Inhibiting CXCL12 blocks fibrocyte migration and differentiation and attenuates bronchiolitis obliterans in a murine heterotopic tracheal transplant model

Abstract

Objectives Fibrocytes are integral in the development of fibroproliferative disease post lung transplantation. Undifferentiated fibrocytes (CD45+Col1+CXCR4+) preferentially traffic via the CXCR4/CXCL12 axis and differentiate into smooth muscle actin producing (CD45+CXCR4+αSMA+) cells. We postulated that an antibody directed against CXCL12 would attenuate fibrocyte migration and fibro-obliteration of heterotopic tracheal transplant allografts. Methods A total alloantigenic mismatch murine heterotopic tracheal transplant model of obliterative bronchiolitis was used. Animals were treated with either goat-anti-human CXCL12 F(ab′)2 or Goat IgG F(ab′)2. Buffy coat, bone marrow, and trachea allografts were collected and analyzed by flow cytometry. Tracheal luminal obliteration was assessed via hematoxylin/eosin and Direct Red 80 collagen stain. Results Compared to controls, anti-CXCL12 treated animals showed a significant decrease in tracheal allograft fibrocyte populations at 7 and 21 days post-transplantation. Bone marrow and buffy coat aspirates showed the same trend at 7 days. In anti-CXCL12 treated mice, there was a 35% decrease in luminal obliteration at 21 days (65.00 [interquartile range = 38]% vs. 100 [10]% obliterated; p=0.010) and decreased luminal collagen deposition at 21 and 28 days post transplantation (p=0.042 and 0.012, respectively). Conclusions Understanding the role of fibrocytes in airway fibrosis post lung transplantation may lead to a paradigm shift in treatment strategy. Anti-CXCL12 antibody afforded protection against infiltrating fibrocytes and reduced deterioration of tracheal allografts. Thus the CXCR4/CXCL12 axis is a novel target for the treatment of fibro-obliteration post lung transplantation and quantification of fibrocyte populations may provide clinicians with a biomarker of fibrosis allowing individualized drug therapy.

Local Origin of Mesenchymal Cells in a Murine Orthotopic Lung Transplantation Model of Bronchiolitis Obliterans

“…In heterotopic tracheal transplant models, mesenchymal cells have been shown to be derived from the recipient rather than the donor, 29 and the fibrocyte population is being investigated. 27,28 Similar findings of recipient derivation of mesenchymal cells was suggested in an intrapulmonary tracheal transplant model of BO using immunofluorescent staining. 56 The contrary finding of the predominant donor origin of collagen Ieexpressing cells in murine lung allografts in the present study could reflect the investigation of fibrosis in a whole-lung allograft rather than in an isolated trachea.…”

Rapamycin Blocks Fibrocyte Migration and Attenuates Bronchiolitis Obliterans in a Murine Model

“…According to our previous studies [11], peak tracheal allograft fibrocyte infiltration occurs 7 days post transplantation. Therefore, flow cytometry was used to assess blood, bone marrow, and tracheal allograft fibrocyte levels in animals sacrificed on day 7.…”

“…Flow cytometry was performed as previously described [11]. Single cell suspensions were isolated from bone marrow, blood, and tracheal grafts.…”

“…In a bleomycin-treated murine model of IPF, treatment with an anti-CXCL12 antibody or a direct CXCR4 antagonist have both shown protective effects against the development of fibrosis [10, 17]. Similarly, our lab has demonstrated that treatment with an anti-CXCL12 antibody effectively attenuates allograft fibro-obliteration in a murine HTT model of BO [11]. Xu and colleagues have corroborating data, reporting a significant reduction in luminal obliteration after treatment with a CXCR4 antagonist in the murine HTT model [18].…”

“…Our lab has previously shown that blocking this axis with an anti-CXCL12 antibody reduces fibrocyte levels in the circulation and in transplanted allografts in a murine heterotopic tracheal transplant (HTT) model of BO [11]. Furthermore, anti-CXCL12 treatment limits the allograft fibro-obliteration characteristic of BO.…”