Fig. 1From: Evolving insights into the improvement of adoptive T-cell immunotherapy through PD-1/PD-L1 blockade in the clinical spectrum of lung cancerThe putative origin of lung cancer stem cells in lung anatomical sites. In the trachea and main bronchi, airway basal cells are considered as a stem cell population, precursors of squamous cell lung carcinoma. Pulmonary neuroendocrine (PNE) cells are thought to serve as a precursor for the progress of small cell lung carcinoma. It is also believed that adenocarcinomas can originate from broncho alveolar stem cells or pneumocytes of type I and type IIBack to article page