Apoptotic Bodies

Cellular life after death

Apoptotic bodies (ApoBDs) are a peculiar type of extracellular vesicle (EV) that are the remnants of cells having undergone apoptosis, or programmed cell death. Dying cells release variable numbers of these closed, subcellular pieces that are typically quite large for EVs (0.5 – 2 microns), and may contain an assortment of cellular components including, but not limited to:

• Proteins, intact or degraded
• Various lipids
• DNA fragments
• RNA (mRNA, miRNA, rRNA)
• Chromatin
• Portions of cytosol
• Organelles, degraded or intact

From trash to treasure

ApoBDs were once seen simply as the “garbage bags” left over after cells live out their lives. While it’s true the vesicles are engulfed and further disassembled by macrophages and other clean-up cells, this view evolved dramatically when it was discovered that ApoBDs were capable of delivering genetic information and other useful materials to healthy recipient cells, bolstering essential processes such as immune response and tissue regeneration.

In fact, the formation of ApoBDs is the result of a highly coordinated cell disassembly operation. The number and quality of ApoBDs created depends on the type of cell undergoing apoptosis, although researchers have yet to unravel the mechanisms behind this cellular decision-making.

The therapeutic advantage

These recent discoveries have led to more focused research into applying the natural process of ApoBD formation on several fronts:

• Immunotherapy and vaccine development: ApoBDs contain tumor and pathogen-derived antigens that can, reportedly, be recognized by the immune system and trigger T cell activation against appropriate targets.
• Regenerative therapies: Evidence is emerging that ApoBDs released by stem cells contain signaling cues and usable materials that induce cell division in neighboring stem cells, providing healing support to damaged tissue with efficacy that rivals or betters that provided by other EVs.
• Drug-delivery platforms: Although not as well researched for this purpose as the smaller EVs, the ability of ApoBDs to carry and transfer molecules such as DNA, microRNA and proteins to recipient cells implies they may also be effective vehicles for drug delivery.
• Diagnostic tools: Quantification of ApoBDs is already used as an effective histological diagnostic tool in gastrointestinal biopsies; it’s possible that use of these EVs can be extended to diagnosing other diseases or conditions associated with prevalent cell death (e.g., infection, transplant rejection, drug-induced injury, brain injury, immune disorders and cancer treatments).

A great deal more research will be required to understand the nature and unlock the full potential of apoptotic bodies. For now, however, it’s at least certain that these vesicular “garbage bags” are much more accurately described as “recycling bins.”