ANTITUMOR X ANTI-CD3 BIFUNCTIONAL ANTIBODIES REDIRECT T-CELLS ACTIVATED IN-VIVO WITH STAPHYLOCOCCAL-ENTEROTOXIN-B TO NEUTRALIZE PULMONARY METASTASES

T-cell antitumor activities are limited by the requirement of two spec ific major histocompatibility complex restricted steps, T-helper cell activation and cytotoxic T-lymphocyte targeting. The aim of this study was to investigate whether bypassing these major histocompatibility c omplex restricted steps using nonspecific in vivo activation of T-cell s with staphylococcal enterotoxin-B (SE-B) and retargeting with antitu mor x anti-CD3 bifunctional antibody (BFA) could provide an effective antitumor response. C3H/HeN mice were injected i.v. with CL-62 melanom a cells, which express the human melanoma antigen p97, and were treate d 10 min later with SE-B and/or anti-CD3 (500A2) x anti-p97 (96.5) BFA . Pulmonary metastases were counted 14 days following injections. SE-B alone induced a dose-dependant activation of T-cells as measured by i ncreased interleukin-2 receptor expression and enhanced proliferative responses. SE-B doses greater than 10 mu g significantly reduced the n umber of pulmonary metastases versus control (P < 0.01). Combined trea tment with SE-B (50 mu g) and BFA (5 to 50 mu g) significantly decreas ed pulmonary metastases compared to treatment with SE-B alone (P < 0.0 5). Similar reductions in metastases were observed with the F(ab')2 BF A but not with the unconjugated antitumor component of the BFA. Combin ed treatments with SE-B plus BFA accomplished better tumor neutralizat ion than adoptively transferred in vitro activated splenocytes (4 x 10 (7)) retargeted with BFA (5-100 pg; P < 0.05). These studies demonstra te that T-cells can be activated in vivo by SE-B and retargeted with s mall doses of BFA In this immunocompetent syngeneic pulmonary metastas is model, SE-B plus BFA provided a dramatic antitumor response.