In vitro sensitivity of transplantable leukemias to endogenous granuloid (GCE, GI-2) and lymphoid (T4, T4-1) inhibitors of proliferation.

The effect on cell proliferation of crude granulocyte and thymocyte extracts (GCE, T4) and of their target-specific fractions (GI-2, T4-1) was studied in cultures with transplantable subacute myeloid and lymphoid leukemia (ML, LL). In the dose rage studied (1-500 microgram/ml) each factor reduced 3H-TdR incorporation into acid-insoluble DNA of bone marrow, thymus and spleen cells with ML or LL as a function of the dose, approximately linearly. Normal bone marrow proved to be less sensitive to GCE than the ML one: according to parallel line bioassay by a factor of mu = 0.56. The reactivity of LL spleen and thymus is also higher to medium T4-1 concentrations (50-200 microgram/ml) than that of normal lymphoid populations. T4-1 inhibits 3H-TdR incorporation into the DNA of LL spleen cells submaximally in 90': this effect lasts for greater than 7 hours. Because of its more homogeneous cell composition and higher sensitivity, subacute myeloid leukemia is more suitable for screening endogenous granuloid inhibitors than are homologous normal cell cultures.