Novel Therapy for Atherosclerosis Using Recombinant Immunotoxin Against Folate Receptor β–Expressing Macrophages

Background Folate receptor β ( FR β) is induced during macrophage activation. A recombinant immunotoxin consisting of the truncated P seudomonas exotoxin A ( PE 38) conjugated to an anti‐ FR β antibody (anti– FR β‐ PE 38) has been reported to kill activated macrophages in inflammatory diseases. To elucidate the effect of an immunotoxin targeting FR β on atherosclerosis, we determined the presence of FR β‐expressing macrophages in atherosclerotic lesions and administered the FR β immunotoxin in apolipoprotein E–deficient mice. Methods and Results The FR β‐expressing macrophages were observed in atherosclerotic lesions of apolipoprotein E–deficient mice. At 15 or 35 weeks of age, the apolipoprotein E–deficient mice were divided into 3 groups and were intravenously administered 0.1 mg/kg of anti–FRβ‐PE38 (immunotoxin group), 0.1 mg/kg of PE38 (toxin group), or 0.1 mL of saline (control group) every 3 days, for a total of 5 times for each age group. The mice were analyzed at 21 or 41 weeks of age. Treatment with the immunotoxin resulted in 31% and 22% reductions in atherosclerotic lesions of the 21‐ and 41‐week‐old mice, respectively ( P <0.05). Administration of immunotoxin reduced the numbers of FR β‐ and tumor necrosis factor‐α–expressing macrophages, reduced cell proliferation, and increased the number of apoptotic cells ( P <0.05). Real‐time polymerase chain reaction demonstrated that the expression of FR β and tumor necrosis factor‐α mRNA was significantly decreased in the immunotoxin group ( P <0.05). Conclusions These results suggest that FR β‐expressing macrophages exist in the atherosclerotic lesions of apolipoprotein E–deficient mice and that FR β immunotoxin administration reduces the progression of atherosclerotic lesions in younger and older individuals. The recombinant FR β immunotoxin targeting activated macrophages could provide a novel therapeutic tool for atherosclerosis.