IFN-γ signaling¶
Confidently known¶
- human JAK1/JAK2 LOF causes primary and acquired anti-PD-1 resistance (Zaretsky 2016 NEJM1, Shin 20172). Tumor cells become IFN-γ-insensitive and fail to upregulate PD-L1 or ISGs. Rare but biochemically definitive.
- mouse PTPN2 loss in tumor cells sensitizes to ICI by amplifying IFN-γ/JAK-STAT response (Manguso 2017 in vivo CRISPR screen)3. The screen also re-identified PD-L1, CD47, and IFN-γ pathway components as canonical modulators. PTPN2 is now a clinical target.
- human mouse IFN-γ sensing is necessary for anti-PD-1 efficacy in most histologies. The mechanism — CD8 IFN-γ → tumor IFN-γR → JAK1/2 → STAT1 → antigen processing (B2M, TAP, MHC-I), ISG induction, and adaptive PD-L1 upregulation — is among the most biochemically definitive axes in the field.
Human-study evidence¶
| Study | N | Feature | Effect | 95% CI / p | Method |
|---|---|---|---|---|---|
| Zaretsky 2016 | n=4 (melanoma patients with late relapse on pembrolizumab) | acquired JAK1/JAK2 LOF or B2M truncation | acquired resistance mechanism 3 of 4 relapse tumors harbored a candidate lesion | — | paired WES + functional IFN-γ / MHC-I assays |
| Shin 2016 | n=39 (23 melanoma + 16 MMR-deficient CRC non-responders) | biallelic JAK1/JAK2 LOF | primary-resistance prevalence ~4% melanoma, ~6% MMR-d CRC non-responders | — | WES + cell-line IFN-γ / ISG induction assays |
Contradictions / surprises¶
- human mouse IFN-γ signaling has dual roles. Adaptive PD-L1 upregulation is a canonical IFN-γ-driven resistance mechanism (Sharma 2017 review)4; the same axis is what anti-PD-1 exploits therapeutically. The clinical question is whether a given tumor has defective (primary resistance via JAK/STAT LOF) or intact-but-hijacked (adaptive resistance via IFN-γ → PD-L1/IDO induction) IFN-γ signaling.
- human JAK2 amplification at 9p24.1 in classical Hodgkin lymphoma is an extreme case of intact-but-hijacked IFN-γ signaling — massive PD-L1 upregulation explains cHL's unusually high response rate to anti-PD-1. The boundary between "IFN-γ defective" and "IFN-γ over-engaged" is tumor-type specific.
Human-study evidence¶
No human-study citations in this section.
Suspected but unconfirmed¶
- mouse No new suspected mechanisms in this period's window. AGPAT3 (below) is better classified as emerging.
Human-study evidence¶
No human-study citations in this section.
Emerging¶
- mouse IFN-γ → IRF1 → AGPAT3 → ether-phospholipid remodeling → ferroptosis sensitivity (this period)5. Extends IFN-γ consequences beyond antigen presentation and apoptosis to a lipidomic vulnerability. AGPAT3 loss impairs IFN-γ-mediated tumor elimination; higher tumor AGPAT3 correlates with improved ICI survival in retrospective analysis. Preclinical / associative; no pharmacologic AGPAT3 modulator tested.
Human-study evidence¶
No human-study citations in this section.
Practical takeaways¶
- A tumor showing high baseline PD-L1 in response to an inflamed TME suggests intact IFN-γ signaling (good PD-1 response prospect). A tumor with poor PD-L1 despite CD8 infiltration raises the possibility of JAK/STAT pathway defect.
- JAK1/2 LOF testing is not standard of care but may help triage patients on the edge of an ICI decision, particularly in primary non-response after initial high-TMB expectations.