PROJECT SUMMARY
The following proposal outlines a 5-year career training plan that will prepare Dr. Alexander Holtz to be an
independent physician-scientist and leader in the field of induced pluripotent stem cell (iPSC) biology and
cellular therapies for pulmonary vascular disorders. Pulmonary vascular diseases, such as pulmonary
hypertension (PH), are devastating illnesses associated with high morbidity and mortality with frustratingly
limited treatment options. Endothelial cell dysfunction is a core mechanistic driver of these disorders, especially
in cases where gene mutations impact endothelial cell biology (FOXF1, BMPR2, etc.). Dr. Holtz’s long-term
vision is to develop autologous endothelial replacement therapies where patient-derived iPSCs are generated,
undergo gene-correction ex vivo, and then are differentiated to endothelial cells (iEndos) to provide a limitless
supply of healthy donor endothelial cells for transplantation without the need for lifelong immunosuppression.
Dr. Holtz presents his initial discoveries that patterning of iEndos with BMP9 shifts cells towards a ‘lung-like’
molecular profile, including induction of the lung endothelial cell marker TMEM100, and enables durable
engraftment of transplanted iEndos into the mouse lung microvasculature. He also shows that this BMP9-
mediated patterning process requires active Notch signaling. Using this novel system, Dr. Holtz will test the
hypothesis that BMP9 and Notch signaling cooperatively induce TMEM100 expression to produce functional,
engraftable cells for treatment of monogenic pulmonary vascular disorders. Specifically, he will 1) assess the
differentiation capacity, longevity, and progenitor function of engrafted iEndos in the lung microvasculature; 2)
utilize a ‘competitive lung reconstitution assay’ to delineate the functional role of BMP9- and Notch-mediated
induction of TMEM100 to facilitate iEndo engraftment and to test the translational potential of iEndos derived
from gene-corrected PH patient-specific hiPSCs (BMPR2, FOXF1); and 3) test the efficacy of endothelial
replacement therapies in immunocompetent hosts using a mouse model of FOXF1-mediated pulmonary
vascular disease. This work will provide a fundamental advancement towards developing endothelial
replacement therapies for a broad range of congenital and acquired pulmonary vascular diseases. Dr. Holtz
has 90% protected time from Boston Children’s Hospital Division of Genetics and Genomics to accomplish
these aims under the guidance of Dr. Darrell Kotton at the Center for Regenerative Medicine at Boston
University/Boston Medical Center. He has assembled a remarkable team of advisors with diverse expertise to
assist in his career development and scientific research. Dr. Holtz details a comprehensive training plan that
takes advantage of his unique cross-institutional collaboration that includes mentored research, didactic
coursework, attendance and presentation at national meetings, preparation of manuscripts, and acquiring
additional grant support culminating in an R01. Dr. Holtz has the commitment of both institutions to accomplish
these goals and transition to an independent physician-scientist position by the end of the award.