⁃ Presence of a suitable related HLA-haploidentical bone marrow donor.a. The donor and recipient must be identical at at least one allele of each of the following genetic loci: HLA-A, HLA-B, HLA-Cw, HLA-DRB1, and HLA-DQB1. A minimum match of 5/10 is therefore required, and will be considered sufficient evidence that the donor and recipient share one HLA haplotype.

⁃ 1 year-50 years

⁃ Patients must have a confirmed histopathologic diagnosis and be classified as high risk defined by having an expected survival of \< 10%. Examples include:

• Neuroblastoma or ganglioneuroblastoma

‣ Failure to achieve at least a PR after induction therapy with COG ANBL0532 or standard chemotherapy

⁃ Refractory to induction chemotherapy with COG ANBL0532 or standard chemotherapy

⁃ Patients with high risk disease as defined in Appendix 1 whose autologous peripheral blood stem cell product is contaminated with neuroblastoma or who do not have an autologous product available

⁃ Patients with high risk disease as defined in Appendix 1 who do not meet eligibility requirements/organ function requirements for myeloablative conditioning. Patients with \>5 identified lesions on the end of induction (COG ANBL0532 or standard chemotherapy) MIBG scan

• Stage 4 rhabdomyosarcoma

• Metastatic Ewing Sarcoma

• Osteosarcoma with metastatic disease beyond the lungs and/or with lung metastases not amenable to resection

• Desmoplastic small round cell tumor

• Any other solid tumor and soft tissue sarcoma with an estimated \<10% chance of survival will be considered on a case by case basis at the departmental tumor board and/or sarcoma meeting

⁃ Previous therapy:

• It is expected that patients will have received upfront standard of care therapy for their respected disease

• Patients who relapse after either single or tandem autologous BMT are eligible (\> 6 months must have elapsed from start of last BMT).

• Patients must be recovered from the acute toxicities of any prior chemo/radio/immunotherapy or BMT

⁃ Patients do not need to have measurable disease at time of enrollment. Patients with measurable disease must have stable disease by RECIST criteria on two scans at least 6 weeks apart.

⁃ Patients with adequate organ function as measured by

• Cardiac: Left ventricular ejection fraction at rest must be ≥ 35%, or shortening fraction \> 25%.

• Hepatic: Bilirubin ≤ 3.0 mg/dL; and ALT, AST, and Alkaline Phosphatase \< 5 x ULN.

• Renal: Serum creatinine within normal range for age, or if serum creatinine outside normal range for age, then renal function (creatinine clearance or GFR) \> 40 mL/min/1.73m2.

• Pulmonary: FEV1, FVC, DLCO (diffusion capacity) \> 50% predicted (corrected for hemoglobin); if unable to perform pulmonary function tests, then O2 saturation \> 92% on room air.

⁃ Good performance status (Karnofsky/Lansky 60-100)

⁃ Patients (Parents/guardians for those \<18) and donors must be able to sign consent forms.

⁃ Patients must be willing to participate in all stages of treatment

⁃ Criteria for recipient ineligibility Patients will not be excluded on the basis of sex, racial or ethnic background.

⁃ HIV-positive

⁃ Donor (donor anti-recipient) ABO incompatibility if an ABO compatible donor is available.

⁃ Positive leukocytotoxic crossmatch

⁃ Women of childbearing potential who currently are pregnant (HCG+) or who are not practicing adequate contraception

⁃ Uncontrolled viral, bacterial, or fungal infections.

⁃ Criteria for donor eligibility Age \>0.5 years

⁃ Donors must meet the selection criteria as defined by the Foundation for the Accreditation of Hematopoietic Cell Therapy (FACT).

⁃ Lack of recipient anti-donor HLA antibody Note: In some instances, low level, non-cytotoxic HLA specific antibodies may be permissible if they are found to be at a level well below that detectable by flow cytometry. This will be decided on a case-by-case basis by the PI and one of the immunogenetics directors.

⁃ In the event that two or more eligible donors are identified, the following order of priority will be used to determine the preferred donor:

⁃ Medically and psychologically fit and willing to donate

⁃ Killer Immunoglobulin Receptor (KIR) Haplotype B Donor

⁃ Red blood-cell compatibility (in order of preference)

• RBC cross-match compatible

∙ Minor ABO incompatibility

∙ Major ABO incompatibility

⁃ For CMV seronegative recipients, a CMV seronegative donor. For CMV seropositive recipients, a CMV seropositive donor is preferred.

⁃ When possible, HLA-mismatched donors will be prioritized over HLA-matched to maximize an allogeneic benefit.

⁃ If more than one preferred donor is identified from the above list and there is no medical reason to prefer one of them, then the following guidelines are recommended:

⁃ If the patient is male, choose a male donor

⁃ Choose the youngest preferred donor

⁃ If the patient and family express a strong preference for a particular donor, use that one.