Recent developments in understanding the pathogenesis of aplastic anemia.

Area of Science:

• Hematology
• Stem Cell Biology
• Immunology

Background:

• Aplastic anemia (AA) is characterized by bone marrow failure.
• Potential causes include hematopoietic stem cell abnormalities, dysregulated hematopoiesis, or an altered hematopoietic environment.

Purpose of the Study:

• To review current understanding of the pathogenetic mechanisms underlying aplastic anemia.
• To explore the roles of stem cell injury, immune suppression, and the microenvironment in AA pathogenesis.

Main Methods:

• Review of studies in human patients and animal models.
• Analysis of bone marrow transplantation data.
• In vitro studies of hematopoietic stem cells and immune interactions.

Main Results:

• Evidence strongly suggests that injuries to hematopoietic stem cells are the most frequent cause of AA in humans and murine models.
• While immune suppression of hematopoiesis is implicated in some human AA cases, defective humoral or cellular control has not been identified.
• Abnormalities of the hematopoietic microenvironment are suggested but lack direct supporting studies.

Conclusions:

• Aplastic anemia likely represents a heterogeneous group of diseases with shared clinical and morphological characteristics.
• Hematopoietic stem cell injury is a primary mechanism, with immune-mediated damage playing a role in some instances.