Combining bempegaldesleukin (CD122-preferential IL-2 pathway agonist) and NKTR-262 (TLR7/8 agonist) improves systemic antitumor CD8(+) T cell cytotoxicity over BEMPEG+RT

BACKGROUND: Tumor cell death caused by radiation therapy (RT) triggers antitumor immunity in part because dying cells release adjuvant factors that amplify and sustain dendritic cell and T cell responses. We previously demonstrated that bempegaldesleukin (BEMPEG: NKTR-214, an immunostimulatory IL-2 cytokine prodrug) significantly enhanced the antitumor efficacy of RT through a T cell-dependent mechanism. Because RT can induce either immunogenic or tolerogenic cell death, depending on various factors (radiation dose, cell cycle phase), we hypothesized that providing a specific immunogenic adjuvant, like intratumoral therapy with a novel toll-like receptor (TLR) 7/8 agonist, NKTR-262, would improve systemic tumor-specific responses through the activation of local innate immunity. Therefore, we evaluated whether intratumoral NKTR-262 combined with systemic BEMPEG treatment would elicit improved tumor-specific immunity and survival compared with RT combined with BEMPEG. METHODS: Tumor-bearing mice (CT26; EMT6) received BEMPEG (0.8 mg/kg; intravenously), RT (12 Gy × 1), and/or intratumoral NKTR-262 (0.5 mg/kg). Flow cytometry was used to evaluate CD4(+) and CD8(+) T cell responses in the blood and tumor 7 days post-treatment. The contribution of specific immune subsets was determined by depletion of CD4(+), CD8(+), or NK cells. CD8(+) T cell cytolytic activity was determined by an in vitro CTL assay. Data are representative of 1–2 independent experiments (n=5–14/group) and statistical significance was determined by 1-way analysis of variance (ANOVA) or repeated measures ANOVA (p value cut-off of 0.05). RESULTS: BEMPEG+NKTR-262 significantly improved survival compared with BEMPEG+RT in a CD8(+) T cell-dependent manner. Response to BEMPEG+NKTR-262 was characterized by a significant expansion of activated CD8(+) T cells (GzmA(+); Ki-67(+); ICOS(+); PD-1(+)) in the blood, which correlated with reduced tumor size (p<0.05). In the tumor, BEMPEG+NKTR-262 induced higher frequencies of GzmA(+) CD8(+) T cells exhibiting reduced expression of suppressive molecules (PD-1(+)), compared with BEMPEG+RT (p<0.05). Further, BEMPEG+NKTR-262 treatment induced greater tumor-specific CD8(+) T cell cytolytic function than BEMPEG+RT. CONCLUSIONS: BEMPEG+NKTR-262 therapy elicited more robust expansion of activated CD8(+) T cells compared with BEMPEG+RT, suggesting that intratumoral TLR stimulation provides superior antigen presentation and costimulatory activity compared with RT. A clinical trial of BEMPEG+NKTR-262 for patients with metastatic solid tumors is in progress (NCT03435640).