• Age ≥ 12 years old

• Histologically-confirmed locally advanced or metastatic soft tissue or bone sarcoma scheduled to undergo resection or biopsy as part of standard of care

• Liposarcoma expansion cohort: histologically confirmed unresectable recurrent/metastatic liposarcoma scheduled to undergo resection or biopsy as part of standard of care

• Participants undergoing resection should have other measurable disease or be high risk for recurrence within 12 month per investigator assessment and has prior approval by PI.

• Measurable disease according to RECIST 1.1 present prior to infusion of attIL12-TIL. If the only measurable disease is the same as the lesion biopsied for the study, it needs to be at least 2 cm in largest diameter.

• Participants must have received at least 1 prior line of systemic therapy for the treatment of sarcoma, unless no standard therapy exists for a specific sarcoma subtype.

• At least 3 weeks must have elapsed since the last cytotoxic chemotherapy or immunotherapy prior to tumor tissue collection. For targeted therapies, at least 4 half-lives or 3 weeks must have elapsed prior to tumor tissue collection (whichever is shorter). Standard of care anti- cancer therapy will be permitted following tumor tissue collection but prior to initiation of cyclophosphamide such that at least 3 weeks must have elapsed since last cytotoxic chemotherapy or immunotherapy prior to starting treatment with cyclophosphamide. For targeted therapies, at least 4 half-lives or 3 weeks must have elapsed prior to initiation of treatment with cyclophosphamide (whichever is shorter). Investigational anti-cancer therapy will not be permitted.

• At least 2 weeks must have elapsed for palliative radiation to any tumor site other than the tumor site identified for tissue collection

• Participants must have organ and marrow function as defined below

⁃ Absolute neutrophil count (ANC) \> 1 K/uL, Hemoglobin \> 9 g/dL, Platelets \> 100 K/mm3

⁃ Serum creatinine \</= 2 mg/dL OR creatinine clearance \> 50 mL/min

⁃ Aspartic transaminase (AST) . 1.5 x upper limit of normal (ULN), Alanine transaminase (ALT) \</= 1.5 x ULN, Bilirubin ≤ 1.5 x ULN

⁃ Women of childbearing potential (WOCBP) must agree to use method(s) of contraception: at least one highly effective or two effective accepted methods of contraception to avoid conception throughout the study in such a manner that the risk of pregnancy is minimized. Suggested precautions should be used to minimize the risk or pregnancy for at least 1 month before start of therapy, and while women are on study for up to 3 months after T cell infusion.

⁃ WOCBP include any female who has experienced menarche and who has not undergone successful surgical sterilization (hysterectomy, bilateral tubal ligation or bilateral oophorectomy) or is not postmenopausal

⁃ Men must be willing and able to use an acceptable method of birth control such as latex condom during the dosing period and for at least 3 months after completion of the study agent administration (T cell infusion) if their sexual partners are WOCBP.

⁃ Signed Informed Consent and if applicable, pediatric assent