To make the CLL1-CD28 chimeric antigen receptor T cells, the investigators will collect the patient's blood and stimulate them with growth factors to make the cells grow. To get the CLL-1 antibody and CD28 to attach to the surface of the T cell, we put the antibody gene into the T cell. This is done using a virus called a retrovirus that has been made for this study and will carry the antibody gene into the T cell. This virus also helps investigators find the T cells in the patient's blood after they are injected. Because the patient will have received cells with a new gene in them the patient will be followed for a total of 15 years to see if there are any long term side effects of gene transfer.

When the patient enrolls on this study, the patient will be assigned a dose of CLL-1 chimeric antigen receptor- T cells. Several studies suggest that the T cells that we give to the patient need room to be able to grow and work well and that this may not happen if there are too many other T cells already in circulation the patient's body. Because of that, the patient will receive two chemotherapy medications before receiving the CLL-1 chimeric antigen receptor- T cells.

One medication is called cyclophosphamide and the other fludarabine. The patient will receive 3 daily doses of each drug, ending at least one day before receiving the chimeric antigen receptor- T cells. These drugs will lower the numbers of the patient's T cells before we give them the CLL-1 chimeric antigen receptor T cells and will also help lower the number of other cells that may block the chimeric antigen receptor- T cells from working well. Although we do not expect any effect on the patient's cancer with the doses that will be received, these drugs are part of many treatment plans that are used to treat leukemia.

Patients will be given an injection of cells into the vein through an IV at the assigned dose. The injection will take from 1 to 10 minutes. Before patients receive the injection, they may be given a dose of Benadryl and Tylenol. The treatment will be given by the Center for Cell and Gene Therapy at Texas Children's Hospital or Houston Methodist Hospital.

Investigators will monitor patients in the clinic after the injection for up to 3 hours, and they will have to remain locally for at least 3 weeks after the infusion. If patients have any side effects, they may have to be admitted to the hospital for evaluation and management. If after a 4 week evaluation period following the infusion, the patient has achieved a complete response, his/her cancer doctors may decide if you should go on to have a bone marrow transplant, at which time the patient will be removed from the treatment portion of the study.

BEFORE BEING TREATED, PATIENTS WILL RECEIVE A SERIES OF STANDARD MEDICAL TESTS:

• Physical exam and History
• Blood tests to measure blood cells, kidney and liver function
• Pregnancy test for female patients who are of child bearing potential -Measurements of your tumor by bone marrow studies

PATIENTS WILL RECEIVE STANDARD MEDICAL TESTS DURING TREATMENT AND AFTER:

• Physical exams and History
• Blood tests to measure blood cells, kidney and liver function
• Measurements of your tumor by bone marrow studies 4-6 weeks after the infusion and then per standard of care.

To learn more about the way the CLL-1 chimeric receptor-T cells are working and how long they last in the body, extra blood will be drawn. The total amount on any day is about 10 teaspoons (50 mL) or no more than 3 mL per 2.2 pounds body weight in children. This amount is considered safe but may be lowered if you are anemic. This blood may be taken from a central line if you have one. Blood will be taken before the chemotherapy drugs, several hours after the T cell infusion, at 1 week, 2 weeks, 3 weeks, 4 weeks, 6 weeks, and 8 weeks after the infusion, at 3 months, 6 months, 9 months, at 1 year, every 6 months for 4 years, then yearly for a total of 15 years.

If patients have a bone marrow exam while they are on this study, we may ask to have a piece of bone marrow to look for CLL-1 chimeric receptor- T cells.

If a patient decides to withdraw at any time during the study, both samples and data collected during his/her participation will be kept.