Grant Awarded in 2008


Accumulation of Misguided Lymphocytes and Dendritic Cells:
A New Model for LCH


Principal Investigator and Co-Investigator
Carl E. Allen MD, PhD (PI) and Kenneth L. McClain MD, PhD
Texas Children’s Hospital/Baylor College of Medicine - Houston, Texas USA

Date of Award
September 2008

Amount of Award
$25,000
This study was also supported by the Histiocytosis Association of Canada.

Layperson Summary
Background:
Langerhans Cell Histiocytosis (LCH) is a potentially fatal disease characterized by invasive tumors infiltrated with pathologic dendritic cells and activated T-cells.  Normal Langerhans cells are located in the skin.  The job of these cells is to recognize signals from the environment and to activate the immune system to respond to “danger” signals.  According to the current model of LCH, Langerhans cells in the skin become inappropriately activated and proliferate in LCH lesions.

Specific Aims and Hypothesis:
Identifying the cause of LCH is an essential step to developing a rational cure for patients.  Due to lack of reliable animal and in vitro models, we have developed a strategy to harvest a tremendous amount of data from a small number of cells from rare LCH biopsy samples using RNA amplification and “gene chip” techniques.  We are now able to ask fundamental questions regarding cell-specific gene expression, lymphocyte activation and trafficking to LCH lesions, clonality of CD207+ cells and CD3 cells, and identification of the cell of origin of LCH.  The central hypothesis of this study is that LCH arises due to accumulation of blood-derived dendritic cells and activated T-cells rather than from malignant transformation of epidermal Langerhans cells.

Potential Impact:
The ultimate goal of these experiments is to identify genes, proteins, and pathways that can be used to diagnose and cure patients with LCH.  These experiments may also provide insight into dendritic cell biology and tumor immunology.

Twelve Month Report
Background:  
Langerhans Cell Histiocytosis (LCH) is a potentially fatal disease characterized by invasive tumors infiltrated with pathologic dendritic cells and activated T-cells. Normal Langerhans cells are located in the skin. The job of these cells is to recognize signals from the environment and to activate the immune system to respond to “danger” signals. According to the current model of LCH, Langerhans cells in the skin become inappropriately activated and proliferate in LCH lesions.

Specific Aims and Hypothesis:
Identifying the cause of LCH is an essential step to developing a rational cure for patients. Due to lack of reliable animal and in vitro models, we have developed a strategy to harvest a tremendous amount of data from a small number of cells from rare LCH biopsy samples using RNA amplification and “gene chip” techniques. We are now able to ask fundamental questions regarding cell-specific gene expression, lymphocyte activation and trafficking to LCH lesions, clonality of CD207+ cells and CD3 cells, and identification of the cell of origin of LCH. The central hypothesis of this study is that LCH arises due to accumulation of blood-derived dendritic cells and activated T-cells rather than from malignant transformation of epidermal Langerhans cells.

1. Gene Expression Studies: The major series of experiments in this study was to evaluate global gene expression in LCH lesions. Many genes not previously associated with LCH were identified as significantly expressed in the pathologic CD207+ LCH cells. Some of these genes have functions in recruiting other immune cells to sites of inflammation. LCH is thought to arise from a class of cells called dendritic cells. The current model of LCH suggests that it occurs due to dysregulation or transformation of the mature skin Langerhans cell. A major finding from this study is that the LCH CD207+ cells express genes typical of immature dendritic cells. This leads us to propose a new model of LCH in which lesions arise from accumulation of these immature dendritic cells that come from peripheral blood, not skin. This model will be tested further in the 2009 HAA Grant.

2. LCH Protein Studies: We also set out to look for LCH-specific biomarkers in peripheral blood. Based on results from the gene expression studies, we first evaluated expression of osteopontin, a protein involved in recruiting white blood cells to sites of inflammation. We found that plasma levels of osteopontin in patients with active LCH were very high. In addition to testing osteopontin, we also developed a reliable method to simultaneously test hundreds of plasma proteins that may also play a role in LCH pathogenesis. Osteopontin and other LCH-associated proteins may be useful in diagnosis, prognosis, and as therapeutic targets. We are further testing LCH-associated plasma proteins in a 2009 HAA Grant.

3. Clonality in LCH: Landmark papers on LCH in the 1990s suggested that LCH arises from a “clonal” population, meaning the pathologic CD207+ cells arise from a single parent cell. This type of growth is characteristic of cancer, but can also occur as a result of immune dysregulation. The purpose of this aim was to re-evaluate clonality with modern techniques in order to reproduce this important observation. We still need to validate the results from this project, but our early data supports the original findings that LCH may be a “clonal” disease

4. Cell of Origin of LCH: As discussed above, our gene expression studies suggest LCH may not arise from epidermal Langerhans cells. In this Aim, we proposed to evaluate gene expression in a new population of CD207+ cells in the skin that was recently described by our collaborators, Drs. Merad, Collin and Ginhoux. Our pilot studies show that the dermal CD207+ cells are not very similar to the LCH CD207+ cells with respect to global gene expression. We will continue to pursue the very important problem of the cell of origin of LCH in our 2009 HAA Grant.

Publications

IL-17A is not Expressed by CD207+ Cells in Langerhans Cell Histiocytosis Lesions
Nature Medicine 15, 483 - 484 (2009)

Cell-Specific Gene Expression in Langerhans Cell Histiocytosis Lesions Reveals a Distinct Profile Compared with Epidermal Langerhans Cells
The Journal of Immunology April 15, 2010 vol. 184 no. 8 4557-4567

 

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