Making stem cells infarct avid

A major factor limiting the engraftment of transplanted stem cells after myocardial infarction is the low rate of retention in the infarcted site. Our long-term objective is to improve engraftment by enabling stem cells to recognize and bind infarcted tissue. To this end, we proposed to modify the surface of embryonic stem cells (ESCs) with the C2A domain of synaptotagmin I; this allows the engineered stem cells to bind to dead and dying cardiac cells by recognizing phosphatidylserine (PS). The latter is a molecular marker for apoptotic and necrotic cells. The C2A domain of synaptotagmin I, which binds PS with high affinity and specificity, was attached to the surface of mouse ESCs using the biotin-avidin coupling mechanism. Binding of C2A-ESCs to dead and dying cardiomyocytes was tested in vitro. After the surface modification, cellular physiology was examined for viability, pluripotency, and differentiation potential. C2A covalently attached to the ESC surface at an average of about 1 million C2A molecules per cell under mild conjugation reaction conditions. C2A-ESCs avidly bound to dying, but not viable, cardiomyocytes in culture. The normal physiology of C2A-modified ESCs was maintained. The binding of C2A-ESCs to moribund cardiomyocytes demonstrates that the retention of transplanted cells may be improved by conferring these cells with the ability to bind infarcted tissue. Once established, this novel approach may be applicable to other types of transplanted therapeutic cells.