Sequential Roles of VLA-4/VCAM-1 Interactions and CXCR4/CXCL12 Cues in the Early Phases of Injured Lung Regeneration by Lung Cell Transplantation

Lung cell transplantation has demonstrated remarkable regenerative potential in various mouse models of lung injury, including pulmonary fibrosis. However, early processes governing donor cell lung homing and fate following transplantation remain poorly understood. This study interrogates mechanisms underlying donor cell homing, extravasation, and formation of regenerative patches inside recipient lungs after i.v. infusion of CD45- lung cells. Naphthalene (NA) and total body irradiation (TBI) were used to induce lung injury. Donor derived lung cell suspensions were infused intravenously, and donor cell localization were analyzed at various time points using flow cytometry and immuno-fluorescence. The functional roles of VCAM-1/VLA-4 and CXCL12/CXCR4 interactions in early donor cell homing to injured lungs were assessed by incubating donor cells with anti-VLA-4 or anti-CXCR4 blocking antibodies or by pre-treatment of recipient mice with anti-VCAM-1 antibody. At 24 hours post-infusion, only 0.8% of infused cells accumulated inside the lungs, with approximately a third of the cells within the pulmonary vasculature. By day seven, 97% of donor cells were found in the lung parenchyma. These donor cells were highly proliferative and formed regenerative patches by day 21. Blocking VLA-4 or CXCR4 inhibited adhesion of infused cells to blood vessels early after infusion and interfered with subsequent formation of regenerative donor-derived lung patches at 6 weeks post-infusion. This study highlights the sequential roles of VLA-4/VCAM-1 and CXCR4/CXCL12 interactions in facilitating donor lung cell homing and regenerative patch formation in injured lungs.