HL-60 cells are an immortalized human cell line widely used in biomedical research. These cells were originally derived from a patient with leukemia and have since become a valuable tool in laboratories worldwide. Their consistent characteristics and predictable behavior make them suitable for studying various biological processes. Researchers utilize HL-60 cells to study cellular mechanisms and disease progression.
Origin of the HL-60 Cell Line
The HL-60 cell line was established in 1977 from the peripheral blood of a 36-year-old woman diagnosed with acute promyelocytic leukemia (APL). The “HL” in HL-60 stands for Human Leukemia, indicating their origin. This isolation was a significant scientific achievement, as HL-60 was among the first human myeloid leukemia cell lines successfully cultured in continuous suspension.
The patient’s cells provided a unique and stable source for studying this aggressive form of blood cancer. Prior to this, achieving long-term human myeloid leukemia suspension cultures was challenging. The establishment of HL-60 cells by S.J. Collins and his team marked a breakthrough, enabling consistent in vitro research into leukemia and related diseases.
Unique Biological Properties
HL-60 cells have distinct characteristics that make them useful as a research model. They grow in suspension culture, remaining floating in the culture medium rather than attaching to a surface. This suspension growth simplifies the process of harvesting cells for experiments, making them easier to manage.
These cells are classified as promyelocytes, an immature stage of myeloid white blood cells. In their undifferentiated state, HL-60 cells exhibit a round, lymphoblastic morphology, with diameters ranging from 9 to 25 micrometers. HL-60 cells can also be prompted to differentiate into various specialized cell types.
Induced Differentiation Pathways
The ability of HL-60 cells to undergo directed differentiation is a primary reason for their extensive use in research. Scientists add specific chemical compounds to the culture medium to induce these immature promyelocytes to mature into different specialized immune cells. This process mimics the natural development of blood cells, allowing researchers to observe changes in cell function and gene expression.
For instance, exposure to compounds like dimethyl sulfoxide (DMSO) or all-trans retinoic acid (ATRA) causes HL-60 cells to differentiate into cells resembling neutrophils. Neutrophils are a type of white blood cell involved in the innate immune response, and the differentiated HL-60 cells can perform functions such as phagocytosis and generate reactive oxygen species, similar to their natural counterparts. The differentiation period for neutrophil-like cells ranges from three to seven days.
Conversely, treatment with phorbol esters, such as phorbol 12-myristate 13-acetate (PMA) or 1,25-dihydroxyvitamin D3, guides HL-60 cells to differentiate into cells resembling macrophages or monocytes. Macrophages are another type of immune cell involved in engulfing cellular debris and pathogens. This induced maturation allows researchers to study the development and function of these diverse immune cell types in a controlled laboratory environment.
Major Research Applications
HL-60 cells are widely applied in biomedical research due to their unique properties and differentiation capabilities. In cancer research, they serve as a model for studying the mechanisms of acute myeloid leukemia. Researchers use them to investigate how leukemic cells proliferate and to identify potential new anti-cancer drugs. Their use in preclinical studies helps evaluate the effectiveness and toxicity of new therapeutic compounds before human trials.
Their utility extends to immunology, where differentiated HL-60 cells act as models for various immune processes. For example, neutrophil-like or macrophage-like HL-60 cells are used to study phagocytosis, the process by which cells engulf particles, and to understand inflammatory responses. They also provide a platform for investigating apoptosis, which is programmed cell death, and for developing vaccine targets.