With the first FDA-approved PROTAC now on the market, targeted protein degradation is expanding beyond oncology and into autoimmune and inflammatory disease.
May 15, 2026
The May 2026 FDA approval of vepdegestrant (Veppanu) for ESR1-mutated, ER-positive/HER2-negative advanced breast cancer provided the first regulatory validation of a PROTAC therapy. At the same time, targeted protein degradation (TPD) programs are increasingly moving beyond oncology and into immunology.
Programs from Kymera, Sanofi, Novartis, Monte Rosa, and others are testing whether oral degraders can address inflammatory pathways that have traditionally been treated with biologics. The opportunity is significant, but so are the engineering and safety challenges.
1. Why Targeted Protein Degradation Is Moving Into Autoimmune Disease
Autoimmune and inflammatory diseases such as psoriasis, atopic dermatitis, hidradenitis suppurativa, lupus, and rheumatoid arthritis affect large patient populations and often require long-term treatment. Many of today's most effective medicines are injectable biologics.
TPD offers a different therapeutic concept. Rather than inhibiting a protein's active site, a degrader recruits the cell's protein-disposal machinery to remove the target protein itself. In principle, this can address proteins that are difficult to inhibit conventionally, including scaffold proteins and transcription factors. It may also create opportunities for oral medicines that modulate pathways currently dominated by biologics.
That possibility should not be overstated: oral exposure, target selectivity, durability, and long-term safety all need to be demonstrated program by program. But the growing number of clinical immunology assets shows that TPD has moved beyond a purely conceptual extension from oncology.
2. PROTACs vs. Molecular Glues: Different Drug-Design Challenges
PROTACs: oral exposure beyond the Rule of Five
PROTACs typically combine a ligand for the target protein, a ligand for an E3 ubiquitin ligase, and a linker. Their size and polarity often place them well beyond conventional small-molecule design rules, including Lipinski's Rule of Five. As a result, membrane permeability and oral bioavailability can be difficult to achieve.
Developers are using conformational control and 'molecular chameleon' behavior to reduce the effective polar surface exposed during membrane passage. Intramolecular hydrogen bonding and dynamic conformations can allow a large molecule to remain sufficiently soluble in aqueous environments while becoming less polar as it crosses a lipid membrane. These strategies are important if PROTACs are to support chronic oral dosing.
Molecular glues: smaller molecules, harder discovery
Molecular glues do not require a long linker connecting two independent ligands, so they can retain more conventional small-molecule properties. Their challenge has historically been predictability. Molecular glues often work by reshaping or stabilizing an interaction between an E3 ligase and a new substrate, and many early examples were discovered empirically rather than designed from first principles.
Structural biology, computational chemistry, and machine-learning approaches are increasingly being used to predict protein-protein interactions and ternary complexes. These tools may make molecular-glue discovery more systematic, although the field remains less programmable than the strongest marketing language sometimes implies.
3. Key Autoimmune Targets: IRAK4, STAT6, and VAV1
IRAK4: degrading both catalytic and scaffold functions
IRAK4 participates in Toll-like receptor and IL-1 receptor signaling as both a kinase and a scaffold protein. This makes it an attractive example of why degradation can differ from catalytic inhibition: removing the entire protein can potentially suppress functions that remain intact when only the kinase domain is inhibited.
Kymera and Sanofi developed the oral IRAK4 degrader KT-474 and advanced it into clinical testing in hidradenitis suppurativa and atopic dermatitis. In June 2025, the companies announced that Sanofi would not advance KT-474 and would instead prioritize the next-generation degrader KT-485, which Kymera described as having improved preclinical selectivity, potency, and safety characteristics. The public company update did not identify a single clinical event as the sole reason for the transition.
STAT6: an oral approach to the IL-4/IL-13 pathway
STAT6 is a central transcription factor downstream of IL-4 and IL-13 signaling, a pathway already validated by biologic therapies such as dupilumab. Because transcription factors are often difficult to inhibit with conventional small molecules, STAT6 has become an important test of whether degradation can offer an oral alternative to pathway-blocking biologics.
Kymera's KT-621 has provided an early clinical test of this thesis. In Phase 1b data presented in 2026, Kymera reported median STAT6 degradation of 98% in blood and 94% in skin in the studied dose groups, along with changes in downstream biomarkers. These are early data and should not be interpreted as proof of clinical equivalence to dupilumab; later-stage trials will be needed to establish efficacy, safety, and durability.
VAV1: exploiting immune-cell biology
VAV1 is highly enriched in hematopoietic cells and plays a role in T-cell and B-cell receptor signaling. Monte Rosa's MRT-6160 is a VAV1-directed molecular glue degrader licensed to Novartis for development in immune-mediated diseases.
Monte Rosa reported greater than 90% VAV1 degradation in its Phase 1 study, together with inhibition of T- and B-cell functional readouts and cytokine release in ex vivo stimulation assays. The program has since advanced toward multiple Phase 2 studies under the Novartis collaboration. As with other immune degraders, the clinical question is not only how deeply the target can be degraded, but whether that depth produces an acceptable balance between disease control and immune competence.
4. Beyond Systemic Oral Degraders: Local and Extracellular Strategies
Local delivery and tissue-restricted degradation
One way to reduce systemic risk is to limit where a degrader is active. For dermatologic or gastrointestinal disease, developers can explore topical or gut-restricted molecules that maintain high local exposure while minimizing systemic concentrations. Soft-drug design may further allow molecules to be rapidly inactivated if they enter the circulation.
Extracellular protein degradation
Conventional PROTACs use the intracellular ubiquitin-proteasome system and therefore do not directly address extracellular cytokines or membrane proteins. Newer technologies such as LYTACs and antibody-based degradation systems are being developed to recruit endocytic or lysosomal pathways instead.
These approaches could broaden the range of degradable targets, including extracellular proteins relevant to immune disease. However, they remain an emerging area and should be viewed as complementary experimental platforms rather than established replacements for neutralizing antibodies.
5. Safety Challenges for Chronic Targeted Protein Degradation
Dependence on a limited set of E3 ligases
Many clinical degraders still rely on a relatively small number of E3 ligases, particularly CRBN and VHL. Expanding the E3-ligase toolbox could enable greater tissue selectivity and may reduce some liabilities associated with broadly expressed ligases. The long-term consequences of repeated recruitment of the same ligase in chronic disease are still being studied.
Off-target degradation
The history of thalidomide illustrates why unintended protein degradation matters. Its teratogenicity is linked in part to cereblon-dependent degradation of developmental proteins including SALL4. Modern degraders are designed with much greater mechanistic understanding, but the example remains a reminder that degradation of an unintended physiologic protein can have serious consequences.
Balancing efficacy with immune competence
Autoimmune treatment aims to control pathologic immune activity without eliminating normal host defense. Deep degradation of a central immune-pathway protein could increase infection risk if the therapeutic window is too narrow. For chronic systemic degraders, long-term safety and dose selection may therefore be as important as the maximum percentage of target degradation.
What Comes Next for Targeted Protein Degradation in Immunology?
The move from oncology into autoimmune disease is more than a change of indication. It requires different assumptions about dosing duration, tolerability, patient risk, and the value of oral administration.
PROTACs are testing whether very large, beyond-Rule-of-Five molecules can become practical chronic oral medicines. Molecular glues are testing whether difficult immune targets can be addressed with smaller, more drug-like molecules. At the same time, local and extracellular degradation technologies are expanding the design space.
The field is promising, but claims that degraders will broadly replace biologics remain premature. The most informative data over the next several years will come from controlled clinical studies showing whether deep target degradation translates into durable clinical benefit without unacceptable infection or off-target risk.
Why This Matters
For immunology and drug-discovery teams, targeted protein degradation is becoming a practical development modality rather than an oncology-only concept. The key opportunity is access to difficult targets and oral dosing; the key constraint is whether the same potency can be delivered with the safety profile required for chronic autoimmune disease.
References
• U.S. Food and Drug Administration. FDA approval of vepdegestrant (Veppanu), May 1, 2026.
• Kymera Therapeutics. Sanofi IRAK4 collaboration update: KT-485 prioritized and KT-474 not advanced, June 25, 2025.
• Kymera Therapeutics. KT-621 Phase 1b data presented at AAD 2026.
• Monte Rosa Therapeutics. MRT-6160 Phase 1 results and 2026 development updates.
• J. Med. Chem. 2024;67(13):11421-11434.
• Science. 2025;389(6755):eadt6736.
• Nature Reviews Drug Discovery. 2024;23:126-140.
Reprinted from BiG. BiG Bio Innovation Society is a nonprofit life-science industry platform connecting researchers, companies, investors, and innovators, and is an affiliated association of Direct2Lab.
