Current Projects

1. Graft-versus-host disease (GVHD). GVHD is a multi-organ system disorder in which donor T cells recognize host alloantigens present on antigen-presenting cells and tissues in the context of an inflammatory response. Studies are directed toward identifying and modifying signals that drive or inhibit acute and chronic GVHD generation. These include the analysis of positive costimulatory molecules and negative regulators of the immune response that counterbalance positive costimulation as well as intracellular signaling and metabolic pathways along with pro- and anti-inflammatory cytokines that regulate these responses at the level of the GVHD target organ. We have analyzed the biochemical events associated with tolerance induction and have applied these findings to the development of new approaches to induce tolerance via the use of inhibitors of signal transduction or cell cycle progression. We are also examining cell based therapies such as regulatory T cells (see below) and myeloid-derived suppressor cells. We have also used a newly developed model of chronic GVHD that results from T:B cooperativity, leading to alloantibody and subsequently, collagen deposition, culminating in multi-organ system injury and pulmonary and liver fibrosis.

2. Regulatory T cells. We have developed new approaches to propagate and expand CD4+25+ T regulatory cells that can suppress alloresponses and GVHD . We are analyzing the biochemical, molecular, cytokine and cell surface factors that regulate murine and human CD4+25+ T cell development, expansion and function in vitro and in vivo. We are also investigating how CD4+25+ T cells affect hematopoiesis and immune function in mice including models of human lymphohematopoiesis.The in vivo biological effects of our immune manipulations are being monitored using whole-body imaging techniques to track donor effector or regulatory T cells using transgenic mice expressing green fluorescent protein and firefly luciferase. Some of these studies have been translated into the clinic.

3. Immune post-transplant. Because GVHD and the conditioning regimens used for bone marrow transplantation induce severe thymic injury, we also are exploring new approaches to protect the thymic epithelial cells (TEC) against injury including the use of cytokines that stimulate TEC proliferation/repair, agents that protect against genotoxic stress, and those that repair stromal cell injury in the thymus and periphery. The mechanism(s) responsible for the protective effects of these biological agents are being explored in wild-type and in transgenic mice with disruptions of various signaling pathways. Within TECs, we are examining the thymocyte signals that regulate TEC function and characterizing the effects of micro-RNA regulation on TEC regeneration and function. In complimentary studies, we are developing strategies to induce pluriopotent progenitor cells to differentiate into TECs, which will be used as a cellular therapy to replace damaged TEC. We also are analyzing the mature T cell response to foreign antigens in transplanted mice to better understand the qualitative defects associated with post-transplant T cell reconstitution and applying those to novel strategies to repair injury stromal cells in peripheral lymphoid organs.
 
4. Graft-versus-leukemia (GVL). Projects are ongoing to identify the host mechanisms responsible for tumor-mediated immune suppression of endogenous T effector cells, focusing on negative regulators of immune response expressed on the cell surface or via intracellular pathways. Adoptive T cell immunotherapy is being tested using new approaches to generate T effector cells that have superior in vivo cytolytic potential and/or result in increased persistence of transferred T cells. T cell immune therapy is used in combination with approaches that dampen the host immune suppressive response , cause homeostatic expansion of T cells via the induction of lymphopenia, target tumor cells  or support T cell recruitment and survival within secondary lymphoid organs.

5. Gene therapy/repair. As an alternative to transplantation, we are using molecular strategies to correct congenital disorders. To treat immune deficiency disorders, studies are being performed to achieve homologous recombination or site-directed integration for gene replacement using zinc finger nucleases or TALENS in hematopoietic stem cells. Recipients are analyzed for molecular and phenotypic correction.


Dr. Tolar's Research 

Dr. Tolar’s research interests include:

• Integrating clinical observation, molecular biology, immunology, and laboratory research in studying and treating children with lethal diseases—epidermolysis bullosa, bone marrow failure, peroxisomal and lysosomal inborn errors of metabolism, cancer and other devastating disorders.
• Developing cellular therapies (including mesenchymal stromal cells and cellular reprogramming).
• Improving the safety of existing therapies (hematopoietic cell transplantation and its conditioning regimens).
• Investigating mechanisms by which stem cell transplantation is effective in repair of damaged tissues (e.g., heart, skin and brain).

Clinically, Dr. Tolar is currently working on protocols using hematopoietic stem cell transplant as a treatment for epidermolysis bullosa, dyskeratosis congenita, severe aplastic anemia, Fanconi anemia, mucopolysaccharidosis type I – Hurler syndrome, and adrenoleukodystrophy.

Dr. Hippen's Research

Dr. Hippen's research is focused on inhibiting Graft Versus Host Disease (GVHD), which is a frequent and severe complicating factor in bone marrow transplants. GVHD is a T cell mediated disease that arises in autoimmune fashion due to graft-derived immune cells recognizing recipient cells as non-self. Activation of autorective T cells (and those that induce GVHD) is normally prevented by a subset of T cells termed regulatory T cells (Treg). Transplant of donor Treg has been shown to ameliorate disease in mouse models of both GVHD and autoimmunity. Dr. Hippen's specific interest is defining the mechanisms that control human regulatory T cell proliferation and function with the goal of generating large numbers of very active cells that can be co-transferred at the time of bone marrow transplantation and reduce or completely abolish GVHD. These studies have led to 'first-in-man' studies using ex vivo expanded Treg that demonstrated these cells are safe, and can ameliorate GVHD in humans. Dr. Hippen's current projects include: defining Treg signaling pathways that enhance expansion and/or suppressive function and inducing suppressive function using in human T cells (not Treg) via TGFß, nutrient stress, or co-ligation of inhibitory molecules.

Dr. Stefanski's Research

Dr. Stefanski's research is focused on expediting immune reconstitution after transplant. T lymphocytes are critical for effective responses to viruses and fungal infections; after undergoing bone marrow transplantation there are essentially no functional T cells until up to a year after transplant. In her laboratory, she is currently working on T cell reconstitution in order to decrease morbidity and mortality.

Dr. Osborn's Research
Gene Therapy
- Non-viral gene transfer for the treatment of inborn errors of metabolism.

Genome Editing
- Correction of disease specific mutations in a precise manner using homologous recombination.

Cellular Therapy
- Ex vivo correction of murine and human adult stem cells.