Table S13 (see ESM) shows the mean subvisible particle concentrations (ECD ≥ 2 μm) in the PS 8670 and the three lots of RM 8671. Each of the vials of PS 8670 was obtained from the same rack of material, such that vial to vial variability due to the fill process can be assumed to be negligible. The RM 8671 vials, on the other hand, were obtained from multiple racks across the fill sequence. The CV (as calculated from ESM Table S13) for the inter-vial variability of each of the RM 8671 lots is on the same order as observed for PS 8670, indicating little to no vial-to-vial heterogeneity with regard to protein particle content was introduced by the filling process. From Table S13 (see ESM), the variability appears to be high even between vials in a particular lot; however, no clear trend among the racks from which the samples were drawn was observed. Due to the fragile nature of protein particles and the sensitivity of particle production to small changes in vial storage or handling, higher variability in particle concentration is expected. It should be noted that even if the concentration of particles were dissimilar from one vial to another, the amount of protein present in the particles is very minute, on the order of tens to several hundreds of ng/mL, corresponding to <0.005% protein concentration in solution .