Absence Of NKT Cells Research Articles

Japanese Kampo Medicine Juzentaihoto Enhances Antitumor Immunity in CD1d−/− Mice Lacking NKT Cells

Although the Japanese traditional herbal medicine (Kampo), Juzentaihoto (JTT), has been reported to have antitumor effects in several tumor models, its role in tumor immunology remains controversial. In the present study, we tested whether oral administration of JTT enhances antitumor immunity in CD1d−/− mice, in which immunosuppression was partially relieved due to the lack of NKT cells. In a subcutaneous murine syngeneic CT26 colorectal tumor model, JTT had no impact on tumor growth in wild type (WT) BALB/c mice. However, the growth rate of tumors was significantly slower in CD1d−/− mice than in WT mice. Surprisingly, JTT significantly delayed tumor growth in such CD1d−/− mice. In vivo depletion of CD8+ T cells revealed that CD8+ T cells are required for JTT’s antitumor activity. Moreover, tumor-reactive cytotoxic T-lymphocytes were detected exclusively in JTT-treated mice with well-controlled tumors. JTT did not affect the number of tumor-infiltrating CD4+ regulatory T cells. On the contrary, JTT increased the degranulation marker CD107a+ CD8+ T cells and decreased Ly6G+ Ly6Clo polymorphonuclear myeloid-derived suppressor cells in tumor-infiltrating lymphocytes, most probably contributing to the suppression of tumor growth in JTT-treated mice. Nonetheless, JTT had no impact on the proportion of monocytic myeloid-derived suppressor cells. In conclusion, our results indicate that in the absence of NKT cells, JTT augments antitumor immunity by CD8+ T cells, suggesting that this Kampo medicine is a promising anticancer adjuvant when negative immune regulation is partially relieved.

Histone demethylases UTX and JMJD3 are required for NKT cell development in mice

BackgroundNatural killer (NK)T cells and conventional T cells share phenotypic characteristic however they differ in transcription factor requirements and functional properties. The role of histone modifying enzymes in conventional T cell development has been extensively studied, little is known about the function of enzymes regulating histone methylation in NKT cells.ResultsWe show that conditional deletion of histone demethylases UTX and JMJD3 by CD4-Cre leads to near complete loss of liver NKT cells, while conventional T cells are less affected. Loss of NKT cells is cell intrinsic and not due to an insufficient selection environment. The absence of NKT cells in UTX/JMJD3-deficient mice protects mice from concanavalin A‐induced liver injury, a model of NKT‐mediated hepatitis. GO‐analysis of RNA-seq data indicates that cell cycle genes are downregulated in UTX/JMJD3-deleted NKT progenitors, and suggest that failed expansion may account for some of the cellular deficiency. The phenotype appears to be demethylase‐dependent, because UTY, a homolog of UTX that lacks catalytic function, is not sufficient to restore their development and removal of H3K27me3 by deletion of EZH2 partially rescues the defect.ConclusionsNKT cell development and gene expression is sensitive to proper regulation of H3K27 methylation. The H3K27me3 demethylase enzymes, in particular UTX, promote NKT cell development, and are required for effective NKT function.

Lymphocytes in atherosclerosis.

Atherosclerosis is the major cause of cardiovascular disease, and cardiovascular disease remains the primary cause of death in the United States. The primary complication for patients with type 2 diabetes mellitus (T2D) is cardiovascular disease.1–8 Because the incidences of T2D and obesity are drastically increasing in the United States and now worldwide, understanding how atherosclerosis is accelerated in these diseases becomes even more important to discern. Although many scientific advances in research on atherosclerosis have been made by multiple groups during the past 30 years, particularly about the function of endothelial and smooth muscle biology and macrophage foam cell formation in atherosclerotic plaque development, the roles of immune cells in regulating atherosclerosis onset and progression are still being elucidated. It was widely thought that immune cells played little part in atherogenesis until 1986, when Hansson et al9–12 reported the presence of lymphocytes within atherosclerotic lesions; yet it was many years later until it was widely accepted that immune cells play an important role in atherogenesis. Since 1986, the viewpoint has changed significantly, but details on lymphocyte subsets and mechanisms are still emerging. Moreover, controversy still exists on the roles that some lymphocyte subsets play in atherosclerosis. These discrepancies in findings are at least partly because of differences in mouse models used, diet composition, and length of time on diet for atherosclerosis measurements. However, despite a few ongoing controversies, there are many studies on immune cells in atherogenesis in mice that show clear findings.10,12–23 For example, CD4+ T lymphocytes have been shown to accelerate atherosclerosis.18,24–29 Activated CD4 T cells can be distinguished based on their phenotype, and the predominant CD4+ effector T cells studied to date in the context of atherosclerosis are Th1, …

Role of NKT cell in the regulation of antigen presenting cell-function during RSV infection (175.5)

Abstract Survivors of RSV bronchiolitis and pneumonia develop increased susceptibility to asthma. We showed that skewed polarization of dendritic cells (DC) towards plasmacytoid DC (pDC) in the pups in response to RSV is inhibited by exogenous administration of osteopontin (OPN) with an associated Th1 immune response. In the present study, we examined the expression of MHC-II, an indicator of antigen presenting function, on the antigen presenting cells (APC) in the RSV-infected lungs and its dependence on NKT cells. Wild type (WT) and NKT knock out (NKT-/-) pups were infected with RSV and were treated with or without OPN. Expression of MHCII on the lung APCs, including macrophages (MQ) and DCs (pDC; CD11blo/-CD11Clo/-CD45Rhi) and mDC; CD11blo/-CD11ChiCD45Rlo/-), was determined by flowcytometry (FACS). The effect of OPN on MHCII expression in the presence or absence of NKT cells was studied. FACS revealed that expression of MHCII was higher on the pDCs than mDCs in the RSV-infected WT lungs. In the absence of NKT cells, MHCII expression on pDCs was increased. OPN treatment augmented expression of MHCII on MQ and DCs, which was further enhanced in the absence of NKT cells. These data suggest that OPN- induced MHCII expression on the lung APCs is NKT dependent. Further experiments will explore the underlying mechanism of this phenomenon, which may help developing a therapeutic strategy to stop skewed polarization of DC in RSV infected lungs in preventing susceptibility to asthma.

Osteopontin induced inhibition of dendritic cell polarization towards pDC cells is not exclusively mediated by NKT cells (147.28)

Abstract Pediatric post-RSV infection associated bronchial asthma is known to be mediated via an enhanced pulmonary Th2 response. However, adult RSV infection is not known to be associated with this pathology. Further, osteopontin and NKT cell have been reported to be involved with induction of Th1 and Th2 type host-immune responses, respectively. The effect of NKT cells on naïve T helper cells is suggested to be a result of NKT cells’ subsequent modulation of naïve dendritic cells (DCs) towards plasmacytoid DCs (pDCs). So, in our present studies, using an NKT cell KO (CD1d-/-) mouse model, we have studied the role of osteopontin and NKT cells in modulating the polarization of DCs towards pDC in RSV-infected neonatal lungs. Flowcytometry analysis determined that there was an enhanced NKT cell (CD19-CD4+CD1d+) response in the RSV-infected neonatal lungs compared to that in the infected adult lungs. There was a decrease in the NKT cell response to RSV infection in the neonatal lungs upon concomitant administration of exogenous osteopontin as compared to those without osteopontin. Furthermore, in the absence of NKT cells (CD1d-/-), the administration of exogenous osteopontin induced inhibition of DC polarization towards pDC. Thus, differential pDC responses to RSV infection in neonates with exogenous osteopontin administration, even in the absence of NKT cells, warrants investigation into involvement of other factors in the development of RSV-induced bronchial asthma in later life.

1084 CYCLIN El AND Dl CAN DRIVE LIVER REGENERATION IN MICE WITHOUT CDK2

Background and Aims: Liver regeneration is impaired in obese, diabetic rodents developing spontaneous steatohepatitis such as ob/ob and KK-A mice, in which hepatic NKT cells are depleted. In this study, we investigated the differences in hepatic regeneration after partial hepatectomy (PH) in mice selectively depleted NK and/or NKT cells. Methods: Male, 12 week-old CD1d-knockout (KO) mice, which lack NKT cells systemically, and wild type (WT; C57Bl/6) mice were used. Some mice were pretreated with NK1.1 or asialo-GM1 antibody 24hr prior to experiments to deplete NK/NKT cells or NK cells alone, respectively. Mice underwent the 2/3 PH, and the uptake of BrdU and the expression of PCNA in hepatocyte nuclei were detected by immunohistochemistry. Hepatic expression levels of cyclin D1 and IFNg mRNA were analyzed quantitatively by Western blotting and real time RT-PCR, respectively. Results: In CD1d-KO mice, BrdU uptake and PCNA expression were almost similar to those in WT mice 48hr after PH, the labeling indices being nearly 20% and 30%, respectively. In sharp contrast, both parameters after PH was decreased remarkably in WT mice pretreated with an NK1.1 antibody, values reaching only 1.7% and 11.9%, respectively (P < 0.01 vs. WT after PH). Further, expression of cylin D1 in the liver 48hr after PH was nearly normal in CD1d-KO mice, but the levels were almost completely blunted in mice given an NK1.1 antibody. Interestingly, CD1d-KO mice given an asialoGM1 antibody showed impaired regenerative responses as similar to WT mice given an NK1.1 antibody. Hepatic IFNg mRNA was elevated nearly 5-fold in WT mice 6hr after PH, which was not affected by pretreatment with an NK1.1 antibody. Conclusions: These findings clearly indicated that liver regeneration is markedly impaired when both NKT and NK cells are depleted in two different preparations. NK cell-function under regeneration appears to be paradoxical in the presence or absence of NKT cells, and it is unlikely that IFNg plays a regulatory role in regeneration failure caused by simultaneous depletion of NK and NKT cells. It is therefore concluded that NKT and NK cells are coordinately involved in normal regenerative responses in the liver. 1084 CYCLIN E1 AND D1 CAN DRIVE LIVER REGENERATION IN MICE WITHOUT CDK2 W. Hu, Y.A. Nevzorova, J.R. Nowak, U. Haas, N. Moro, Y. Geng, P. Sicinski, M. Barbacid, C. Trautwein, C. Liedtke. Department of Medicine III, University Hospital Aachen, RWTH Aachen University, Aachen, Germany; Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA; Centro Nacional de Investigaciones Oncologicas (CNIO), Madrid, Spain E-mail: whu@ukaachen.de

Prevention of NKT Cell Activation Accelerates Cutaneous Wound Closure and Alters Local Inflammatory Signals

We previously reported that in the absence of NKT cells, wound closure was accelerated in a murine excisional punch wound model. Here, we explored whether purposefully inhibiting NKT cell activation had similar effects on wound closure and the dermal inflammatory response to injury. We found that prevention of NKT cell activation accelerated wound closure in a dose-responsive manner. If anti-CD1d was administered before wounding, NKT cell infiltration into cutaneous wounds was diminished without quantitative changes in cellular infiltrates. Furthermore, prevention of NKT cell activation transiently enhanced the local production of a subset of chemokines, including MIP-2, MCP-1, MIP-1α, and MIP-1β, and altered the relative expression of CD69 and CXCR2 on the surface of both circulating and wound NKT cells. Taken together, these findings suggest that wounding activates NKT cells via CD1d presentation of glycolipid antigen and help further define a role for NKT cells in the regulation of wound inflammation and closure. Many soluble factors have been targeted as potential wound healing therapies, but their clinical success has been limited. Given our findings, the NKT cell may be an attractive target for wound healing therapies.

Gvhd Severity Is Regulated by the Adoptive Transfer Low Numbers of NKT Cells by a Mechanism Distinct From CD4+CD25+ Regulatory T Cells.

Abstract 229NKT cells, a subset of which are CD1d reactive, play an important immunoregulatory role in suppressing dysfunctional immune reactions, including graft-versus-host disease (GVHD). To explore the biological activity and mechanism of donor-type NKT in suppression of GVHD, we utilized highly purified (>95%) populations of donor (C57Bl6; H-2b) NKT (DX5+TCR+CD4+) cells adoptively transferred into lethally irradiated recipient (Balb/c; H-2d) animals with T cell depleted bone marrow (TCD-BM). Highly purified (>95%) NKT cells (5.5×105) from luciferase positive (luc+) C57BL/6 mice were infused into lethally irradiated Balb/c recipients with TCD-BM(5×106) from wild-type (WT) C57BL/6 mice, and the animals were monitored by bioluminescence imaging (BLI). By day 4 after transfer, an NKT derived signal was observed in spleen and lymph node (LN) sites, and between days 7 and 10, NKT had also migrated to the skin. Total photons emitted peaked near day 25 after transplantation, followed by a steady decline. To assess the impact of donor-type NKT cells on GVHD induction by conventional CD4+ and CD8+ T cells (Tcon), we co-transferred various doses of highly purified WT NKT at day 0 with TCD-BM, followed by 5×105 luc+Tcon/animal on day 2. As few as 2.5×104 NKT cells significantly improved survival of mice receiving 5×105 Tcon. Animal survival with Tcon only was 20% and for Tcon with NKT cells was 74%(p=0.0023). In contrast to what is observed with CD4+CD25+FoxP3+ regulatory T cells (Treg), the NKT cells did not suppress Tcon proliferation assayed by both in vivo BLI and in a mixed-leukocyte reaction. Analysis of serum cytokines with or without 2.5×104 NKT, following HCT with TCD-BM and Tcon, indicated the addition of NKT cells resulted in elevated levels of INF-γ, IL-5, and IL-6 in serum; significant differences were not observed in serum levels of IL-2, IL-4, IL-10, IL-17, or TNF-α. Intracellular levels of cytokines in Tcon were analyzed from the same groups. At 8 days after HCT, mice receiving NKT had fewer TNFα-positive cells in LNs (CD4: 45% to 27%; CD8 36% to 24%); by day 11, however, TNFαa levels between groups were equivalent. IFN-γ levels, which were high in both NKT treated and untreated groups at day 8 (85%-95%), decreased significantly in NKT treated mice by day 11 (CD4: 40%; CD8: 43%), but were abundant in Tcon only mice (CD4: 78%; CD8: 80%) (p=.0001). No significant changes were found in the intracellular levels of IL-2, IL-4, IL-5, IL-10, or IL-17 of Tcon in the presence or absence of NKT cells. NKT from both IL-4 -/- and IFN-γ -/- mice were less effective at suppressing GVHD than WT NKT, implicating these cytokines in the suppressive mechanism. Finally, we found that NKT do not have a major impact on the graft-versus-tumor effect of Tcon against a luc+ BCL-1 tumor. These studies indicate that NKT persist in vivo upon adoptive transfer and suppress GVHD, even at extremely low cell numbers, which is important given the relative paucity of this cell population. The mechanisms of GVHD suppression appear to be distinct to those of Treg and involve the production of IL-4 and IFN-γ by NKT resulting in a decrease in Tcon, which produce pro-inflamatory cytokines. Disclosures:No relevant conflicts of interest to declare.

The X-linked lymphoproliferative syndrome gene product SAP regulates B cell function through the FcγRIIB receptor

X-linked lympho-proliferative (XLP) is an immunodeficiency condition caused by mutation or deletion of the gene encoding the adaptor protein SAP/SH2D1A. Besides defects in T cell and NK cell function and an absence of NKT cells, XLP can also manifest as lymphomas resulting primarily from uncontrolled B cell proliferation upon acute infection by Epstein–Barr virus. While it has been demonstrated that SAP regulates the functions of T cells and NK cells through the SLAM family of immunoreceptors, its role in B cells has not been defined. Here we show that SAP forms a ternary complex with the kinase Lyn and the inhibitory IgG Fc receptor FcγRIIB to regulate B cell proliferation and survival. SAP binds directly and simultaneously to the Lyn SH3 domain and an Immuno-receptor Tyrosine-based Inhibitory Motif (ITIM) in FcγRIIB, resulting in the activation of the latter. Moreover, SAP associates with FcγRIIB in mouse splenic B cells and promotes its tyrosine phosphorylation. Expression of SAP in the A20 B cell line led to a marked reduction in Blnk phosphorylation, a decrease in Akt activation, and a near-complete ablation of phosphorylation of the MAP kinases Erk1/2, p38 and JNK upon colligation of FcγRIIB with the B cell receptor (BCR). In contrast, an XLP-causing SAP mutant was much less efficient in eliciting these effects in B cells. Furthermore, compared to A20 cells, SAP transfectants displayed a significantly reduced rate of proliferation and an increased sensitivity to activation-induced cell death. Collectively these data identify an intrinsic function for SAP in inhibitory signaling in B cells and suggests that SAP may play an important role in balancing positive versus negative immune responses.

Regulation of hematopoiesis in vitro and in vivo by invariant NKT cells

AbstractInvariant natural killer T cells (iNKT cells) are a small subset of immunoregulatory T cells highly conserved in humans and mice. On activation by glycolipids presented by the MHC-like molecule CD1d, iNKT cells promptly secrete T helper 1 and 2 (Th1/2) cytokines but also cytokines with hematopoietic potential such as GM-CSF. Here, we show that the myeloid clonogenic potential of human hematopoietic progenitors is increased in the presence of glycolipid-activated, GM-CSF–secreting NKT cells; conversely, short- and long-term progenitor activity is decreased in the absence of NKT cells, implying regulation of hematopoiesis in both the presence and the absence of immune activation. In accordance with these findings, iNKT-cell–deficient mice display impaired hematopoiesis characterized by peripheral-blood cytopenias, reduced marrow cellularity, lower frequency of hematopoietic stem cells (HSCs), and reduced early and late hematopoietic progenitors. We also show that CD1d is expressed on human HSCs. CD1d-expressing HSCs display short- and long-term clonogenic potential and can present the glycolipid α-galactosylceramide to iNKT cells. Thus, iNKT cells emerge as the first subset of regulatory T cells that are required for effective hematopoiesis in both steady-state conditions and under conditions of immune activation.

NKT cells are not critical for HSV‐1 disease resolution

NKT cells are a minor subset of T cells that have important roles in controlling immune responses in disease states including cancer, autoimmunity and pathogenic infections. In contrast to conventional T cells, NKT cells express an invariant TCR and respond to glycolipids presented by CD1d. In this study, we sought to investigate the role of NKT cells in regulating the response to infection with HSV-1, and the mechanism involved, in well-established mouse models. Previous studies of HSV-1 disease in mice have shown clear roles for CD4+ and CD8+ T cells. The role of NKT cells in the resolution of HSV-1 (KOS strain) infection was investigated through flank zosteriform or footpad infection in wild-type versus CD1d-deficient mice, by measurement of viral plaque-forming units at different sites after infection, lesion severity and HSV-1-specific T-cell responses. In contrast to a previous study using a more virulent strain of HSV-1 (SC16 strain), no differences were observed in disease magnitude or resolution, and furthermore, the T-cell response to HSV-1 (KOS strain) was unaltered in the absence of NKT cells. In conclusion, this study shows that NKT cells do not play a general role in controlling the resolution or severity of HSV-1 infection. Instead, the resolution or severity of the infection may depend on the HSV-1 strain under investigation.

NKT cells regulate the development of asthma

Using NKT cell-deficient CD1d knockout and Jα281 knockout mice, we demonstrated that allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, failed to develop in the absence of NKT cells. The failure of NKT cell-deficient mice to develop AHR was not due to an inability of these mice to develop Th2 responses and was reversed by adoptive transfer of tetramer purified NKT cells. These studies are the first to show that pulmonary NKT cells critically regulate the development of asthma and Th2-biased respiratory immunity against nominal exogenous antigens. In addition, our studies suggest that therapies that target NKT cells may be clinically effective in limiting the development of AHR and asthma.

In Vivo Hydrodynamic Delivery of cDNA Encoding IL-2: Rapid, Sustained Redistribution, Activation of Mouse NK Cells, and Therapeutic Potential in the Absence of NKT Cells

In the present study, we have tested the ability of hydrodynamically delivered IL-2 cDNA to modulate the number and function of murine leukocyte subsets in different organs and in mice of different genetic backgrounds, and we have evaluated effects of this mode of gene delivery on established murine tumor metastases. Hydrodynamic administration of the IL-2 gene resulted in the rapid and transient production of up to 160 ng/ml IL-2 in the serum. The appearance of IL-2 was followed by transient production of IFN-gamma and a dramatic and sustained increase in NK cell numbers and NK-mediated cytolytic activity in liver and spleen leukocytes. In addition, significant increases in other lymphocyte subpopulations (e.g., NKT, T, and B cells) that are known to be responsive to IL-2 were observed following IL-2 cDNA plasmid delivery. Finally, hydrodynamic delivery of only 4 mug of the IL-2 plasmid to mice bearing established lung and liver metastases was as effective in inhibiting progression of metastases as was the administration of large amounts (100,000 IU/twice daily) of IL-2 protein. Studies performed in mice bearing metastatic renal cell tumors demonstrated that the IL-2 cDNA plasmid was an effective treatment against liver metastasis and moderately effective against lung metastasis. Collectively, these results demonstrate that hydrodynamic delivery of relatively small amounts of IL-2 cDNA provides a simple and inexpensive method to increase the numbers of NK and NKT cells, to induce the biological effects of IL-2 in vivo for use in combination with other biological agents, and for studies of its antitumor activity.

Cutting Edge: Signaling Lymphocytic Activation Molecule-Associated Protein Controls NKT Cell Functions

X-linked lymphoproliferative disease (XLP) is a fatal immunological disorder that typically manifests following EBV infection. XLP patients exhibit a number of immune defects including abnormal T, B, and NK lymphocyte function. These defects have been attributed to mutations of Src homology 2 domain-containing gene 1A (SH2D1A), the gene encoding signaling lymphocytic activation molecule-associated protein (SAP), an intracellular adaptor molecule expressed in lymphocytes. We have observed that SAP knockout (SAPKO) mice and humans with XLP have a complete lack of CD1d-restricted NKT cells. As expected, SAPKO mice injected with the NKT cell agonist, alpha-galactosylceramide failed to generate NKT cell IFN-gamma or IL-4. Furthermore, in contrast to wild-type littermates, SAPKO mice coinjected with OVA and alpha-galactosylceramide failed to mount OVA-specific CTL responses. These data suggest that an absence of NKT cells may underlie part of the immune dysregulation seen in SAPKO mice and in XLP patients.

Regulation of NKT cell development by SAP, the protein defective in XLP

The adaptor molecule SAP is expressed in T lymphocytes and natural killer (NK) cells, where it regulates cytokine production and cytotoxicity. Here, we show that SAP, encoded by the SH2D1A gene locus, also has a crucial role during the development of NKT cells, a lymphocyte subset with immunoregulatory functions in response to infection, cancer and autoimmune disease. Following stimulation with the NKT cell-specific agonist alpha-galactosyl ceramide (alphaGC), Sh2d1a-/- splenocytes did not produce cytokines or activate other lymphoid lineages in an NKT cell-dependent manner. While evaluating the abnormalities in alphaGC-induced immune responses, we observed that Sh2d1a-/- animals lacked NKT cells in the thymus and peripheral organs. The defect in NKT cell ontogeny was hematopoietic cell autonomous and could be rescued by reconstitution of SAP expression within Sh2d1a-/- bone marrow cells. Seventeen individuals with X-linked lymphoproliferative disease (XLP), who harbored germline mutations in SH2D1A, also lacked NKT cells. Furthermore, a female XLP carrier showed completely skewed X chromosome inactivation within NKT cells, but not T or B cells. Thus, SAP is a crucial regulator of NKT cell ontogeny in humans and in mice. The absence of NKT cells may contribute to the phenotypes of SAP deficiency, including abnormal antiviral and antitumor immunity and hypogammaglobulinemia.

NKT Cells Inhibit the Onset of Diabetes by Impairing the Development of Pathogenic T Cells Specific for Pancreatic β Cells

To determine the precise regulatory effect of NKT cells on CD4 + T cells involved in autoimmune diabetes, we developed an in vivo model in which transferred naive transgenic T cells are stimulated by their antigen in the presence or absence of NKT cells or in the presence of another conventional transgenic αβ T cell. The presence of NKT cells did not block the initial activation and expansion of the CD4 + T cells but did inhibit their IL-2 and IFN-γ production and later proliferation, resulting in an anergic phenotype. These CD4 + T cells did not induce significant insulitis and were unable to destroy the β cells. Thus, NKT cells prevent αβ CD4 T cell differentiation into effector cells.

CD1d-restricted human natural killer T cells are highly susceptible to human immunodeficiency virus 1 infection.

Human natural killer (NK) T cells are unique T lymphocytes that express an invariant T cell receptor (TCR) Vα24-Vβ11 and have been implicated to play a role in various diseases. A subset of NKT cells express CD4 and hence are potential targets for human immunodeficiency virus (HIV)-1 infection. We demonstrate that both resting and activated human Vα24+ T cells express high levels of the HIV-1 coreceptors CCR5 and Bonzo (CXCR6), but low levels of CCR7, as compared with conventional T cells. Remarkably NKT cells activated with α-galactosylceramide (α-GalCer)-pulsed dendritic cells were profoundly more susceptible to infection with R5-tropic, but not X4-tropic, strains of HIV-1, compared with conventional CD4+ T cells. Furthermore, resting CD4+ NKT cells were also more susceptible to infection. After initial infection, HIV-1 rapidly replicated and depleted the CD4+ subset of NKT cells. In addition, peripheral blood NKT cells were markedly and selectively depleted in HIV-1 infected individuals. Although the mechanisms of this decline are not clear, low numbers or absence of NKT cells may affect the course of HIV-1 infection. Taken together, our findings indicate that CD4+ NKT cells are directly targeted by HIV-1 and may have a potential role during viral transmission and spread in vivo.