A human immune system (HIS) mouse model that dissociates roles for mouse and human FcR+ cells during antibody-mediated immune responses

Human immune system (HIS) mice provide a model to study human immune responses in vivo. Currently available HIS mouse models may harbor mouse Fc Receptor (FcR)-expressing cells that exert potent effector functions following administration of human Ig. Previous studies showed that the ablation of the murine FcR gamma chain (FcR-γ) results in loss of antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis in vivo. We created a new FcR-γ-deficient HIS mouse model to compare host (mouse) versus graft (human) effects underlying antibody-mediated immune responses in vivo. FcR-γ-deficient HIS recipients lack expression and function of mouse activating FcRs and can be stably and robustly reconstituted with human immune cells. By screening blood B-cell depletion by rituximab Ig variants, we found that human FcγRs-mediated IgG1 effects, whereas mouse activating FcγRs were dominant in IgG4 effects. Complement played a role as an IgG1 variant (IgG1 K322A) lacking complement binding activity was largely ineffective. Finally, we provide evidence that FcγRIIIA on human NK cells could mediate complement-independent B-cell depletion by IgG1 K322A. We anticipate that our FcR-γ-deficient HIS model will help clarify mechanisms of action of exogenous administered human antibodies in vivo.

Human IRF1 governs macrophagic IFN-γ immunity to mycobacteria

Inborn errors of human IFN-γ-dependent macrophagic immunity underlie mycobacterial diseases, whereas inborn errors of IFN-α/β-dependent intrinsic immunity underlie viral diseases. Both types of IFNs induce the transcription factor IRF1. We describe unrelated children with inherited complete IRF1 deficiency and early-onset, multiple, life-threatening diseases caused by weakly virulent mycobacteria and related intramacrophagic pathogens. These children have no history of severe viral disease, despite exposure to many viruses, including SARS-CoV-2, which is life-threatening in individuals with impaired IFN-α/β immunity. In leukocytes or fibroblasts stimulated in vitro, IRF1-dependent responses to IFN-γ are, both quantitatively and qualitatively, much stronger than those to IFN-α/β. Moreover, IRF1-deficient mononuclear phagocytes do not control mycobacteria and related pathogens normally when stimulated with IFN-γ. By contrast, IFN-α/β-dependent intrinsic immunity to nine viruses, including SARS-CoV-2, is almost normal in IRF1-deficient fibroblasts. Human IRF1 is essential for IFN-γ-dependent macrophagic immunity to mycobacteria, but largely redundant for IFN-α/β-dependent antiviral immunity.

Notch, RORC and IL-23 signals cooperate to promote multi-lineage human innate lymphoid cell differentiation

Innate lymphoid cells (ILCs) include cytotoxic natural killer cells and distinct groups of cytokine-producing innate helper cells which participate in immune defense and promote tissue homeostasis. Circulating human ILC precursors (ILCP) able to generate all canonical ILC subsets via multi-potent or uni-potent intermediates according to our previous work. Here we show potential cooperative roles for the Notch and IL-23 signaling pathways for human ILC differentiation from blood ILCP using single cell cloning analyses and validate these findings in patient samples with rare genetic deficiencies in IL12RB1 and RORC. Mechanistically, Notch signaling promotes upregulation of the transcription factor RORC, enabling acquisition of Group 1 (IFN-γ) and Group 3 (IL-17A, IL-22) effector functions in multi-potent and uni-potent ILCP. Interfering with RORC or signaling through its target IL-23R compromises ILC3 effector functions but also generally suppresses ILC production from multi-potent ILCP. Our results identify a Notch->RORC- > IL-23R pathway which operates during human ILC differentiation. These observations may help guide protocols to expand functional ILC subsets in vitro with an aim towards novel ILC therapies for human disease.

Defects in mucosal immunity and nasopharyngeal dysbiosis in HSC-transplanted SCID patients with IL2RG/JAK3 deficiency

Both innate and adaptive lymphocytes have critical roles in mucosal defense that contain commensal microbial communities and protect against pathogen invasion. Here we characterize mucosal immunity in patients with severe combined immunodeficiency (SCID) receiving hematopoietic stem cell transplantation (HSCT) with or without myeloablation. We confirmed that pretransplant conditioning had an impact on innate (natural killer and innate lymphoid cells) and adaptive (B and T cells) lymphocyte reconstitution in these patients with SCID and now show that this further extends to generation of T helper 2 and type 2 cytotoxic T cells. Using an integrated approach to assess nasopharyngeal immunity, we identified a local mucosal defect in type 2 cytokines, mucus production, and a selective local immunoglobulin A (IgA) deficiency in HSCT-treated SCID patients with genetic defects in IL2RG/GC or JAK3. These patients have a reduction in IgA-coated nasopharyngeal bacteria and exhibit microbial dysbiosis with increased pathobiont carriage. Interestingly, intravenous immunoglobulin replacement therapy can partially normalize nasopharyngeal immunoglobulin profiles and restore microbial communities in GC/JAK3 patients. Together, our results suggest a potential nonredundant role for type 2 immunity and/or of local IgA antibody production in the maintenance of nasopharyngeal microbial homeostasis and mucosal barrier function.

CD116+ fetal precursors migrate to the perinatal lung and give rise to human alveolar macrophages

Despite their importance in lung health and disease, it remains unknown how human alveolar macrophages develop early in life. Here we define the ontogeny of human alveolar macrophages from embryonic progenitors in vivo, using a humanized mouse model expressing human cytokines (MISTRG mice). We identified alveolar macrophage progenitors in human fetal liver that expressed the GM-CSF receptor CD116 and the transcription factor MYB. Transplantation experiments in MISTRG mice established a precursor-product relationship between CD34-CD116+ fetal liver cells and human alveolar macrophages in vivo. Moreover, we discovered circulating CD116+CD64-CD115+ macrophage precursors that migrated from the liver to the lung. Similar precursors were present in human fetal lung and expressed the chemokine receptor CX3CR1. Fetal CD116+CD64- macrophage precursors had a proliferative gene signature, outcompeted adult precursors in occupying the perinatal alveolar niche, and developed into functional alveolar macrophages. The discovery of the fetal alveolar macrophage progenitor advances our understanding of human macrophage origin and ontogeny.

CXCR3 and CXCR5 are highly expressed in HIV-1-specific CD8 central memory T cells from infected patients

New ways of characterizing CD8⁺ memory T cell responses in chronic infections are based on the measurement of chemokine receptor expression (CXCR3, CXCR5, and CX3CR1). We applied these novel phenotyping strategies to chronic HIV infection by comparing healthy donors (HDs), HIV-infected patients receiving antiretroviral therapy (ART), and spontaneous HIV controllers (HICs). In all groups, the memory cells exhibited high proportion of CXCR3⁺ cells. Proportions of CXCR5⁺ and CX3CR1⁺ cells were preferentially observed among central memory cells (Tcm) and effector memory cells (Tem) respectively. Chronic controlled HIV infection impacted the chemokine receptor profile of both HIV-specific and nonspecific CD8⁺ T cells. In total CD8⁺ T cells, the proportions of CXCR3^- CXCR5^- CX3CR1^- Tcm and Tem were lower in HIV-infected patients than in HDs with subtle differences between ART and HICs. Such phenotyping strategy also revealed differences in exhaustion and senescence phenotypes, the CXCR3⁺ CXCR5⁺ CX3CR1^- being more exhausted and senescent than the CXCR3⁺ CXCR5^- CX3CR1^- Tcm fraction. Among HIV-specific CD8⁺ T cells, the vast majority of Tcm cells were CXCR3⁺ and CXCR5⁺ cells in contrast with their nonspecific counterparts. In conclusion, the addition of migration markers contributes to better characterize Tcm/Tem compartment.

Dichotomous metabolic networks govern human ILC2 proliferation and function

Group 2 innate lymphoid cells (ILC2s) represent innate homologs of type 2 helper T cells (T_H2) that participate in immune defense and tissue homeostasis through production of type 2 cytokines. While T lymphocytes metabolically adapt to microenvironmental changes, knowledge of human ILC2 metabolism is limited, and its key regulators are unknown. Here, we show that circulating 'naive' ILC2s have an unexpected metabolic profile with a higher level of oxidative phosphorylation (OXPHOS) than natural killer (NK) cells. Accordingly, ILC2s are severely reduced in individuals with mitochondrial disease (MD) and impaired OXPHOS. Metabolomic and nutrient receptor analysis revealed ILC2 uptake of amino acids to sustain OXPHOS at steady state. Following activation with interleukin-33 (IL-33), ILC2s became highly proliferative, relying on glycolysis and mammalian target of rapamycin (mTOR) to produce IL-13 while continuing to fuel OXPHOS with amino acids to maintain cellular fitness and proliferation. Our results suggest that proliferation and function are metabolically uncoupled in human ILC2s, offering new strategies to target ILC2s in disease settings.

Human T-bet Governs Innate and Innate-like Adaptive IFN-γ Immunity against Mycobacteria

Inborn errors of human interferon gamma (IFN-γ) immunity underlie mycobacterial disease. We report a patient with mycobacterial disease due to inherited deficiency of the transcription factor T-bet. The patient has extremely low counts of circulating Mycobacterium-reactive natural killer (NK), invariant NKT (iNKT), mucosal-associated invariant T (MAIT), and Vδ2+ γδ T lymphocytes, and of Mycobacterium-non reactive classic TH1 lymphocytes, with the residual populations of these cells also producing abnormally small amounts of IFN-γ. Other lymphocyte subsets develop normally but produce low levels of IFN-γ, with the exception of CD8+ αβ T and non-classic CD4+ αβ TH1∗ lymphocytes, which produce IFN-γ normally in response to mycobacterial antigens. Human T-bet deficiency thus underlies mycobacterial disease by preventing the development of innate (NK) and innate-like adaptive lymphocytes (iNKT, MAIT, and Vδ2+ γδ T cells) and IFN-γ production by them, with mycobacterium-specific, IFN-γ-producing, purely adaptive CD8+ αβ T, and CD4+ αβ TH1∗ cells unable to compensate for this deficit.

Dysregulation of tryptophan catabolism at the host-skin microbiota interface in hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic skin disorder of unknown etiology that manifests as recurrent, painful lesions. Cutaneous dysbiosis and unresolved inflammation are hallmarks of active HS, but their origin and interplay remain unclear. Our metabolomic profiling of HS skin revealed an abnormal induction of the kynurenine pathway of tryptophan catabolism in dermal fibroblasts, correlating with the release of kynurenine pathway–inducing cytokines by inflammatory cell infiltrates. Notably, overactivation of the kynurenine pathway in lesional skin was associated with local and systemic depletion in tryptophan. Yet the skin microbiota normally degrades host tryptophan into indoles regulating tissue inflammation via engagement of the aryl hydrocarbon receptor (AHR). In HS skin lesions, we detected contextual defects in AHR activation coinciding with impaired production of bacteria-derived AHR agonists and decreased incidence of AHR ligand-producing bacteria in the resident flora. Dysregulation of tryptophan catabolism at the skin-microbiota interface thus provides a mechanism linking the immunological and microbiological features of HS lesions. In addition to revealing metabolic alterations in patients with HS, our study suggests that correcting AHR signaling would help restore immune homeostasis in HS skin.

Loss of homeostasis of tryptophan metabolism at the host-microbiota interface may contribute to Hidradenitis Suppurativa.

Molecular definition of group 1 innate lymphoid cells in the mouse uterus

Determining the function of uterine lymphocytes is challenging because of the dynamic changes in response to sex hormones and, during pregnancy, to the invading foetal trophoblast cells. Here we provide a genome-wide transcriptome atlas of mouse uterine group 1 innate lymphoid cells (ILCs) at mid-gestation. Tissue-resident Eomes+CD49a+ NK cells (trNK), which resemble human uterine NK cells, are most abundant during early pregnancy, and have gene signatures associated with TGF-β responses and interactions with trophoblast, epithelial, endothelial, smooth muscle cells, leucocytes and extracellular matrix. Conventional NK cells expand late in gestation and may engage in crosstalk with trNK cells involving IL-18 and IFN-γ. Eomes-CD49a+ ILC1s dominate before puberty, and specifically expand in second pregnancies when the expression of the memory cell marker CXCR6 is upregulated. These results identify trNK cells as the cellular hub of uterine group 1 ILCs, and mark CXCR6+ ILC1s as potential memory cells of pregnancy.

The Residual Innate Lymphoid Cells in NFIL3-Deficient Mice Support Suboptimal Maternal Adaptations to Pregnancy

Uterine NK cells are innate lymphoid cells (ILC) that populate the uterus and expand during pregnancy, regulating placental development and fetal growth in humans and mice. We have recently characterized the composition of uterine ILCs (uILCs), some of which require the transcription factor NFIL3, but the extent to which NFIL3-dependent cells support successful reproduction in mice is unknown. By mating Nfil3^−/− females with wild-type males, here we show the effects of NFIL3 deficiency in maternal cells on both the changes in uILCs during pregnancy and the downstream consequences on reproduction. Despite the presence of CD49a⁺Eomes⁻ uILC1s and the considerable expansion of residual CD49a⁺Eomes⁺ tissue-resident NK cells and uILC3s in pregnant Nfil3^−/− mice, we found incomplete remodeling of uterine arteries and decidua, placental defects, and fetal growth restriction in litters of normal size. These results show that maternal NFIL3 mediates non-redundant functions in mouse reproduction.

Composition, Development, and Function of Uterine Innate Lymphoid Cells

Innate lymphoid cells (ILCs), including NK cells, contribute to barrier immunity and tissue homeostasis. In addition to the role of uterine NK cells in placentation and fetal growth, other uterine ILCs (uILCs) are likely to play roles in uterine physiology and pathology. In this article, we report on the composition of uILCs in the endometrium during the luteal phase and in the decidua during early pregnancy. Whereas nonkiller uILC1s and uILC2s are barely detectable in mouse and not detected in humans, a sizeable population of uILC3s is found in human endometrium and decidua, which are mostly NCR⁺ and partially overlap with previously described IL-22–producing uterine NK cells. Development of mouse uILC3 is Nfil3 independent, suggesting unique features of uILCs. Indeed, although the cytokine production profile of mouse uILCs recapitulates that described in other tissues, IL-5, IL-17, and IL-22 are constitutively produced by uILC2s and uILC3s. This study lays the foundation to understand how ILCs function in the specialized uterine mucosa, both in tissue homeostasis and barrier immunity and during pregnancy.

IL-12/15/18-preactivated NK cells suppress GvHD in a mouse model of mismatched hematopoietic cell transplantation

Mismatched hematopoietic cell transplants for treating leukemia are complicated by graft versus host disease (GvHD). Here, we show that adoptively transferred IL‐12/15/18‐preactivated NK cells suppress GvHD in a mouse model of fully mismatched hematopoietic cell transplantation. These IL‐12/15/18‐preactivated NK cells maintained Eomesodermin (Eomes) and T‐bet expression upon transfer and, while there was no evidence of direct killing of donor T cells or host DCs by the IL‐12/15/18‐preactivated NK cells, proliferation of donor T cells was inhibited. Strikingly, the graft versus leukemia effect mediated by donor T cells was retained, resulting in improved overall survival of mice that received lymphoma cells, donor allogeneic T cells, and IL‐12/15/18‐preactivated NK cells. These results suggest that IL‐12/15/18‐preactivated NK cells may be useful in improving immunotherapy of mismatched hematopoietic cell transplantation. Compared with previously proposed protocols, our findings suggest that in vitro NK‐cell preactivation with this cytokine cocktail offers the significant advantage that cytokines do not need to be administered systemically to sustain NK‐cell activity, thus avoiding toxicity.

Immunomodulation of Selective Naive T Cell Functions by p110δ Inactivation Improves the Outcome of Mismatched Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) can treat certain hematologic malignancies due to the graft versus leukemia (GvL) effect but is complicated by graft versus host disease (GvHD). Expression of the p110δ catalytic subunit of the phosphoinositide 3-kinase pathway is restricted to leukocytes, where it regulates proliferation, migration, and cytokine production. Here, in a mouse model of fully mismatched hematopoietic cell transplantation (HCT), we show that genetic inactivation of p110δ in T cells leads to milder GvHD, whereas GvL is preserved. Inactivation of p110δ in human lymphocytes reduced T cell allorecognition. We demonstrate that both allostimulation and granzyme B expression were dependent on p110δ in naive T cells, which are the main mediators of GvHD, whereas memory T cells were unaffected. Strikingly, p110δ is not mandatory for either naive or memory T cells to mediate GvL. Therefore, immunomodulation of selective naive T cell functions by p110δ inactivation improves the outcome of allogeneic HSCT.

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Genetic p110δ inactivation in donor naive T cells mitigates GvHD in mice

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Pharmacological p110δ inactivation in human T cells reduces alloreactivity

Cutting edge: crucial role of IL-1 and IL-23 in the innate IL-17 response of peripheral lymph node NK1.1- invariant NKT cells to bacteria

We have shown previously that peripheral lymph node-resident retinoic acid receptor-related orphan receptor γt(+) NK1.1(-) invariant NKT (iNKT) cells produce IL-17A independently of IL-6. In this study, we show that the concomitant presence of IL-1 and IL-23 is crucial to induce a rapid and sustained IL-17A/F and IL-22 response by these cells that requires TCR-CD1d interaction and partly relies on IL-23-mediated upregulation of IL-23R and IL-1R1 expression. We further show that IL-1 and IL-23 produced by pathogen-associated molecular pattern-stimulated dendritic cells induce this response from NK1.1(-) iNKT cells in vitro, involving mainly TLR2/4-signaling pathways. Finally, we found that IL-17A production by these cells occurs very early and transiently in vivo in response to heat-killed bacteria. Overall, our study indicates that peripheral lymph node NK1.1(-) iNKT cells could be a source of innate Th17-related cytokines during bacterial infections and supports the hypothesis that they are able to provide an efficient first line of defense against bacterial invasion.

Skin and peripheral lymph node invariant NKT cells are mainly retinoic acid receptor-related orphan receptor (gamma)t+ and respond preferentially under inflammatory conditions

Lymph nodes (LNs) have been long considered as comprising few invariant NKT (iNKT) cells, and these cells have not been studied extensively. In this study, we unravel the existence of stable rather than transitional LN-resident NK1.1(-) iNKT cell populations. We found the one resident in peripheral LNs (PLNs) to comprise a major IL-17-producing population and to express the retinoic acid receptor-related orphan receptor (gamma)t (ROR(gamma)t). These cells respond to their ligand alpha-galactosylceramide (alpha-GalCer) in vivo by expanding dramatically in the presence of LPS, providing insight into how this rare population could have an impact in immune responses to infection. PLN-resident ROR(gamma)t(+) NK1.1(-) iNKT cells express concomitantly CCR6, the integrin alpha-chain alpha(E) (CD103), and IL-1R type I (CD121a), indicating that they might play a role in inflamed epithelia. Accordingly, skin epithelia comprise a major ROR(gamma)t(+) CCR6(+)CD103(+)CD121a(+) NK1.1(-) cell population, reflecting iNKT cell composition in PLNs. Importantly, both skin and draining PLN ROR(gamma)t(+) iNKT cells respond preferentially to inflammatory signals and independently of IL-6, indicating that they could play a nonredundant role during inflammation. Overall, our study indicates that ROR(gamma)t(+) iNKT cells could play a major role in the skin during immune responses to infection and autoimmunity.

iNKT cell development is orchestrated by different branches of TGF-beta signaling

Invariant natural killer T (iNKT) cells constitute a distinct subset of T lymphocytes exhibiting important immune-regulatory functions. Although various steps of their differentiation have been well characterized, the factors controlling their development remain poorly documented. Here, we show that TGF-beta controls the differentiation program of iNKT cells. We demonstrate that TGF-beta signaling carefully and specifically orchestrates several steps of iNKT cell development. In vivo, this multifaceted role of TGF-beta involves the concerted action of different pathways of TGF-beta signaling. Whereas the Tif-1gamma branch controls lineage expansion, the Smad4 branch maintains the maturation stage that is initially repressed by a Tif-1gamma/Smad4-independent branch. Thus, these three different branches of TGF-beta signaling function in concert as complementary effectors, allowing TGF-beta to fine tune the iNKT cell differentiation program.

iNKT Cell-development is Orchestrated by Different Branches of TGF-beta Signaling (47.24)

iNKT cells constitute a distinct subset of T lymphocytes exhibiting important immune-regulatory functions. Although different steps of their differentiation have been well characterized, the factors controlling their development remain poorly documented. Here, we show that TGF-β controls the differentiation program of iNKT cells. We demonstrate that TGF-β signaling finely and specifically orchestrates several steps of iNKT cell development. In vivo this multifaceted role of TGF-β involves the concerted action of different pathways of TGF-β signaling. Whereas the Tif-1γ branch controls lineage expansion, the Smad4 branch maintains the maturation stage that is initially repressed by a Tif-1γ/Smad4-independent branch. Thus, these three different branches of TGF-β signaling function in concert as complementary effectors allowing TGF-β to finely tune the iNKT cell-differentiation program.

The context of HLA-DR/CD18 complex in the plasma membrane governs HLA-DR-derived signals in activated monocytes

HLA-DR-derived signals in activated monocytes mediate both pro-inflammatory cytokine production and caspase-independent death, and have been postulated to play a role in inflammation and in its resolution, respectively. Herein, using the monocytic/macrophagic human cell line THP-1 primed with IFNgamma (IFNgamma-primed THP-1), we investigated how HLA-DR may integrate both signals. Our inhibition studies demonstrated that if cell death is dependent on PKCbeta activation, the induction of TNFalpha gene expression relies on PTK activation, in particular the Src family of kinases, but both cell responses implicate the beta2-integrin CD18. Accordingly, sequential immunoprecipitation experiments demonstrated that following engagement of HLA-DR on IFNgamma-primed THP-1 cells, the HLA-DR/CD18 complex physically associates with PKCbeta and with PTK. Pharmacological disruption of lipid rafts microdomains abolished the assembly of HLA-DR/CD18/PTK signaling complex, HLA-DR-mediated tyrosine activation, and the PTK-dependent TNFalpha expression in IFNgamma-primed THP-1 cells. In contrast, HLA-DR/CD18/PKCbeta complex was still formed and able to mediate cell death after cholesterol depletion of these cells. These results indicate that while the integrity of lipid rafts is necessary for the transduction of cytokine gene expression through the HLA-DR/CD18 complex, it is not necessary for the induction of the HLA-DR/CD18-dependent cell death. Thus, our study provides experimental evidence indicating the compartmentalization of HLA-DR/CD18 complex within or outside lipid rafts as a mechanism through which HLA-DR can integrate both PTK and PKCbeta signals leading to activation and death, respectively, of activated monocytes. This might provide new insights into how MHC class II signaling may regulate inflammatory response.

Coordinated Expression of Ig-Like Inhibitory MHC Class I Receptors and Acquisition of Cytotoxic Function in Human CD8+T Cells

MHC class I-specific inhibitory receptors are expressed by a subset of memory-phenotype CD8(+) T cells. Similar to NK cells, MHC class I-specific inhibitory receptors might subserve on T cells an important negative control that participates to the prevention of autologous damage. We analyzed here human CD8(+) T cells that express the Ig-like MHC class I-specific inhibitory receptors: killer cell Ig-like receptor (KIR) and CD85j. The cell surface expression of Ig-like inhibitory MHC class I receptors was found to correlate with an advanced stage of CD8(+) T cell maturation as evidenced by the reduced proliferative potential of KIR(+) and CD85j(+) T cells associated with their high intracytoplasmic perforin content. This concomitant regulation might represent a safety mechanism to control potentially harmful cytolytic CD8(+) T cells, by raising their activation threshold. Yet, KIR(+) and CD85j(+) T cells present distinct features. KIR(+)CD8(+) T cells are poor IFN-gamma producers upon TCR engagement. In addition, KIR are barely detectable at the surface of virus-specific T cells during the course of CMV or HIV-1 infection. By contrast, CD85j(+)CD8(+) T cells produce IFN-gamma upon TCR triggering, and represent a large fraction of virus-specific T cells. Thus, the cell surface expression of Ig-like inhibitory MHC class I receptors is associated with T cell engagement into various stages of the cytolytic differentiation pathway, and the cell surface expression of CD85j or KIR witnesses to the history of qualitatively and/or quantitatively distinct T cell activation events.

CD8+ T cells specific for EBV, cytomegalovirus, and influenza virus are activated during primary HIV infection

Primary viral infections, including primary HIV infection, trigger intense activation of the immune system, with marked expansion of CD38(+)CD8(+) T cells. Whether this expansion involves only viral-specific cells or includes a degree of bystander activation remains a matter of debate. We therefore examined the activation status of EBV-, CMV-, and influenza virus (FLU)-specific CD8(+) T cells during primary HIV infection, in comparison to HIV-specific CD8(+) T cells. The activation markers CD38 and HLA-DR were strongly expressed on HIV-specific CD8(+) T cells. Surprisingly, CD38 expression was also up-regulated on CD8(+) T cells specific for other viruses, albeit to a lesser extent. Activation marker expression returned to normal or near-normal values after 1 year of highly active antiretroviral therapy. HIV viral load correlated with CD38 expression on HIV-specific CD8(+) T cells but also on EBV-, CMV-, and FLU-specific CD8(+) T cells. In primary HIV infection, EBV-specific CD8(+) T cells also showed increased Ki67 expression and decreased Bcl-2 expression, compared with values observed in HIV-seronegative control subjects. These results show that bystander activation occurs during primary HIV infection, even though HIV-specific CD8(+) T cells express the highest level of activation. The role of this bystander activation in lymphocyte homeostasis and HIV pathogenesis remains to be determined.

Impact of antiretroviral therapy and changes in virus load on human immunodeficiency virus (HIV)-specific T cell responses in primary HIV infection

Human immunodeficiency virus (HIV)-specific CD4(+) and CD8(+) T cell responses were evaluated prospectively in a large cohort of subjects with HIV primary infection via long-term follow-up examining different virological profiles related to different treatment interventions. No correlation was observed between baseline virus load and HIV-specific CD4(+) and CD8(+) T cell responses. Highly active antiretroviral therapy (HAART)-induced suppression of viremia was associated with an increase in CD4(+) T cell proliferative responses. The HIV-specific proliferative response also increased, at least in the first 18 months, in subjects with detectable viremia, either treated or untreated. The magnitude of the HIV-specific CD8(+) T cell response decreased with suppression of viremia. In subjects with detectable viremia, the breadth and magnitude of the HIV-specific CD8(+) T cell responses increased progressively. Finally, whether HAART was initiated before or after seroconversion had little effect on HIV-specific CD4(+) and CD8(+) T cell responses.