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Immunotherapy is the practice of administering gradually increasing doses of an allergen in order to reduce the sensitivity and risk of reacting to it. It was first carried out over 100 years ago and is now in widespread use around the world, in particular for hayfever and allergies to house dust mite and pets. It is sometimes referred to as ‘allergy vaccination’ or ‘desensitisation’. More recently, there has been intensive interest in the possibility of applying the same principle to help treat food allergies, which can be potentially life threatening.

Oral Desensitisation (OD) to food, also known as Oral Tolerance Induction (OTI or most commonly OIT), is a treatment that involves giving very small, but gradually increasing, amounts of the food that the child is allergic to. The intention of OIT is to increase the tolerance to the food so that larger amounts of the food can be consumed without causing any symptoms and, as a result, accidental exposures to small amounts should not cause reactions. This treatment has been most studied for milk, egg and peanut. In early 2020, PALFORZIA, a peanut containing capsule, became the first licensed food immunotherapy treatment. Increasingly, OIT has been used for allergies to sesame, treenuts and wheat although as the safety and effectiveness of these seems to mirror that of the other allergens, there have been relatively few published studies, despite the treatment now being widely available in North America.

Over the past decade there has been a large increase in the number of research studies looking into desensitisation and these have included careful observation of how the treatment impacts on the immune system. It appears that regular exposure to the food causing allergy, but at a level below that which causes a reaction, causes the immune system to increase production of a specific antibody called IgG4. This has a blocking effect on the allergic antibody, known as IgE, and enhances tolerance to the food. As IgG4 levels increase, the effect is greater, allowing more of the food to be tolerated. We are still in the infancy of our understanding as to what is really happening at a molecular level but the science is advancing and we hope that soon there will be a simple blood test that will directly guide desensitisation. However, until we have such a ‘biomarker’, desensitisation is very much led by how well the patient is tolerating food and slowly increasing the level of exposure, rather than anything being gained by lots of blood tests.

Most research has been done on desensitisation to milk, egg and particularly peanut. There are a small number of studies looking at OIT to other foods such as chickpea, wheat, sesame and tree nuts and also using other methods e.g. using patches of food on the skin or putting drops under the tongue. PALFORZIA is the only licensed OIT product in the UK, EU and USA. However, OIT to a wide variety of foods is available in many parts of the world as part of routine clinical practice.

This depends on the protocol being used – some are faster than others, as well as the response of the individual patient. A typical protocol will require approximately 8 – 12 steps when the dose of food allergen is increased with at least a two-week gap between doses. However, reactions or other factors (such as incidental illness or missed doses) may mean a longer gap between doses is required or this may just be preferred. Once the top dose (maintenance) has been reached, then the patient needs to continue to take this regularly to maintain the effect. The frequency of this dosing can be reduced (but not stopped) over time without apparent loss of effect.