The effect of regional gene therapy with bone morphogenetic protein-2-producing bone-marrow cells on the repair of segmental femoral defects in rats

Background: Recombinant human bone morphogenetic proteins (rhBMPs) can indu ce bone formation, but the inability to identify an ideal delivery system l imits their clinical application. We used ex vivo adenoviral gene transfer to create BMP-2-producing bone-marrow cells, which allow delivery of the BM P-2 to a specific anatomical site. The autologous BMP-2-producing bone-marr ow cells then were used to heal a critical-sized femoral segmental defect i n syngeneic rats. Methods: Femoral defects in five groups of rats were filled with 5 x 10(6) BMP-2-producing bone-marrow cells, created through adenoviral gene transfer (twenty-four femora, Group I); twenty micrograms of rhBMP-2 (sixteen femor a, Group II); 5 x 10(6) beta-galactosidase-producing rat-bone-marrow cells, created through adenoviral gene transfer of the lacZ gene (twelve femora, Group III); 5 x 10(6) unfected rat-bone-marrow cells (ten femora, Group IV) ; or guanidine hydrochloride-extracted demineralized bone matrix only (ten femora, Group V). Guanidine hydrochloride-extracted demineralized bone matr ix served as a substrate in all experimental groups. Specimens that were re moved two months postoperatively underwent histological and histomorphometr ic analysis as well as biomechanical testing. Results: Twenty-two of the twenty-four defects in Group I (BMP-2-producing bone-marrow cells) and all sixteen defects in Group II (rhBMP-2) had healed radiographically at two months postoperatively compared with only one of t he thirty-two defects in the three control groups (beta-galactosidase-produ cing rat-bone-marrow cells, uninfected rat-bone-marrow cells, and guanidine hydrochloride-extracted demineralized bone matrix alone). Histological analysis of the specimens revealed that defects that had recei ved BMP-2-producing bone-marrow cells (Group I) were filled with coarse tra becular bone at two months postoperatively, whereas in those that had recei ved rhBMP-2 (Group II) the bone was thin and lace-like. Defects that had be en treated with bone-marrow cells producing beta-galactosidase (Group III), uninfected bone-marrow cells (Group IV), or guanidine hydrochloride-extrac ted demineralized bone matrix only (Group V) demonstrated little or no bone formation. Histomorphometric analysis revealed a significantly greater total area of b one formation in the defects treated with the BMP-2-producing bone-marrow c ells than in those treated with the rhBMP-2 (p = 0.036). Biomechanical test ing demonstrated no significant differences, with the numbers available, be tween the healed femora that had received BMP-2-producing bone-marrow cells and the untreated (control) femora with respect to ultimate torque to fail ure or energy to failure. Conclusions: This study demonstrated that BMP-2-producing bone-marrow cells created by means of adenoviral gene transfer produce sufficient protein to heal a segmental femoral defect. We also established the feasibility of ex vivo gene transfer with the use of biologically acute autologous short-ter m cultures of bone-marrow cells. Clinical Relevance: Regional gene therapy is a novel approach to the treatm ent of bone defects. The limited duration of transgenic expression associat ed with first-generation adenoviral vectors is advantageous for this clinic al application. This system of ex vivo gene transfer and the subsequent inf ection of bone-marrow cells with an adenovirus containing the BMP-2 cDNA co uld be adapted to enhance bone formation in humans.