The present study examined the use of replication-defective adenovirus for in vitro production of an immunoadhesin. A recombinant adenovirus, rendered replication defective by deletion of the E1 gene, was constructed to contain the murine interleukin-10 gene fused in frame with the hinge, CH2, and CH3 domains of the murine immunoglobulin gamma 1 heavy chain constant region gene under the control of the human cytomegalovirus promoter. The resultant recombinant virus, Ad5.hCMV.mIL-10:HFc, was used to transduce several cell types. The expressed protein, mIL-10:HFc, is secreted as a disulfide-bonded homodimer. In vitro, a murine pro-B-cell line expressing transfected recombinant murine interleukin-10 receptor proliferated in response to purified mIL-10:HFc. The results obtained demonstrate the relative ease of production of an immunoadhesin using replication-defective adenovirus.