Intratumoral MMAE concentrations consistently correlates with the extent of tumor growth inhibition in tumor xenograft models. IHC analysis reveals that nonbinding control-treated tumors consist of both CD30 + and CD30 - cells, presumably because they do not kill either CD30 + or CD30 - Karpas 299 cells. Only CD30 - cells are found in cAC10-vcMMAF-treated tumors, illustrating that cAC10-vcMMAF eliminates most CD30 + cells. Interestingly, the two tumors that relapses from cAC10-vcMMAE treatment are also found to be CD30 - by the end of study, indicating a small fraction of CD30 - cells might have escaped from bystander killing in these two remaining tumors.
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