Clonal expansion in the Vγ9+Vδ2+ γδ T cell compartment is associated with pyrophosphate metabolite hyporesponsiveness

Human Vγ9+Vδ2+ T cells are traditionally viewed as an innate-like population that responds rapidly to microbial pyrophosphate metabolites (PAgs). However, functional heterogeneity within this compartment is often observed. This study investigates the biological basis for this diversity, specifically focusing on why some Vγ9+Vδ2+ T cells become hyporesponsive to PAg stimulation.

Using a combination of flow cytometry, single-cell TCR sequencing, and transcriptomic profiling, the researchers analyzed Vγ9+Vδ2+ T cell subsets from healthy donors, children in malaria-endemic regions (Mali), and patients undergoing HCMV-associated clinical events (kidney and stem cell transplants). They utilized TCR-transduced cell lines to isolate the functional impact of specific TCR sequences on PAg reactivity and employed structural modeling to understand how TCR-butyrophilin interactions are affected by clonal expansion.

The researchers identified a distinct subset of Vγ9+Vδ2+ T cells defined by a CD27-CD28-CD16+ phenotype. These cells are characterized by highly focused, clonal TCR repertoires and a unique transcriptional signature enriched for cytotoxic and NK-related genes (e.g., perforin, granzyme B) while lacking granzyme K. Functional assays revealed that these CD16+ cells are intrinsically hyporesponsive to PAg stimulation. Structural analysis suggests that this reduced reactivity is linked to specific CDR3δ loop characteristics that hinder effective engagement with the BTN3A1/BTN3A2 complex. Furthermore, this phenotype is shaped by environmental factors; CD16+ Vγ9+Vδ2+ T cells are enriched in the gut and expand in response to chronic infections like malaria and HCMV, suggesting they represent an adaptive-like differentiation state within the γδ T cell compartment.

This study challenges the paradigm that Vγ9+Vδ2+ T cells are a purely invariant, innate-like population. By identifying a specific, clonally expanded, and hyporesponsive subset, the findings provide a framework for understanding how chronic infections and environmental exposures reprogram γδ T cell functionality. This has significant implications for the development of γδ T cell-based immunotherapies and vaccines, as the presence of these hyporesponsive cells may limit the efficacy of treatments relying on PAg-mediated activation.