A Study to Test the Effects and Safety of Riliprubart in People With Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) for Which the Usual Treatments do Not Work

Inclusion Criteria:

Participants are eligible to be included in the study only if all of the following criteria apply:

-Participant must have CIDP or possible CIDP criteria, based on European Academy of Neurology (EAN)/ Peripheral Nerve Society (PNS) Task Force CIDP guidelines, second revision (2021).

• Participant must have either typical CIDP, or one of the following two CIDPvariants: motor CIDP (including motor predominant), multifocal CIDP (also known asLewis Sumner Syndrome). Diagnosis must be confirmed by the adjudication committee.

• Participant must be refractory to either immunoglobulin therapy or corticosteroidtherapy, as defined below.

• Immunoglobulinrefractory subgroup: Historic evidence of failure or inadequateresponse to immunoglobulin therapy prior to screening, defined as no clinicallymeaningful improvement or persistent INCAT score ≥2 after a minimum of:

• One dose of IVIg of 2 g/kg, followed by a second dose of 2 g/kg or twodoses of 1 g/kg, with a separation of approximately 3 weeks between doses (each dose can be divided over 2 to 5 days), as indicated in the EAN/PNS 2021 guidelines OR

• SCIg maintenance therapy with at least 0.2 g/kg weekly for 5 weeks

• Corticosteroidrefractory subgroup:

Historic evidence of failure or inadequate response to corticosteroid therapy prior to screening, defined as no clinically meaningful improvement or persistent INCAT score ≥2 after a minimum of 12 weeks of corticosteroid therapy. Corticosteroid regimen can be daily oral prednisone/prednisolone, at least 60 mg, equivalent to methylprednisolone 48 mg, tapered over 6 to 8 months, or alternative regimens, e.g. pulsed high-dose corticosteroid treatment (40 mg/day oral dexamethasone or 500 mg/day IV methylprednisolone, each daily for 4 days per month for 6 months), as indicated in the EAN/PNS 2021 guidelines A clinically meaningful improvement is defined as one or more of the following:

• A ≥1 point decrease in adjusted INCAT disability score

• An increase in IRODS centile score ≥4 points

• An increase in MRC Sum score ≥3 points

• An improvement in hand grip strength of ≥8 kilopascals or

• Equivalent improvement based on information from medical records and per theInvestigator's judgment

• Participant has an adjusted INCAT score of 2 to 9 --(a score of 2 should be exclusively from the leg disability component ofINCAT).

• Any allowed immunosuppressant drugs (azathioprine, cyclosporine, ormycophenolate mofetil) have been taken for ≥6 months at a stable dose for ≥3months prior to Screening

• Participant may be receiving low-dose oral corticosteroids (≤20 mg/day ofprednisone [or equivalent dose for other oral corticosteroids]), but only iftaken at a stable dose for ≥3 months prior to Screening

• Participant must have active disease, defined by a CIDP disease activity score (CDAS) of ≥ 2 points at Screening

• Participant must have documented vaccinations against encapsulated bacterialpathogens given within 5 years prior to Day 1 or initiated a minimum of 14 daysprior to first dose of study intervention

• All participants must agree to use contraception methods during and after thestudy as required.

• Contraceptive use by men and women participating in the study should beconsistent with local regulations regarding the methods of contraception forthose participating in clinical studies.

• Male participants are eligible to participate if they agree to thefollowing during the study intervention period and for at least 55 weeksafter the last dose of study medication:

• Refrain from donating or cryopreserving sperm PLUS

• Be abstinent from heterosexual intercourse as their preferred and usual lifestyle (abstinent on a long term and persistent basis) and agree to remain abstinent OR

• Must agree to use contraception/barrier as detailed below:

---- A male condom and an additional highly effective contraceptive method asdescribed in the protocol.

-- A female participant is eligible to participate if she is not pregnant orbreastfeeding, and one of the following conditions applies:

• Is a woman of nonchildbearing potential (WONCBP) as defined by the protocol OR

• Is a woman of childbearing potential (WOCBP) and agrees to use a contraceptivemethod that is highly effective (with a failure rate of <1% per year), as describedin Appendix 10.4 Contraception and barrier guidance during the study interventionperiod (to be effective before starting the intervention) and for at least 55 weeksafter the last administration of study intervention and agrees not to donate orcryopreserve eggs (ova, oocytes) for the purpose of reproduction during this period.

• Body weight at Screening of 35 kg to 154 kg (77 to 340 lbs), inclusive

Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply:

• Polyneuropathy of other causes, including but not limited to: hereditarydemyelinating neuropathies, neuropathies secondary to infection or systemic disease,diabetic neuropathy, drug- or toxin-induced neuropathies, multifocal motorneuropathy, polyneuropathy related to Immunoglobulin M (IgM) monoclonal gammopathy,POEMS syndrome, and lumbosacral radiculoplexus neuropathy.

• Sensory CIDP, Distal CIDP and focal CIDP variants.

• Any other neurological or systemic disease that can cause symptoms and signsinterfering with treatment or outcome assessments

• Poorly controlled diabetes (HbA1c >7%)

• Serious infections requiring hospitalization within 30 days prior to Screening andany active infection requiring treatment during screening or presence of a conditionthat may predispose the participant to increased risk of infection (eg, medicalhistory such as known immunodeficiency or history of recurrent infections)

• Clinical diagnosis of Systemic Lupus Erythematosus (SLE) or family history of SLE.For a participant with an antinuclear antibody (ANA) titer ≥1:160 and a positiveanti-double-stranded DNA (anti-dsDNA) at Screening, SLE diagnosis must be ruled outprior to enrollment.

• Sensitivity to any of the study interventions, or components thereof, or drug orother allergy that, in the opinion of the Investigator, contraindicatesparticipation in the study. Specifically, history of any hypersensitivity reactionto riliprubart or its components or of a severe allergic or anaphylactic reaction toany humanized or murine monoclonal antibody.

• Any other clinically meaningful medical history or ongoing medical condition (asdetermined by the Investigator at Screening) that might impact benefitriskassessment, jeopardize the safety of the participant, or compromise the quality ofthe data collected in this study; or history or presence of other significantconcomitant illness that would adversely affect participation in this study, perInvestigator's judgment.

• Documented history of attempted suicide over the 6 months prior to the Screeningvisit, presence of suicidal ideation of category 4 or 5 on CSSRS during screening,OR if in the Investigator's judgment, the participant is at risk for a suicideattempt.

• Evidence of CIDP worsening within the 6 weeks following a prior vaccination that, inthe opinion of the Investigator, constituted a relapse

• Recent or planned major surgery that could confound the results of the trial or putthe participant at undue risk

• Participant has received immunoglobulins (IVIg or SCIg) within 8 weeks prior toScreening

• Treatment with plasma exchange within the 8 weeks prior to Screening

• Prior treatment with riliprubart

• Prior treatment with (any time) with highly immunosuppressive/chemotherapeuticmedications with sustained effects, eg, mitoxantrone, alemtuzumab, cladribine

• Prior treatment (any time) with total lymphoid irradiation or bone marrowtransplantation

• Prior treatment with B-cell-depleting agents such as rituximab within 6 months priorto riliprubart dosing, or until return of B-cells counts to normal levels, whicheveris longer

• Use of any specific complement system inhibitor (eg, eculizumab) within 12 weeks or 5 times the halflife of the product, whichever is longer, prior to Screening

• Treatment within 6 months prior to dosing with immunosuppressive/ chemotherapeuticmedications, such as cyclophosphamide, methotrexate, tacrolimus, interferon, ortumor necrosis factor (TNF)α inhibitors. Certain immunosuppressants commonly used inCIDP (azathioprine, cyclosporine, or mycophenolate mofetil) are allowed, asindicated under inclusion criterion.

• Any vaccination received within 28 days prior to dosing (with few exceptions to beconfirmed at screening)

• Participation in another clinical trial with an investigational drug or receipt ofan investigational product within 12 weeks or 5 times the halflife of the product,whichever is longer, prior to Screening

• Any screening laboratory values outside normal limits or abnormal ECG considered inthe Investigator's judgment to be clinically significant in the context of thistrial.

• Positive result of any of the following tests:

• hepatitis B surface antigen (HBsAg)

• antihepatitis B core antibodies (anti-HBc Ab) (unless anti-hepatitis B surfaceantibodies [antiHBs Ab] are also positive, indicating natural immunity)

• antihepatitis C virus (antiHCV) antibodies

• antihuman immunodeficiency virus 1 and 2 (antiHIV1 and antiHIV2) antibodies

• Pregnancy, defined as a positive result of a highly sensitive urine or serumpregnancy test, or lactation

• Accommodation in an institution because of regulatory or legal order; eg, imprisonedor legally institutionalized

• Participant not suitable for participation, whatever the reason, as judged by theInvestigator, including medical or clinical conditions, or potential risk fornoncompliance to study procedures

• Participants are employees at the clinical study site or other individuals directlyinvolved in the conduct of the study, or immediate family member of such individuals

• Any country related specific regulation that would prevent the participant fromentering the study

• Treatment with efgartigimod within 8 weeks prior to screening