Earle A Chiles Research Institute, Providence Cancer Institute, Portland, OR, USA.
Sutro Biopharma, South San Francisco, CA, USA.
J Immunother Cancer. 2022 Apr;10(4). doi: 10.1136/jitc-2021-004218.
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.
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).
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.
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).
放射治疗 (RT) 引起的肿瘤细胞死亡部分触发了抗肿瘤免疫，因为死亡细胞释放佐剂因子，这些因子可放大和维持树突状细胞和 T 细胞的反应。我们之前证明，bempegaldesleukin（BEMPEG：NKTR-214，一种免疫刺激的 IL-2 细胞因子前药）通过 T 细胞依赖的机制显著增强了 RT 的抗肿瘤疗效。因为 RT 可以诱导免疫原性或耐受原性细胞死亡，这取决于各种因素（辐射剂量、细胞周期阶段），所以我们假设提供一种特定的免疫原性佐剂，如用新型 Toll 样受体 (TLR) 7/8 激动剂 NKTR-262 进行肿瘤内治疗，将通过激活局部先天免疫来提高全身肿瘤特异性反应。因此，我们评估了与 RT 联合 BEMPEG 相比，肿瘤内 NKTR-262 联合全身 BEMPEG 治疗是否会引发改善的肿瘤特异性免疫和生存。
荷瘤小鼠（CT26；EMT6）接受 BEMPEG（0.8mg/kg；静脉内）、RT（12Gy×1）和/或肿瘤内 NKTR-262（0.5mg/kg）。流式细胞术用于评估治疗后 7 天血液和肿瘤中 CD4 和 CD8 T 细胞反应。通过耗尽 CD4、CD8 或 NK 细胞来确定特定免疫亚群的贡献。通过体外 CTL 测定测定 CD8 T 细胞细胞毒性活性。数据代表 1-2 个独立实验的结果（n=5-14/组），并通过单因素方差分析（ANOVA）或重复测量 ANOVA（p 值截止值为 0.05）确定统计学意义。
BEMPEG+NKTR-262 以 CD8 T 细胞依赖性方式显著提高了与 BEMPEG+RT 的存活率。BEMPEG+NKTR-262 的反应特征是血液中激活的 CD8 T 细胞（GzmA；Ki-67；ICOS；PD-1）显著扩增，这与肿瘤缩小相关（p<0.05）。在肿瘤中，与 BEMPEG+RT 相比，BEMPEG+NKTR-262 诱导了更高频率的 GzmA CD8 T 细胞，其表达抑制分子（PD-1）减少（p<0.05）。此外，与 BEMPEG+RT 相比，BEMPEG+NKTR-262 治疗诱导了更强的肿瘤特异性 CD8 T 细胞细胞毒性功能。
与 BEMPEG+RT 相比，BEMPEG+NKTR-262 治疗引起了更强烈的激活 CD8 T 细胞扩增，表明肿瘤内 TLR 刺激提供了比 RT 更优越的抗原呈递和共刺激活性。一项针对转移性实体瘤患者的 BEMPEG+NKTR-262 的临床试验正在进行中（NCT03435640）。
