Comparison of in vitro antibody-targeted cytotoxicity using mouse, rat and human effectors

Area of Science:

• Immunology
• Cancer Biology
• Pharmacology

Background:

• Antibodies can induce tumor cell death via complement-mediated and cell-mediated cytotoxicities.
• Clinical application of antibody-based cancer therapies is limited by challenges in preclinical modeling.
• Species-specific differences in immune effector functions complicate the selection of appropriate animal models.

Purpose of the Study:

• To investigate the species-specific immunological reasons behind the differential efficacy of the mouse monoclonal antibody (mAb) 3F8 against experimental tumors in mice and rats.
• To compare the in vitro antibody-dependent cytotoxicity (ADCC) mediated by polymorphonuclear neutrophils (PMN), natural killer (NK) cells, and complement from mouse, rat, and human systems.

Main Methods:

• In vitro antibody-dependent cytotoxicity assays were performed using sera and effector cells (PMN, NK cells) from mice, rats, and humans.
• The potency of complement-mediated cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC) was assessed by measuring specific release.
• Interleukin-2-activated NK cell cytotoxicity was also evaluated across species.

Main Results:

• Mouse IgG3 mAb 3F8-dependent complement-mediated cytotoxicity was significantly higher with rat and human sera (over 70% specific release) compared to mouse serum (20%).
• PMN-mediated ADCC showed substantial activity with human (35%-70%) and rat (25%-60%) effectors, but was undetectable with mouse PMN.
• While IL-2-activated NK cell cytotoxicity was antibody-independent, it was significantly more potent in humans and rats (60%-70% specific release) than in mice (10%).

Conclusions:

• The rat immune system, particularly its complement and PMN functions, demonstrates greater capacity for mediating 3F8 antibody-dependent cytotoxicity compared to the mouse.
• These findings suggest that the rat may be a more relevant preclinical model than the mouse for evaluating the in vivo antitumor efficacy of mouse IgG3 monoclonal antibodies.
• Understanding species-specific effector functions is crucial for the successful clinical translation of antibody-based cancer therapies.