The production of biopharmaceutical proteins in mammalian cells by transient expression or stable transformation requires robust and viable cells. Cell line engineering must therefore balance improved cell growth and viability with high productivity. We tested the ability of nonmammalian phosphatidylethanolamine-binding proteins to enhance cell proliferation in monolayers and suspension cultures. The tobacco protein NtFT4 improved the proliferation of multiple human cell lines. Viable cell density is usually impaired by efficient transfection, but we found that the number of HEK-293T(NtFT4) cells at the peak of protein expression was twice that of standard HEK-293T cells, and the antibody yield increased by approximately one-third. Improved growth and viability were observed in different cell lines, in different culture media, and also after transient transfection, suggesting the beneficial trait is consistent and transferable. Additional modifications could boost the productivity of high-density HEK-293T(NtFT4) cells even further as we showed for a fluorescent marker protein and recombinant antibody expressed in monolayer cultures. The HEK-293T(NtFT4) cell line provides a new human model platform that increases cell proliferation, also achieving a fundamental improvement in recombinant protein expression.