This is a Phase I/II, first-in-human study consisting of four sequential parts and an open-label extension (OLE). The safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of single doses of crovalimab will be evaluated in healthy volunteers (HV) during part 1. The safety, tolerability, PK and PD of multiple doses of crovalimab will be evaluated in participants with paroxysmal nocturnal hemoglobinuria (PNH) in parts 2, 3, 4, and OLE of the study. Efficacy of crovalimab will be evaluated in Parts 2, 3, and 4.

Inclusion Criteria:

Part 1 (HVs only):

• Healthy male volunteers, aged between 21 and 55 years inclusive
• Participants with a negative hepatitis B surface antigen (HBsAg), hepatitis B core antibody (HBcAb), hepatitis C antibody, and human immunodeficiency virus (HIV) test result
• Participants who have been vaccinated against hepatitis B
• No evidence of Neisseria meningococci in nasopharyngeal swab
• Neisseria meningitidis vaccination against serogroups B and A, C, W, and Y
• Non-smokers, or former smokers, who have not smoked for at least 60 days prior to screening

Parts 2, 3 and 4 (PNH participants only):

• Male or female participants with PNH between 18 and 75 years of age
• Neisseria meningitidis vaccination in accordance with most current local guidelines or standard of care (SOC) for participants at increased risk for meningococcal disease (Part 2 and 4)
• Participant has been vaccinated with Neisseria meningitidis vaccine(s) in accordance with most current local guidelines or SOC for participants at increased risk for meningococcal disease or is being revaccinated if applicable (Part 3 and 4)
• Antibiotic prophylaxis for meningococcal infection must be initiated prior to initiation of crovalimab therapy if the time period between initial Neisseria meningitidis vaccination and first dose of crovalimab is less than 2 weeks (Part 2 and 4)
• Antibiotic prophylaxis of meningococcal infection may be initiated prior to initiation of crovalimab therapy based on local guidelines or SOC for participants at increased risk for meningococcal disease e.g., splenectomized patients (Parts 2 and 4)
• Stable dose for greater than or equal to (>/=) 28 days prior to screening of other therapies (immunosuppressant therapy, corticosteroids, iron supplements)

Part 2 and 4 (currently untreated PNH participants who are candidates for treatment with complement inhibitors only):

• PNH participants who have not been treated with any complement inhibitor or if previously treated stopped treatment due to lack of efficacy based on a single missense C5 heterozygous mutation
• Serum LDH levels at least 1.5-fold above the ULN at screening
• Hepatitis B participants can be enrolled if their liver function test values are less than 2 x ULN and there is no liver function impairment

Part 3 and 4 (PNH participants currently treated with eculizumab only):

• PNH participants who have been treated continuously with eculizumab for at least 3 months preceding enrollment in the trial
• Participants receive regular infusions of eculizumab
• Subjects with a negative hepatitis B surface antigen (HBsAg), hepatitis B core antibody (HBcAb), hepatitis C antibody, and HIV test result

OLE only - PNH participants:

• PNH participants who have completed Parts 2, 3 and 4 respectively
• PNH participants who derived, in the investigator's opinion, benefit from treatment with crovalimab
• Vaccination currency for Neisseria meningitidis serotypes A, C, W, Y and B should be maintained throughout the OLE

All Parts:

• Female participants should use proper means of contraception

Exclusion Criteria:

Part 1 (HVs only):

• Any clinically relevant history or the presence of moderate to severe respiratory, renal, hepatic, gastrointestinal, hematological, lymphatic, neurological, cardiovascular, psychiatric, musculoskeletal, or connective tissue disease
• Any major illness within 1 month before the screening
• Prior splenectomy
• History of clinically significant hypersensitivity (example: drugs, excipients) or allergic reactions
• History or presence of clinically significant electrocardiogram (ECG) abnormalities or cardiovascular disease
• Any contra-indication for receiving Neisseria meningitides vaccination and antibiotic prophylaxis therapy as required in the study
• Congenital or acquired complement deficiency
• Carriers of Neisseria meningitides based on cultures from nasopharyngeal swabs
• Known active viral, bacterial or fungal infection including herpes, herpes zoster or cold sores, during the last 14 days prior to first study drug administration
• Signs of parasitic infection (example: eosinophilia, diarrhea)
• History of significant recurrent infections in the opinion of the investigator

Parts 2, 3 and 4 - PNH participants only:

• Evidence of moderate to severe concurrent renal, liver, cardiac, pulmonary or gastrointestinal disease not related to PNH as determined by the investigator
• History of an illness that, in the opinion of the study investigator, might confound the results of the study or that poses an additional risk to the participant by his or her participation in the study
• History of bone marrow transplantation
• Treatment with azathioprine or erythrocyte-stimulating agents within 14 days prior to first study drug administration
• Splenectomy <1 year before start of crovalimab.

Part 3 and 4 - PNH patients only:

• Any evidence of sero-positive auto-immune connective tissue diseases (such as systemic lupus erythematosus, or rheumatoid arthritis)
• Any evidence of active inflammatory conditions (including inflammatory bowel disease, or cryoglobulinemia)

All Parts:

• Under active therapy with intravenous immunoglobulin (IVIG)
• Mentally incapacitated or history of a clinically significant psychiatric disorder over the previous 5 years
• Known or suspected hereditary complement deficiency
• History of meningococcal meningitis
• History of allergic or anaphylactic reactions to human, humanized, or murine monoclonal antibodies or known hypersensitivity to any constituent of the product
• Any major episode of infection requiring hospitalization or treatment with intravenous (IV) antibiotics within 28 days prior to screening or oral antibiotics within 2 weeks prior to screening and up to first study drug administration
• History of or currently active primary or secondary immunodeficiency, including known history of human immunodeficiency virus (HIV) infection
• Evidence of chronic active hepatitis C infection
• Evidence of malignant disease including myelodysplastic syndrome, or malignancies diagnosed within the previous 5 years
• Pregnant or breastfeeding, or intending to become pregnant during the study, including the OLE period, within 46 weeks (approximately 10.5 months) after the final dose of crovalimab

Qualified researchers may request access to individual patient level data through the clinical study data request platform (www.vivli.org). Further details on Roche's criteria for eligible studies are available here (https://vivli.org/members/ourmembers/). For further details on Roche's Global Policy on the Sharing of Clinical Information and how to request access to related clinical study documents, see here (https://www.roche.com/innovation/process/clinical -trials/data-sharing/)