Subcutaneous immunoglobulin (SCIg) is an investigational immune therapy from CSL Behring that is being studied for the treatment of myasthenia gravis (MG).

The therapy is already approved to treat primary immunodeficiency diseases under the brand name Hizentra but is not yet approved to treat myasthenia gravis. It is administered as an injection under the skin.

How SCIg works

MG is an autoimmune disease that is caused when the immune system mistakenly produces auto-antibodies that target proteins involved in sending signals between nerve cells and muscle cells, resulting in a lack of muscle control and weakness.

Antibodies are immune proteins designed to bind to a specific target and direct the immune system to attack it. Auto-antibodies refer to these antibodies specifically produced against the body’s own proteins.

Intravenous immunoglobulin (IVIg), or immunoglobin injected into the bloodstream, is often used off-label to treat severe chronic symptoms of MG. It consists of a pool of immunoglobulin proteins, purified from the blood of many healthy donors, that is administered as a slow infusion into the patient’s bloodstream over several hours.

IVIg contains a range of natural antibodies involved in the body’s defense mechanism against infected and diseased cells. The exact mechanism of how IVIg therapy works in myasthenia gravis is not yet known.

One theory is that as both the damaging auto-antibodies and the antibodies introduced by IVIg can compete to use the same machinery in the body, they result in fewer auto-antibodies being able to cause damage.

SCIg is a new formulation of immunoglobulin, given as an under-the-skin injection using a portable infusion pump. While IVIg must be administered in a clinical setting and over an extended period of time, SCIg offers the option of flexible home administration, reducing the number of hospital visits required and the amount of time it takes to administer the treatment. This has the potential to offer an improved quality of life for patients compared to standard IVIg.

SCIg in clinical trials for MG

An open-label Phase 3 clinical trial (NCT02774239) is currently recruiting up to 30 patients with worsening MG at two sites in Canada. Patients will receive an escalating dose of SCIg over a four-week period to assess the safety, efficacy, and cost-effectiveness of the therapy.

The primary outcome will be the change in the quantitative myasthenia gravis (QMG) score, but the trial will also assess improvements in patients’ quality of life score and manual muscle testing (MMT) score. The trial was initiated in October 2014 and is estimated to be completed in December 2018.

In April 2017, results from the first 20 patients who completed the trial were announced. Patients showed a significant reduction in the QMG score by 5.12 points, suggesting that the treatment may be effective in treating worsening MG. Patients also reported an improved quality of life.

An open-label Phase 2 study (NCT02100969) is currently recruiting up to 25 patients with myasthenia gravis in the U.S. and Canada to assess the safety and efficacy of SCIg. The primary objective of the trial is to measure change in patients’ QMG score after 12 weeks of treatment. Other measures include a range of questionnaires to assess the change in disease severity and quality of life, such as the myasthenia gravis-specific activities of daily living scale (MG-ADL), and to monitor for adverse events potentially caused by the treatment. The trial started in January 2015 and is expected to be completed in December 2018.

An earlier Phase 2 clinical trial (NCT01828294) was terminated due to issues enrolling patients at the listed U.S. sites.

In 2016, researchers published the results of a retrospective cohort study of SCIg used as a therapy to manage chronic MG in the scientific journal PLoS One. The study assessed the response of nine chronic MG patients at Ottawa Hospital in Canada before and after receiving SCIg.

The study reported that the symptoms of myasthenia gravis were reduced and patients’ quality of life were improved. They also reported fewer side effects compared to standard IVIg treatment.

Other details

Common side effects of SCIg when used as a treatment for primary immunodeficiency diseases include redness, bruising, itching, and swelling where the medicine was injected. Other side effects may include nausea, vomiting, diarrhea, bloating, stomach pain, tiredness, headache, migraine, mild itching or rash, back pain, or pain elsewhere in the body.

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