Immunology Graduate Group

Andrew D. Wells, Ph.D.
Assistant Professor, Pathology and Laboratory Medicine

Address: 916F Abramson Research Center (CHOP)
Office Phone: 215-590-8710
Lab Phone: 215-590-0344
Fax: 215-590-7384
Email: adwells@mail.med.upenn.edu

Education:
Ph.D., University of Wisconsin-Madison
B.A., Miami University

Research Interests

Cell cycle control of T cell responses.

Research Summary
 
T cells must proliferate and differentiate in order to attack pathogens, initiate autoimmune pathology, or reject transplanted organs. T cell proliferation drives the expansion of the pool of antigen-reactive cells, but remarkably, also appears to drive effector differentiation and anergy avoidance at the single-cell level (J.I. 162:5212, J.C.I. 108:895). In my laboratory, we are particularly interested in defining signaling pathways that regulate T cell cycle progression, and also in understanding the biological basis for the link between cell division and T cell differentiation.

Regulation of T cell cycle progression, differentiation and tolerance by cyclin-dependent kinase inhibitors. Naturally-encoded inhibitors of cyclin-dependent kinases (CDK) are important negative regulators of cell proliferation. We are using mice genetically engineered to lack these inhibitory proteins, as well as retroviral vectors that overexpress these factors, to investigate whether modulation of cell cycle progression can directly influence T cell differentiation and tolerance induction, and in turn whether these factors can be targeted in approaches to induce tolerance during transplantation. To date, we have found that T cells deficient in the expression of the CDK inhibitors p27kip1 or p18ink4 are hyper-responsive to growth factor receptor signals, and are refractory to the anti-proliferative and anergy-inducing effects of treatments that induce tolerance in normal T cell populations. These CDK inhibitors play an important role in tolerance induction in vivo, as our studies show that p27kip1-deficient mice reject MHC-mismatched cardiac allografts under therapeutic conditions that would normally result in long-term organ transplant survival in wild type mice.

Role of the E2F family of transcription factors in T cell differentiation and tolerance. The six members of the E2F family of transcription factors have crucial, non-overlapping roles in the regulation of cell proliferation, gene expression and differentiation in many normal and malignant tissues, but their role in the control of T cell responses is poorly understood. We are investigating the expression and function of these factors during T cell proliferation, differentiation and tolerance induction, and in turn whether the activity of these factors can be targeted in approaches to induce tolerance during transplantation. For instance, our preliminary experiments have shown that tolerant T cells express primarily anti-mitogenic E2F family members, while effector T cells express primarily pro-mitogenic family members. We have also constructed retroviral expression vectors that encode E2F1 through 6, and are using these vectors to enforce expression of individual E2F family members in primary T cells. Using this gain-of-function approach, we plan to identify the constellation of immune-relevant genes that these transcription factors control in T cells, and how these factors contribute to cell cycle control, differentiation and tolerance in T cells.

Epigenetic regulation of gene expression during T cell differentiation and tolerance. In eukaryotic cells, the DNA that constitutes each chromosome is wrapped around octamers of histone proteins called nucleosomes, which are in turn incorporated into higher-order structures that allow efficient packaging of the ~3 billion nucleotides of the genome into each cell's nucleus. Whether a particular gene is wrapped tightly around a nucleosome, and whether the nucleosomes are in turn packed together loosely vs. tightly, can have a major influence on its expression. The expression of many genes required for T cell differentiation and function are controlled by the physical structure of the chromosomal DNA in which they are located. This structure is regulated by chemical modification of DNA or nucleosomes, including methylation and acetylation, and cell division is proposed to be a 'window of opportunity' for these epigenetic changes to occur. Our current data suggest that demethylation of DNA and remodeling of the chromatin surrounding such genes as IL-2 and IFN??occurs after T cell activation, and that these transcription-promoting events do not occur efficiently in T cells undergoing tolerance induction. How these epigenetic modifications are achieved, and whether DNA methylation and chromatin structure are directly involved in silencing gene expression during tolerance induction, is entirely unknown. Defining the contribution of these epigenetic mechanisms to T cell differentiation will likely be crucial for a more sophisticated understanding of the decision between immunity and tolerance.

 

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