Microrheology of Monoclonal Antibodies during Gelation under Low pH Conditions

Non-native aggregation of monoclonal antibodies (mAbs)
during downstream
processing can reduce their efficacy (e.g., in immunotherapies) and
the total yield. The pH of mAb solutions was lowered, similar to steps
during viral inactivation and protein A chromatography, and a continuous
phase transition to a physically cross-linked gel was observed via
microrheology. The dynamic power-law scaling of the shear modulus
on the frequency, G′(ω) ∝ G″(ω) ∝ ωn, was calculated using time-cure superposition, yielding a
dynamical critical exponent, n = 0.52 ± 0.05.
Dynamic light scattering showed a similar power law scaling exponent
of μ = 0.49 ± 0.04 about the gel point which is related
to the fractal dimension. Circular dichroism showed large increases
in the β-sheet content of the mAbs at low pHs combined with
a large increase in fluorescence of a ThT stained sample. Thus, mAb
gelation seems to occur via the formation of amyloid fibrils that
cause a continuous phase transition that is well described by a dynamic
scaling model for percolation.