Immunotherapies in Neuromyelitis Optica Spectrum Disorder

Introduction:

Aquaporin-4 immunoglobulin G antibodies (AQP4-IgG) were discovered to be a unique clinical entity associated with an uncommon and severe inflammatory autoimmune disorder of the central nervous system (CNS) known as neuromyelitis optica spectrum disorder (NMOSD).

NMO/NMOSD can cause significant disability and usually presents as optic neuritis and longitudinally widespread transverse myelitis. Globally, the frequency of NMOSD is relatively comparable and seldom goes above 5/100,000.

Currently, NMOSD is diagnosed using the international consensus-based diagnostic criteria from 2015. It is easy to diagnose AQP4-IgG-positive NMOSD using these criteria. However, it is also possible to identify AQP4-IgG-negative patients who meet these criteria.

What Is Neuromyelitis Optica Spectrum Disorder (NMOSD)?

An uncommon inflammatory condition called neuromyelitis optica spectrum disorder typically affects the spinal cord and optic nerves, but the brain is less frequently affected. It frequently results in abrupt loss of eyesight, paralysis, or both. After the initial episode, symptoms normally improve.

As both conditions exhibit sporadic symptoms, NMOSD and multiple sclerosis (MS) are occasionally confused with one another. Devic's disease or Devic's illness are other names for it.

The term neuromyelitis optica spectrum disorder is relatively recent and related to various illnesses. Along with closely related disorders, it comprises a condition formerly known as neuromyelitis optica.

The autoimmune illness NMOSD causes demyelination. In other words, the body's immune system attacks the myelin coating that surrounds nerves.

What Is the Etiology of NMOSD?

NMOSD's etiology is currently unknown. Although NMOSD was once thought to be a form of multiple sclerosis, more recent research has clarified the distinctions in the course, symptoms, and treatment of the two conditions.

Whole-genome sequencing has identified major histocompatibility complexes and certain genotypes associated with an increased risk of NMOSD. The major histocompatibility complex genetic variation of NMOSD resembles systemic lupus erythematosus (an autoimmune disorder in which the body's immune system unintentionally targets healthy tissue, mainly kidneys, brain, skin, joints, and other organs) more than multiple sclerosis (an autoimmune condition and a long-term (chronic) disorder of the central nervous system).

NMOSD is an autoimmune disorder mediated by humoral immunity. AQP4, expressed on the surface of astrocytes, is bound by certain antibodies secreted by B-lymphocytes, which subsequently deposit and eliminate the protein. The synthesis of AQP4-IgG may not be the only way B-cells contribute to the pathophysiology of NMOSD; an imbalance between pro- and anti-inflammatory B-cell activities may also be at play.

Following their attraction to the wounded tissue, other inflammatory cells, such as neutrophils, eosinophils, and macrophages, release inflammatory mediators that lead to myelin loss and axonal injury. According to a study, peripheral blood neutrophils in NMOSD exhibit a primed phenotype.

What Are the Symptoms of NMOSD?

Severe NMOSD episodes can cause abrupt blindness or partial paralysis, among other significant consequences. Typical signs and symptoms include:

• Blindness in one or both eyes or blurry vision.

• Paralysis or weakness in the arms or legs.

• Painful convulsions.

• Lack of feeling in every part of the body, or numbness.

• Enduring nausea.

• Vomiting fits without control.

• Recurring hiccups.

• Bowel or bladder problems.

• Issues with sleeping.

How Is NMOSD Diagnosed?

Early diagnosis is crucial. The likelihood of permanent harm to the neurological system grows with even one episode of NMOSD. The procedure for diagnosing comprises:

• A thorough medical history and an evaluation of the current symptoms.

• A neurologic examination to:

  • Assess the motor skills and coordination.

  • Determine whether one feels any numbness.

  • Evaluate the speaking, eyesight, recall, and cognitive abilities.

• The optic nerves, spinal cord, and brain can all be examined using an MRI (magnetic resonance imaging).

• To check for symptoms of NMOSD, have a spinal tap (lumbar puncture) to look at the fluid around the brain and spinal cord.

• Exams of the eyes to check for color loss or blurred vision.

• The AQP4-IgG antibody, present in roughly 70 percent of NMOSD cases, can be found through blood testing.

If one experiences at least one of the following symptoms and the AQP4-IgG test is positive, the doctor may diagnose NMOSD.

• Optic nerve inflammation (optic neuritis).

• Transverse myelitis is an inflammation of the spinal cord.

• An unrelated bout of nausea or vomiting or hiccups.

• A brain condition exhibiting MRI abnormalities that are consistent with non-motor cognitive impairment.

One will only be diagnosed with NMOSD if they have optic neuritis, transverse myelitis, and one other symptom of NMOSD if the AQP4-IgG test is negative.

What Are the Treatments for NMOSD?

Initial therapies consist of:

• Anti-inflammatory Drugs: The doctor can advise an IV corticosteroid treatment, such as Methylprednisolone, to lessen inflammation.

• PLEX: Plasma exchange therapy, or PLEX, may begin before or soon after the conclusion of the steroid cycle. During PLEX, the blood's liquid component is removed from the blood cells and replaced with synthetic plasma. As a result, there is less AQP4-IgG antibody in the blood.

• Immunosuppressive Drugs: If inflammation continues, some drugs may alter the immune system's response to inflammation and stop fresh attacks.

What Are the Immunotherapies Used in NMOSD?

Immunotherapy should be started as soon as feasible for NMOSD patients because any subsequent attacks run the risk of causing severe, frequently irreversible impairment. Nevertheless, little information is available regarding immunotherapy regimens, therapy response predictions, or treatment comparisons.

The therapy of NMOSD involved using fifteen distinct immunotherapeutic medications, suggesting a varied approach for the group. A few of the drugs are as follows:

1. Rituximab (RTX):

• A chimeric monoclonal antibody called Rituximab attaches to CD20-positive B cells and causes them to become depleted. Numerous retrospective and prospective investigations covering AQP4-IgG-positive and—negative (adult and pediatric) patients have shown their therapeutic efficacy in treating NMOSD, reducing attack rates by over 80 percent.

• It is widely advised to use Rituximab (RTX) as first-line therapy to stop NMOSD relapses. However, there is no agreement on the recommended dosing regimen for RTX because of off-label use and a shortage of large-scale prospective randomized controlled trials.

2. Azathioprine (AZA):

• A counterpart of purines, Azathioprine, prevents lymphocyte activation and differentiation. Because of its supposedly delayed onset of action, it is frequently used in conjunction with oral glucocorticoids for up to six months from the start of therapy.

• Among the existing immunotherapies with potential benefits for NMOSD patients is Azathioprine (AZA). The immunosuppressive medication that is most frequently used to stop relapses is called Azathioprine (AZA). Its efficacy during extended follow-up in bigger populations is uncertain, nevertheless.

3. Mycophenolate Mofetil (MMF):

• Mycophenolate mofetil, a prodrug of mycophenolic acid, inhibits inosine-5'-monophosphate dehydrogenase, which depletes guanosine nucleotides preferentially in T- and B-lymphocytes, hence suppressing lymphocyte proliferation. Approximately six to 12 weeks pass before the entire therapeutic benefit manifests. At the very least, Mycophenolate mofetil, combined with overlapping oral glucocorticoids, is advised for the first three months of therapy.

• NMOSD may be effectively treated with Mycophenolate mofetil (MMF), a nonsteroidal immunosuppressive drug that is beneficial in reducing the side effects of long-term high-dose steroid therapy. But most research has been done in the past.

4. Eculizumab:

• Humanized monoclonal antibody Eculizumab interacts to complement protein C5, causing the final complement cascade to be disrupted. It was first licensed in 2007 to treat paroxysmal nocturnal hemoglobinuria (PNH), and later, it was approved for other indications, such as myasthenia gravis. Originally, it was designed for rheumatological illnesses.

5. Ravulizumab:

• A monoclonal antibody that targets the complement factor C5, Ravulizumab is a long-lasting treatment. Its half-life is four times longer than Eculizumab's and has been designed to display altered intracellular antibody recycling. Consequently, it should only be given intravenously once every eight weeks. It is currently authorized for the management of myasthenia gravis, aHUS, and PNH.

• The EMA recently approved Ravulizumab for the treatment of adult patients with AQP4-IgG. Because of its simpler application scheme, it can potentially replace Eculizumab, the existing complement inhibitor, in other indications.

6. Inebilizumab:

• A humanized monoclonal antibody called Inebilizumab binds to CD19-positive B-cells, including CD19-positive subpopulations of plasma cells that produce (auto) antibodies and deplete them.

• As a result of Inebilizumab's considerable reduction in the attack rate in patients with NMOSD compared to the placebo, the phase III randomized placebo-controlled study (N-Momentum) and its OLE were postponed to finish the trial's blinded phase earlier than planned.

7. Satralizumab:

• Developed as a humanized monoclonal IgG2 antibody, Satralizumab has a longer half-life than Tocilizumab and optimized antibody recycling.

• During these trials, Satralizumab was beneficial for patients with AQP4-IgG-positive NMOSD but not for those with AQP4-IgG-negative NMOSD. Patients who tested negative for AQP4-IgG lacked the power to make firm conclusions.

8. Interferons (IFNs):

• By modifying and balancing the Th1 and Th17 responses that are unique to a certain disease, interferons have a significant impact on the pathophysiology of CNS-autoimmune disorders. The suppressive effects of IFN-β (type I IFN), which is a frequent therapeutic for multiple sclerosis, on Th1 cells exacerbate symptoms in NMOSD.

9. Mitoxantrone:

• In the late 1990s and early 2000s, the first long-term immunosuppressant (IS) for NMOSD was Mitoxantrone (MiTX), an anthracene-dione antineoplastic drug. They are inferior to INF. Because of MiTX's effect on B cells and its use in patients with extremely active relapsing-remitting multiple sclerosis (MS), it has been used in NMOSD.

10. Glatiramer Acetate (GA):

• The effectiveness of glutamate acetate (GA), an established treatment for relapsing-remitting multiple sclerosis, in preventing attacks in neuromyelitis optica spectrum disease (NMOSD) is still being investigated.

Conclusion:

An uncommon autoimmune disease of the central nervous system, neuromyelitis optica spectrum disorder (NMOSD) primarily presents as longitudinally widespread transverse myelitis with recurring episodes of optic neuritis. Aquaporin-4 antibodies (AQP4-abs) were found to be pathogenic, and the recently revised diagnostic criteria emphasize both their detection and typical clinical manifestation. Prognosis and attack risk are also correlated with the existence of AQP4-abs. A chronic progressive illness course is extremely uncommon, although episodes of inflammatory diseases are linked to a significant chance of long-term disability, such as blindness and paraplegia. Currently, attack prevention using immunosuppressive medications is seen to be the best course of action.