Chelation therapy can be toxic and has the potential to cause kidney damage, irregular heartbeat, and even death."[135] Cytokine therapy (or Klehr's autologous tumor therapy) – a so-called immunotherapy with a therapeutic substrate made of cytokines from the cancer patients' blood.[136][137] The inventor of this method is Nikolaus Walther Klehr, a dermatologist, who practiced it in his private clinics in Salzburg and Munich.[138] The patients were mainly from Slovenia, Poland and other Eastern European countries.