Abstract Rationale The long-term survival of lung transplant recipients remains low, with chronic lung allograft dysfunction (CLAD) accounting for roughly 40% of mortality after the first year. The most virulent phenotype of CLAD is restrictive allograft syndrome (RAS), with the average patient surviving just 6-18 months post-diagnosis. New therapeutic options must target the mechanisms unique to CLAD phenotypes to improve patient prognoses. Our previous work implicated both intragraft accumulation of antibody-secreting cells (ASCs), and IL6 trans-signaling-mediated fibrogenic transformation of lung-resident mesenchymal cells (MCs) in RAS pathogenesis. Additional data demonstrated that CXCL12 and IL6 expression in a subtype of MCs is mediated through an IL6 trans-signaling-mediated JAK1/2 to p-STAT3 (Tyr705) mechanism, with clear inferences for ASC recruitment and survival, and fibrogenesis in RAS. This led us to investigate the in vivo relevance of IL6 trans-signaling inhibition via novel soluble gp130Fc drug candidate Olamkicept in our murine model of RAS to ameliorate intragraft ASC infiltration and reduce allograft fibrogenesis. Methods Single, left lung transplants used B6D2F1/J donors and C57BL/6J recipients to generate RAS allografts. Mice were treated with Olamkicept (2.5 mg/kg, 1x weekly, intraperitoneal injections) or saline, and harvested at day 28 post-transplant. Allografts were then processed for either immunohistochemistry (IHC), flow cytometry, ELISA, hydroxyproline, and organoculture. Results A 50% reduction in CXCL12 protein expression, and a ∼40% reduction in circulating donor-specific IgGs (but not IgMs) was observed in Olamkicept-treated allografts when compared to saline controls. Organoculture results recapitulated these findings, with Olamkicept-treated allografts demonstrating 50% reductions in both intra-allograft CXCL12 protein and donor-specific IgGs. Utilizing Blimp1EYFP reporter mice as recipients, FACS analyses revealed that Olamkicept treatment reduced not only Blimp1+CD138+ ASCs, but also total CD45+ and CD19+ cells compared to allograft controls. These findings were confirmed via immunostaining. Analysis of CCSP via IHC revealed near complete loss of epithelial integrity in allograft controls, but was largely preserved in Olamkicept-treated allografts. Movat Pentachrome staining showed decreased collagen deposition with Olamkicept treatment, and quantitative assessment of collagen deposition via hydroxyproline assay confirmed a significant reduction in fibrosis. Conclusions Delineation of the role for IL6 trans-signaling in CXCL12 induction by lung-resident MCs furnished the basis for novel therapeutic targeting of this pathway via Olamkicept. Our data provide the first evidence for use of Olamkicept in both remediation of local humoral immune infiltration and fibrosis, with implications for rapid translation to lung transplant patient care. This abstract is funded by: NIH/NHLBI, Cystic Fibrosis Foundation
Tadokoro et al. (Fri,) studied this question.