Research Department of Haematology, UCL Cancer Institute, London, UK.
Autolus Ltd, London, UK.
J Immunother Cancer. 2023 Jun;11(6). doi: 10.1136/jitc-2023-006699.
We used a proliferating ligand (APRIL) to construct a ligand-based third generation chimeric antigen receptor (CAR) able to target two myeloma antigens, B-cell maturation antigen (BCMA) and transmembrane activator and CAML interactor.
The APRIL CAR was evaluated in a Phase 1 clinical trial (NCT03287804, AUTO2) in patients with relapsed, refractory multiple myeloma. Eleven patients received 13 doses, the first 15×10 CARs, and subsequent patients received 75,225,600 and 900×10 CARs in a 3+3 escalation design.
The APRIL CAR was well tolerated. Five (45.5%) patients developed Grade 1 cytokine release syndrome and there was no neurotoxicity. However, responses were only observed in 45.5% patients (1×very good partial response, 3×partial response, 1×minimal response). Exploring the mechanistic basis for poor responses, we then compared the APRIL CAR to two other BCMA CARs in a series of in vitro assays, observing reduced interleukin-2 secretion and lack of sustained tumor control by APRIL CAR regardless of transduction method or co-stimulatory domain. There was also impaired interferon signaling of APRIL CAR and no evidence of autoactivation. Thus focusing on APRIL itself, we confirmed similar affinity to BCMA and protein stability in comparison to BCMA CAR binders but reduced binding by cell-expressed APRIL to soluble BCMA and reduced avidity to tumor cells. This indicated either suboptimal folding or stability of membrane-bound APRIL attenuating CAR activation.
The APRIL CAR was well tolerated, but the clinical responses observed in AUTO2 were disappointing. Subsequently, when comparing the APRIL CAR to other BCMA CARs, we observed in vitro functional deficiencies due to reduced target binding by cell-expressed ligand.
我们使用一种增殖配体（APRIL）构建了一种配体为基础的第三代嵌合抗原受体（CAR），能够靶向两种骨髓瘤抗原，B 细胞成熟抗原（BCMA）和跨膜激活剂和钙调蛋白相互作用因子。
APRIL CAR 在复发/难治性多发性骨髓瘤患者的 1 期临床试验（NCT03287804，AUTO2）中进行了评估。11 名患者接受了 13 剂治疗，前 15×10 CARs，随后的患者在 3+3 递增设计中接受了 75、225、600 和 900×10 CARs。
APRIL CAR 耐受性良好。5 名（45.5%）患者发生 1 级细胞因子释放综合征，无神经毒性。然而，仅在 45.5%的患者中观察到应答（1×非常好的部分缓解，3×部分缓解，1×微小缓解）。为了探索应答不佳的机制基础，我们随后在一系列体外检测中比较了 APRIL CAR 与两种其他 BCMA CAR，观察到无论转导方法或共刺激结构域如何，APRIL CAR 均导致白细胞介素-2 分泌减少和肿瘤持续控制缺失。APRIL CAR 还存在干扰素信号受损，无自动激活证据。因此，我们专注于 APRIL 本身，与 BCMA CAR 结合物相比，我们确认了对 BCMA 的相似亲和力和蛋白稳定性，但细胞表达的 APRIL 对可溶性 BCMA 的结合减少，对肿瘤细胞的亲和力降低。这表明膜结合的 APRIL 折叠或稳定性较差，从而削弱了 CAR 激活。
APRIL CAR 耐受性良好，但 AUTO2 中观察到的临床应答令人失望。随后，当我们将 APRIL CAR 与其他 BCMA CAR 进行比较时，我们观察到由于细胞表达的配体结合减少导致体外功能缺陷。
