Specificity of the immunocapture for melanoma exosomes was verified by showing that: (i) consistently, non-MTEX were CSPG4(−); only MTEX were CSPG4(+) (SFig. 2a,b); (ii) exosomes from HDs’ plasma were negative for CSPG4 (SFig. 2c); (iii) only MTEX were highly enriched in MAAs (SFig. 4a); (iv) MTEX were CSPG4 (+) but CD3(−); only non-MTEX carried CD3 (SFig. 2d); (v) in spiking experiments, where melanoma exosomes were added to exosomes obtained from HDs (1:1), the captured fraction contained all CSPG4(+) exosomes, while the non-captured fraction was CSPG4(−) (data not shown). Here, CSPG4 is linked to melanoma.