[18F]Fluoropropyl-Trimethoprim

This is a phase 1, open-label study to evaluate the feasibility, safety and preliminary efficacy of huCART19-IL18-eDHFR cells administered in patients with relapsed or refractory follicular lymphoma. This study will be initiated as a single arm study (Treatment Arm A), which will evaluate the use of huCART19-IL18-eDHFR cells without prior lymphodepletion. In this Treatment Arm A, all subjects will receive a single flat dose of 7x10\[6\] huCART19-IL18-eDHFR cells (Dose Level 1; DL1). Additional treatment arms may also be introduced in the future, via subsequent amendment(s). Co-expression of eDHFR within huCART19-IL18 cells will allow the trafficking of the transduced CAR T cells to be visualized by PET/CT imaging using an investigational radiolabeled imaging agent \[18F\]Fluoropropyl-Trimethoprim (also known as \[18F\]FP-TMP). The feasibility of using \[18F\]FP-TMP PET/CT imaging to detect and measure the eDHFR-expressing CAR T cells will be investigated, as well as its ability to provide insight into CAR T cell pharmacokinetics, biodistribution, and persistence.