# Part IV — Targeted Arms: Genetics/HLA, Prevention, the Diagnostic Gap, and the Therapeutic Pipeline

*Four linked deep-dives that connect EoE mechanism (Parts I–III) to the project's translational program: (A) the genetic and HLA architecture; (B) prevention and the atopic march, with the teplizumab/T1D template; (C) the diagnostic status quo and its unmet need; and (D) the approved and pipeline therapeutics, grounded in a live ClinicalTrials.gov analysis. Part IV of a four-part systematic review. All citations DOI-verified; trial data from ClinicalTrials.gov.*

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## A. Genetics, HLA, and the GWAS architecture

### A.1 EoE is heritable but environment-dominated
Family and twin studies establish substantial familial clustering: EoE in first-degree relatives is 1.8–2.4%, recurrence risk ratios are 10–64× the general population, and combined gene-plus-shared-environment heritability is ~72% — yet the twin analysis concludes that **environmental (especially shared-environment) cues dominate over genetic ones** (Alexander 2014, doi:10.1016/j.jaci.2014.07.021). This is the pivotal fact for the prevention arm (§B): risk is high enough to enrich an at-risk cohort, but environmental enough to be modifiable.

### A.2 The GWAS loci and the susceptibility-vs-effector split
Genome-wide association studies identified the first and most reproducible EoE risk locus at **5q22, spanning TSLP** (Rothenberg 2010, doi:10.1038/ng.547), followed by additional loci including **2p23 (CAPN14)** and others from a four-locus GWAS (Sleiman 2014, doi:10.1038/ncomms6593). The recurring theme, reinforced by this project's own GWAS-overlap analysis, is a **susceptibility-vs-effector split**: genetic risk concentrates in genes controlling epithelial barrier and type-2 initiation (TSLP, CAPN14, filaggrin), while the strongest *expression* effectors (CCL26, ALOX15, POSTN) are downstream amplifiers not themselves GWAS hits. CAPN14 uniquely bridges the two — a risk gene whose product is directly IL-13-induced (Part II §12). Genetics review context: Kottyan & Rothenberg (doi:10.1038/mi.2017.4).

### A.3 HLA class II and antigen presentation
Because EoE is CD4/class-II-restricted, the HLA-II region is a mechanistically privileged locus, and HLA associations have been reported for EoE. HLA variation shapes which food peptides can be presented (the basis of the personalized-panel work), and the broader principle that HLA variation drives immune-disease risk is well established (Dendrou 2018, doi:10.1038/nri.2017.143). The index-case work illustrated the clinical corollary: HLA determines presentation *capacity* (e.g. DQ2.2 presenting gluten) but not *pathology* — the functional T-cell response does (Part III §4).

## B. Prevention and the atopic march

### B.1 The march as an interceptable trajectory
At-risk children commonly progress: skin-barrier dysfunction/atopic dermatitis → food sensitization → allergic rhinitis/asthma → EoE. Because the familial risk is quantified (§A.1) and the architecture is environment-dominated, prevention is biologically plausible — the disease is not genetically fixed. (Full synthesis in the companion `atopic_march_prevention_review.md`.)

### B.2 Prevention already works in allergy — three paradigms
- **Early oral antigen introduction:** LEAP (Du Toit 2015, doi:10.1056/nejmoa1414850) and EAT (Perkin 2016, doi:10.1056/nejmoa1514210) show early introduction prevents food allergy — timing/route of first antigen encounter determines tolerance vs sensitization.
- **Allergen immunotherapy prevents progression:** AIT reduces new sensitizations and asthma onset in monosensitized children (Pajno 2001, doi:10.1046/j.1365-2222.2001.01161.x; EAACI prevention guidance, Halken 2017, doi:10.1111/all.13317).
- **Skin-barrier support:** prophylactic emollient reduces atopic-dermatitis incidence in high-risk infants (Simpson 2014, doi:10.1016/j.jaci.2014.08.005), damping the upstream epicutaneous-sensitization step.

### B.3 The teplizumab/T1D template
Type-1 diabetes provides the proof that a brief immune-directed course in a pre-symptomatic at-risk person delays disease: teplizumab (anti-CD3) delayed clinical T1D by ~2 years (Herold 2019, doi:10.1056/nejmoa1902226 — Part III §5). The EoE translation: stratify at-risk children by HLA + sensitization + family history (the T1D staging analogy), then apply an antigen-specific tolerizing intervention — teplizumab's disease-modification with food-peptide specificity for a favorable pediatric safety profile. **Honest limit:** no trial has yet shown prevention of EoE *onset*; this is a well-motivated hypothesis built on adjacent-disease evidence.

## C. The diagnostic status quo and unmet need

### C.1 The current pathway is burdensome
Trigger identification today requires **empiric dietary elimination followed by serial endoscopy with biopsy** after each elimination/reintroduction cycle — months of dietary restriction, repeated sedated procedures, and frequent ambiguity (multiple triggers, aeroallergen contribution, incomplete remission). This is the burden Part I §9 quantified and the specific problem the project's diagnostic targets.

### C.2 Biomarkers and less-invasive monitoring
Efforts to reduce endoscopy include minimally-invasive sampling (cytosponge/string test), and blood/tissue biomarkers (periostin, eotaxin-3, EDN), but none yet identifies the *causal food* — they measure disease activity, not the trigger. The antigen-specific T-cell approach (Part III) is distinctive precisely because it aims to name the food, not just quantify inflammation.

### C.3 The presentation-vs-pathology lesson
The project's index-case calibration demonstrated the core diagnostic principle: a binding/presentation panel is only a prior; the **functional pathogenic-Th2 readout is the specificity-defining step**. The wheat false positive (presented on DQ2.2 but tolerated) is the case that proves a diagnostic must end in a functional assay — the boundary any commercial assay must respect.

## D. The therapeutic pipeline (ClinicalTrials.gov analysis)

A systematic pull of EoE interventional trials from ClinicalTrials.gov (157 trials; 93 in Phase 2/3/4) maps the current landscape:

### D.1 Approved / established
- **Swallowed topical corticosteroids** — budesonide (Straumann 2010, doi:10.1053/j.gastro.2010.07.048) and fluticasone (Konikoff 2006, doi:10.1053/j.gastro.2006.08.033); orodispersible budesonide and APT-1011 (fluticasone orally-disintegrating tablet) are formulation-optimized successors in late-phase trials.
- **PPIs** — first-line, acid-independent anti-inflammatory effect (Part I §5).
- **Dietary elimination** — the only causal therapy (Part I §8).
- **Dupilumab (anti–IL-4Rα)** — the first FDA-approved biologic for EoE, pivotal Phase 3 LIBERTY-EoE-TREET (Dellon 2022, doi:10.1056/nejmoa2205982); the most-represented drug in the current trial set (8 late-phase trials in this pull). Validates the IL-4/IL-13 axis (Part II §10) as a therapeutic target.

### D.2 The biologic pipeline (type-2 axis)
From the trial analysis, the active late-phase pipeline targets successive nodes of the Part II circuit:
- **Anti–IL-13:** cendakimab (CC-93538) — multiple Phase 2/3 trials, directly targeting the central effector cytokine.
- **Anti–IL-5 / IL-5Rα:** mepolizumab and benralizumab — benralizumab depletes eosinophils but a recent trial showed histologic response without full symptom benefit (Kliewer/Dellon 2024, doi:10.1056/nejmoa2313318), an instructive dissociation of eosinophil count from symptoms.
- **Anti–Siglec-8:** lirentelimab (AK002) — targeting mast cells and eosinophils (mechanistically adjacent to the project's SIGLEC6 mast-targeting rationale, Part II §2).
- **Anti-TSLP:** tezepelumab — targeting the upstream alarmin (Part II §10; genetically anchored at 5q22, §A.2).
- **Other mechanisms:** etrasimod (S1P-receptor modulator), losartan (TGF-β/remodeling axis, targeting fibrosis).

### D.3 Where the project's targets and modalities fit
The pipeline is dominated by **cytokine/receptor blockade** (downstream, non-antigen-specific, requires chronic dosing). The project's contributions occupy two under-populated niches: (i) **novel effector/receptor targets** beyond the crowded IL-13/IL-5 space — SIGLEC6 (mast-state-specific), IL1RL1/ST2 (receptor-side IL-33 blockade), CCL26/CCR3 (eosinophil recruitment); and (ii) **antigen-specific modalities** (diagnostics and tolerance therapeutics, Part III) that address the *cause* rather than the downstream cytokines — a categorically different and largely unoccupied approach in the current pipeline.

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### Synthesis
The four arms converge on the project's thesis. Genetics (§A) shows EoE is environment-dominated and CD4/HLA-centric — modifiable and antigen-specific-addressable. Prevention (§B) shows brief antigen-directed intervention modifies related diseases (teplizumab, LEAP, AIT), motivating an EoE prophylactic. The diagnostic gap (§C) is concrete and quantified — serial endoscopy to name a trigger — and the presentation-vs-pathology lesson defines what a valid diagnostic must do. The pipeline (§D) is crowded with downstream cytokine blockers but nearly empty of antigen-specific approaches and of the project's novel targets, defining the white space. Together with Parts I–III, this establishes both the mechanistic foundation and the unmet-need rationale for the project's diagnostic, therapeutic, and prevention programs.

*Evidence base: genetics/HLA, prevention, and therapeutics Tier-1/2 references in the master library; 157-trial ClinicalTrials.gov pull for the pipeline. Primary trials and GWAS cited inline; the prevention arm is detailed in the companion review.*