MLC-activation by acute lymphatic leukemia blasts.

The MLC-activating potential of 25 ALL blasts (16 "common" ALL, 6 T-ALL, 3 not identified) was investigated. Mitomycin-treated leukemic blasts or X-irradiated lymphocytes were cultured with heparinized whole blood from different healthy donors. MLC activation by blast cells was expressed as percentage of MLC activation by X-irradiated lymphocytes. Leukemic blasts showed a heterogeneous pattern of MLC activation, ranging from 2% to 245%. Eleven out of 25 cases of ALL poorly stimulated the MLC (2% to 33% response). Twelve ALL stimulated a normal response (50% to 120%); and 2/25 ALL stimulated a supranormal response (more than 200%). Four of six cases of T-ALL stimulated the MLC as efficiently as irradiated lymphocytes, 2/6 were among the poor stimulators. Most poor stimulator blasts had, however, normal MLC-activating properties if, instead of whole blood, isolated lymphocytes were used as the responding cells. The poor activation of lymphocytes by some leukemic blasts in whole blood appeared to be associated with impaired release of blastogenic factor(s) during the MLBC. No evidence for active suppressor mechanisms was found. The significance of the MLC-activating properties of leukemic blasts for the classification and immunotherapeutic use of ALL is discussed.