PCR-based monitoring of clonal H-RS cells in different blood and tissue samples from two patients with relapsed HD for 3 years from March 1994 to May 1997. Collection of samples analyzed from a patient with NS-HD (patient no. 1) and from a patient with MC-HD (patient no. 2). (▧) Specific PCR products were amplified from these samples with clone-specific primers. (□) No PCR products were detected in the DNA samples. (*) Single-cell PCR was performed from a frozen tissue section. Abbreviations: BM, bone marrow aspirate; LN, lymph node tissue; AP, apheresis material; LI, liver tissue; SP, spleen cells; PB, peripheral blood; CD34⁺, MACS-separated CD34⁺ cells.