Pressure-Induced Increase in PD-L1 Expression May Dull Effect of CAR T-Cell Therapy

Elevated pressure in the tumor microenvironment may dampen the effect of chimeric antigen receptor (CAR)-T cell therapy, a new study has found.

The study of constructed αROR1‐CAR T cells showed an increase of programmed death-ligand 1 (PD-L1) expression when exposed to elevated pressure, driving resistance to CAR T cell-mediated cytotoxicity. However, the findings also suggest that adding PD-1/PD-L1 inhibitors to CAR T-cell therapy could help address this.

The findings come as researchers continue to try and translate the successes of CAR T-cell therapy seen in B cell malignancies to solid tumors. Unlike hematologic malignancies, solid tumors have cancer cells that are densely packed with an insufficient amount of nutrients and oxygen, as well as tumor interstitial fluid pressure (TIFP).

“TIFP was initially thought to dampen chemotherapy simply by blocking drug delivery. However, recent studies show that TIFP can actively modulate signaling transduction, cancerous proliferation, and metastasis,” described the study researchers. “Lowering TIFP has shown promising results in improving cancer chemotherapy. However, compared to hypoxia and nutrient starvation, research on TIFP in vivo and in vitro remains scarce.”

The researchers co-cultured the αROR1‐CAR T cells with A549, both with and without pressure, finding that the cells exposed to elevated pressure (an additional 100 mmHg) were more resistant to cytotoxicity, with reduced apoptosis and cell death.

They also found that elevated pressure led to an increase in resistance to CAR-T cells in a time-dependent fashion. While 1-day preconditioning showed no significant effect, 7-day and 14-day preconditioning showed a significant increase in resistance. The group observed a similar pattern for upregulation in PD-L1. However, when adding pembrolizumab and cemiplimab to the cells, pressure-induced resistance was significantly reduced. The 2 treatments also increased apoptotic cell death in the A549 cells. These findings were confirmed in xenograft mice.

The group did not observe differences expression of αROR1‐CAR or cytokine production based on pressure preconditioning. There were no changes in IL-2, IFN-γ, or TNF-α with pressure conditioning.

“Our study did not find any effect of TIFP on cytokine release and cytotoxicity CAR-T cells, consistent with a study in a hypertension mouse model. In that study, increasing systolic pressure activated T cell, however, such pressure did not affect cytokine production in isolated human T cells and monocytes, nor did it affect the T-cell proliferation in these settings,” wrote the researchers. “However, we cannot rule out the possibility that CAR-T cells are affected by pressure in vivo under the tumor microenvironment. The lack of activation of CAR-T cells by pressure in our study could simply be due to the ex vivo environment, where multiple cytokines required for T cell activation are missing. It would be interesting to study in vivo if CAR-T cells could be activated by elevated pressure either in mice models or human subjects.”

Reference

Ou Z, Dou X, Tang N, Liu G. Pressure increases PD‐L1 expression in A549 lung adenocarcinoma cells and causes resistance to anti‐ROR1 CAR T cell‐mediated cytotoxicity. Sci Rep. Published online April 28, 2022. doi:10.1038/s41598-022-10905-6