Core Framework & Diagram How Does the Tumor ‘Turn Off’ Immune Switches?
July 8, 20261 Min Read How Does the Tumor Transform Immune Cells?
July 9, 2026Tumors don't just evade the immune system — they actively turn off every immune 'switch'
—— From PD-L1 to LAG-3, from CD47 to adenosine: the complete map of tumor immune switch engineering.
I. PD-1/PD-L1: the 'most classic immune switch' that already changed cancer treatment
The PD-1 signaling system's design logic in normal immune responses: T cells fight at full power in the acute infection phase, secreting large amounts of IFN-γ; IFN-γ induces surrounding cells to upregulate PD-L1; PD-L1 binds to PD-1 on T cell surfaces, sending a 'the infection is controlled, it's time to stop' ceasefire signal. This design is perfect in acute infection — ensuring inflammation has a beginning and an end. But tumors converted this 'ceasefire signal' into their own 'permanent shield': when CTLs enter the tumor and secrete IFN-γ, tumor cells sense IFN-γ and immediately upregulate PD-L1 — not for 'repair' but to brake CTLs.
PD-L1's two sources have different predictive significance for treatment response: tumor cell intrinsic PD-L1 (driven by genetic changes, like PTEN loss → PI3K activation → PD-L1 upregulation) — this PD-L1 is highly expressed whether or not T cells have entered the tumor; adaptive PD-L1 (IFN-γ induced, only present when T cells exist) — this PD-L1 high expression actually reflects 'T cells are fighting inside the tumor,' and response rates to PD-1 inhibitors are usually higher. This explains why 'intrinsic PD-L1 positive but no T cell infiltration (cold tumor)' patients often respond worse to PD-1 inhibitors than expected.
2. LAG-3, TIM-3, TIGIT: the 'multiple brake system' of T cell exhaustion
In the tumor microenvironment, T cells aren't just having 'one brake applied by PD-1' — they're being simultaneously stopped by multiple inhibitory receptors. LAG-3: structurally similar to CD4, frequently co-expressed with PD-1 on the same exhausted T cell under chronic antigen exposure — the two work synergistically, making the T cell's exhaustion degree far deeper than expressing PD-1 alone. In 2022, the combination of LAG-3-targeting monoclonal antibody relatlimab with PD-1 inhibitor nivolumab (Opdualag) extended median progression-free survival from 4.6 months to 10.1 months (more than double) in first-line melanoma treatment, receiving FDA approval — the third immune checkpoint target after CTLA-4 and PD-1 to have proven clinical efficacy.
TIM-3: highly expressed when T cells reach the 'terminally exhausted' state, recognizing ligands like galectin-9 — TIM-3-positive T cells have almost completely lost proliferative capacity and cytotoxicity. TIGIT: simultaneously suppresses NK cell and T cell function through binding CD155 — a key brake node connecting two immune layers. Clinical significance of multiple exhaustion checkpoint co-expression: in TME, T cells with triple co-expression of PD-1+LAG-3+TIM-3 are the most deeply functionally exhausted and hardest to 'rescue' with a single checkpoint inhibitor.
3. CD47: 'Don't eat me' signal — tumor manipulation of innate immunity
CD47 is a 'don't eat me' signal molecule expressed on normal cell surfaces. It tells macrophages 'I'm a normal cell, don't engulf me' through binding SIRPα on macrophage surfaces. Cancer cells systematically upregulate CD47 expression during evolution — almost all solid tumors and blood system tumors show CD47 expression significantly higher than normal tissue. High CD47 expression lets tumor cells both evade NK cell 'Missing Self' recognition (by maintaining MHC-I) and evade macrophage 'don't eat me' checking (by upregulating CD47) — complete protection with a 'dual pass.'
CD47 blockade treatment logic: anti-CD47 antibodies blocking CD47-SIRPα signal let macrophages 'drop their hesitation,' actively engulfing tumor cells. After engulfing, macrophages present tumor antigens to T cells, initiating adaptive immune responses — a 'bridge effect' connecting innate and adaptive immunity. The main challenge is CD47 also being highly expressed on red blood cells; anti-CD47 antibodies may cause hemolytic anemia, requiring slow titration from low doses.
4. Adenosine pathway (CD39/CD73/A2a receptor): metabolic 'immune anesthetic'
The adenosine production chain: extracellular ATP (released by damaged/dying cells, an important 'danger signal' activating immune cells) → CD39 converts ATP to AMP → CD73 converts AMP to adenosine. Normally, this chain acts in the tissue repair phase, gradually converting the post-acute-injury ATP signal ('danger, summon immune cells') into an adenosine signal ('okay, time to wrap up inflammation'). Tumor cells and Tregs in the tumor microenvironment highly express CD39 and CD73. ATP released from cancer cell necrosis or chemotherapy killing is rapidly metabolized by CD39/CD73 to adenosine — ATP that should have become an 'immune activation signal' is converted into an 'immune suppression signal.'
Adenosine acts on T cells and NK cells through A2a receptors: activates cAMP pathway, suppressing TCR signal transduction and cytokine secretion; induces T cells to express PD-1, cooperating with PD-L1 to reinforce exhaustion; on NK cells, suppresses NKG2D receptor expression, weakening NK cell sensitivity to stress ligands. Early data from adenosine pathway treatment targets (A2aR antagonists, anti-CD73 antibodies) combined with PD-1 inhibitors show some activity in PD-1 monotherapy non-responding patients.
5. TGF-β: the 'most comprehensive' immune suppression switch
TGF-β is the most important immunosuppressive cytokine in the tumor microenvironment, with multi-target immunosuppressive functions: directly suppresses CTLs (downregulates perforin and granzyme B expression, weakening direct killing capacity); induces Tregs (converts naive T cells into inducible Tregs, continuously secreting more TGF-β, forming a self-amplifying immunosuppressive loop); reprograms macrophages (polarizes M1 type to M2 type, making TAMs secrete VEGF and MMP as 'tumor helpers'); drives EMT (core driving signal of EMT, granting cancer cells migratory and invasive capacity while enhancing immune evasion); and constructs physical barriers (activates fibroblasts into CAFs, forming physical barriers blocking immune cells from entering the tumor).
TGF-β targeting challenge: TGF-β is a key regulator of normal tissue development, wound healing, and immune homeostasis — systemic TGF-β inhibition causes serious cardiac toxicity and hemorrhagic anemia side effects. The most promising strategy is bispecific molecules: one end targeting PD-L1 (guiding the molecule to localize to the tumor microenvironment), the other end carrying a TGF-β trap (capturing local TGF-β). The representative molecule is M7824 (bintrafusp alfa, PD-L1×TGF-β bispecific fusion protein), showing preliminary activity in multiple tumors.
6. Why 'combination strategies' are inevitable
From PD-L1 to CD47, from adenosine to TGF-β, the immune switches tumors manipulate form an intricate, mutually backed-up 'multiple defense line' system. This system's existence is the inevitable result of tumor evolution — under continuous immune system selection pressure, only cancer cells that simultaneously evolved multiple escape mechanisms could survive under immune surveillance and develop into clinically visible tumors. Releasing one brake (like PD-1) causes the tumor to compensate by enhancing another brake (like upregulating LAG-3, TIM-3). This is the core mechanism of primary and secondary resistance to PD-1 inhibitors, and the fundamental logic driving 'dual/triple checkpoint combination' research.
7. Patient perspective: how to ask the key questions at consultations
Understanding tumor's 'immune switch engineering,' patients have more questions to actively raise when communicating with oncologists. Several questions worth raising in follow-up: Has my tumor had PD-L1 expression testing and TMB (tumor mutation burden) testing? How do the results affect treatment selection? If PD-1 monotherapy progresses, will LAG-3 or TIM-3 co-expression be tested to consider combination strategies? Is my tumor 'hot' or 'cold' — if cold, what 'warming' strategies can be considered? Are there adenosine pathway or TGF-β-related clinical trials for my tumor type? These answers help you understand your treatment plan and build an 'informed collaboration' relationship with your physician.
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