A range of immunotherapies have become novel alternatives for the treatment of cancers. These therapies enable the mobilization of the patient's own immune system to recognize and destroy cancerous cells. Promising results from a number of clinical trials have led to a diverse range of therapeutic orientations, including the use of antibodies to inhibit immune checkpoints.

Generally speaking, the currently-authorized protocols are long and onerous. Moreover, the problem of tumoral resistance to complete eradication remains an obstacle. Research in the setting is thus very active and focused on finding new therapeutic targets and developing treatments that are more efficacious and less deleterious for patients.

HLA-G is an immunosuppressive protein that, under normal circumstances, plays primarily a role in maternal-fetal tolerance. However, some tumors are able to hijack its immunosuppressive nature to escape from the host's immune response. Indeed, HLA-G is variably expressed in numerous cancers and often associated with poor prognoses. The protein is garnering great attention as a potential therapeutic target because studies done in vitro and in murine models have shown that its inhibition is crucial for the restoration of antitumoral immune response.

In a manuscript published in Scientific Reports, researchers from SRHI and the Argentinian lab LIAN presented their unprecedented inactivation of HLA-G in two human tumor cell lines using the Crispr/Cas9 gene editing technique.

This latter makes it possible to cleave DNA at a precise location in the genome of any cell. To achieve that action, the gene editing system deploys a single guide RNA (sgRNA) associated with the Cas9 enzyme; the first guides the complex to a specific DNA sequence and the second acts as "molecular scissors" to cleave it.

The Franco-Argentinian team tested different sgRNA/CAS9 combinations targeting exons 1 and 2 of the gene coding for HLA-G in the two cell lines. The researchers were thus able to generate a number of cancer cell clones wherein HLA-G expression was low, and for some even non-existent.

Earlier studies had shown that HLA-G inhibits natural killer (NK) cell¹ degranulation, which is part of the cytolytic action of that type of immune cell. To determine the effect of HLA-G on NK cell degranulation with the generated cell clones, the researchers co-cultured the NK cells with cancer cells expressing or not expressing HLA-G (HLA-G+ or HLA-G- respectively). And indeed, they observed greater degranulation activity by the NK cells in the presence of HLA-G- cells compared to HLA-G+ cells.

The team's results open doors to the development of Crispr/Cas9 gene editing strategies aimed at deactivating HLA-G expression in patients and thus improving the immune system's ability to attack cancer cells.

Although the Crispr/Cas9 technology shows enormous therapeutic potential for many diseases, there are a number of obstacles to overcome before it can be used safely and efficaciously in humans. The authors of the study presented here propose the use of adeno-associated virus (AAV) vectors to ensure the best possible transport and delivery of the sgRNA/Cas9 system to the cells of interest in patients. Once rendered inoffensive, AAV vectors have the advantages of low immunogenicity, easy production and sustained expression of the transported genetic material.

1 : natural killer cells are cytotoxic lymphocytes able to lyse cells showing transformation toward malignancy or infection by viruses or other intracellular pathogens.