Immunology: immune checkpoint blockade: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Immunology: immune checkpoint blockade

Sample item

A patient with metastatic melanoma treated with an antibody against PD-1 develops watery diarrhoea eight weeks later, and colonic biopsy shows lymphocytic colitis. What is the best explanation?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Loss of an inhibitory checkpoint on T cells unleashes autoimmune inflammation

PD-1 on activated T cells transmits an inhibitory signal when it binds PD-L1, and tumours exploit this to escape. Blocking the pathway restores antitumour T cell activity but also removes tolerance, causing immune-related adverse events such as colitis, dermatitis, hepatitis and endocrinopathies. These are managed with corticosteroids.

Option by option

  • A. Direct bacterial infection due to antibody-mediated killing of enterocytes

    These antibodies act on T cells and do not kill enterocytes; infection is not the mechanism.

  • B. Cytokine release from CAR T cells

    No CAR T cells were given to this patient.

  • C. Serum sickness due to murine antibody

    Anti-PD-1 antibodies are humanised or human, so serum sickness from murine antibody is not the explanation.

  • D. Loss of an inhibitory checkpoint on T cells unleashes autoimmune inflammation (correct)

    Correct. Releasing the T cell brake permits immune-related colitis and other autoimmune toxicity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Loss of an inhibitory checkpoint on T cells unleashes autoimmune inflammation. PD-1 on activated T cells transmits an inhibitory signal when it binds PD-L1, and tumours exploit this to escape.

Why is "Direct bacterial infection due to antibody-mediated killing of entero…" not the answer?

These antibodies act on T cells and do not kill enterocytes; infection is not the mechanism.

Why is "Cytokine release from CAR T cells" not the answer?

No CAR T cells were given to this patient.

Why is "Serum sickness due to murine antibody" not the answer?

Anti-PD-1 antibodies are humanised or human, so serum sickness from murine antibody is not the explanation.

What concept does this question test?

It tests Immunology: immune checkpoint blockade in Microbiology. Blocking the pathway restores antitumour T cell activity but also removes tolerance, causing immune-related adverse events such as colitis, dermatitis, hepatitis and endocrinopathies. These are managed with corticosteroids.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Immunology: immune checkpoint blockade?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.