• Inclusion Criteria for Cohort 1:

‣ Age \>= 18 years.

⁃ Karnofsky performance status (KPS) score of \>=70.

⁃ All participants must have adequate organ function defined as:

• Peripheral absolute neutrophil count \>=1000/mm\^3.

∙ Platelet count \>=100,000/mm\^3 (transfusion independent, defined as not receiving platelet transfusions for at least 7 days prior to enrollment).

∙ Absolute lymphocyte count (ALC) \>= 300/μL and/or Cluster of differentiation 3 (CD3) count of \>=150/μL.

∙ Creatinine clearance or radioisotope glomerular filtration rate \>= 50 mL/min/1.73m\^2.

∙ Total Bilirubin \<= 1.5 x ULN except for Gilbert's syndrome and

∙ Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \<= 3x upper limit of normal (ULN).

∙ Left ventricular ejection fraction (LVEF) \>= 40% by echocardiogram or multi-gated acquisition scanning (MUGA).

∙ Adequate pulmonary function, defined as no evidence of dyspnea at rest and pulse oximetry \> 92% while breathing room air.

⁃ Pathological criteria: EGFRvIII+ GBM from most recent surgery, confirmed by a Clinical Laboratory Improvement Amendments (CLIA)-certified lab using a next-generation sequencing panel.

⁃ MGMT promoter must be unmethylated or with a methylation index \< 3.

⁃ Must have completed at least standard of care (SOC) external beam radiotherapy (EBRT) as initial therapy.

⁃ Participants must be anticipated to be able to complete E-SYNC T cell infusion within 12 weeks after completion of EBRT.

⁃ All participants must be off systemic steroids for 3 days or more prior to leukapheresis.

⁃ Must be willing to provide voluntary informed consent for apheresis (and tissue screening if needed) and for study treatment.

⁃ NOTE: There are two sets of eligibility criteria for Cohort 2. Step 1 defines eligibility for tissue screening and apheresis, and Step 2 defines eligibility for study enrollment and E-SYNC T cell treatment.

• Inclusion Criteria for Cohort 2, Step 1:

‣ Age \>=18 years.

⁃ KPS score \>=70.

⁃ All participants must have adequate organ function defined as:

• Peripheral absolute neutrophil count \>=1000/mm\^3.

∙ Platelet count \>=100,000/mm\^3 (transfusion independent, defined as not receiving platelet transfusions for at least 7 days prior to enrollment).

∙ Absolute lymphocyte count (ALC) \>= 300/μL and/or CD3 count of \>=150/μL.

∙ Creatinine clearance or radioisotope glomerular filtration rate \>= 50 mL/min/1.73m\^2.

∙ Total Bilirubin \<= 1.5 x ULN except for Gilbert's syndrome and

∙ Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \<= 3x upper limit of normal (ULN).

∙ Left ventricular ejection fraction (LVEF) \>= 40% by echocardiogram or multi-gated acquisition scanning (MUGA).

∙ Adequate pulmonary function, defined as no evidence of dyspnea at rest and pulse oximetry \> 92% while breathing room air.

⁃ Pathological criteria: EGFRvIII+ GBM from most recent surgery, as defined by an EGFRvIII + H-score of \>=250 based on central review.

⁃ All participants must be off systemic steroids for 3 days or more prior to leukapheresis.

⁃ Must be willing to provide voluntary informed consent for apheresis (and tissue screening if needed).

• Inclusion Criteria for Cohort 2, Step 2. Note: Prior to Step 2, participants must have undergone leukapheresis in Step 1. In addition:

‣ KPS score \>=70.

⁃ Must have received at least SOC EBRT as initial therapy; any number of prior recurrences is allowed.

⁃ Pathological criteria: EGFRvIII+ GBM from most recent surgery, as defined by an EGFRvIII + H-score of \>=250 based on central review.

⁃ Must have radiographic progression consistent with the Response assessment in neuro-oncology criteria (RANO) criteria for progressive disease (PD)

⁃ Recurrence must be surgically amenable, with expectation for ability to resect at least 500mg of tumor tissue

⁃ Participants with reproductive potential agree to use reliable and double barrier method of contraception during the study and for at least 6 months after the last study intervention, including refraining from donating sperm during this period.

⁃ Females of childbearing potential must have a negative serum beta-Human Chorionic Gonadotropin (hCG) pregnancy test prior to receiving study interventions.

⁃ All participants must have adequate organ function defined as:

• Peripheral absolute neutrophil count \>=1000/mm\^3.

∙ Platelet count \>=100,000/mm\^3 (transfusion independent, defined as not receiving platelet transfusions for at least 7 days prior to enrollment).

∙ Absolute lymphocyte count (ALC) \>= 300/μL and/or CD3 count of \>=150/μL.

∙ Creatinine clearance or radioisotope glomerular filtration rate \>= 50 mL/min/1.73m\^2.

∙ Total Bilirubin \<= 1.5 x ULN except for Gilbert's syndrome and

∙ Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \<= 3x upper limit of normal (ULN).

∙ Coagulation tests prothrombin time (PT) and partial thromboplastin time (PTT) have to be within normal limits, unless the participant has been therapeutically anticoagulated for previous venous thrombosis.

∙ Adequate pulmonary function, defined as no evidence of dyspnea at rest and pulse oximetry \> 92% while breathing room air.

∙ Adequate cardiac function, confirmed within the last 12 months, defined as left ventricular ejection fraction (LVEF) \>= 40% by echocardiogram or multi-gated acquisition scanning (MUGA).

⁃ Must be willing to provide voluntary informed consent for apheresis (and tissue screening if needed).