PD-L1 checkpoint blockade promotes regulatory T cell activity that underlies therapy resistance

Despite the clinical success of immune checkpoint blockade (ICB), in certain cancer types, most patients with cancer do not respond well. Furthermore, in patients for whom ICB is initially successful, this is often short-lived because of the development of resistance to ICB. The mechanisms underlying primary or secondary ICB resistance are incompletely understood. Here, we identified preferential activation and enhanced suppressive capacity of regulatory T cells (T_reg cells) in αPD-L1 therapy-resistant solid tumor-bearing mice. T_reg cell depletion reversed resistance to αPD-L1 with concomitant expansion of effector T cells. Moreover, we found that tumor-infiltrating T_reg cells in human patients with skin cancer, and in patients with non-small cell lung cancer, up-regulated a suppressive transcriptional gene program after ICB treatment, which correlated with lack of treatment response. αPD-1/PD-L1-induced PD-1⁺ T_reg cell activation was also seen in peripheral blood of patients with lung cancer and mesothelioma, especially in nonresponders. Together, these data reveal that treatment with αPD-1 and αPD-L1 unleashes the immunosuppressive role of T_reg cells, resulting in therapy resistance, suggesting that T_reg cell targeting is an important adjunct strategy to enhance therapeutic efficacy.

Host genetics and tumor environment determine the functional impact of neutrophils in mouse tumor models

Background

Neutrophils have been reported to have protumor, antitumor or neutral effects in cancer progression. The underlying causes for this functional variability are not clear.

Methods

We studied the role of neutrophils in six different mouse tumor models by intratumoral injection of antimicrobial peptides or vaccination. Changes in systemic and intratumoral immune cells were analyzed by flow-cytometry and mass-cytometry. The role of neutrophils was studied by antibody-mediated neutrophil depletion. Neutrophils from different mouse strains were compared by RNA sequencing.

Results

The antimicrobial peptide Omiganan reduced the growth of TC-1 tumors in BL/6 mice and CT26 tumors in BALB/c mice. No significant effects were observed in B16F10, MC38 and 4T1 tumors. Growth delay was associated with increased abundance of neutrophils in TC-1 but not CT26 tumors. Systemic neutrophil depletion abrogated Omiganan efficacy in TC-1 but further reduced growth of CT26, indicating that neutrophils were required for the antitumor effect in TC-1 but suppressed tumor control in CT26. Neutrophils were also required for a therapeutic vaccine-induced T-cell mediated control of RMA tumors in BL/6 mice. Clearly, the circulating and intratumoral neutrophils differed in the expression of Ly6G and CD62L, between TC-1 and CT26 and between blood neutrophils of tumor-naïve BL/6 and BALB/c mice. RNA-sequencing revealed that neutrophils from BL/6 mice but not BALB/c mice displayed a robust profile of immune activation, matching their opposing roles in TC-1 and RMA versus CT26.

Conclusions

Neutrophil functionality differs strongly between mouse strains and tumor types, with consequences for tumor progression and therapy.

CD39 identifies a microenvironment-specific anti-inflammatory CD8+ T-cell population in atherosclerotic lesions

BACKGROUND AND AIMS

CD8⁺ T-cells have been attributed both atherogenic and atheroprotective properties, but analysis of CD8⁺ T-cells has mostly been restricted to the circulation and secondary lymphoid organs. The atherosclerotic lesion, however, is a complex microenvironment containing a plethora of inflammatory signals, which may affect CD8⁺ T-cell activation. Here, we address how this environment affects the functionality of CD8⁺ T-cells.

METHODS AND RESULTS

We compared the cytokine production of CD8⁺ T-cells derived from spleens and enzymatically digested aortas of apoE^-/- mice with advanced atherosclerosis by flow cytometry. Aortic CD8⁺ T-cells produced decreased amounts of IFN-γ and TNF-α compared to their systemic counterparts. The observed dysfunctional phenotype of the lesion-derived CD8⁺ T-cells was not associated with classical exhaustion markers, but with increased expression of the ectonucleotidase CD39. Indeed, pharmacological inhibition of CD39 in apoE^-/- mice partly restored cytokine production by CD8⁺ T-cells. Using a bone-marrow transplantation approach, we show that TCR signaling is required to induce CD39 expression on CD8⁺ T-cells in atherosclerotic lesions. Importantly, analysis of human endarterectomy samples showed a strong microenvironment specific upregulation of CD39 on CD8⁺ T-cells in the plaques of human patients compared to matched blood samples.

CONCLUSIONS

Our results suggest that the continuous TCR signaling in the atherosclerotic environment in the vessel wall induces an immune regulatory CD8⁺ T-cell phenotype that is associated with decreased cytokine production through increased CD39 expression in both a murine atherosclerotic model and in atherosclerosis patients. This provides a new understanding of immune regulation by CD8⁺ T-cells in atherosclerosis.