Intravitreally-Injected Myeloid Cells Isolated From Human Bone Marrow or Peripheral Blood Promote Vessel Repair in the Mouse OIR Model

Abstract

Purpose:: We have previously shown that myeloid progenitors isolated from mouse bone marrow differentiate into microglia and effectively promote repair of retinal vasculature in the mouse oxygen-induced retinopathy (OIR) model. In this study, we identify and characterize similar populations of myeloid cells from human bone marrow and peripheral blood that exhibit comparable repair activity in the OIR model.

Methods:: Anticoagulated human bone marrow or peripheral blood was collected from healthy donors and red blood cells were removed by lysis using ammonium chloride. The resulting nucleated cells were then sorted by FACS to obtain various myeloid subpopulations. Cells were injected intravitreally at P7 into C57BL6J mice for the OIR model. Neovascular area and vascular obliteration area were calculated at P17.

Results:: A population of human bone marrow cells similar to previously studied mouse cells (CD44hi-expressing myeloid cells) was isolated. This population of cells was CD44hi, CD11a+, CD11b+, CD11c+, CD14+, CD33+ and CD46+. After injection of human cells into mouse eyes, no evidence of rejection or toxicity was observed. These human bone marrow cells were efficacious in reducing neovascularization by 35% and area of vascular obliteration by 32% compared to vehicle injection. Using human peripheral blood, monocytes were isolated by labeling with an antibody against CD14. A population containing monocytes and granulocytes was sorted based on positive labeling for CD33. Alternatively, monocytes and granulocytes were isolated by FACS on the basis of their characteristic light scattering properties. Peripheral myeloid cells were efficacious in reducing neovascularization by as much as 50% and vascular obliteration as much as 76% compared to vehicle controls.

Conclusions:: We demonstrate that a population exists in human bone marrow that is effective at promoting vascular repair in the OIR model. We have also found that active cells are present in the myeloid fraction of human peripheral blood as well. Injection of human cells into the immunocompetent mouse vitreous was well tolerated without any adverse events observed. These results suggest that cell therapy to promote vascular repair, rather than destruction, for ischemic retinopathies may be feasible using myeloid cells from human bone marrow or peripheral blood.

Keywords: retinal neovascularization • microglia • ischemia