A 31-year-old woman with invasive squamous cell carcinoma of the cervix expresses HPV type 16 antigens. Which cells recognize and kill these virus-infected tumor cells?

• A. NK cells
• B. CD8+ T lymphocytes
• C. B lymphocytes
• D. CD4+ T helper cells

Answer: (B)

Cytotoxic CD8+ T lymphocytes are the immune cells that recognize and kill cells presenting viral peptides on MHC class I molecules. Virus-infected tumor cells, like those caused by HPV16, process viral proteins in the cytosol and display peptide fragments on MHC I. CD8+ T cells with T cell receptors specific for those peptide-MHC I complexes become activated as cytotoxic T lymphocytes and destroy the target cell by releasing perforin and granzymes or engaging Fas-FasL pathways to induce apoptosis.

B cells and CD4+ T helper cells don’t directly kill infected cells—B cells produce antibodies or present antigen, and CD4+ T cells provide help to other immune cells. NK cells can kill some stressed or MHC I–deficient cells via innate mechanisms but the targeted, antigen-specific recognition and killing of these virus-infected tumor cells is driven by CD8+ T lymphocytes.