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Timothy R Catchpole, Karl G Csaky; Bv8 expression and Anti-VEGF Refractoriness in Patients with Neovascular Age-Related Macular Degeneration (nvAMD). Invest. Ophthalmol. Vis. Sci. 2014;55(13):614.
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Intravitreal injections of anti-VEGF agents have become the mainstay of therapy for nvAMD. However, the long-term response to anti-VEGF therapy is highly variable, with 10 - 20% of subjects requiring only a few injections to control the choroidal neovascularization activity while over 50% of patients requiring frequent, almost monthly, injections (a condition termed anti-VEGF refractoriness). Expression of the pro-angiogenic chemokine Bv8 in CD11b-positive cells has been linked to anti-VEGF refractoriness in animal models (Shojaei et al Nature 2007). Here we investigate Bv8 expression in circulating CD11b-positive cells in nvAMD subjects to determine if there is a correlation between Bv8 levels and response to anti-VEGF treatment.
Peripheral blood mononuclear cells (PBMC’s) were isolated via the FICOLL Hypaque method from subjects with nvAMD. Subjects were classified as refractory or non-refractory to anti-VEGF treatment based on frequency of anti-VEGF injections in the preceding 12 months prior to recruitment. CD11b-positive populations were isolated using magnetic bead sorting (Miltenyi Biotec). RNA was isolated from the sorted cells and quantitative Bv8 gene expression was analyzed using Taqman qPCR. Relative Quantification (RQ) values were determined by normalizing to the subject demonstrating the lowest Bv8 expression.
CD11b-positive cells comprised on average 28.3% of the PBMC population (range 16.2-51.5%), comparable to reported numbers in the literature. Subjects classified as refractory to anti-VEGF treatment (n=17) had an average RQ value of 6.5±4 (range 1.4-12.7). A majority of the subjects classified as non-refractory (6 of 8) had an RQ value below the average of the refractory group (average = 4.7±2.7, range 1-9.4).
These initial results suggest that elevated Bv8 levels may be associated with anti-VEGF refractoriness in nvAMD. More subjects will be recruited to determine if this observation is statistically significant. If validated, Bv8 expression in CD11b-positive cells may be a promising target for co-therapy alongside anti-VEGF treatment, improving the efficacy for refractory nvAMD subjects.
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