Comparison of the biological activities of human recombinant interleukin-2(125) and native interleukin-2

Human interleukin-2 proteins (IL-2), purified to homogeneity from both the Jurkat cell line and from genetically engineered Escherichia coli, were compared in a variety of biological systems. The gene coding for the recombinant IL-2 protein used in these studies contained a site-specific modification resulting in the replacement of a cysteine residue with a serine residue at position 125 in the encoded polypeptide. The specific activity was 2-4 X 10(6) units/mg for both the recombinant IL-2(125) and the native IL-2 molecules when measured by DNA synthesis in the murine HT2 cell line. The abilities of these two molecules to support the short-term proliferation and the long-term growth of mitogen- and alloantigen-activated peripheral blood mononuclear cells (PBMC) from humans and of mitogen-activated PBMC from cats, cows, sheep, and horses were equivalent. In addition, both molecules were directly mitogenic for human PBMC and induced the production of interferon-gamma. Human PBMC treated with IL-2 generated enhanced levels of cytotoxic cells against both natural killer (NK)-sensitive and NK-resistant targets. In all of these systems and assays, recombinant IL-2(125) had the same range of biological activity and potency as homogeneous native IL-2.