CD63 and small cell lung carcinoma: In particular, CD63 and CD81, two well-known specific exosomal markers of the Tetraspanins family [37], were expressed in isolated PBMC-EXs (Figure 2C), whereas the Calnexin (a known negative marker for exosomes) was selectively expressed only by SCLC cells and by donor PBMCs from SCLC patients, and it was absent in PBMC-EXs, thus confirming the identity of PBMC-EXs (Supplementary Figure S1).