Early pathologic findings of bronchiolitis obliterans after allogeneic hematopoietic stem cell transplantation: a proposal from a case

Characterization of localized macrophages in bronchiolitis obliterans after allogeneic hematopoietic cell transplantation

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) remains one of the most devastating manifestations of chronic graft-versus-host disease in hematopoietic cell transplantation (HCT). Recent findings of BOS after lung transplantation indicate that donor (lung)-derived lung-resident macrophages contribute to BOS, suggesting that differences in the origin of immune cells and localized antigen-presenting cells cause the onset of BOS.

METHODS

We identified the phenotype and origin of infiltrating macrophages using immunohistochemistry and fluorescence in situ hybridization in eight sex-mismatched HCT recipients who underwent lung transplantation for BOS after HCT.

RESULTS

Most of the infiltrating macrophages appeared to be derived from donor (hematopoietic) cells in patients who developed BOS following HCT. Macrophages observed in the early-stage region of BOS were positive for cluster of differentiation (CD)68 and inducible nitric oxide synthase (iNOS) and negative for CD163 and CD206, suggesting an M1 phenotype. In the late-stage region, macrophages were negative for CD68 and iNOS in all patients, but also positive for CD163 and CD206 in some patients.

CONCLUSIONS

Donor-derived M1-macrophages may be involved in the pathogenesis of the early-stage region of BOS. In addition, some macrophages in the late-stage region showed M2 polarization that might be involved in fibrosis.

Lung histology predicts outcome of bronchiolitis obliterans syndrome after hematopoietic stem cell transplantation

Bronchiolitis obliterans (BO) is a severe complication after allogeneic hematopoietic stem cell transplantation with an unfavorable prognosis. Lung biopsy remains the gold standard for diagnosis. In this retrospective single-center study, we describe 33 patients who underwent biopsy for suspected BO. Ten patients had constrictive BO (CBO); 9 had lymphocytic bronchiolitis (LB), characterized by lymphocytic infiltration of the bronchioles. Six additional patients (4, CBO; 2, LB) had concomitant infection; 8 had other pathological diagnoses. Seven patients with CBO and 3 with LB met the National Institutes of Health consensus BO syndrome definition criteria. An additional 7 patients with histologically confirmed CBO did not meet the consensus definition, 4 of them because of concomitant airway infection. At diagnosis, there were no significant differences between the CBO and LB groups in clinical presentation; pulmonary function tests (median forced expiratory volume in one second [FEV1] at baseline, 90.4% and 99% predicted, at time of video-assisted thoracoscopic surgery, 55.1% and 60.8% for CBO and LB groups, respectively); and chest scans. Treatment was similar in both groups but outcome was different depending on histological findings. FEV1 significantly improved in LB patients compared with CBO patients. Survivals at 1 and 3 years were 77% ± 12% and 60% ± 14% for patients with CBO and 91% ± 9% for patients with LB (P = .028). Lung biopsy in patients with suspected BO enables better characterization of the pattern of BO syndrome. In contrast to CBO, LB is associated with a good long-term prognosis.