Development of High-affinity TCR for Imaging in the Brain

Edward J. Collins, Ph.D.

University of North Carolina School of Medicine

Funded in December, 2007: $200000 for 3 years
LAY SUMMARY . ABSTRACT . BIOGRAPHY .

LAY SUMMARY

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Studying Metastatic Melanoma in the Brain

The researchers will develop a technique for identifying melanoma cells that have metastasized to the brain and for studying the effects of immunotherapies designed to strengthen immune T cell responses to the melanoma cells.

Melanoma is a highly malignant cancer. Melanoma patients have an impaired blood-brain-barrier that allows the cancer cells to enter the brain and spread. In fact, brain metastases often already exist by the time the diagnosis is made. Finding brain metastases is critical, since most deaths from melanoma are due to brain metastases that resist conventional treatment. While melanoma patients have numerous immune T cells, these cells have been inactivated by the tumors.  Receptors for immune T cells are able to differentiate between normal and cancer cells, by recognizing peptides (amino acids) that are bound to proteins on the melanoma cell surface. Since there are many copies of T cell receptors and of proteins on melanoma cell surfaces, however, the immune T receptors bind only weakly to the cancer cells. 

The investigators will produce high affinity T cell receptors from T cells isolated from melanoma patients. They will undertake efforts to strengthen the ability of the T cell receptors to bind to the proteins on the melanoma cell surface. The investigators will use various imaging probes, including PET, SPECT and MRI probes, coupled with these strengthened T cell receptors, to identify melanoma cells in the brain. They also will see if the imaging probes enable them to determine how immune cells interact with the tumor in response to immunotherapies designed to strengthen T cell actions.

Significance:  The new high affinity T cell receptor probes may provide the ability to visualize melanoma metastases in the brain, to aid in diagnosis, and to assess the effects of immunotherapies in strengthening immune T cell responses against the tumors.

ABSTRACT

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Development of High-affinity TCR for Imaging in the Brain

Melanoma is a highly malignant disease and, in many cases, brain metastases already exist at the time of diagnosis.  Most of the deaths from melanoma are due to metastases that resist conventional treatment so finding them is critical.  Our long-term goal is to develop diagnostic and therapeutic tools for use in cancer and other diseases.  The goal of this project is to develop enhanced affinity T cell receptors (TCR) targeted towards melanoma in order to image those tumors in the brain.  We will use T cell receptors isolated from melanoma patients as a preliminary scaffold for this reagent.  The complementarity determining loops 1 and 2 (CDR1 and CDR2) of the two TCR chains will be randomly mutated to create libraries of potentially enhanced affinity TCR. 

In Specific Aim 1, we will  develop high-affinity, melanoma-specific TCR.  We will isolate TCR from single T cells that have infiltrated metastatic tumors.  These TCR will be manipulated to become high affinity but retain their peptide-specificity.  Using phage display, we will pan the library for high affinity TCR using recombinant peptide/MHC complexes. The project is novel because we will use receptors that are already “programmed” to recognize the antigen but that couldn’t function as a marker because of their inherently low affinity.  Our long-term goal is to produce four different high affinity TCR specific for four melanoma antigenic peptides.  By using four TCR, we greatly increase the likelihood that melanoma from different patients will be visualized.

In Specific Aim 2, we will create a recombinant probe useful for brain imaging of metastatic melanoma.  We will create a set of recombinant TCR, of various sizes and conjugate them to metals or nanomaterials for use in PET, SPECT and MR, when the high affinity TCR is available, it will be incorporated into the “best” sized reagent.  Although these initial experiments will not occur in humans, the TCR are isolated from humans, do recognize human melanoma antigens, and should function in humans as well as in mice.  Our lab is unique in its ability to accomplish this task because of the melding of immunology and biophysical techniques. If we are successful, we will be able to identify HLA-A2+ melanoma cells in the brain and determine where and how other immune cells are interacting with the tumor.

INVESTIGATOR BIOGRAPHIES

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Edward J. Collins, Ph.D.

Dr. Collins is an Associate Professor in the Department of Microbiology and Immunology at the University of North Carolina at Chapel Hill.  In 1990, he received his Ph. D. from the University of Texas at Austin in Biochemistry, studying the x-ray crystallographic structures of toxins (ricin, pokeweed antiviral protein) that were to be used as immunotoxins for cancer treatment.  His study of Immunology began during his Postdoctoral Fellowship with Don Wiley at Harvard University, where he studied the structure and function of human leukocyte antigens (HLA).  He has been studying how T cells recognize HLA for the past 10 years and hopes to use that understanding of the proteins to design high affinity targeting agents for cancer imaging.