EZH1/2 inhibition improves immunotherapy response through MHC Class II de-repression and neutrophil reprogramming

Why do some lung cancer patients respond to immunotherapy while others see no benefit? While PD-1 inhibitors have revolutionized oncology, only about 18% of patients with lung squamous cell carcinoma achieve a durable response. This gap suggests that the tumor's internal environment is actively hiding itself from the immune system.

A new study from the University of Kentucky proposes that the problem isn't just the immune system's strength. It involves the tumor's ability to remain "invisible." Researchers report that targeting an epigenetic regulator (a protein that controls how genes are turned on or off) called EZH1/2 can make lung cancer cells more visible. This occurs by increasing the expression of MHC Class II proteins—the molecular "flags" that tell T cells a cell is dangerous. Crucially, the study finds this process also reprograms the bone marrow to produce more mature, anti-tumor neutrophils (a type of white blood cell).

The invisibility of squamous cell carcinoma

Current immunotherapy relies on "checkpoint inhibitors" like anti-PD1 to prevent cancer cells from sending a "stop" signal to T cells. However, for this to work, the T cells must first recognize the tumor. This recognition is facilitated by the Major Histocompatibility Complex (MHC), a set of proteins on the cell surface that presents fragments of internal proteins to the immune system. Think of MHC as a security badge scanner. If the tumor does not display the right badges, the T cells simply walk past.

In lung squamous cell carcinomas, the epigenetic machinery often silences the genes responsible for producing these MHC flags. The authors note that this creates a fundamental barrier to treatment success. Even if you remove the "stop" signal with anti-PD1, the T cells remain blind. Furthermore, these tumors are often crowded with immature neutrophils. In this context, these cells can actually help the tumor grow rather than fight it.

De-repressing the immune flag

The researchers investigated whether inhibiting EZH1/2 could flip this switch. They used valemetostat, a dual EZH1/2 inhibitor, to see if it could "de-repress" (reactivate) the silenced MHC genes. The mechanism operates through two distinct but complementary pathways.

First, at the local tumor level, the authors report that valemetostat treatment leads to a significant up-regulation of both MHC Class I and MHC Class II on tumor cells .

By removing the epigenetic brakes, the drug forces the tumor to display the proteins the immune system needs to see. Second, the study identifies a systemic effect. Valemetostat appears to reshape the bone marrow. Instead of producing the immature, tumor-promoting neutrophils typically seen in cancer, the drug drives "systemic neutrophil maturation." The authors observe that these treated neutrophils exhibit more mature nuclear morphologies .

They also show different transcriptional profiles (patterns of gene activity). This shifts them toward a state that inhibits tumor growth .

Evidence from 3D tumoroids and mice

The authors validated these findings using a syngeneic graft mouse model. In this model, they found that while single-agent treatments slowed growth, only the combination of valemetostat and anti-PD1 achieved actual tumor regression . To move beyond simple mouse models, the team engineered a 3D air-liquid interface culture system. These "multi-cultures" contain tumoroids (small, 3D clusters of tumor cells), lung mesenchymal cells, and T cells. This setup simulates the complex architecture of a real lung .

In these controlled environments, the authors demonstrate that bone marrow from mice treated with valemetostat possesses potent anti-tumor properties .

Interestingly, they discovered that this effect depends on MHC Class II signaling. When they blocked MHC Class II in the culture, the ability of the bone marrow to inhibit tumor growth was significantly diminished . This suggests that the "reprogrammed" immune cells rely on a coordinated cytokine network (chemical messengers) to orchestrate the attack. The paper also notes a strong negative correlation between EZH2 and MHC II expression in human patient datasets .

Unresolved questions in immune reprogramming

Despite the compelling results, several mechanistic gaps remain. The authors report that while valemetostat increases MHC expression, they have not yet determined the exact cause of CEBPE upregulation. It is unclear if this is a direct result of EZH2 inhibition or an indirect downstream consequence. This distinction is vital for understanding how to target the pathway.

There is also a question regarding the primary driver of clearance. The study shows that neutrophils are reprogrammed and MHC is increased. However, it is not yet clear if the neutrophils directly kill the tumor. Alternatively, they might act by creating a better environment for T cells to thrive. Finally, the researchers acknowledge a functional trade-off. Their Ezh2-deficient neutrophils showed reduced migration and "NET" formation (a process where neutrophils release web-like structures). However, these cells maintained their ability to kill bacteria. This suggests that we might trade some innate immune efficiency for a more targeted anti-tumor response.

The verdict on epigenetic sensitization

Is this ready for the clinic? Not yet, but the biological logic is sound. The study provides a clear rationale for using EZH1/2 inhibitors as "sensitizers." These drugs could make existing immunotherapies more effective in squamous cell lung cancers. By addressing both the tumor's ability to hide (MHC II) and the systemic immune environment (neutrophil maturation), the researchers have identified a dual-pronged attack. This approach goes beyond simple checkpoint blockade. For researchers looking at the next generation of combination therapies, this work shifts the focus. It moves from merely "unmasking" the tumor to actively "rearming" the patient's entire immune system.

Figures from the paper