Kymera Therapeutics has presented new preclinical data for its investigational drug, KT-579, an oral treatment designed to target a key driver of autoimmune diseases.

The data was showcased at the American College of Rheumatology (ACR) Annual Meeting 2025, taking place from 24-29 October in Chicago, US. The findings position KT-579 as a potential future treatment for autoimmune conditions like systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and Sjögren’s syndrome.

Targeting a Master Regulator of Immunity

According to the Massachusetts (US)-based company, KT-579 is an IRF5 degrader. IRF5 is a protein known as a “master regulator of innate immunity”, orchestrating multiple inflammatory pathways. Kymera’s approach uses its proprietary targeted protein degradation platform.

Instead of just inhibiting IRF5, KT-579 is designed to completely remove the protein from cells. This unique mechanism offers the potential for broad suppression of the multiple pathogenic signaling cascades that IRF5 activates, which are implicated in various autoimmune disorders.

Currently, KT-579 is in IND-enabling studies, the final stage of research before seeking regulatory approval to begin human trials. The company has announced its intention to advance the oral therapy into Phase I clinical testing in early 2026.

Demonstrating Broad Preclinical Efficacy

The newly presented data demonstrates that KT-579 achieved robust, disease-modifying activity across multiple preclinical models of SLE and RA.

In lupus models, the investigators outline the scientific rationale for targeting the transcription factor IRF5, which sits downstream of endosomal toll-like receptor (TLR) activation (particularly TLR7, TLR8, TLR9) and regulates pro-inflammatory cytokines (TNFα, IL-6, IL-12, IL-23), type I interferons and autoantibody production.

The treatment significantly reduced key disease markers, including interferon-stimulated genes and serum autoantibodies, and protected against kidney disease progression. Functional assays in healthy donor and SLE patient-derived PBMCs showed that KT-579 suppressed TLR7/8-induced cytokines and TLR9-induced IgG secretion.

In RA models, KT-579 produced a dose-dependent reduction in joint swelling and protected against bone destruction. Additional experiments confirmed its ability to block pro-inflammatory cytokines and prevent pathogenic T cell differentiation.

In the human cell-based assays, KT-579 demonstrated high selectivity for IRF5 over related IRF family members. Downstream of toll-like receptor (TLR) activation, treatment with KT-579 reduced key pro-inflammatory cytokines in monocyte, macrophage, and dendritic cell settings (e.g., following TLR4, TLR7, TLR8 stimulation). These findings indicate that KT-579 mitigates innate immune activation at potencies in the nanomolar range, consistent with a robust functional degradation of IRF5.

In in-vivo experiments using the antigen-induced arthritis (AIA) mouse model of RA, daily oral administration of KT-579 achieved approximately 90 % IRF5 degradation. This was correlated with significant reductions in joint swelling, systemic pro-inflammatory cytokines (IL-12, IL-6, CXCL1), and infiltrating Th1-type T cells in the joint tissue. Remarkably, the effect size was comparable to the JAK inhibitor Pfizer’s Xeljanz (tofacitinib), though the mechanism of action is distinct.

Preclinical safety studies further showed deep IRF5 depletion across species with no adverse signals at exposures up to 200-fold greater than predicted human efficacious levels.