Establishment of Transplantable Tumor Lines and in vitro Cell Lines of Malignant Thymoma Developed in a BUF/Mna Rat

A spontaneous malignant thymoma was found in an 18‐month‐old female BUF/Mna rat and serially transplanted subcutaneously in both syngeneic BUF/Mna rats (designated as MTH‐R) and KSN nude mice (MTH‐NM) for more than 5 years. Both tumors shared the histological appearance of sarcomatoid carcinoma as seen in the original tumor. However, MTH‐NM grew faster than MTH‐in the respective hosts. The MTH‐NM grew in both KSN‐nude mice and BUF/Mna‐ rnu/rnu rats but not in BUF/Mna rats the host of the original tumor. Three continuous tissue culture cell lines (MTHC‐1, MTHC‐2 and MTHC‐3) were established from the MTH‐NM tumors at the 2nd, 15th and 17th transplantation generations, respectively. The MTH‐NM tumors and latter two tissue culture cell lines carried one or more mouse chromosomes, probably acquired by cell fusion with mouse cells during passages in vivo. The presence of the mouse chromosomes was confirmed by the presence of mouse DNA and of antibodies to the MTHC‐2 and MTHC‐3 cells in the sera of BUF/Mna rats transplanted with MTH‐NM.