Titration of the different bifunctional conjugates for induction of CTL mediated tumor cell lysis. Increasing concentrations ranging from 0 to 1 µg/ml (abscissa) of the three anti-tumor marker Fab-HLA-A2/Flu conjugates were incubated for 1 h at 37°C with different tumor target cell lines, followed by the addition of specific CTL for a 4 h ⁵¹Cr release assay. (A) Anti-CEA Fab-HLA-A2/Flu was incubated with LoVo cells (filled squares) or SK-BR-3 cells (open circles). (B) Anti-ErbB2 Fab-HLA-A2/Flu was incubated with SK-BR-3 cells (filled circles), LoVo cells (open squares) or Daudi cells (open diamonds). (C) Anti-CD20 Fab-HLA-A2/Flu was incubated with Daudi (filled diamonds) B lymphoma cells and with SK-BR-3 (open circles) carcinoma cells. Results are expressed as % specific target cell lysis. The conjugate concentration which induces 50% specific lysis is indicated in each panel.