Oncolytic Viruses Target Cancer Cells by Exploiting Defective Antiviral Responses
The correct answer is: By exploiting defective antiviral responses in cancer cells.
Primary Mechanism of Cancer Cell Targeting
Oncolytic viruses (OVs) achieve tumor selectivity through a fundamental vulnerability in cancer cells: their compromised antiviral defense mechanisms. Cancer cells frequently have defective interferon signaling pathways and impaired innate immune responses—alterations that originally provided growth advantages but now render them susceptible to viral infection and replication 1, 2.
Why This Mechanism is Primary
Selective replication: OVs are either naturally occurring or genetically engineered to preferentially infect and replicate within cancer cells while sparing normal, healthy cells 3, 4
Tumor-specific defects: The selectivity stems from cancer cells' inherent molecular abnormalities, particularly in antiviral response pathways, which normal cells maintain intact 1
Direct oncolysis: Once inside cancer cells, OVs replicate and directly lyse tumor cells, then spread to adjacent malignant cells 2, 4
Why Other Options Are Incorrect
Indiscriminate infection (Option 1) is fundamentally wrong—the defining characteristic of OVs is their selective targeting of cancer over normal cells 3.
Using tumor cells as intermediaries for immune targeting (Option 3) describes a secondary mechanism. While OVs do activate antitumor immune responses and modulate the tumor microenvironment after initial infection 4, this is not the primary targeting mechanism.
Only infecting immune cells near tumors (Option 4) is incorrect. Though neutrophils can serve as delivery vehicles for OVs in certain contexts 5, the viruses themselves target and infect the cancer cells directly, not immune cells as their primary target.
Clinical Relevance
Understanding this mechanism is critical because:
Engineering strategies focus on enhancing tumor-specific promoters (hTERT, E2F1) and redirecting viral entry toward tumor-associated antigens (EGFR, HER2, EpCAM) 1
Safety profile depends on maintaining selectivity for cells with defective antiviral responses
Combination approaches leverage both the direct oncolytic effect and subsequent immune activation for maximal therapeutic benefit 2