Cutting edge: lymphatic vessels, not blood vessels, primarily mediate immune rejections after transplantation

Abstract

The purpose of this study was to determine the relative importance of blood vessels (hemangiogenesis) versus lymphatic vessels (lymphangiogenesis) in mediating immunological responses after transplantation. Using the murine model of corneal transplantation, graft survival was compared in differentially prevascularized and avascular recipient beds. Donor corneas (C57BL/6) were transplanted into uninflamed or inflamed avascular, prehemvascularized only or prehemvascularized and prelymphvascularized recipient murine eyes (BALB/C). Selective inhibition of lymphangiogenesis was achieved using antivascular endothelial growth factor receptor 3 Abs and anti-integrin alpha5 small molecules. Grafts placed into only prehemvascularized recipient beds had a similarly good graft survival compared with grafts placed into completely avascular, normal recipients, whereas the pre-existence of lymphatic vessels significantly deteriorated corneal graft survival (p < 0.05). Lymphatic vessels seem to contribute significantly to graft rejection after (corneal) transplantation. That may allow for selective, temporary, perioperative antilymphangiogenic treatment to promote graft survival without affecting blood vessels, even after solid organ transplantation.

FIGURE 1

Generation of different transplantation models. Schematic diagram showing the generation of normal-risk (avascular), high-risk (inflamed and hemvascularized and lymphvascularized), avascular high-risk (inflamed, but avascular, recipients), and alymphatic high-risk recipient beds (inflamed and hemvascularized, but no lymphatic vessels) as transplantation models.

FIGURE 2

Lymphatic vessels in the recipient bed prior to transplantation determine graft survival. In the 2 wk prior to transplantation (when corneal suture placement was used to induce pathologic corneal neovascularization in the recipient bed), mice were treated with VEGF-Trap_R1R2 (a [red line] and c; resulting in no blood or lymphatic vessels, but reduced inflammation in the recipient bed at the time of transplantation), the VEGFR3 Ab mF4-31C1 (a [green line] and d; resulting in no lymphatic vessels, but only blood vessels present in the recipient bed at the time of transplantation), or the JSM6427 integrin α5β1 inhibitor (b [blue line] and e; resulting in no lymphatic vessels, but only blood vessels, present in the recipient bed at the time of transplantation). Graft survival was compared with prehemvascularized and prelymphvascularized controls (a and b [black line], f: “high-risk” recipient bed) and avascular recipient controls (a and b [dotted line], g: “low-risk” recipient bed). The graft survival was significantly better when transplants were placed into recipient beds lacking lymphatic vessels compared with beds with lymphatic vessels present at the time of transplantation (VEGF-Trap versus high-risk: p < 0.0001; VEGFR3 versus high-risk: p < 0.0002; n = 10; JSM6427 versus high-risk: p < 0.032, n = 23; Kaplan–Meyer survival curve). (c–g) Representative images of recipient corneal beds at the time of transplantation after corneas were treated with VEGF-Trap_R1R2 (c), mF4-31C1 (VEGFR3 Ab) (d ), JSM6427 (e), or untreated high-risk (f ) and normal-risk (g) recipient beds (original magnification ×100). Green, blood vessels; red, lymphatic vessels; arrow, prevascularized cornea.