Identification of cancer stem cell subpopulations of CD34⁺ PLC/PRF/5 that result in three types of human liver carcinomas

CD34⁺ stem cells play an important role during liver development and regeneration. Thus, we hypothesized that some human liver carcinomas (HLCs) might be derived from transformed CD34⁺ stem cells. Here, we determined that a population of CD34⁺ cells isolated from PLC/PRF/5 hepatoma cells (PLC) appears to function as liver cancer stem cells (LCSCs) by forming HLCs in immunodeficient mice with as few as 100 cells. Moreover, the CD34⁺ PLC subpopulation cells had an advantage over CD34^- PLCs at initiating tumors. Three types of HLCs were generated from CD34⁺ PLC: hepatocellular carcinomas (HCCs); cholangiocarcinomas (CC); and combined hepatocellular cholangiocarcinomas (CHCs). Tumors formed in mice transplanted with 12 subpopulations and 6 progeny subpopulations of CD34⁺ PLC cells. Interestingly, progenies with certain surface antigens (CD133, CD44, CD90, or EPCAM) predominantly yielded HCCs. CD34⁺ PLCs that also expressed OV6 and their progeny OV6⁺ cells primarily produced CHC and CC. This represents the first experiment to demonstrate that the OV6⁺ antigen is associated with human CHC and CC. CD34⁺ PLCs that also expressed CD31 and their progeny CD31⁺ cells formed CHCs. Gene expression patterns and tumor cell populations from all xenografts exhibited diverse patterns, indicating that tumor-initiating cells (TICs) with distinct antigenic profiles contribute to cancer cell heterogeneity. Therefore, we identified CD34⁺ PLC cells functioning as LCSCs generating three types of HLCs. Eighteen subpopulations from one origin had the capacity independently to initiate tumors, thus functioning as TICs. This finding has broad implications for better understanding of the multistep model of tumor initiation and progression. Our finding also indicates that CD34⁺ PLCs that also express OV6 or CD31 result in types of HLCs. This is the first report that PLC/PRF/5 subpopulations expressing CD34 in combination with particular antigens defines categories of HLCs, implicating a diversity of origins for HLC.