Efficacy of an Anti-TSLP Monoclonal Antibody in the Management of Chronic Bronchial Disease Induced by Bronchiolitis Obliterans Syndrome in Allogeneic Hematopoietic Stem Cells Transplantation Recipients

Inclusion Criteria: 1. Adult recipients, minimum age 18 2. Recipient of an allogeneic bone marrow or haematopoietic stem cell transplant 3. At more than 3 years after the date of the transplantation 4. BOS defined by the occurrence of a new fixed obstructive ventilatory disorder after the allograft (accepted criteria: FEV1/FVC ≤70% and FEV1 \< 75% pred value and decline of more than 10% over less than 2 years OR FEV1/FVC \> 70% and FEV1 \< 75% pred value and decline of FEV1 more than 10% over less than 2 years and Normal TLC \> 80% OR decline of FEV1 more than 10% over less than 2 years and TLC \> 120% and/or RV/TLC \> 40%) 5. Presenting an exacerbation profile: 2 or more moderate to severe bronchial exacerbations in the previous 12 months 6. On optimal inhaled therapy comprising at least one long-acting bronchodilator and one inhaled corticosteroid for at least three months. 7. Stable dose of systemic immunosuppressive regimen for the last 4 weeks 8. Being covered by a national health insurance 9. Signed consent form Exclusion Criteria: 1. Patients with an indication to increase their immunosuppressive treatment, in particular due to active GVH 2. FEV1\< 20% theorical value 3. Being deprived of liberty or under guardianship 4. Absence of signed consent 5. Hypersensitivity (allergy) to tezelumab or to any of the excipients of TEZPIRE 6. A helminth parasitic infection diagnosed within 6 months prior to Visit 1 that has not been treated with, or has failed to respond to, standard of care therapy 7. Respiratory infection in the course of treatement (including acute bacterial and viral infection, long term treatment for fungal or non-tuberculosis mycobacteria) 8. History of documented immune complex disease (Type III hypersensitivity reactions) following any biologic therapy 9. Severe GVHD scleroderma-like manifestations of skin making subcutaneous injections of the investigational treatment impossible or overly difficult 10. Pregnant, breastfeeding or lactating women