E rosette-positive agar colonies containing the Philadelphia chromosome in chronic myeloid leukaemia

In an attempt to document possible T-cell involvement in chronic myeloid leukaemia, E rosette-positive colonies (ERPC) were grown in agar culture using a T-cell-conditioned medium. Colonies were grown from whole mononuclear cells (WMN), nonadherent E rosette-positive (NAT+) and nonadherent E rosette-negative (NAT-) cells. Cells collected from the colonies after 10 d in culture were 99-100% E rosette-positive. 8 metaphases were obtained from both NAT+ and NAT- ERPCs. In NAT- ERPCs, 5 out of 8 metaphases were positive for the Philadelphia (Ph1) chromosome as compared to 1 Ph1 positive out of 8 metaphases in the NAT+ ERPCs. These results suggest that, at least in this particular patient we studied, a subpopulation of E rosette-positive cells derived from the NAT- cell fraction express the Ph1 chromosome.