Expression and purification of two anti-CD19 single chain Fv fragments for targeting of liposomes to CD19-expressing cells.

Antibody-targeted liposomal anticancer drugs combine the specificity of antibodies with large payloads of entrapped drugs. We previously showed that liposomal doxorubicin (DXR) targeted via anti-CD19 monoclonal antibodies (mAb) or their Fab' fragments against the B-cell antigen CD19 led to improved therapeutic effects in murine B-cell lymphoma models relative to non-targeted liposomal DXR. We now are examining the use of anti-CD19 single chain fragments of the antibody variable region (scFv) as a targeting moiety, to test the hypothesis that scFv have advantages over full-sized mAb or Fab' fragments. We expressed two different anti-CD19 scFv constructs, HD37-C and HD37-CCH in E. coli, and purified the scFvs using two different methods. The HD37-CCH construct was selected for coupling studies due to its relative stability and activity in comparison to HD37-C. When coupled to liposomes, the HD37-CCH scFv showed increased binding in vitro to CD19-positive Raji cells, compared to non-targeted liposomes. Cytotoxicity data showed that HD37-CCH scFv-targeted liposomes loaded with DXR were more cytotoxic than non-targeted liposomal DXR. Our results suggest that anti-CD19 scFv constructs should be explored further for their potential in treating B-lymphoid leukemias and lymphomas.