Comparison of the performance of anti‐CD7 and anti‐CD38 bispecific antibodies and immunotoxins for the delivery of saporin to a human T‐cell acute lymphoblastic leukemia cell line

Abstract

We have investigated the cytotoxic performance of two different anti-CD7/anti-saporin BsAb's (HB2 x DB7-18 and Q1.1), three anti-CD38/anti-saporin BsAb's (OKT10 x RabSap, OKT10 x DB7-18 and Q4.1) and an anti-CD7 (HB2-Sap) and anti-CD38-saporin (OKT10-Sap) immunotoxin for delivering the ribosome inactivating protein (rip) to the human T-cell acute lymphoblastic leukemia cell line HSB-2. In the case of CD7 as target molecule the immunotoxin outperformed both anti-CD7 BsAb's being six times more effective than HB2 x DB7-18 and 98 times more so than Q1.1 at effectively inhibiting protein synthesis in a dose dependent manner. The chemically constructed HB2 x DB7-18 BsAb was more effective at inhibiting protein synthesis and cell growth in target HSB-2 cells in a dose dependent manner than the quadroma produced BsAb Q1.1. Both BsAb demonstrated a prozone effect used at concentrations above 0.1 nM though this was more pronounced for Q1.1 than for HB2 x DB7-18. The prozone effect was partially though not completely reversed by increasing the concentration of saporin in the system. In the case of CD38 as target molecule the anti-CD38 IT OKT10-Sap performed poorly, never actually achieving its IC50. Two BsAb's constructed with monoclonal anti-saporin Fab arms each recognizing a different epitope on the saporin molecule also performed poorly. In contrast the BsAb OKT10 x RabSap constructed with Fab derived from a rabbit polyclonal anti-saporin antiserum performed in a dose dependent manner achieving its IC50 at a concentration of 1.3 nM. This BsAb also exhibited a prozone effect. These results exemplify the importance of cross linking adjacent target molecules on the cell surface in order to achieve effective delivery of saporin to the cell interior.

More Is Not Necessarily Better: Prozone-Like Effects in Passive Immunization with IgG

“…For bacteria, similar results have been described for Ab neutralization assays of Chlamydia trachomatis and bactericidal assays of Pseudomonas aeruginosa in vitro (36,37). The existence of prozone-like effects is not limited to microbial Ab neutralization assays because a prozone was described for a bispecific cytotoxic Ab in an assay against leukemic cells (38).…”

Activated T–cell-mediated Immunotherapy With a Chimeric Receptor Against CD38 in B-cell Non-Hodgkin Lymphoma

“…Although an immunotoxin and a saporin-conjugated anti-CD38 antibody have been developed, they are potentially toxic to cells which are not positive for CD38. [17][18][19][20][21][22][23] Moreover, as antibodies, in general, last a long time in the peripheral blood, it is difficult to precisely manipulate their concentrations. Furthermore, it was recently reported that T-cell adoptive immunotherapy by using genetically modified autologous CD20-specific T cells was promising treatment for B-NHL.…”

“…Consequently, anti-CD38 antibodies or antibody variants have been produced as immunotoxins or ''bispecific'' reagents for the treatment of CD38-positive malignancies. [17][18][19][20][21][22][23] A clinical study with an anti-CD38 antibody conjugated to saporin is currently underway. Although CD38 is considered an important molecular target for immunotherapy with CARs, NK cells and activated T cells retain CD38 on their surface, and these effector cells may react with each other or themselves upon the transduction of CARs.…”

Neutralizing Monoclonal Antibody to Edema Toxin and Its Effect on Murine Anthrax

“…Prozone-like effects occur both in vivo and in vitro, and these phenomena are often underappreciated and poorly understood. Prozones have been observed in a variety of systems, including Ab-dependent cellular cytotoxicity against viruses (36), Ab-mediated complement activation (20), and Ab-mediated protection against fungi (35,39) and tumors (10). Although the mechanism responsible for the shapes of these curves in this study is beyond the scope of this study, we note that prozone-like effects probably exist for Ab-mediated neutralization of EF and could conceivably play a role in this system.…”