A-109 A novel multi-cytokine inhibitory strategy in treating HTLV-1 diseases
Authors: Tagaya Yutaka 
Published: April 2019

Human T-cell leukemia virus-I (HTLV-1) is the most oncogenic human virus and arguably the most carcinogenic agent to humans (Gallo, Willems and Tagaya, 2017, Martin et al, 2018). Nevertheless, HTLV-1 is not receiving the deserving attention. We have been advocating for HTLV-1 to enhance the visibility of its research and to make the public aware of its biological and social importance for the past few years as a part of HTLV-1 task force of Global Virus Network (GVN), and we believe we are seeing some promising changes.

Despite nearly 40 years of extensive research on the mechanisms by which HTLV-1 causes multiple human diseases including adult T-cell leukemia (ATL), HAM/TSP (HTLV-1 associate myelopathy/Tropical Spastic Paraparesis), and immunosuppressive condition leading to bacterial infections, no reliable cures are available for these diseases. HTLV-1 infection to CD4 T-cells enhances the production of multiple cytokines by CD4 T-cells through the transactivating nature of virus genes such as Tax. This causes a by-stander activation of CD8 T-cells and turn them into inflammatory cells, which contributes to worsening the disease burden in HTLV-1 diseases. For example, the damages to spinal cord cells in HAM/TSP is caused by the inflammatory CD8 T-cells. We have shown that such activation of CD8 T-cells is mainly caused by the cooperation of IL-2 and IL-15, 2 sibling cytokines belonging to the common gamma (γc)-family (Nata et al 2015, Massoud et al 2015) and that only the co-inhibition of these 2 cytokines, but not the inhibition of either of them, effectively suppresses the activation of CD8 T-cells isolated from HAM/TSP patients in an ex vivo assay system. The co-inhibition of 2 cytokines is a clinical challenge because currently available modalities do not allow to accomplish the goal without adverse effects. For example, monoclonal antibodies need to be combined, but is infeasible in the clinic from the viewpoint of cost. Bispecific antibodies do not exist to co-inhibit these 2 cytokines. Signal inhibitors such as Jak kinase inhibitors will have profound side effects by broadly blocking non-γc cytokines such as Erythropoietin and Thrombopoietin and causing severe anemia and bleeding tendency. Even specific JAk3 inhibitors, if available, will cause immunodeficiency by blocking IL-7 and significantly reducing the number of T-cells when used chronically. We thus developed a novel technology to develop inhibitors which block only desired members of the γc-family cytokines. We noted that all γc-tyokines (eg, IL-2, -4, -7, -9-, 15, and −21) use their D-helices to interact with the shared γc-receptor subunit. Accordingly, we found that the D-helices from 6 γc-cytokine show modest conservation in their primary structure. We postulated that a short peptide mimicking these D-helices might inhibit multiple γc-cytokines by competing with them in the binding to the γc, and that leveraging the conserved and non-conserved positions in this region across all γc-cytokines might allow us to synthesize a specific inhibitor to a given choice of γc-cytokines. We in fact successfully synthesized several peptides showing inhibition to only selected γc-cytokines, but not all γc-cytokines with different target spectrums. Among them is the BNZ-1 peptide which blocks IL-2, IL-15 and IL-9. In an ex vivo assay using T-cells derived from HAM/TSP patients, BNZ-1 effectively blocked the proliferation and activation of HAM/TSP T-cells whereas mAb for IL-2 or IL-15 only showed marginal inhibition, suggesting that this compound represents a novel therapeutic candidate for HAM/TSP. It is likely that BNZ-1 could treat chronic ATL as well since chronic ATL has been shown to pathogenically involve IL-2 and IL-15 produced by HTLV-1 infected CD4 T-cells. We have tested the safety, pharmacokinetics and pharmacodynamics of the PEGylated form of the BNZ-1 peptide (BNZ-1/PEG) in animal models (mouse and non-human primate) and in healthy human volunteers (Phase I study) and observed that it blocks IL-2 and IL-15 activity effectively in humans, and that a weekly or biweekly administration maintains the drug level above the minimum effective dose. BNZ-1/PEG has been approved as an IND for treating HAM/TSP and T-cell malignancies (CD8 type LGL-leuekmia/cutaneous T-cell Lymphoma (CTCL)). Currently we are conducting a phase II clinical trial involving LGL-leukemia/CTCL (see a poster presented by J Geh et al) and are aiming at starting a trial involving HAM/TSP in the near future.