Efficient production of highly bioactive interleukin-15 in the silkworm silk gland bioreactor

Interleukin-15 (IL-15) is a pleiotropic cytokine that plays a key regulatory role in immune responses and inflammation by promoting the proliferation and survival of natural killer (NK) cells and CD8⁺ T cells. However, the large-scale production of bioactive recombinant human interleukin-15 (rhIL-15) remains challenging due to the limitations of conventional expression systems. In this study, we developed a transgenic silkworm bioreactor for the efficient production of bioactive rhIL-15 in the posterior silk glands (PSG) using the fibroin heavy chain (FibH) expression system. The human IL-15 coding sequence was fused with the N-terminal domain of FibH and introduced into the silkworm genome via piggyBac-mediated germline transformation. The recombinant protein was successfully expressed in PSG and secreted into the cocoons, achieving a yield of 14.18 mg/g cocoon shell. Transgenic silkworms exhibited normal growth and cocoon traits comparable to those of wild-type controls. The purified rhIL-15 effectively promoted mouse cytotoxic T lymphocyte line (CTLL-2) cell proliferation, increased intracellular ATP levels, inhibited apoptosis, and upregulated the expression of downstream target genes, including Myc, Pim1, and Bcl2. Importantly, its bioactivity was comparable to that of a commercial IL-15 standard. Collectively, these findings demonstrate that the silkworm silk gland bioreactor represents a robust and potentially cost-effective platform for the production of bioactive rhIL-15. Furthermore, the resulting functionalized silk fibers may hold promise for applications in immunomodulatory biomaterials.