The purpose of this study is to test an experimental approach called cell therapy for neuroblastoma or retinoblastoma. This study will take a patient's own white blood cells (T cells) and change them to turn against the cancer. These cells are an experimental treatment and have not been approved by the FDA. CAR T cells have been used to treat other cancers, but GPC2 CAR T cells have not been administered to human patients prior to this clinical trial.

If they choose to participate in this study, active participation will last approximately 12 months. Participants will also be asked to sign consent to a separate long term follow-up protocol to monitor their health for up to 15 years after their last GPC2 CAR T treatment.

This study will assess the safety and effectiveness of GPC2 CAR T cells. Overall, approximately 45 subjects will be enrolled on this study.

This study enrolls patients with refractory, progressive, or relapsed solid tumors. The purpose of this study is to find out whether a drug called PEEL-224 ("the study drug") is safe and effective when given as monotherapy (a drug given by itself) and as part of a combination therapy together with other chemotherapy drugs.

The purpose of this study is to test an experimental approach called cell therapy for neuroblastoma. This study will take a patient's own white blood cells (T cells) and change them to turn against the cancer. CART cells have been used to treat other cancers, but PHOX2B CART cells have not been administered to human patients prior to this clinical trial. Participants will be given PHOX2B cells via an IV and then monitored for up to 12 months.

Participants will also be asked to sign consent to a separate long term follow-up protocol to monitor their health for up to 15 years after their last PHOX2B CART treatment.