Commentary on “Comparative efficacy and safety of PSCA CAR-engineered Vδ1 γδ T cells for immunotherapy of pancreatic cancer”

Abstract

Adoptive transfer of unmodified γδ T cells has shown limited clinical benefit, prompting a shift toward chimeric antigen receptor (CAR) engineering to enhance activation, persistence, and tumor specificity. CAR technology positions γδ T cells as promising carriers due to their innate-like cytotoxicity and HLA-independent recognition. Evidence from αβ CAR T-cell trials indicates that γδ CAR T cells can persist for months to years post-infusion, suggesting their potential contribution to long-term immune surveillance against cancer. Among γδ subsets, Vγ9Vδ2 T cells dominate peripheral blood and have been preferentially used for CAR engineering. Recent advances, however, enable the expansion of Vδ1 T cells, known for their tissue residency and resistance to exhaustion. In a key comparative study, Li et al benchmarked PSCA-targeted CARs in Vδ1, Vγ9Vδ2, and αβ T cells, showing similar short-term tumor control but distinct transcriptional and phenotypic programs. These findings highlight the need for subset-specific optimization of γδ CAR-T therapies. Early studies in hematologic malignancies could provide a practical proof of concept, before tackling the additional challenges of solid tumors. Such focused development may be essential to advance the γδ CAR-T field amid tightening industry investment.

Given the limited clinical activity observed with adoptively transferred natural γδ T cells, the field has shifted toward engineering strategies that provide both additional activation signals and tumor antigen specificity through CARs.¹ The introduction of CAR technology has emerged as a promising strategy to enhance γδ T-cell potency and redirect their activity toward tumor cells, thereby transforming them into highly effective antitumor effectors.^{1 2} Interestingly, accumulating evidence suggests that γδ T cells may contribute to long-term CAR-T cell persistence when primary αβ T cells are engineered without prior selection for CD4⁺ or CD8⁺ subsets. Given that peripheral blood contains 1–10% γδ T cells, predominantly of the Vγ9Vδ2 subtype, these cells become transduced during manufacturing and potentially persist after infusion. Indeed, two clinical studies of conventional αβ T cell-derived CAR-T products have reported γδ CAR-T cells persisting from months to years post-infusion. In one anti-CD19 CAR-T trial, γδ CAR-T cells were detected both early (2.5 months) and at long-term follow-up (7.2 years), expressing cytotoxic markers such as granzyme B, CD57, and T-bet, consistent with sustained effector function.³ A similar finding was reported in another pediatric anti-CD19 CAR-T study, where γδ CAR-T cells were observed at early post-infusion time points in a subset of patients.⁴ Although the clinical relevance of these populations remains to be fully understood, their persistence raises important questions about their contribution to therapeutic outcomes, and has fueled growing interest in γδ T cells as carriers for CAR constructs, positioning them as promising candidates for next-generation allogeneic CAR-T cell products.¹ Their HLA-independent antigen recognition and innate-like cytotoxicity¹ underscore their potential as an “off-the-shelf” cell therapy platform, with a reduced risk of graft-versus-host disease, although some γδ T cells have been reported to exhibit allo-HLA reactivity.⁵ Moreover, γδ T-cell infiltration into tumors has been associated with improved prognosis across multiple cancer types.⁶ However, it is important to acknowledge that sustained persistence remains a major challenge for allogeneic CAR-T cell therapies, largely due to host-versus-graft immune responses that do not occur in autologous settings.

Adoptive transfer of unmodified γδ T cells has historically relied on expansion protocols that start with unselected γδ T cells, and use bisphosphonates to promote proliferation. Given the higher frequency of Vγ9Vδ2 γδ T cells in peripheral blood, and the nature of stimulating agents during most expansion protocols,¹ these approaches typically result in a predominant expansion of the Vγ9Vδ2 subset. Consequently, most CAR-engineering studies progressing to clinic have used highly enriched Vγ9Vδ2 γδ T cells as carriers (table 1). The heterogeneous composition of bulk γδ T-cell products can, however, lead to variability in function, persistence, and manufacturing consistency,⁷ whereas subset-defined approaches aim to improve product standardization and predictability. Therefore, some studies have chosen to purify Vγ9Vδ2 γδ T cells before engineering. In addition, more recently, the development of dedicated expansion technologies for Vδ1 γδ T cells has enabled the extension of CAR engineering strategies to this subset.⁸ This is also reflected by the relatively small number of clinical studies using Vδ1 γδ T cells as carriers so far. To date, however, only very limited head-to-head comparisons have been conducted^{9 10} to determine which γδ T-cell carrier type may offer a higher likelihood of clinical success, or how these compare to αβ T cells, which are still the gold standard carriers, due to their clinical success. Within this context, the study by Li et al provides important new insights by performing in vivo benchmarking of Vδ1, Vγ9Vδ2, and conventional αβ T cells engineered with a PSCA-targeted CAR. The results demonstrated comparable tumor control in a pancreatic cancer model, indicating that, at least in terms of short-term tumor control, all carrier types exhibit equivalent potency.¹¹ These findings further imply that in studies reporting long-term tumor control after engineering αβ T cells, where CAR-transduced γδ T cells were also detected at low frequency before infusion,^{3 4} the persisting Vδ1 CAR-T cells may not merely represent residual, functionally inert cells that survived the treatment process. Rather, they might have been actively involved in the initial antitumor response, although at low frequency, and subsequently maintained as long-lived effector or memory-like populations. This notion is further supported by studies in disease-free survivors of acute leukemia following allogeneic bone marrow transplantation, where increased frequencies of γδ T cells have been observed (reviewed in studies by Beringer et al and Janssen et al^{1 2}). These findings highlight the potential role of γδ T cells in sustaining long-term immune persistence, making them attractive candidates for CAR-T cell therapy.

Table 1. Preclinical and clinical studies exploring γδ CAR-T cell therapy. The studies in green explore γδ CAR-T cell therapy in hematological malignancies, those in red explore solid tumors, and those in blue explore γδ CAR-T cell therapy in both.

Cell source	Hematological or solid malignancy	Mode of action/ target	Co-administration	Phase	Name/program	Clinical identifier
Highly enriched Vγ9Vδ2 γδ T cell
Allogeneic	Relapsed or refractory B-cell malignancies	Anti-CD19 CAR	NA	Phase 1	UTAA09	NCT06092047 (ref.18)
Allogeneic	Relapsed or refractory multiple myeloma	Anti-BCMA CAR	NA	Phase 1 (recruiting)	UTAA17	NCT06279026 (ref.19)
Allogeneic	Relapsed or refractory B-cell acute lymphoblastic leukemia	Anti-CD19 CAR	NA	Phase 1 (recruiting)	QH103	NCT06056752 (ref.20)
Allogeneic	Relapsed or refractory B-cell non-Hodgkin’s lymphoma	Anti-CD19 CAR	NA	Phase 1/2 (recruiting)	CHN-PLAGH-BT-072	NCT05554939 (ref.21)
Allogeneic	Relapsed or refractory B-cell non-Hodgkin’s lymphoma	Bispecific anti-CD19 and anti-CD20 CAR	NA	Phase 1 (recruiting)	LUCAR-G39D	NCT06395870 (ref.22)
Allogeneic	Relapsed or refractory T-cell-derived malignancies	Anti-CD7 CAR	NA	Phase 1	PA3-17	NCT05170568 (ref.23)
Allogeneic	Relapsed or refractory AML	Anti-CD123 CAR	NA	Phase 1	CAR-γδT cell for AML	NCT04796441/NCT05388305 (ref.24 25)
Allogeneic	Relapsed or refractory T-cell acute lymphoblastic leukemia	Anti‑CD38 CAR	NA	Preclinical	Anti-CD38KO/CD38-CAR γδ T cells	NA (ref. 26)
Allogeneic	Advanced hematological or solid malignancies	Anti-NKG2D ligand CAR	NA	Phase 1 (recruiting /early stage)	CTM‑N2D	NCT05302037 (ref.27)
Allogeneic	Advanced malignant solid tumors	Anti-NKG2D ligand CAR	NA	Phase 1 (completed)	UTAA06	NCT06372236 (ref.28)
Allogeneic	Relapsed/refractory triple-negative breast cancer, non-small cell lung cancer, colorectal cancer, glioblastoma	Anti-HLA-G CAR	NA	Phase 1/2 (recruiting)	CAR001	NCT06150885 (ref.29)
Allogeneic/haploidentical	Relapsed or refractory solid tumors	Anti-NKG2D ligand CAR	NA	Phase 1	CTM-N2D-101	NCT04107142 (ref.30)
Allogeneic	Malignant brain glioma and meningeal metastasis	Anti-B7H3 CAR	NA	Phase 1/2 (recruiting)	QH104	NCT06018363/NCT06592092 (ref.31 32)
Autologous	GPC3/mesothelin expressing solid tumors	Anti-GPC3/mesothelin CAR	PD-1/PDL-1/CTLA-4 antibodies	Phase 1 (recruiting)	GPC3/Mesothelin-CAR	NCT06196294 (ref.33)
Autologous	End-stage metastatic castration-resistant prostate cancer	Anti-PSCA γδ 8t28Z CAR	NA	Phase 1 (recruiting)	MSGV1-PSCA-8T28Z	NCT06193486 (ref.34)
Allogeneic	Multiple myeloma	Anti-folate receptor-α CAR	NA	Preclinical	Anti‑CD38‑CAR γδ T cells	NA (ref.35)
Allogeneic	Triple-negative breast cancer	Anti-MCSP CAR	NA	Preclinical	7×19 CAR-γδtγδ	NA (ref.36)
Allogeneic	Melanoma	Anti-CD123 CAR	NA	Preclinical	MCSP-CAR	NA (ref.37)
Allogeneic	Neuroblastoma	Anti-GD2 CAR	NA	Preclinical	GD2 CAR γδ (Vδ1/Vδ2)	NA (ref.10)
Vδ2 γδ T cells
Allogeneic	B-cell malignancies	Anti-CD20 CAR	NA	Phase 1 (terminated)	ADI-001	NCT04735471 (ref38)
Allogeneic	Neuroblastoma	Anti-GD2 CAR	NA	Preclinical	GD2-DAP10 CAR	NA (ref.39 40)
Allogeneic	Solid tumors	Anti-MUC1-Tn CAR	NA	Preclinical	MUC1‑Tn CAR γδ T cells	NA (ref.9)
Allogeneic	NKG2D ligand positive tumors	Anti-NKG2D CAR	NA	Preclinical	NKG2Dz-CAR	NA (ref.41)
Vδ1 γδ T cells
Allogeneic	Relapsed or refractory AML	Anti-CD123 CAR	NA	Preclinical	CD123CAR-DOT	NA (ref.8)
Allogeneic	Relapsed or renal cell carcinoma	Anti-CD70 CAR	NA	Phase 1/2	ADI-270	NCT06480565 (ref.42)
Allogeneic	Hepatocellular carcinoma	Anti-glypican-3 CAR+sIL15	NA	Preclinical	ADI-200	NA (ref.43)
Allogeneic	Multiple solid tumors	Anti-B7H3 CAR	IL-2 co-expression	Preclinical	B7‑H3‑CAR Vδ1	NA (ref.44)

AML, acute myeloid leukemia; CAR, chimeric antigen receptor; CTLA-4, cytotoxic T-lymphocytes-associated protein 4; IL, interleukin; PD-1, programmed cell death protein-1; PD-L1, programmed death-ligand 1.

The capacity of engineered T cells to persist long-term as guardians against cancer may be important not only in diseases such as acute lymphoblastic leukemia, but also in more complex malignancies characterized by high tumor heterogeneity and a strongly immunosuppressive microenvironment, such as multiple myeloma. In these settings, early loss of circulating CAR-T cells has been associated with a significantly increased risk of relapse, underscoring the central role of CAR-T cell persistence in maintaining therapeutic efficacy.¹² However, the concept of memory γδ T cells is less well explored compared with αβ T cells, partly because many circulating human γδ T cells already exhibit an effector, or terminally differentiated phenotype.^{1 2} Single-cell transcriptomic studies provided further evidence that engineered memory cells may be important for improving clinical outcomes. For example, single-cell longitudinal analyses have highlighted transcriptional signatures associated with persistent CAR-T cells in multiple myeloma, revealing that long-lived CAR-T cells display memory-like transcriptional features, increased clonality, and enhanced metabolic fitness. Moreover, these persistent populations exhibit reduced expression of exhaustion-related genes¹³ and modulation of co-stimulatory signaling has shown that transcriptional states can be reshaped and linked to distinct functional outcomes in mouse models.¹⁴ The study by Li et al now adds comparative data for PSCA CAR-engineered Vδ1 and Vγ9Vδ2 γδ T cells, revealing distinct transcriptional programs. The authors observed a more balanced immunophenotype for Vδ1 γδ T cells, characterized by strong expression of cytotoxic markers, downregulation of immune checkpoint molecules (eg, programmed cell death protein-1), and retention of memory subsets, consistent with a less differentiated and less exhausted phenotype. However, this did not translate into a significantly increased efficacy of Vδ1 CAR-T cells in mouse models,¹¹ raising the question of whether these transcriptional differences, are truly relevant for in vivo behavior. Nonetheless, mouse models cannot fully recapitulate the complex tumor microenvironment or the dynamics of long-term memory formation observed in humans. Moreover, the type of mouse model used can substantially influence experimental outcomes. For example, in a study of MUC1-Tn-targeting Vγ9Vδ2 CAR-T cells, the killing capacity against breast cancer cell lines was similar between conventional αβ CAR-T cells and Vγ9Vδ2 CAR-T cells, while the Vγ9Vδ2 CAR-T cells were more potent against gastric tumor cell lines. Yet, αβ CAR-T cells demonstrated superior persistence on in vitro restimulation.⁹

Together, these studies indicate that Vδ1 CAR-T cells often display a more favorable balance between effector function, persistence, and resistance to exhaustion, whereas Vγ9Vδ2 CAR-T cells achieve rapid cytotoxic responses, but may require additional support to sustain activity. These differences highlight the need to analyze Vδ1 and Vγ9Vδ2 CAR-T cells separately, rather than treating γδ T cells as a uniform population. Understanding their distinct biology is essential for optimizing γδ CAR-T cell design and translation, for instance, favoring Vδ1 γδ T cells for solid tumors where persistence and infiltration are critical, and Vγ9Vδ2 γδ T cells for hematologic malignancies where rapid expansion is advantageous. However, compared with bulk γδ T-cell products, such subset-specific approaches introduce practical challenges, including increased manufacturing complexity, higher costs, and regulatory hurdles. Moreover, intrinsic differences in starting frequency, expansion kinetics, and transduction efficiency complicate direct potency comparisons. Vδ1 γδ T cells may be particularly advantageous in autologous settings (eg, acute lymphoblastic leukemia), where long-term persistence is critical for tumor eradication.³ In contrast, both Vδ1 and Vγ9Vδ2 subsets may be suitable for allogeneic products, with subset-specific homing guiding tumor selection. For example, glioblastoma is enriched for Vγ9Vδ2 γδ T cells¹⁵ and might benefit from using engineered Vγ9Vδ2 γδ T cells, whereas other solid tumors, such as prostate cancer, are predominantly infiltrated by Vδ1 γδ T cells¹ and may preferentially benefit from engineered Vδ1 γδ T cells as reported by Li et al.¹¹

For clinical development, the relevance of long-term persistence may be particularly important when autologous products are used. Whether this benefit also extends to allogeneic “off-the-shelf” products remains questionable, as these are typically rapidly rejected by the host immune system. In allogeneic “off-the-shelf” settings, where γδ CAR-T cells are intended to provide transient antitumor activity, limited persistence may not be disadvantageous. Instead, short-lived but potent responses could enhance safety and enable redosing strategies. Another important consideration is the disease context for early clinical testing. Demonstrating efficacy in hematologic malignancies or autoimmune diseases could offer a feasible proof of concept for γδ CAR T therapy, either autologous or allogeneic, before addressing the additional challenges of solid tumors, such as antigen heterogeneity, immune exclusion, and an immunosuppressive microenvironment. Establishing success in a controlled setting with αβ T cells as proven carriers, particularly those engineered for allogeneic use with αβ T cell receptor (TCR) knockout,¹⁶ may therefore accelerate confidence, clinical acceptance, and investment in this platform. Given the current financial headwinds in the engineering T-cell therapy field, illustrated by the withdrawal of several industrial pipelines, including Takeda’s discontinuation of its γδ T-cell therapy program (https://www.oncologypipeline.com/apexonco/takedas-cancer-prospects-dim-further), prioritizing lower-risk, high-impact indications may be critical to sustaining momentum, and validating the platform’s clinical potential. This consideration is especially important if academic pharma needs to take the first successful steps.¹⁷

In conclusion, the comparative preclinical study by Li et al¹¹ represents an important step forward for γδ CAR-T cell development. By directly comparing Vδ1, Vγ9Vδ2, and αβ T-cell carriers, it provides valuable insight into subset-specific strengths and limitations that bulk γδ T-cell approaches cannot reveal. Extending such comparative studies into both hematologic and solid tumor models, and ultimately into early-phase clinical trials, will be key to defining the optimal indications, persistence profiles, and manufacturing strategies for next-generation γδ CAR-T therapies.