Lymphopenia-induced Proliferation Research Articles

PD-1 Controls Tonic Signaling and Lymphopenia-Induced Proliferation of T Lymphocytes.

Recovery of the T lymphocyte compartment within a lymphopenic host by lymphopenia-induced proliferation (LIP) is regulated by inter- and intraclonal competition for limited resources, including homeostatic cytokines and peptide:MHC (pMHC) complexes with which the TCR can interact at least weakly to yield a tonic signal. Importantly, the process of LIP can synergize with other factors that promote T cell activation to drive inflammatory disease. While reconstitution of the lymphoid compartment of immune deficient Rag−/− mice by transfer of wild-type hematopoietic stem cells (HSC) does not generally result in an overt disease phenotype, transfer of HSC deficient in expression of the co-inhibitory molecule PD-1 results in severe systemic autoimmunity driven by newly generated T cells that emerge from the thymus into the periphery and undergo LIP. Importantly, autoimmunity does not appear to depend on a response to exogenous (i.e., gut flora-derived) antigens. PD-1 is well known to be upregulated during T cell activation in response to cognate antigens, but it is unclear whether PD-1 has a role in controlling LIP of T cells in the absence of cognate antigen, i.e., in response to tonic pMHC. We examined whether PD-1 controls LIP of newly generated T cells by controlling the response to tonic pMHC or the homeostatic cytokine IL-7. We found that PD-1-deficient T cells have a proliferative advantage over WT T cells during LIP and this effect is MHC-II dependent and independent of IL-7Rα signaling. Furthermore, our data suggest that signals through IL-7Rα can be dispensable for LIP and may instead be of increased importance for T cell survival in conditions of high competition for limited pMHC (e.g., post-LIP, in a lymphoreplete host). We hypothesize that autoimmunity post-PD-1−/− HSC transplant is the result of an overzealous T cell response to normally tonic self-pMHC precipitated by the synergy of LIP and PD-1 deficiency. Furthermore, potentiation of TCR signals in response to normally tonic self-pMHC may contribute to the success of PD-1 blockade in cancer immunotherapy.

Endogenous Secondary TCRs Promote Homeostatic Advantage Via Recognition of Self-Antigens

Abstract Our laboratory studies how non-thymically selected secondary TCRs contribute to the T cell repertoire. We have previously demonstrated that peripheral T cells naturally expressing 2 TCRs have increased response to autoantigens. We hypothesized that this could promote homeostatic proliferation of T cells expressing 2 TCRs, which may cause autoimmune risk. To examine secondary TCRs in homeostasis, we performed competitive transfers of CFSE-labeled T cells from B6.Ly5.1 and B6.TCRα+/−.Thy1.1 (lacking secondary TCRs) into irradiated B6 recipients. T cells injected at a 1:1 ratio demonstrated a disadvantage for TCRα+/− T cells in lymphopenia-induced proliferation (LIP), with TCRα+/−/wt donor cell ratios of 0.6±0.1 at 8 d after transfer and 0.5±0.4 at 28 d after transfer. T cell population skewing resulted from increased proliferation of wild-type cells. The homeostatic advantage of secondary TCRs was less in chronic LIP (cLIP) (transfer into TCRα-knockout mice), with TCRα+/−/wt donor cell ratios of 0.8±0.3 at 8 d after transfer and 0.7±0.3 at 28 d after transfer. There was no difference between wt and TCRα+/− T cells in proliferative response to stimulation via anti-CD3/CD28, nor were differences observed for expression of CD3, CD5, or CD127. LIP and cLIP depend on signaling through the TCR, though reactivity to self-antigens is thought to drive LIP as opposed to endogenous antigens from commensal microflora in cLIP. Our results suggest that the advantage for secondary TCRs in homeostatic expansion reflects increased ability to interact with self-pMHC antigens. Current effort is focused to understand how this affects protective and autoreactive peripheral T cell repertoires during aging or iatrogenic lymphopenia.

IL-7-dependent STAT1 activation limits homeostatic CD4 T cell expansion

Abstract IL-7 regulates homeostatic mechanisms that maintain the overall size of the T cell pool throughout life. We show that under steady state conditions, IL-7 signaling is principally mediated by activation of Signal Transducers and Activators of Transcription 5 (STAT5). In contrast, under lymphopenic conditions there is a modulation of STAT1 expression resulting in an IL-7-dependent STAT1 and STAT5 activation. Consequently, the IL-7-induced transcriptome is altered with enrichment of interferon (IFN) stimulated genes (ISGs). Moreover, STAT1 overexpression was associated with reduced survival in CD4 T cells undergoing Lymphopenia-Induced Proliferation (LIP). We propose a model in which T cells undergoing LIP upregulate STAT1 protein, “switching on” an alternate IL-7-dependent program. This mechanism could be a physiological process to “sense space” regulating the size of the CD4 T cell pool. During HIV infection the virus could exploit this pathway leading to the homeostatic dysregulation of the T cell pools observed in these patients.

Intestinal microbiota link lymphopenia to murine autoimmunity via PD-1+CXCR5\u2212/dim B-helper T cell induction

T cell lymphopenia results in peripheral homeostatic expansion to maintain the T cell immune system, which is termed lymphopenia-induced proliferation (LIP). LIP is a potential risk for expanding autoreactive clones to become pathogenic in human and murine autoimmune diseases. However, the ontogeny of T cells that induce autoantibody production by autoreactive B cells in LIP remains unclear. Transfer of CD4+CD25− conventional T (Tc) cells into T-cell-deficient athymic nude mice has been previously reported as a LIP-induced autoimmune model which develops organ-specific autoimmune diseases and systemic antinuclear antibodies (ANAs). We show here that via LIP in this model, Tc cells proliferated and differentiated into PD-1+CXCR5−/dim B-helper T cells, which promoted splenic germinal center (GC) formation, provided help for autoantibody-producing B cells, and had distinctive features of follicular helper T (Tfh) cells except that they do not express high CXCR5. Intestinal microbiota were essential for their generation, since depletion of them in recipient mice by antibiotics resulted in a reduction of LIP-induced PD-1+CXCR5−/dim B-helper T cells and an amelioration of autoimmune responses. Our findings will contribute to the elucidation of the mechanism of lymphopenia-induced autoimmunity and autoantibody production, and will pave the way for microbiota-targeted novel therapeutic approaches to systemic autoimmune diseases.

Two Strikes and You're Out? The Pathogenic Interplay of Coinhibitor Deficiency and Lymphopenia-Induced Proliferation.

Lymphopenia-induced proliferation (LIP) occurs when resources for T cell survival in a host are in excess. LIP has been associated with the development of inflammatory disease in situations where an additional disease-predisposing cofactor is present during LIP. This has led to the view of LIP-driven autoimmunity as a two hit model; however, not all cofactors have equal ability to precipitate autoimmunity and we have recently shown that in some circumstances, such as the absence of the coinhibitory molecule PD-1, additional hits are required. Herein we review factors controlling LIP, including coinhibitory molecules and other attenuators of TCR signaling, with a focus on their contribution to LIP-driven autoimmunity. Rather than viewing LIP-associated autoimmunity as an n-hit model, we suggest a more quantitative view of lymphopenia with respect to the factors that promote LIP as a tool to predict autoimmune potential and to inform tumor immunotherapy approaches.

Weakly self-reactive T-cell clones can homeostatically expand when present at low numbers.

T-cell division is central to maintaining a stable T-cell pool in adults. It also enables T-cell expansion in neonates, and after depletion by chemotherapy, bone marrow transplantation, or infection. The same signals required for T-cell survival in lymphoreplete settings, IL-7 and T-cell receptor (TCR) interactions with self-peptide MHC (pMHC), induce division when T-cell numbers are low. The strength of reactivity for self-pMHC has been shown to correlate with the capacity of T cells to undergo lymphopenia-induced proliferation (LIP), in that weakly self-reactive T cells are unable to divide, implying that T-cell reconstitution would significantly skew the TCR repertoire toward TCRs with greater self-reactivity and thus compromise T-cell diversity. Here, we show that while CD4+ T cells with low self-pMHC reactivity experience more intense competition, they are able to divide when present at low enough cell numbers. Thus, at physiological precursor frequencies CD4+ T cells with low self-pMHC reactivity are able to contribute to the reconstitution of the T-cell pool.

Gut Microbial Membership Modulates CD4 T Cell Reconstitution and Function after Sepsis.

Transient lymphopenia is one hallmark of sepsis, and emergent data indicate the CD4 T cell compartment in sepsis survivors is numerically and functionally altered (when examined at the Ag-specific level) compared with nonseptic control subjects. Previous data from our laboratory demonstrated Ag-independent, lymphopenia-induced homeostatic proliferation to be a contributing mechanism by which CD4 T cells numerically recover in sepsis survivors. However, we reasoned it is also formally possible that some CD4 T cells respond directly to Ag expressed by gut-resident microbes released during polymicrobial sepsis. The effect of gut microbiome leakage on CD4 T cells is currently unknown. In this study, we explored the number and function of endogenous CD4 T cells specific for segmented filamentous bacterium (SFB) after cecal ligation and puncture (CLP)-induced sepsis using mice that either contained or lacked SFB as a normal gut-resident microbe. Interestingly, SFB-specific CD4 T cells underwent Ag-driven proliferation in CLP-treated SFB(+), but not in SFB(-), mice. Moreover, CLP-treated SFB(+) mice showed resistance to secondary lethal infection with recombinant SFB Ag-expressing virulent Listeria (but not wild-type virulent Listeria), suggesting the CLP-induced polymicrobial sepsis primed for a protective response by the SFB-specific CD4 T cells. Thus, our data demonstrate that the numerical recovery and functional responsiveness of Ag-specific CD4 T cells in sepsis survivors is, in part, modulated by the intestinal barrier's health discreetly defined by individual bacterial populations of the host's microbiome.

Cutting Edge: Innate Lymphoid Cells Suppress Homeostatic T Cell Expansion in Neonatal Mice.

In adult mice, lymphopenia-induced proliferation (LIP) leads to T cell activation, memory differentiation, tissue destruction, and a loss of TCR diversity. Neonatal mice are lymphopenic within the first week of life. This enables some recent thymic emigrants to undergo LIP and convert into long-lived memory T cells. Surprisingly, however, most neonatal T cells do not undergo LIP. We therefore asked whether neonate-specific mechanisms prevent lymphopenia-driven T cell activation. In this study, we show that IL-7R-dependent innate lymphoid cells (ILCs) block LIP of CD8(+) T cells in neonatal but not adult mice. Importantly, CD8(+) T cell responses against a foreign Ag are not inhibited by neonatal ILCs. This ILC-based inhibition of LIP ensures the generation of a diverse naive T cell pool in lymphopenic neonates that is mandatory for the maintenance of T cell homeostasis and immunological self-tolerance later in life.

Overexpression of total STAT1 during lymphopenia-induced proliferation leads to decrease CD4 T cell survival

Abstract To preserve the size and diversity of the T cell repertoire throughout life, homeostatic mechanisms regulate both survival and proliferation through IL-7 and TCR signaling. IL-7 signals through a heterodimer receptor composed of the IL-7Rα and the γc chains. Binding of IL-7 to its receptor leads to activation of STAT5 and induction of target genes implicated in survival and proliferation signals. IL-7/IL-7R signaling can also activate STAT1 and STAT3 but the function of IL-7-dependent activation of these transcription factors is largely unknown. Under lymphopenic conditions, IL-7 modulates the expression levels of total STAT1 (t-STAT1) leading to an IL-7-dependent STAT1 signaling in addition to STAT5. We generated a transgenic mouse that overexpress STAT1 in CD4 and CD8 T cells to understand the contribution of IL-7-dependent STAT1 activation on T cell homeostasis in the setting of lymphopenia. We found that under lymphopenia-induced proliferation T cells from the STAT1 transgenic mouse upregulates t-STAT1 leading to diminish CD4 T cell survival. This mechanism could be a physiological mechanism to regulate the expansion of the CD4 T cell pool under lymphopenic conditions.

Requirement of interleukin 7 signaling for anti-tumor immune response under lymphopenic conditions in a murine lung carcinoma model.

Induction of lymphopenia before adoptive transfer of T cells was followed by lymphopenia-induced proliferation (LIP) and generated a potent anti-tumor immune response in rodents and in a clinical setting. Previously, we reported that CD28 signaling is essential for the differentiation of functional effector cytotoxic T lymphocytes (CTLs) under lymphopenic conditions and sequential LIP of T cells. In this study, to clarify the correlation between LIP and the anti-tumor effect, LIP was inhibited with interleukin 7 (IL7) receptor blockade at various stages, and the anti-tumor effect then assessed. We confirmed that IL7 signaling at the start of LIP is crucial for the anti-tumor immune response. In contrast, continuous IL7 signaling was not required for tumor regression, although LIP of naïve CD8+ T cells is usually regulated by IL7. The expansion and migration of CTLs in lymphopenic hosts depend on IL7 signaling during the induction phase. Here, we propose that IL7 signaling and subsequent LIP of T cells have distinct roles in the induction of T cell immunity during lymphopenia.

Lymphopenia-induced proliferation in the absence of functional Autoimmune regulator (Aire) induces colitis in mice

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by mutations in Autoimmune regulator (Aire), a transcriptional regulator of negative selection in thymus. However, Aire is also expressed in periphery, but the full range of Aire's peripheral function is unknown. Here, we transferred lymphocytes from wildtype donors into lymphopenic recipients with or without functional Aire. Following cell proliferation thus took place in Aire-sufficient or deficient environment. The wildtype lymphocytes hyperproliferated and induced disease in lymphopenic Aire−/− but not in Aire+/+ recipients. The disease was characterized by diarrhea, inflammation, and colitis, and in some recipients pancreatitis, gastritis, and hepatitis was also found. Our results identify Aire as an important regulator of peripheral T cell homeostasis in gastrointestinal tissues. Given a suitable trigger the absence of peripheral Aire leads to dysregulated T cell proliferation and disease.

PD-1 is not required for natural or peripherally induced regulatory T cells: Severe autoimmunity despite normal production of regulatory T cells.

The expression of the coinhibitor PD-1 on T cells is important for the establishment of immune homeostasis. We previously found that PD-1 is particularly critical for the control of self-tolerance during lymphopenia-induced proliferation of recent thymic emigrants (RTEs). Previous studies suggested that PD-1 modulates the generation of Treg cells, particularly peripherally induced Treg (pTreg) cells, and controls Th17 cells. However, these conclusions were derived indirectly from studies on the ligand PD-L1, and not PD-1 itself. Herein we directly tested whether T-cell PD-1 expression was needed for Treg cell generation and examined if a paucity of Treg cells or enhanced Th17 cells could explain the severe lymphopenia-potentiated autoimmunity caused by PD-1 KO RTEs. Employing the murine FoxP3(EGFP) reporter system to simultaneously monitor conversion of WT and PD-1 KO T cells to pTreg cells in the same animal, we found that PD-1 deficiency did not inhibit pTreg cell generation or lead to Th17-cell-mediated autoimmunity. Surprisingly, pTreg cell numbers were increased in PD-1 KO versus WT cell populations. Furthermore, we noted an increased conversion to pTreg cells by RTEs. Our data suggest that the primary role for PD-1 is to restrain T-cell activation/proliferation to self-Ags rather than promote generation of Treg cells.

IL-18 synergizes with IL-7 to drive slow proliferation of naive CD8 T cells by costimulating self-peptide-mediated TCR signals.

Naive T cell populations are maintained in the periphery at relatively constant levels via mechanisms that control expansion and contraction and are associated with competition for homeostatic cytokines. It has been shown that in a lymphopenic environment naive T cells undergo expansion due, at least in part, to additional availability of IL-7. We have previously found that T cell-intrinsic deletion of TNFR-associated factor (TRAF) 6 (TRAF6ΔT) in mice results in diminished peripheral CD8 T cell numbers. In this study, we report that whereas naive TRAF6ΔT CD8 T cells exhibit normal survival when transferred into a normal T cell pool, proliferation of naive TRAF6ΔT CD8 T cells under lymphopenic conditions is defective. We identified IL-18 as a TRAF6-activating factor capable of enhancing lymphopenia-induced proliferation (LIP) in vivo, and that IL-18 synergizes with high-dose IL-7 in a TRAF6-dependent manner to induce slow, LIP/homeostatic-like proliferation of naive CD8 T cells in vitro. IL-7 and IL-18 act synergistically to upregulate expression of IL-18R genes, thereby enhancing IL-18 activity. In this context, IL-18R signaling increases PI3K activation and was found to sensitize naive CD8 T cells to a model noncognate self-peptide ligand in a way that conventional costimulation via CD28 could not. We propose that synergistic sensitization by IL-7 and IL-18 to self-peptide ligand may represent a novel costimulatory pathway for LIP.

Innate immune cell CD45 regulates lymphopenia-induced T cell proliferation.

The leukocyte-specific tyrosine phosphatase, CD45, severely impacts T cell development and activation by modulating TCR signaling. CD45-deficient (CD45KO) mice have reduced peripheral T cell numbers where CD8 T cells are underrepresented. In this article, we show that CD45KO mice are unable to support efficient homeostatic proliferation, affecting CD8 T cells more than CD4 T cells. Using CD45-RAG1 double-deficient (45RAGKO) mice, we show that lymphopenia-induced proliferation (LIP) of CD45-sufficient T cells is defective in a host environment lacking CD45 on innate immune cells. We identify two deficiencies in the 45RAGKO mice that affect LIP. One involves CD11c(+) cells and the second the production of IL-7 by lymphoid stromal cells. CD45KO dendritic cells were not defective in foreign Ag-induced T cell proliferation, yet CD45KO CD11c(+) cells were unable to rescue the spontaneous LIP in the 45RAGKO mice. This was in contrast with the CD45-sufficient CD11c(+) cells that partially rescued this spontaneous proliferation and did so without affecting IL-7 levels. The absence of CD45 also led to reduced IL-7 production by lymphoid stromal cells, suggesting an indirect effect of CD45 on innate immune cells in influencing IL-7 production by lymphoid stromal cells. These findings demonstrate a novel role for CD45 on innate immune cells in promoting lymphopenia-induced T cell proliferation and suggest that innate immune cells may communicate with stromal cells to regulate IL-7 production.

Zap70 is essential for long-term survival of naive CD8 T cells.

Survival of naive T cells requires engagement of TCR with self-peptide major histocompatibility Ags. The signaling pathways required to transmit this survival signal are poorly understood. In this study, we asked whether the tyrosine kinase Zap70 is required to transmit survival signals in naive CD8 T cells. In the absence of Zap70 expression, thymic development is completely blocked. Using a tetracycline-inducible Zap70 transgene (TetZap70), thymic development of Zap70-deficient TCR transgenic F5 mice was restored. Feeding mice doxycycline to induce Zap70 expression resulted in repopulation of the peripheral naive compartment. Zap70 transgene expression was then ablated by withdrawal of doxycycline. Survival of Zap70-deficient naive CD8 T cells depended on host environment. In hosts with a replete T cell compartment, naive T cells died rapidly in the absence of Zap70 expression. In lymphopenic hosts, Zap70-deficient T cells survived far longer, in an IL-7-dependent manner, but failed to undergo lymphopenia-induced proliferation. Analyzing mixed bone marrow chimeras revealed that intact Zap70-dependent signaling was important for integration of recent thymic emigrants into the mature naive compartment. Finally, we asked whether adaptor function conferred by Zap70 tyrosines 315 and 319 was necessary for transmission of homeostatic TCR signals. This was done by analyzing F5 mice expressing mutant Zap70 in which these residues had been mutated to alanines (Zap70(YYAA)). Inducible Zap70 expression rescued thymic development in F5 TetZap70 Zap70(YYAA) mice. However, in the absence of wild-type Zap70 expression, the Zap70(YYAA) mutant failed to transmit either survival or proliferative homeostatic signals.

Homeostatic expansion as a barrier to lymphocyte depletion strategies.

Following lymphodepletion, lymphocytes repopulate the immune space both through enhanced thymopoiesis and proliferation of residual nondepleted peripheral lymphocytes. The term homeostatic proliferation (alternatively homeostatic expansion or lymphopenia-induced proliferation) refers to the latter process. Homeostatic proliferation is especially relevant to reconstitution of the lymphocyte compartment following immunodepletion therapy in transplantation. Repopulating lymphocytes can skew toward an effector memory type capable of inducing graft rejection, autoimmunity, or, in the case of allogeneic bone marrow transplantation, graft versus host disease. Here we review recent studies exploring the biologic mechanisms underlying homeostatic proliferation and explore implications for therapy in transplantation. Two immune-depleting agents, alemtuzumab and rabbit antithymocyte globulin, have been well characterized in their abilities to induce an effector-memory phenotype in repopulating lymphocytes. Additionally, we have gained new understandings of the mechanisms by which the cytokines interleukin-7 and interleukin-15 regulate this process. Recent studies have also explored the functions of noncytokine and signaling molecules in lymphopenia-induced proliferation. Finally, we have seen the promise and limitations of several therapeutic approaches, including recombinant interleukin-7 therapy, CD8-targeted antibodies, and peri-transplant cyclophosphamide, to treat posttransplant lymphopenia and reduce the risks of immune dysregulation following homeostatic proliferation. Immune dysfunction following homeostatic proliferation is a special challenge in transplantation. A deeper understanding of the underlying biology has led to a number of promising new therapies to overcome this problem.

THU0058 Intestinal Microbiota Plays A Critical Role in the Production of Antinuclear Antibodies in Lymphopenia-Induced Autoimmunity

BackgroundProduction of antinuclear autoantibodies (ANAs) is one of the major characteristics of the systemic autoimmune diseases, such as systemic lupus erythematosus (SLE), but the mechanisms of their production are not...

Tyk2-dependent bystander activation of conventional and nonconventional Th1 cell subsets contributes to innate host defense against Listeria monocytogenes infection.

IL-12, which is produced in response to intracellular bacteria, such as Listeria monocytogenes, promotes the development of pathogen-specific Th1 cells that play an important role in host defense. However, it has also been known that CD44(high) memory-phenotype CD4 T cells with Th1 functions naturally occur in naive mice, and that lymphopenia-induced proliferation of naive CD4 T cells generates memory-phenotype CD4 T cells with Th1 functions, although their differentiation mechanism and contribution to host defense are unclear. In this study, we analyzed the development and the functions of the different subsets of Th1 cells by using mice lacking tyrosine kinase 2 (Tyk2), a member of the Janus kinase family critically involved in IL-12 signaling. In contrast with the case of conventional Ag-specific Th1 cells, the development of naturally occurring Th1 cells was not impaired in Tyk2-deficient mice. In addition, Th1 cells were normally generated from Tyk2-deficient naive CD4 T cells via lymphopenia-induced proliferation. Nevertheless, all these Th1 subsets, including conventional Ag-induced Th1 cells, produced IFN-γ in response to IL-12 in a Tyk2-dependent manner. Importantly, such Tyk2-dependent bystander IFN-γ production of any Th1 subsets conferred early protection against L. monocytogenes infection. Thus, Tyk2-mediated IL-12 signaling is differentially required for the development of different Th1 cell subsets but similarly induces their bystander IFN-γ production, which contributes to innate host defense against infection with intracellular bacteria.

Initial IL7R signaling regulate the induction of effector CD8+ T cells and subsequent anti-tumor immune response in lymphopenic host (CCR3P.208)

Abstract Induction of lymphopenia and adoptive transfer of T cells are followed by lymphopenia-induced proliferation (LIP), and generated a anti-tumor immune response. However, the distinct role of redundant IL7 in lymphopenic host and subsequent LIP of T cells for anti-tumor immune response has been unclear, since multiple mechanisms are involved in the anti-tumor immune response under lymphopenic conditions. To clarify the correlation between LIP and the anti-tumor effect, LIP was inhibited by IL7R blockade with anti-IL7Ra mAb at various stages, and the anti-tumor effect was assessed. When LIP was occurred, the growth of transplanted LLC expressing model antigen gp33, was markedly regressed. Using IL7R blockade with mAb at various stages, we found that IL7R signaling at the start of LIP is crucial for the anti-tumor immune response. Although some reports focused on the benefit of IL7 for the improvement of effector T cell function, later IL7R blockade did not arrest the expansion of CTLs, and anti-tumor effect was occurred. IFN-g production also depend on IL7R signaling during induction phase, but not later phase, and, the expression of co-inhibitory molecules, PD-1, on CTLs was unchanged in IL7R blockade hosts. In conclusion, our results demonstrated that initial IL7R signaling and subsequent LIP regulated the expansion of IL7Ra+ effector precursors mainly, but that the effector function of CTL precursors and migration into tumor did not require IL7R signaling.

ITK signals tune CD8+ T cell homeostatic proliferation and anti-tumor immunity (LYM4P.747)

Abstract IL-2 inducible T cell kinase (ITK) is a Tec family non-receptor tyrosine kinase. Loss of ITK perturbs CD8+ T cell homeostasis and leads to spontaneous acquisition of innate memory/effector phenotype. However, Itk-/- naïve CD8+ T cells develop on an OTI Rag-/- background, and we use these cells to show here that ITK tunes lymphopenia-induced proliferation (LIP) and antigen sensitivity during CD8+ T cell homeostatic expansion. Experimental analysis and computational simulations revealed that in a lymphopenic environment, naïve Itk-/- CD8+ T cells exhibit massive and immediate homeostatic expansion, accompanied by significant death and followed by population collapse. The enhanced immediate expansion of Itk-/- cells is CD8+ T cell-intrinsic and is independent of recipient MHCI, but dependent on donor CD8+ T cell-T cell interaction. The lack of ITK resulted in enhanced antigen sensitivity and effector program in homeostatically expanded (HP) CD8+ T cells. These Itk-/- HP CD8+ T cells exhibit robust anti-tumor immunity in an antigen specific manner, independent of CD4+ T cell help. These data suggest that ITK intrinsically regulates TcR tuning of homeostatic cytokines during homeostasis of CD8+ T cells and that targeting ITK may have clinical benefit in cancer therapy by generating superior anti-tumor responses.