Criteria for Screening  Tumor  Patient must have a diagnosis of ependymoma that is recurrent or progressive. All tumors must have histologic verification either at the time of diagnosis or recurrence.  Prior Therapy  Patient must have received standard of care therapy including maximal safe surgical resection followed by local adjuvant radiation therapy prior to enrollment.  Adequate Pre-trial Tumor Tissue  Patient must have adequate pre-trial tumor material available to determine HER2 status. Tumor tissue from the most recent resection or biopsy of recurrent disease in preferred. If unavailable, tumor tissue from prior recurrences or from the time of initial diagnosis is acceptable.  a. One exception will be patients who have previously received HER2-directed therapy (including but not limited to trastuzumab); these patients will need evaluation of tumor HER2 status after stopping treatment due to the possibility of HER2 downregulation or loss.  Tumor biopsy will not be performed for the purpose of HER2 screening. Patients will not be eligible for screening on PBTC-059 if tumor tissue is not available or inadequate for HER2 testing. Tumor screening by Immunohistochemistry (IHC) will be done centrally using the testing method validated at Texas Children's Hospital. Sample for screening must be shipped within 7 days of enrollment for screening.  Known HIV Positivity  Patients that are known to be HIV-positive are ineligible due to the unknown safety and efficacy of infusing these patients with CAR T cells genetically modified using retroviral vectors. Additionally, the immunosuppression used for treatment in this study will pose an unacceptable risk.  Age  Patient must be ≥ 1 but ≤ 21 years of age at the time of screening consent.  Screening Consent  The patient or parent/guardian can understand the consent and is willing to sign a written informed consent document according to institutional guidelines. Age- and developmentally appropriate assent should be obtained as required by institutional guidelines.  Potential Eligibility for Study Treatment Enrollment  Patients are screened for this trial should be reasonably anticipated to meet the criteria for treatment described in Section 3.3 if their tumor is HER2-positive.  Criteria for Procurement  All subjects must meet following inclusion and exclusion eligibility criteria at the time of peripheral blood procurement for manufacturing the HER2 CAR T-cell product. No exceptions will be given. All clinical and laboratory evaluations to establish eligibility for procurement must be done within 14 days prior to enrollment. See Section 6.1 for details of laboratory requirements and planning of procurement blood collection date.  Procurement Inclusion Criteria  Tumor  Patient must have been screened and determined to have a diagnosis of a HER2-positive recurrent or progressive ependymoma.  Performance Score  Karnofsky Performance Scale (KPS for > 16 years of age) or Lansky Performance Score (LPS for ≤ 16 years of age) (Appendix C) assessed within one week of procurement must be ≥ 60%. Patients who are unable to walk because of neurologic deficits, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score provided the neurological deficit is stable as described in Section 3.3.1.7.  Prior Therapy  Patients must have received last dose of cytotoxic chemotherapy greater than 21 days preceding the date of enrollment for procurement.  Organ Function  Patient must have adequate organ and bone marrow function as defined below:  Peripheral absolute neutrophil count (ANC) > 1.0 x 109 cells/L Platelet count ≥ 75 100 x 109 cells/L (unsupported, defined as no platelet transfusion within 4 days) Hemoglobin ≥ 8 g/dL (may receive red blood cell transfusions) Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN) for age Alanine transaminase (ALT /SGPT) and Aspartate aminotransferase(AST/SGOT) ≤ 3 x institutional upper limit of normal (ULN) for age Serum creatinine < 1.5 x institutional upper limit of normal for age and gender. Patients that do not meet the criteria but have a 24-hour Creatinine Clearance or Glomerular filtration rate (GFR) (radioisotope or iothalamate) ≥ 70 mL/min/1.73 m2 are eligible.  Pulmonary Function  Oxygen saturation as measured by pulse oximetry is ≥ 93% on room air.  Concomitant Medication  Patients who are receiving systemic corticosteroids must be on a stable or decreasing dose for at least two weeks prior to procurement, and corticosteroid dose must be less than or equal to dexamethasone 0.75 mg/m2/day (or equivalent). Use of topical, ocular, intranasal, or inhaled corticosteroids are permitted.  Procurement Consent  The patient or parent/guardian can understand the consent and is willing to sign a written informed consent document according to institutional guidelines. Age- and developmentally appropriate assent should be obtained as required by institutional guidelines.  Potential Eligibility for Study Enrollment  Patients whose blood samples have been successfully procured for this trial should be reasonably anticipated to meet the criteria for treatment described in Section 3.3 and to begin treatment within 180 days from the date of procurement. The treatment slot will not be held beyond the specified 180 days, and such patients may not be able to receive treatment on this study depending on slot availability.  Procurement Exclusion Criteria  1. Known HIV Positivity  Patients who are known to be HIV-positive are ineligible due to the unknown safety and efficacy of infusing these patients with CAR T cells genetically modified using retroviral vectors. Additionally, the immunosuppression used for treatment in this study will pose an unacceptable risk.  Criteria for Treatment  All Phase I (Stratum 1) and Surgical (Stratum 2) subjects must meet following inclusion and exclusion eligibility criteria at the time of enrollment for treatment. No exceptions will be given. Imaging studies must be done within 14 days prior to enrollment. All other clinical and laboratory evaluations to establish eligibility for treatment must be done 7 days prior to enrollment.  Treatment Inclusion Criteria  Diagnosis  Patients with a histologically confirmed diagnosis of HER2 positive ependymoma that is recurrent or progressive. Histologic verification may be from time of diagnosis or time of recurrence. In cases where there is question of recurrence, histologic verification, or verification of progression on follow up imaging is required prior to enrolling for protocol treatment.  Disease Status  Phase I (Stratum 1) - Patients must have evaluable disease to be eligible. Evaluable disease includes either measurable OR non-measurable disease, defined as follows:  Measurable disease (enhancing or non-enhancing tumor):  at least 1 cm, or at least two times (in both perpendicular diameters) the MRI slice thickness, plus the interslice gap.  Non-measurable disease (tumor that is too small to be accurately measured):  less than 1 cm in at least one perpendicular dimension, or less than two times the MRI slice thickness, plus the interslice gap.  Note: Leptomeningeal disease is considered non-measurable but evaluable.  Surgical Study (Stratum 2) - Patients with measurable disease (Section 3.3.1.2.1) in whom tumor resection is clinically indicated and feasible after the CAR T cell infusion.  Age  Patient must be ≥ 1 but ≤ 22 years of age at the time of enrollment for treatment.  HER2 CAR T cell product  The patient must have, at a minimum, one prescribed dose of the cryopreserved, autologous HER2 CAR T cell product available for infusion.  Prior Anti-neoplastic Therapy  Cytotoxic chemotherapy: Patients must not have received cytotoxic chemotherapy for at least 28 days prior to study enrollment for treatment and must have recovered from the acute treatment related toxicities (defined as < grade 1 if not defined in eligibility criteria; excludes alopecia) prior to entering this study.  Biological, targeted, or investigational agents (anti-neoplastic): Patients must have a period of at least 28 days from the last receipt of said drug and must have recovered from all acute toxic effects.  For agents that have known acute adverse events occurring beyond 28 days after administration, this period must be extended beyond the time during which adverse events are known to occur.  Monoclonal antibodies, checkpoint inhibitors, and other agents with known prolonged half-lives: Patient must have recovered from any acute toxicity potentially related to the agent and received their last dose of the agent ≥ 28 days prior to study enrollment.  Adoptive cellular therapies: Patient must have recovered from any acute toxicity potentially related to the cellular product and received their last dose of the cellular product at least 90 days prior to study enrollment. (Note: Patients who have previously received an adoptive cellular therapy may continue long-term follow up evaluations per the prior study's evaluation schedule as needed for assessment of long-term toxicities including genotoxicity.)  Radiation: Patients must have had their last fraction of:  a. Craniospinal irradiation, whole brain radiation, total body irradiation or radiation to >50% of pelvis or spine ≥ 3 months prior to enrollment (90 days) prior to enrollment.  b. Focal palliative irradiation to the tumor ≥ 42 days prior to enrollment. c. Patients who receive tumor-directed radiation (non-palliative) should have confirmed disease progression on the imaging study done at least 6 weeks after the completion of the last fraction of radiation.  Surgery: Patients must have not had surgery within 14 days of enrollment for treatment and must have adequate wound healing and recovered from other acute effects from surgery. One exception is the placement of central venous catheter which will be allowed at any time point until treatment initiation on the study.  Growth Factors  Patients must be off all colony-forming growth factor(s) for at least 7 days prior to enrollment (e.g., filgrastim, sargramostim, or erythropoietin). 14 days must have elapsed if the patient received a long-acting formulation.  Corticosteroids  Patients who are receiving systemic corticosteroids must be on a stable or decreasing dose for at least 14 days prior to enrollment for treatment, and corticosteroid dose must be less than or equal to dexamethasone 0.5 mg/m2/day (or equivalent) during the 14 days preceding enrollment. Use of topical, ocular, intranasal, or inhaled corticosteroids are permitted.  Neurologic Status  In patients with neurological deficits, deficits should be stable for a minimum of 7 days prior to enrollment. A baseline detailed neurological exam should clearly document the neurological status of the patient at the time of enrollment for treatment on the study.  Patients with seizure disorders may be enrolled if seizures are well controlled.  Performance Status  Karnofsky Performance Scale (KPS for > 16 years of age) or Lansky Performance Score (LPS for ≤ 16 years of age) (Appendix C) assessed within one week of enrollment must be ≥ 60%. Patients who are unable to walk because of neurologic deficits, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score.  Organ Function  Patients must have adequate organ and bone marrow function as defined in Section 3.2.1.4.  Pregnancy Prevention  Patients of childbearing or child fathering potential must be willing to use a medically acceptable form of birth control, which includes abstinence, while being treated on this study.  Informed Consent  The patient or parent/guardian can understand the consent and is willing to sign a written informed consent document according to institutional guidelines. Age- and developmentally appropriate assent should be obtained as required by institutional guidelines.  Patients who meet eligibility criteria per Section 3.3.1.2.1 must be enrolled using Phase I treatment consent (Stratum 1). Patients who meet eligibility criteria per Section 3.3.1.2.2 must be enrolled using Surgical Study treatment consent (Stratum 2).  Treatment Exclusion Criteria  Patients with Bulky Tumors on Imaging Studies  Bulky tumors will be defined as those:  > 6 cm in single maximum dimension, or tumor causing uncal herniation or mass effect leading to midline shift with or without symptoms or signs of impending herniation or obstruction to Cerebrospinal fluid (CSF) flow. Infratentorial tumors with symptoms or signs arising from brain stem involvement by the tumor. Patients with stable cranial nerve deficit(s) secondary to prior surgery will not be excluded. Surgical Study (Stratum 2): Patients who have urgent need for surgical resection of tumor. Pregnancy or Breast-feeding  Pregnant women or nursing mothers are excluded from this study.  a. Female patients of childbearing potential must have a negative serum or urine pregnancy test within 7 days of start of enrollment for treatment. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required.  Pregnant or breast-feeding women are excluded from this study because there is an unknown but potential risk of adverse events to the fetus or the nursing infant with the use of T cells genetically modified to express HER2 CAR. Pre-clinical studies in mice demonstrate the target antigen HER2 is necessary for normal fetal development of cardiac trabeculae, cranial sensory ganglia, and motor neuron development.75 Additionally, the lymphodepleting chemotherapy drugs fludarabine and cyclophosphamide are both Pregnancy Class D drugs.  4. Concurrent Illness  Patients with active autoimmune disease, documented history of autoimmune disease/syndrome, or any other condition that requires ongoing systemic steroids or systemic immunosuppressive agents, except a. Patients with vitiligo or resolved asthma/atopy b. Patients with hypothyroidism stable on hormone replacement or Sjogren's syndrome c. Patients requiring physiologic doses of corticosteroids (up to 0.5 mg/m2/day dexamethasone equivalent)  History of or ongoing pneumonitis or significant interstitial lung disease  Ongoing or active uncontrolled infection  Patients with any clinically significant unrelated systemic illness (serious infections or significant cardiac, pulmonary, hepatic or other organ dysfunction), that in the opinion of the investigator, would compromise the patient's ability to tolerate protocol therapy, put them at additional risk for toxicity or would interfere with the study procedures or results.  Patients with any of the following cardiac diseases  New York Heart Association (NYHA) functional class III or IV Clinically significant cardiac arrhythmia including, but not limited to, Torsade de pointes or requiring a pacemaker Left ventricular ejection fraction below 50% as determined by echocardiography (ECHO)  Known HIV positivity  a. HIV-positive patients are ineligible due to the unknown safety and efficacy of infusing these patients with CAR T cells genetically modified using retroviral vectors. Additionally, the immunosuppression used for treatment in this study will pose an unacceptable risk.  5. Concomitant Medications  Patients who are receiving any other anti-cancer or investigational drug therapy are ineligible.  Patients who have received the last vaccination of a live vaccine ≤ 30 days prior to enrollment are ineligible.  Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella, yellow fever, rabies, Bacillus Calmette-Guérin (BCG), and typhoid (oral) vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed; however, intranasal influenza vaccines (e.g., Flu-Mist®) are live attenuated vaccines and must meet timeline for live vaccine.  Herbal preparations/medications (except for vitamins) including, but not limited to: St. John's wort, Kava, ephedra (ma huang), gingko biloba, dehydroepiandrosterone (DHEA), yohimbe, saw palmetto, black cohosh, and ginseng. Patients should stop using all herbal medications and dietary supplements at least 7 days prior to enrollment.  6. Inability to participate  Patients who in the opinion of the investigator are unwilling or unable to return for required follow-up visits or obtain follow-up studies required to assess toxicity to therapy or to adhere to drug administration plan, other study procedures, and study restrictions.  7. Allergy  Patients with a history of allergic reactions attributed to compounds of similar chemical or biologic composition (murine protein-containing products, Dimethylsulfoxide (DMSO), or dextran 40).