The higher frequency and faster kinetics of RR formation in HeLa compared to COS-7 cells could be based on other differences between these cell types, as COS-7 is originated from green monkey kidney while HeLa is from a human cervical cancer, and previous reports shows higher expression of IMPDH2 in cancer cells [34, 35]. The gene discussed is IMPDH2; the disease is cervical carcinoma.