Interleukin-15:Interleukin-15 receptor scaffold for creation of multivalent targeted immune molecules

Human interleukin-15 (hIL-15) and its receptor (hIL-15R) are co-expressed in antigen presenting cells allowing trans-presentation of the cytokine to immune effector cells. We exploited the high-affinity interactions between hIL-15 and the extracellular hIL-15R sushi domain (hIL-15RSu) to create a functional scaffold for the design of multispecific fusion protein complexes. Using single-chain T cell receptors (scTCRs) as recognition domains linked to the IL-15:IL-15R scaffold, we generated both bivalent and bispecific complexes. In these fusions, the scTCR domains retain the antigen-binding activity and the hIL-15 domain exhibits receptor binding and biological activity. As expected, bivalent scTCR fusions exhibited improved antigen binding due to increased avidity, whereas fusions comprising two different scTCR domains were capable of binding two cognate peptide/MHC complexes. Bispecific molecules containing scTCR and scCD8 domains also exhibit enhanced binding to peptide/MHC complexes, demonstrating that the IL-15:IL-15R scaffold displays flexibility necessary to support multi-domain interactions with a given target. Surprisingly, functional heterodimeric molecules could be formed by co-expressing the TCR and chains separately as fusions to the hIL-15 and hIL-15RSu domains. Together, these properties indicate that the hIL-15 and hIL-15RSu domains can be used as versatile, functional scaffold for generating novel targeted immune molecules.