Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy in the world.

It is a malignant clonal proliferation of lymphoid progenitor cells, but most commonly of the B cell lineage (B ALL). .

Acute Lymphoblastic Leukemia (ALL) is a heterogeneous disease that causes malignant hematological disorders at any age. It mainly affects children aged 2 to 5; in fact, 60% of pediatric leukemia cases are ALL, with an incidence of 3-4 cases per 100,000 per year. It is divided into two subtypes B-ALL and T-ALL depending on whether transformation occurs in B- or T-cell precursors, respectively .

Leukemic cells apply multiple immune evasion mechanisms resulting in tumor progression. One of the most important immune escape mechanisms is over expression of immune checkpoint receptors and their ligands such as PD-1 and PD-L1 .

The PD-1 receptor plays a crucial role in a broad spectrum of immune regulatory mechanisms .

It is a negative co-receptor that down regulates T-cell activity .

PDL 1, which is known as B7 H1 , is a cell surface protein of B7 family member .

PD L1 is expressed on all types of lympho hematopoietic cells at variable levels and is constitutively expressed on T cells, B cells, macrophages, and dendritic cells .

Tumors exploit the PD-1/PD-L1 pathway to evade host immune surveillance .

PD-1/PD-L1 pathway controls the induction and maintenance of immune tolerance within the tumor microenvironment. The activity of PD-1 and its ligands PD-L1 or PD-L2 are responsible for T cell activation, proliferation, and cytotoxic secretion in cancer to produce anti-tumor immune responses .

Inclusion Criteria:

• Age range from 1 day to 18 years old
• Patients who are newly diagnosed and under treatment of acute lymphoblastic leukemia

Exclusion Criteria:

• Other types of acute leukemia rather than acute lymphoblastic leukemia