Bronchiolitis obliterable syndrome (BOS) is the most common cause of death in long-term survivors after lung transplantation and refractory to most interventions. Many risk factor for BOS were identified in previous studies such as acute cellular rejection, lymphocytic bronchiolitis, cytomegalovirus (CMV) and non-CMV respiratory infections, injury to the allograft or airways, Primary graft dysfunction, HLA mismatching, and organizing pneumonia. (Belperio JA. et al.). Neutrophils and their released products may be involved in the development of BOS. Neutrophilia was repeatedly observed in the bronchoalveolar lavage fluid of patients after lung transplantation. In addition, infiltration of neutrophils into the bronchial epithelium has been detected in patients with higher degrees of active airway damage. Neutrophils are capable of causing severe damage to the lung tissue by releasing toxic proteases and reactive oxygen species if not counterbalanced by the antiprotease/ antioxidant screen of the lung. Based on this background, a causal relationship between neutrophilia and the development of BOS has been proposed. (Hirsch J. et al.) Detection of unopposed Neutrophile elastase (NE) activity in BAL appears to correlate with poor outcome due to refractory BOS. Unopposed NE in these subjects may not only serve as a marker of evolving graft dysfunction but also participate in damaging the airways of the allograft and inhibit adequate bacterial clearance. Prevention of neutrophil sequestration or inhibition of NE may prevent or attenuate airway damage and improve bacterial clearance mechanisms. (Nutley D et al.) These data demonstrate the importance of neutrophils and unopposed NE in the pathogenesis of BOS and call for new approach to prevent or modulate BOS targeting this mechanism.

AAT is the main inhibitor of neutrophil elastase in the lower airways and patients with AAT deficiency have low concentrations of the protein in this region of the lung. This explains the proteinase/antiproteinase theory of the development of emphysema in deficient patients in which the amount of elastase released in the lung exceeds the amount of AAT. The net result is persistence of elastase activity leading to lung destruction and the pathological changes of emphysema. (Abusriwil H. et al.) The administration of the AAT is to address proteinase/antiproteinase imbalance.

Administration of AAT will help to prevent further destruction of the lung architecture and reduce the inflammatory dysregulation that causes pulmonary dysfunction. It is expected that by attacking a specific and previously untreated key component part of the pathophysiological cycle of BOS, AAT therapy would decrease the prevalence of BOS in lung transplant recipients and prolong life expectancy of these patients.

Inclusion Criteria:• Patients aged ≥18 years

• Signature of informed consent
• Lung transplant recipient in the past 6 months.
• Stable concomitant therapy >2 weeks prior to visit 1
• Non-tobacco user of any kind
• No significant abnormalities in serum hematology, serum chemistry to the Principal Investigator's judgment((Hg>8g/dL ,Creatinine<2mg/dl,Liver enzymes<3*ULN)
• Non-pregnant, non-lactating female subjects, whose screening pregnancy test is negative and who are using contraceptive methods deemed reliable by the investigator, or who are more than 5 years post-menopausal or surgically sterilized or whose way-of-life excludes sexual activity.
• Sexually active female subjects of child-bearing potential, as well as male subjects, must use a medically acceptable effective contraceptive method (for male - method such us condoms; for female - methods such as oral contraceptive medication used for at least two weeks before study start, or a combination of any two of the following: diaphragm, cervical cap, condom or spermicide), before study start and throughout the entire duration of the study.

Exclusion Criteria:• Diagnosis of BOS with according to Estenne M. et al.

• Hospitalization within 1 month before study entry, not due to an airway disease
• Severe liver cirrhosis with ascites
• Hypersplenism
• Grade III/IV esophageal varices;
• Active pulmonary exacerbation within the 4 weeks prior to screening
• History of massive hemoptysis: greater than 200 cc in a 24 hour period
• Pregnancy or breastfeeding
• Any serious or active medical or psychiatric illness which, in the opinion of the investigator, would interfere with patient treatment, assessment, or compliance with the protocol.
• Fever at the time of the start of first (day #1) inhalation (oral temperature >38ºC)
• Evidence of uncontrolled hypertension
• Pulse >120/min (prior to study drug administration)
• Any serious malignancy except for basal and squamous (scaly or plate-like) cell skin cancer within the previous 3 years prior to study start
• Receipt of exogenous AAT within the last 6 months
• Previous enrolment in this study (subject can not be enrolled twice into the study)
• Evidence of congestive heart failure or other clinically significant cardiovascular conditions: myocardial infarction during the last year, arrhythmia requiring drug treatment during the last year, uncontrolled hypertension
• Current smoker (someone who has smoked within 4 weeks prior to screening)
• Subjects with an additional clinically significant inter-current illness (beside lung disease) (e.g., cardiac, hepatic, renal, endocrine, respiratory, neurological, hematological, neoplastic, immunological and skeletal) that the investigator determines that it could interfere with the safety or other assessments of this study
• Any evidence of alcohol abuse or history of abuse of illegal and/or legally prescribed drugs such as barbiturates, benzodiazepines, amphetamines, cocaine, opioids, and cannabinoids
• Being a sexually active female of child-bearing age without adequate contraception
• Any other factor that, in the opinion of the investigator, would prevent the subject form complying with the requirements of the protocol