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Beatriz Painho, MSc PhD Student

Miguel de Almeida Fuzeta, PhD Scientist

Marta H. G. Costa, PhD Principal Scientist

Margarida Serra, PhD Head of Stem and Immune Cells Bioengineering Lab

iBET, Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras, Portugal 

Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal

Live/dead staining of a cell population comprising γδ T cells derived from umbilical cord blood hematopoietic stem/progenitor cells.
Live cells are depicted in green, while red indicates dead cells. Scale bar = 100 µm

What?

Gamma delta (γδ) T cells are a unique subset of immune cells within the T cell family, displaying T cell receptors (TCRs) composed of γ and δ chains (rather than α and β chains, present in αβ T cells). Unlike their better-known counterparts, αβ T cells, which recognize peptide antigens presented by the Major Histocompatibility Complex molecules (MHC), γδ T cells are not MHC-restricted¹. This positions γδ T cells as promising candidates to be adopted in allogeneic and “off-the-shelf” immunotherapies, so multiple patients could benefit from a γδ T cell-based product without the need for individual HLA matching^2,3.

Why?

The diverse potential of γδ T cells highlights their critical role in immune surveillance and promising application in cancer immunotherapy.  γδ T cells are versatile: they can recognize infected/cancer cells and respond quickly without prior exposure (innate-like immunity), while being able to perform TCR-mediated responses and clonal expansion (adaptive-like immunity)^1,2. Thus, γδ T cells act through a combination of mechanisms present in both αβ T cells (T cell receptor signaling and co-stimulation) and natural killer (NK) cells (NK receptor signalling such as NKG2D, DNAM-1 and NKp44), broadening the immune response⁴. 

As antigen recognition is not MHC-restricted, γδ T cells can be safely applied in allogeneic and off-the-shelf therapy settings due to the low risk of causing Graft-versus-Host Disease (GvHD). Moreover, their function circumvents several cancer immune evasion strategies, such as downregulation of MHC molecules or low neoantigen load, that currently limit αβ T cell activation^3,5.

Who?

γδ T cells were first identified in the mid-1980s by researchers noticing that T cell diversity was not restricted to the αβ TCRs^6,7. Since then, the unique function of γδ T cells has been investigated and translated into products with promising therapeutic potential. γδ T cells have mostly been used for cancer immunotherapy, with encouraging research supporting their use across multiple conditions, offering hope as an alternative treatment for cancer patients who do not respond to first-line therapies. In this context, γδ T cell-based therapies are currently being tested in clinical trials for haematological cancers, such as leukaemia as well as solid tumours, such as brain, colorectal, lung and breast cancers^3,8.  

When?

γδ T cells develop in the thymus from progenitor T cells. When thymocytes are at a double negative CD4^- CD8^- stage, they can either differentiate into αβ T cells or γδ T cells, upon commitment to either lineage dependent on Notch signalling and TCR signal strength⁹. The human γδ TCR repertoire is diverse, resulting from the combination of the different Vγ (Vγ 2-5, Vγ8 or Vγ9) and Vδ chains (Vδ1-8) and from the somatic recombination of the V(D)J segments. Theoretically, up to 10⁷-10⁸ variants are able to be generated, with the most common variants being Vδ1, Vδ2 and Vδ3, and therefore commonly used to classify subtypes of γδ T cells¹⁰. 

Where?

γδ T cells represent 1-10% of the total human CD3⁺ T-cell population. They can be found throughout the body and while they represent a small fraction of circulating T cells in peripheral blood (<5%), their prevalence is higher in peripheral tissues (such as the skin, intestine and lungs)^4,10,11. Their biodistribution across distinct tissues and organs differs according to the γδ T cell subtypes, with their proportion increasing in disease states and correlating with better clinical outcomes⁵.

Vγ9Vδ2 T cells and Vδ1 T cells play a central role in γδ T cell-based immunotherapies. Vδ2 are the most extensively studied subtype and the first to be applied in clinical settings, since they are mostly found in peripheral blood and are consequently easier to obtain. On the other hand, Vδ1 T cells are highly enriched in mucosal tissues and have been described to be a key component of tumour infiltrating lymphocytes (TILs)². 

How?

Instead of relying on antigen-presenting cells and MHC molecules, γδ T cells can directly recognize and bind to target cells, releasing cytokines and directing the immune response to kill cancerous and infected cells. This uniqueness in γδ T cells led to several clinical trials designed to assess their therapeutic potential, particularly in cancer immunotherapy^2,3.

Adoptive cell therapies have been developed using expanded unmodified γδ T cells in allogeneic setting for treatment of hematological cancers, including acute myeloid leukemia (AML) by Takeda (NCT05886491). γδ T cells have also been tested for treatment of solid tumors both in autologous setting, namely in glioblastoma by IN8bio (NCT04165941) and in allogeneic setting to treat lung cancer at Fuda Cancer Hospital, Guangzhou (NCT03183232 and NCT03183219).

In an effort to improve efficacy and specificity of γδ T cell therapies, CAR-transduced γδ T cell products are also being tested in clinical settings. These include CD20-specific CAR-transduced Vδ1 T cells to treat B cell lymphomas, by Adicet (NCT04735471) and NKG2D ligand-specific CAR γδ T cells to treat solid tumors including colorectal and breast cancers, by CytoMed (NCT04107142 and NCT05302037). Also aiming at higher specificity, antibody conjugated γδ T cells have been tested, namely anti-CD20 conjugated Vδ1 T cells to treat Non-Hodgkin lymphoma by Acepodia (NCT05653271) and anti-EGFR conjugated Vδ2 T cells for solid tumors expressing EGFR, also by Acepodia (NCT06415487).

The development of standardized, chemically-defined and scalable manufacturing approaches to generate γδ T cells with high therapeutic efficacy will be essential to accelerate adoption of these cells in cancer treatment. In this context, our group at iBET - Instituto de Biologia Experimental e Tecnológica (Oeiras, Portugal) has recently joined efforts with OneChain Immunotherapeutics (Barcelona, Spain) to develop a novel allogeneic dual-targeted CAR γδ T cell product for treatment of T cell acute lymphoblastic leukemia (T-ALL), using a standardized and scalable approach. For this purpose, we are using hematopoietic stem/progenitor cells (HSPC) as a source of Vδ1 T cells (CARxALL project, funded by the European Union’s EIC Transition programme).

Did you know that…

γδ T cells are viewed as key cells that work as a “bridge” between innate and adaptive immunity? Like innate immune cells, γδ T cells do not require pre-exposure to the pathogen to initiate an immune response (similarly to NK cells and macrophages). In fact, γδ T cells combine activation mechanisms used by NK cells, through expression of NK cell receptors (e.g. NKG2D, DNAM-1, NKp30) that promote cytotoxic function, with TCR signalling characteristic of conventional T cells.

References

1.                Hayday, A. C. γδ T Cell Update: Adaptate Orchestrators of Immune Surveillance. J. Immunol. 203, 311–320 (2019).

2.                Mensurado, S., Blanco-Domínguez, R. & Silva-Santos, B. The emerging roles of γδ T cells in cancer immunotherapy. Nat. Rev. Clin. Oncol. 20, 178–191 (2023).

3.                Hayday, A., Dechanet-Merville, J., Rossjohn, J. & Silva-Santos, B. Cancer immunotherapy by γδ T cells. Science 386, eabq7248 (2024).

4.                Costa, G. P., Mensurado, S. & Silva-Santos, B. Therapeutic avenues for γδT cells in cancer. Journal for ImmunoTherapy of Cancer 11, (2023).

5.                Saura-Esteller, J. et al. Gamma Delta T-Cell Based Cancer Immunotherapy: Past-PresentFuture. Front. Immunol. 13, (2022).

6.                Saito, H. et al. Complete primary structure of a heterodimeric T-cell receptor deduced from cDNA sequences. Nature 309, 757–762 (1984).

7.                Hayday, A. C. et al. Structure, organization, and somatic rearrangement of T cell gamma genes. Cell 40, 259–269 (1985).

8.                Zhu, D. et al. Potential of gamma/delta T cells for solid tumor immunotherapy. Front. Immunol. 15, 1466266 (2024).

9.                Ciofani, M. & Zúñiga-Pflücker, J. C. Determining γ δ versus α β T cell development. Nat. Rev. Immunol. 10, 657–663 (2010).

10.            Hu, Y. et al. γδ T cells: origin and fate, subsets, diseases and immunotherapy. Signal Transduction and Targeted Therapy 8, 1–38 (2023).

Ribot, J. C., Lopes, N. & Silva-Santos, B. γδ T cells in tissue physiology and surveillance. Nat. Rev. Immunol. 21, 221–232 (2021).