Sublingual immunotherapy (SLIT) – treatment at the tip of your tongue

Allergen immunotherapy, practiced since the early 20th century, involves progressive administration of allergens to induce immune tolerance. Subcutaneous immunotherapy (SCIT), the gold standard, shows 90% symptom improvement. Benefits include reduced symptoms, medication use, and long-term effects lasting up to 10 years, with preventive advantages in children against asthma and new sensitivities.

Revered consultant medical oncologist Dr Amit Shah discusses all you need to know.

With this success rate with SCIT, why is SLIT therapy coming into focus?

Intranasal immunotherapy shows weak mucosal responses and may trigger asthma, while bronchial administration risks severe adverse events like anaphylaxis. Oral immunotherapy has limited efficacy as the treatment is swallowed. These factors limit their use compared to other methods.

What are the weaknesses of SCIT?

Inconvenience: Patients often need to visit clinics multiple times for injections. This may include weekly visits with gradually increasing doses (known as ‘build-up’ immunotherapy), which can last up to 5 years. During the COVID-19 pandemic, this issue was exacerbated as patients missed doses due to hospital site closures. Additionally, a 30-minute post-dose waiting period is required to monitor for any anaphylactic reactions.

Expense: Patients may incur costs for parking, travel, and sometimes co-payments.

Invasiveness: Injections can cause pain at the injection site, and some patients may experience needle-phobia.

Potentially severe systemic reactions: There is a risk of anaphylaxis and delayed local reactions, making it essential that SCIT (subcutaneous immunotherapy) is administered in facilities equipped with adequate staff and equipment to manage these events.

What are the mechanisms of SLIT?

Sublingual immunotherapy (SLIT) involves allergen uptake by oral dendritic cells, which migrate to lymph nodes, increasing Treg (CD4+CD25+) activity. Tregs enhance immune regulation, increasing TGF-Beta, IL-10, and suppressing specific T-cell responses. This shifts the Th2/Th1 balance, favoring Th1 (cell-mediated immunity) over Th2 (allergy-related interleukins). The shift reduces Th2 activity and allergen-specific IgE, promoting immunotherapy effectiveness.

What are the benefits of SLIT?                                                                    

Sublingual immunotherapy (SLIT) offers significant advantages, including convenience—patients need only an initial clinic visit, with daily home administration thereafter. This proved invaluable during the COVID-19 pandemic. SLIT eliminates needles, reducing pain and anxiety, and may provide cost benefits by minimising travel, co-pays, and time off work. It has a superior safety profile compared to SCIT, with a lower risk of anaphylaxis and reduced exposure to in-office infection risks.

While local side effects like oral itching and swelling occur in 50-80% of cases, anaphylaxis is extremely rare—1 per 100 million doses compared to SCIT’s 1 in 1 million risk. Despite these benefits, further cost-effectiveness studies are needed to solidify SLIT's long-term economic and clinical advantages.

There have been no reported fatalities as of February 2022. However, for safety reasons, clinics recommend that patients carry EpiPen auto-injectors, which should be part of the protocol during any immunotherapy course.

How is SLIT administered?

SLIT involves placing a 1cc or single antigen drop under the tongue, with dose adjustments made cautiously if needed. A 10-day buildup period is typical. The drop should remain under the tongue for one minute before swallowing, and no food or drink is allowed for five minutes afterward. The initial buildup dose is administered in the physician’s office to observe for 30 minutes and provide instructions. Children taking SLIT require adult supervision, and an epinephrine auto-injector must be prescribed for safety.

What are the contraindications for SLIT?

Not all patients are suitable for SLIT. Physicians must assess the patient’s ability to comply with strict at-home dosing, as unlike in-office treatments, adherence cannot be directly monitored. SLIT is not recommended for patients with severe, unstable asthma, those who experience severe systemic reactions to the initial dose, or individuals with eosinophilic esophagitis or inflammatory oral lesions. Caution is also advised for patients on beta-blockers due to an increased risk and difficulty in managing anaphylaxis. Ensuring patient suitability is critical to minimising risks and maximising the effectiveness of the treatment.

Is SLIT effective?

SLIT has been evaluated using both subjective and objective measures across various patient groups, including adults and children with allergic rhinitis, conjunctivitis, and asthma. Studies focus on symptom reduction, medication use, and quality of life, alongside immunologic changes and skin test reactivity. Most research has centered on single-antigen approaches, with a need for more multi-antigen studies. A 2007 review by Leatherman et al. found 30 out of 36 studies demonstrated SLIT’s efficacy in improving symptoms and managing allergens like weeds, grass, dust mites, trees, and mold.

Several FDA-approved tablets are available, including Ragwitek, Grastek, Odactra, and Oralair.

If you would like to book a consultation with Dr Shah, simply visit his Top Doctors profile today.