Inhibition of growth of human tumor xenografts in athymic mice treated with ricin toxin A chain-monoclonal antibody 791T/36 conjugates.

Immunotoxin constructed by conjugating ricin A chain to monoclonal antibody 791T/36 specifically inhibits growth of human tumor xenografts which express the gp72 antigen recognized by the antibody component. Dose schedule tests showed that the major response was obtained during the first 5 days of treatment and further prolonged treatment did not improve therapy. Expression of gp72 antigen on tumor cells derived from xenografts in immunotoxin-treated mice was not markedly altered indicating that treatment did not lead to the expansion of tumor antigen deficient tumor cells. The experiments indicate that treatment for short duration with immunotoxin may be the most effective protocol.