CD45RB Status of CD8+ T Cell Memory Defines T Cell Receptor Affinity and Persistence

Low-affinity CD8+ T cells provide interclonal help to high-affinity CD8+ T cells to augment alloimmunity

Following solid organ transplantation, small precursor populations of polyclonal CD8+ T cells specific for any graft-expressed antigen preferentially expand their high-affinity clones. This phenomenon, termed "avidity maturation," results in a larger population of CD8+ T cells with increased sensitivity to alloantigen, posing a greater risk for graft rejection. Using a mouse model of minor-mismatched skin transplantation, coupled with the tracking of 2 skin graft-reactive CD8+ T cell receptor-transgenic tracer populations with high and low affinity for the same peptide-major histocompatibility complex, we explored the conventional paradigm that CD8+ T cell avidity maturation occurs through T cell receptor affinity-based competition for cognate antigen. Our data revealed "interclonal CD8-CD8 help," whereby lower/intermediate affinity clones help drive the preferential expansion of their higher affinity counterparts in an interleukin-2/CD25-dependent manner. Consequently, the CD8-helped high-affinity clones exhibit greater expansion and develop augmented effector functions in the presence of their low-affinity counterparts, correlating with more severe graft damage. Finally, interclonal CD8-CD8 help was suppressed by costimulation blockade treatment. Thus, high-affinity CD8+ T cells can leverage help from low-affinity CD8+ T cells of identical specificity to promote graft rejection. Suppressing provision of interclonal CD8-CD8 help may be important to improve transplant outcomes.

Interrogations of single-cell RNA splicing landscapes with SCASL define new cell identities with physiological relevance

RNA splicing shapes the gene regulatory programs that underlie various physiological and disease processes. Here, we present the SCASL (single-cell clustering based on alternative splicing landscapes) method for interrogating the heterogeneity of RNA splicing with single-cell RNA-seq data. SCASL resolves the issue of biased and sparse data coverage on single-cell RNA splicing and provides a new scheme for classifications of cell identities. With previously published datasets as examples, SCASL identifies new cell clusters indicating potentially precancerous and early-tumor stages in triple-negative breast cancer, illustrates cell lineages of embryonic liver development, and provides fine clusters of highly heterogeneous tumor-associated CD4 and CD8 T cells with functional and physiological relevance. Most of these findings are not readily available via conventional cell clustering based on single-cell gene expression data. Our study shows the potential of SCASL in revealing the intrinsic RNA splicing heterogeneity and generating biological insights into the dynamic and functional cell landscapes in complex tissues.

Local delivery of cell surface-targeted immunocytokines programs systemic anti-tumor immunity

Cytokine therapies are potent immunotherapy agents but exhibit severe dose-limiting toxicities. One strategy to overcome this involves engineering cytokines for intratumoral retention following local delivery. Here, we develop a localized cytokine therapy that elicits profound anti-tumor immunity by engineered targeting to the ubiquitous leukocyte receptor CD45. We designed CD45-targeted immunocytokines (αCD45-Cyt) that, upon injection, decorated the surface of leukocytes in the tumor and tumor-draining lymph node (TDLN) without systemic exposure. αCD45-Cyt therapy eradicated both directly treated tumors and untreated distal lesions in multiple syngeneic mouse tumor models. Mechanistically, αCD45-Cyt triggered prolonged pSTAT signaling and reprogrammed tumor-specific CD8+ T cells in the TDLN to exhibit an anti-viral transcriptional signature. CD45 anchoring represents a broad platform for protein retention by host immune cells for use in immunotherapy.

The Entangled World of Memory T Cells and Implications in Transplantation

Memory T cells that are specific for alloantigen can arise from a variety of stimuli, ranging from direct allogeneic sensitization from prior transplantation, blood transfusion, or pregnancy to the elicitation of pathogen-specific T cells that are cross-reactive with alloantigen. Regardless of the mechanism by which they arise, alloreactive memory T cells possess key metabolic, phenotypic, and functional properties that render them distinct from naive T cells. These properties affect the immune response to transplantation in 2 important ways: first, they can alter the speed, location, and effector mechanisms with which alloreactive T cells mediate allograft rejection, and second, they can alter T-cell susceptibility to immunosuppression. In this review, we discuss recent developments in understanding these properties of memory T cells and their implications for transplantation.

Identifying cancer-associated leukocyte profiles using high-resolution flow cytometry screening and machine learning

Background

Machine learning (ML) is a valuable tool with the potential to aid clinical decision making. Adoption of ML to this end requires data that reliably correlates with the clinical outcome of interest; the advantage of ML is that it can model these correlations from complex multiparameter data sets that can be difficult to interpret conventionally. While currently available clinical data can be used in ML for this purpose, there exists the potential to discover new "biomarkers" that will enhance the effectiveness of ML in clinical decision making. Since the interaction of the immune system and cancer is a hallmark of tumor establishment and progression, one potential area for cancer biomarker discovery is through the investigation of cancer-related immune cell signatures. Hence, we hypothesize that blood immune cell signatures can act as a biomarker for cancer progression.

Methods

To probe this, we have developed and tested a multiparameter cell-surface marker screening pipeline, using flow cytometry to obtain high-resolution systemic leukocyte population profiles that correlate with detection and characterization of several cancers in murine syngeneic tumor models.

Results

We discovered a signature of several blood leukocyte subsets, the most notable of which were monocyte subsets, that could be used to train CATboost ML models to predict the presence and type of cancer present in the animals.

Conclusions

Our findings highlight the potential utility of a screening approach to identify robust leukocyte biomarkers for cancer detection and characterization. This pipeline can easily be adapted to screen for cancer specific leukocyte markers from the blood of cancer patient.

Architecture of the SARS-CoV-2-specific T cell repertoire

The T cell response plays an indispensable role in the early control and successful clearance of SARS-CoV-2 infection. However, several important questions remain about the role of cellular immunity in COVID-19, including the shape and composition of disease-specific T cell repertoires across convalescent patients and vaccinated individuals, and how pre-existing T cell responses to other pathogens—in particular, common cold coronaviruses—impact susceptibility to SARS-CoV-2 infection and the subsequent course of disease. This review focuses on how the repertoire of T cell receptors (TCR) is shaped by natural infection and vaccination over time. We also summarize current knowledge regarding cross-reactive T cell responses and their protective role, and examine the implications of TCR repertoire diversity and cross-reactivity with regard to the design of vaccines that confer broader protection against SARS-CoV-2 variants.

Tetraspanin CD53 controls T cell immunity through regulation of CD45RO stability, mobility, and function

T cells depend on the phosphatase CD45 to initiate T cell receptor signaling. Although the critical role of CD45 in T cells is established, the mechanisms controlling function and localization in the membrane are not well understood. Moreover, the regulation of specific CD45 isoforms in T cell signaling remains unresolved. By using unbiased mass spectrometry, we identify the tetraspanin CD53 as a partner of CD45 and show that CD53 controls CD45 function and T cell activation. CD53-negative T cells (Cd53^-/-) exhibit substantial proliferation defects, and Cd53^-/- mice show impaired tumor rejection and reduced IFNγ-producing T cells compared with wild-type mice. Investigation into the mechanism reveals that CD53 is required for CD45RO expression and mobility. In addition, CD53 is shown to stabilize CD45 on the membrane and is required for optimal phosphatase activity and subsequent Lck activation. Together, our findings reveal CD53 as a regulator of CD45 activity required for T cell immunity.

A long-acting interleukin-7, rhIL-7-hyFc, enhances CAR T cell expansion, persistence, and anti-tumor activity

Chimeric antigen receptor (CAR) T cell therapy is routinely used to treat patients with refractory hematologic malignancies. However, a significant proportion of patients experience suboptimal CAR T cell cytotoxicity and persistence that can permit tumor cell escape and disease relapse. Here we show that a prototype pro-lymphoid growth factor is able to enhance CAR T cell efficacy. We demonstrate that a long-acting form of recombinant human interleukin-7 (IL-7) fused with hybrid Fc (rhIL-7-hyFc) promotes proliferation, persistence and cytotoxicity of human CAR T cells in xenogeneic mouse models, and murine CAR T cells in syngeneic mouse models, resulting in long-term tumor-free survival. Thus, rhIL-7-hyFc represents a tunable clinic-ready adjuvant for improving suboptimal CAR T cell activity.

IL4I1 Accelerates the Expansion of Effector CD8+ T Cells at the Expense of Memory Precursors by Increasing the Threshold of T-Cell Activation

IL4I1 is an immunoregulatory enzyme that inhibits CD8 T-cell proliferation in vitro and in the tumoral context. Here, we dissected the effect of IL4I1 on CD8 T-cell priming by studying the differentiation of a transgenic CD8 T-cell clone and the endogenous repertoire in a mouse model of acute lymphocytic choriomeningitis virus (LCMV) infection. Unexpectedly, we show that IL4I1 accelerates the expansion of functional effector CD8 T cells during the first several days after infection and increases the average affinity of the elicited repertoire, supporting more efficient LCMV clearance in WT mice than IL4I1-deficient mice. Conversely, IL4I1 restrains the differentiation of CD8 T-cells into long-lived memory precursors and favors the memory response to the most immunodominant peptides. IL4I1 expression does not affect the phenotype or antigen-presenting functions of dendritic cells (DCs), but directly reduces the stability of T-DC immune synapses in vitro, thus dampening T-cell activation. Overall, our results support a model in which IL4I1 increases the threshold of T-cell activation, indirectly promoting the priming of high-affinity clones while limiting memory T-cell differentiation.

Relationship of 2D Affinity to T Cell Functional Outcomes

T cells are critical for a functioning adaptive immune response and a strong correlation exists between T cell responses and T cell receptor (TCR): peptide-loaded MHC (pMHC) binding. Studies that utilize pMHC tetramer, multimers, and assays of three-dimensional (3D) affinity have provided advancements in our understanding of T cell responses across different diseases. However, these technologies focus on higher affinity and avidity T cells while missing the lower affinity responders. Lower affinity TCRs in expanded polyclonal populations almost always constitute a significant proportion of the response with cells mediating different effector functions associated with variation in the proportion of high and low affinity T cells. Since lower affinity T cells expand and are functional, a fully inclusive view of T cell responses is required to accurately interpret the role of affinity for adaptive T cell immunity. For example, low affinity T cells are capable of inducing autoimmune disease and T cells with an intermediate affinity have been shown to exhibit an optimal anti-tumor response. Here, we focus on how affinity of the TCR may relate to T cell phenotype and provide examples where 2D affinity influences functional outcomes.

CD45: a critical regulator in immune cells to predict severe and non-severe COVID-19 patients

The ongoing outbreak of COVID-19 has been announced by the World Health Organization as a worldwide public health emergency. The aim of this study was to distinguish between severe and non-severe patients in early diagnosis. The results showed that the mortality of COVID-19 patients increased accompanied by age. Host factors CRP, IL-1β, hs-CRP, IL-8, and IL-6 levels in severe pneumonia patients were higher than in non-severe patients. CD3, CD8, and CD45 counts were decreased in COVID-19 patients. The results of this study suggest that the K-values of CD45 might be useful in distinguishing between severe and non-severe cases. The cut-off value for CD45 was -94.33. The K-values for CD45 in non-severe case were above the cut-off values, indicating a 100% prediction success rate for severe and non-severe cases following SARS-CoV-2 infection. The results confirmed that immune system dysfunction is a potential cause of mortality following COVID-19 infection, particularly for the elderly. CD45 deficiency dysfunction the naïve and memory T lymphocytes which may affects the long-term effectiveness of COVID-19 vaccines. K-values of CD45 might be useful in distinguishing between severe and non-severe cases in the early infection. May be CD45 could increase the diagnostic sensitivity.

T-cell repertoire analysis and metrics of diversity and clonality

The recent developments of high-throughput bulk and single-cell sequencing technologies accelerated the understanding of the complexity of immune repertoire dynamics combined to transcriptomics. Also, profiling of cellular repertoires in health or disease requires statistical metrics to capture clonal diversity characterized by clones frequency, repertoire richness and convergence. Here we present the common technologies of bulk and single-cell sequencing of T-cell receptors (TCRs), discuss current knowledge regarding computational tools clustering and predicting specificity of TCR repertoires based on shared structural motifs and review main indices for repertoire diversity and convergence analyses. These tools represent potential biomarkers to decipher the fitness of immune repertoires in diseased or treated patients but also the presages and promises of computational approaches to revolutionize personalized immunotherapy.

P2X7 Receptor at the Crossroads of T Cell Fate

The P2X7 receptor is a ligand-gated, cation-selective channel whose main physiological ligand is ATP. P2X7 receptor activation may also be triggered by ARTC2.2-dependent ADP ribosylation in the presence of extracellular NAD. Upon activation, this receptor induces several responses, including the influx of calcium and sodium ions, phosphatidylserine externalization, the formation of a non-selective membrane pore, and ultimately cell death. P2X7 receptor activation depends on the availability of extracellular nucleotides, whose concentrations are regulated by the action of extracellular nucleotidases such as CD39 and CD38. The P2X7 receptor has been extensively studied in the context of the immune response, and it has been reported to be involved in inflammasome activation, cytokine production, and the migration of different innate immune cells in response to ATP. In adaptive immune responses, the P2X7 receptor has been linked to T cell activation, differentiation, and apoptosis induction. In this review, we will discuss the evidence of the role of the P2X7 receptor on T cell differentiation and in the control of T cell responses in inflammatory conditions.