Croese J, Giacomin P, Navarro S, et al. Experimental hookworm infection and gluten microchallenge promote tolerance in celiac disease. J Allergy Clin Immunol. 2014 Aug 29. [Epub ahead of print]
Open design: All participants were inoculated with 20 Necator americanus (NA) third-stage larvae (L3). Participants received 10 NA at commencement of the trial and a second inoculation of 10 NA 4 to 8 weeks later. Each participant was subjected to 3 escalating gluten challenge (GC) events in the form of wheat pasta, starting 4 weeks after the final inoculation with NA.
Dose Escalations and Time Frames
- Microchallenge: 10 mg gluten daily for 6 weeks, then 50 mg gluten daily for 6 weeks
- GC-1 g phase: 25 mg gluten daily plus 1 g gluten twice weekly for 12 weeks (followed by a 10-wk washout period where participants maintained a gluten free diet [GFD])
- GC-3 g phase: 10 mg gluten daily for 1 week, 50 mg gluten daily for 1 week, then 3 g gluten daily or 60 to 75 straws of spaghetti for 2 weeks.
Monitoring continued for 2 weeks after GC-3g. The total duration of the trial was 52 weeks.
Twelve adults with diet-managed HLA-DQ2 celiac disease (CeD) participated. Participants were adherent to a GFD for an average of 12.5 years with exception of a 5-day GC. Mean age was 53 years, age range was 39 to 67 years, and there were 9 females. Two gluten-intolerant subjects were withdrawn after the gluten microchallenge. Ten completed GC-1g, and 8 enrolled in and completed GC-3g.
Study Parameters Assessed
Two strategies were used in this study to mitigate autoimmunity: 1) duodenal immunomodulation with NA infection and 2) desensitization with a protracted antigen microchallenge intended to mimic inadvertent gluten exposure.
Primary Outcome Measures
- Median duodenal villous height-to-crypt depth (Vh:Cd) ratios
- Mean immunoglobulin (Ig) A‒tissue transglutaminase (tTG) titers
Secondary Outcome Measures
- Quality of life scores
- Celiac symptom indices
- Intraepithelial lymphocyte percentage
- Marsh scores
- Percentage of intestinal T-cells expressing interferon-gamma (IFN-γ)
- Percentage of CD4+ forkhead box P3 (Foxp3)+ regulatory T cells
Infection with NA followed by GC did not lead to significant changes in histology, which would normally be expected in a CeD person exposed to gluten. Median Vh:Cd ratios were unchanged after GC (2.60-2.63; P=.98). Local immunity response appeared dampened in the GC-3 group where mean IgA-tTG titers significantly declined after GC-3 g (slope: ‒1.012; 95% confidence interval: ‒1.166- ‒0.363; P=.005). This is in contrast with the increase in IgA-tTG typically seen in CeD individuals following gluten exposure.
Secondary outcomes included significantly improved quality of life (46.3-40.6; P=.05); unchanged celiac symptom indices (24.3-24.3; P=.53); unchanged intraepithelial lymphocyte percentages (32.5-35.0; P=.47); unaltered Marsh scores; decreased intestinal T-cells expressing IFN-γ (23.9%-11.5%; P=.04); and increased CD4+Foxp3+regulatory T cells (0.19%-1.12%; P=.001).
Mechanism of Action of Necator americanus‒induced Immunomodulation
NA is a helminth; some helminths cause significant pathology (eg, river blindness, elephantiasis), but all helminths may induce immunomodulation in human populations.1 This immunomodulation is the result of historical coevolution between helminths and humans. Helminths are traditionally classified as parasites, but they may be more accurately considered to be commensals2 or conditionally mutualistic.3 Infection with 10 to 20 NA L3 larvae—which will produce at least 50 eggs/g feces measured 4 to 6 weeks after inoculation— is sufficient to induce an immunoregulatory response.4 Hookworm infection skews the immune response toward a Th2 phenotype and subsequently decreases the inflammatory TH1/Th17 response, as is seen by suppression of inflammatory cytokines IFN-γ and IL-17 in the duodenal epithelium.5 Self-tolerance and immune homeostasis may further be improved by expansion of CD4+Foxp3+ regulatory T cells and promotion of antiinflammatory cytokines IL-10 and transforming growth factor-β.6
In the study under review, of the 12 CeD patients on a GFD who were infected with NA, 10 (83%) tolerated an initial 10 mg gluten microchallenge. Two participants left the trial for reasons unrelated to gluten intolerance. Of the 8 who completed the entire trial, all were able to consume up to a bowl of spaghetti per day for 2 weeks without increasing any markers of celiac-mediated inflammation. During this time, their quality of life improved. Neither Croese et al nor we are suggesting that NA infection will allow CeD patients to flagrantly consume daily gluten for the rest of their lives, but NA should certainly be considered for CeD patients who are at risk of accidental gluten consumption, especially those with allergic or autoimmune comorbidities that may benefit from hosting NA.
Reintroduction of “old friends” like helminths into the human gastrointestinal ecosystem may prove to be a valuable intervention for the expanding population of those suffering from celiac disease. . .
In a previous study, NA infection followed by aggressive GC (16 g/d, or the equivalent of 10 slices of wheat bread per day) caused a robust decrease in the Vh:Cd ratio,7 indicating a damaging effect. In the current study, gluten microchallenge to mimic inadvertent exposure was used to initiate expansion of gluten-specific T-regulatory cells; this may be a necessary part of using NA to achieve gluten tolerance. One participant in this study with active CeD upon enrollment was unable to tolerate the gluten microchallenge. This participant retained adverse histology (Marsh 3A score) for the duration of the trial and did not improve 12 weeks after returning to a putative GFD. The authors speculated this participant’s active disease was due to ongoing inadvertent gluten exposure.
The take-home message is this: People with CeD who have Marsh 3A scores or greater or who are unable to tolerate inadvertent microscopic amounts of gluten may not benefit from NA and intentional escalating GC. CeD patients who have lower Marsh scores and are able to tolerate inadvertent gluten exposure may experience increased gluten tolerance and improved quality of life with NA infection.
Other Potential Considerations for Necator americanus Use
Trials to date examining the safety of helminthic therapies in people with allergic rhinoconjunctivitis and asthma have not shown significant benefit, possibly due to small trial size, short duration, and incorrect timing of trials.8 Inoculation with NA appears to be safe and possibly effective for people with Crohn’s disease.9 Correale and Farez observed that parasite-infected multiple sclerosis (MS) patients showed significantly lower numbers of exacerbations and fewer new lesions on magnetic resonance imaging compared with uninfected MS patients, suggesting that parasite infections can alter the course of MS.10 According to Von Mutius and Verecelli, early-life exposure to helminths, including neonatal exposure, may be necessary to develop physiological and immune processes necessary to mitigate allergic and asthmatic responses.2
Infection with NA has been demonstrated to be safe in several studies. NA is not transmissible by autoreinfection, direct person-to-person contact, or aberrant migration and is not able to reproduce inside the bowel.9 Anemia is the primary adverse event associated with hookworm infection but is an uncommon finding in well-nourished populations with a small to moderate populations of NA.11 In the present study, hemoglobin levels actually increased significantly (P=<.001) after NA inoculation. Infection typically causes a maculopapular rash at the site of inoculation, eosinophilic enteropathy, moderate colic, and peripheral eosinophilia.8,9 All symptoms typically resolve themselves. NA infection can last from 2 years to 5 years and is easily terminated with anthelminthic therapies.11
Hookworms used for the treatment of a human disease or condition are regulated as a biological product as defined in Section 351 of the Public Health Service Act.12 Districts may detain without physical examination all imported hookworms, eggs, and larvae being manufactured or distributed without an Investigational New Drug permit or biological license.13
US clinicians may monitor treatment and provide medical advice for patients who are hosting NA or other helminths. Monitoring could include complete blood counts with differential, as well as parameters associated with CeD or other relevant conditions. Reintroduction of “old friends”14 like helminths into the human gastrointestinal ecosystem may prove to be a valuable intervention for the expanding population of those suffering from celiac disease, autoimmune disease, and allergic and inflammatory disorders by aiding in remission and improving quality of life.