Lab. Anne-Marie SCHMITT-VERHULST
Molecular bases for T lymphocyte function
   Current Projects
updated - novembre 30, 2006   
Molecular bases for the plasticity in the differentiation program of CD8 T cells

Naïve CD8 T cells may develop into effectors capable of eliminating virally-infected cells or neoplasms. However, evidence for their incomplete differentiation has been reported, in particular in responses to subdominant viral Ag or those involving low affinity anti-tumor CD8 T cells.
To understand the molecular basis for this plasticity in CD8 T cell differentiation, we have analysed the response of monoclonal alloreactive naïve CD8 T cells to weak or strong TCR agonist alloantigens in vitro and in a corresponding model of graft-vs-host reaction in vivo.
Together with crystallographic studies by the group of B. Malissen, we defined the structural basis for the threshold-controlled responses elicited by each of these peptide/MHC ligands. Combining gene profiling kinetics with analysis of rate limiting signaling pathways, we identified the ERK, STAT5 and NF-KB pathways as sequential contributors to the differentiation and survival of effector T cells involving TCR, IL-2R and members of the TNFR family (4-1BB, OX40, GITR), respectively. This temporal control of gene expression permits cytokine receptor signaling to rescue abortive TCR signaling, such as that induced in response to weak or partial TCR agonists. Based on gene expression profiling, molecular targets whose activation or inactivation may boost or dampen CD8 T effector and memory cells were also identified. Manipulation of these targets may, respectively, increase anti-tumor responses or prevent graft-vs-host reactions.
For a cluster of genes, effects of IL-2 on transcript expression in differentiating CD8 T cells can be mimicked by CA-STAT5 - Verdeil et al J. Immuno 2006  
 
Signaling and dynamics of membrane receptors at T cell immune synapse (IS).

Mechanisms regulating the expression of the TCR/CD3 complex that may control initiation and termination of the T cell response to Ag have also been addressed.
We showed, in particular, that the recruitment of the adaptor cbl to the IS contributes to (i) dampen Protein Tyrosine Kinase activation, and (ii) anchor the TCR/CD3 complex towards a degradation pathway, two mechanisms leading to the down-regulation of T cell responses.
Further analyses of the components required at the IS in the initiation and effector phases of Cytolytic T lymphocyte (CTL) responses will be extended to monitor the integrity of these pathways in pathological situations of CD8 T cell dysfunction as in tumor bearing hosts.

  Dynamic interaction of a CTL (labeled with the Ca2+ indicator Fura-2) with its antigen-expressing target cell
  Claude Boyer & Kossai Zaoui
Immune responses to a cancer/testis tumor Ag expressed on induced melanomas

To establish the status of immune effectors towards transformed cells expressing potential tumor Ag (TA), a conditional tumor model has been developed in the mouse in which deletion of tumor suppressor genes in melanocytes is concomittant with expression of the known natural mouse “cancer/testis” TA P1A (collaboration: B. Van den Eynde (ICP, Bruxelles) and A. Berns (NKI Amsterdam)).


Mouse model of induced melanoma expressing
a known cancer/testis tumor antigen
Huijbers et al 2006 Cancer Res.

This model permits evaluation of the fate of naïve TA-specific T cells at the initiation of tumor development and during tumor progression. With the additional development of a mouse deleted for the endogenous expression of TA P1A, which also shares with human “cancer/testis” TA an ectopic expression in medullary thymic epithelial cells, this model provides all the tools necessary to establish the impact of the endogenous TA tissue distribution on deletional or regulatory mechanisms imposed on the development of anti-TA immune reactivity. This analysis will take advantage of the tools previously developed in the laboratory to trace P1A-reactive CD8 T cells and our experience with the analysis of CD8 T cell functional programs.
The induced melanoma will also provide a model to study the interactions between a developing tumor and its microenvironment. In particular, the patterns of tumor progression observed in these mice will be correlated with gene expression profiles within tumors and tumor infiltrates. The impact of tumor development on components of innate and adaptive immunity will be determined. Tumor-induced suppressor cell populations that may impede anti-tumor responses will be identified and attempts to remove them or to induce resistance to their action will be evaluated.