An aberrant immune-epithelial progenitor niche drives viral lung sequelae

The long-term physiological consequences of respiratory viral infections, particularly in the aftermath of the COVID-19 pandemic-termed post-acute sequelae of SARS-CoV-2 (PASC)-are rapidly evolving into a major public health concern^1-3. While the cellular and molecular aetiologies of these sequelae are poorly defined, increasing evidence implicates abnormal immune responses^3-6 and/or impaired organ recovery^7-9 after infection. However, the precise mechanisms that link these processes in the context of PASC remain unclear. Here, with insights from three cohorts of patients with respiratory PASC, we established a mouse model of post-viral lung disease and identified an aberrant immune-epithelial progenitor niche unique to fibroproliferation in respiratory PASC. Using spatial transcriptomics and imaging, we found a central role for lung-resident CD8⁺ T cell-macrophage interactions in impairing alveolar regeneration and driving fibrotic sequelae after acute viral pneumonia. Specifically, IFNγ and TNF derived from CD8⁺ T cells stimulated local macrophages to chronically release IL-1β, resulting in the long-term maintenance of dysplastic epithelial progenitors and lung fibrosis. Notably, therapeutic neutralization of IFNγ + TNF or IL-1β markedly improved alveolar regeneration and pulmonary function. In contrast to other approaches, which require early intervention¹⁰, we highlight therapeutic strategies to rescue fibrotic disease after the resolution of acute disease, addressing a current unmet need in the clinical management of PASC and post-viral disease.