Influence of leukaemic cells on the colony formation of human bone marrow cells in vitro II. Suppressive effects of leukaemic cell extracts.

The influence of leukaemic cells on the colony formation of human bone marrow cells was studied in vitro as an extension of our previous work (Chiyoda et al., 1975). An extract of leukaemic bone marrow cells significantly suppressed colony forming ability of the normal bone marrow cells, whereas an extract of normal bone marrow cells did not suppress it except in two cases. The suppressive effect of normal bone marrow cells, however, was obviously less intense than that of leukaemic cells. This suppressive effect was dose dependent and was fairly stable to heat treatment. These results suggest that leukaemic bone marrow cells contain factor(s) which suppress normal colony formation.