In vitro development of lymphocytes that function as progenitors for mucus‐secreting lymphokine‐activated killer (LAK) cells

Two different types of cultures developed when two different interleukin 2 (IL‐2) preparations were introduced into cultures of lymph node cells of nulnu (nude) mice maintained on an embryonic fibroblast monolayer. In the first, human recombinant IL‐2 (rIL‐2) stimulated the generation of colonies of large cytotoxic cells identified as lymphokine‐activated killer (LAK) cells that, when grown on mesenchyme fibroblastoid monolayers prepared from 16‐ to 18‐day embryos, could be triggered to synthesize and secrete flowing mucoid material. In the second culture, crude supernatant from cultures of rat spleen cells stimulated by concanavalin A stimulated the appearance and multiplication of blast cells that, after 20 days, differentiated into lymphocytes. This population was homogeneously composed of “wandering” lymphocytes and could be kept in a stable resting form for at least 2 months without loss of viability. When exposed to rIL‐2, this whole lymphocyte population underwent a transformation into blast cells that, on the fourth day, generated granules, became cytotoxic, and differentiated into granular mucus‐secreting LAK cells. When low numbers of these transformed premitotic blast cells were plated on mitomycin C‐treated embryonic fibroblast monolayers, one cell out of 15 to 20 generated a clone of LAK cells. The study demonstrates that both effector and “memory” arms of differentiation can be stimulated in vitro.