Abstract 16907: Modification of Hemeoxygenase-1 Expression Enhances the Therapeutic Potency of CD34+ Cells in Ischemic Tissue Repair

Abstract

The potency of cell-based therapy in ischemic tissue repair is limited by low viability and retention of transplanted cells. The hemeoxygenase system catabolizes heme cleavage and has been shown to exert cytoprotection via its anti-oxidative, -apoptotic, -inflammatory properties. HO-1, inducible in various pathologic states, has been shown to influence progenitor cell biology. We hypothesized that HO-1 over-expression enhances the therapeutic potency of CD34+ cells for ischemic tissue repair. CD34+ from healthy donors were enriched from the peripheral blood mononuclear cell fraction of healthy donors after G-CSF mobilization (Isolex 300i). Adenoviral transduction of HO-1/GFP or GFP led to a substantial increase of HO-1 expression (HO-1/18s RNA expression: 62-fold increase, protein expression: 20-fold increase; n=3). After allowing 48 hrs for target gene expression, CD34+ cells were FACS-sorted for GFP followed by overnight recovery in-vitro. A low-therapeutic dose (10^5 cells/kg) of HO-1+/GFP+ (HO-1) or GFP+ (GFP) CD34+ cells was locally injected into the border zone after complete ligation of the left coronary artery in 8-week-old, male nude mice (saline control: 2x 15 μl). At day 28, LV ejection fraction of mice treated with HO-1 over-expressing CD34+ cells was significantly improved (fractional shortening: saline 19±2%, HO-1 30±1%, GFP 24±1%; n=6-8/group, P<0.01). This functional improvement can be explained by a preservation of the border-zone: the number of lectin+ capillaries was increased (lectin staining: saline 73±5/hpf, HO-1 99±4/hpf, GFP 79±7/hpf; n=7-8/group, P<0.01) with the use of HO-1 modified CD34+ cells while lectin+/alpha-smooth-muscle actin+ structures indicative for resistance vessels remained unchanged (P=ns). Apoptosis of resident myocardial cells was attenuated (TUNEL staining: saline 69±5/hpf, HO-1 31±3, GFP 54±9, P<0.05). As a result, the infarct size in mice treated with HO-1 modified cells was reduced (Masson-trichrome staining: saline 39±1%, HO-1 36±2%, GFP 42±1%; n=6-8/group, P<0.05). Ongoing studies are addressing the underlying mechanism(s) on cellular basis as well as the clinical relevance. Conclusion: HO-1 gene modification enhances the therapeutic potency of CD34+ in ischemic tissue repair.