  This study presents theoretical results for physico-chemical properties of
system of molecules modeling bi-specific antibodies, such as,
dual-variable-domain monoclonal antibodies (DVD-Ig) and Fabs-In-Tandem
Immunoglobulin (FIT-Ig). These molecules are representatives of the engineered
proteins that combine the function and specificity of two monoclonal
antibodies. Individual molecules are here depicted as an assembly of nine (or
in case of the Fit-Ig eleven) hard spheres, organized to resemble the Y-shaped
object. The effects of the increased size, asymmetry, and flexibility of
individual molecules on measurable properties of such systems of molecules are
investigated. We examined the liquid-liquid phase separation, the second virial
coefficient $B_2$, and viscosity under various experimental conditions. The
calculations are compared with the data for regular monoclonal antibodies and
discussed in view of the experimental results for DVD-Ig solutions available in
literature.
