IL23A Antibody

What is IL23A and why is it a significant research target?

IL23A (interleukin 23 subunit alpha) is a 189-amino acid residue protein encoded by the IL23A gene in humans that associates with IL12B to form the pro-inflammatory cytokine IL-23. This heterodimeric cytokine plays crucial roles in both innate and adaptive immunity . IL23 is a validated target with genetic linkage to various human autoimmune diseases, making antibodies against it valuable therapeutic tools and research reagents . The protein is primarily expressed in the tonsil, testis, lymph node, bone marrow, and appendix, featuring post-translational modifications and secretion into the extracellular space . IL23P19 is a commonly used synonym in the scientific literature .

How do different anti-IL23 antibodies vary in their binding mechanisms?

Anti-IL23 antibodies exhibit distinct binding mechanisms that directly impact their efficacy. Most therapeutic antibodies target the p19 subunit (IL23A) specifically, but differ in how they inhibit receptor interaction. Risankizumab and guselkumab bind to the p19 subunit and block its interaction with the IL-23Rα receptor subunit directly . In contrast, tildrakizumab demonstrates a unique inhibitory mechanism - it can still allow IL-23 to bind to IL-23Rα, but reduces this affinity approximately 200-fold (from 0.8 nM to 190 nM), suggesting negative allosteric modulation rather than competitive inhibition . This mechanistic diversity explains the varying potencies observed in functional assays and highlights the importance of selecting the appropriate antibody for specific research applications.

What experimental readouts best measure anti-IL23A antibody activity?

The most informative experimental readouts for measuring anti-IL23A antibody activity include:

• STAT3-driven luciferase reporter assays using cells expressing human IL-23Rα and IL-12Rβ1 receptors

• Phosphorylated STAT3 (pSTAT3) assays using human whole blood, measuring increases in CD45+CD161hi cells

• IL-17 production in mouse splenocytes stimulated with IL-23

• Surface plasmon resonance (SPR) for measuring binding kinetics

These complementary approaches provide comprehensive functional assessment. For instance, in the STAT3 reporter assay, risankizumab demonstrated an IC50 of 23 pM, showing 2.6-fold higher potency than guselkumab (59 pM), 9-fold higher than tildrakizumab (203 pM), and 14-fold higher than ustekinumab (316 pM) . Similarly, the whole blood pSTAT3 assay revealed a comparable potency ranking, confirming these findings through different methodological approaches .

How should researchers select an appropriate anti-IL23A antibody for their specific applications?

When selecting an anti-IL23A antibody, researchers should consider:

• Target specificity: Determine whether the antibody binds specifically to the p19 subunit (IL23A) versus the p40 subunit (shared with IL-12)

• Binding affinity: Higher affinity antibodies generally offer greater sensitivity in detection assays and more complete blockade in functional studies

• Application compatibility: Verify validation for specific techniques (WB, ELISA, IHC, etc.) as demonstrated in published citations

• Species reactivity: Confirm cross-reactivity with the species being studied (human versus mouse models)

• Clone characteristics: Evaluate complementarity-determining regions (CDRs) for potential sequence liabilities that might affect stability and performance

Commercial anti-IL23A antibodies vary significantly in these parameters. For instance, some are specifically validated for Western Blot applications with mouse reactivity , while others offer broader application profiles including WB, ELISA, immunohistochemistry on frozen sections (IHC-fr), and neutralization assays with human specificity . Each application may require different antibody characteristics for optimal results.

What are the critical methodological considerations when measuring IL23A antibody binding affinity?

Measuring binding affinity of anti-IL23A antibodies requires careful attention to several methodological factors:

• Selection of appropriate recombinant antigen: Use mammalian-expressed human recombinant IL-23 with minimal linkers or tags to most accurately represent the native cytokine structure

• Equilibration time: Allow sufficient equilibration time to reach steady state when measuring high-affinity interactions (KD < 100 pM)

• Temperature control: Perform binding studies at physiologically relevant temperatures (e.g., 37°C) rather than room temperature

• Analytical technique selection: Surface plasmon resonance (SPR) or biolayer interferometry (BLI) are preferred for kinetic analysis, while ELISA-based approaches may be suitable for relative ranking

• Format considerations: For accurate measurements, capture antibodies on the chip surface using anti-human IgG Fc polyclonal antibodies and interact with different concentrations of single-chain or heterodimeric IL-23

These considerations are critical to generating reliable binding data. For example, researchers developing BI 655066 (risankizumab) ensured accurate measurements of KD values in the picomolar range by carefully controlling these parameters .

What controls should be included when validating IL23A antibody specificity?

A comprehensive validation panel for IL23A antibody specificity should include:

• Negative controls:

  • Isotype-matched irrelevant antibody

  • Non-expressing cell lines or tissues

  • IL23A knockout/knockdown samples

• Cross-reactivity controls:

  • IL12 (shares p40 subunit) to confirm p19-specific binding

  • Related cytokines (IL-6, IL-17, etc.)

  • Single p19 subunit versus heterodimeric IL-23

• Positive controls:

  • Recombinant IL23 at known concentrations

  • Lipopolysaccharide-stimulated THP-1 cells (natural IL-23 expression)

  • Tissues with confirmed IL23A expression (tonsil, lymph node)

• Functional validation:

  • IL-17 production inhibition in mouse splenocytes

  • STAT3 phosphorylation assays

Proper controls ensure antibody specificity, particularly distinguishing between the p19 (IL23A) and p40 subunits, which is critical since p40 tends to be immunodominant in antibody generation .

How do different anti-IL23A antibodies compare in potency across multiple functional assays?

Different anti-IL23A antibodies demonstrate varying potencies across functional assays, as illustrated in the comparative data below:

*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.0001 compared to risankizumab

This data reveals several important insights:

• Risankizumab consistently demonstrates the highest potency across assays

• The potency ranking remains consistent (risankizumab > guselkumab > tildrakizumab > ustekinumab)

• The whole blood assay generally shows lower IC50 values than the reporter assay

• The difference between IC50 and IC80 values is substantially greater for tildrakizumab and ustekinumab than for risankizumab and guselkumab, suggesting steeper dose-response curves for the latter

These differences reflect the distinct binding mechanisms and affinities of these antibodies, with implications for both research applications and therapeutic efficacy .

What approaches can be used to develop bispecific antibodies targeting IL23A and other inflammatory pathways?

Developing bispecific antibodies targeting IL23A and other inflammatory pathways involves several sophisticated approaches:

• Target selection: Identify complementary inflammatory pathways with genetic linkage to the same diseases. The IL23A-TL1A combination exemplifies this approach, as both targets are clinically validated with genetic links to autoimmune diseases .

• Structural design: Engineer tetravalent structures that maintain the binding characteristics of each parental antibody. For the HXN-1003 bispecific, this involved preserving the p19-specific binding of the anti-IL23 arm while ensuring high-affinity binding to both TL1A trimers and monomers .

• Functional validation: Test for independent blocking of each target and potential synergistic effects. This can be assessed through:

  • IL-23 reporter and mouse splenocyte activation assays for IL-23 function

  • Target-specific assays (e.g., TF-1 apoptosis and DR3-NFκB-Luc reporter assays for TL1A)

  • Combined stimulation assays (e.g., IL-22 secretion in mouse splenocytes co-stimulated with IL-23 and TL1A)

• In vivo model selection: Validate efficacy in transgenic models expressing both human targets under disease conditions relevant to the intended indication (e.g., DSS-induced colitis, IMQ-induced psoriasis, or subcutaneous cytokine-induced dermatitis models) .

The HXN-1003 bispecific demonstrated superior efficacy compared to individual antibodies and even their combination in multiple disease models, highlighting the potential advantages of this approach .

How can researchers overcome the immunodominance of p40 when developing novel anti-IL23A antibodies?

Overcoming the immunodominance of the p40 subunit when developing novel anti-IL23A antibodies requires strategic immunization and screening approaches:

• Design of hybrid immunogens: Create chimeric proteins using mouse p40 and human p19 subunits to direct the immune response toward the p19 component. This approach minimizes the immuno-dominance of p40 that typically results in low-affinity p19-specific antibodies .

• Expression system optimization: Express the hybrid cytokine in mammalian cells as individual p40 and p19 subunits without linkers to mimic the native cytokine structure, rather than using commercially available linked versions that may alter epitope accessibility .

• Functional screening: Select antibodies based on both binding affinity to recombinant human IL-23 and functional inhibition of IL-23-induced IL-17 production in mouse splenocytes, ensuring the identification of functionally relevant antibodies .

• Sequence analysis: Analyze CDRs for potential deamidation sites, iso-aspartic isomerization hot spots, atypical glycosylation sites, and undesirable CDR composition to ensure manufacturability and stability .

This approach has successfully generated diverse, high-affinity antibodies with minimal sequence liabilities, as demonstrated in the development of BI 655066 (risankizumab), which showed only a small number of potential deamidation and aspartate isomerization sequence sites .

What are the most common sources of variability in IL23A antibody experiments and how can they be controlled?

Common sources of variability in IL23A antibody experiments include:

• Antigen preparation variability: Different recombinant IL-23 preparations may vary in activity and structure. Researchers should compare their recombinant IL-23 with naturally expressed IL-23 (e.g., from THP-1 cells) to ensure biological equivalence . Always use the same lot of recombinant protein for comparative studies.

• Cell responsiveness: The sensitivity of reporter cell lines or primary cells can drift over time or vary between donors. Establish standard curves with reference antibodies during each experiment, and for primary cell assays, consider using pooled donors or normalized readouts.

• Assay conditions:

  • Temperature effects: Binding affinity measurements at room temperature versus physiological temperature (37°C) can significantly differ

  • Buffer composition: Ionic strength and pH can alter binding characteristics

  • Incubation times: Insufficient equilibration time for high-affinity antibodies can skew results

• Detection system sensitivity: Different detection systems (e.g., luminescence vs. fluorescence) have varying dynamic ranges. Use systems with appropriate sensitivity for the expected IC50 range of your antibodies.

• Analytical methods: Different curve-fitting approaches can yield varying IC50 values. Standardize analysis methods and report confidence intervals as shown in the comparative studies .

Controlling these variables requires rigorous standardization of protocols, inclusion of reference antibodies with known characteristics, and careful validation of critical reagents and cell lines.

How should researchers reconcile conflicting data between binding affinity and functional potency of IL23A antibodies?

When binding affinity and functional potency data for IL23A antibodies conflict, researchers should follow this systematic approach to reconciliation:

• Consider binding mechanism: High binding affinity doesn't necessarily translate to high functional potency if the binding mode doesn't efficiently block receptor interactions. Tildrakizumab illustrates this principle—despite binding to p19, it reduces IL-23's affinity for IL-23Rα through allosteric modulation rather than direct competitive inhibition .

• Examine epitope specificity: Map the binding epitopes to determine if the antibody targets regions critical for receptor engagement. Antibodies targeting different epitopes on the p19 subunit may show different functional outcomes despite similar binding affinities.

• Assess antibody valency effects: Bivalent binding can increase apparent affinity (avidity) without proportionally increasing functional potency depending on the spatial arrangement of epitopes.

• Compare assay relevance: Different functional assays measure distinct aspects of IL-23 biology. The whole blood pSTAT3 assay more closely represents physiological conditions than reporter cell lines, potentially explaining discrepancies .

• Analyze dose-response relationships: Compare the slopes of dose-response curves. Shallow curves (as seen with tildrakizumab) may indicate complex inhibition mechanisms requiring higher concentrations for complete inhibition despite reasonable IC50 values .

This reconciliation approach can reveal important insights about antibody mechanism of action and guide the selection of antibodies for specific research applications.

What experimental approaches can distinguish between direct competitive inhibition and allosteric modulation by anti-IL23A antibodies?

To distinguish between direct competitive inhibition and allosteric modulation mechanisms of anti-IL23A antibodies, researchers can employ these specialized experimental approaches:

• Equilibrium binding studies with receptor:

  • Measure binding of IL-23 to IL-23Rα in the presence and absence of saturating antibody concentrations

  • Calculate affinity constants (KD) in both conditions

  • Significant reduction without complete abolishment (as seen with tildrakizumab reducing affinity from 0.8 nM to 190 nM) suggests allosteric modulation

• Ternary complex formation analysis:

  • Determine if antibody-bound IL-23 can still bind to IL-23Rα (as observed with tildrakizumab)

  • Employ surface-based techniques (SPR/BLI) with sequential addition of components

  • Analyze binding kinetics changes rather than simple binding/non-binding outcomes

• Structural studies:

  • Use X-ray crystallography or cryo-EM to visualize antibody-antigen complexes

  • Identify binding epitopes and conformational changes induced by antibody binding

  • Compare with receptor binding sites to predict mechanism

• Kinetic competition experiments:

  • Measure association/dissociation rates of IL-23 to its receptor with pre-bound antibody

  • True competitive inhibitors will prevent association entirely

  • Allosteric modulators may alter kinetic parameters without completely preventing binding

• Dose-response curve analysis:

  • Competitive inhibitors typically produce parallel shifts in agonist dose-response curves

  • Allosteric modulators often change both potency and maximal effect

These approaches, particularly the equilibrium binding studies demonstrating reduced but not abolished receptor binding, were crucial in identifying tildrakizumab's unique allosteric inhibition mechanism .

How do thermostability and other biophysical properties impact IL23A antibody performance in research applications?

Thermostability and other biophysical properties significantly impact IL23A antibody performance in various ways:

• Thermostability impact on shelf-life and handling: Higher thermostability correlates with extended shelf-life and reduced aggregation during freeze-thaw cycles or temperature fluctuations. Researchers should evaluate thermal transition temperatures (Tm) and aggregation onset temperatures to predict stability during experimental procedures .

• Solubility effects on concentration-dependent applications: Antibodies with higher solubility allow preparation of higher stock concentrations without aggregation, enabling more consistent dilution series for dose-response studies and reducing variability in high-concentration applications.

• Charge distribution influence on non-specific binding: Net charge and charge distribution affect non-specific binding to cellular components and labware. Antibodies with excessive positive or negative charge may show increased background in immunoassays or tissue staining.

• Hydrophobicity correlation with aggregation propensity: Antibodies with hydrophobic CDRs show higher aggregation tendency, potentially interfering with functional assays by forming multimeric complexes with altered binding characteristics or causing precipitation during storage.

• Glycosylation effects on clearance and functional activity: Glycosylation patterns impact antibody half-life in vivo and may alter binding to Fc receptors, affecting functional readouts in cell-based assays involving Fc-mediated effects.

When designing long-term studies, researchers should prioritize antibodies with superior biophysical profiles, particularly for applications requiring extended incubation periods, multiple freeze-thaw cycles, or use under challenging buffer conditions .

What are the emerging technologies for studying the structural basis of IL23A antibody interactions?

Several emerging technologies are advancing our understanding of the structural basis of IL23A antibody interactions:

• Cryo-electron microscopy (Cryo-EM): Allows visualization of antibody-antigen complexes in near-native states without crystallization, providing insights into conformational changes induced by antibody binding. This approach is particularly valuable for understanding how antibodies like tildrakizumab induce allosteric modulation of IL-23/IL-23Rα interactions .

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS): Identifies regions of altered solvent accessibility upon antibody binding, mapping epitopes and conformational changes with peptide-level resolution without requiring protein crystallization.

• Single-molecule FRET (smFRET): Measures distances between fluorophore-labeled positions on IL-23 and its receptor in the presence and absence of antibodies, revealing dynamic conformational changes that may not be captured by static structural methods.

• Molecular dynamics simulations: Complement experimental structural data by predicting conformational changes and energetics of antibody-antigen interactions, particularly useful for understanding allosteric effects.

• AlphaFold and other AI-based structure prediction tools: Enable modeling of antibody-antigen complexes with increasing accuracy, accelerating epitope mapping and mechanism of action studies.

• Surface plasmon resonance imaging (SPRi): Allows multiplexed analysis of antibody binding to arrays of IL-23 variants, enabling high-throughput epitope mapping and affinity measurements.

These technologies collectively provide a more comprehensive understanding of how antibodies like risankizumab achieve superior potency through optimal epitope targeting and binding kinetics, informing both therapeutic development and research applications .

How might dual targeting of IL23A and other inflammatory pathways overcome resistance mechanisms in autoimmune diseases?

Dual targeting of IL23A and other inflammatory pathways offers several mechanisms to overcome resistance in autoimmune diseases:

• Redundant pathway inhibition: Autoimmune diseases typically involve multiple inflammatory pathways. The HXN-1003 bispecific antibody targeting both IL23 and TL1A simultaneously addresses parallel pathways that may compensate for each other when only one is blocked .

• Synergistic anti-inflammatory effects: Combined IL23 and TL1A inhibition produces greater than additive effects, as demonstrated in mouse splenocyte activation assays where the bispecific antibody showed superior activity compared to individual antibodies and equal activity to their combination .

• Reduced escape mechanism development: Targeting two independent pathways simultaneously decreases the likelihood of developing resistance through single-pathway adaptations, similar to combination therapy principles in cancer treatment.

• Enhanced efficacy in heterogeneous disease manifestations: Different tissues or disease stages may be driven by varying contributions of each pathway. Dual targeting ensures comprehensive coverage across these variations, as evidenced by HXN-1003's superior performance in multiple disease models :

  • DSS-induced colitis (intestinal inflammation)

  • IMQ-induced psoriasis (skin inflammation)

  • Dermatitis induced by hTL1A and hIL23 (skin inflammation)

• Potential for dose reduction: Synergistic effects may enable lower effective doses, potentially reducing side effects while maintaining efficacy.

These advantages explain why the HXN-1003 bispecific antibody outperformed both individual antibodies and their combination in animal models, suggesting that engineered bispecifics may overcome limitations observed with single-target therapies or even combination therapies using separate antibodies .

What key considerations should guide researchers in selecting between commercially available anti-IL23A antibodies?

Researchers selecting between commercially available anti-IL23A antibodies should consider these key factors:

• Epitope specificity: Determine whether the antibody targets the p19 subunit specifically, as antibodies targeting p40 will inhibit both IL-12 and IL-23 signaling. Commercial listings often specify "Anti-IL23 P19 antibody" to indicate p19 specificity .

• Validated applications: Match the antibody to your specific application needs. The search results show antibodies validated for various applications including Western Blot (WB), ELISA, immunohistochemistry (IHC-fr, IHC-p), immunofluorescence (IF), and neutralization assays (Neut) .

• Species reactivity: Ensure compatibility with your experimental system. Available antibodies include those reactive with human and/or mouse IL-23A, with fewer options for other species .

• Citation record: Consider antibodies with demonstrated utility in published research. Some commercial antibodies have substantial citation records (e.g., 29 citations for an Abcam anti-IL-23 antibody) .

• Format and conjugation: Select appropriate formats (unconjugated, biotin-conjugated, or fluorophore-conjugated) based on detection methods. Available conjugates include Biotin, Cy3, Dylight488, and others .

• Technical support and validation data: Evaluate the quality and extent of supporting data provided by manufacturers, including figures demonstrating antibody performance in relevant applications.

• Cost-effectiveness: Consider both price and quantity options, which vary significantly between suppliers ($245-$499 for comparable products) .

For research focusing on mechanism of action or requiring high sensitivity, antibodies with documented binding characteristics and functional activity data should be prioritized over those with limited validation information.

How might emerging understanding of IL23A signaling pathways influence future antibody development strategies?

Emerging understanding of IL23A signaling pathways is reshaping antibody development strategies in several ways:

• Epitope-focused design: As our understanding of critical IL-23/IL-23R interaction sites improves, antibody development can target specific epitopes that most effectively disrupt signaling. This contrasts with earlier approaches that simply selected for high-affinity binders without detailed structural knowledge .

• Signaling node selection: Recognition that IL-23 represents just one node in a complex inflammatory network has shifted development toward multi-specific approaches targeting complementary pathways, as exemplified by the IL-23/TL1A bispecific antibody that demonstrated superior efficacy in multiple disease models .

• Tissue-specific targeting: Growing appreciation of tissue-specific IL-23 signaling differences is driving development of antibodies optimized for particular disease locations, potentially through tissue-targeted delivery or selection of epitopes that preferentially block signaling in specific cellular contexts.

• Downstream mediator inhibition: Better characterization of IL-23 signaling cascades beyond immediate receptor interactions (including JAK-STAT pathways and transcriptional networks) offers opportunities for developing antibodies that modulate specific downstream effects rather than blocking all IL-23 functions.

• Patient stratification biomarkers: Identification of genetic variants or biomarkers associated with differential IL-23 pathway activation allows development of companion diagnostics alongside targeted antibodies, enabling personalized treatment approaches.

• Alternative binding modes: The discovery that tildrakizumab employs allosteric modulation rather than competitive inhibition has opened exploration of diverse inhibition mechanisms that may offer unique therapeutic profiles or overcome resistance mechanisms .

These evolving strategies represent a shift from empirical antibody development toward rational design based on mechanistic understanding of IL-23 biology, potentially yielding more effective and precisely targeted therapeutic and research tools.

What novel experimental models are being developed to better evaluate IL23A antibody efficacy and mechanisms?

Novel experimental models being developed to better evaluate IL23A antibody efficacy and mechanisms include:

• Humanized mouse models: Transgenic mice expressing human IL-23 receptors or human immune system components provide more translational platforms for evaluating antibody efficacy. The hIL23/hTL1A transgenic mice used in the bispecific antibody study represent this approach, allowing testing of human-specific antibodies in mouse disease models .

• 3D organoid cultures: Patient-derived intestinal, skin, or joint organoids that maintain tissue architecture and cellular diversity offer more physiologically relevant systems than traditional cell lines for assessing antibody effects on tissue-specific IL-23 signaling.

• Co-culture systems: Advanced co-culture platforms incorporating multiple cell types (e.g., epithelial cells, immune cells, and fibroblasts) allow investigation of complex intercellular signaling networks mediated by IL-23 and evaluation of antibody effects on these networks.

• Microfluidic organ-on-chip models: These systems recapitulate tissue-specific microenvironments with controlled fluid flow, enabling assessment of antibody distribution, binding kinetics, and functional effects under conditions more closely resembling in vivo settings.

• Single-cell analysis platforms: Technologies integrating antibody treatment with single-cell RNA sequencing or proteomics reveal cell-specific responses to IL-23 inhibition, identifying differential sensitivities and resistance mechanisms at unprecedented resolution.

• In vivo imaging with labeled antibodies: Non-invasive tracking of fluorescently or radioisotope-labeled anti-IL23A antibodies in animal models provides insights into tissue distribution, target engagement, and clearance kinetics.

• Combinatorial disease models: Models incorporating multiple inflammatory triggers or genetic susceptibilities better represent the complex pathophysiology of autoimmune diseases and allow evaluation of antibody efficacy across disease subtypes.