Why allosteric TYK2 inhibition is a distinct drug class

Allosteric TYK2 inhibitors work by binding the JH2 pseudokinase domain of tyrosine kinase 2 rather than the catalytic active site—a structural distinction that delivers greater than 100-fold selectivity over JAK1, JAK2, and JAK3 in biochemical and cellular assays. This selectivity is not incidental: the JH2 regulatory binding pocket is structurally unique to TYK2 and absent in other JAK family members, as confirmed by crystal structure analysis of TYK2 JH2 bound to allosteric inhibitors.

The functional consequence of JH2 inhibition is a selective block of the cytokine pathways that TYK2 mediates: IL-12, IL-23, and type I interferon signalling. These three pathways are central to the pathogenesis of psoriasis, inflammatory bowel disease, systemic lupus erythematosus, and multiple sclerosis—precisely the indications targeted by Ventyx’s lead compounds. According to structural and biochemical studies published in peer-reviewed literature, pharmacological stabilisation of the TYK2 pseudokinase domain blocks autoimmune pathways in both mice and humans without impeding JAK1, JAK2, or JAK3 signalling.

This mechanistic precision matters commercially because the FDA has issued boxed warnings across the entire pan-JAK inhibitor class, citing cardiovascular risk, malignancy, and venous thromboembolism. Compounds that inhibit only TYK2’s regulatory domain are mechanistically distinct from JAK1/2/3 inhibitors and are not subject to the same class-wide regulatory designation—a competitive and regulatory opening that both Bristol-Myers Squibb and now Lilly have moved to exploit.

VTX958 and the Ventyx immune pathway portfolio

VTX958 is Ventyx Biosciences’ lead asset: a selective allosteric inhibitor of the TYK2 JH2 domain with Phase 1 and Phase 2 clinical data in psoriasis demonstrating dose-dependent suppression of IL-12/IL-23/IFN-alpha signalling and a favourable pharmacokinetic profile. Active clinical development is underway in Crohn’s disease, ulcerative colitis, and systemic lupus erythematosus—four indications where TYK2-dependent cytokine pathways are mechanistically implicated.

In SLE, patient cohort data show elevated TYK2-dependent interferon gene signatures, particularly in lupus nephritis. In IBD, intestinal biopsies from Crohn’s disease and ulcerative colitis patients demonstrate upregulated TYK2 expression and STAT4 phosphorylation; murine colitis models treated with TYK2 inhibitors show reduced Th1 and Th17 differentiation and ameliorated disease. These mechanistic data underpin the multi-indication development strategy that makes VTX958 strategically valuable beyond psoriasis alone.

“TYK2 inhibitors may achieve broader type I and type II cytokine blockade—covering IL-12, IL-23, and the interferon pathway—versus biologic anti-IFN agents, with the additional advantage of oral dosing.”

Crucially, the Ventyx portfolio acquired by Lilly is not a single-asset deal. Two additional mechanisms complement VTX958. VTX002 is a selective S1P1 receptor agonist for ulcerative colitis and Crohn’s disease, designed to modulate lymphocyte trafficking via S1P1 without engaging S1P2, S1P3, S1P4, or S1P5 receptors—a selectivity profile intended to achieve gut-restricted efficacy with reduced cardiac and pulmonary off-target effects compared to siponimod and ozanimod. VTX3232 is a selective NLRP3 inflammasome inhibitor that blocks caspase-1 activation and IL-1beta/IL-18 maturation, with preclinical activity demonstrated in gout, SLE, and IBD models. This three-mechanism structure gives Lilly combinatorial flexibility across IBD, lupus, and inflammatory disease that no single JAK or TYK2 asset could provide.

The TYK2 patent landscape: 18+ Ventyx families and rising competition

Ventyx Biosciences filed more than 18 patent families covering TYK2 inhibitor scaffolds, all published in January 2023 and all targeting allosteric inhibition through the JH2 pseudokinase domain. The chemical diversity of these filings is notable: the portfolio spans tricyclic heterocycles, fused bicyclic heterocycles, bicyclic heterocycles, pyridinones, tetrahydropyridopyrimidines, dihydropyranopyrimidines, bicyclic dihydropyrimidines, spiro-ring compounds, tricyclic dihydropyrimidines, heterocyclic compounds, imidazopyrimidines, spirocyclic compounds, fused ring compounds, azaindoles, indoles, azanaphthalenes, thiophenes, and pyrimidinones. This breadth of scaffold coverage creates a dense intellectual property thicket around the JH2 allosteric binding pocket.

Bristol-Myers Squibb holds the foundational patent position in this space through its pyrrolopyridazine TYK2 JH2 allosteric inhibitor patent family, which covers deucravacitinib and related deuterated analogs with claims across psoriasis, psoriatic arthritis, IBD, SLE, and multiple sclerosis. BMS’s discovery work, published in peer-reviewed journals, established the structural basis for JH2-selective inhibition and the >100-fold JAK selectivity that has become the benchmark for the class, according to research published in Nature and related journals.

AbbVie has taken a differentiated approach, filing patents for dual TYK2/JAK1 inhibitor compounds intended to provide broader cytokine pathway coverage while maintaining selectivity over JAK2 and JAK3 to reduce haematological and thrombotic side effects. Pfizer has filed patents covering selective TYK2 JH2 domain inhibitor scaffolds for atopic dermatitis, psoriasis, and Crohn’s disease. AstraZeneca has filed patents for macrocyclic TYK2 inhibitors—a structurally novel scaffold class—targeting psoriasis, atopic dermatitis, SLE, and IBD. The convergence of four major pharmaceutical companies on the same JH2 allosteric pocket, alongside Lilly’s Ventyx acquisition, signals that TYK2 selectivity has moved from a scientific hypothesis to a validated commercial priority, as tracked by organisations including WIPO in its annual technology trend reports.

Pan-JAK safety signals and the regulatory opening for TYK2 selectivity

Pan-JAK inhibitors—including tofacitinib (Pfizer), baricitinib (Lilly/Incyte), upadacitinib (AbbVie), and filgotinib (Galapagos/Gilead)—share class-wide safety risks that have reshaped the regulatory and prescribing environment. Systematic review of JAK inhibitor safety across the drug class identifies infection, malignancy, and venous thromboembolism as recurring concerns, with the FDA applying boxed warnings to the entire class. Pan-JAK inhibitors inhibit multiple JAK family members simultaneously; JAK2 inhibition in particular is associated with haematological effects, while JAK3 inhibition affects lymphocyte function in ways that contribute to infection risk.

Lilly’s existing JAK asset, baricitinib, is a JAK1/2 inhibitor approved for rheumatoid arthritis and atopic dermatitis—and carries the class-wide boxed warning. The strategic logic of the Ventyx acquisition is therefore partly defensive as well as offensive: VTX958 provides Lilly with a next-generation immunology asset that is mechanistically distinct from baricitinib, positioned to capture patients and prescribers seeking the efficacy of JAK pathway modulation without the safety concerns that have constrained pan-JAK market uptake. Regulatory agencies including the EMA have similarly scrutinised the pan-JAK class, reinforcing the commercial value of TYK2 selectivity.

The clinical evidence supporting this differentiation is anchored by deucravacitinib’s Phase 3 results: a PASI 75 response of 58.4% at week 16 versus 35.1% for apremilast and 12.7% for placebo. Long-term extension data for deucravacitinib show sustained PASI responses up to two years with a favourable safety profile. These results establish the clinical proof-of-concept that TYK2 allosteric inhibition delivers meaningful efficacy in psoriasis—the data platform on which VTX958’s Phase 2 programme is building.

Competitive dynamics: BMS, AbbVie, Pfizer, AstraZeneca, and Lilly’s position

The TYK2 inhibitor competitive landscape is defined by BMS’s first-mover advantage with deucravacitinib and the subsequent entry of four major pharmaceutical companies—Lilly (via Ventyx), AbbVie, Pfizer, and AstraZeneca—each pursuing differentiated positions within the same JH2 allosteric mechanism. The competitive dynamics differ by indication, clinical stage, and chemical scaffold.

In psoriasis, deucravacitinib is already approved and building real-world prescribing data. VTX958’s Phase 2 programme in psoriasis is therefore a head-to-head challenger in an indication where the class is already validated. The key differentiators Lilly will need to establish are either superior efficacy, a more convenient dosing profile, or an expanded label spanning multiple autoimmune conditions that justifies physician preference over the established agent. Clinical development in ClinicalTrials.gov-registered studies is ongoing across all four VTX958 indications.

In IBD, the competitive picture is more open. Upadacitinib (AbbVie) is approved for Crohn’s disease and ulcerative colitis as a JAK1-selective inhibitor, but carries the pan-JAK boxed warning. TYK2-selective agents have not yet demonstrated clinical efficacy in IBD in Phase 3 trials, making this an indication where VTX958 could establish a first-in-class TYK2 label if Phase 2 results are positive. The mechanistic rationale is strong: intestinal biopsies from IBD patients show upregulated TYK2 expression and STAT4 phosphorylation, and TYK2 inhibition in murine colitis models reduces Th1 and Th17 differentiation.

In SLE, the competitive landscape includes approved biologic agents targeting the interferon pathway—most notably anifrolumab (AstraZeneca), an anti-IFNAR monoclonal antibody. Comparative analysis of interferon pathway suppression strategies in SLE suggests that TYK2 inhibitors may achieve broader type I and type II cytokine blockade (covering IL-12, IL-23, and the IFN pathway simultaneously) versus biologic anti-IFN agents, with the additional advantage of oral dosing. If VTX958 can demonstrate this broader cytokine coverage in SLE clinical trials, it would represent a meaningful differentiation from both biologics and pan-JAK inhibitors. The protective TYK2 variant P1104A identified in genome-wide association studies provides further genetic validation of TYK2 as a therapeutic target in neuroinflammatory and autoimmune conditions including multiple sclerosis.

AbbVie’s dual TYK2/JAK1 inhibitor approach represents the most mechanistically distinct competitive strategy: by combining TYK2 and JAK1 inhibition, AbbVie aims for broader cytokine coverage than TYK2-only agents while avoiding JAK2/3-associated haematological and thrombotic risks. Whether this dual approach offers a clinical advantage over selective TYK2 inhibition—or introduces additional safety complexity—is a question that will only be resolved in clinical trials. The data from organisations such as the FDA on JAK class safety will continue to shape prescriber and regulatory attitudes toward any JAK-containing combination strategy.

For Lilly, the Ventyx acquisition achieves three strategic objectives simultaneously: it adds a next-generation immunology asset that is mechanistically distinct from baricitinib; it provides multi-indication pipeline depth across psoriasis, IBD, and SLE with a single platform mechanism; and it delivers the most extensive TYK2 scaffold patent portfolio in the industry—18+ families spanning every major heterocyclic chemotype—creating IP coverage that is difficult for competitors to design around. The integration of VTX002 (S1P1) and VTX3232 (NLRP3) further broadens Lilly’s ability to address IBD and inflammatory disease through complementary, non-JAK mechanisms.