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Better Cancer Treatment: Chimeric Antigen Receptor Modified γδ T Cells

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The engineering of chimeric antigen receptor (CAR) T cells has redefined cancer immunotherapy, producing transformative clinical outcomes in hematological malignancies. However, conventional CAR-T therapies face persistent barriers in solid tumors, including antigen heterogeneity, an immunosuppressive tumor microenvironment, and safety risks such as cytokine release syndrome and graft-versus-host disease. γδ T cells have emerged as a promising alternative effector population for CAR engineering, due to their MHC-independent antigen recognition, natural cytotoxicity against transformed or infected cells, and tissue-homing properties. Recent studies have provided crucial insights into molecular optimization of CAR structures tailored for γδ T cells, innovative methods for their generation and expansion, expansion of their antigen-targeting repertoire, and characterization of effector mechanisms during tumor engagement.

γδ T Cells

γδ T cells constitute a distinct subset of T lymphocytes that bridge the gap between innate and adaptive immunity. In contrast to conventional αβ T cells, which depend on peptide antigens presented by MHC molecules, γδ T cells recognize non-peptidic phosphoantigens, lipids, and stress-induced ligands. certain disease or infection contexts (e.g., CMV infection, malaria, or cancer). γδ T cells normally represent 1-5 % of T cells in human peripheral blood, but frequencies can expand significantly, sometimes reaching 10-20% in patients with cancer or infections. The anti-cancer properties of γδ T cells are multifaceted. These cells exert direct cytotoxicity through the release of perforin and granzyme B, as well as through the engagement of death receptor pathways. They also respond to metabolic and oxidative stress by recognizing ligands upregulated under malignant transformation via specific receptors. Furthermore, γδ T cells secrete cytokines including IFN-γ and TNF-α, which enhance dendritic cell maturation and macrophage activation, thereby amplifying broader immune responses. They also facilitate recruitment and activation of NK and αβ T cells, contributing to sustained antitumor immunity. In comparison to αβ T cells, γδ T cells are unique in their independence from MHC-restricted recognition, their rapid activation kinetics, and their low propensity to induce GvHD. While αβ T cells exist primarily within the blood and lymphoid organs, γδ T cells populate epithelial and tumor-associated tissues, granting them superior access to tumor microenvironments. Their immediate effector capabilities and resistance to exhaustion make them attractive candidates for engineered immunotherapies. Table 1. Comparison of γδ T Cells and Conventional αβ T Cells

Feature	γδ T Cells	Conventional αβ T Cells (CD4⁺ / CD8⁺)
Antigen Recognition	MHC-independent (stress ligands, phosphoantigens)	MHC-restricted peptide antigens
Tissue Distribution	Enriched in mucosa, skin, and tumor beds	Primarily blood and lymphoid organs
Activation Kinetics	Rapid, innate-like	Slower, antigen-dependent
GvHD Risk	Minimal	High in allogeneic settings
Effector Functions	Cytotoxicity and immunoregulation	Helper or cytotoxic depending on subset
Clinical Advantage	Universal donor potential and solid tumor penetration	Proven efficacy in hematologic malignancies

Chimeric Antigen Receptor (CAR) Structure Specific for γδ T Cells

The classical CAR structure consists of four principal elements: an extracellular single-chain variable fragment (scFv) responsible for antigen recognition, a hinge or spacer region that provides flexibility and determines synaptic geometry, a transmembrane domain that anchors the receptor, and intracellular signaling domains that initiate activation and costimulation. In αβ CAR-T cell platforms, the intracellular region typically combines the CD3ζ activation motif with one or more costimulatory domains, such as CD28 or 4-1BB, which influence effector function and persistence. However, γδ T cells exhibit distinct intracellular signaling architecture compared to αβ T cells. In addition to TCR-associated CD3 signaling, γδ T cells utilize adaptor proteins including DAP10, DAP12, and FcRγ, which mediate NK-like cytotoxic responses. They are also highly responsive to signals transmitted through NKG2D, CD16, and other activating receptors. These differences necessitate careful re-engineering of CAR constructs to align with γδ-specific signaling pathways. Conventional CAR designs optimized for αβ T cells may trigger excessive tonic signaling or suboptimal activation in γδ T cells, leading to premature exhaustion or limited cytotoxic potency. Recent innovations have introduced γδ-optimized CAR architectures that incorporate alternative costimulatory domains and NK-associated motifs to better synchronize with innate signaling. The use of DAP10 or 2B4 domains has been shown to enhance cytotoxic responses, while shortened hinge regions minimize nonspecific Fc interactions. Additionally, incorporating IL-15 transgenes improves persistence, and inclusion of NKG2D or CD16 transmembrane regions enhances receptor stability and signaling integration with innate pathways.

Antigenic Targets for CAR γδ T Cells

The targeting landscape for γδ CAR-T cells is characterized by their ability to integrate engineered antigen recognition with innate stress-ligand sensing. This dual-recognition feature reduces the risk of antigen escape and expands applicability to antigen-heterogeneous tumors. Studies have demonstrated effective targeting of classical tumor-associated antigens such as GD2, HER2, and EGFR. CAR γδ T cells targeting GD2 have shown potent activity in neuroblastoma and melanoma models, while HER2-directed constructs have induced tumor regression in breast and gastric cancer without severe off-tumor toxicity. EGFR and its mutant variant EGFRvIII have also served as viable targets in glioblastoma, where γδ T cells demonstrated superior infiltration and persistence relative to αβ CAR-T cells. Beyond traditional tumor-associated antigens, γδ CAR-T cells can engage stress-induced molecules. These ligands are frequently upregulated in malignant or metabolically stressed cells, providing a natural recognition axis that complements CAR specificity. Preclinical studies have further demonstrated the potential of dual-CAR systems, in which a tumor antigen-specific CAR is combined with a stress-ligand–responsive CAR, yielding enhanced clearance and reduced relapse in neuroblastoma models. Additionally, the application of γδ CAR-T cells in infectious disease prophylaxis has gained attention. Constructs targeting viral antigens such as cytomegalovirus (CMV) glycoprotein B and Epstein–Barr virus (EBV) gp350 have demonstrated antiviral activity in transplant models, highlighting their versatility beyond oncology. Table 2. Antigen Targets and Applications for CAR γδ T Cells

Antigen Type	Example Targets	Cancer Type / Model	Outcome
Tumor-associated	GD2, HER2, EGFR	Neuroblastoma, breast, glioblastoma	Strong cytotoxicity, reduced antigen escape
Stress-induced	MICA, MICB, ULBP	Multiple solid tumors	Enhanced innate recognition and killing
Dual-target	GD2 + MICA	Neuroblastoma	Superior tumor clearance and reduced relapse
Viral	EBV gp350, CMV gB	Post-transplant infection models	Reduced viral reactivation and relapse

Cellular Events During CAR γδ T Cell Effector Function

The effector dynamics of γδ CAR-T cells differ significantly from those of αβ CAR-T cells. Imaging studies have demonstrated that γδ CAR-T cells form immune synapses more rapidly and release cytotoxic granules with higher efficiency. This rapid response is attributed to their pre-armed state, which allows them to initiate cytolysis without prior antigen priming. Transcriptomic profiling has revealed that γδ CAR-T cells express lower levels of exhaustion-associated genes such as PD-1, LAG-3, and TOX, and exhibit superior mitochondrial function and glycolytic capacity. These features support their ability to sustain prolonged cytotoxic activity within nutrient-depleted and hypoxic tumor microenvironments. CAR γδ T cells also display improved migratory and infiltrative capabilities. Elevated expression of CXCR3 and CXCR4 enhances trafficking to inflamed and hypoxic tumor regions, while secretion of chemokines such as CCL3 and IFN-γ facilitates secondary immune recruitment. This ability to promote dendritic cell maturation and NK cell activation extends their impact beyond direct tumor lysis, contributing to a coordinated, multi-cellular antitumor immune response. Table 3. Cellular Effector Mechanisms of CAR γδ T Cells

Effector Mechanism	Key Molecules	Functional Advantage	Evidence
Rapid synapse formation	LFA-1, F-actin polarization	Accelerated tumor lysis	High-resolution microscopy
Reduced exhaustion	Low PD-1/TOX expression	Sustained cytotoxicity	Transcriptomic analysis
Enhanced infiltration	CXCR3, CXCR4	Improved penetration of hypoxic tumors	In vivo models
Immune recruitment	CCL3, IFN-γ	Dendritic and NK cell activation	Cytokine secretion assays

Next Steps for CAR γδ T Cells: Clinical Trials and Future Directions

The clinical development of CAR γδ T cell therapies has progressed rapidly, with several early-phase trials demonstrating encouraging safety and efficacy outcomes. In8bio’s INB-200 and INB-300 programs, which test autologous and allogeneic γδ CAR-T cells in glioblastoma and leukemia, have shown feasibility and early clinical responses. Adicet Bio’s ADI-001, a CD20-targeting γδ CAR-T product, achieved an overall response rate of 75% in patients with refractory B-cell lymphoma, marking one of the first successful demonstrations of γδ CAR-T efficacy in humans. Lava Therapeutics’ γδ engager bispecific antibodies (e.g., LAVA-051) further exemplify the translational potential of γδ-directed immunotherapies as intermediate steps toward fully engineered CAR platforms. Despite these promising advances, challenges remain. Standardized manufacturing remains a critical bottleneck. Enhancing persistence and tumor trafficking continues to be a central objective, with efforts focused on metabolic conditioning and chemokine receptor engineering. Ensuring safety through suicide switches and logic-gated CAR systems is essential for reducing the risk of on-target, off-tumor toxicity. The future of CAR γδ T cell therapy likely lies in universal, allogeneic products derived from iPSCs or edited peripheral blood cells. Such “off-the-shelf” platforms, when combined with combinatorial approaches involving checkpoint blockade, cytokine support, or oncolytic virus therapy, could offer scalable, durable, and cost-effective immunotherapy solutions.

Conclusion

CAR γδ T cell therapy integrates the innate tumor surveillance and immunoregulatory potential of γδ T cells with the targeted precision of chimeric antigen receptor engineering. Through advances in receptor design, expansion methodology, and translational development, this approach has emerged as one of the most promising frontiers in cancer immunotherapy. Unlike αβ CAR-T therapies, which face limitations in antigen escape, persistence, and allogeneic applicability, γδ CAR-T cells offer a universal, MHC-independent, and safer therapeutic option with demonstrated efficacy in both hematologic and solid tumor contexts. As clinical evidence accumulates and next-generation platforms evolve, γδ CAR-T cells are poised to redefine the boundaries of cellular immunotherapy by enabling broad, durable, and accessible cancer treatment. Table 4. Clinical trials of CAR γδ T-cell therapy

Trial name	Phase	Indication	CAR target / product	Cell source	Status
ADI-001 — allogeneic γδ T therapy	Phase 1	Relapsed / refractory B-cell malignancies (e.g., NHL, CLL)	ADI-001 (γδ T cell product; CAR-modified)	Allogeneic γδ T cells	Recruiting / Phase 1 dose-escalation (per registry).
Haplo/Allogeneic NKG2D-L targeting CAR-γδ cells (dose escalation)	Phase 1	Various advanced solid tumors / hematologic indications (dose escalation)	CAR targeting NKG2D ligands (NKG2DL) on tumor cells	Haplo/allogeneic CAR-γδ T cells	Active / dose escalation (registry record).
CTM-N2D — Allogeneic NKG2DL-targeting CAR γδ T cells	Early phase (I/first-in-human)	Advanced solid tumors (NKG2DL-expressing)	NKG2DL-targeted CAR on γδ T cells	Allogeneic	Registered / recruiting or not yet completed (registry listing).
Novel γδ T cell therapy (DRI) + temozolomide — glioblastoma	Phase 1/early	Glioblastoma (newly diagnosed or recurrent — combined with TMZ)	Modified γδ T cells	Autologous / modified γδ T cells (investigator record)	Active / safety trial (registry).

Disclaimer: This blog post is intended solely for educational and scientific informational purposes. Any mention of therapeutic drug names, including FDA-approved medications, is for the purpose of accurate reporting and discussion of biomedical research and does not constitute medical advice, endorsement, or promotion. Readers should not interpret the content as a recommendation for any specific treatment. Always consult a qualified healthcare professional for medical advice or treatment decisions.

About Marin Biologic Laboratories

Our Recent Publication/Meeting Presentation on Gene Therapy

1. Development of VNX-101, an Adeno-Associated Virus with Less Immunogenicity and Efficient Long-Term Expression of a CD19 T-Cell Engager. Molecular Therapy Methods & Clinical Development, published online July 24, 2025.

2. Development of a Pharmacokinetic (PK) Mouse Serum GLP ELISA for an Anti–CD19–AntiCD3 Diabody bioRxiv 2025.03.19.644217; doi: https://doi.org/10.1101/2025.03.19.644217.

3. Cell-Based Potency Assay for Anti-CD3-Anti-CD19 Diabody. bioRxiv 2025.04.15.648836v1 https://www.biorxiv.org/content/10.1101/2025.04.15.648836v1.

4. American Society of Hematology (ASH) Annual Meeting 2024. Abstract link: Using Gene Therapy to Solve Challenges with CAR-T Cell Immunotherapy: Lead Selection and Preclinical Development of an Adeno-Associated Virus with Reduced Immunogenicity Exhibiting Efficient and Long-Term Expression of an Anti-CD19 T-Cell Engager.

Comprehensive Assay Solutions for In Vitro and Cell Based Potency Assays and Pharmacokinetics Studies- Our Expertise

With 30 years of expertise in cell culture, cell-based assays, and preclinical/clinical PK/PD analysis, we specialize in offering assay services essential for a wide variety of therapeutic drug development programs, preclinical studies, IND/BLA applications, and commercialization. Our comprehensive services include both preclinical non-GLP and GLP assays, as well as non-GMP and GMP assays, providing critical support throughout the entire development pipeline. Watch the following video and explore our latest presentation on the development and validation of potency and pharmacokinetic (PK) assays for AAV vectors, highlighting innovative methodologies and industry-leading expertise.