Researchers evaluate the efficacy of a

tumour cell-specific therapeutic monoclonal antibody in co-culture experiments.

Tumour cells alone show minimal cell death when exposed to the antibody. When

peripheral blood mononuclear cells (PBMCs) are added, significant tumour cell

death occurs. Blocking Fc gamma receptors on the immune cells prevents killing,

while inhibition of the complement system has no measurable effect.

Which mechanism best explains the

observed tumour cell death?