CD8(+) T cell anergy is a critical mechanism of peripheral tolerance, poorly investigated in response to immunotherapy. Here, using a pancreatic islet allograft model and CD3 antibody therapy, we ...showed, by single cell gene profiling, that intragraft CD8(+) lymphocytes coexpressing granzyme B and perforin were selectively depleted through the Fas/FasL pathway. This step led to long-standing anergy of the remaining CD8(+) T cells marked by the absence of cytotoxic/inflammatory gene expression also confirmed by transcriptome analysis. This sustained unresponsiveness required the presence of the alloantigens. Furthermore, tissue-resident CD8(+) lymphocytes produced TGFβ and expressed the inhibitory receptors PD-1 and PD-L1. Blockade of TGFβ downregulated PD-1 and PD-L1 expression and precipitated graft rejection. Neutralizing PD-1, PD-L1 or TGFβRII signaling in T cells also abrogated CD3 antibody-induced tolerance. These studies unravel novel mechanisms underlying CD8(+) T cell anergy and reveal a cell intrinsic regulatory link between the TGFβ and the PD-1/PD-L1 pathways.
CD4+ T cell help to CD8+ T cell responses requires that CD4+ and CD8+ T cells interact with the same antigen presenting dendritic cell (Ag+DC), but it remains controversial whether helper signals are ...delivered indirectly through a licensed DC and/or involve direct CD4+/CD8+ T cell contacts and/or the formation of ternary complexes. We here describe the first in vivo imaging of the intact spleen, aiming to evaluate the first interactions between antigen-specific CD4+, CD8+ T cells and Ag+DCs. We show that in contrast to CD4+ T cells which form transient contacts with Ag+DC, CD8+ T cells form immediate stable contacts and activate the Ag+DC, acquire fragments of the DC membranes by trogocytosis, leading to their acquisition of some of the DC properties. They express MHC class II, and become able to present the specific Marilyn peptide to naïve Marilyn CD4+ T cells, inducing their extensive division. In vivo, these CD8+ T cells form direct stable contacts with motile naïve CD4+ T cells, recruiting them to Ag+DC binding and to the formation of ternary complexes, where CD4+ and CD8+ T cells interact with the DC and with one another. The presence of CD8+ T cells during in vivo immune responses leads to the early activation and up-regulation of multiple functions by CD4+ T lymphocytes. Thus, while CD4+ T cell help is important to CD8+ T cell responses, CD8+ T cells can interact directly with naïve CD4+ T cells impacting their recruitment and differentiation.
Thymus transplants can correct deficiencies of the thymus epithelium caused by the complete DiGeorge syndrome or FOXN1 mutations. However, thymus transplants were never used to correct T ...cell-intrinsic deficiencies because it is generally believed that thymocytes have short intrinsic lifespans. This notion is based on thymus transplantation experiments where it was shown that thymus-resident cells were rapidly replaced by progenitors originating in the bone marrow. In contrast, here we show that neonatal thymi transplanted into interleukin 7 receptor-deficient hosts harbor populations with extensive capacity to self-renew, and maintain continuous thymocyte generation and export. These thymus transplants reconstitute the full diversity of peripheral T cell repertoires one month after surgery, which is the earliest time point studied. Moreover, transplantation experiments performed across major histocompatibility barriers show that allogeneic transplanted thymi are not rejected, and allogeneic cells do not induce graft-versus-host disease; transplants induced partial or total protection to infection. These results challenge the current dogma that thymocytes cannot self-renew, and indicate a potential use of neonatal thymus transplants to correct T cell-intrinsic deficiencies. Finally, as found with mature T cells, they show that thymocyte survival is determined by the competition between incoming progenitors and resident cells.
Natural killer (NK) cell development is thought to occur in the bone marrow. Here we identify the transcription factor GATA-3 and CD127 (IL-7R alpha) as molecular markers of a pathway of mouse NK ...cell development that originates in the thymus. Thymus-derived CD127+ NK cells repopulated peripheral lymphoid organs, and their homeostasis was strictly dependent on GATA-3 and interleukin 7. The CD127+ NK cells had a distinct phenotype (CD11b(lo) CD16- CD69(hi) Ly49(lo)) and unusual functional attributes, including reduced cytotoxicity but considerable cytokine production. Those characteristics are reminiscent of human CD56(hi) CD16- NK cells, which we found expressed CD127 and had more GATA-3 expression than human CD56+ CD16+ NK cells. We propose that bone marrow and thymic NK cell pathways generate distinct mouse NK cells with properties similar to those of the two human CD56 NK cell subsets.
Summary
Thymus transplants were never used to correct T‐cell intrinsic deficiencies, as it is generally believed that thymocytes have short intrinsic lifespans. This notion is based on multiple ...thymus transplantation experiments, where it was shown that thymus‐resident cells were rapidly replaced by progenitors migrating from the bone marrow (BM). This substitution occurs even when bone marrow precursors are unable to generate T cells, as in Rag1/2− or severe combined immunodeficiency (SCID)‐deficient mice. In contrast, two groups reported that neonatal thymi transplanted into mice that cannot respond to IL‐7 harbor populations with extensive capacity to self‐renew, which maintain continuous thymocyte generation for several months after surgery. The consequences of this self‐renewal capacity differed in these two laboratories. We found that these thymus transplants rapidly reconstitute the full diversity of peripheral T‐cell repertoires 1 month after surgery, the earliest time point studied. Moreover, transplantation experiments performed across major histocompatibility barriers show that allogeneic‐transplanted thymi are not rejected, and allogeneic cells do not induce graft‐versus‐host disease, both syngeneic and allogeneic transplants inducing rapid protection from infection. These results indicate a potential use of neonatal thymus transplants to correct T‐cell intrinsic deficiencies. The other group observed that continuous thymocyte renewal from BM precursors was fundamental to prevent tumor development. In the absence of this input, thymocytes from the transplanted thymus generated tumors with all the characteristics of T‐cell acute lymphoblastic leukemia (T‐ALL). Moreover, they suggested that the absence of BM competition was responsible for the T‐ALLs developing in X‐linked severe combined immunodeficiency (SCID)‐X1 patients, deficient in the expression of IL2‐Rγc. These patients were treated with autologous CD34+ cells transfected with virus vectors expressing γc in the absence of myeloablation. We here review the potential therapeutic impact of thymus transplantation and compare the results of these two laboratories aiming to find an answer to the ‘Dr Jekill versus Mr. Hyde’ status of thymus transplantation experiments.
Immune responses are efficient because the rare antigen-specific naïve cells are able to proliferate extensively and accumulate upon antigen stimulation. Moreover, differentiation into memory cells ...actually increases T cell accumulation, indicating improved productive division in secondary immune responses. These properties raise an important paradox: how T cells may survive the DNA lesions necessarily induced during their extensive division without undergoing transformation. We here present the first data addressing the DNA damage responses (DDRs) of CD8 T cells in vivo during exponential expansion in primary and secondary responses in mice. We show that during exponential division CD8 T cells engage unique DDRs, which are not present in other exponentially dividing cells, in T lymphocytes after UV or X irradiation or in non-metastatic tumor cells. While in other cell types a single DDR pathway is affected, all DDR pathways and cell cycle checkpoints are affected in dividing CD8 T cells. All DDR pathways collapse in secondary responses in the absence of CD4 help. CD8 T cells are driven to compulsive suicidal divisions preventing the propagation of DNA lesions. In contrast, in the presence of CD4 help all the DDR pathways are up regulated, resembling those present in metastatic tumors. However, this up regulation is present only during the expansion phase; i.e., their dependence on antigen stimulation prevents CD8 transformation. These results explain how CD8 T cells maintain genome integrity in spite of their extensive division, and highlight the fundamental role of DDRs in the efficiency of CD8 immune responses.
In this essay we suggest that the primary goal of the cells of the immune
system is to ensure their own growth and survival. In adults, in steady-state
conditions, the number and distribution of ...lymphocyte populations is under
homeostatic control. New lymphocytes that are continuously produced in primary
and secondary lymphoid organs must compete with resident cells for survival. We
discuss recent findings supporting lymphocyte survival as a continuous active
process and implicating cognate receptor engagement as fundamental survival
signals for both T and B lymphocytes. The conflict of survival interests
between different cell types gives rise to a pattern of interactions that
mimics the behavior of complex ecological systems. In their flight for survival
and in response to competition, lymphocytes use different survival signals
within different ecological niches during cell differentiation. This is the
case for T and B lymphocytes and also for naive and memory activated T and
B cells. We discuss how niche differentiation allows the co-existence of
different cell types and guarantees both repertoire diversity and efficient
immune responses.
Natural regulatory T (Treg) cells interfere with multiple functions, which are crucial for the development of strong anti-tumour responses. In a model of 4T1 mammary carcinoma, depletion of ...CD25+Tregs results in tumour regression in Balb/c mice, but the mechanisms underlying this process are not fully understood. Here, we show that partial Treg depletion leads to the generation of a particular effector CD8 T cell subset expressing CD11c and low level of PD-1 in tumour draining lymph nodes. These cells have the capacity to migrate into the tumour, to kill DCs, and to locally regulate the anti-tumour response. These events are concordant with a substantial increase in CD11b+ resident dendritic cells (DCs) subsets in draining lymph nodes followed by CD8+ DCs. These results indicate that Treg depletion leads to tumour regression by unmasking an increase of DC subsets as a part of a program that optimizes the microenvironment by orchestrating the activation, amplification, and migration of high numbers of fully differentiated CD8+CD11c+PD1lo effector T cells to the tumour sites. They also indicate that a critical pattern of DC subsets correlates with the evolution of the anti-tumour response and provide a template for Treg depletion and DC-based therapy.
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