A Study to Test the Efficacy and Safety of Riliprubart Against the Usual Treatment of Intravenous Immunoglobulin (IVIg) in People With Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)

Eligibility Criteria

• * Participant must have CIDP or possible CIDP criteria, based on European Academy of Neurology (EAN)/ Peripherial Nerve Society (PNS) Task Force CIDP guidelines, second revision (2021).
• * Participant must have either typical CIDP, or one of the following 2 CIDP variants: motor CIDP, multifocal CIDP (also known as Lewis Sumner Syndrome). Diagnosis must be confirmed by the study adjudication committee.
• * Participants must have responded to IVIg in the past 5 years. Response must be an objective clinically meaningful improvement defined by at least one of the following: ≥1 point decrease in adjusted INCAT score, ≥4 points increase in I-RODS total score, ≥3 points increase in the MRC-SS, ≥8 kilopascal improvement in mean grip strength (1 hand), or an equivalent improvement based on information documented in medical records as per the Investigator's judgment.
• * Participant must be on a stable maintenance dosage of IVIg, defined as no change greater than 10% in frequency or dose of IVIg within 8 weeks prior to Screening, and remaining stable until baseline.
• * Participant must have residual disability, defined as an INCAT score of 2 to 9 at Screening that is confirmed at baseline (a score of 2 should be exclusively from leg disability component of INCAT).
• * Participant must be receiving treatment with IVIg within a standard maintenance dosing regimen, defined as per EAN/PNS 2021 CIDP guidelines: 0.4 to 1 g/kg every 2 to 6 weeks.
• * Participants receiving IVIg infusions at home are eligible, as long as IVIg infusions are switched to a hospital or infusion center setting at least 1 cycle prior to baseline.
• * Participant must have active disease, defined by a CIDP disease activity score (CDAS) XE " CDAS " \\f Abbreviation \\t "CIDP disease activity score" of ≥2 points at Screening.
• * Participant must have documented vaccinations against encapsulated bacterial pathogens given within 5 years of Screening or initiated a minimum of 14 days prior to first dose of study intervention.
• * All participants must agree to use contraception methods during and after the study as required.
• * Contraceptive use by men and women participating in the study should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
• * A male participant is eligible to participate if they agree to the following during the study intervention period and for at least 55 weeks after the last dose of study medication.
• * Refrain from donating or cryopreserving sperm.
• * Must agree to use contraception/barrier as detailed below:
• * A male condom and an additional highly effective contraceptive method (Contraceptive and barrier guidance per protocol) when having sexual intercourse with a woman of childbearing potential (WOCBP) who is not currently pregnant.
• * A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies:
• * Is a woman of nonchildbearing potential (WONCBP) as defined by the protocol. OR
• * Is a WOCBP and agrees to use a contraceptive method that is highly effective (with a failure rate of \<1% per year), preferably with low user dependency, as described in the protocol during the study intervention period (to be effective before starting the intervention) and for at least 55 weeks after the last administration of study intervention and agrees not to donate or cryopreserve eggs (ova, oocytes) for the purpose of reproduction during this period.
• * Polyneuropathy of other causes, including but not limited to hereditary demyelinating neuropathies, neuropathies secondary to infection or systemic disease, diabetic neuropathy, drug- or toxin-induced neuropathies, multifocal motor neuropathy, polyneuropathy related to IgM monoclonal gammopathy, POEMS XE " POEMS " \\f Abbreviation \\t "polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes" syndrome, lumbosacral radiculoplexus neuropathy.
• * Sensory CIDP, distal CIDP and focal CIDP variants.
• * Any other neurological or systemic disease that can cause symptoms and signs interfering with treatment or outcome assessments.
• * Poorly controlled diabetes (HbA1c XE " HbA1c " \\f Abbreviation \\t "glycated hemoglobin" \>7%).
• * Serious infections requiring hospitalization within 30 days prior to Screening, any active infection requiring treatment during Screening, or presence of a condition that may predispose the participant to increased risk of infection (eg, medical history such as known immunodeficiency or history of recurrent infections).
• * Clinical diagnosis of Systemic Lupus Erythematosus (SLE)
• * Sensitivity to any of the study interventions, or components thereof, or drug or other allergy that, in the opinion of the Investigator, contraindicates participation in the study. Specifically, history of any hypersensitivity reaction to riliprubart or its components or of a severe allergic or anaphylactic reaction to any humanized or murine monoclonal antibody.
• * Any contraindication related to the administration of immunoglobulins (eg hypersensitivity, chronic kidney disease, thromboembolic diseases or recent thromboembolic event, known history of IgA XE " IgA " \\f Abbreviation \\t "immunoglobulin A" deficiency at the time of Screening).
• * Any other clinically meaningful medical history or ongoing medical condition (as determined by the Investigator at Screening) that might impact the benefit-risk assessment, jeopardize the safety of the participant, or compromise the quality of the data collected in this study; or history or presence of other significant concomitant illness that would adversely affect participation in this study, per the Investigator's judgment.
• * Documented history of attempted suicide over the 6 months prior to the Screening visit, presence of suicidal ideation of category 4 or 5 on the C-SSRS XE " C-SSRS " \\f Abbreviation \\t "Coiumbia-Suicide Severity Rating Scale" during Screening, OR if in the Investigator's judgment, the participant is at risk for a suicide attempt.
• * Evidence of CIDP worsening within the 6 weeks following a prior vaccination that, in the opinion of the Investigator, constituted a relapse.
• * Recent or planned major surgery that could confound the results of the trial or put the participant at undue risk.
• * Treatment with plasma exchange within 8 weeks prior to Screening.
• * Treatment within 3 months prior to dosing with immunosuppressive/ immunomodulator medication, or corticosteroids (except ≤20 mg/day of prednisone or equivalent which is allowed), or prior treatment (at any time) with highly immunosuppressive/ chemotherapeutic medications with sustained effects (eg, mitoxantrone, alemtuzumab, or cladribine).
• * Prior treatment with riliprubart.
• * Use of any specific complement system inhibitor (eg, eculizumab) within 12 weeks or 5 times the half-life of the product, whichever is longer, prior to Screening.
• * Prior treatment (any time) with total lymphoid irradiation or bone marrow transplantation.
• * Prior treatment with B-cell depleting agents such as rituximab within 6 months prior to riliprubart dosing, or before B-cell counts return to normal levels, whichever is longer.
• * Any vaccination received within 28 days prior to dosing (with few exceptions to be confirmed at screening).
• * Participation in another clinical trial with an investigational drug or receipt of an investigational product within 12 weeks or 5 times the half-life of the product (whichever is longer) prior to Screening.
• * Any Screening laboratory values outside normal limits or abnormal ECG considered in the Investigator's judgment to be clinically significant in the context of this trial.
• * Positive result of any of the following tests:
• * HBsAg XE " HBsAg " \\f Abbreviation \\t "Hepatitis B surface antigen" .
• * Anti-HBc Ab XE " HBc Ab " \\f Abbreviation \\t "Hepatitis B core antibodies" ; unless anti-HBs Ab XE " HBs Ab " \\f Abbreviation \\t "Hepatitis B surface antibody" are also positive, indicating natural immunity.
• * Anti-HCV XE " HCV " \\f Abbreviation \\t "Hepatitis C virus" antibodies.
• * Anti-HIV1 XE " HIV1" \\f Abbreviation \\t "human immunodeficiency virus 1" and anti-HIV2 XE " HIV2" \\f Abbreviation \\t "human immunodeficiency virus 2" antibodies.
• * Pregnancy, defined as a positive result of a highly sensitive urine or serum pregnancy test, or lactation.
• * Accommodation in an institution because of regulatory or legal order; imprisoned or legally institutionalized.
• * Participant not suitable for participation, whatever the reason, as judged by the Investigator, including medical or clinical conditions, or participants potentially at risk of noncompliance to study procedures.
• * Participants are employees of the clinical study site or other individuals directly involved in the conduct of the study, or immediate family members of such individuals XE " ICH " \\f Abbreviation \\t "Internation Council of Harmonization" XE " GCP " \\f Abbreviation \\t "Good clinical practice" .
• * Any country-related specific regulation that would prevent the participant from entering the study as defined by the protocol.