[show abstract][hide abstract] ABSTRACT: Hematopoietic stem cell (HSC) therapy for myocardial repair is limited by the number of stem cells that migrate to, engraft in, and proliferate at sites of injured myocardium. To alleviate this limitation, we studied whether a strategy using a bispecific antibody (BiAb) could target human stem cells specifically to injured myocardium and preserve myocardial function. Using a xenogeneic rat model whereby ischemic injury was induced by transient ligation of the left anterior descending artery (LAD), we determined the ability of a bispecific antibody to target human CD34+ cells to specific antigens expressed in ischemic injured myocardium. A bispecific antibody comprising an anti-CD45 antibody recognizing the common leukocyte antigen found on HSCs and an antibody recognizing myosin light chain, an organ-specific injury antigen expressed by infarcted myocardium, was prepared by chemical conjugation. CD34+ cells armed and unarmed with this BiAb were injected intravenously in rats 2 days postmyocardial injury. Immunohistochemistry studies showed that the armed CD34+ cells specifically localized to the infarcted region of the heart, colocalized with troponin T-stained cells, and colocalization with vascular structures. Compared to unarmed CD34+ cells, the bispecific antibody improved delivery of the stem cells to injured myocardium, and such targeted delivery was correlated with improved myocardial function 5 weeks after infarction (p < .01). Bispecific antibody targeting offers a unique means to improve the delivery of stem cells to facilitate organ repair and a tool to study stem cell biology.
[show abstract][hide abstract] ABSTRACT: The mouse is an important model for the development of therapeutic stem cell/bone marrow cell implantation to treat ischemic myocardium. However, its small heart size hampers accurate implantation into the left ventricular (LV) wall. Precise injections have required surgical visualization of the heart, which is subject to complications and is impractical for delayed or repeated injections. Furthermore, the thickness of the myocardium is comparable to the length of a needle bevel, so surgical exposure does not prevent inadvertent injection into the LV cavity. We describe the use of high-resolution echocardiography to guide nonsurgical injections accurately into the mouse myocardial wall. We optimized this system by using a mixture of ultrasound contrast and fluorescent microspheres injected into the myocardium, which enabled us to interpret the ultrasound image of the needle during injection. Quantitative dye injection studies demonstrated that guided closed-chest injections and open-chest injections deliver comparable amounts of injectate to the myocardium. We successfully used this system in a mouse myocardial infarction model to target the injection of labeled cells to a region adjacent to the infarct. Intentional injection of tracer into the LV cavity resulted in a small accumulation in the myocardium, suggesting that non-guided cell injections into mouse hearts may appear to be successful even if the majority of the injectate is lost in the chamber. The use of this system will allow more precise cellular implantation into the mouse myocardium by accurately guiding injections to desired locations, confirming successful implantation of cells, in a clinically relevant time frame.
[show abstract][hide abstract] ABSTRACT: Coronary heart disease is currently the leading killer in the western world. Therapeutic angiogenic agents are currently being examined for treatment of this disease. We have recently demonstrated the effective use of Pleiotrophin (PTN) as a therapeutic agent for treatment of ischemic myocardium. We have also shown that injection of the biopolymer fibrin glue preserves left ventricular geometry and prevents a deterioration of cardiac function following myocardial infarction. Due to the low transfection efficiency of naked plasmid injections, we examined the use of PTN plasmid and the biopolymer as a gene-activated matrix in the myocardium. In this study, we demonstrate that delivery of PTN plasmid in fibrin glue increases neovasculature formation compared to injection of the naked plasmid in saline.