Specific lysis of allogeneic cells after activation of CD3- lymphocytes in mixed lymphocyte culture

Human CD3^- lymphocyte populations were obtained by treating peripheral blood lymphocytes with mAbs directed to CD3, CD4, and CD8 surface antigens. The resulting populations were cultured with irradiated allogeneic cells; at day 4, 100 U/ml IL-2 were added and cultures continued for an additional 10 d. The resulting populations were CD3^- CD2⁺ CD7⁺ and displayed cytolytic activity against PHA-induced blast cells bearing the stimulating alloantigens but not against autologous or unrelated allogeneic blast cells. When CD3^- populations were cultured with irradiated autologous cells, no cytolytic activity could be detected either against autologous or allogeneic blast cells. On the other hand, K562 target cells were lysed by both MLC-derived CD3^- cell populations regardless of the origin (autologous or allogeneic) of the stimulating cells. CD3^- clones were further derived from MLC-stimulated CD3^- populations. These clones displayed a cytolytic pattern similar to the original MLC populations as only specific PHA blasts could be lysed. These clones did not express detectable surface TCR-α/β or -γ/δ molecules and lacked productive mRNA for TCR α and β chains, while small amounts of TCR-γ mRNA were detectable in one of four clones tested. Also mRNA for CD3 γ and δ chains were undetectable in all clones, however, CD3 ε mRNA was consistently present.