In vitro primary allo-CTL generation by enucleated antigen-presenting cells.

It is generally thought that only viable cells can elicit a primary cytotoxic T-lymphocyte (CTL) response. We present evidence that this is not so, since enucleated tumor cells can generate a strong cytolytic response of unprimed allogeneic human T lymphocytes. Cytoplasts (enucleated cells) were obtained by incubation with cytochalasin B and subsequent isopycnic centrifugation. Their purity was assessed by electron microscopy and flow cytometry. Membrane fractions were prepared by nitrogen cavitation, and used in parallel with cytoplasts and intact cells as stimulators in primary allo-CTL generation; although all cell fractions expressed high amounts of class I and II histocompatibility antigens, as assessed by flow cytometry and ELISA technique, only the cytoplasts generated a strong cytotoxic response of naive peripheral T cells, like that induced by intact cells. The dogma that an intact and metabolically active stimulator cell is required for the primary generation of CTLs is questioned.