1320 Identification of PD1-IL2 TAP – a PD-1 blocking immunoconjugate harboring a tumor-activatable masked IL-2 payload lacking binding to IL2Ra/CD122

Background

Immunocytokines provide the opportunity to simultaneously address distinct and complementary mechanisms of action and to deliver cytokine payloads to specific immune cells ('cis-signaling') resulting in enhanced anti-tumor activity. However, there is increasing evidence that use of constitutively active IL-2 payload limits the therapeutic index of PD1-IL2 immunocytokines due to systemic toxicity resulting from potent IL-2 induced immune cell activation and release of pro-inflammatory cytokines in the periphery.

Methods

To overcome this issue, we have generated a conditionally activatable PD1-IL2 immunoconjugate consisting of an optimized and masked IL-2 payload conjugated to a human PD-1 blocking antibody. Using our novel chemical protein synthesis technology, we generated an IL-2 TAP (Tumor Activated Payload) variant lacking binding to IL2Rb/CD122. The IL-2 TAP protein harbors a protease-cleavable sequence which would be processed specifically in the tumor microenvironment to yield the unmasked and activated IL-2 payload.

Results

In vitro, efficient blockade of binding to CD122 translates into significantly reduced pSTAT5 induction by masked PD1-IL2 TAP in PD-1 negative cells. Following protease-mediated processing and further enhancement by cis-signaling, activated PD1-IL2 TAP exhibits a 10,000-fold increase in potency in cells expressing PD-1. We confirmed stability of the IL-2 TAP payload in plasma and observed efficient activation ex vivo by primary human tumor tissue but not by healthy or normal adjacent tissue. In line with this, we observed a long plasma half-life for PD1-IL2 TAP in a PK/PD study performed in mice expressing human PD-1. The IC was very well tolerated at high doses and there was no evidence for TMDD indicating that PD1-IL2 TAP was indeed stable in circulation. Importantly, PD1-IL2 TAP was able to induce a strong local expansion of CD8+ T cells specifically within the tumor microenvironment, and intra-tumoral PD effects correlated with the induction of potent and durable anti-tumor efficacy.

Conclusions

Collectively, the data indicate that, using Bright Peak's chemical synthesis and ligation technology, we were able to generate a conditionally activatable PD1-IL 2 TAP immunoconjugate that exhibits a significantly increased therapeutic index, thus, mitigating the known safety risks associated with ICs harboring potent non-masked IL-2 payloads.