Follow-Up Evaluation for Gene-Therapy-Related Delayed Adverse Events After Participation in Pediatric Oncology Branch Clinical Trials

Background: \- Gene therapy involves changing the genes inside the body s cells to stop disease. It is very closely regulated. People who have had this therapy may have problems months or even years later. Researchers do not know the long-term side effects, so they want to study people who have had the therapy. They want the study to continue over the next 15 years. Objective: \- To study over time the negative side effects from genetically engineered cellular therapy. This will be studied in people who have been in Pediatric Oncology Branch (POB) gene therapy trials. Eligibility: \- People who are currently or were previously in a research study with gene therapy in the National Cancer Institute POB. Design: * Participants blood will be tested right before they get the genetically changed cells. They will get the cells as part of another study. * For the next year, they will come back to the clinic or see their doctor at home at least every 3 months. They will answer questions about their health and blood will be drawn. * For the next 5 years, they will go to the clinic or see their own doctor once a year. They will have physical exam and blood will be drawn. * For 10 years after that, they will be asked every year for health information. * Participants will keep their contact information up to date with researchers. They may be phoned for more health information. * If the participant was under 18 years old when given the gene therapy and turns 18 during this follow-up, they will be asked to sign a new consent form when they turn 18.

* INCLUSION CRITERIA: * Participants must be identified eligible for, participating in, or have participated in a POB genetically engineered cellular therapy clinical trial and have received/or be scheduled to receive a genetically engineered cellular therapy. * All monitoring and testing described in this protocol will pertain ONLY to genetically engineered cellular therapy received at the National Institutes of Health (NIH). RCR/RCL monitoring and persistence will NOT be followed for cells administered at another institution.