Question

Read the following passage adapted from Hanahan and Weinberg (2011).

Transplantation experiments have shown that cancer cells that originally arose in immunodeficient mice are often inefficient at initiating secondary tumors in immunocompetent hosts that share a common genetic background with the cancerous mice (except for the immune deficiency). In contrast, cancer cells from tumors arising in immunocompetent mice are equally efficient at initiating transplanted tumors in both types of hosts.

Briefly discuss how an understanding of evolution by natural selection helps you explain the observation described in the passage.

Answer 1

• Immunoediting is a form of natural selection
• Immunogenic cancer cell clones are eliminated in immunocompetent hosts
• Weaker immunogenic variants are left behind to grow and generate tumours
• These weak immunogenic cells colonize both immunodeficient and immunocompetent hosts
• The transformed clones have immune-evasive phenotypes because of selective pressure by an immune response
• Cancers that develop within the immune system will harbour immune-evasive traits
• Cancers that develop in immunodeficient settings will not harbour immune-evasive traits
• Tumours from the immunodeficient mice were not able to grow when transplanted onto immunocompetent mice because no immune selection occurred