Production of Bioactive Soluble Interleukin-15 in Complex with Interleukin-15 Receptor Alpha from a Conditionally-Replicating Oncolytic HSV-1

Abstract

Oncolytic type-1 herpes simplex viruses (oHSVs) lacking the γ134.5 neurovirulence gene are being evaluated for treatment of a variety of malignancies. oHSVs replicate within and directly kill permissive cancer cells. To augment their anti-tumor activity, oHSVs have been engineered to express immunostimulatory molecules, including cytokines, to elicit tumor-specific immune responses. Interleukin-15 (IL-15) holds potential as an immunotherapeutic cytokine because it has been demonstrated to promote both natural killer (NK) cell-mediated and CD8+ T cell-mediated cytotoxicity against cancer cells. The purpose of these studies was to engineer an oHSV producing bioactive IL-15. Two oHSVs were constructed encoding murine (m)IL-15 alone (J100) or with the mIL-15 receptor α (mIL-15Rα, J100D) to determine whether co-expression of these proteins is required for production of bioactive mIL-15 from oHSV. The following were demonstrated: i) both oHSVs retain replication competence and cytotoxicity in permissive tumor cell lines. ii) Enhanced production of mIL-15 was detected in cell lysates of neuro-2a cells following J100D infection as compared to J100 infection, suggesting that mIL-15Rα improved mIL-15 production. iii) Soluble mIL-15 in complex with mIL-15Rα was detected in supernates from J100D-infected, but not J100-infected, neuro-2a, GL261, and CT-2A cells. These cell lines vary in permissiveness to oHSV replication and cytotoxicity, demonstrating soluble mIL-15/IL-15Rα complex production from J100D was independent of direct oHSV effects. iv) The soluble mIL-15/IL-15Rα complex produced by J100D was bioactive, stimulating NK cells to proliferate and reduce the viability of syngeneic GL261 and CT-2A cells. v) J100 and J100D were aneurovirulent inasmuch as no neuropathologic effects were documented following direct inoculation into brains of CBA/J mice at up to 1x107 plaque forming units. The production of mIL-15/mIL-15Rα from multiple tumor lines, as well as the lack of neurovirulence, renders J100D suitable for investigating the combined effects of oHSV and mIL-15/IL-15Rα in various cancer models.

Immunobiology of the IL-15/IL-15Rα complex as an antitumor and antiviral agent

“…In mouse models, IL-15 superagonist caused regression of melanoma, pancreatic tumor, glioblastoma and Burkitt′s lymphoma, whereas IL-15 alone did not (31, 40, 57, 58). In addition, IL-15/IL-15Ra fusion proteins and IL-15/IL-15Ra–expressing adenovirus expression systems have also been more efficacious than IL-15 in improving survival and/or tumor clearance of primary lung cancer, mammary tumor, prostate cancer and metastatic colon carcinoma (50–52, 56) (Table V).…”

“…A similar effect was observed when IL-15/IL-15 Rα-transduced DCs were administered to improve NK cell-mediated killing of the human Burkitt’s lymphoma cell line (57). In addition, oncolytic type-1 herpes simplex virus (oHSV) expression of IL-15 and IL-15 Rα resulted in soluble IL-15/IL-15 Rα production and greatly enhanced NK cell cytotoxic killing of tumor cells, although these tumor cell lines are not permissive to oHSV replication and killing (58). Improved anti-tumor effect was also observed in myxoma virus expressing a fusion protein of IL-15/IL-15 Rα, which increased the number of tumor-infiltrating NK and CD8+ T cells in mice challenged with melanoma (59).…”

“…IL-15 superagonist has demonstrated improved biological activity and augmented anti-tumor potency compared to native IL-15 in preclinical studies, thus having generated robust interest in the application of IL-15 superagonist as an anti-cancer agent (31, 40, 50–52, 56–58). As seen in Table VI, there are a total of nine actively ongoing and five prearranged phases I/II clinical trials in cancer patients with IL-15 superagonist and one phase I clinical trial on HIV patients at this time.…”

“…Chang et al showed adenovirus-delivered IL-15/IL-15 Rα did not cause apparent liver injury in wild type mice (79). Similarly, no neuropathological changes were observed in wild type mice receiving IL-15/IL-15 Rα-expressing herpes simplex viruses intracranially (58). Long-term engraftment with T cells co-expressing chimeric antigen receptors and IL-15/IL-15 Rα complex persisted, but neither proliferated aberrantly nor elicited host toxicity in the absence of tumor (54).…”

Armed oncolytic viruses: A kick-start for anti-tumor immunity

“…Cytokines GM-CSF HSV [22,48,121] Adenocarcinoma [33], Metastised (phase I) a [22,34] Breast cancer [121], Melanoma (phase I) a [121,122] Improved peripheral blood mononuclear cell response [124] Grade 1 and 2 [22,34], AdV [34,110,122] CD3+ T cell infiltration [33] MV [33] Long-term immunity against rechallenge with tumor cells [33] VSV [123] NDV [124] IL-12…”