CD34 positive refers to cells that have a specific protein, CD34, on their surface. This protein acts as a marker, allowing scientists and doctors to identify and isolate these cells. The marker itself is a transmembrane glycoprotein, a type of protein that spans the cell’s outer membrane. While the CD34 marker is not exclusive to one cell type, it is most famously associated with hematopoietic stem cells found in bone marrow and blood.
Understanding CD34 Positive Stem Cells
CD34 positive cells are most often hematopoietic stem cells (HSCs), the foundational cells of the blood and immune system. Located in bone marrow, these cells are multipotent, meaning they can develop into all specialized blood cells. This includes red blood cells that transport oxygen, white blood cells that fight infection, and platelets necessary for blood clotting.
The generation of new blood cells, known as hematopoiesis, relies on this stem cell population. HSCs have the capacity for self-renewal, allowing them to create more stem cells. They also undergo differentiation, a process where they mature into a specific type of blood cell. This dual capability allows the body to sustain its stem cell pool while replacing old blood cells.
These stem cells are rare, making up only a small fraction of cells in the bone marrow. Despite their low numbers, they are vital for health. Without a healthy population of HSCs, the body cannot produce the necessary components of blood, which can lead to severe and life-threatening conditions.
Measuring CD34 Positive Cells
The number of CD34 positive cells in a blood or bone marrow sample is a medically significant figure. This count is performed using a technology called flow cytometry. The process involves staining a sample with fluorescently-labeled antibodies designed to attach to the CD34 protein. A flow cytometer then passes the sample through a laser, detecting and counting each fluorescent cell to provide an accurate tally.
This cell count is a biomarker for assessing the health and recovery of the hematopoietic system. For instance, after chemotherapy damages bone marrow and suppresses its ability to produce blood cells, doctors measure the CD34 positive cell count. A rising number indicates that the bone marrow is recovering and generating new stem cells.
The measurement is also important for stem cell collection before a transplant. Patients or donors are given medications to mobilize stem cells from the bone marrow into the bloodstream. Doctors monitor the concentration of CD34 positive cells in the blood, and the collection procedure begins only once the count reaches a sufficient threshold.
Use in Stem Cell Transplantation
CD34 positive cells are used in hematopoietic stem cell transplantation to treat various cancers, blood disorders, and immune system diseases. The process begins with mobilizing the stem cells using medications like granulocyte-colony stimulating factor (G-CSF). This drug stimulates the bone marrow to produce and release a large number of HSCs into the blood.
When circulating CD34 positive cells reach an optimal level, collection via apheresis begins. In this non-surgical procedure, blood is drawn and sent through a machine that isolates the CD34 positive stem cells. The remaining blood components are returned to the body. This process may be repeated over several days to collect enough cells.
The collected cells are prepared for transplantation. In an autologous transplant, cells are collected from the patient before high-dose chemotherapy and infused back into them afterward. In an allogeneic transplant, cells are collected from a healthy, matched donor and infused into the patient.
The infusion is similar to a blood transfusion, delivering the stem cells into the patient’s bloodstream. These cells travel to the bone marrow, where they engraft and begin to produce new, healthy blood cells. This process rebuilds the patient’s blood and immune system.
Relevance in Blood Cancers
The CD34 marker is also relevant in the diagnosis and prognosis of certain blood cancers. In some leukemias, like Acute Myeloid Leukemia (AML), the cancerous blast cells can also express the CD34 protein. The presence of this marker suggests the cancer may have originated from a more primitive, stem-like cell that became malignant.
The expression of CD34 on leukemic blasts helps classify the cancer’s specific subtype. Identifying the cancer cells as CD34 positive provides insights into the nature of the disease. For some leukemias, this characteristic is associated with a more aggressive form or a higher likelihood of relapse after treatment.
This information helps inform treatment strategies and prognosis discussions. While the presence of the CD34 marker is just one of many factors considered, it contributes to a more personalized understanding of the disease at a cellular level. It highlights that the marker used to isolate healthy stem cells can also be a feature of the malignant cells they are meant to replace.