Tumour cell killing using chemically engineered antibody constructs specific for tumour cells and the complement...

Immunotherapy using MoAbs is inefficient due to limited activation of human effectors by mouse antibodies and multiple protective mechanisms available to host cells against autologous complement. We have used chemically engineered antibody constructs and human complement in vitro to specifically target and kill neoplastic B lymphoid cells (Raji). Fab'gamma Fc gamma2 chimaeric antibody (specific for human CD37) was used to activate the classical pathway of human complement on Raji cells, whilst CD59 was neutralized using one of two different bispecific F(ab'gamma)2 antibody constructs which contained both cell-targeting (anti-CD19 or anti-CD38) and CD59-neutralizing moieties. When either bispecific construct was used to neutralize CD59, 15-25% of cells were lysed. If CD55 was also neutralized using specific antibody, Raji cells were efficiently killed (70% lysis). When added to a mixture of target (Raji) and bystander (K562) cells, one bispecific antibody (anti-CD38 x anti-CD59) could be specifically delivered to Raji, avoiding significant uptake on CD59-expressing bystander cells (K562). The second bispecific antibody (anti-CD19 x anti-CD59) bound equally well to either cell type. Cell-specific targeting was dependent upon combination of a low-affinity anti-CD59 Fab'gamma with a high-affinity anti-tumour cell Fab'gamma. When Raji and K562 cells were mixed and incubated with a combination of the engineered constructs and anti-CD55 antibodies, Raji cell lysis (30-40%) was observed in the absence of K562 killing. We propose that combinations of these constructs may be of use for treatments such as ex vivo purging of autologous bone marrow or in vivo targeting of tumour cells.