Inclusion Criteria:

• Provide written informed consent from subjects, an impartial witness (for a subject who is physically unable to sign the informed consent form, but able to provide his/her consent by some other means [e.g., speaking, nodding, blinking]), or the subject’s legally authorized representative (LAR) (for a subject who lacks capacity to consent for him/herself [e.g., a subject without mental capacity to consent]), prior to beginning any study procedures.
• Cervical spinal cord injury who meet either of the following criteria:
  • AIS A with ISNCSCI neurological level of injury between C4 and C7 (for C4, the subject must have at least 1 point of motor activity within the ZPP inclusive of C5 to T1);
  • AIS B or C with ISNCSCI neurological level of injury between C4 and C7, and UEMS ≤ 28.
• Male and female subjects, age between 18 and 70 years at time of consent.
• Body mass index (BMI) < 40 kg/m^2.
• Acute traumatic spinal cord injury subjects who can receive MT-3921 as soon as possible after the injury, at least within 48 hours from the time of the injury.
• Willing and able to participate in all aspects of the study, including completion of subjective evaluations, attendance at scheduled clinic visits, and compliance with all protocol requirements as evidenced by providing informed consent.
• Both female and male subjects of childbearing potential must agree to use of contraception or abstinence during the study.

Exclusion Criteria:

• Any concomitant injury that, in the judgement of the Investigator, interferes with the performance, interpretation or validity of neurological examinations (including fractures requiring casts), such as but not limited to multiple spinal cord lesions, brachial/lumbar plexus injury, cauda equina injury or traumatic brain injury defined by a Glasgow Coma Scale (GCS) <14 at time of examination.
• Poly-traumatic Injury as defined by Injury Severity Score (ISS) values > 25 at time of Screening.
• Penetrating spinal cord injuries.
• Complete transection of the spinal cord or spinal cord contusion size > 3 cm determined by MRI.
• Subjects who are highly anticipated to be dependent on long-term mechanical ventilation (e.g., beyond 10-14 days), which would interfere with study procedures including neurological exams.
• Any other significant pre-existing medical conditions prior to spinal cord injury or current conditions that, in the judgement of the Investigator, may increase the risks associated with study participation, and would preclude successful participation in the study.
• Subjects with history of active hepatitis B, hepatitis C, or human immunodeficiency virus (HIV), except for adequately treated hepatitis B (HBV) and hepatitis C virus (HCV) with documentation of sustained virologic response defined as undetectable HCV RNA at least 12 weeks after the end of treatment.
• History of anaphylaxis or significant allergy to any food and medications.
• History or presence of malignancy within the last 3 years prior to screening, except subjects who have been treated successfully with no recurrence for >1 year of basal cell or squamous cell carcinoma of the skin or in-situ cervical cancer.
• Subjects with hereditary fructose intolerance.
• Psychoactive substance use disorder at any time during the 3 months preceding study entry (as defined by Diagnostic and Statistical Manual of Mental Disorders [DSM-5]).
• Participation in any clinical trial of a new chemical entity within 12 weeks prior to Screening.
• Pregnant or nursing women.