Background IL-7 receptor activation is essential for the proper development and homeostasis of T-cell subpopulations, and maintenance of the TCR clonal repertoire. Emerging evidence indicates potential clinical utility of IL-7 for immunotherapy of lymphopenia, oncology, and other indications. Here we report the discovery of MDK1319, a small novel peptidyl agonist of IL-7R. This peptide is structurally unrelated to IL-7, with a MW less than 5000D. To improve in vivo properties, we fused MDK1319 to an IgG-Fc-domain to construct MDK-701, which exhibits biological properties similar to those of IL-7 in vitro, and when administered to non-human primates.
Methods Peptides were selected from peptide libraries by screens designed to identify molecules binding simultaneously to the Rα and γc subunits of the human IL-7 receptor. Synthetic peptides, and peptides fused to IgG Fc-domains were evaluated for efficacy, potency, and quality of signaling in IL-7-responsive cell lines and human lymphocytes. PK/PD properties in non-human primates were also determined.
Results MDK1319 and MDK-701 activate the major IL-7R signaling pathways, JAK-STAT (pSTAT5), and PI3K (pAKT), and induce proliferation in human PBMCs, exhibiting lymphocyte subpopulation selectivity, kinetics, efficacy, and potency similar to those of IL-7. Agonism is attributable to direct activation of IL-7R, as shown by dependence on the presence of the IL-7Rα subunit for response in test cells, and insensitivity to IL-7 neutralizing antibodies. MDK1319 and MDK-701 do not activate nor inhibit any other (off target) Rγc family receptors at concentrations 100-fold greater than required for maximal IL-7R activation. MDK-701 administered to cynomologous macaques (single dose, IV at 1 mg/kg) exhibits a circulating terminal half life of ~32 hr; and induces peripheral lymphocyte profiles similar to IL-7 treatment, including initial reduction (tissue migration), followed by sustained elevation of peripheral lymphocytes remaining above baseline for 29 days, with no observed adverse effects.
Conclusions In addition to the utility of Fc-fusion MDK-701 for monotherapy, the small peptidyl nature of the active peptide MDK1319, fusable to recombinant protein partners, offers opportunities for incorporation into bispecific molecules, linking IL-7 activity to a variety of useful functions. These include synergistic cytokine activities, checkpoint blockade, and tissue targeting. Cells engineered to secrete MDK1319 display autocrine stimulation potentially useful in T-cell therapeutics. The structural novelty of MDK1319 substantially decreases risk of cross reactivity of any anti-drug immune response with endogenous IL-7, and may provide a safer alternative to modified forms of IL-7 reported to produce significant anti-IL-7 immunogenicity.
Ethics Approval Animal studies were performed by Envol Biomedical or Charles Rivers Laboratories, as approved by the Institution Ethics Boards with the following study and approval numbers:Envol Biomedical 7037-20 MDK2002; 7037-20: PK/PD Cynomolgus monkeysCharles Rivers Laboratories 20200121001K; US19001: PK Mouse The use of human PBMC in this study was authorized under Minimal Risk Research Related Activities at Stanford Blood Center (SQL 79075)
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