[Edaily Reporter KIM SAE-MI ] With the U.S. Food and Drug Administration (FDA) approving a new oncolytic virus therapy for the first time in about 11 years, attention in South Korea is turning to SillaJen, Inc.(215600), which is developing an antiviral platform. This is because the company is developing the “SJ-600 Series” with the goal of intravenous administration, having improved the delivery method—a limitation often cited in existing oncolytic virus therapies.

First FDA Approval of an Antiviral Cancer Therapy in 11 Years… A Signal for a Resurgence in the Field?

According to the biotech industry on the 19th, the U.S. Food and Drug Administration (FDA) granted accelerated approval on the 6th to Replimune’s anticancer virus therapy “Tudriqev.” This is the first anticancer virus therapy approved by the FDA since Amgen’s “Imlygic” in 2015.

Tudriqev was approved for use in combination with Bristol-Myers Squibb’s (BMS) immunotherapy “Opdivo” for adults with unresectable, advanced cutaneous melanoma whose disease has progressed after receiving anti-PD-1 therapy. The treatment involves directly injecting a genetically modified herpes simplex virus type 1 (HSV-1) into the tumor to destroy cancer cells and induce an immune response.

The objective response rate (ORR) for the Tudrikev and Opdivo combination therapy was 24.2%, and the median duration of response (mDOR) was 14.1 months. Based on these results, the FDA granted accelerated approval. As this is an accelerated approval, Replimun must further demonstrate the drug’s clinical utility through confirmatory clinical trials in the future.

Replimun faced two setbacks during the Tudrikev approval process. The FDA issued Seohans (Letters of Complete Response) in July 2025 and last April, raising concerns regarding the single-arm clinical trial design and the evidence of efficacy. Following a resubmission and a review by the Advisory Committee, the company received accelerated approval on its third attempt.

Expectations for

Oncolytic Virus Reevaluation Rise… SillaJen, Inc. Differentiates Itself with

“Intravenous Administration”
The biotech industry expects this approval to provide new momentum for the oncolytic virus sector, which has seen few new drug approvals in recent years. The reasoning is that since the strategy of combining oncolytic viruses with immune checkpoint inhibitors to improve treatment outcomes for patients who did not respond to existing therapies has led to actual approval, companies currently developing related technologies may also be reevaluated.

A biotech industry official stated, “With the FDA’s approval of Replimun, the entire field of oncolytic viruses is undergoing a reevaluation,” adding, “Now that the market uncertainty that had persisted for years has been resolved, the development and commercialization of related therapies will accelerate further.”

In South Korea, attention is focused on SillaJen, Inc.’s next-generation platform, the “SJ-600 Series,” which the company has been developing for anticancer viruses. The SJ-600 Series is an oncolytic virus platform based on the vaccinia virus, with its core feature being the expression of “CD55”—a human complement regulatory protein—on the virus surface. The development goal is to enhance the efficiency of systemic administration via intravenous injection by reducing the problem of oncolytic viruses being eliminated by complement and neutralizing antibodies in the blood before they reach the tumor.

Since the SJ-600 Series is currently in the preclinical stage, it is difficult to directly compare it with Tudrikev, which has completed human clinical trials. However, it is worth noting that the company has adopted a differentiation strategy in terms of the route of administration.

Todrikev uses an intratumoral (IT) administration method, in which the drug is injected directly into tumor lesions that are accessible via injection. In contrast, SillaJen, Inc. is developing the SJ-600 series as an oncolytic virus platform that can be administered intravenously (IV). While intratumoral administration has the advantage of delivering the drug directly to the tumor, it may face limitations when applied to deep lesions that are difficult to access via injection or to lesions that have spread throughout the body.

In contrast, SillaJen, Inc. is developing the SJ-600 series as an anticancer virus that can be delivered systemically via intravenous (IV) administration. To achieve this, the virus is designed to express CD55 on its envelope to evade attack by the complement system—the innate immune system in the blood. SillaJen, Inc.’s goal is to maintain viral activity even in environments where neutralizing antibodies have formed, thereby enabling repeated intravenous administration.

Accumulating Preclinical Data on SJ-600… Accelerating Production and Patent Acquisition

Results from related preclinical studies have also been announced. In a study published in 2023 in the international journal *Journal for ImmunoTherapy of Cancer* (JITC), SJ-607—a candidate in the SJ-600 series—demonstrated resistance to viral neutralization by serum. Anticancer effects were confirmed in animal models following a single intravenous administration.

Research results on SJ-650, a follow-up candidate, regarding CD55-based immune evasion and systemic administration were also published this year in the journal *Molecular Therapy*. The research team confirmed that SJ-650 maintained its anticancer efficacy even in an immunocompetent breast cancer animal model where neutralizing antibodies were present.

Oncolytic viruses infect and destroy cancer cells while simultaneously releasing tumor antigens to induce an immune response. If the feasibility of repeated intravenous administration is confirmed in clinical trials, there is potential to expand the scope of application to tumors that are difficult to treat with direct injection or to cancers with systemic metastases. This is why attention is focused on whether the SJ-600 series will enter clinical trials.

SillaJen, Inc. is also establishing a production system to support the clinical development of the SJ-600 series. Last year, the company signed a comprehensive collaboration agreement with ReiThera, an Italian contract development and manufacturing organization (CDMO), to prepare for the production of clinical trial drugs, while also expanding its portfolio of domestic and international patents.

A SillaJen, Inc. official emphasized, “Based on our expertise and data from leading global Phase 3 clinical trials with oncolytic viruses, SillaJen, Inc. is accelerating the development process for the SJ-600 series,” adding, “The results validated through various preclinical studies have been published in world-renowned academic journals, thereby securing technical credibility.”