Antitumor Immunity May Be Enhanced by Tregs Expressing FOXP3 Variant

Research in mice carried out by scientists at Indiana University School of Medicine and at the First Affiliated Hospital, School of Medicine, Zhejiang University, has found that regulatory T (T_reg) cells that express a shortened form of FOXP3 (FOXP3^dE2) can promote cytotoxic T cell-mediated antitumor activity. The study also showed that a synthetic molecule—a morpholino oligo —that reprogrammed T_reg cells to express this shorter FOXP3 variant boosted antitumor activity in mouse models and patient-derived tumor organoids. The findings could inform treatments to overcome tumor immunosuppression by T_reg cells that express full-length FOXP3 (FOXP3^FL).

First author Yujing Li, PhD, together with senior and corresponding authors Baohua Zhou, PhD, and Xiongbin Lu, PhD, at Indiana University School of Medicine, reported on their studies in Science Immunology, in a paper titled “Reprogramming intratumoral T_reg cells by morpholino-mediated splicing of FOXP3 for cancer immunotherapy.” In their paper the team commented, “Our results suggest that promoting FOXP3^dE2 isoform expression reprograms T_reg cells to T helper-like cells, thereby enhancing antitumor immunity.”

The emergence of cancer immunotherapy, including immune checkpoint inhibitors (ICI) and adoptive cell transfer (ACT), has revolutionized cancer treatment over the past decade, the authors wrote. However, success is limited to a relatively small subset of patients and cancer types. Tumor-infiltrating T_reg cells can suppress effective immunity against tumors, the team pointed out, and so “…identification of factors that influence T_reg homeostasis and function is important for the development of T_reg-targeting therapies to facilitate antitumor immunity.”

FOXP3 is a master regulatory gene that governs the molecular and functional features of T_reg cells, the researchers further explained. “FOXP3 directs gene expression responsible for the development and maintenance of immunosuppressive functions of T_reg cells.” And while mice only carry a single, full length version of FOXP3^FL, humans also express a form of FOXP3 that lacks exon 2 (FOXP3^dE2) and is associated with proinflammatory functions and autoimmune disease.

By contrast, T_reg cells that express FOXP3^FL inhibit inflammation, which can dampen antitumor immunity. “… the ratio of these two isoforms is skewed towards FOXP3^dE2 in autoimmune diseases, suggesting FOXP3dE2 may have a bona fide pro-inflammatory function rather than the immunosuppressive activities of its counterpart FOXP3^FL,” the investigators commented.

Representative images of hematoxylin and eosin (H&E) staining of major organs harvested at the endpoint. Histopathology was analyzed by a third party pathologist and no major treatment related lesions were observed. Data represent mean ± SD. ns: not significant by one way ANOVA with Tukey’s multiple comparisons test (B - G). [Yujing Li] — Representative images of hematoxylin and eosin (H&E) staining of major organs harvested at the endpoint. Histopathology was analyzed by a third party pathologist and no major treatment related lesions were observed. Data represent mean ± SD. ns: not significant by one way ANOVA with Tukey’s multiple comparisons test (B – G). [Yujing Li]

To investigate how FOXP3^dE2 affects tumor immune responses, Li and colleagues examined data from patients with triple-negative breast cancer in The Cancer Genome Atlas (TCGA) and analyzed survival data from 27 TCGA cancer types.

They determined that FOXP3^dE2 expression was linked to better patient survival in multiple cancers, while FOXP3^FL expression was associated with poorer outcomes. Furthermore, they found that genetically modified mice with T_reg cells that express FOXP3^dE2 (dE2 T_reg cells) were resistant to tumor growth in several types of cancers. The researchers examined immune cells from the tumor microenvironment and found that dE2 T_reg cells boosted the activation and accumulation of tumor-infiltrating cytotoxic T cells. “Our immunophenotyping results suggested that tumor-infiltrating dE2 T_reg cells are dysfunctional, allowing more efficient antitumor immunity in Foxp3^dE2 mice,” they stated. In addition, dE2 T_reg cells downregulated genes related to immune suppression and T_reg cell stability and upregulated helper T cell features.

The investigators in addition designed a synthetic molecule known as a morpholino, which can bind to FOXP3 mRNA and skip the expression of exon 2—thus shifting FOXP3^FL to FOXP3^dE2. “Our finding that dE2 T_reg cells are less suppressive, become Th-like cells, and promote antitumor immunity suggests modulation of FOXP3 mRNA alternative splicing could be a promising approach for cancer immunotherapy,” they suggested. “A morpholino (MO) is a type of sequence-specific oligomer that can recognize and bind to mRNA, leading to the knockdown of the gene or exon skipping.”

The experimental results showed that morpholino treatment enhanced antitumor immunity in mice and in patient-derived breast cancer and colorectal cancer tumor organoids. “Our study suggests that the MO-mediated FOXP3 isoform shifting is a potentially promising immunotherapeutic approach for cancer treatment,” the authors stated.

The post Antitumor Immunity May Be Enhanced by Tregs Expressing FOXP3 Variant appeared first on GEN – Genetic Engineering and Biotechnology News.