Imlifidase

Imlifidase Overview

Imlifidase (chemically designated as immunoglobulin G-degrading enzyme of Streptococcus pyogenes, or IdeS; molecular weight approximately 35 kDa) is a recombinant cysteine endopeptidase. Chemically, it belongs to the class of organic compounds known as amino acids, peptides, and analogues within the organic acids superclass. Structurally, it is an engineered protein derived from the human pathogen Streptococcus pyogenes consisting of a single polypeptide chain containing an active site triad composed of cysteine, histidine, and aspartic acid residues.

In transplant immunology, nephrology, and selective immunosuppression, Imlifidase functions as an IgG-degrading endopeptidase and desensitization agent (ATC code L04AA41 for selective immunosuppressants). Formulated as a sterile powder for concentrate for solution for intravenous infusion (marketed under the trade name Idefirix containing 11 mg imlifidase per vial), it is indicated for the desensitization treatment of highly sensitized adult kidney transplant patients with a positive crossmatch against an available deceased donor. Highly sensitized patients possess pre-existing donor-specific anti-HLA antibodies (DSA) that present a high risk of hyperacute or severe antibody-mediated rejection (AMR). By rapidly cleaving circulating human IgG antibodies into functionally inactive fragments, Imlifidase enables successful HLA-incompatible kidney transplantation in patients who would otherwise remain on dialysis indefinitely. Although granted conditional marketing authorization by the European Medicines Agency (EMA) in August 2020, Imlifidase has not been approved by the US FDA.

What Is Imlifidase and How Does It Work?

Imlifidase acts primarily through specific endopeptidase cleavage of the heavy chains of human Immunoglobulin G (IgG), leading to rapid destruction of donor-specific antibodies and inhibition of Fc-mediated effector functions.

Its primary chemical, physiological, and immunological mechanisms include:

• Specific Heavy Chain Cleavage: Imlifidase specifically targets human IgG subclasses (IgG1, IgG2, IgG3, and IgG4) without cleaving other immunoglobulin classes (IgA, IgM, IgE, or IgD). It cleaves human IgG in a distinct two-step enzymatic reaction at the lower hinge region between alanine-249 and glycine-250 of the heavy chains.
• Generation of Inactive IgG Fragments: The first enzymatic cleavage converts intact bivalent IgG into a single-cleaved intermediate. The second cleavage yields one homodimeric Fc fragment and one F(ab’)2 fragment, disrupting structural integrity.
• Elimination of Fc Effector Functions: Cleavage separates the antigen-binding F(ab’)2 regions from the Fc region. Lacking an intact Fc domain, the fragments cannot bind to C1q to activate complement or bind to Fc-gamma receptors (Fc-gamma-R) on immune effector cells, completely eliminating complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC).
• Rapid Reduction of Donor-Specific Antibodies: Following intravenous infusion, Imlifidase cleaves both plasma and extravascular IgG pools within 2 to 6 hours, converting a positive donor-recipient crossmatch into a negative crossmatch to permit kidney transplantation.
• Transient Window of Desensitization: Systemic IgG levels remain depleted for 1 to 2 weeks post-infusion until endogenous IgG synthesis gradually restores circulating levels, providing a therapeutic window during which standard maintenance immunosuppressive therapy is established.

Is Imlifidase FDA Approved?

Imlifidase has not received full approval for commercial marketing in the United States by the US FDA, classifying its current approval status as Not Approved.

What Is Imlifidase Used For?

• Desensitization of highly sensitized adult kidney transplant candidates with a positive crossmatch against an available deceased donor.
• Conversion of positive donor-specific anti-HLA crossmatches to negative crossmatches prior to kidney transplantation.
• Investigational management of severe antibody-mediated rejection (AMR) in solid organ transplantation and severe autoimmune diseases (such as Goodpasture’s disease and systemic lupus erythematosus).

Before Taking Imlifidase: Contraindications & Precautions

Do not administer Imlifidase to patients with active, severe, or uncontrolled systemic bacterial, viral, or fungal infections. Avoid in patients with known severe hypersensitivity to Imlifidase or formulation excipients. Exercise extreme caution because profound IgG depletion temporarily removes systemic humoral immunity, placing patients at risk for severe opportunistic infections.

Who Should Not Take Imlifidase?

• Patients with active, severe, or systemic infectious diseases (e.g., active sepsis, active tuberculosis, untreated viral hepatitis).
• Individuals with known severe hypersensitivity to Imlifidase or Streptococcus pyogenes proteins.
• Patients who are not undergoing immediate kidney transplantation with planned post-transplant maintenance immunosuppression.

Imlifidase, Pregnancy & Safety

Adequate and well-controlled reproductive toxicity studies in pregnant women are lacking. Maternal IgG antibodies cross the placenta via Fc-receptor transport pathways during pregnancy; Imlifidase administration can cleave maternal IgG and impair passive transplacental immunity to the fetus. Imlifidase is not recommended for use during pregnancy unless the potential maternal benefit of kidney transplantation outweighs the potential fetal risks. Breastfeeding should be discontinued during treatment, as it is unknown whether Imlifidase is excreted into human breast milk.

Tell Your Doctor Before Taking Imlifidase

Inform your transplant surgeon, nephrologist, or medical team if you have any active infection, recent fever, history of recurrent bacterial infections, prior treatment with equine or rabbit antithymocyte globulin (ATG), or recent vaccinations.

Imlifidase Dosage & Administration

Formulated as a sterile lyophilized powder for concentrate for solution for intravenous infusion containing 11 mg imlifidase per single-use vial.

Standard Imlifidase Dosing

• Desensitization Dosing (Adults): Administered as a single intravenous dose of 0.25 mg/kg body weight, calculated based on actual patient body weight.
• Crossmatch Re-Evaluation: Crossmatch testing should be repeated within 2 to 6 hours post-infusion. If crossmatch remains positive, a second dose of 0.25 mg/kg may be administered within 24 hours (maximum 2 doses total).

How Imlifidase Is Administered

• Reconstitute each 11 mg vial with sterile water for injection, then dilute in 0.9% sodium chloride infusion solution.
• Administered strictly via intravenous infusion through a dedicated line over 15 to 60 minutes.
• Administer premedications (corticosteroids, antihistamines, and antipyretics) prior to infusion to reduce infusion-related reactions.

Imlifidase Clinical Efficacy & Safety Profile

In pivotal open-label Phase 2 clinical trials in highly sensitized kidney transplant candidates, a single infusion of Imlifidase rapidly cleaved circulating donor-specific anti-HLA IgG antibodies, converting positive donor crossmatches to negative within 2 to 6 hours in 95% to 100% of treated patients. This rapid cleavage enabled successful deceased donor kidney transplantation in patients who had spent years on transplant waiting lists. Post-transplant 1-year graft survival rates were comparable to standard deceased donor kidney transplants, though early antibody-mediated rejection (AMR) occurred in approximately 30% of patients as endogenous IgG antibodies repopulated, requiring protocol management with plasmapheresis, IVIG, and memory B-cell depletion.

Imlifidase Side Effects & Safety Profile

Common adverse effects include severe infections (urinary tract infections, sepsis, pneumonia, CMV reactivation), infusion-related reactions, fever, headache, myalgia, elevated liver enzymes, and transient anemia. Serious adverse risks include life-threatening bacterial or viral sepsis, severe antibody-mediated rejection upon IgG repopulation, and severe hypersensitivity. Holds no FDA Black Box Warning due to unapproved status.

Common Imlifidase Side Effects

• Infectious & Systemic: Urinary tract infections, viral upper respiratory infections, fever (pyrexia), chills, and fatigue.
• Gastrointestinal & Neurological: Nausea, vomiting, diarrhea, headache, myalgia, and transient elevated hepatic transaminases.

Serious Imlifidase Adverse Events

• Severe Opportunistic Infections: Life-threatening bacterial sepsis, fungal infections, cytomegalovirus (CMV) reactivation, and BK virus nephropathy resulting from transient total IgG depletion.
• Late Antibody-Mediated Rejection (AMR): Rebound surge of donor-specific anti-HLA antibodies (DSA) at 1 to 2 weeks post-transplant as endogenous IgG production recovers, triggering acute vascular rejection.
• Infusion-Related Reactions & Anaphylaxis: Flushing, dyspnea, hypotension, bronchospasm, and severe hypersensitivity reactions during or immediately following intravenous infusion.

Managing Imlifidase Side Effects

Administer prophylactic anti-infective medications (anti-bacterial, anti-fungal, and anti-CMV agents) routinely post-transplantation. Monitor donor-specific antibody levels closely during the first 2 to 4 weeks post-transplant and manage AMR with plasmapheresis, IVIG, or monoclonal antibodies.

Imlifidase Drug Interactions & What to Avoid

Co-administration with antibody-based biopharmaceuticals requires careful timing due to enzymatic cleavage.

Imlifidase Drug-Drug Interactions

• Intravenous Immunoglobulin (IVIG) & Monoclonal Antibodies (e.g., Rituximab, Basiliximab, ATG): Imlifidase cleaves all human and humanized IgG-based therapies; administration of IVIG or monoclonal antibodies within 96 hours after Imlifidase will result in enzymatic cleavage and loss of therapeutic efficacy.
• Blood Products containing IgG (e.g., Whole Blood, Packed Red Blood Cells, Plasma): Transfused IgG will be cleaved by circulating Imlifidase, lowering efficacy and producing excess cleavage fragments; avoid unneeded transfusions immediately post-infusion.
• Inactivated & Live Vaccines: Vaccinations administered during total IgG depletion will fail to elicit an appropriate humoral immune response.

Imlifidase, Food & Alcohol

Systemic intravenous administration is unaffected by food or alcohol intake. Patients should avoid unpasteurized foods to minimize infection risk during post-transplant immunosuppression.

Imlifidase: Missed Dose, Overdose & Storage

Administered as a single pre-transplant dose in a hospital setting. Overdose prolongs IgG depletion. Store vials under refrigeration (2°C–8°C).

Missed Dose of Imlifidase

Not applicable; administered as a single, carefully timed pre-operative infusion in the hospital immediately prior to deceased donor kidney transplantation.

Imlifidase Overdose & Emergency

Overdose results in prolonged complete suppression of systemic IgG levels, extending the duration of severe infection vulnerability. Emergency management involves strict protective isolation, broad-spectrum prophylactic anti-infective therapy, and close monitoring of serum IgG recovery.

How to Store Imlifidase

Store lyophilized powder vials in a refrigerator between 2°C and 8°C (36°F to 46°F) in the original carton to protect from light. Do not freeze. Reconstituted and diluted solutions should be used immediately or within 24 hours if stored at 2°C to 8°C. Keep strictly out of reach of children.

Imlifidase Patient Management & Monitoring

Requires continuous pre- and post-transplant crossmatch evaluation, IgG tracking, and infection screening.

Tests Before Starting Imlifidase

Baseline donor-specific anti-HLA antibody (DSA) profiling, T- and B-cell flow-cytometric crossmatch, complete blood count (CBC with differential), baseline serum IgG levels, screening for active infections (HIV, HBV, HCV, CMV, EBV), and baseline renal/hepatic panel.

Monitoring During Imlifidase Treatment

Post-infusion crossmatch testing at 2 to 6 hours; daily monitoring of serum IgG levels post-transplant; monitoring CBC, renal function, and signs of infection; routine monitoring of DSA levels at weeks 1, 2, and 4 post-transplant to detect antibody rebound.

Imlifidase Do’s and Don’ts

• Do receive all recommended prophylactic antibiotics, antivirals, and antifungals as prescribed by your transplant team.
• Do report any fever, chills, sore throat, or incision pain to your medical team immediately.
• Do not receive live vaccines during or immediately following desensitization therapy.
• Do not administer intravenous immunoglobulin (IVIG) or antibody medications within 96 hours of receiving Imlifidase.

Frequently Asked Questions

References

• DrugBank Database – Imlifidase Clinical Profile (DB15258)
• Classyfire Database – Amino Acids, Peptides, and Analogues / Organic Compounds Taxonomy Profile
• European Medicines Agency (EMA) Summary of Product Characteristics – Idefirix (Imlifidase) Powder for Concentrate

Legal Disclaimer

The detailed medical and chemical information provided on this specific web page is intended strictly for educational and informational purposes regarding complex pharmacological mechanisms. It absolutely does not constitute professional medical advice, medical diagnosis, or specific treatment recommendations. Always consult a licensed healthcare provider before making any personal decisions regarding complex medical conditions, medication adjustments, or dietary changes.