THP-1 cells. Coloured scanning electron micrograph (SEM) of cultured THP-1 cells. THP-1 stands for human acute monocytic leukaemia cell line, the descendants of cells taken from the blood of a 1 year old male with acute monocytic leukaemia (bone marrow cancer). These cells are used in cancer research for analysing the characteristics and mechanics of leukaemia. They are also used to test their resistance to specific drugs. Magnification: x1670 when printed 10 centimetres wide.