First-in-Class Antibody Targeting USAG-1 Enters Human Trials to Regrow Teeth Naturally

For generations, the loss of a permanent tooth has been an irreversible biological event, leaving patients with a limited menu of mechanical workarounds. Dentures, bridges, and titanium implants have advanced significantly over the decades, but they remain artificial substitutes that cannot fully replicate the periodontal ligaments, nerves, and blood vessels of a natural tooth. Now, a Japanese biotechnology company is advancing a clinical trial that treats tooth loss not as a structural deficit to be patched, but as a biological pathway to be reawakened, potentially changing the future of dental care forever. Toregem BioPharma, a specialized biotech spinout from Kyoto University founded in 2020, is currently moving its experimental drug TRG-035 into Phase II human clinical trials. The drug is a first-in-class humanized monoclonal antibody designed to regenerate missing teeth directly from the patient's own tissue. By targeting a specific protein that actively suppresses dental growth in the jaw, the intravenous therapy aims to unlock a latent biological capability that every human possesses but rarely uses after childhood. If the clinical data holds up, the treatment could eventually render traditional prosthetics obsolete for millions of patients.[3]

The underlying science of the treatment hinges on the biological concept of the 'third dentition.' Humans naturally grow two distinct sets of teeth over a lifetime: the deciduous baby teeth that emerge in infancy, and the permanent adult teeth that replace them. However, researchers have discovered that humans also carry a dormant third set of vestigial tooth buds buried deep within the jawbone. Under normal physiological circumstances, these secondary buds never develop because the body actively suppresses their growth once the adult teeth are in place. The biological 'off-switch' keeping these third-generation buds dormant is a specific protein known as USAG-1, or uterine sensitization-associated gene-1. In the context of dental development, USAG-1 functions as a strict molecular gatekeeper. It works by inhibiting bone morphogenetic protein (BMP) signaling, a crucial pathway that dictates the formation of bone, cartilage, and dental structures. As long as the USAG-1 protein remains active and circulating in the jaw, the third set of tooth buds remains permanently locked in a latent, undeveloped state.[1][2]

TRG-035 is explicitly designed to neutralize this biological barrier. As an anti-USAG-1 antibody, the drug binds directly to the suppressor protein and blocks its inhibitory function. By removing the molecular brakes, the therapy allows the body's natural BMP signaling pathways to resume their work. Theoretically, this prompts the dormant tooth buds to awaken and grow into fully functional teeth, complete with their own natural enamel, dentin, and root structures, perfectly integrated into the patient's jawbone. The foundational evidence for this regenerative mechanism was established in a series of landmark animal studies published in 2021. Researchers engineered a specific lineage of mice with a genetic deficiency that prevented them from growing teeth, mimicking severe congenital tooth agenesis. When these toothless mice were administered the USAG-1 neutralizing antibody, they successfully grew new, structurally sound teeth. This breakthrough demonstrated that the dormant biological machinery could be pharmacologically reactivated, providing the first tangible proof that antibody therapy could reverse genetic tooth loss.[1][3]

Because mice have vastly different dental patterns than humans, the research team subsequently tested the antibody on ferrets. Ferrets are highly valuable in dental research because they possess a diphyodont dental pattern—meaning they naturally grow both baby and adult teeth in a sequence much like humans do. A single injection of the antibody in the ferrets triggered the growth of a complete, functional third set of teeth without causing severe adverse physiological effects, providing the critical proof-of-concept needed to justify human translation. The highly anticipated transition from animal models to human testing officially began in late 2024. Kyoto University Hospital launched a Phase I clinical trial enrolling 30 healthy adult men between the ages of 30 and 64, each of whom was missing at least one molar. The primary objective of this initial phase was strictly to evaluate the safety, dosing, and tolerability of the intravenous antibody in humans, rather than to measure actual tooth regrowth in the participants.[2]

With the Phase I safety window concluding without any reports of serious adverse events, Toregem BioPharma recently secured an additional $5.3 million in Pre-Series C financing in mid-2026, bringing its total clinical funding to over $29 million. This new capital injection is specifically earmarked to launch Phase II clinical trials across Japan, shifting the focus from healthy adult volunteers to the drug's first true target patient population, where the clinical stakes are significantly higher. The upcoming Phase II trials will focus exclusively on children suffering from severe congenital hypodontia, a rare genetic condition characterized by the absence of six or more permanent teeth from birth. Affecting roughly 0.1 percent of the global population, the condition presents profound clinical challenges for pediatric dentists. Because children's jawbones are still actively growing and shifting, traditional titanium implants cannot be safely placed until adulthood, forcing pediatric patients to rely on removable dentures that can severely impede nutrition, speech development, and normal facial bone growth.[1]

For these young patients, TRG-035 represents a potential curative treatment rather than a decades-long management strategy. By regrowing the missing teeth naturally while the jaw is still developing, the therapy could eliminate years of invasive dental surgeries and prosthetic adjustments. Recognizing the high unmet medical need for congenital tooth agenesis, Japan's Ministry of Health, Labour and Welfare has already granted the experimental drug Orphan Medicinal Product designation, expediting its regulatory pathway. While pediatric congenital conditions serve as the initial clinical proving ground, the company's ultimate commercial ambition is vastly broader. Toregem hopes to eventually expand the therapy's application to the millions of adults who have lost teeth due to severe decay, advanced periodontal disease, or traumatic injury. The global scale of acquired tooth loss is staggering; the World Health Organization estimates that nearly 23 percent of adults over the age of 60 suffer from complete edentulism, meaning the loss of all their natural teeth.[2][3]

However, independent dental experts caution that significant clinical uncertainties remain before the therapy can be reliably applied to age-related tooth loss. One major biological question is whether older adults retain a sufficient population of dental epithelial cells—the foundational stem cells required for tooth development—to respond to the USAG-1 blockade. While children with congenital agenesis still possess highly active dental tissues, a 70-year-old jawbone may lack the cellular raw material necessary to grow a new tooth, even if the molecular brakes are successfully removed. Another critical hurdle facing the researchers is spatial targeting. Dentists and molecular biologists have raised concerns about whether a systemically administered intravenous antibody can be precisely directed to regrow a single specific missing tooth without inadvertently triggering hyperdontia—the uncontrolled growth of extra teeth in other, healthy parts of the mouth. Ensuring that the drug only activates dormant buds in empty sockets, rather than disrupting existing healthy teeth, will be a primary focus of advanced clinical testing.

Despite these formidable biological challenges, the momentum behind the research is undeniable. Toregem BioPharma has publicly stated an aggressive target of 2030 for broad commercial availability, assuming the upcoming Phase II and Phase III trials demonstrate both impeccable safety and definitive efficacy in regrowing human teeth. The continuous influx of venture capital and government grants suggests that biotech investors and public health officials alike share this optimism for a regenerative breakthrough. Even if the commercial timeline stretches further into the next decade, the development of TRG-035 marks a fundamental paradigm shift in dental medicine. By proving that the biological pathways for tooth generation remain intact and accessible long after childhood, researchers are fundamentally reframing how we view oral health. They are opening the door to a future where the dentist's chair offers true biological regeneration, treating tooth loss as a reversible condition rather than a permanent deficit.[2][3]