Assesment of JL1 Expression in B-cell Acute Lymphoblastic Leukemia

Acute Lymphoblastic Leukemia (ALL) is characterized by a rapidly progressive disease. It accounts for approximately 75% of all cases of childhood leukemias, that produces large and immature cells (20% or more lymphoblasts in the bone marrow (BM) and/or the blood) that can't carry out their normal BM function (Terwilliger and Abdul-Hay, 2017).

The main cause of ALL lies in the genetic or acquired injury to DNA of a single cell in the BM with the presence of risk factors such as radiation, benzene exposure, Down syndrome and past treatment with chemotherapeutic agents which leads to uncontrolled and exaggerated growth and accumulation of lymphoblasts which fail to function as normal blood cells. This results in blocking the production of normal blood cells and leads to anemia, thrombocytopenia and neutropenia. The most frequent signs are lymphadenopathies, hepatosplenomegaly, fever, anemia, signs of hemorrhage, and bone tenderness.

The prognostic factors of ALL include patients' factors such as age, white blood cell (WBC) count and genetic factors such as chromosome and gene changes along with the immunophenotypic characteristics of the leukemic blast cells and the individual response to therapy.

JL1 is a CD43 epitope and mucin family cell surface glycoprotein that is expressed on leukemic cells. It is expressed on hematopoietic cells at different stages of differentiation including early stage lymphoid precursors and late stage of myeloid cells. Expression patterns of JL1 antigen occurs on cell surface of leukemic cells, BM cells and phytohemagglutinin (PHA)-activated lymphocytes. Most leukemic cells usually express JL1 even in weak positive cases.

JL1 is usually expressed in about 60% of acute leukemia regardless of the lineage. It was also detected on CD34+ CD10+ lymphoid precursors and some immature myeloid cells in BM. An anti-JL1 (a monoclonal antibody that is selectively reactive with antigen in spite of the differences in the molecular weight) is mixed with a toxic substance that target the leukemic cells which leads to the emergence of its role as a therapeutic agent.