Decay accelerating factor (CD55)-mediated attenuation of complement: therapeutic implications for age-related macular degeneration.
OBJECTIVE
Sequence variations in complement proteins are associated with age-related macular degeneration (AMD). The terminal pathway of complement results in the formation of the membrane attack complex (MAC) on the cell surface, resulting in their lysis. MAC has been documented on the retinal pigment epithelium (RPE), choroidal blood vessels, and drusen of AMD eyes. Here the investigators test the hypothesis that increasing the expression of decay accelerating factor (CD55) on RPE cells may result in reduced MAC-mediated damage.


METHODS
The investigators constructed a recombinant adenovirus expressing human CD55 (AdCAGCD55). Mouse hepatocytes were infected with AdCAGCD55 or negative controls and subsequently incubated with normal human serum (NHS). Cell lysis and MAC formation were measured by FACS and immunocytochemistry, respectively. Adult mice were injected in the subretinal space with either AdCAGCD55 or controls; after 1 week of CD55 transgene expression, the eyecups were excised, challenged with NHS, and quantified for human MAC formation.


RESULTS
Control-infected or uninfected mouse hepatocytes lyse at a rate of 93% and 94%, respectively. AdCAGCD55- infected mouse hepatocytes lyse at a rate of 29%. Lysis was confirmed to occur in the presence of MAC, which was reduced by 67% when cells were infected by AdCAGCD55. Mice injected in the subretinal space with AdCAGCD55 exhibited a 55.7% reduction in MAC formation on the RPE relative to controls.


CONCLUSIONS
Adenovirus-mediated delivery of hCD55 to murine RPE confers protection against human complement. The investigators propose that the expression of hCD55 on RPE cells warrants investigation as a potential therapy for AMD.
Ma
Kelly N
KN
Department of Ophthalmology, Tufts University School of Medicine, Boston, MA 02111, USA.
Cashman
Siobhan M
SM
Sweigard
J Harry
JH
Kumar-Singh
Rajendra
R
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015153:Blotting, Western; D018958:CD55 Antigens / Q000235:genetics / Q000627:therapeutic use*; D002460:Cell Line; D015938:Complement Membrane Attack Complex / Q000378:metabolism*; D003165:Complement System Proteins / Q000502:physiology*; D005434:Flow Cytometry; D015870:Gene Expression / Q000502:physiology; D015316:Genetic Therapy; D005822:Genetic Vectors; D006461:Hemolysis / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism / Q000821:virology; D006801:Humans; D007150:Immunohistochemistry; D008268:Macular Degeneration / Q000378:metabolism / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D019076:Transgenes
D018958:CD55 Antigens; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins