A cDNA coding for human interleukin-2 (IL-2) has been cloned from a cDNA library prepared from partially purified IL-2 mRNA. The DNA sequence codes for a polypeptide which consists of 153 amino acids including a putative signal sequence. A biologically active polypeptide, characteristic of human IL-2, was produced when the cDNA was fused to a simian virus 40 promoter sequence and used to transfect cultured monkey COS cells.

Interleukin-2 (IL-2) is a lymphokine originally described as a humoral factor required for the continued proliferation of activated T-cell clones. It also seems to be involved in the mitogenic response of thymocytes, in augmenting natural killer cell activity, in the generation of cytotoxic T cells and in the induction of other lymphokines such as gamma-interferon and a B-cell growth factor (BCGF-1). More recently, there has been evidence for the involvement of IL-2 per se in the stimulation of B-cell growth (ref. 10 and T. Kishimoto and J. Vilcek, personal communications). We have reported previously the cloning and expression of a human IL-2 complementary DNA. The cDNA encodes biologically active IL-2 which would consist of 153 amino acids, including a signal sequence. Because so much of the work on IL-2 has been done in the human and mouse, we sought to obtain cDNA encoding murine IL-2, and we now report the cloning, expression and sequence analysis of murine IL-2 cDNAs. The longest cDNA insert encodes a polypeptide of 169 amino acids, containing unique repeats of a CAG sequence which would encode 12 consecutive glutamine residues within the active IL-2 molecule.

We have cloned a chromosomal DNA segment which covers the entire sequence for the murine interleukin-2 gene and analysed the structure of the gene. The coding regions are separated into four blocks by three introns each of which is located similarly to the corresponding human gene. The exon sequences can be aligned perfectly with the previously cloned cDNA sequence. Of particular interests is the presence of sequences within the 5'-flanking region which are highly conserved between mouse and man. The conserved region which spans more than 400 base pairs may play a role in the regulation of IL-2 gene expression.

BSF-2 (B cell stimulatory factor-2/IL-6) is a member of the lymphokine family and responsible for B cell differentiation. Expression plasmids of human BSF-2 cDNA were constructed using a trp promotor/operator and a trpA terminator. In an extract of Escherichia coli HB101 holding "direct" expression plasmid pBSF-2D, activity of BSF-2 was detected, but overproduction was not observed. A "fused" expression system was therefore developed to prepare the recombinant protein. In this system, cDNA was expressed as a fused protein with human IL-2 N-terminal peptide. In the case of the fused BSF-2 expression plasmid, pBSF-2F, inclusion bodies were observed and overproduction of the protein occurred. As this fused protein had a Phe-Arg-Ala sequence at the junction of hIL-2 and BSF-2, it was possible to process mature BSF-2 from the fused BSF-2 by treatment with kallikrein and aminopeptidase P. From 1 liter of E. coli culture, 45 mg of mature BSF-2 was purified; it had a relative biological activity equal to that of natural BSF-2 purified from T cells.