NKTR-255 is a polymer-conjugated IL-15 with unique mechanisms of action on T and natural killer cells.

NKTR-255 is a PEG conjugate of recombinant human IL-15 (rhIL-15) being examined as a potential cancer immunotherapeutic. Since IL-15 responses can be mediated by trans or cis presentation via IL-15Rα or soluble IL-15/IL-15Rα complexes, we investigated the role of IL-15Rα in driving NKTR-255 responses using defined naive and memory OVA-specific CD8+ T cells (OT-I) and NK cells in mice. NKTR-255 induced a 2.5- and 2.0-fold expansion of CD8+ T and NK cells, respectively, in WT mice. In adoptive transfer studies, proliferation of naive and memory WT OT-I T cells in response to NKTR-255 was not impaired in IL-15Rα-/- mice, suggesting trans presentation was not utilized by NKTR-255. Interestingly, naive IL-15Rα-/- OT-I cells had deficient responses to NKTR-255, while memory IL-15Rα-/- OT-I cell responses were partially impaired, suggesting that naive CD8+ T cells are more dependent on cis presentation of NKTR-255 than memory CD8+ T cells. In bone marrow chimera studies, IL-15Rα-/- and WT NK cells present in WT recipients had similar responses to NKTR-255, suggesting that cis presentation is not utilized by NK cells. NKTR-255 could form soluble complexes with IL-15Rα; binding to murine IL-15Rα generated superagonists that preferentially stimulated NK cells, showing that conversion to IL-15Rß agonist biases the response toward NK cells. These findings highlight the ability of NKTR-255 to utilize IL-15Rα for cis presentation and act as an IL-15Rαß agonist on CD8+ T cells.

A bispecific antibody agonist of the IL-2 heterodimeric receptor preferentially promotes in vivo expansion of CD8 and NK cells.

The use of recombinant interleukin-2 (IL-2) as a therapeutic protein has been limited by significant toxicities despite its demonstrated ability to induce durable tumor-regression in cancer patients. The adverse events and limited efficacy of IL-2 treatment are due to the preferential binding of IL-2 to cells that express the high-affinity, trimeric receptor, IL-2Rαßγ such as endothelial cells and T-regulatory cells, respectively. Here, we describe a novel bispecific heavy-chain only antibody which binds to and activates signaling through the heterodimeric IL-2Rßγ receptor complex that is expressed on resting T-cells and NK cells. By avoiding binding to IL-2Rα, this molecule circumvents the preferential T-reg activation of native IL-2, while maintaining the robust stimulatory effects on T-cells and NK-cells in vitro. In vivo studies in both mice and cynomolgus monkeys confirm the molecule's in vivo biological activity, extended pharmacodynamics due to the Fc portion of the molecule, and enhanced safety profile. Together, these results demonstrate that the bispecific antibody is a safe and effective IL-2R agonist that harnesses the benefits of the IL-2 signaling pathway as a potential anti-cancer therapy.

CD122-directed interleukin-2 treatment mechanisms in bladder cancer differ from αPD-L1 and include tissue-selective γδ T cell activation.

BACKGROUND: Anti-programmed death-ligand 1 (αPD-L1) immunotherapy is approved to treat bladder cancer (BC) but is effective in <30% of patients. Interleukin (IL)-2/αIL-2 complexes (IL-2c) that preferentially target IL-2 receptor ß (CD122) augment CD8+ antitumor T cells known to improve αPD-L1 efficacy. We hypothesized that the tumor microenvironment, including local immune cells in primary versus metastatic BC, differentially affects immunotherapy responses and that IL-2c effects could differ from, and thus complement αPD-L1. METHODS: We studied mechanisms of IL-2c and αPD-L1 efficacy using PD-L1+ mouse BC cell lines MB49 and MBT-2 in orthotopic (bladder) and metastatic (lung) sites. RESULTS: IL-2c reduced orthotopic tumor burden and extended survival in MB49 and MBT-2 BC models, similar to αPD-L1. Using antibody-mediated cell depletions and genetically T cell-deficient mice, we unexpectedly found that CD8+ T cells were not necessary for IL-2c efficacy against tumors in bladder, whereas γδ T cells, not reported to contribute to αPD-L1 efficacy, were indispensable for IL-2c efficacy there. αPD-L1 responsiveness in bladder required conventional T cells as expected, but not γδ T cells, altogether defining distinct mechanisms for IL-2c and αPD-L1 efficacy. γδ T cells did not improve IL-2c treatment of subcutaneously challenged BC or orthotopic (peritoneal) ovarian cancer, consistent with tissue-specific and/or tumor-specific γδ T cell contributions to IL-2c efficacy. IL-2c significantly altered bladder intratumoral γδ T cell content, activation status, and specific γδ T cell subsets with antitumor or protumor effector functions. Neither IL-2c nor αPD-L1 alone treated lung metastatic MB49 or MBT-2 BC, but their combination improved survival in both models. Combination treatment efficacy in lungs required CD8+ T cells but not γδ T cells. CONCLUSIONS: Mechanistic insights into differential IL-2c and αPD-L1 treatment and tissue-dependent effects could help develop rational combination treatment strategies to improve treatment efficacy in distinct cancers. These studies also provide insights into γδ T cell contributions to immunotherapy in bladder and engagement of adaptive immunity by IL-2c plus αPD-L1 to treat refractory lung metastases.

Modeling the receptor pharmacology, pharmacokinetics, and pharmacodynamics of NKTR-214, a kinetically-controlled interleukin-2 (IL2) receptor agonist for cancer immunotherapy.

Cytokines are potent immune modulating agents but are not ideal medicines in their natural form due to their short half-life and pleiotropic systemic effects. NKTR-214 is a clinical-stage biologic that comprises interleukin-2 (IL2) protein bound by multiple releasable polyethylene glycol (PEG) chains. In this highly PEG-bound form, the IL2 is inactive; therefore, NKTR-214 is a biologic prodrug. When administered in vivo, the PEG chains slowly release, creating a cascade of increasingly active IL2 protein conjugates bound by fewer PEG chains. The 1-PEG-IL2 and 2-PEG-IL2 species derived from NKTR-214 are the most active conjugated-IL2 species. Free-IL2 protein is undetectable in vivo as it is eliminated faster than formed. The PEG chains on NKTR-214 are located at the region of IL2 that contacts the alpha (α) subunit of the heterotrimeric IL2 receptor complex, IL2Rαßγ, reducing its ability to bind and activate the heterotrimer. The IL2Rαßγ complex is constitutively expressed on regulatory T cells (Tregs). Therefore, without the use of mutations, PEGylation reduces the affinity for IL2Rαßγ to a greater extent than for IL2Rßγ, the receptor complex predominant on CD8 T cells. NKTR-214 treatment in vivo favors activation of CD8 T cells over Tregs in the tumor microenvironment to provide anti-tumor efficacy in multiple syngeneic models. Mechanistic modeling based on in vitro and in vivo kinetic data provides insight into the mechanism of NKTR-214 pharmacology. The model reveals that conjugated-IL2 protein derived from NKTR-214 occupy IL-2Rßγ to a greater extent compared to free-IL2 protein. The model accurately describes the sustained in vivo signaling observed after a single dose of NKTR-214 and explains how the properties of NKTR-214 impart a unique kinetically-controlled immunological mechanism of action.