Objective: Intimal hyperplasia plays an important role in a variety of types of vascular remodeling, particularly luminal narrowing after vascular injury. The vascular smooth muscle cells (VSMCs) in the neointimal area are a synthetic phenotype and have different epitopes from VSMCs in the normal media. The synthetic VSMCs in the neointima contain various possible antigens that can be targeted by the immune system. In this study, we tried to develop a new immunotherapy, which targets the synthetic VSMCs, for prevention of neointimal formation after angioplasty.
Method and results: Rabbits were repeatedly immunized with fixed xenogenic rat cultured VSMCs suspended in adjuvant as immunogens or injected with adjuvant and phosphate-buffered saline (PBS) or rat hepatocytes as controls every 2 weeks for 3 times. One week after the last immunization/injection, balloon injury of the left common carotid artery was performed. Four weeks after the injury, rabbits were euthanized and the neointimal lesion formation was assessed. The mean neointimal area of the PBS-injected, non-immunized group and the rat hepatocyte-immunized, control group was not statistically different (0.339 +/- 0.036 and 0.350 +/- 0.041 mm(2), P = NS). However, immunization with rat VSMCs significantly reduced the intimal lesion area (0.219 +/- 0.0286 mm(2); P < 0.05 vs. PBS-injected, non-immunized group and rat hepatocyte-immunized group.) PCNA-immunopositive proliferating VSMCs in the neointima were suppressed by the rat VSMC immunization (1.34 +/- 0.49% vs. 5.78 +/- 0.47%; P < 0.05 vs. PBS-injected, non-immunized group). Rat VSMC immunization induced antibodies which had strong cross-reactivity against rabbit synthetic VSMCs. In experiments in vitro, proliferation and migration of rabbit VSMCs that were stimulated by serum, angiotensin (AT) II, platelet-derived growth factor (PDGF)-BB, fibroblast growth factor (FGF), and the phorbol ester PMA were significantly suppressed by treatment with immunoglobulin extracted from the VSMC-immunized rabbit plasma, implying that the immunoglobulin had some global effects on VSMCs. The rat VSMC-immunized rabbit immunoglobulin bound the rabbit AT1a receptor protein, which was expressed in COS7 cells by transfection of rabbit AT1a receptor pcDNA3. This binding to AT1a receptor may be one of mechanisms of the effects of VSMC-immunized immunoglobulin.
Conclusion: Xenogenic, synthetic rat VSMC immunization in rabbits induced auto-antibodies against synthetic rabbit VSMCs in a cross-reaction. The induced auto-antibodies against synthetic VSMCs may provide a possibility of new immunotherapy for vascular remodeling that forms neointimal lesions.