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Running interference
Interleukin-2 (IL-2) binds to receptors on multiple different types of T cells. CD8 T cells, which can kill tumor cells, have IL-2 receptors with two subunits. When IL-2 binds to these, it promotes the T cells’ activation. In contrast, regulatory T cells dampen the antitumor immune response, and they express a different type of IL-2 receptor, which contains CD25 in addition to the other two subunits. CD25 binds IL-2 tightly but does not signal. To address this, Arenas-Ramirez et al. developed an anti–IL-2 antibody that can block CD25, such that delivering the antibody together with IL-2 allows IL-2 to bind specifically to the two-subunit IL-2 receptors and promote an antitumor immune response without interference from regulatory T cells.
Abstract
Interleukin-2 (IL-2) immunotherapy is an attractive approach in treating advanced cancer. However, by binding to its IL-2 receptor α (CD25) subunit, IL-2 exerts unwanted effects, including stimulation of immunosuppressive regulatory T cells (Tregs) and contribution to vascular leak syndrome. We used a rational approach to develop a monoclonal antibody to human IL-2, termed NARA1, which acts as a high-affinity CD25 mimic, thereby minimizing association of IL-2 with CD25. The structure of the IL-2–NARA1 complex revealed that NARA1 occupies the CD25 epitope of IL-2 and precisely overlaps with CD25. Association of NARA1 with IL-2 occurs with 10-fold higher affinity compared to CD25 and forms IL-2/NARA1 complexes, which, in vivo, preferentially stimulate CD8+ T cells while disfavoring CD25+ Tregs and improving the benefit–to–adverse effect ratio of IL-2. In two transplantable and one spontaneous metastatic melanoma model, IL-2/NARA1 complex immunotherapy resulted in efficient expansion of tumor-specific and polyclonal CD8+ T cells. These CD8+ T cells showed robust interferon-γ production and expressed low levels of exhaustion markers programmed cell death protein-1, lymphocyte activation gene-3, and T cell immunoglobulin and mucin domain-3. These effects resulted in potent anticancer immune responses and prolonged survival in the tumor models. Collectively, our data demonstrate that NARA1 acts as a CD25-mimobody that confers selectivity and increased potency to IL-2 and warrant further assessment of NARA1 as a therapeutic.
- Copyright © 2016, American Association for the Advancement of Science
