Modeling Idiopathic Pulmonary Fibrosis in Humanized Severe Combined Immunodeficient Mice

Abstract

Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease of unknown etiopathogenesis with limited therapeutic options. IPF is characterized by an abundance of fibroblasts and loss of epithelial progenitors, which cumulates in unrelenting fibrotic lung remodeling and loss of normal oxygenation. IPF has been challenging to model in rodents; nonetheless, mouse models of lung fibrosis provide clues as to the natural progression of lung injury and remodeling, but many have not been useful in predicting efficacy of therapeutics in clinical IPF. We provide a detailed methodologic description of various iterations of humanized mouse models, initiated by the i.v. injection of cells from IPF lung biopsy or explants specimens into severe combined immunodeficiency (SCID)/beige or nonobese diabetic SCID g mice. Unlike cells from normal lung samples, IPF cells promote persistent, nonresolving lung remodeling in SCID mice. Finally, we provide examples and discuss potential advantages and pitfalls of humanspecific targeting approaches in a humanized SCID model of pulmonary fibrosis.

Targeting Lysyl oxidase-like 2 in Idiopathic Pulmonary Fibrosis

“…In our study using a humanized SCID mouse model to examine pulmonary fibrosis, we did not observe either a preventative or therapeutic effect of Simtuzumab. The introduction of primary lung cells from IPF explants initiates and sustains a fibrotic response in the lungs of humanized SCID mice and we have observed that this model is responsive to anti-fibrotic therapies 19 , although Nintedanib showed no therapeutic effect in the humanized SCID IPF fibroblast model 21 . The failure of Simtuzumab in this model was unlike that observed in the bleomycin-induced pulmonary fibrosis model 16 , and highlights the need for multiple model testing before moving a target into the clinic.…”

“…Normal and IPF lung explants were acquired from consented donors. Fresh explant cells were isolated as previously described 19 .…”

“…Since the failure of Simtuzumab in this IPF trial was unexpected given the convincing preclinical data generated in mouse, we undertook both in vitro and in vivo studies to address the efficacy of Simutuzumab in translational studies. Specifically, we examined the effect of this mAb in primary human fibroblasts from both normal lung donor samples and explanted IPF lung samples and in a humanized SCID model of IPF 19 . Overall, our data suggested that targeting the cross-linking of ECM with Simtuzamab promoted IPF fibroblast to myofibroblast transition and increased IPF fibroblast invasion.…”

“…Thus, the presence of Simtuzumab appeared to accelerate the outgrowth of both normal and IPF fibroblasts from dissociated lung samples.Preventative or therapeutic targeting of LOXL2 fails to alter lung fibrosis in a humanized SCID mouse model of IPFOur last study addressed the role of LOXL2 in vivo using a humanized SCID model of IPF in which approximately half a million freshly isolated mixed cell populations from explanted IPF lungs are injected intravenously into SCID mice to initiate the lung fibrotic process19 . In this model, fibrosis appears in the lung approximately 30-35 days after human cell injection and the fibrosis persist beyond the day 63 timepoint we typically end our studies19 .In our present study, we employed a preventative treatment modality that involved the injection of 15 mg/kg of IgG or Simtuzumab twice a week up to day 35. In a separate therapeutic study, injections of either IgG or Simtuzumab at 15 mg/kg twice a week began at day 35 and continued up to the termination of the study at day 63.…”

Interleukin-13 disrupts type 2 pneumocyte stem cell activity

“…POSTN has been identified as a biomarker that is associated with IPF prognosis (63,64), but to the best of our knowledge, POSTN levels have not been directly correlated with IL-13 levels in IPF. Next, it has been proposed by others that direct targeting of IL-13 may enhance the expression of profibrotic/inflammatory transcripts (65), and alternative indirect IL-13-targeting strategies should be considered. Moreover, our data suggest that IL-4 and IL-13 have redundant effects on AEC2 stem cell biology, and targeting only 1 of these cytokines with a specific monoclonal antibody may be insufficient.…”