Genetically Engineered Cells (FH-FOLR1 ST CAR T Cells) for the Treatment of Advanced Refractory or Recurrent/Progressive Osteosarcoma, FIERCe Trial

Inclusion Criteria:

• Age 1-75 years at the time of enrollment

• Tissue confirmation of osteosarcoma diagnosis

• Must have received an anthracycline-based regimen or been deemed ineligible toreceive this therapy

• Must have at least one of the following in the 6 months prior to trial consent:

• New site of measurable disease by radiographic imaging or histologicconfirmation

• New site of evaluable disease by radiographic imaging or histologicconfirmation

• Greater than 20% increase in at least one tumor dimension documented by CT/MRI,AND a minimum absolute increase of 5 mm in longest dimension of existinglesion(s) (previously irradiated lesions may be included)

• Persistent measurable disease or fludeoxyglucose F-18 (FDG)-PET avid bonemetastasis that has failed to achieve complete remission to upfrontconventional therapy (surgery, radiotherapy, and/or chemotherapy)

• All anti-cancer therapy must be discontinued at enrollment/time of apheresis, withthe following washout periods observed:

• Chemotherapy and biologic agents: ≥ 7 days prior to enrollment

• Steroid use: All corticosteroid therapy (unless physiologic replacement dosingand/or topical administration (e.g., inhaled or dermatologic) ≥ 7 days prior toenrollment

• Tyrosine kinase inhibitor (TKI) use: ≥ 7 days prior to enrollment

• Antitumor antibody therapy (including immune checkpoint inhibitor) must be ≥ 3half-lives or 30 days, whichever is shorter, from time of enrollment

• FOLR1 targeting therapy must be discontinued at least 30 days prior toenrollment

• Gene modified cellular therapy: At enrollment, must be at least 30 days frommost recent gene modified cell therapy infusion and document no evidence ofmodified cells in the peripheral blood OR must be at least 60 days from mostrecent gene modified cell therapy

• Washout periods not applicable to patients with apheresis product or usable Tcell product available for use at time of enrollment

• Potential trial participants should have recovered to grade 1 from clinicallysignificant adverse events of their most recent therapy/intervention prior toenrollment

• Ability to understand and willingness to sign a written informed consent document.

• Females of child-bearing potential and fertile male participants must be willing touse an effective contraceptive method before, during, and for at least 12 monthsafter the FOLR1 CART cell infusion

• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 (if treated atadult facility) or Lansky/Karnofsky score ≥ 60 (if treated at pediatric facility).Participants who are unable to walk because of paralysis, but who are up in awheelchair, will be considered ambulatory for purposes of assessing performancestatus

• Life expectancy ≥ 8 weeks

• Able to tolerate apheresis, including placement of temporary apheresis catheter, ifnecessary, or already has an apheresis product available for use in manufacturing

• Participants with a prior or concurrent malignancy whose natural history ortreatment does not have the potential to interfere with the safety or efficacyassessment of the investigational regimen are eligible for this trial

• Participants with treated brain metastases are eligible if they meet the followingcriteria:

• Follow-up brain imaging taken at screening demonstrates no evidence ofprogression and that imaging occurs 3 months after central nervous system (CNS)-directed therapy has been completed

• No ongoing, symptomatic CNS pathology requiring medical intervention

• Serum creatinine ≤ 1.5 x upper limit of normal (ULN) based on age and gender; orestimated creatinine clearance > 50 mL/min as calculated using the Cockcroft-Gaultformula and not dialysis dependent

• Age: 1 to < 2 years; maximum serum creatinine (mg/dL): 0.6 (male), 0.6 (female)

• Age: 2 to < 6 years; maximum serum creatinine (mg/dL): 0.8 (male), 0.8 (female)

• Age: 6 to < 10 years; maximum serum creatinine (mg/dL): 1 (male), 1 (female)

• Age: 10 to < 13 years; maximum serum creatinine (mg/dL): 1.2 (male), 1.2 (female)

• Age: 13 to < 16 years; maximum serum creatinine (mg/dL): 1.5 (male), 1.4 (female)

• Age: ≥ 16 years; maximum serum creatinine (mg/dL): 1.7 (male), 1.4 (female)

• Total bilirubin ≤ 3 x ULN or conjugated bilirubin ≤ 2 mg/dL. Participants withsuspected Gilbert syndrome may be included if total bilirubin (Bili) > 3 mg/dL butno other evidence of hepatic dysfunction

• Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) < 5 x ULN

• Pulmonary: ≤ grade 1 dyspnea at rest and arterial oxygen saturation (SaO2) ≥ 92% onambient air. If pulmonary function tests (PFTs) are performed based on the clinicaljudgement of the treating physician, participants with forced expiratory volume in 1second (FEVI) ≥ 50% of predicted and diffusion capacity of the lung for carbonmonoxide (DLCO) (corrected) of ≥ 40% of predicted will be eligible

• Left ventricular ejection fraction (LVEF) may be established with echocardiogram orMUGA scan, and left ejection fraction must be ≥ 50% or shortening fraction ≥ 28%

• Absolute neutrophil count (ANC) ≥ 500 cells/ mm^3

• Hemoglobin ≥ 8 g/dL

• Platelets ≥ 100,000 per mm^3

• Participants receiving blood product transfusion are acceptable as long as they arenot determined to be transfusion refractory

Exclusion Criteria:

• Active autoimmune disease: Participants with active autoimmune disease requiringimmunosuppressive therapy are excluded. Case by case exemptions are possible withapproval by PI

• Corticosteroid therapy at a dose equivalent of > 15 mg of prednisone per day (orequivalent). Pulsed corticosteroid use for disease control is acceptable. Forparticipants weighing ≤ 30 kg, systemic steroids ≥ 0.5 mg prednisoneequivalent/kg/day

• Concurrent use of other investigational anti-cancer agents

• Active uncontrolled infection: HIV positive participants on highly activeantiretroviral therapy (HAART) with a CD4 count > 500 cells/mm^3 are consideredcontrolled, as are individuals with a history of hepatitis C who have successfullycompleted antiviral therapy with an undetectable viral load, and those withhepatitis B who have hepatitis well controlled on medication

• Uncontrolled concurrent illness: Participants may not have uncontrolled orconcurrent illness including, but not limited to, symptomatic congestive heartfailure, unstable angina pectoris, or cardiac arrhythmia that would limit compliancewith study requirements

• Active treatment for prior immune related adverse event to any immunotherapy:Participants receiving ongoing treatment for prior serious immune-related adverseevents are excluded, with exception of hormone supplementation or corticosteroidtherapy at equivalent of > 15 mg prednisone (or equivalent) per day, unlessotherwise approved by PI

• Significant underlying neurologic disease: Study participants must not havesignificant active underlying neurologic disease, unless approved by PI. Peripheralneuropathy related to diabetes or prior chemotherapy is acceptable

• Pregnant, possibly pregnant or those expecting to conceive or father children forthe duration of the trial through 4 months after T cell infusion

• Participants unwilling to provide consent/assent for participation in the study and 15-year follow-up period if CAR T cell therapy is administered

• Other medical, social, or psychiatric factor that interferes with medicalappropriateness and/or ability to comply with study, as determined by the PI

• Known allergic reactions to any of the components of study treatments