ERBB2 and neoplasm: Besides finding a correlation between CD3 affinity and distribution to T-cell-rich tissues, they also observed that higher affinity for the tumor antigen (HER2) was associated with both optimized tumor-killing activity in mouse in vivo studies and a more severe toxicity profile in cynomolgus monkey studies, and suggested that a dose-fractionation strategy could increase the tolerability of such a bsAb.