Clonal selection of human T-cell leukemia virus-infected cells in vivo and in vitro.

Human T-cell leukemia virus (HTLV) subgroup I is associated with adult T-cell leukemia (ATL), but in endemic areas a significant percentage of the normal population are also carriers of HTLV. A unique property of HTLV has been its capacity to transform normal human T-cells in vitro. We have examined the state of the HTLV provirus in the leukemic cells of ATL patients, primary cell lines established from these patients and normal seropositive people, and normal T-cells transformed in vitro. We found that, in all cases, the infected cells are monoclonal or oligoclonal. Furthermore, the populations of infected cells of fresh and long-term cultured cell lines from the same leukemic patient appear to be different. We propose that the latter represents normal T-cells transformed in vitro rather than the primary leukemic cells. It is of interest that the T-cells newly infected with HTLV have an in vitro growth advantage over the primary HTLV-containing tumor cells. The results also suggest that clonal selection of infected cells occurs in vitro, resulting in cells that are immortalized and exhibit some characteristics of the primary leukemic cells. However, these cells may be at an earlier phase of transformation as compared to the circulating leukemic cells.