Breaking through immune suppression with CAR T cells

Since 2017, the United States Food and Drug Administration (FDA) has approved six chimeric antigen receptor (CAR) T cell therapies for treating blood cancers (1). Behind the excitement around these therapies is the concern about patients’ short-lived responses to CAR T cell infusions, limiting their chances of long-term survival. CAR T cells have even lower efficacy for solid tumors because immunosuppressive factors in the tumor microenvironment (TME) inhibit T cell activity, thereby promoting tumor development and evading therapies.

Scientists have made efforts to identify immunosuppressive genes that contribute to T cell dysfunction in the TME, such as using CRISPR to knock out genes for loss-of-function screening. In a recent study published in Nature, researchers at the New York Genome Center and New York University took a different approach by targeting positive regulators that boost T cell function, presenting the possibility of armoring CAR T cells with enhanced tumor killing abilities (2).

To discover genes that can improve a T cell’s antitumor activity, Neville Sanjana, a geneticist at the New York Genome Center, and his team screened nearly 12,000 genes. The researchers constructed a lentiviral library containing a collection of protein coding genes in the human genome and transduced the library into T cells. They monitored the proliferation of these T cells and captured numerous highly expressed genes involved in diverse immune processes, such as lymphocyte proliferation and interferon production. The top ranked gene, to the team’s surprise, was lymphotoxin-β receptor (LTBR).

LTBR is a tumor necrosis factor receptor that mediates cytokine release and cell apoptosis, which helps regulate lymphoid organogenesis and inflammation. Although T and B cells often express the ligands for LTBR, the receptor itself is typically absent in these cells (3).

To understand how exogenous LTBR impacts T cell functions, Sanjana and his team used single cell sequencing to profile T cell transcriptomes. They found that LTBR triggered the upregulation of various genes, enhancing multiple immune responses, including boosting cytokine secretion, promoting T cell proliferation, and decreasing cell apoptosis.

Based on their sequencing data, the authors pinpointed nuclear factor (NF)-κB, a key immune response regulator, as the most significant upregulated gene in LTBR-transduced T cells. NF-κB typically coordinates various transcription factors in different pathways to trigger inflammatory responses and promote immune cell development (4). In LTBR-transduced T cells, the researchers confirmed that NF-κB also upregulated several key inflammatory pathways and transcriptions factors, such NF-κB p65 and p52. These data helped Sanjana and his team identify which signaling pathways LTBR acts on to stimulate T cell immune activities.

The team then coexpressed LTBR with FDA-approved CARs and tested their antigen specific responses and cytotoxicity in patients’ T cells. They discovered that compared to the original CAR T cells, LTBR CAR T cells demonstrated increased cytokine secretion and cytotoxicity against tumor cells. These results highlight the potential of engineering T cells using immune enhancing genes as an approach to improving CAR T immunotherapy, especially for solid cancers.