A population of CHO cells constitutively overexpressing a clone of human IgG2/kappa. CHO cells are regarded as the workhorse of recombinant protein expression and biopharmaceutical production. Under certain conditions such as when protein synthesis and protein folding efficiency exceed the capacity of ER-to-Golgi transport, export ready IgG species can progressively accumulate in the ER until a phase separation threshold of the protein is reached to crystallize. This human IgG2/kappa clone induced rod-shaped crystalline body in the ER of engineered CHO cells. Protein crystallization events physically prevented cytokinesis, without hampering nuclear division. The net result was the multi-nucleation and marked cell enlargement. The size of crystal-laden cells became markedly larger than the cells that do not house crystals.