Phosphopeptides as shared targets for donor derived T cell therapy of AML
Acute myelogeneous leukemia (AML) remains a therapeutic dilemma both for children and adults with long-term cure rates still only 50-70%, even after a tissue type-matched bone marrow transplant. While immunotherapies have shown striking promise in children with drug resistant forms of acute lymphoblastic leukemia, their application to patients with AML has been limited because the proteins and protein fragments, called peptides, that have thus far been identified on AML cells as potential targets for immunotherapies are also expressed by normal bone marrow cells that produce white cells, called neutrophils, that are essential day to day for protection against infections. However, recent evidence has shown that AML cells -- unlike normal marrow cells -- use and breakdown high levels of certain proteins needed for their malignant growth. Furthermore, we and others have found that cancer-fighting immune T cells found in healthy individuals can recognize fragments of these distinctive breakdown products called phosphopeptides, if they are presented by an HLA molecule on the surface of the AML cell. We propose to grow immune T cells that recognize these phosphopeptides and determine how well they distinguish AML cells from normal marrow cells and how effective they are at killing AML cells, both in the test tube and in immunocompromised mice that have transplants of human AML cells.
Project Goals:
Due to the pressing need for suitable AML targets, we propose to determine the extent to which distinctive AML protein fragments, called “phosphopeptides,” can be targeted by immune T cells present in healthy donors. Just as healthy individuals have immune T cells that can find protein fragments from viruses, we and others have found that healthy individuals have T cells that can also find phosphopeptides that are found on AML cells, albeit at lower frequencies in the bloodstream. We hypothesize that these specialized T cells in healthy donors could be used to treat or prevent relapse if they were to be administered to an appropriately tissue matched AML patient. Our project goals are three:
1. From our curated list of phosphopeptides found on AML cells, we wish to determine how well these phosphopeptides stick to the surface of AML cells. The resulting findings are an important gauge of the ability of these phosphopeptides to stimulate the immune system.
2. We will use the stickiest phosphopeptides to immunize T cells from healthy individuals in a test tube. The immunized T cells will then be tested and compared for their ability to selectively kill AML cells and not normal blood cells in the test tube. These results will help us assess how effective these cells would be in treating a patient without any side effects that may hurt their blood cells.
3. Using T cells that we find kill AML cells in the test tube, we will treat immunocompromised mice bearing AML cells from pediatric patients. We will determine if these T cells preferentially home to and kill AML tumors. We will also determine if these T cells confer AML-bearing mice with a survival benefit and if they cause any toxic side effects. These results will give us a better idea of how these cells will react against leukemic cells in a patient without causing damage to other tissues, giving us an initial assessment of their leukemia-selectivity and safety.
Project Update 2024:
Acute myelogeneous leukemia (AML) remains a therapeutic dilemma both for children and adults with long-term cure rates still only 50-70%, even after a tissue type-matched bone marrow transplant. We and others have found that cancer-fighting immune T cells found in healthy individuals can recognize fragments of distinctive breakdown products called phosphopeptides presented on the surface of the AML cell. We hypothesize that these specialized T cells in healthy donors could be used to treat or prevent relapse if they were to be administered to an appropriately tissue matched AML patient. Our first goal was to determine how well previously unstudied phosphopeptides stick to the surface of AML cells. Using a model cell line we generated to understand understudied tissue types, we confirmed that a selected panel of phosphopeptides could stick to the cell surface. These results validate that we can use a novel set of phosphopeptides derived from understudied tissue types to expand the patient population eligible for a phosphopeptide therapy. Our second goal was to use these novel phosphopeptides to immunize T cells in a test tube. We found that, in comparison to previously characterized phosphopeptides, the novel set of phosphopeptides could only elicit the desired T cells in major or minor frequencies depending on the patient population. This required us to generate more sensitive reagents and improve the in vitro expansion process for generating immunized T cells. With these adjustments, we were able to detect and expand a population of immunized T cells. We will now determine how effective these T cells are at killing AML tumors from pediatric patients. Our third goal aims to treat mice bearing AML tumors from pediatric patients to model a cellular therapy treatment setting for pediatric AML. To reliably generate immunized T cells for treatment of animals, we have shown that we can genetically modify transplant donor T cells to redirect their specificity to a target of interest, foregoing the lengthy immunization process in a test tube. Using the receptors of immunized T cells from our second goal, we have shown we can redirect the specificity of donor T cells to kill AML cells, and now will test them in AML tumors in mice. These studies will allow us to determine if such T cells provide a survival benefit as well as if they cause any toxic side effects.
