Reducing recovery time after bone marrow transplant

Bone marrow transplants (BMTs) help thousands of patients with various diseases and cancers, such as leukemia and lymphoma. Patients receive chemotherapy or radiation therapy to kill the cancerous or diseased cells, but this destroys the bone marrow’s ability to produce new blood cells and leaves them without a working immune system. After patients undergo this therapy, they receive donated bone marrow to resupply the body with new blood-forming stem cells. It takes the immune system about three months to fully recover, and patients remain at a high risk for infection during this time.

One way to hasten patient recovery would be to have more stem cells to transplant. Dr. Bruce Blazar received a Discovery Science research grant from Regenerative Medicine Minnesota (RMM) to test ways to overcome the current obstacles to increasing the number of stem cells in the transplant before giving it to the patient.

The problem now is that blood-forming stem cells cultured in the laboratory do not have the same abilities to function in the donor as the donor’s blood-forming stem cells. Therefore, Dr. Blazar is collaborating with Five Prime Therapeutics to screen and test various proteins that could help develop useful blood-forming stem cells in the laboratory that have the same beneficial properties as donated cells.

If successful, patients would recover faster and have fewer problems after transplant. This is just one of the many examples of the potential that regenerative medicine holds for the future of medical advancement and patient care.

Grant Title: Identification of novel protein drivers of definitive hematopoiesis

Public Abstract: Our primary objective is to improve the efficacy and safety of hematopoietic cell transplantation (HCT) used to treat congenital and acquired non-malignant and malignant diseases using allogeneic or autologous grafts, dependent upon the indication for HCT. Uniform complications include slow hematopoietic or immune recovery due to chemoradiotherapy conditioning regimen injury to the host. By identifying and expanding rare hematopoietic stem cells (HSC), HCT recovery would be dramatically hastened. For allogeneic HCT, donor graft T cells that attack the host can be avoided by infusing high HSC number to overwhelm rejection capacity. For autologous HCT, HSC genome editing could be used to correct underlying genetic defects in HSC/progeny. Beyond HCT, HSC/progeny can facilitate tissue repair, as vehicles for protein replacement therapies, or to modulate immune system responses resulting in autoimmunity or elimination of residual tumor. Since HSC give rise to all blood components (red cells; white blood cells; platelets), HSC and their differentiated progeny could be used therapeutically for cell replacement, as vehicles for protein replacement or to induce immune system tolerance, permitting solid organ transplants.

Induced pluripotent stem cells (iPSC) are created by “reprogramming” adult cell types back into stem-cells capable of producing nearly all types of tissue. As iPSC can be grown indefinitely in the lab, they represent a potentially unlimited reservoir of “off-the-shelf” tissue-matched cells, including HSC. Since iPSC are amenable to genetic manipulation, they represent an ideal platform for the production of gene-corrected autologous HSC for treatment of genetic disease. Specific conditions to convert iPSC into rare, definitive-type HSC required are unknown and are being urgently sought.

To address this problem, we have developed a novel genetic reporter with which human iPSC can be modified so that they indicate by fluorescence their successful conversion to definitive-type hematopoietic stem/progenitors (HSPC). This system is designed to allow high throughput screening of conditions for their ability to convert iPSC into HSC capable of engrafting after transplant. Our collaborators at Five Prime Therapeutics have developed a unique system for the rapid production and screening of a protein library constituting what represents essentially the entire repertoire of human extracellular proteins, which we will apply to our modified, “reporter” iPSC to identify previously unknown proteins that promote formation of definitive HSPC. Identified “hits” will be verified, and cells produced by exposure to these proteins will be characterized and tested for their ability to engraft immunodeficient mice as preclinical proof-of-concept for true HSC activity (defined by the properties of stem cell self-renewal with full multi-lineage differentiation potential and in vivo repopulation).

Our screen will identify biologically active proteins that promote (or as derivative value of the screen, inhibit) the formation and/or expansion of iPSC-derived HSPC that can be used to improve and expand HCT applications, for transfusion or cell-based protein replacement therapies, and as a platform to add immune regulatory or effector cells to treat autoimmunity and cancer. The ability to derive HSC from iPSC would revolutionize HCT, resulting in a nearly unlimited supply of tissue-matched, off-the-shelf HSC for transplants, overcoming significant HC limitations while simultaneously opening the door for the production of gene-corrected autologous HSC for the treatment of a wide-array of genetic diseases. Fundamental insights into the regulation of HSC would be gained that may lead to in vivo approaches to stimulate hematopoiesis or in future studies allow us to pursue testing of inhibitory proteins to replace conditioning therapy.