Mapping the Developmental Trajectories and TCR Repertoire of SAP-Dependent Innate-Like Gamma Delta (γδ) T Cells

Core Concepts

SLAM-associated protein (SAP) regulates the developmental programming and TCR repertoire of innate-like gamma delta (γδ) T cell subsets, including γδT17, γδT1, and γδNKT cells, at multiple checkpoints during thymic development.

Abstract

The study used a single-cell proteogenomics approach to comprehensively map the developmental trajectories and TCR repertoire of innate-like γδ T cells in the thymus and lungs of wild-type (B6) and SAP-deficient (B6.SAP-/-) mice.
Key insights:

In the embryonic day 17 (E17) thymus, SAP deficiency resulted in a significant loss of an immature Gzma+Blk+Etv5+Tox2+ γδT17 precursor population, and a concomitant increase in CD4+CD8+ Rorc+Ptcra+Rag1+ thymic γδ T cells, suggesting SAP promotes entry into the γδT17 pathway while inhibiting diversion into the αβ T cell-like pathway.
SAP-dependent alterations in thymic γδ T cell development were associated with changes in the TCR repertoire, including decreased frequencies of TRGV4/TRDV5 clonotypes in the mature γδT17 population and their increased presence in the αβ T cell-like population.
In the neonatal thymus, SAP deficiency led to decreased frequencies of immature BLK+RORγt+ γδT17 precursors, increased immature S1pr1+ γδ T cells, and a near-complete loss of mature γδNKT and non-γδNKT γδT1 cells.
In the adult lung, innate-like γδT1 and γδT17 cells exhibited highly restricted TCR repertoires, with Vγ4 γδT1 cells preferentially using TRAV13-4(DV7) and Vγ6 γδT17 cells using TRGV6/TRDV4. These restricted TCR repertoires were disrupted in the absence of SAP.
Together, these data demonstrate that SAP-dependent regulation of γδ T cell developmental programming shapes the innate-like TCR repertoire in the thymus and periphery.

Stats

SAP deficiency resulted in a significant decrease in the frequency of the immature CD24pos BLKpos MAFpos RORγtpos γδT17 precursor population in the E17 thymus.
The frequency of CD4+CD8+ Rorc+Ptcra+Rag1+ thymic γδ T cells was significantly increased in B6.SAP-/- mice compared to B6 mice at E17.
In the neonatal thymus, the frequency of the immature CD24pos BLKneg RORγtpos γδ T cell population was significantly increased in B6.SAP-/- mice.
The frequencies of mature γδNKT (Zbtb16+, Icos+, Il4+) and non-γδNKT γδT1 (Tbx21+, Slamf7+, Il2rb+) cells were dramatically decreased in the adult B6.SAP-/- thymus compared to B6.

Quotes

"SAP deficiency resulted in both a significant loss of an immature Gzma+Blk+Etv5+Tox2+ γδT17 precursor population, and a significant increase in Cd4+Cd8+ Rorc+Ptcra+Rag1+ thymic γδ T cells."
"SAP-dependent diversion of embryonic day 17 thymic γδ T cell clonotypes into the αβ T cell developmental pathway was associated with a decreased frequency of mature clonotypes in neonatal thymus, and an altered γδ TCR repertoire in the periphery."
"Innate-like γδT1 and γδT17 cells exhibited highly restricted TCR repertoires, with Vγ4 γδT1 cells preferentially using TRAV13-4(DV7) and Vγ6 γδT17 cells using TRGV6/TRDV4. These restricted TCR repertoires were disrupted in the absence of SAP."

Key Insights Distilled From

SLAM/SAP signaling regulates discrete γδ T cell developmental checkpoints and shapes the innate-like γδ TCR repertoire

by Mistri,S. K.... at www.biorxiv.org 01-12-2024

https://www.biorxiv.org/content/10.1101/2024.01.10.575073v2

Deeper Inquiries

How might the SAP-dependent alterations in thymic γδ T cell development and TCR repertoire impact the functional capabilities of peripheral γδ T cell subsets in response to pathogens, tumors, and autoimmunity?

The SAP-dependent alterations in thymic γδ T cell development and TCR repertoire can have significant implications for the functional capabilities of peripheral γδ T cell subsets. For instance, the observed changes in the developmental checkpoints of γδT17 and γδT1 subsets in the thymus, as well as the altered TCR repertoire, can influence the differentiation and activation of these subsets in the periphery.
In the context of pathogens, the skewed development of γδT17 and γδT1 subsets due to SAP deficiency may lead to impaired immune responses. γδT17 cells are crucial for mucosal immunity and defense against certain pathogens, particularly those that require IL-17-mediated responses. A disruption in the development of these cells could compromise the host's ability to mount an effective immune response against such pathogens. On the other hand, alterations in the γδT1 subset, which is associated with IFN-γ production, could impact the immune response to intracellular pathogens and tumors.
Moreover, changes in the TCR repertoire, such as the loss of specific clonotypes associated with γδNKT cells, can affect the recognition and response to antigens presented by these subsets. This could result in a diminished ability to recognize and eliminate infected or transformed cells, leading to compromised immune surveillance against pathogens and tumors. Additionally, the altered TCR repertoire may also impact the development of autoimmune responses by affecting the recognition of self-antigens.

How might the SAP-dependent alterations in thymic γδ T cell development and TCR repertoire impact the functional capabilities of peripheral γδ T cell subsets in response to pathogens, tumors, and autoimmunity?

The SLAM/SAP axis is a critical signaling pathway that regulates the development and function of innate-like γδ T cell subsets. In addition to SLAM/SAP, other signaling pathways and transcriptional regulators may interact to fine-tune the developmental programming of these γδ T cell subsets. Some of the key players that might interact with the SLAM/SAP axis include:

Notch Signaling: Notch signaling has been implicated in γδ T cell development and differentiation. It may synergize with SLAM/SAP signaling to regulate the expression of key transcription factors and cytokines involved in γδ T cell lineage commitment.

TCR Signaling: The TCR signaling pathway plays a crucial role in γδ T cell activation and effector functions. Cross-talk between TCR signaling and SLAM/SAP signaling pathways may coordinate the development and function of γδ T cell subsets.

Transcription Factors: Transcription factors like T-bet, GATA3, and RORγt are known to regulate the differentiation of γδ T cell subsets. Interactions between these transcription factors and the SLAM/SAP axis could modulate the fate and function of γδ T cells.

Cytokine Signaling: Cytokines such as IL-23, IL-4, and IL-17 are critical for the polarization and effector functions of γδ T cell subsets. The interplay between cytokine signaling pathways and SLAM/SAP signaling may shape the immune response mediated by γδ T cells.

By integrating signals from these pathways and regulators, the SLAM/SAP axis can orchestrate the development and function of innate-like γδ T cell subsets in a precise and coordinated manner.

How might the SAP-dependent changes in γδ T cell development and TCR repertoire influence the host response at barrier sites like the skin, gut, and lungs?

The SAP-dependent changes in γδ T cell development and TCR repertoire can have a profound impact on the host response at barrier sites like the skin, gut, and lungs, where γδ T cells play a crucial role in mucosal immunity. These changes can influence the host response in the following ways:

Skin Immunity: In the skin, γδ T cells are involved in wound healing, tissue repair, and defense against pathogens. SAP-dependent alterations in γδ T cell development may affect the balance between protective immune responses and tissue homeostasis in the skin. Changes in the TCR repertoire could impact the recognition of skin-specific antigens and the immune response to cutaneous pathogens.

Gut Immunity: γδ T cells in the gut mucosa are essential for maintaining intestinal homeostasis, regulating immune responses, and protecting against pathogens. SAP-dependent changes in γδ T cell development may disrupt the balance of regulatory and effector γδ T cell subsets in the gut, leading to dysregulated immune responses and increased susceptibility to gut-related disorders.

Lung Immunity: In the lungs, γδ T cells play a critical role in immune surveillance, defense against respiratory pathogens, and tissue repair. Alterations in γδ T cell development and TCR repertoire due to SAP deficiency could impact the immune response to lung infections, inflammatory lung diseases, and respiratory allergens.

Overall, the SAP-dependent changes in γδ T cell development and TCR repertoire can influence the host response at barrier sites by modulating the function, activation, and specificity of γδ T cell subsets involved in mucosal immunity. These alterations may have implications for immune protection, inflammatory responses, and tissue repair at barrier sites in the body.