ADAM9 and Decreased total leukocyte count: As white blood cells express low ADAM9 levels and do not seem to cleave the ADAM9-responsive peptide linker (Figure 2A,H and [9]), leukopenia in the OPT-MSN-treated mice is most likely not due to off-target cytotoxicity by white-blood-cell-dependent cap removal and paclitaxel release.