The goal of this observational study is to learn about dynamic changes of Torquetenovirus (TTV) load in Chinese renal transplant recipients. The main questions it aims to answer are: - Is there correlation between TTV load and rejection? - Is there correlation between TTV load and infection? - Can changes in the TTV load of kidney transplant recipients predict rejection or infection? Participants will: - receive 13 follow-up visits within 1 year after kidney transplantation - provide 2 ml of whole blood for TTV load testing and other related testing at each follow-up - provide 10 ml of whole blood for dd-cfDNA testing at four follow-ups (1, 3, 6 and 12 months after transplantation) - provide 1 ml of serum for donor-specific antibody testing at three follow-ups (1, 6 and 12 months after transplantation)