Body weight > 30 kg Weight ? 35 kg DONOR: Weight >= 20 kg and patient or guardian able to provide consent DONOR: Donors who are not expected to meet the minimum target dose of marrow cells (1 x 10^8 nucleated cells/kg recipient ideal body weight) Adequate renal function with normal serum creatinine, or if creatinine above or below institutional normal range, a calculated glomerular filtration rate of ? 50 mL/min/1.73m2 (e.g., as calculated by the Cockcroft Gault formula) using actual body weight; if subject has body mass index > 30 kg/m2, lean body weight must be used. In the haplo cohort, the weight of the haplo donor must be ? 20 kg. Weight ? 35 kg DONOR: Age >= 4 and weight of >= 15 kg Patients who are 20% below their ideal body weight Patient weight >= 100 kg; patients >= 70 kg with MUDs must be discussed with the principal investigator DONOR: weight of at least 35 kg An actual body weight > 40kg Has a body weight ? 40kg at the time of enrollment Body weight >= 30 kg. Weight over 40 kilograms (kg) STRATUM B: Must meet the following weight and body surface area (BSA) restrictions:\r\n* For enrollment on dose level 0A, must have a weight >= 16kg and < 32kg\r\n* For enrollment on dose level 0B must have a weight >= 32kg and BSA >= 0.55m^2\r\n* For enrollment on dose level 1, must have a weight >= 16kg and BSA >= 0.55m^2\r\n* For enrollment on dose level 2, must have a weight >= 16kg and BSA >= 0.63m^2\r\n* For enrollment on dose levels 3 or 4A, must have a weight >= 16kg \r\n* For enrollment on dose levels 4B or 5, must have a weight >= 20kg and =< 106kg Body weight < 50 kilograms (110 pounds) or a body mass index ? 35 kg/m2. Body weight > 30 kg. Body weight > 30 kg Patient body weight must be above the minimum necessary for the patient to receive the ONC201 dose indicated for the currently enrolling dose level. The minimum body weight ranges from 10 to 35kg depending on the dose level. Body weight of greater than or equal to (>=) 39 kilogram (kg) at Screening Body weight > 30 kg Body weight > 35 kg Body weight > 30 kg Weight < 30 kg Body weight of at least 40 kilograms DONOR: At least 40 kilogram body weight CELL PROCUREMENT: Pediatric subjects (weight must be >= 10 kg) Weight over 40 kg Stable dose of corticosteroids for 2 weeks prior to enrollment, i.e. the patient’s steroid dose (mg/kg) will remain unchanged (e.g. 0.5 mg/kg) in the 2 weeks preceding enrollment; allowances will be made for up or down titrating the dose based on changes in body weight DONOR: Weight > 35 kg Significant weight loss (> 20% of body weight [BW]) within past 6 months prior to inclusion into the trial or actual body weight of less than 50 kg Patients with body weight < 30 kg Body weight > 30 kg Weight > 30kg (required for flat dose-based administration of study agents) PRIOR TO CELL PROCUREMENT: For pediatric subjects (weight must be ? 10 kg) Weight ? 15 kg (33 lb) Patients with a weight of < 39 kg DONOR: Weight >= 40 kg Weight > 50 kg Body weight < 3 kg. DONOR: Weight >= 40 kg DONOR: Weight < 20 kg In addition, each unit will have a cryopreserved dose of at least 1.5 x 10^7 total nucleated cells/recipient body weight (TNC/kg) DONOR: Weight >= 20kg Body weight of greater than or equal to (>=) 39 kilogram (kg) at Screening Body weight of greater than 30 kg Clearance to be calculated using Cockcroft formula: Males: 1.23 x (140 - age) x weight (kg) - serum creatinine (?mol/l) ; Females: 1.05 x (140 - age) x weight (kg) - serum creatinine (?mol/l) For patients whose body weight exceeds ideal body weight (IBW) by more than 20%, adjusted body weight may be used for calculation of PBSC dose Body weight > 30 kg Body weight > 30 kg DONORS: Body weight of at least 40 kilograms Body weight < 40 kg DONOR: At least 40 kilogram body weight Weight >= 15 kg Weight < 30 kg Body weight < 40 kilograms Body weight < 40 kilograms. Body weight ? 175 kg. (140 - age) x (weight in kg) x (0.85 if female)/ 72 x (serum creatinine in mg/dL) Body weight > 30 kilograms. Body weight > 30 kg In the opinion of the investigator, patients who are significantly below their ideal body weight Patients that in the opinion of the investigators are significantly below their ideal body weight Current body mass index (BMI) >= 25 kg/m^2 and weight =< 400 lbs, and willing to lose > 5% of their body weight; NOTE: participants should not have weight loss greater than 5% of body weight in the last 6 months; all weights for determination of eligibility may be determined by self-reported of weight if not documented in the medical records; exceptions that are felt to be due to surgical or other procedures (e.g., mastectomies or reconstruction) may be allowed with prior approval of the Protocol Chair/designee DONOR: Weight (Wt) > 25 kg DONOR: At least 40 kilogram body weight DONOR: Body weight of at least 40 kilograms Body weight > 30 kg Weight < 30 kg Subjects with a body weight > 140 kg (for Cohorts dosing 20 mg/kg of ALXN1007 and higher only). Weight of at least 10kg. Weight between 40 kg and 180 kg Weight >= 45 kg Patients whom, in the opinion of the investigators, are significantly below their ideal body weight Body weight >= 45 kilogram (kg) and a body mass index >= 19 kilogram per squaremeter (kg/m^2)and <40 kg/m^2 (inclusive); In the opinion of the investigator, patients who are significantly below their ideal body weight Weight ?3rd percentile for age and gender (and ?3.0 kg) In the opinion of the investigator, patients who are significantly below their ideal body weight. Patients who are 13 years old or older and have more than 45 kg of body weight will be eligible after consultation with their pediatric attending Body weight < 35 kg (77 pounds) Weight ? 34 kg. Body weight > 30 kg Body weight > 150 kg Weight >= 45 kg Weight > 10 kg (22 lbs) Patient weight >= 50 kg Obesity (body weight > 140 Kg) Body weight must be >= 20 kilograms (kg) if suspension is not available Weight > 110kg weight of less than or equal to 45 kg (for sites using cefuroxime only). Weight between 50 kg to 130 kg Patient weight at least 3.3 kg. Body weight > 30 kg Normal weight (BMI < 25.0 kg/m^2) Body weight between 50 kg (110 lb) and 110 kg (243 lb), inclusive Body weight greater than 350 lbs (158 Kg) Body weight > 137 Kg (300 lbs) Body weight greater than 350 lbs (158 Kg) Unexplained change in weight (> 4.5 kg) within the past 6 months