A SUPERANTIGEN-ANTIBODY FUSION PROTEIN FOR T-CELL IMMUNOTHERAPY OF HUMAN B-LINEAGE MALIGNANCIES

The bacterial superantigen staphylococcal enterotoxin A (SEA) is an ef ficient activator of cytotoxic T cells when presented on major histoco mpatibility complex (MHC) class II molecules of target cells. Our prev ious studies showed that such SEA-directed T cells efficiently lysed c hronic B-lymphocytic leukemia (B-CLL) cells. Next, we made a mutated S EA-protein A (SEAm-PA) fusion protein with more than 1,000-fold reduce d binding affinity for MHC class II compared with native SEA. The fusi on protein was successfully used to direct T cells to B-CLL cells coat ed with different B lineage-directed monoclonal antibodies (MoAbs). In this communication, we constructed a recombinant anti-CD19-Fab-SEAm f usion protein, The MHC class II binding capacity of the SEA part was d rastically reduced by a D227A point mutation, whereas the T-cell activ ation properties were retained. The Fab part of the fusion protein dis played a binding affinity for CD19(+) cells in the nanomolar range, Th e anti-CD19-Fab-SEAm molecule mediated effective, specific, rapid, and perforin-like T-cell lysis of B-CLL cells at low effector to target c ell ratios, Normal CD19(+) B cells were sensitive to lysis, whereas CD 34(+) progenitor cells and monocytes/macrophages were resistant. A pan el of CD19(+) B-cell lines representing different B-cell developmental stages were efficiently lysed, and the sensitivity correlated with su rface ICAM-1 expression. The anti-CD19-Fab-SEAm fusion protein mediate d highly effective killing of tumor biopsy cells representing several types of B-cell non-Hodgkin's lymphoma (B-NHL). Humanized severe combi ned immune deficiency (SCID) mice carrying Daudi lymphoma cells were u sed as an in vivo therapy model for evaluation of the anti-CD19-Fab-SE Am fusion protein. Greater than 90% reduction in tumor weight was reco rded in anti-CD19-Fab-SEAm-treated animals compared with control anima ls receiving an irrelevant Fab-SEAm fusion protein. The present result s indicate that MoAb-targeted superantigens (SASs) may represent a pro mising approach for T-cell-based therapy of CD19(+) B-cell malignancie s. (C) 1997 by The American Society of Hematology.