ERBB2 and cancer: Treatment with unconjugated anti-HER2 antibodies with wt or mutant Fc led to a small reduction in cancer cell viability in both STING WT or KO co-cultures similarly, likely due to the cell-growth inhibitory effect of the anti-HER2 antibodies on SKBR3 cells, accounting for some of the residual activity seen with the Fc-mutant ADC in the STING KO cancer cell co-cultures (Supplementary Fig. 12b, and c).