Abstract 1839: CLN-617 is a first-in-class fusion protein that retains IL-2 and IL-12 in the injected tumor and potently triggers systemic anti-tumor immunity
Authors: Mehta Naveen K. , Rakhra Kavya , Meetze Kristan , Wittrup K. Dane , Michaelson Jennifer S. , Baeuerle Patrick A. 
Published: June 2023

Abstract
Despite clinical evidence of anti-tumor activity, cytokine therapies have been hampered by a narrow therapeutic window and limited efficacy. Two cytokines of interest are IL-2 and IL-12, which synergize to proliferate and activate T cells and natural killer cells. However, the only approved human IL-2 product (Proleukin) is rarely used in the clinic due to systemic toxicities, and no IL-12 product has been approved to date due to severe dose-limiting toxicities. Here, we describe CLN-617, a first-in-class therapeutic designed for intratumoral (IT) injection and retention, that co-delivers IL-2 and IL-12 in a safe and effective manner. CLN-617 is a single-chain fusion protein comprised of human IL-2, leukocyte-associated immunoglobulin-like receptor 2 (LAIR2), human serum albumin (HSA), and human IL-12. LAIR2 and HSA functionally retain CLN-617 in the injected tumor by binding collagen and increasing molecular weight, respectively.
A murine surrogate of CLN-617, mCLN-617, was delivered either IV or IT in B16F10 tumor-bearing mice. The concentration of mCLN-617 as measured in serum two hours after IT administration was &lt;5% that of the concentration following IV administration, demonstrating robust retention of mCLN-617 in the tumor. Following mCLN-617 treatment, durable and complete responses with no significant body weight loss were observed in checkpoint-refractory tumor models, including B16F10, CT26, and MC38.
mCLN-617 triggered a robust systemic anti-tumor immune response based on three lines of evidence. First, in mice implanted with two MC38 tumors, 70% of injected tumors and 40% of non-injected tumors were eradicated. When combined with IV-administered anti-PD1 antibody, &gt;90% of both injected and non-injected tumors showed a complete response, while anti-PD1 alone exhibited no anti-tumor activity. Second, in mice implanted with an MC38 tumor in the flank and with luciferase-expressing MC38 cells delivered to the liver via intra-splenic injection, the injected flank tumor exhibited ~90% growth inhibition with either mCLN-617 monotherapy or anti-PD1 co-administration. Growth of established metastatic tumors, as measured by luciferase signal, was inhibited by mCLN-617 monotherapy, and metastatic tumor burden significantly regressed in combination with anti-PD1, while anti-PD1 alone exhibited no anti-tumor activity in the metastases. Third, in mice bearing two MC38 flank tumors, tumor-specific CD8+ T cells expanded in both the injected and non-injected tumors and in peripheral blood. We conclude that IT-administered mCLN-617 is efficiently retained in the injected tumor, thereby preventing systemic toxicity of the two cytokines, yet can activate and remodel systemic immunosurveillance for clearance of non-injected distal lesions.
A phase I trial of CLN-617 in patients with advanced solid tumors is expected to commence in 2023.
Citation Format: Naveen K. Mehta, Kavya Rakhra, Kristan Meetze, K. Dane Wittrup, Jennifer S. Michaelson, Patrick A. Baeuerle. CLN-617 is a first-in-class fusion protein that retains IL-2 and IL-12 in the injected tumor and potently triggers systemic anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1839.