibody to the Notch ligand DL4 revealed specific staining in cTEC. Somewhat unexpectedly we found that DL4 was highly expressed in the embryonic thymus but weakly expressed in the adult. Analysis and reconstitution of mutant mice with an early block in T cell development further revealed that lymphostromal interactions control DL4 expression on cTEC. These data suggest a model in which "crosstalk" between thymocytes and cTEC can quantitatively regulate the rate of Notch-1-dependent thymopoiesis by controlling DL4 expression levels. This model is currently being directly tested in transgenic models where DL4 expression on cTEC can be regulated in vivo.

Role of c-Myc in the development of NKT cells and CD8αα IEL

In addition to conventional T cells our group has a longstanding interest in the development of natural killer T (NKT) cells. NKT cells are a subset of regulatory T cells that recognize glycolipid antigens associated with non-polymorphic CD1d molecules via a semi-invariant TCR. In contrast to conventional T cells the developmental pathway of NKT cells involves agonist selection of CD4+ CD8+ thymic precursor cells interacting with self CD1d: glycolipid complexes via their semi-invariant TCR. Using mice that have specific inactivation of the transcription factor c-Myc in CD4+ CD8+ thymocytes and their progeny we have discovered that c-Myc plays a selective role in NKT cell development without affecting the development of conventional T cells. In the absence of c-Myc NKT cell precursors are blocked at an immature stage in a cell autonomous fashion. Thus c-Myc plays a critical role early in NKT cell development, perhaps by inhibiting proliferation of precursor cells responding to agonist signals.
The murine gut epithelium contains a large population of thymus-derived intraepithelial lymphocytes (IELs), including both conventional CD4+ and CD8αβ+ T cells (expressing TCRαβ) and unconventional CD8αα+ T cells (expressing either TCRαβ or TCRγδ). Whereas conventional IELs are widely accepted to arise from recirculation of activated CD4+ and CD8αβ+ T cells from the secondary lymphoid organs to the gut, the origin and developmental pathway of unconventional CD8αα IELs remain controversial. We found that CD4-Cre-mediated inactivation of c-Myc, selectively impairs the development of CD8αα TCRαβ IELs. In the absence of c-Myc, CD4– CD8– TCRαβ+ thymic precursors of CD8αα TCRαβ IELs are present but fail to develop on adoptive transfer in immunoincompetent hosts. Residual c-Myc–deficient CD8αα TCRαβ IEL display reduced proliferation and increased apoptosis, which correlate with significantly decreased expression of interleukin-15 receptor subunits and lower levels of the antiapoptotic protein Bcl-2. Transgenic overexpression of human BCL-2 resulted in a pronounced rescue of CD8αα TCRαβ IEL in c-Myc–deficient mice. Taken together, our data support a model in which c-Myc controls the development of CD8αα TCRαβ IELs from thymic precursors by regulating interleukin-15 receptor expression and consequently Bcl-2–dependent survival.

Recent publications (2006 - 2010)

Isabel Ferrero, Research Associate

Emma Fiorini, Research Associate

Vijay Kumar Chennupati, Postdoctoral Fellow

Catherine Fumey, Technical Assistant

Anne Wilson, Senior Lecturer and Coordinator of Flow Cytometry Facility