Background
Regulatory T cells (Tregs) are considered potential targets in cancer immunotherapy, as tumor-infiltrating Tregs express higher levels of CTLA-4. One promising way to evoke effective anti-tumor immunity in cancer patients is by using an FcR affinity-enhanced anti-CTLA-4 antibody to deplete Tregs though ADCC/ADCP activity. Although anti-CTLA-4 antibodies with common FcR affinity-enhancing Fc, non-fucosylated Fc, are being clinically developed, the numbers of NKs or macrophages are not sufficient to demonstrate ADCC/ADCP activity in all tumors, resulting in limited efficacy. Therefore, stronger FcR affinity-enhanced Fc is needed to demonstrate efficacy in across all tumors. Moreover, the systemic depletion of Tregs could potentially cause autoimmune side effects. Consequently, new approaches for selective intratumoral Tregs depletion are needed for the clinical development of therapeutics targeting CTLA-4 on Tregs. Here, we report ROSE12, a novel FcR affinity-enhanced anti-CTLA-4 antibody which depletes Tregs only in the presence of ATP. Extracellular ATP concentration is well known to be elevated in tumor tissue while remaining tightly regulated in non-tumor tissue. This suggests that ROSE12 can selectively deplete Tregs in tumor tissue without affecting non-tumor tissue.
Methods
We evaluated the in vitro FcRIIa- and FcRIIIa- affinity, ATP-dependent binding affinity to hCTLA-4, and ADCC activity of ROSE12. We assessed in vivo anti-tumor efficacy in human CTLA-4 knock-in (hCTLA-4KI) mice treated with mROSE12 antibody, which has the same variable region as ROSE12 with FcR affinity-enhanced mouse surrogate Fc. We also evaluated intratumoral Treg depletion and T cell activation in non-tumor tissues using flow cytometry in CTLA-4KI mice treated with mROSE12 and FcR affinity-enhanced ipilimumab.
Results
ROSE12 showed ATP-dependent binding to human CTLA-4 and demonstrated stronger FcRIIa- and FcRIIIa- affinity than non-fucosylated ipilimumab. Consistent with the binding profile, ROSE12 showed enhanced ADCC activity in the presence of ATP, outperforming non-fucosylated ipilimumab. The mROSE12 antibody demonstrated anti-tumor efficacy in a tumor bearing mouse model, and unlike FcR affinity-enhanced ipilimumab, ROSE12 did not induce systemic T cell activation in normal tissue. Also, consistent with its anti-tumor efficacy, ROSE12 depleted intratumoral Tregs. Furthermore, ROSE12 was well tolerated in cynomolgus monkeys in a repeated-dose toxicity study.
Conclusions
ROSE12 is a novel FcR affinity-enhanced anti-CTLA-4 switch antibody with potent anti-tumor efficacy and a wide therapeutic window due to its tumor-selective activity. These results strongly support the clinical testing of ROSE12 for the treatment of solid tumors. Currently, ROSE12 is undergoing a phase 1 clinical study (NCT05907980).
Ethics Approval
All animal studies were reviewed and approved by the Institutional Animal Care and Use Committee (IACUC). All studies using human material were approved by Chugai Pharmaceutical Co., Ltd.’s Research Ethics Committee.