Cell tracking detection of human DNA in mice transplanted with human PB-MNC and PB-MNC+. DNA was extracted from mouse tissues and amplified using PCR to detect the human-specific P17H8 satellite sequence. Agarose gel analysis of PCR products demonstrated the presence of a 1171-bp human-specific fragment as early as one hour after cell injection mainly in the ipsilateral hemisphere and in the lungs of PB-MNC+ and unstimulated PB-MNC-treated mice. At D1 after injection, human DNA was readily detectable in the lungs, spleen, liver, and kidneys and in the contralateral hemisphere, whereas human DNA was still present in the ipsilateral hemisphere and had increased in the lungs. Signal disappeared from all organs, including brain, by D14 ().