[Show abstract][Hide abstract] ABSTRACT: Precursor B cell acute lymphoblastic leukemia (pre-B ALL) affects five to six thousand adults and almost three thousand children every year. Approximately 25% of the children and 60% of the adults die from their disease, highlighting the need for new therapies that complement rather than overlap chemotherapy and bone marrow transplantation. Immunotherapy is a class of therapies where toxicities and mechanisms of action do not overlap with those of chemotherapy. Because CD19 is a B cell- restricted membrane antigen that is expressed on the majority of pre-B tumor cells, a CD19-based immunotherapy is being developed for ALL. In this study, the anti-tumor activities of immunotoxins (ITs) constructed by conjugating a murine monoclonal antibody (MAb), HD37, or its chimeric (c) construct to recombinant ricin toxin A chain (rRTA) were compared both in vitro using human pre-B ALL and Burkitt's lymphoma cell lines and in vivo using a disseminated human pre-B ALL tumor cell xenograft model. The murine and chimeric HD37 IT constructs were equally cytotoxic to pre-B ALL and Burkitt's lymphoma cells in vitro and their use in vivo resulted in equivalent increases in survival of SCID mice with human pre-B ALL tumors when compared with control mice.
[Show abstract][Hide abstract] ABSTRACT: CD19 is an attractive therapeutic target for treating human B-cell tumors. In our study, chimeric (c) divalent (cHD37) and tetravalent (cHD37-DcVV) anti-CD19 monoclonal antibodies (MAbs) were constructed, expressed and evaluated for their binding to human 19-positive (CD19(+)) tumor cell lines. They were also tested for proapoptotic activity and the ability to mediate effector functions. The antitumor activity of these MAbs was further tested in mice xenografted with the CD19(+) Burkitt's lymphoma cell line, Daudi or the pre-B acute lymphoblastic leukemia (ALL) cell line, NALM-6. The cHD37 and cHD37-DcVV MAbs exhibited specific binding and comparable proapoptotic activity on CD19(+) tumor cell lines in vitro. In addition, the cHD37 and cHD37-DcVV MAbs were similar in their ability to mediate antibody-dependent cell-mediated phagocytosis (ADCP). However, the tetravalent cHD37-DcVV MAb bound more avidly, had a slower dissociation rate, and did not internalize as well. It also had enhanced antibody-dependent cellular cytotoxicity (ADCC) with human but not murine effector cells. The cHD37 and cHD37-DcVV MAbs exhibited comparable affinity for the human neonatal Fc receptor (FcRn) and similar pharmacokinetics (PKs) in mice. Moreover, all the HD37 constructs were similar in extending the survival of mice xenografted with Daudi or NALM-6 tumor cells. Therefore, the cHD37 and cHD37-DcVV MAbs have potent antitumor activity and should be further developed for use in humans. Although not evident in mice, due to its increased ability to mediate ADCC with human but not mouse effector cells, the cHD37-DcVV MAb should have superior therapeutic efficacy in humans.
International Journal of Cancer 09/2010; 129(2):497-506. · 6.20 Impact Factor