SLIT vs SCIT: A Q&A

Sublingual immunotherapy (SLIT) is gaining acceptance in otolaryngology circles, but is it really any better than subcutaneous injections? Which patients can benefit from it? How can it affect practice?

These are questions ENT Today set out to answer by asking three physicians who use SLIT in practice: Bradley F. Marple, MD, Professor of Otolaryngology at University of Texas Southwestern Medical School; Mary Morris, MD, an allergist and partner at Allergy Associates of La Crosse, and Medical Director for Allergy Choices in Wisconsin; and Steven B. Levine, MD, Assistant Clinical Professor of Otolaryngology at Yale University.

What is SLIT, and how is it used?

Dr. Levine: Sublingual immunotherapy (SLIT) is the application of FDA-approved antigens to the sublingual mucosa rather than injected as they are with traditional subcutaneous immunotherapy (SCIT). It’s the same concentration of antigen, and the same units of antigens per milliliter of solution. It’s just the diluent that’s different.

How does SLIT work? How does its mode of action differ from that of SCIT?

Dr. Morris: Once the antigens are placed under the tongue, it appears that dendritic cells take up the antigen, migrate to cervical lymphatic nodes, and have an effect on T-regulatory cells, which then cause a systemic response. It takes advantage of the mucosal immune system, which behaves differently from the humoral immune system.

Research has found that once the antigen drops are placed under the tongue, within 30 seconds those antigens are taken up by dendritic cells and go below the mucosal surface-where they’re not washed away. They remain there for about 18 to 20 hours while they start doing their job of sending the signals to the T-regulatory cells.

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Figure. Once a patient decides on SLIT versus injection therapy, the first dose is administered in the office, but subsequent doses may be taken at home.

Dr. Marple: Some data suggest that the antigens remain within the tissues adjacent to the oral mucosa and only minimally gain access to the systemic circulation, and some suggest that antigen is retained within the local submucosal lymphatic tissue. Most data suggest that very little antigen migrates to the regional cervical lymph nodes.

What triggered the idea for this mode of delivery of antigens?

Dr. Morris: The idea really got going in Europe. Around 1986, injection IT was practically banned in England because of some deaths that were linked to the therapy. If you were going to get injection-based immunotherapy it had to be in a hospital. This prompted people to start looking to see if there was a safer way of doing immunotherapy. Europe led the way in this, though my father, an allergy researcher, was one of the first people in the US to publish something on SLIT, in 1969 and 1970.