Hematopoiesis Basics

Hematopoiesis

• Hematopoiesis is the process of creating blood cells from hematopoietic stem cells (HSCs) in the bone marrow.
• HSCs are foundational cells that differentiate into all blood cell types (red blood cells, white blood cells, and platelets).
• HSCs are capable of self-renewal, ensuring a continuous supply of blood cells throughout life and essential for immune system function.
• Hematopoiesis is the process where all blood cells originate from Hematopoietic Stem Cells (HSCs). This primarily occurs in the bone marrow.
• HSCs (self-renewing and multipotent) divide into Common Lymphoid Progenitors (CLPs) which produce B-cells, T-cells, and natural killer (NK) cells, and Common Myeloid Progenitors (CMPs) which produce red blood cells, platelets, and innate immune cells.
• HSCs are crucial for generating all blood cells, including immune cells. Without them, the immune system cannot function.
• Bone Marrow Transplantation uses HSCs to regenerate a patient's immune system, commonly used in treating leukemia and after radiation.
• Gene Therapy involves engineering HSCs to carry corrected versions of faulty genes.
• CRISPR/Cas9 gene-editing tools can delete or modify defective genes in HSCs.

CD Markers

• CD markers (Cluster of Differentiation) are proteins on the surface of immune cells used to identify and classify different cell types.
• Examples include CD4 and CD8 found on T-helper and cytotoxic T-cells, respectively, and CD45 (B220) present on white blood cells, involved in signaling.
• SCA-1 (Stem Cell Antigen-1) is used to identify and enrich populations of HSCs.

Hematopoietic Stem Cell (HSC) Isolation

• The objective is to isolate pure populations of HSCs from bone marrow.
• Techniques include negative selection to remove cells with markers for differentiated cell types (e.g., B220 for B-cells, CD4/CD8 for T-cells).
• Positive selection enriches HSCs using markers like SCA-1 and Thy-1.

Flow Cytometry (FACS)

• A technique used to sort and analyze cells based on their surface markers.
• Cells are labeled with fluorescent antibodies specific to markers.
• A laser detects the fluorescence and sorts cells into distinct populations.
• Antibodies labeled with fluorescent dyes bind to specific cell markers.
• Mature B-cells (B220+IgM+) appear as double-positive in FACS analysis.

Hematopoietic Lineages

• Lymphoid Lineage produces B-cells, T-cells, and natural killer cells (adaptive and innate immunity).
• Myeloid Lineage produces granulocytes, macrophages, platelets, and red blood cells (innate immunity).

Immunological Memory

• Memory B and T cells are long-lived cells that "remember" previous infections, enabling faster and stronger immune responses upon re-infection.

Mechanism of Differentiation

• Differentiation occurs during the primary immune response.
• Transcription factors regulate gene expression, affecting or hindering immune cell differentiation.
• Zfx is vital for T-cell and HSC renewal. Notchi is crucial for T-cell development and Wnt Signaling Pathway is essential in regulating stem cell growth, differentiation and self-renewal.

Age and the Immune System

• Aging impacts the immune system, reducing lymphocyte precursor production and immune responses.
• Strategies to rejuvenate immune function include stem cell therapy.

Stem Cell Applications

• Stem cell therapy can cure diseases like leukemia through bone marrow transplants.
• They have potential for gene therapy to correct genetic defects.
• Techniques like CRISPR/Cas9 are used for gene editing and engineering HSCs to rectify immune deficiencies.

Hematopoietic Differentiation Tree

• HSC is the origin of all blood cells, branching into lymphoid and myeloid progenitors.
  • Lymphoid progenitors differentiate into B-cells (antibody production), T-cells (cell-mediated immunity), and natural killer (NK) cells (immune defense).
  • Myeloid progenitors differentiate into granulocytes, macrophages, erythrocytes (red blood cells for oxygen transport), and platelets (blood clotting).