Connie J. Kim

Identification of an innate T helper type 17 response to intestinal bacterial pathogens

Interleukin 17 (IL-17) is a central cytokine implicated in inflammation and antimicrobial defense. After infection, both innate and adaptive IL-17 responses have been reported, but the type of cells involved in innate IL-17 induction, as well as their contribution to in vivo responses, are poorly understood. Here we found that Citrobacter and Salmonella infection triggered early IL-17 production, which was crucial for host defense and was mediated by CD4+ T helper cells. Enteric innate T helper type 17 (iTH17) responses occurred principally in the cecum, were dependent on the Nod-like receptors Nod1 and Nod2, required IL-6 induction and were associated with a decrease in mucosal CD103+ dendritic cells. Moreover, imprinting by the intestinal microbiota was fully required for the generation of iTH17 responses. Together, these results identify the Nod-iTH17 axis as a central element in controlling enteric pathogens, which may implicate Nod-driven iTH17 responses in the development of inflammatory bowel diseases.

Sigmoid Th17 populations, the HIV latent reservoir, and microbial translocation in men on long-term antiretroviral therapy.

Objective:Th17 cells play an important role in mucosal defence and repair and are highly susceptible to infection by HIV. Antiretroviral therapy (ART) suppresses HIV viremia and can restore CD4+ numbers in the blood and gastrointestinal mucosa, but the resolution of systemic inflammation and gut microbial translocation is often incomplete. We hypothesized that this might relate to persistent dysregulation of gut CD4+ Th17 subsets. Methods:Blood and sigmoid biopsies were collected from HIV-uninfected men, chronically HIV-infected, ART-naive men, and men on effective ART for more than 4 years. Sigmoid provirus levels were assayed blind to participant status, as were CD4+ Th17 subsets, systemic markers of microbial translocation, and cellular immune activation. Results:There was minimal CD4+ Th17 dysregulation in the blood until later stage HIV infection, but gastrointestinal Th17 depletion was apparent much earlier, along with increased plasma markers of microbial translocation. Plasma lipopolysaccharide (LPS) remained elevated despite overall normalization of sigmoid Th17 populations on long-term ART, although there was considerable interindividual variability in Th17 reconstitution. An inverse correlation was observed between plasma LPS levels and gut Th17 frequencies, and higher plasma LPS levels correlated with an increased gut HIV proviral reservoir. Conclusion:Sigmoid Th17 populations were preferentially depleted during HIV infection. Despite overall CD4+ T-cell reconstitution, sigmoid Th17 frequencies after long-term ART were heterogeneous and higher frequencies were correlated with reduced microbial translocation.

Mucosal Th17 Cell Function Is Altered during HIV Infection and Is an Independent Predictor of Systemic Immune Activation

Mucosal Th17 cells maintain the gut epithelial barrier and prevent invasion by luminal bacteria through a delicate balance of immunosuppressive and proinflammatory functions. HIV infection is characterized by mucosal Th17 depletion, microbial translocation, and immune activation. Therefore, we assessed the function of blood and sigmoid Th17 cells during both early and chronic HIV infection, as well as the impact of short- and long-term antiretroviral therapy. Th17 cells were defined as IL-17a+ CD4 T cells, and their functional capacity was assessed by the coproduction of the inflammatory cytokines IL-22, TNF-α, and IFN-γ, as well as the immunoregulatory cytokine IL-10. Gut Th17 cells had a much greater capacity to produce proinflammatory cytokines than did those from the blood, but this capacity was dramatically reduced from the earliest stages of HIV infection. Immunoregulatory skewing of mucosal Th17 cell function, characterized by an increased IL-10/TNF-α ratio, was uniquely seen during early HIV infection and was independently associated with reduced systemic immune activation. Antiretroviral therapy rapidly restored mucosal Th17 cell numbers; however, normalization of mucosal Th17 function, microbial translocation, and mucosal/systemic immune activation was much delayed. These findings emphasize that strategies to preserve or to more rapidly restore mucosal Th17 function may have important therapeutic benefit.

IL-10-Producing B Cells Are Induced Early in HIV-1 Infection and Suppress HIV-1-Specific T Cell Responses

A rare subset of IL-10-producing B cells, named regulatory B cells (Bregs), suppresses adaptive immune responses and inflammation in mice. In this study, we examined the role of IL-10-producing B cells in HIV-1 infection. Compared to uninfected controls, IL-10-producing B cell frequencies were elevated in both blood and sigmoid colon during the early and chronic phase of untreated HIV-1 infection. Ex vivo IL-10-producing B cell frequency in early HIV-1 infection directly correlated with viral load. IL-10-producing B cells from HIV-1 infected individuals were enriched in CD19+TIM-1+ B cells and were enriched for specificity to trimeric HIV-1 envelope protein. Anti-retroviral therapy was associated with reduced IL-10-producing B cell frequencies. Treatment of B cells from healthy donors with microbial metabolites and Toll-like receptor (TLR) agonists could induce an IL-10 producing phenotype, suggesting that the elevated bacterial translocation characteristic of HIV-1 infection may promote IL-10-producing B cell development. Similar to regulatory B cells found in mice, IL-10-producing B cells from HIV-1-infected individuals suppressed HIV-1-specific T cell responses in vitro, and this suppression is IL-10-dependent. Also, ex vivo IL-10-producing B cell frequency inversely correlated with contemporaneous ex vivo HIV-1-specific T cell responses. Our findings show that IL-10-producing B cells are induced early in HIV-1 infection, can be HIV-1 specific, and are able to inhibit effective anti-HIV-1 T cell responses. HIV-1 may dysregulate B cells toward Bregs as an immune evasion strategy.

SHIP Is Required for Dendritic Cell Maturation

Although several groups have investigated the role of SHIP in macrophage (Mϕ) development and function, SHIP’s contribution to the generation, maturation, and innate immune activation of dendritic cells (DCs) is poorly understood. We show herein that SHIP negatively regulates the generation of DCs from bone marrow precursors in vitro and in vivo, as illustrated by the enhanced expansion of DCs from SHIP−/− GM-CSF cultures, as well as increased numbers of DCs in the spleens of SHIP-deficient mice. Interestingly, however, these SHIP−/− DCs display a relatively immature phenotype and secrete substantially lower levels of IL-12 after TLR ligand stimulation than wild type DCs. This, in turn, leads to a dramatically reduced stimulation of Ag-specific T cell proliferation and Th1 cell responses in vitro and in vivo. This immature phenotype of SHIP−/− DCs could be reversed with the PI3K inhibitors LY294002 and wortmannin, suggesting that SHIP promotes DC maturation by reducing the levels of the PI3K second messenger phosphatidylinositol-3,4,5-trisphosphate. These results are consistent with SHIP being a negative regulator of GM-CSF–derived DC generation but a positive regulator of GM-CSF–derived DC maturation and function.

Effect of Antiretroviral Therapy on HIV Reservoirs in Elite Controllers

Elite controllers suppress human immunodeficiency virus (HIV) viremia to below the limit of detection in the absence of antiretroviral therapy (ART). However, precise frequencies of CD4(+) T cells carrying replication-competent HIV and/or the dynamics of the infectious viral reservoirs in response to initiation and discontinuation of ART in elite controllers are unknown. We show that the size of the pool of CD4(+) T cells harboring infectious HIV diminished significantly after initiation of ART and rebounded to baseline upon cessation of therapy. Our data provide compelling evidence that persistent viral replication occurs in untreated elite controllers even in the absence of detectable plasma viremia.

Effect of raltegravir intensification on HIV proviral DNA in the blood and gut mucosa of men on long-term therapy: a randomized controlled trial.

Background:Highly active antiretroviral therapy (HAART) dramatically reduces plasma HIV-1 viremia. However, despite completely suppressive HAART, it has been suggested that low-levels of viral replication may persist in the gut mucosa and elsewhere in individuals on long-term HAART. Objective:We conducted a double-blind randomized, placebo-controlled trial evaluating whether intensification of HAART in long-term virologically suppressed individuals with raltegravir is associated with a reduction in the level of proviral HIV-1 DNA in CD4+ T cells in blood and the sigmoid colon (gut). Methods:Long-term (>4 years) virologically suppressed HIV-infected individuals on standard HAART were randomized 1 : 1 in a double-blind fashion to receive raltegravir (400 mg twice/day) or placebo for 48 weeks. After week 48, all participants were treated with raltegravir to week 96. Blood and sigmoid biopsies were sampled and the frequency of CD4+ T cells carrying HIV-1 proviral DNA was determined. Results:Twenty-four study patients were recruited. At 48 weeks, no difference was apparent between participants receiving raltegravir or placebo in blood HIV-1 proviral levels (P = 0.62), CD4+ T-cell counts (P = 0.25) and gut proviral loads (P = 0.74). Similarly, prolonged raltegravir intensification up to week 96 had no further effect on both blood and gut HIV-1 proviral loads and blood CD4+ T-cell counts. Conclusion:In long-term virologically suppressed patients on standard HAART, intensification with raltegravir did not result in further decay of CD4+ T cells carrying HIV-1 proviral DNA in either the blood or gut after 48 or 96 weeks of therapy, or in any increase in CD4+ T-cell counts.

Expression Of Membrane Drug Efflux Transporters In The Sigmoid Colon Of Hiv-infected And Uninfected Men.

The use of antiretroviral therapy (ART) as pre‐exposure prophylaxis (PrEP) has gained global attention as a promising HIV prevention strategy in men who have sex with men. Permeability of these agents in the rectal mucosa may be partially regulated by interactions with drug efflux transporters, P‐glycoprotein (P‐gp), multidrug resistance‐associated proteins (MRPs) and/or breast cancer resistance protein (BCRP). The objective of this work was to investigate the expression of drug efflux transporters in recto‐sigmoid colon tissues of HIV‐infected and uninfected men, and evaluate the association of ART and/or HIV infection with drug transporter expression. MDR1/P‐gp, MRPs (1–4) and BCRP mRNA and protein expression were detected in sigmoid colon biopsies of HIV‐uninfected individuals. Biopsies from HIV‐infected, ART‐naïve participants revealed a significant downregulation of P‐gp and MRP2 protein levels compared to HIV‐uninfected individuals. Biopsies from HIV‐infected ART‐treated patients showed 1.9‐fold higher P‐gp protein expression and 1.5‐fold higher MRP2 protein expression compared to the ones obtained from the HIV‐infected ART‐naïve patients. This is a first report demonstrating that HIV infection or ART could alter expression of drug efflux transporters in gut mucosa which in turn could affect the permeability of PrEP antiretroviral agents across this barrier, a highly vulnerable site of HIV transmission.

Early HIV-1 infection is associated with reduced frequencies of cervical Th17 cells.

Background:The hallmark of HIV infection is progressive but variable rates of systemic and mucosal CD4 depletion, leading to immunodeficiency. The impact of early HIV infection on cervical CD4+ T-cell populations in humans remains poorly described. Methods:We analyzed cytobrush-derived immune cells by flow cytometry and cytokines in cervicovaginal lavage from participants in early HIV (<6 months postinfection), chronic HIV, and HIV-uninfected controls. Results:CD4:CD8 ratios declined rapidly in both the cervix and the blood following HIV infection. In contrast, absolute cervical CD4+ T-cell counts in early HIV were comparable to HIV-uninfected participants, declining only in chronic infection. Early HIV infection was associated with increases in RANTES and MIP3a in cervicovaginal fluids. Concurrently, slight increases in activated cells (CD38+HLA-DR+) and higher levels of CTLA4 expression on Tregs in the cervix were observed. Although study groups did not differ with respect to levels of CCR5, integrin B7, or CD69, the frequencies of Th17 cells (defined as CCR6+CCR10−) was reduced by >10-fold in early HIV infection and Th1 cells (defined as CCR6−CXCR3+) were reduced by >2-fold. Although CCR6+CCR10− cells did not differ in HIV receptor expression, these cells produced higher levels of interferon gamma and interleukin 17. Conclusions:These data support the model of initial CD4+ T-cell depletion followed by overall T-cell influx in response to infection and concomitant increases in immune activation, inflammation, and regulatory markers. These data are among the earliest characterization of the cellular milieu in the female genital tract following male-to-female HIV transmission.

Intensifying Antiretroviral Therapy With Raltegravir and Maraviroc During Early Human Immunodeficiency Virus (HIV) Infection Does Not Accelerate HIV Reservoir Reduction

Background. Persistent human immunodeficiency virus (HIV) within the CD4+ T-cell reservoir is an obstacle to eradication. We hypothesized that adding raltegravir and maraviroc to standard combination antiretroviral therapy (cART) during early HIV infection could substantially reduce viral reservoirs as a step towards eradication. Methods. A prospective, randomized, double-blinded, placebo-controlled pilot trial enrolled 32 participants with documented early (<6 months) HIV infection to either standard cART (emtricitabine/tenofovir/lopinavir/ritonavir) or intensive cART (standard regimen + raltegravir/maraviroc). Human immunodeficiency virus reservoirs were assessed at baseline and at 48 weeks by (1) proviral DNA, (2) cell-associated RNA, and (3) replication-competent virus, all from purified blood CD4+ T cells, and (4) gut proviral DNA. A multiassay algorithm (MAA) on baseline sera estimated timing of infection. Results. Thirty individuals completed the study to the 48-week endpoint. The reduction in blood proviral burden was −1.03 log DNA copies/106 CD4+ T cells versus −.84 log in the standard and intensive groups, respectively (P = .056). Overall, there was no significant difference in the rate of decline of HIV-associated RNA, replication-competent virus in blood CD4+ T cells, nor proviral gut HIV DNA to 48 weeks. Individuals who presented with more recent HIV infection had significantly lower virus reservoirs, and cART tended to reduce their reservoirs to a greater extent. Conclusions. Intensive cART led to no additional reduction in the blood virus reservoir at 48 weeks compared with standard cART. Human immunodeficiency virus reservoir size is smaller earlier in HIV infection. Other novel treatment strategies in combination with early cART will be needed to eliminate the HIV latent reservoir.