Your eligibility for the trial will be confirmed. This includes verification that you are between 3 months and 25 years of age at the time of transplant.

You must be in complete remission, which means less than 5% abnormal cells in your bone marrow and no signs of disease in other parts of your body.

If you are female and able to become pregnant, a pregnancy test will be performed, which must be negative.

You will be assigned to one or more specific parts of the trial based on your age, donor type, and other medical factors.

You will receive a conditioning regimen, which is a combination of medications given before the transplant to prepare your body. The specific medications and doses depend on which part of the trial you are enrolled in.

The conditioning may include total body irradiation (radiation treatment to the whole body) at different dose levels, either 8 Gray or 12 Gray, combined with other medications.

Medications used in conditioning may include: busulfan (given through a vein), etoposide (given through a vein), cyclophosphamide (given through a vein), fludarabine (given through a vein), thiotepa (given through a vein), or treosulfan (given through a vein).

These medications work to eliminate any remaining disease cells and suppress your immune system so your body will accept the transplanted cells.

You will receive the stem cell transplant, also called hematopoietic stem cell transplant or HSCT. This involves receiving healthy blood-forming cells from a donor through a vein.

The donor may be a matched sibling, a matched unrelated donor, or a mismatched family donor, depending on availability and your specific situation.

The transplant may use cells collected from bone marrow, peripheral blood, or cord blood.

You will receive medications to prevent graft-versus-host disease, a condition where the transplanted cells attack your body. The specific approach depends on your donor type.

Preventive medications may include anti-t lymphocyte immunoglobulin (given through a vein), which helps prevent your body from rejecting the transplant.

If you receive cells from a mismatched family donor, prevention may involve either post-transplant cyclophosphamide (given through a vein after the transplant) or removal of specific cell types from the donor cells before transplant.

Additional medications such as methylprednisolone (a steroid given through a vein) may be used.

If you are between 3 months and 18 years old, received cells from a matched donor, and develop acute graft-versus-host disease (grades II to IV), you may be assigned to receive additional treatment.

You will receive either corticosteroids (anti-inflammatory medications) alone or corticosteroids combined with ruxolitinib.

If assigned to receive ruxolitinib, it will be given as tablets or oral solution by mouth. The treatment response will be evaluated at day 28 after starting this therapy.

If you are younger than 2 years old at the time of transplant and your disease cells expressed a marker called CD19, you may receive maintenance therapy.

This maintenance therapy consists of up to four cycles of blinatumomab, a medication given through continuous infusion into a vein.

This treatment is designed to reduce the risk of disease returning after transplant.

You must be in complete remission and have no signs of disease in your brain or spinal fluid at the time this treatment begins.

You will be monitored regularly for signs of disease relapse, transplant complications, and overall health.

Blood tests will be performed to assess various factors, including a measurement called EASIX, which helps predict transplant-related complications.

If your donor has a different blood type than yours (called ABO major incompatibility), special monitoring will be performed according to standard procedures at the treatment center.

Follow-up will continue for several years after transplant, with specific assessments at 2 years and 4 years to evaluate treatment outcomes.