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Adaptive immune resistance

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In one sentence

Adaptive immune resistance is a tumor's induced defense in which interferon gamma released by attacking T cells switches on PD-L1 and other inhibitory signals that restrain those same T cells.

The intuition

Imagine a building whose doors lock only when someone knocks. A locked door then tells you that someone came. Adaptive resistance works the same way: the brake is pulled in response to the attack, so its presence is partly a sign that an immune response reached the tumor. The analogy breaks because PD-L1 can also be switched on by tumor signaling without any T cells.

How it works

  1. A T cell recognizes a tumor peptide on human leukocyte antigen (HLA) and releases interferon gamma.
  2. Interferon gamma signals through JAK1 and JAK2 kinases in nearby tumor and immune cells.
  3. Those cells raise programmed death-ligand 1 (PD-L1), among other inhibitory signals.
  4. PD-L1 binds programmed cell death protein 1 (PD-1) on the T cell and damps its activity.

Early evidence for this loop in people came from melanocytic lesions: 98% of PD-L1-positive tumors had tumor-infiltrating lymphocytes, compared with 28% of PD-L1-negative tumors, PD-L1-positive cells sat right next to the lymphocytes, and interferon gamma was found at that interface (Taube et al., 2012). The alternative, called innate or constitutive resistance, is PD-L1 driven by the cancer cell's own signaling, regardless of T cells.

Why it matters in cancer

  • It links "hot" to PD-L1. A lymphocyte-rich tumor is more likely to stain for PD-L1, because the lymphocytes induce it. See hot, excluded and cold patterns.
  • It is the step PD-1 and PD-L1 drugs block. Immune-checkpoint inhibitors interrupt step 4.
  • It explains one escape route. A tumor that loses JAK1 or JAK2 cannot respond to interferon gamma, so it loses this induced PD-L1 along with interferon-driven antigen display; see immune escape.

Common confusions

  • PD-L1-positive is not "the tumor is suppressing the immune system on its own". In adaptive resistance, the signal is a reaction to T cells.
  • PD-L1-negative is not "no immune attack". Staining is patchy, assays differ and other brakes exist; see PD-L1 scoring.
  • Adaptive resistance is not acquired resistance. "Acquired resistance" means a tumor that responded to treatment and then stopped responding.

Try it

A biopsy shows PD-L1 staining only at the border where lymphocytes gather, and none in the tumor center. Which kind of PD-L1 expression does that pattern suggest?

Answer: Adaptive (induced) expression, because it tracks the immune cells. Spread evenly through a tumor with no lymphocytes would suggest constitutive expression. The pattern is suggestive, not proof.

Explain it back

"In adaptive resistance, ___ from T cells causes ___, which ___." One answer: "interferon gamma; PD-L1 on nearby cells; restrains those T cells through PD-1."

Takeaway

Induced PD-L1 is a brake pulled by the attack itself, which is why it often marks tumors that T cells have reached.

Sources and scope

Source-checked November 7, 2026, against the PubMed abstract. Mechanism concept; no treatment recommendation. Expert and learner review pending.

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