The CTLA-4 immune checkpoint protein regulates PD-L1:PD-1 interaction via transendocytosis of its ligand CD80.

CTLA-4 and PD-1 are key immune checkpoint receptors that are targeted in the treatment of cancer. A recently identified physical interaction between the respective ligands, CD80 and PD-L1, has been shown to block PD-L1/PD-1 binding and to prevent PD-L1 inhibitory functions. Since CTLA-4 is known to capture and degrade its ligands via transendocytosis, we investigated the interplay between CD80 transendocytosis and CD80/PD-L1 interaction. We find that transendocytosis of CD80 results in a time-dependent recovery of PD-L1 availability that correlates with CD80 removal. Moreover, CD80 transendocytosis is highly specific in that only CD80 is internalised, while its heterodimeric PD-L1 partner remains on the plasma membrane of the antigen-presenting cell (APC). CTLA-4 interactions with CD80 do not appear to be inhibited by PD-L1, but efficient removal of CD80 requires an intact CTLA-4 cytoplasmic domain, distinguishing this process from more general trogocytosis and simple CTLA-4 binding to CD80/PD-L1 complexes. These data are consistent with CTLA-4 acting as modulator of PD-L1:PD-1 interactions via control of CD80.

Therapeutic gene editing of T cells to correct CTLA-4 insufficiency.

Heterozygous mutations in CTLA-4 result in an inborn error of immunity with an autoimmune and frequently severe clinical phenotype. Autologous T cell gene therapy may offer a cure without the immunological complications of allogeneic hematopoietic stem cell transplantation. Here, we designed a homology-directed repair (HDR) gene editing strategy that inserts the CTLA-4 cDNA into the first intron of the CTLA-4 genomic locus in primary human T cells. This resulted in regulated expression of CTLA-4 in CD4+ T cells, and functional studies demonstrated CD80 and CD86 transendocytosis. Gene editing of T cells isolated from three patients with CTLA-4 insufficiency also restored CTLA-4 protein expression and rescued transendocytosis of CD80 and CD86 in vitro. Last, gene-corrected T cells from CTLA-4-/- mice engrafted and prevented lymphoproliferation in an in vivo murine model of CTLA-4 insufficiency. These results demonstrate the feasibility of a therapeutic approach using T cell gene therapy for CTLA-4 insufficiency.

Differences in CD80 and CD86 transendocytosis reveal CD86 as a key target for CTLA-4 immune regulation.

CD28 and CTLA-4 (CD152) play essential roles in regulating T cell immunity, balancing the activation and inhibition of T cell responses, respectively. Although both receptors share the same ligands, CD80 and CD86, the specific requirement for two distinct ligands remains obscure. In the present study, we demonstrate that, although CTLA-4 targets both CD80 and CD86 for destruction via transendocytosis, this process results in separate fates for CTLA-4 itself. In the presence of CD80, CTLA-4 remained ligand bound, and was ubiquitylated and trafficked via late endosomes and lysosomes. In contrast, in the presence of CD86, CTLA-4 detached in a pH-dependent manner and recycled back to the cell surface to permit further transendocytosis. Furthermore, we identified clinically relevant mutations that cause autoimmune disease, which selectively disrupted CD86 transendocytosis, by affecting either CTLA-4 recycling or CD86 binding. These observations provide a rationale for two distinct ligands and show that defects in CTLA-4-mediated transendocytosis of CD86 are associated with autoimmunity.

Patient and Medical Oncologists' Perspectives on Prescribed Lifestyle Intervention-Experiences of Women with Breast Cancer and Providers.

This study explored the perspectives and experiences of breast cancer patients and medical oncologists with regards to participation in a lifestyle intervention at a tertiary cancer treatment center. A thematic approach was used to understand the context within which a lifestyle intervention was recommended and experienced, to inform future lifestyle programming and promote uptake. Twelve women with breast cancer receiving adjuvant chemotherapy and eight medical oncologists completed interviews. Findings suggest receiving a prescription for a lifestyle intervention from a trusted health professional was influential to women with breast cancer. The intervention offered physical, psychological, emotional, social, and informational benefits to the women and oncologists perceived both physiological and relational benefit to prescribing the intervention. Challenges focused on program access and tailored interventions. Lifestyle prescriptions are perceived by women with breast cancer to have numerous benefits and may promote lifestyle interventions and build rapport between oncologists and women. Oncology healthcare professionals play a pivotal role in motivating women's participation in lifestyle interventions during breast cancer treatment. Maintenance programs that transition patients into community settings and provide on-going information and follow-up are needed.

Characterization of CTLA4 Trafficking and Implications for Its Function.

CTLA4 is an essential negative regulator of T-cell immune responses and a key checkpoint regulating autoimmunity and antitumor responses. Genetic mutations resulting in quantitative defects in the CTLA4 pathway are also associated with the development of immune dysregulation syndromes in humans. It has been proposed that CTLA4 functions to remove its ligands CD80 and CD86 from opposing cells by a process known as transendocytosis. A quantitative characterization of CTLA4 synthesis, endocytosis, degradation, and recycling and how these affect its function is currently lacking. In a combined in vitro and in silico study, we developed a mathematical model and identified these trafficking parameters. Our model predicts optimal ligand removal in an intermediate affinity range. The intracellular CTLA4 pool as well as fast internalization, recovery of free CTLA4 from internalized complexes, and recycling is critical for sustained functionality. CD80-CTLA4 interactions are predicted to dominate over CD86-CTLA4. Implications of these findings in the context of control of antigen-presenting cells by regulatory T cells and of pathologic genetic deficiencies are discussed. The presented mathematical model can be reused in the community beyond these questions to better understand other trafficking receptors and study the impact of CTLA4 targeting drugs.