Gamma-delta T cells are gaining considerable attention as a powerful immunotherapy tool against cancer. What underpins their promise? How will they be applied in the clinic?
Gamma-delta (γδ) T cells are a promising, new immunotherapy platform due to their power to recognize and kill tumor cells and the indication from clinical trials that gamma-delta T cell therapies have a high safety profile. This blog describes the promise of gamma-delta T cells and explains what therapeutic strategies scientists pursue.
Importantly, there lies a great power in employing single-cell sequencing in the development of gamma-delta T-cell therapy. It is namely possible to perform an in-depth characterization of the gamma-delta T cell clonotypes and subsets in patient material and preclinical samples.
How to perform Single-cell Gamma-Delta T Cell analysis
To provide more background on how single-cell sequencing can aid scientists working with gamma-delta T cells, let’s take a look at the current state of therapy development.
Jump to a section:
- The promise of gamma-delta T cells
- Main methods of gamma-delta T cell therapy
- Opportunities for drug development with Single Cell
What is the promise of gamma-delta T cells?
Gamma-delta T cells –also known by the name of γδ T lymphocytes and, in jargon, as “Gamma’s” – are a class of T cells that are attributed a promising role for cell and immunotherapy. That promise is underpinned mainly by four observations:
1. Their role in the immune system is versatile
Mechanism of disease-studies show that gamma-delta T cells occupy a unique role in our defence against infection and cancer. They roam around the blood system performing immunosurveillance, can recognize malignant cells, and can directly induce apoptosis (‘recognize and kill’), as well as recruit adaptive immune cells for a durable immune response.
2. Their presence correlates with good prognosis
Studies of tumor infiltrates and other material from cancer patients show that gamma-delta T cell presence correlates with better disease outcomes. In other words, having more active γδ T cells in the tumor seems to be beneficial for patients. This is true for various cancer types including blood cancers and solid tumors.
There exist different types of gamma-delta T cell subsets. Vγ9Vδ2 T cells are the most abundant γδ T cell subset in blood and tumor infiltrates. They have thus been the main focus for gamma-delta T cell therapy efforts. However, the fact that Vγ9Vδ2 T cells are absent in non-primate experimental models such as mice (see Karunakaran et al., 2014) has prompted preclinical research into other gamma-delta T cell subtypes. Less dominant subtypes such as those of the Vδ1 class show similar signs of antitumor potency and have also enjoyed recent attention.
3. Good results in preclinical and early clinical studies
In a preclinical setting, researchers could show that high gamma-delta T cell numbers can prevent tumor formation in mice (e.g.: Girardi et al., 2001) and non-human primates (e.g., Sicard et al., 2005).
Moreover, researchers have performed several clinical trials (Ma et al. (2023) review 28 of them) aimed at boosting Gamma’s in cancer patients. Overall, the signs are quite promising. More details are discussed in the next section.
4. Safety and MHC-independence
As observed in the previously mentioned review by Ma et al., healthy humans have so far shown no worse than grade 2 (bothersome, but not dangerous) side effects from gamma-delta T cell therapy. This is a remarkable trait of Gamma’s compared to, e.g., alpha-beta T cells.
Importantly, transfusions with gamma-delta T cells probably do not require donor matching and are safe from graft vs. host disease. This is because Gamma’s operate independently of antigen presentation. Your body’s cells recruit most immune cells by MHCs: cell surface proteins that activate an immune response when they carry foreign antigens.
These proteins differ from person to person, like blood groups, which creates the risk of a dangerous immune response to the transfusion or of the transfused material to the patient. This risk can decrease by matching patients’ MHC type to their donors’; understandably a highly limiting factor in treatment. However, gamma-delta T cells do not perform immunosurveillance and diseased cell recognition by MHC, alleviating risk and the limits of donor matching.
Main methods of gamma-delta T cell therapy
Gamma-delta T cells have a natural reactivity against cancer or infected cells. However, many tumors exert stress on the immune system that causes cancer patients to become immunocompromised, or evade an immune response in other ways.
Hence, the main focus of drug developers has been to find a way to safely increase gamma-delta T cell numbers in the body, stimulate their overall activity, or boost a specific reactivity against the tumor. In other words, gamma-delta T cell immunotherapy is about how to “safely unleash the anticancer power of immune cells.” (Ma et al., 2023)
Broadly speaking, you could say drug developers employ four strategies to achieve this.
Based on: Saura-Esteller et al. (2022) – CC-BY 4.0
1. Unmodified T cells
Due to their MHC-independent capacities, described above, T cell transfers from donors to patients are an apparently safe and relatively simple strategy. It involves isolating Gamma’s from donor blood and expanding the cells ex vivo, before transplanting them into the immunocompromised cancer patient. This can also be done with autologous T cells, i.e., T cells isolated from the patient themselves if they are healthy enough for this.
Since 2019, clinical trials have tested this strategy on various cancers, using various methods of T-cell expansion, with overall positive results and a good safety profile (per Saura-Esteller et al., 2022)
Within this category, multiple strategies exist for optimal expansion and post-transfusion stimulation, such as various combination therapies with drugs or antibodies.
2. Modified T cells
Before transfusion, it is possible to genetically modify T cells to increase their reactivity to specific tumor cells. The most prevalent technique is introducing chimeric antigen receptors (CARs) to patient or allogeneic T cells.
CAR-T cell therapy applied to conventional alpha-beta T cells has shown very successful results on B cell malignancies. This has invited a lot of resources to this field, which has recently broadened to include CAR gamma-delta T cells. Moreover, since CAR T-cell therapies with alpha-beta cells increasingly encounter safety issues, the apparent low risk of Gamma’s makes this a compelling strategy.
3. Antibody-based strategies
It is possible to increase γδ T cell engagement with tumor cells using tumor-targeting antibodies. Antibody-based immunotherapy is a relatively well-established cancer therapy strategy that can be optimized to elicit γδ T cells specifically.
Again, clinical trials on several cancer types show that Gamma’s produce a good safety profile and the results are carefully encouraging.
4. Modify tumors
γδ T cells recognize tumors by detecting the levels of isopentenyl pyrophosphate (IPP), a normal cell metabolite found at very high levels in many cancer types. Gamma’s interpret high IPP levels as a danger signal and react by proliferating and activating their cell-killing capabilities.
It is possible to modify tumors to increase their IPP excretion, thus potentially increasing the γδ T cell response. Researchers hence screen existing drugs for their potential to increase IPP production in cancer cells in the lab.
Besides that, some pharmaceutical companies interrogate other modalities, such as gene therapy, to modify tumors. An example is ImmunoTox TM by American Gene Technologies, which uses a lentiviral vector to integrate a gene in cancer cells to increase IPP (also named phosphoantigen) production and thus activate γδ T cells.
Other pharmaceutical companies developing gamma-delta T cell antitumor platforms include the following:
Organizations are per 2022. Source: Saura-Esteller et al. (2022) – CC-BY 4.0
Opportunities for gamma-delta T cells in drug development
Most scientists writing about gamma-delta T cells observe that therapy opportunities can further improve as researchers unearth more details about their functionality and clonal diversity.
“Different parameters concerning human γδ T-cell function and phenotype within tissues are still poorly understood,” write Lawand et al. (2017). Going more into specifics, Saura-Esteller et al. (2022) observe that “the complete repertoire of antigens recognized by γδ-T cell receptors and the specificity of each γδ T subset is still not fully understood.”
In other words, studying gamma-delta T cells in (pre)clinical contexts and in the lab is still crucial for therapy development.
T-cell receptor sequencing
One of the main methods for studying gamma-delta T cell diversity, clonality, and function is gamma-delta T cell receptor (TCR) sequencing. By examining the specific gamma-delta TCR sequences of a T cell population, researchers can gain a better understanding of how these cells recognize and respond to different antigens and contribute to an antitumor response.
Going beyond the characterization of a population, single-cell gamma-delta TCR sequencing generates a high-resolution profile of the clones and cell states present within a γδ T cell population. For example, it can analyze which clones are abundant in the donor material that holds the most curative power. Developers of CAR gamma-delta T cell therapy can also apply it to analyzing which clones are expanded ex vivo and how that affects the therapy’s efficacy.
More information
Our protocol works by integrating 10x Genomics Single Cel Immune Profiling with a custom T cell receptor amplification strategy. Our scientific poster explains this protocol, while also showing results from in-house analysis of donor material.
