However, since many, if not all, of the current trials lack target engagement markers confirming the ability of the agent to reach the target TNFα producing cells, it would be of particular interest to study access of anti-TNFα antibodies or antibody-like proteins into sputum plugs where we suggest the main fraction of steroid resistant cells reside in COPD. The gene discussed is TNF; the disease is chronic obstructive pulmonary disease.