Sustained impairment of IFN-gamma secretion in suppressed HIV-infected patients despite mature NK cell recovery: evidence for a defective reconstitution of innate immunity

Comparative analysis of within-host dynamics of acute infection and viral rebound dynamics in postnatally SHIV-infected ART-treated infant rhesus macaques

Viral dynamics of acute HIV infection and HIV rebound following suspension of antiretroviral therapy may be qualitatively similar but must differ given, for one, development of adaptive immune responses. Understanding the differences of acute HIV infection and viral rebound dynamics in pediatric populations may provide insights into the mechanisms of viral control with potential implications for vaccine design and the development of effective targeted therapeutics for infants and children. Mathematical models have been a crucial tool to elucidate the complex processes driving viral infections within the host. Traditionally, acute HIV infection has been modeled with a standard model of viral dynamics initially developed to explore viral decay during treatment, while viral rebound has necessitated extensions of that standard model to incorporate explicit immune responses. Previous efforts to fit these models to viral load data have underscored differences between the two infection stages, such as increased viral clearance rate and increased death rate of infected cells during rebound. However, these findings have been predicated on viral load measurements from disparate adult individuals. In this study, we aim to bridge this gap, in infants, by comparing the dynamics of acute infection and viral rebound within the same individuals by leveraging an infant nonhuman primate Simian/Human Immunodeficiency Virus (SHIV) infection model. Ten infant Rhesus macaques (RMs) orally challenged with SHIV.C.CH505 375H dCT and given ART at 8 weeks post-infection. These infants were then monitored for up to 60 months post-infection with serial viral load and immune measurements. We use the HIV standard viral dynamics model fitted to viral load measurements in a nonlinear mixed effects framework. We find that the primary difference between acute infection and rebound is the increased death rate of infected cells during rebound. We use these findings to generate hypotheses on the effects of adaptive immune responses. We leverage these findings to formulate hypotheses to elucidate the observed results and provide arguments to support the notion that delayed viral rebound is characterized by a stronger CD8+ T cell response.

Multimeric immunotherapeutic complexes activating natural killer cells towards HIV-1 cure

BACKGROUND

Combination antiretroviral therapy (cART) has dramatically extended the life expectancy of people living with HIV-1 and improved their quality of life. There is nevertheless no cure for HIV-1 infection since HIV-1 persists in viral reservoirs of latently infected CD4+ T cells. cART does not eradicate HIV-1 reservoirs or restore cytotoxic natural killer (NK) cells which are dramatically reduced by HIV-1 infection, and express the checkpoint inhibitors NKG2A or KIR2DL upregulated after HIV-1 infection. Cytotoxic NK cells expressing the homing receptor CXCR5 were recently described as key subsets controlling viral replication.

METHODS

We designed and evaluated the potency of "Natural killer activating Multimeric immunotherapeutic compleXes", called as NaMiX, combining multimers of the IL-15/IL-15Rα complex with an anti-NKG2A or an anti-KIR single-chain fragment variable (scFv) to kill HIV-1 infected CD4+ T cells. The oligomerization domain of the C4 binding protein was used to associate the IL-15/IL-15Rα complex to the scFv of each checkpoint inhibitor as well as to multimerize each entity into a heptamer (α form) or a dimer (β form). Each α or β form was compared in different in vitro models using one-way ANOVA and post-hoc Tukey's tests before evaluation in humanized NSG tg-huIL-15 mice having functional NK cells.

RESULTS

All NaMiX significantly enhanced the cytolytic activity of NK and CD8+ T cells against Raji tumour cells and HIV-1+ ACH-2 cells by increasing degranulation, release of granzyme B, perforin and IFN-γ. Targeting NKG2A had a stronger effect than targeting KIR2DL due to higher expression of NKG2A on NK cells. In viral inhibition assays, NaMiX initially increased viral replication of CD4+ T cells which was subsequently inhibited by cytotoxic NK cells. Importantly, anti-NKG2A NaMiX enhanced activation, cytotoxicity, IFN-γ production and CXCR5 expression of NK cells from HIV-1 positive individuals. In humanized NSG tg-huIL-15 mice, we confirmed enhanced activation, degranulation, cytotoxicity of NK cells, and killing of HIV-1 infected cells from mice injected with the anti-NKG2A.α NaMiX, as compared to control mice, as well as decreased total HIV-1 DNA in the lung.

CONCLUSIONS

NK cell-mediated killing of HIV-1 infected cells by NaMiX represents a promising approach to support HIV-1 cure strategies.

CD3+CD56+ and CD3-CD56+ lymphocytes in the cerebrospinal fluid of persons with HIV-1 subtypes B and C

The transactivator of transcription (Tat) is a HIV regulatory protein which promotes viral replication and chemotaxis. HIV-1 shows extensive genetic diversity, HIV-1 subtype C being the most dominant subtype in the world. Our hypothesis is the frequency of CSF CD3+CD56+ and CD3-CD56dim is reduced in HIV-1C compared to HIV-1B due to the Tat C30S31 substitution in HIV-1C. 34 CSF and paired blood samples (PWH, n = 20; PWoH, n = 14) were studied. In PWH, the percentage of CD3+CD56+ was higher in CSF than in blood (p < 0.001), comparable in both compartments in PWoH (p = 0.20). The proportion of CD3-CD56dim in CSF in PWH was higher than PWoH (p = 0.008). There was no subtype differences. These results showed CNS compartmentalization of NKT cell response in PWH.

Natural killer cells during acute HIV-1 infection: clues for HIV-1 prevention and therapy

Despite progress in preexposure prophylaxis, the number of newly diagnosed cases with HIV-1 remains high, highlighting the urgent need for preventive and therapeutic strategies to reduce HIV-1 acquisition and limit disease progression. Early immunological events, occurring during acute infection, are key determinants of the outcome and course of disease. Understanding early immune responses occurring before viral set-point is established, is critical to identify potential targets for prophylactic and therapeutic approaches. Natural killer (NK) cells represent a key cellular component of innate immunity and contribute to the early host defence against HIV-1 infection, modulating the pathogenesis of acute HIV-1 infection (AHI). Emerging studies have identified tools for harnessing NK cell responses and expanding specialized NK subpopulations with adaptive/memory features, paving the way for development of novel HIV-1 therapeutics. This review highlights the knowns and unknowns regarding the role of NK cell subsets in the containment of acute HIV-1 infection, and summarizes recent advances in selectively augmenting NK cell functions through prophylactic and therapeutic interventions.

Mechanisms of immune aging in HIV

Massive CD4+ T-cell depletion as well as sustained immune activation and inflammation are hallmarks of Human Immunodeficiency Virus (HIV)-1 infection. In recent years, an emerging concept draws an intriguing parallel between HIV-1 infection and aging. Indeed, many of the alterations that affect innate and adaptive immune subsets in HIV-infected individuals are reminiscent of the process of immune aging, characteristic of old age. These changes, of which the presumed cause is the systemic immune activation established in patients, likely participate in the immuno-incompetence described with HIV progression. With the success of antiretroviral therapy (ART), HIV-seropositive patients can now live for many years despite chronic viral infection. However, acquired immunodeficiency syndrome (AIDS)-related opportunistic infections have given way to chronic diseases as the leading cause of death since HIV infection. Therefore, the comparison between HIV-1 infected patients and uninfected elderly individuals goes beyond the sole onset of immunosenescence and extends to the deterioration of several physiological functions related to inflammation and systemic aging. In light of this observation, it is interesting to understand the precise link between immune activation and aging in HIV-1 infection to figure out how to best care for people living with HIV (PLWH).

Identification of the predominant human NK cell effector subset mediating ADCC against HIV-infected targets coated with BNAbs or plasma from PLWH

The potential of immunotherapy strategies utilizing broadly neutralizing antibodies (BNAbs), such as 3BNC117 and 10-1074, to limit viral replication while also facilitating clearance of HIV infected cells has heightened interest in identifying the predominant NK effector subset(s) capable of mediating antibody dependent cellular cytotoxicity (ADCC). Utilizing advanced polychromatic flow cytometry, we identified that CD57 positive NK cells from ART-suppressed in People Living With HIV (PLWH) expressed significantly higher levels of the CD16 FcγR receptor, 2B4 ADCC coreceptor, and HLA-DR activation marker while NKG2C positive NK cells expressed significantly higher levels of the CD2 ADCC coreceptor (p < 0.001, n = 32). Functionally, CD57 positive NK cells from ART-suppressed PLWH with either high or low NKG2C expansion exhibited significantly enhanced degranulation and IFN-γ production against heterologous gp120-coated ADCC targets coated with HIV reference plasma compared to CD57 negative NK cells (p = 0.0029, n = 11). CD57 positive NK cells from control donors lacking NKG2C expansion also exhibited significantly more degranulation and IFN-γ production at every timepoint tested against both heterologous ADCC targets (p = 0.019, n = 9) and HIV-1 infected autologous CD4⁺ primary T cells coated with BNAbs. Together, our data support CD57 positive and NKG2C positive NK cells as the predominant ADCC effector subsets capable of targeting HIV-infected CD4⁺ cells in the presence of 3BNC117 and 10-1074 immunotherapy.

The Architecture of Circulating Immune Cells Is Dysregulated in People Living With HIV on Long Term Antiretroviral Treatment and Relates With Markers of the HIV-1 Reservoir, Cytomegalovirus, and Microbial Translocation

Long-term changes in the immune system of successfully treated people living with HIV (PLHIV) remain incompletely understood. In this study, we assessed 108 white blood cell (WBC) populations in a cohort of 211 PLHIV on stable antiretroviral therapy and in 56 HIV-uninfected controls using flow cytometry. We show that marked differences exist in T cell maturation and differentiation between PLHIV and HIV-uninfected controls: PLHIV had reduced percentages of CD4+ T cells and naïve T cells and increased percentages of CD8+ T cells, effector T cells, and T helper 17 (Th17) cells, together with increased Th17/regulatory T cell (Treg) ratios. PLHIV also exhibited altered B cell maturation with reduced percentages of memory B cells and increased numbers of plasmablasts. Determinants of the T and B cell composition in PLHIV included host factors (age, sex, and smoking), markers of the HIV reservoir, and CMV serostatus. Moreover, higher circulating Th17 percentages were associated with higher plasma concentrations of interleukin (IL) 6, soluble CD14, the gut homing chemokine CCL20, and intestinal fatty acid binding protein (IFABP). The changes in circulating lymphocytes translated into functional changes with reduced interferon (IFN)- γ responses of peripheral blood mononuclear cells to stimulation with Candida albicans and Mycobacterium tuberculosis. In conclusion, this comprehensive analysis confirms the importance of persistent abnormalities in the number and function of circulating immune cells in PLHIV on stable treatment.

Antibody cooperative adsorption onto AuNPs and its exploitation to force natural killer cells to kill HIV-infected T cells

HIV represents a persistent infection which negatively alters the immune system. New tools to reinvigorate different immune cell populations to impact HIV are needed. Herein, a novel nanotool for the specific enhancement of the natural killer (NK) immune response towards HIV-infected T-cells has been developed. Bispecific Au nanoparticles (BiAb-AuNPs), dually conjugated with IgG anti-HIVgp120 and IgG anti-human CD16 antibodies, were generated by a new controlled, linker-free and cooperative conjugation method promoting the ordered distribution and segregation of antibodies in domains. The cooperatively-adsorbed antibodies fully retained the capabilities to recognize their cognate antigen and were able to significantly enhance cell-to-cell contact between HIV-expressing cells and NK cells. As a consequence, the BiAb-AuNPs triggered a potent cytotoxic response against HIV-infected cells in blood and human tonsil explants. Remarkably, the BiAb-AuNPs were able to significantly reduce latent HIV infection after viral reactivation in a primary cell model of HIV latency. This novel molecularly-targeted strategy using a bispecific nanotool to enhance the immune system represents a new approximation with potential applications beyond HIV.

Residual immune dysfunction under antiretroviral therapy

The usage of combination antiretroviral therapy in people with HIV (PWH) has incited profound improvement in morbidity and mortality. Yet, PWH may not experience full restoration of immune function which can manifest with non-AIDS comorbidities that frequently associate with residual inflammation and can imperil quality of life or longevity. In this review, we discuss the pathogenesis underlying chronic inflammation and residual immune dysfunction in PWH, as well as potential therapeutic interventions to ameliorate them and prevent incidence or progression of non-AIDS comorbidities. Current evidence advocates that early diagnosis and prompt initiation of therapy at high CD4 counts may represent the best available approach for an improved immune recovery in PWH.

Non-linear multidimensional flow cytometry analyses delineate NK cell phenotypes in normal and HIV-infected chimpanzees

Natural killer (NK) cells are primary immune effector cells with both innate and potentially adaptive functions against viral infections, but commonly become exhausted or dysfunctional during chronic diseases such as human immunodeficiency virus (HIV). Chimpanzees are the closest genetic relatives of humans and have been previously used in immunology, behavior and disease models. Due to their similarities to humans, a better understanding of chimpanzee immunology, particularly innate immune cells, can lend insight into the evolution of human immunology, as well as response to disease. However, the phenotype of NK cells has been poorly defined. In order to define NK cell phenotypes, we unbiasedly quantified NK cell markers among mononuclear cells in both naive and HIV-infected chimpanzees by flow cytometry. We identified NKG2D and NKp46 as the most dominant stable NK cells markers using multidimensional data reduction analyses. Other traditional NK cell markers such as CD8α, CD16 and perforin fluctuated during infection, while some such as CD56, NKG2A and NKp30 were generally unaltered by HIV infection, but did not delineate the full NK cell repertoire. Taken together, these data indicate that phenotypic dysregulation may not be pronounced during HIV infection of chimpanzees, but traditional NK cell phenotyping used for both humans and other non-human primate species may need to be revised to accurately identify chimpanzee NK cells.

Aberrant natural killer (NK) cell activation and dysfunction among ART-treated HIV-infected adults in an African cohort

BACKGROUND

We examined NK cell phenotypes and functions after seven years of ART and undetectable viral loads (<50 copies/ml) with restored CD4 T-cell counts (≥500 cells/μl) and age-matched healthy-HIV-uninfected individuals from the same community.

METHODS

Using flow-cytometry, NK cell phenotypes were described using lineage markers (CD56^+/-CD16^+/-). NK cell activation was determined by expression of activation receptors (NKG2D, NKp44 and NKp46) and activation marker CD69. NK cell function was determined by CD107a, granzyme-b, and IFN-gamma production.

RESULTS

CD56 dim and CD56 bright NK cells were lower among ART-treated-HIV-infected than among age-matched-HIV-negative individuals; p = 0.0016 and p = 0.05 respectively. Production of CD107a (P = 0.004) and Granzyme-B (P = 0.005) was lower among ART-treated-HIV-infected relative to the healthy-HIV-uninfected individuals. NKG2D and NKp46 were lower, while CD69 expression was higher among ART-treated-HIV-infected than healthy-HIV-uninfected individuals.

CONCLUSION

NK cell activation and dysfunction persisted despite seven years of suppressive ART with "normalization" of peripheral CD4 counts.

NK cells in treated HIV-infected children display altered phenotype and function

BACKGROUND

Chronic HIV infection is known to trigger a population redistribution and alteration in the functional capacity of natural killer (NK) cells. Because of improved antiretroviral treatments, there are rising numbers of adolescents and young adults worldwide who are living with HIV infection since birth.

OBJECTIVE

We sought to determine how NK-cell phenotypic and functional subsets are altered in treated pediatric patients.

METHODS

NK cells were contrasted among 29 HIV-unexposed and uninfected controls (5-19 years), 23 HIV-exposed but uninfected patients (3-19 years), and 25 HIV-infected patients (3-19 years) using multiparametric flow cytometry.

RESULTS

Although most NK-cell markers did not differ, activating receptors such as NKp46, DNAX accessory molecule-1, and NKG2C and stimulatory receptors such as CD2 and CD11c were expressed by a higher frequency of NK cells in HIV-infected patients than in controls. Interestingly, there were less differences between HIV-infected and HIV-exposed but uninfected children. There was an inverse relationship between CD4/CD8 T-cell ratio (as a marker of disease progression) and CD11c and NKG2C frequency and CD69 upregulation on stimulation among HIV-infected patients.

CONCLUSIONS

A chronic NK-cell activation phenotype persists in HIV-infected children receiving antiretroviral therapy and is associated with declining CD4/CD8 T-cell ratios. A lower CD4/CD8 T-cell ratio was associated with higher baseline granzyme B (P = .0068; R² = 0.29) and degranulation potential (P = .022; R² = 0.22) in stimulated NK cells. Thus, NK cells in HIV-infected children receiving treatment have reduced functional potential and an activated phenotype that distinguishes them from uninfected children.

KIR and HLA-C Genetic Polymorphisms Influence Plasma IP-10 Concentration in Antiretroviral Therapy-Naive HIV-Infected Adult Zimbabweans

Past studies on the relationship between Killer cell Immunoglobulin-like Receptor (KIR) and Human Leukocyte Antigen (HLA) genetic variation and chronic immune activation (CIA) in HIV infection are not uniformly consistent. Moreover, interferon-γ-induced protein 10 (IP-10) is a soluble biomarker of immune activation, with high plasma concentrations predicting accelerated disease progression in HIV infection. Thus, we investigated the association of KIR and HLA-C genetic polymorphisms with plasma IP-10 concentration in 183 treatment-naive chronically HIV-infected adults of Bantu origin from Zimbabwe. KIR genetic variation was determined using allele-specific primer PCR while HLA-C typing was characterized by sequencing. Plasma IP-10 was quantified using enzyme-linked immunosorbent assay. The KIR2DL3 gene was significantly associated with CIA as observed from IP-10 concentrations among KIR2DL3 carriers (265.20 pg/mL, IQR: 179.99-385.19) compared with KIR2DL3 noncarriers (183.56 pg/mL; IQR: 110.98-230.81; p = 0.001) and among KIR2DL3+HLA-C2 carriers (226.23 pg/mL, IQR: 187.96-394.73) compared with KIR2DL3+HLA-C2 noncarriers (212.86 pg/mL, IQR: 160.15-344.99; p = 0.017), respectively. Similarly, IP-10 concentrations were significantly higher (p = 0.030) in the KIR3DS1 carriers (313.86 pg/mL, IQR: 230.05-469.20) compared with KIR3DS1 noncarriers (246.01 pg/mL, IQR: 169.58-373.32). Thus, KIR and HLA-C could be playing important roles in HIV-associated immune activation. The elevation of IP-10 in KIR2DL3 and KIR2DL3+C2 could potentially be explained by increased IFN-γ secretion from activated NK cell activation due to the absence of KIR2DL3's cognate C1 ligand. To the best of our knowledge, this is the first study on a potential link between KIR and HLA-C genetic determinants and plasma IP-10 concentration in this population sample. Future studies are called for in other world populations for biomarkers of disease progression and mechanisms of IP-10 variability in HIV infection.

Imbalance of the two main circulating dendritic cell subsets in patients with myasthenia gravis

Although it is well documented that circulating dendritic cells (DCs) have specialized features during many kinds of physiological and pathological conditions, there are few reports about the features of DCs in the peripheral blood of myasthenia gravis (MG) patients. We investigated the quantitative and component features of DCs and their implications in MG. Peripheral blood samples from different kinds of MG patients were collected and their clinical characteristics were recorded. Using flow cytometry, we distinguished circulating DC subsets [plasmacytoid DCs (pDCs) and myeloid DCs (mDCs)] and enumerated their densities in peripheral blood. Absolute numbers of circulating pDCs were significantly decreased in naïve MG patients compared with healthy controls, resulting in a markedly lower ratio of the pDC to mDC percentage in total circulating DCs (pDCs/mDCs), suggesting an imbalance in the proportions of the two main circulating DC subsets. The clinical status of MG patients was improved after drug treatment, together with increased pDCs/mDCs. In a longitudinal follow-up, we observed that circulating mDCs were significantly reduced after 1 month of therapy with a corticosteroid and immunosuppressant, resulting in recovery of pDCs/mDCs. Although the exact meaning of the proportion change in circulating DC subsets is unknown, pDCs/mDCs might reflect the balance between the autoimmune response and immune tolerance of a patient. Moreover, changes in pDCs/mDCs during treatment might be a promising marker to predict the efficacy of a specific drug used for MG patients.

In Vitro Exposure to Prostratin but Not Bryostatin-1 Improves Natural Killer Cell Functions Including Killing of CD4+ T Cells Harboring Reactivated Human Immunodeficiency Virus

In the attempt of purging the HIV-1 reservoir through the “shock-and-kill” strategy, it is important to select latency-reversing agents (LRAs) devoid of deleterious effects on the antiviral function of immune effector cells. Here, we investigated two LRAs with PKC agonist activity, prostratin (PRO) and bryostatin-1 (BRY), for their impact on the function of natural killer (NK) cells, the major effectors of innate immunity whose potential in HIV-1 eradication has emerged in recent clinical trials. Using NK cells of healthy donors, we found that exposure to either PRO or BRY potently activated NK cells, resulting in upmodulation of NKG2D and NKp44 activating receptors and matrix metalloprotease-mediated shedding of CD16 receptor. Despite PRO and BRY affected NK cell phenotype in the same manner, their impact on NK cell function was diverse and showed considerable donor-to-donor variation. Altogether, in most tested donors, the natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) of NK cells were either improved or maintained by PRO, while both activities were impaired by BRY. Moreover, we analyzed the effect of these drugs on the capacity of treated NK cells to kill autologous latently infected CD4⁺ T cells reactivated via the same treatment. First, we found that PRO but not BRY increased upmodulation of the ULBP2 ligand for NKG2D on reactivated p24⁺ cells. Importantly, we showed that clearance of reactivated p24⁺ cells by NK cells was enhanced when both targets and effectors were exposed to PRO but not to BRY. Overall, PRO had a superior potential compared with BRY as to the impact on key NK cell functions and on NK-cell-mediated clearance of the HIV-1 reservoir. Our results emphasize the importance of considering the effects on NK cells of candidate “shock-and-kill” interventions. With respect to combinative approaches, the impact on NK cells of each LRA should be re-evaluated upon combination with a second LRA, which may have analogous or opposite effects, or with immunotherapy targeting NK cells. In addition, avoiding co-administration of LRAs that negatively impact ADCC activity by NK cells might be essential for successful application of antibodies or vaccination to “shock-and-kill” strategies.

Effects of HIV infection and ART on phenotype and function of circulating monocytes, natural killer, and innate lymphoid cells

HIV infection causes upregulation of markers of inflammation, immune activation and apoptosis of host adaptive, and innate immune cells particularly monocytes, natural killer (NK) and innate lymphoid cells (ILCs). Although antiretroviral therapy (ART) restores CD4 T-cell counts, the persistent aberrant activation of monocytes, NK and ILCs observed likely contributes to the incomplete recovery of T-cell effector functions. A better understanding of the effects of HIV infection and ART on the phenotype and function of circulating monocytes, NK, and ILCs is required to guide development of novel therapeutic interventions to optimize immune recovery.

Assessing immune aging in HIV-infected patients

Many of the alterations that affect innate and adaptive immune cell compartments in HIV-infected patients are reminiscent of the process of immune aging, characteristic of old age. These alterations define the immunological age of individuals and are likely to participate to the decline of immune competence with HIV disease progression. It is therefore important to characterize these changes, which point toward the accumulation of highly differentiated immunocompetent cells, associated with overall telomere length shortening, as well as understanding their etiology, especially related to the impact of chronic immune activation. Particular attention should be given to the exhaustion of primary immune resources, including haematopoietic progenitors and naïve cells, which holds the key for effective hematopoiesis and immune response induction, respectively. The alteration of these compartments during HIV infection certainly represents the foundation of the immune parallel with aging.

Alterations of the NK cell pool in HIV/HCV co-infection

BACKGROUND

A relevant proportion of human immunodeficiency virus (HIV) infected patients is co-infected with the hepatitis C virus (HCV). HCV co-infection in HIV-positive patients is associated with faster progression of liver disease in comparison to HCV mono-infection. Natural killer (NK) cells critically modulate the natural course of HCV infection. Both HIV and HCV mono-infection are associated with alterations of the NK cell pool. However, little data is available concerning phenotype and function of NK cells in HIV/HCV co-infection.

METHODS

A total of 34 HIV/HCV co-infected, 35 HIV and 39 HCV mono-infected patients and 43 healthy control persons were enrolled into this study. All HIV-positive patients were under effective antiretroviral therapy. NK cell phenotype, IFN-γ production and degranulation were studied by flow cytometry.

RESULTS

NK cell frequency in HIV/HCV co-infection was significantly lower than in healthy individuals but did not differ from HIV and HCV mono-infection. HIV/HCV co-infection was associated with significantly decreased expression of the maturation/differentiation markers CD27/62L/127 on NK cells but increased expression of CD57 compared to healthy controls. Of note, expression also differed significantly from HCV mono-infection but was similar to HIV mono-infection, suggesting a pronounced impact of HIV on these alterations. Similar findings were made with regard to the NK cell receptors NKG2A/C and NKp30. More importantly, NK cells in co-infection displayed a highly impaired functional activity with significantly lower IFN-γ production and degranulation than in healthy donors as well as HIV and HCV mono-infection, suggesting a synergistic effect of both viruses.

CONCLUSIONS

Our data indicate that HIV/HCV co-infection is associated with significant alterations of the NK cell pool, which might be involved in the rapid progression of liver disease in co-infected patients and which mainly reflect alterations observed in HIV mono-infection.

Role of Natural Killer Cells in HIV-Associated Malignancies

Now in its fourth decade, the burden of HIV disease still persists, despite significant milestone achievements in HIV prevention, diagnosis, treatment, care, and support. Even with long-term use of currently available antiretroviral therapies (ARTs), eradication of HIV remains elusive and now poses a unique set of challenges for the HIV-infected individual. The occurrence of HIV-associated non-AIDS-related comorbidities outside the scope of AIDS-defining illnesses, in particular non-AIDS-defining cancers, is much greater than the age-matched uninfected population. The underlying mechanism is now recognized in part to be related to the immune dysregulated and inflammatory status characteristic of HIV infection that persists despite ART. Natural killer (NK) cells are multifunctional effector immune cells that play a critical role in shaping the innate immune responses to viral infections and cancer. NK cells can modulate the adaptive immune response via their role in dendritic cell (DC) maturation, removal of immature tolerogenic DCs, and their ability to produce immunoregulatory cytokines. NK cells are therefore poised as attractive therapeutic targets that can be harnessed to control or clear both HIV and HIV-associated malignancies. To date, features of the tumor microenvironment and the evolution of NK-cell function among individuals with HIV-related malignancies remain unclear and may be distinct from malignancies observed in uninfected persons. This review intends to uncouple anti-HIV and antitumor NK-cell features that can be manipulated to halt the evolution of HIV disease and HIV-associated malignancies and serve as potential preventative and curative immunotherapeutic options.

Study of Natural Cytotoxicity Receptors in Patients with HIV/AIDS and Cancer: A Cross-Sectional Study

The NCR receptors play a fundamental role in the cytotoxicity mediated by NK cells against tumor cells. In the current study, we investigated possible HIV/AIDS-related changes in the expression of the NCR receptors comparing healthy donors, HIV/AIDS patients, and HIV/AIDS patients with cancer (HIV/AIDSWC). The NCRs were quantified in NK cells (NK^dim and NK^bright) and T lymphocytes from peripheral blood samples by flow cytometry. We found a significant decrease in the frequency of NK cells expressing NKp46 in HIV/AIDS group (p = 0.0012). There was a decrease in the frequency of NK cells expressing NKp46 in the HIV/AIDSWC group; however, this was not statistically significant. We found a significant decrease in the frequency of NK cells expressing NKp30 in the HIV/AIDS group (p = 0.0144). There was a decrease in the frequency of NK cells expressing NKp30 and in the HIV/AIDSWC group, but this was not statistically significant. There were no changes in the distribution of NK cells and their subtypes in both groups.

Increased CD56(bright) NK cells in HIV-HCV co-infection and HCV mono-infection are associated with distinctive alterations of their phenotype

Background

HIV-HCV co-infection is associated with accelerated progression to hepatic fibrosis, cirrhosis and hepatocellular carcinoma than HCV mono-infection. The contribution of innate immunity during HIV-HCV co-infection has been a relatively under-investigated area. Natural killer (NK) cells are pivotal sentinels of innate immunity against viruses and tumour cells. In this study we evaluated the effect of HIV-HCV co-infection on peripheral blood NK cell subsets with emphasis on the phenotype of CD56^bright NK cells.

Methods

Sixty patients were included in the study; HIV mono-infected (n = 12), HCV mono-infected (n = 15), HCV-HIV co-infected (n = 21) and healthy controls (n = 16). PBMCs were isolated and immunophenotyping of NK cells was performed by flowcytometry.

Results

We observed an expansion of CD56^bright NK cell subset in HIV-HCV co-infection as compared to healthy controls and HIV mono-infected group. All the infected groups had an upregulated expression of the activating receptor NKG2D on CD56^bright NK cells in comparison to healthy controls while not differing amongst themselves.

The expression of NKp46 in HIV-HCV co-infected group was significantly upregulated as compared to both HIV as well as HCV mono-infections while NKp30 expression in the HIV-HCV co-infected group significantly differed as compared to HIV mono-infection. The CD56^bright NK cell subset was activated in HIV-HCV co-infection as assessed by the expression of CD69 as compared to healthy controls but was significantly downregulated in comparison to HIV mono-infection. CD95 expression on CD56^bright NK cells followed the same pattern where there was an increased expression of CD95 in HIV mono-infection and HIV-HCV co-infection as compared to healthy controls. In contrast to CD69 expression, CD95 expression in HCV mono-infection was decreased when compared to HIV mono-infection and HIV-HCV co-infection. Finally, expression of CXCR3 on CD56^bright NK cells was increased in HIV-HCV co-infection in comparison to HIV mono-infection while remaining similar to HCV mono-infection.

Conclusion

Thus, HIV-HCV co-infection is able to modulate the phenotype of CD56^bright NK cell subset in a unique way such that NKp46 and CXCR3 expressions are distinct for co-infection while both mono-infections have an additive effect on CD56^bright, CD69 with CD95 expressions. HCV mono-infection has a dominant effect on NKp30 expression while NKG2D and CD127 expressions remained same in all the groups.

HIV mono-infection is associated with an impaired anti-hepatitis C virus activity of natural killer cells

OBJECTIVE

Hepatitis C virus (HCV) infection in HIV(+) patients is associated with faster liver disease progression compared with HCV mono-infection. HIV-associated immune defects are considered to play an important role in this context. Here, we analyzed the effects of HIV infection on natural killer (NK)-cell-mediated anti-HCV activity.

DESIGN

NK cell phenotype and interferon gamma (IFN-γ) production, NK cell-mediated inhibition of HCV replication and CD4 T-cell/NK cell interactions were studied in treatment naive HIV (n = 22), and HIV patients under combined antiretroviral therapy (n = 29), compared with healthy controls (n = 20).

METHODS

NK cell-mediated inhibition of HCV replication was analyzed using the HuH7A2HCVreplicon model. IFN-γ production of NK cells as well as interleukin-2 secretion of CD4 T lymphocytes were studied by flow cytometry.

RESULTS

Peripheral blood mononuclear cells from HIV(+) patients displayed a significantly impaired anti-HCV activity, irrespective of combined antiretroviral therapy. This could in part be explained by HIV-associated decline in NK cell numbers. In addition, NK cell IFN-γ production was significantly impaired in HIV infection. Accordingly, we found low frequency of IFN-γ(+) NK cells in HIV(+) patients to be associated with ineffective inhibition of HCV replication. Finally, we show that CD4 T-cell-mediated stimulation of NK cell IFN-γ production was dysregulated in HIV infection with an impaired interleukin-2 response of NK cells.

CONCLUSION

HIV infection has a strong suppressive effect on anti-HCV activity of NK cells. This may contribute to low spontaneous clearance rate and accelerated progression of HCV-associated liver disease observed in HIV(+) patients.

Early ART Results in Greater Immune Reconstitution Benefits in HIV-Infected Infants: Working with Data Missingness in a Longitudinal Dataset

Background

Early initiation of anti-retroviral treatment (ART) decreases mortality as compared to deferred treatment, but whether it preserves immune cells from early loss or promotes their recovery remains undefined. Determination of complex immunological endpoints in infants is often marred by missing data due to missed visits and/or inadequate sampling. Specialized methods are required to address missingness and facilitate data analysis.

Methods

We characterized the changes in cellular and humoral immune parameters over the first year of life in 66 HIV-infected infants (0–1 year of age) enrolled in the CHER study starting therapy within 12 weeks of birth (n = 42) or upon disease progression (n = 24). A convenience cohort of 23 uninfected infants aged 0–6 months born to mothers with HIV-1 infection was used as controls. Flow cytometry and ELISA were used to evaluate changes in natural killer (NK) cells, plasmacytoid dendritic cells (pDC), and CD4⁺ or CD8⁺ T-cell frequencies. Data missingness was assessed using Little's test. Complete datasets for analysis were created using Multiple Imputation (MI) or Bayesian modeling and multivariate analysis was conducted on the imputed datasets.

Results

HIV-1-infected infants had greater frequency of CD4⁺ T cells with naïve phenotype, as well as higher serum IL-7 levels than HIV exposed/uninfected infants. The elevated data missingness was completely at random, allowing the use of both MI and Bayesian modeling. Both methods indicate that early ART initiation results in higher CD4⁺ T cell frequency, lower expression of CD95 in CD8⁺ T cell, and preservation of naïve T cell subsets. In contrast, innate immune effectors appeared to be similar independently of the timing of ART initiation.

Conclusions

Early ART initiation in infants with perinatal HIV infection reduces immune activation and preserves an early expansion of naïve T-cells with undiminished innate cell numbers, giving greater immune reconstitution than achieved with deferred ART. Both statistical approaches concurred in this finding.

HIV patients stable on ART retain evidence of a high CMV load but changes to Natural Killer cell phenotypes reflect both HIV and CMV

Background

Whilst ART corrects many effects of HIV disease, T cell populations retain features of accelerated immunological aging.

Methods

Here we analyse phenotypic changes to natural killer (NK) cells in HIV patients who began ART with <200 CD4 T-cells/µl and maintained virological control for 12–17 years, compared with CMV seropositive and seronegative healthy control donors.

Results

Humoral responses to CMV antigens (lysate, gB, IE-1) remain elevated in the patients (P < 0.0001) despite the long duration of ART. Patient’s NK cells responded poorly to K562 cells when assessed by CD107a and IFNγ, but this could not be attributed to CMV as responses were low in CMV-seronegative controls. Moreover HIV (and not CMV) increased expression of CD57 on CD56^lo cells.

Conclusions

Comparisons with published studies suggest that CMV accelerates age-related increases in CD57 expression but levels plateau by 60–70 years of age, so the effect of CMV disappears. In HIV patients the plateau is higher and perhaps reached sooner.

Electronic supplementary material

The online version of this article (doi:10.1186/s12981-015-0080-9) contains supplementary material, which is available to authorized users.

Accumulation of Cytotoxic CD16+ NK Cells in Simian Immunodeficiency Virus-Infected Lymph Nodes Associated with In Situ Differentiation and Functional Anergy

Recent evidence suggests that even in treated infections, human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication may continue in lymph nodes (LN), serving as a potential virus reservoir. Here we investigated the effects of lentivirus infection on natural killer (NK) cell frequencies, phenotypes, and functions in naive and acutely or chronically SIVmac239-infected rhesus macaques. Compared to that in naive animals, we observed a 3-fold-greater frequency of cytotoxic CD16(+) CD56(-) NK cells in LN of chronically infected macaques. However, NK cells did not appear to be trafficking to LN, as homing markers CD62L and CCR7 did not increase on circulating NK cells during infection. LN NK cells demonstrated enhanced cytotoxicity in acute infection, with 2-fold increases in perforin expression and 3-fold increases in CD107a expression following mitogen stimulation. Lysis of K562 cells by LN NK cells from acutely infected animals was greater than lysis by preinfection samples from the same animals. LN NK cells from chronically infected animals lysed K562 cells more efficiently than LN NK cells from uninfected animals, but importantly, surrogate markers of cytotoxicity in infected macaques were disproportionately greater than ex vivo killing. Furthermore, Tim-3, an indicator of activation and/or exhaustion, was upregulated 3-fold on LN NK cells in chronically infected animals. Collectively, these data suggest that LN NK cells are skewed toward a cytotoxic phenotype during SIV infection but may become dysfunctional and exhausted in chronic disease.

IMPORTANCE

The accumulation of CD16(+) CD56(-) NK cells in the SIV-infected lymph node without changes in NK homing to the LN could suggest that these cells are differentiating in situ. Surprisingly, this increase in frequency of the cytotoxic subset of NK cells is not accompanied by an increase of similar magnitude in the cytolytic function of LN lymphocytes. This functional modulation, together with the higher Tim-3 expression observed on LN NK cells isolated from chronically infected animals than on those from naive macaques, is indicative of an exhausted phenotype. This exhaustion could contribute to the robust replication of HIV and SIV in the LN during acute and chronic stages of infection, allowing the survival of infected cells and maintenance of a viral reservoir.

Plasmacytoid dendritic cell and functional HIV Gag p55-specific T cells before treatment interruption can inform set-point plasma HIV viral load after treatment interruption in chronically suppressed HIV-1(+) patients

The identification of immune correlates of HIV control is important for the design of immunotherapies that could support cure or antiretroviral therapy (ART) intensification-related strategies. ART interruptions may facilitate this task through exposure of an ART partially reconstituted immune system to endogenous virus. We investigated the relationship between set-point plasma HIV viral load (VL) during an ART interruption and innate/adaptive parameters before or after interruption. Dendritic cell (DC), natural killer (NK) cell and HIV Gag p55-specific T-cell functional responses were measured in paired cryopreserved peripheral blood mononuclear cells obtained at the beginning (on ART) and at set-point of an open-ended interruption from 31 ART-suppressed chronically HIV-1(+) patients. Spearman correlation and linear regression modeling were used. Frequencies of plasmacytoid DC (pDC), and HIV Gag p55-specific CD3(+)  CD4(-)  perforin(+)  IFN-γ(+) cells at the beginning of interruption associated negatively with set-point plasma VL. Inclusion of both variables with interaction into a model resulted in the best fit (adjusted R(2)  = 0·6874). Frequencies of pDC or HIV Gag p55-specific CD3(+)  CD4(-)  CSFE(lo)  CD107a(+) cells at set-point associated negatively with set-point plasma VL. The dual contribution of pDC and anti-HIV T-cell responses to viral control, supported by our models, suggests that these variables may serve as immune correlates of viral control and could be integrated in cure or ART-intensification strategies.

The effect of HIV infection on the host response to bacterial sepsis

Bacterial sepsis is an important cause of morbidity and mortality in patients with HIV. HIV causes increased susceptibility to invasive infections and affects sepsis pathogenesis caused by pre-existing activation and exhaustion of the immune system. We review the effect of HIV on different components of immune responses implicated in bacterial sepsis, and possible mechanisms underlying the increased risk of invasive bacterial infections. We focus on pattern recognition receptors and innate cellular responses, cytokines, lymphocytes, coagulation, and the complement system. A combination of factors causes increased susceptibility to infection and can contribute to a disturbed immune response during a septic event in patients with HIV. HIV-induced perturbations of the immune system depend on stage of infection and are only in part restored by combination antiretroviral therapy. Immunomodulatory treatments currently under development for sepsis might be particularly beneficial to patients with HIV co-infection because many pathogenic mechanisms in HIV and sepsis overlap.

Impaired natural killer cell responses are associated with loss of the highly activated NKG2A(+)CD57(+)CD56(dim) subset in HIV-1 subtype D infection in Uganda

Objective:

Of the predominant HIV-1 subtypes in Uganda, subtype D infection confers a worse prognosis. HIV-1 infection causes perturbations to natural killer (NK) cells, and yet these cells can exert immune pressure on the virus and influence clinical outcome. Here, we studied NK cell activation and function in Ugandans with chronic untreated HIV-1 subtype D infection in comparison to uninfected community matched controls.

Methods:

Cryopreserved peripheral blood mononuclear cells (PBMCs) from 42 HIV-infected individuals and 28 HIV-negative controls were analysed using eight-colour flow cytometry. NK cell surface expression of CD16, CD56, CD57, HLA-DR and NKG2A were used to investigate activation, maturation and differentiation status. NK cell function was evaluated by measuring interferon-gamma (IFNγ) production in response to K562 cells, or interleukin (IL)-12 and IL-18.

Results:

CD56^dim NK cells from HIV-infected individuals produced less IFNγ in response to IL-12 and IL-18 than did CD56^dim NK cells from uninfected controls. Infected individuals had lower levels of CD56^dim NK cells coexpressing the differentiation markers NKG2A and CD57 than controls. In addition, their NKG2A⁺CD57⁺ CD56^dim NK cells displayed elevated activation levels as assessed by HLA-DR expression. Cytokine-induced IFNγ production correlated directly with coexpression of CD57 and NKG2A on CD56^dim NK cells.

Conclusion:

HIV-1 subtype D infection is associated with impaired NK cell responsiveness to cytokines, decline of the NKG2A⁺CD57⁺ CD56^dim NK cell subset, as well as elevated activation in this subset. These alterations within the NK cell compartment may contribute to immunopathogenesis of HIV-1 subtype D infection in Ugandans.

The natural killer cell interferon-gamma response to bacteria is diminished in untreated HIV-1 infection and defects persist despite viral suppression

OBJECTIVE

Natural killer (NK) cells are important in innate immune responses to bacterial and viral pathogens. HIV-1 infection is associated with opportunistic bacterial infections and with microbial translocation, but the nature of the NK cell response to bacteria during HIV-1 infection has not been studied extensively. The objective of this study was to compare NK cell responses to bacteria in HIV-1-infected versus that in uninfected individuals.

METHODS

Multicolor flow cytometry was used to evaluate the ability of blood NK cell subsets (CD56CD16, CD56CD16, and CD56CD16) from treated, virally suppressed, and untreated viremic subjects with chronic HIV-1 infection and uninfected controls, to secrete interferon gamma (IFN-γ) in response to the in vitro stimulation of peripheral blood mononuclear cells with heat-killed commensal Escherichia coli or pathogenic Salmonella typhimurium.

RESULTS

All 3 NK cell subsets produced IFN-γ in response to bacteria, but CD56CD16 NK cells were least responsive. Untreated HIV-1-infected donors had increased frequencies of CD56CD16 NK cells and lower overall frequencies of IFN-γ-producing NK cells responding to E. coli and S. typhimurium than did NK cells from uninfected donors. These NK cell defects were not fully restored in antiretroviral therapy-treated donors. Monocytes were necessary for NK cells to respond to bacteria, but the HIV-associated defect was intrinsic to NK cells because the addition of normal monocytes did not restore IFN-γ production in response to bacteria.

CONCLUSIONS

Functional defects and numeric alterations of NK cell subsets lead to decreased frequencies of bacteria-reactive, IFN-γ-producing NK cells in HIV-1-infected subjects, even those on antiretroviral therapy.

Activation of NK cells is associated with HIV-1 disease progression

The main predictor of HIV-1 disease progression is CD8(+) T cell activation, characterized by elevated expression of CD38 and HLA-DR. NK cells are also activated in viremic HIV-1-infected individuals. However, the relationship between NK cell activation and HIV-1 disease progression remains undefined. We characterized NK cell activation and its association with disease progression in treatment of naive HIV-1-infected individuals, who naturally maintained low/undetectable viremia (elite and viremic controllers), compared with progressors and AIDS subjects, and treated individuals. Our results show that CD38 expression on NK cells, predominantly in the cytotoxic CD56(dim)CD16(+) subset, is associated with HIV-1 disease progression (CD4(+) T cell count and pVL), T cell activation (percentage of CD38(+)HLA-DR(+) T cells), sCD14, inflammation, and innate immune activation. Moreover, NK cell activation is increased in HIV-1-infected subjects progressing to AIDS but not in elite and viremic controllers. ART partially reduces the proportion of activated NK cells. Furthermore, our results show that individuals, who naturally control viremia, maintain low levels of innate immune activation similar to those of uninfected controls.

Baseline and Dynamic Expression of Activating NK Cell Receptors in the Control of Chronic Viral Infections: The Paradigm of HIV-1 and HCV

Natural killer (NK) cell function is regulated by a balance between the triggering of activating and inhibitory receptors expressed on their surface. A relevant effort has been focused so far on the study of KIR carriage/expression setting the basis for NK cell education and self-tolerance. Focus on the evolution and regulation of activating NK receptors has lagged behind so far. Our understanding of activating receptor expression and regulation has recently improved by evidences derived from in vitro and in vivo studies. Virus infection - either acute or chronic - determines preferential expansion of NK cells with specific phenotype, activating receptors, and with recall-like functional activity. Studies on patients with viral infection (HIV and HCV) and specific diverging clinical courses confirm that inter-individual differences may exist in baseline expression of natural cytotoxicity receptors (NKp46 and NKp30). The findings that patients with divergent clinical courses have different kinetics of activating receptor density expression upon NK cell activation in vitro provide an additional, time-dependent, functional parameter. Kinetic changes in receptor expression thus represent an additional parameter to basal receptor density expression. Different expression and inducibilities of activating receptors on NK cells contribute to the high diversity of NK cell populations and may help our understanding of the inter-individual differences in innate responses that underlie divergent disease courses.

Higher NK cell IFN-γ production is associated with delayed HIV disease progression in LTNPs

Natural killer (NK) cells are important effectors of the innate immune system that help control viral infections and tumorigenesis. However, the relationship between NK cell function and HIV disease progression remains poorly defined. In this study, we examined the function of NK cells in Chinese patients who were HIV-infected but treatment-naïve. These individuals include primary HIV-infected patients (PHIs), typical progressors (TPs), and long-term nonprogressors (LTNPs). We observed an increase of CD56(dim) NK cells in PHIs, but the production of interferon-gamma (IFN-γ) and CD107a expression in PHIs were not altered compared with normal control subjects (NCs). However, the NK cells from LTNPs exhibited increased activities in IFN-γ production, CD107a expression and granzyme B change after K562 stimulation compared with NCs. Furthermore, the percentage of IFN-γ(+)CD107a(-) NK cells in LTNPs was higher than that in TPs, PHIs and NCs; levels of IFN-γ production in LTNP NK cells exhibited an inverse correlation with viral loads. Similar correlations, however, were not observed in the PHI and TP groups. Taken together, these data demonstrate that enhanced NK cell function may contribute to the control of HIV infection, and increased IFN-γ secretion may be associated with delayed disease progression.

Cytometry, immunology, and HIV infection: three decades of strong interactions

Flow cytometry (FCM) has been extensively used to investigate immunological changes that occur from infection with the human immunodeficiency virus (HIV). This review describes some of the most relevant cellular and molecular changes in the immune system that can be detected by FCM during HIV infection. Finally, it will be discussed how this technology has facilitated the understanding not only of the biology of the virus but also of the mechanisms that the immune system activates to fight HIV and is allowing to monitor the efficacy of antiretroviral therapy.

No monkey business: why studying NK cells in non-human primates pays off

Human NK (hNK) cells play a key role in mediating host immune responses against various infectious diseases. For practical reasons, the majority of the data on hNK cells has been generated using peripheral blood lymphocytes. In contrast, our knowledge of NK cells in human tissues is limited, and not much is known about developmental pathways of hNK cell subpopulations in vivo. Although research in mice has elucidated a number of fundamental features of NK cell biology, mouse, and hNK cells significantly differ in their subpopulations, functions, and receptor repertoires. Thus, there is a need for a model that is more closely related to humans and yet allows experimental manipulations. Non-human primate models offer numerous opportunities for the study of NK cells, including the study of the role of NK cells after solid organ and stem cell transplantation, as well as in acute viral infection. Macaque NK cells can be depleted in vivo or adoptively transferred in an autologous system. All of these studies are either difficult or unethical to carry out in humans. Here we highlight recent advances in rhesus NK cell research and their parallels in humans. Using high-throughput transcriptional profiling, we demonstrate that the human CD56^bright and CD56^dim NK cell subsets have phenotypically and functionally analogous counterparts in rhesus macaques. Thus, the use of non-human primate models offers the potential to substantially advance hNK cell research.

HIV infection deregulates innate immunity to malaria despite combination antiretroviral therapy

OBJECTIVE

Malaria and HIV-1 adversely interact, with HIV-positive individuals suffering higher parasite burdens and worse clinical outcomes. However, the mechanisms underlying these disease interactions are unclear. We hypothesized that HIV coinfection impairs the innate immune response to malaria, and that combination antiretroviral therapy (cART) may restore this response. Our aim was to examine the innate inflammatory response of natural killer (NK), natural killer T (NKT), and γδ T-cells isolated from the peripheral blood of HIV-infected therapy-naive donors to malaria parasites, and determine the effect of cART on these responses.

METHODS

Freshly isolated peripheral blood mononuclear cells from 25 HIV-infected individuals pre-cART (month 0) and post-cART (months 3 and 6), and HIV-negative individuals at matched time-points, were cultured in the presence of Plasmodium falciparum parasitized erythrocytes. Supernatants and cells were collected to assess cytokine production and phenotypic changes.

RESULTS

Compared to HIV-negative participants, NKT, NK, and γδ T-cell subsets from participants with chronic HIV infection showed marked differences, including decreased production of interferon γ (IFNγ) and tumor necrosis factor (TNF) in response to malaria parasites. IFNγ production was linked to interleukin-18 receptor (IL-18R) expression in all three cell types studied. Six months of cART provided partial cellular reconstitution but had no effect on IL-18R expression, or IFNγ and TNF production.

CONCLUSION

These data suggest that HIV infection impairs the inflammatory response of innate effector cells to malaria, and that the response is not fully restored within 6 months of cART. This may contribute to higher parasite burdens and ineffective immune responses, and have implications for vaccination initiatives in coinfected individuals.

Influence of episodes of intermittent viremia ("blips") on immune responses and viral load rebound in successfully treated HIV-infected patients

Presenting episodes of intermittent viremia (EIV) under combination antiretroviral therapy (cART) is frequent, but there exists some controversy about their consequences. They have been described as inducing changes in immune responses potentially associated with a better control of HIV infection. Conversely, it has been suggested that EIV increases the risk of virological failure. A retrospective analysis of a prospective, randomized double-blinded placebo-controlled study was performed. Twenty-six successfully treated HIV-infected adults were randomized to receive an immunization schedule or placebo, and after 1 year of follow-up cART was discontinued. The influence of EIV on T cell subsets, HIV-1-specific T cell immune responses, and viral load rebound, and the risk of developing genotypic mutations were evaluated, taking into account the immunization received. Patients with EIV above 200 copies/ml under cART had a lower proportion of CD4(+) and CD4(+)CD45RA(+)RO(-) T cells, a higher proportion of CD8(+) and CD4(+)CD38(+)HLADR(+) T cells, and higher HIV-specific CD8(+) T cell responses compared to persistently undetectable patients. After cART interruption, patients with EIV presented a significantly higher viral rebound (p=0.007), associated with greater increases in HIV-specific lymphoproliferative responses and T cell populations with activation markers. When patients with EIV between 20 and 200 copies/ml were included, most of the differences disappeared. Patients who present EIV above 200 copies/ml showed a lower CD4(+) T cell count and higher activation markers under cART. After treatment interruption, they showed greater specific immune responses against HIV, which did not prevent a higher virological rebound. EIV between 20 and 200 copies/ml did not have this deleterious effect.

HIV-1 and the immune response to TB

TB causes 1.4 million deaths annually. HIV-1 infection is the strongest risk factor for TB. The characteristic immunological effect of HIV is on CD4 cell count. However, the risk of TB is elevated in HIV-1 infected individuals even in the first few years after HIV acquisition and also after CD4 cell counts are restored with antiretroviral therapy. In this review, we examine features of the immune response to TB and how this is affected by HIV-1 infection and vice versa. We discuss how the immunology of HIV-TB coinfection impacts on the clinical presentation and diagnosis of TB, and how antiretroviral therapy affects the immune response to TB, including the development of TB immune reconstitution inflammatory syndrome. We highlight important areas of uncertainty and future research needs.

The impact of HIV-1 infection and exposure on natural killer (NK) cell phenotype in Kenyan infants during the first year of life

Natural killer (NK) cells play an important role in the containment of HIV replication during primary infection, though their functions are impaired during chronic HIV infection. Infants experience more rapid HIV disease progression than adults, but contributions of infant NK cells to containing HIV infection are unknown. The aim of this study was to determine the impact of HIV infection on infant NK cell phenotype by evaluating samples and data from a cohort study of women and their infants, conducted in Nairobi, Kenya between 1999 and 2003. The percentage and phenotype of NK cells was evaluated longitudinally by multi-parameter flow cytometry over the first year of life in HIV-infected (HIV+, = 16), HIV-exposed uninfected (HIV-EU, n = 6), and healthy unexposed controls (HIV–, n = 4). At birth, NK subset distributions based on expression of CD56 and CD16 did not differ between HIV+, HIV-EU, or HIV– infants. However, HIV infection was associated with a subsequent decline in NK cells as a percentage of total lymphocytes (p < 0.001), and an expanding proportion of CD56-CD16+ NK cells (p < 0.001). Activated CD38^brightCD69+ NK cells were more frequent in the HIV+ infants, followed by HIV-EU and HIV- infants, in both CD56^dim (p = 0.005) and CD56^bright compartments (p = 0.03). HIV infection and exposure was also associated with a significant decline in the percentage of perforin-expressing NK cells in the CD56^dim compartment over the first year of life, with HIV+ infants losing approximately 2.5% (p < 0.001) and HIV-EU infants losing 3.0% (p = 0.01) of perforin+ cells per month. Thus, infant HIV infection is associated with alterations in NK cell subsets, activation, and cytolytic potential that could contribute to their poor control over HIV infection. Furthermore, exposure to HIV infection in infants who escaped infection is also associated with alterations in NK cells that may contribute to the reduced ability to fight infections that is observed in HIV-EU infants.

Receptor modulation and functional activation of human CD34+ Lin- -derived immature NK cells in vitro by Mycobacterium bovis Bacillus Calmette-Guerin (BCG)

It is not yet clear whether immature NK (iNK) cells are bystanders to or rather participate in immune responses to pathogens that may colocalize in areas of NK-cell maturation such as bone marrow or lymph nodes. Mycobacteria, including Bacillus Calmette-Guerin (BCG), have been shown to interact with peripheral NK cells and in vivo may colocalize in areas of iNK-cell development. We studied infection with BCG of human cord blood CD34(+) Lin(-)-derived cultures containing myelomonocytes and iNK cells in vitro. Increased iNK-cell DNAM-1 expression, transient natural cytotoxicity receptor modulation, and production of IFN-γ were observed. Transcriptional receptor modulation was associated to BCG challenge, which determined increased iNK-cell cytotoxic activity against tumor cell lines and also increased killing of immature dendritic cells (iDCs). No requirement for cell contact was recorded for BCG-induced iNK-cell activation, while cytokine production including IL-18, IL-10, GM-CSF, and TGF-β contributed to the observed effects. Thus, iNK cells are affected by mycobacteria in vitro and may contribute to shaping of adaptive mature innate responses through iDC-iNK cross-talk. In addition, iNK-cell activation by BCG may represent a novel additional mechanism contributing to the effects observed upon BCG administration in vivo.

HIV RNA suppression and immune restoration: can we do better?

HAART has significantly changed the natural history of HIV infection: patients receiving antiretrovirals are usually able to control viremia, even though not all virological responders adequately recover their CD4+ count. The reasons for poor immune restoration are only partially known and they include genetic, demographic and immunologic factors. A crucial element affecting immune recovery is immune activation, related to residual viremia; indeed, a suboptimal virological control (i.e., low levels of plasma HIV RNA) has been related with higher levels of chronic inflammation and all-cause mortality. The sources of residual viremia are not yet completely known, even though the most important one is represented by latently infected cells. Several methods, including 2-LTR HIV DNA and unspliced HIV RNA measurement, have been developed to estimate residual viremia and predict the outcome of antiretroviral therapy. Considering that poor immunologic responders are exposed to a higher risk of both AIDS-related and non-AIDS-related diseases, there is a need of new therapeutic strategies, including immunomodulators and drugs targeting the latent viral reservoirs, in order to face residual viremia but also to “drive” the host immunologic responses.

NK cell function and antibodies mediating ADCC in HIV-1-infected viremic and controller patients

Natural killer (NK) cells have been suggested to play a protective role in HIV disease progression. One potent effector mechanism of NK cells is antibody-dependent cellular cytotoxicity (ADCC) mediated by antiviral antibodies binding to the FcγRIIIa receptor (CD16) on NK cells. We investigated NK cell-mediated ADCC function and the presence of ADCC antibodies in plasma from 20 HIV-1-infected patients and 10 healthy donors. The HIV-positive patients were divided into two groups: six who controlled viremia for at least 8 y without treatment (controllers), and 14 who were persistently viremic and not currently on treatment. Plasma from both patient groups induced NK cell IFN-γ expression and degranulation in response to HIV-1 envelope (Env) gp140-protein-coated cells. Patient antibodies mediating ADCC were largely directed towards the Env V3 loop, as identified by a gp140 protein lacking the V3 loop. Interestingly, in two controllers ADCC-mediating antibodies were more broadly directed to other parts of Env. A high viral load in patients correlated with decreased ADCC-mediated cytolysis of gp140-protein-coated target cells. NK cells from both infected patients and healthy donors degranulated efficiently in the presence of antibody-coated HIV-1-infected Jurkat cells. In conclusion, the character of ADCC-mediating antibodies differed in some controllers compared to viremic patients. NK cell ADCC activity is not compromised in HIV-infected patients.

Unconventional repertoire profile is imprinted during acute chikungunya infection for natural killer cells polarization toward cytotoxicity

Chikungunya virus (CHIKV) is a worldwide emerging pathogen. In humans it causes a syndrome characterized by high fever, polyarthritis, and in some cases lethal encephalitis. Growing evidence indicates that the innate immune response plays a role in controlling CHIKV infection. We show here that CHIKV induces major but transient modifications in NK-cell phenotype and function soon after the onset of acute infection. We report a transient clonal expansion of NK cells that coexpress CD94/NKG2C and inhibitory receptors for HLA-C1 alleles and are correlated with the viral load. Functional tests reveal cytolytic capacity driven by NK cells in the absence of exogenous signals and severely impaired IFN-γ production. Collectively these data provide insight into the role of this unique subset of NK cells in controlling CHIKV infection by subset-specific expansion in response to acute infection, followed by a contraction phase after viral clearance.

Chikungunya virus (CHIKV) infection, which is responsible for devastating human illness, is rapidly becoming a global concern. The spread of this disease throughout tropical areas, where it now affects nearly 40 countries, underlines the need to improve our understanding of this infection. In 2008, CHIKV was listed as a US National Institute of Allergy and Infectious Disease (NIAID) category C priority pathogen. Natural killer (NK) cells are cytotoxic effector cells that play a vital role in the innate immune system by limiting acute infection, as previously described for several other diseases. This report describes the first phenotypic and functional analysis of NK cells soon after infection by this virus. The key element of this study was the detailed analysis of the expansion of NK cells. Coexpression of NKG2C activating receptors and HLA-C1 ligands is associated with viral load, impaired IFN-γ production, and significant cytolytic functions. We found that NK cells were able to sense CHIKV from the beginning of infection and contributed to the clearance of the infected cells through the expansion of a unique NK-cell subset.

Specific prebiotics modulate gut microbiota and immune activation in HAART-naive HIV-infected adults: results of the "COPA" pilot randomized trial

Intestinal mucosal immune system is an early target for human immunodeficiency virus type 1 (HIV-1) infection, resulting in CD4(+) T-cell depletion, deterioration of gut lining, and fecal microbiota composition. We evaluated the effects of a prebiotic oligosaccharide mixture in highly active antiretroviral therapy (HAART)-naive HIV-1-infected adults. In a pilot double-blind, randomized, placebo-controlled study, 57 HAART-naive HIV-1-infected patients received a unique oligosaccharide mixture (15 or 30 g short chain galactooligosaccharides/long chain fructooligosaccharides/pectin hydrolysate-derived acidic oligosaccharides (scGOS/lcFOS/pAOS) daily) or a placebo for 12 weeks. Microbiota composition improved significantly with increased bifidobacteria, decreased Clostridium coccoides/Eubacterium rectale cluster, and decreased pathogenic Clostridium lituseburense/Clostridium histolyticum group levels upon prebiotic supplementation. In addition, a reduction of soluble CD14 (sCD14), activated CD4(+)/CD25(+) T cells, and significantly increased natural killer (NK) cell activity when compared with control group were seen in the treatment group. The results of this pilot trial highly significantly show that dietary supplementation with a prebiotic oligosaccharide mixture results in improvement of the gut microbiota composition, reduction of sCD14, CD4(+) T-cell activation (CD25), and improved NK cell activity in HAART-naive HIV-infected individuals.

Involvement of activating NK cell receptors and their modulation in pathogen immunity

Natural Killer (NK) cells are endowed with cell-structure-sensing receptors providing inhibitory protection from self-destruction (inhibitory NK receptors, iNKRs, including killer inhibitory receptors and other molecules) and rapid triggering potential leading to functional cell activation by Toll-like receptors (TLRs), cytokine receptors, and activating NK cell receptors including natural cytotoxicity receptors (NCRs, i.e., NKp46, NKp46, and NKp44). NCR and NKG2D recognize ligands on infected cells which may be endogenous or may directly bind to some structures derived from invading pathogens. In this paper, we address the known direct or indirect interactions between activating receptors and pathogens and their expression during chronic HIV and HCV infections.

Metabolic and anthropometric parameters contribute to ART-mediated CD4+ T cell recovery in HIV-1-infected individuals: an observational study

BACKGROUND

The degree of immune reconstitution achieved in response to suppressive ART is associated with baseline individual characteristics, such as pre-treatment CD4 count, levels of viral replication, cellular activation, choice of treatment regimen and gender. However, the combined effect of these variables on long-term CD4 recovery remains elusive, and no single variable predicts treatment response. We sought to determine if adiposity and molecules associated with lipid metabolism may affect the response to ART and the degree of subsequent immune reconstitution, and to assess their ability to predict CD4 recovery.

METHODS

We studied a cohort of 69 (48 females and 21 males) HIV-infected, treatment-naïve South African subjects initiating antiretroviral treatment (d4T, 3Tc and lopinavir/ritonavir). We collected information at baseline and six months after viral suppression, assessing anthropometric parameters, dual energy X-ray absorptiometry and magnetic resonance imaging scans, serum-based clinical laboratory tests and whole blood-based flow cytometry, and determined their role in predicting the increase in CD4 count in response to ART.

RESULTS

We present evidence that baseline CD4+ T cell count, viral load, CD8+ T cell activation (CD95 expression) and metabolic and anthropometric parameters linked to adiposity (LDL/HDL cholesterol ratio and waist/hip ratio) significantly contribute to variability in the extent of CD4 reconstitution (ΔCD4) after six months of continuous ART.

CONCLUSIONS

Our final model accounts for 44% of the variability in CD4+ T cell recovery in virally suppressed individuals, representing a workable predictive model of immune reconstitution.

NK-cell phenotype at interruption underlies widely divergent duration of CD4+-guided antiretroviral treatment interruption

Long-term side effects may represent a relevant burden of antiretroviral treatment (ART) in HIV-infected patients with good CD4 immune reconstitution over extended time spans. CD4-guided treatment interruption (TI) has been evaluated to address this point and may result in a wide spectrum of time off ART in different patient cohorts. We studied whether differences in innate immune responses, in particular NK cells, are associated to patterns of longer (LoTI) or a shorter (ShTI) TI. Clinical cohort parameters were analyzed on a group of patients widely diverging for TI duration (<9 versus >18 months) on samples before TI, including NK-cell analysis and function by natural cytotoxicity receptor (NCR)-triggered γ-IFN production. Although persistently reduced NCR expression (NKp30) and function were observed in both LoTI and ShTI patients on ART compared with healthy donors, relevant differences were observed at baseline TI in those patients who subsequently developed LoTI course. Lower expression of NKG2D and NKp46 on NK cells. This also translates in reduced γ-IFN production in redirected functional assays. Thus, differences in innate immune balance exist during ART, may be associated to differential control of HIV infection and their understanding could explain clinical differences in individual patients that are not reflected by CD4(+) cell counts alone.

Natural killer cells that respond to human immunodeficiency virus type 1 (HIV‐1) peptides are associated with control of HIV‐1 infection

Human immunodeficiency virus (HIV)-specific natural killer (CD3- cells), CD4, and CD8 T cellular responses were determined in 79 HIV‐1-infected women in response to HIV‐1 peptide pools (Gag, Pol, Nef, Reg, and Env) with use of a whole‐blood intracellular cytokine staining assay that measures interferon-γ and/or interleukin-2. HIV‐specific CD3- cell responses to any region (Env and Reg predominantly targeted) were associated with lower viral load (P = .031) and higher CD4 T cell count (P = .015). Env‐specific CD3- cell responses were stronger in women who had both Gag CD4 and CD8 T cell responses and, in turn, was associated with lower viral load (P = .005). CD3- cell responders had significantly higher representation of CD4 T cell responses to Env and Reg (P = .012 and P = .015, respectively) and higher magnitudes of CD4 T cell responses (P = .017 and P = .037, respectively) than did nonresponders. Peptide‐specific natural killer cells are associated with markers of less severe disease progression among HIV‐1-infected women (lower viral load and higher CD4 T cell count) and with stronger HIV‐specific T cell responses.