B7H3 CAR T Cell Immunotherapy for Recurrent/Refractory Solid Tumors in Children and Young Adults

Inclusion Criteria:

* Participants age ≤ 26 years at the time of consent for study participation; the first 2 participants enrolled and treated with CAR T cells in both Arms A and B will be ≥ 15 years. and ≤ 26 years at time of consent for study participation
* Histologically diagnosed malignant, non-primary CNS solid tumor
* Evidence of refractory or recurrent disease
* Lansky or Karnofsky score ≥ 50
* Life expectancy ≥ 8 weeks
* Recovered from significant acute toxic effects of all prior chemotherapy, immunotherapy and radiotherapy
* If no apheresis product or usable T cell product is available, all chemotherapy has been discontinued ≥ 7 days prior to enrollment
* If no apheresis or usable T cell product is available, all biologic therapy has been discontinued ≥ 7 days prior to enrollment
* If no apheresis product or T cell product is available, all systemic corticosteroid therapy has been discontinued ≥ 7 days prior to enrollment (physiologic replacement dosing is allowed)
* If no apheresis product or usable T cell product is available, at least 3 half-lives or 30 days (whichever is shorter) from time of last dose of anti-tumor directed antibody therapy (including checkpoint inhibitor) at time of enrollment
* If no apheresis product or usable T cell product is available, at least 6 weeks post last dose of myeloablative therapy and autologous and/or allogeneic stem cell transplant, or non-myeloablative therapy and allogeneic stem cell transplant (all timed from stem cell infusion). Participants who receive autologous stem cell infusion following non-myeloablative therapy are eligible once all other eligibility requirements are met.
* If no apheresis product or usable T cell product is available, participants who have received genetically modified cell therapy must be at least 30 days from most recent cell infusion prior to enrollment
* If no apheresis product or usable T cell product is available, participants with neuroblastoma must be at least 12 weeks from I131 MIBG therapy.
* Adequate organ function
* Adequate laboratory values
* Participant is able to tolerate apheresis (including placement of temporary apheresis catheter, if necessary), or already has an apheresis product available for use in manufacturing.
* Participants of childbearing potential must agree to use highly effective contraception

Exclusion Criteria:

* Presence of active malignancy other than primary malignant solid tumor diagnosis
* Current relevant CNS pathology
* Receiving external beam radiation therapy at time of enrollment
* Presence of active GVHD, or receiving immunosuppressive therapy for treatment or prevention of GVHD within 4 weeks prior to enrollment
* Participant is pregnant or breastfeeding
* Participant has presence of active severe infection
* Participant has presence of any condition that, in the option of an investigator, would prohibit the participant from undergoing treatment under this protocol
* Participant has primary immunodeficiency syndrome
* Unwilling or unable to provide consent/assent for participation in the study and 15 year follow up period