Kinetics of Myeloid-Derived Suppressor Cell Frequency and Function during Simian Immunodeficiency Virus Infection, Combination Antiretroviral Therapy, and Treatment Interruption.

During chronic lentiviral infection, poor clinical outcomes correlate both with systemic inflammation and poor proliferative ability of HIV-specific T cells; however, the connection between the two is not clear. Myeloid-derived suppressor cells (MDSC), which expand during states of elevated circulating inflammatory cytokines, may link the systemic inflammation and poor T cell function characteristic of lentiviral infections. Although MDSC are partially characterized in HIV and SIV infection, questions remain regarding their persistence, activity, and clinical significance. We monitored MDSC frequency and function in SIV-infected rhesus macaques. Low MDSC frequency was observed prior to SIV infection. Post-SIV infection, MDSC were elevated in acute infection and persisted during 7 mo of combination antiretroviral drug therapy (cART). After cART interruption, we observed MDSC expansion of surprising magnitude, the majority being granulocytic MDSC. At all stages of infection, granulocytic MDSC suppressed CD4+ and CD8+ T cell proliferation in response to polyclonal or SIV-specific stimulation. In addition, MDSC frequency correlated significantly with circulating inflammatory cytokines. Acute and post-cART levels of viremia were similar, however, the levels of inflammatory cytokines and MDSC were more pronounced post-cART. Expanded MDSC during SIV infection, especially during the post-cART inflammatory cytokine surge, likely limit cellular responses to infection. As many HIV curative strategies require cART interruption to determine efficacy, our work suggests treatment interruption-induced MDSC may especially undermine the effectiveness of such strategies. MDSC depletion may enhance T cell responses to lentiviral infection and the effectiveness of curative approaches.

Antigen specificities and proviral integration sites differ in HIV-infected cells by timing of antiretroviral treatment initiation.

Despite effective antiretroviral therapy (ART), persons living with HIV (PWH) harbor reservoirs of persistently infected CD4+ cells, which constitute a barrier to cure. Initiation of ART during acute infection reduces the size of the HIV reservoir, and we hypothesized that in addition, it would favor integration of proviruses in HIV-specific CD4+ T cells, while initiation of ART during chronic HIV infection would favor relatively more proviruses in herpesvirus-specific cells. We further hypothesized that proviruses in acute-ART-initiators would be integrated into antiviral genes, whereas integration sites in chronic-ART-initiators would favor genes associated with cell proliferation and exhaustion. We found the HIV DNA distribution across HIV-specific vs. herpesvirus-specific CD4+ T cells was as hypothesized. HIV integration sites (IS) in acute-ART-initiators were significantly enriched in gene sets controlling lipid metabolism and HIF-1α-mediated hypoxia, both metabolic pathways active in early HIV infection. Persistence of these infected cells during prolonged ART suggests a survival advantage. IS in chronic-ART-initiators were enriched in a gene set controlling EZH2 histone methylation; and methylation has been associated with diminished LTR transcription. These differences we found in antigen specificities and IS distributions within HIV-infected cells might be leveraged in designing cure strategies tailored to the timing of ART initiation.

Central obesity is a contributor to systemic inflammation and monocyte activation in virally suppressed adults with chronic HIV in Kenya.

OBJECTIVES: Heightened systemic inflammation is common in obese individuals and persons with HIV (PWH) and is independently associated with an increased risk of cardiovascular diseases (CVDs). We investigated the combined effect of central obesity, a surrogate measure of visceral fat and HIV on circulating levels of inflammatory cytokines among Kenyan adults. DESIGN: A cross-sectional study. METHODS: We analysed and compared data from 287 virally suppressed PWH and 277 noninfected Kenyan adults, including biomarkers of gut epithelial dysfunction (intestinal fatty acid binding protein), monocyte activation (soluble CD163 and CD14) and inflammation [interleukin (IL)-1ß, IL-6, TNF-α and hsCRP] by HIV/central obesity status (HIV-positive/obese, HIV-negative/obese, HIV-positive/nonobese and HIV-negative/nonobese). Central obesity was defined as waist circumference more than 80 cm for women and more than 94 cm for men. We assessed the association of HIV/obesity status with elevated biomarkers (>75th percentile) using logistic regression. RESULTS: Median age for participants was 44 years and 37% were centrally obese. Levels of all biomarkers were higher among the HIV-positive/obese compared with the HIV-negative/nonobese (P < 0.05 for all comparisons). The HIV-positive/obese group had the greatest odds of having elevated inflammatory biomarkers compared with other groups even after adjustment of age, BMI and other conventional CVD risk factors (P < 0.05 for all). Additional adjustment for sCD163 in the multivariate model substantially attenuated the association for HIV-positive/obesity with IL-1ß, IL-6 and TNF-α but not hsCRP. The contribution of HIV-positive/obesity to inflammation was independent of the degree of immunosuppression. CONCLUSION: Central obesity is prevalent among virally suppressed African PWH and is associated with greater inflammation and monocyte activation independent of other comorbidities and HIV-specific factors.

Endothelial Dysfunction Is Related to Monocyte Activation in Antiretroviral-Treated People With HIV and HIV-Negative Adults in Kenya.

BACKGROUND: Residual monocyte activation may contribute to increased risk for endothelial dysfunction and subsequent atherosclerotic cardiovascular diseases (CVDs) among people with HIV (PWH) on antiretroviral therapy (ART). We examined the relationship between monocyte activation and endothelial activation in PWH in Kenya. METHODS: Serum levels of markers of endothelial activation (soluble/circulating intercellular [sICAM-1] and vascular [sVCAM-1] cell adhesion molecule-1), intestinal barrier dysfunction (intestinal fatty acid binding protein [I-FABP]), and monocyte activation (soluble CD14 [sCD14]) were measured in 275 PWH on ART and 266 HIV-negative persons. Linear regression was used to evaluate associations, adjusting for demographic and traditional CVD risk factors. RESULTS: Among 541 participants, the median age was 43 years, 50% were female, and most PWH were virally suppressed (97%). sICAM-1 and sVCAM-1 levels were significantly higher in PWH than in HIV-negative participants (P < .001 for both). After further adjustment for traditional CVD risk factors, HIV infection remained associated with 49% (95% CI, 33% to 67%) greater sICAM-1 and 30% (95% CI, 14% to 48%) greater sVCAM-1 relative to uninfected controls. Adjustment for sCD14 substantially attenuated the difference between PWH and HIV-negative individuals. In a stratified analysis of PWH, both sICAM-1 and sVCAM-1 were positively associated with sCD14 (P < .001). CONCLUSIONS: Despite viral suppression, African PWH have evidence of enhanced endothelial activation associated with sCD14, suggesting that monocyte activation plays a role in atherosclerotic plaque development. Future studies are needed to determine mechanistic pathways leading to monocyte activation in this population.

Is Infant Immunity Actively Suppressed or Immature?

Almost 7 million children under the age 5 die each year, and most of these deaths are attributable to vaccine-preventable infections. Young infants respond poorly to infections and vaccines. In particular, dendritic cells secrete less IL-12 and IL-18, CD8pos T cells and NK cells have defective cytolysis and cytokine production, and CD4pos T cell responses tend to bias towards a Th2 phenotype and promotion of regulatory T cells (Tregs). The basis for these differences is not well understood and may be in part explained by epigenetic differences, as well as immaturity of the infant's immune system. Here we present a third possibility, which involves active suppression by immune regulatory cells and place in context the immune suppressive pathways of mesenchymal stromal cells (MSC), myeloid-derived suppressor cells (MDSC), CD5pos B cells, and Tregs. The immune pathways that these immune regulatory cells inhibit are similar to those that are defective in the infant. Therefore, the immune deficiencies seen in infants could be explained, in part, by active suppressive cells, indicating potential new avenues for intervention.

Global health: a successful context for precollege training and advocacy.

Despite a flourishing biomedical and global health industry too few of Washington state's precollege students are aware of this growing sector and emerging ideas on bacteria, fungi, parasites and viruses. Against the backdrop of numerous reports regarding declining precollege student interest in science, a precollege program was envisioned at Seattle Biomedical Research Institute (as of 2010, Seattle BioMed) to increase youth engagement in biomedical research and global health, increase community interest in infectious diseases and mobilize a future biomedical workforce. Since 2005, 169 rising high school juniors have participated in the BioQuest Academy precollege immersion program at Seattle BioMed. Assembling in groups of 12, students conduct laboratory experiments (e.g., anopheline mosquito dissection, gene expression informed tuberculosis drug design and optimizing HIV immunization strategies) related to global health alongside practicing scientific mentors, all within the footprint the institute. Laudable short-term impacts of the program include positive influences on student interest in global health (as seen in the students' subsequent school projects and their participation in Seattle BioMed community events), biomedical careers and graduate school (e.g., 16.9% of teens departing 2008-2009 Academy report revised goals of attaining a doctorate rather than a baccalaureate diploma). Long-term, 97% of alumni (2005-2008) are attending postsecondary schools throughout North America; eight graduates have already published scientific articles in peer-reviewed journals and/or presented their scientific data at national and international meetings, and 26 have been retained by Seattle BioMed researchers as compensated technicians and interns. Providing precollege students with structured access to practicing scientists and authentic research environments within the context of advancing global health has been a robust means of both building a future pool of talented leaders and engaged citizenry and increasing the visibility of health disparities within the community.

Functional characterization of class Ia- and non-class Ia-restricted Chlamydia-reactive CD8+ T cell responses in humans.

CD8(+) T cells are a key immune component for the eradication of many intracellular pathogens. This study aims to characterize the human CD8(+) T cell response to naturally processed chlamydial Ags in individuals exposed to the intracellular pathogen Chlamydia trachomatis. By using C. trachomatis-infected autologous dendritic cells (DCs) as stimulators, Chlamydia-reactive CD8(+) T cell responses were detected in all 10 individuals tested. The majority of the Chlamydia-reactive CD8(+) T cells were non-MHC class Ia restricted in all three of the individuals tested. From one donor, three non-class Ia-restricted and two class Ia-restricted Chlamydia-specific CD8(+) T cells were cloned and characterized further. All five T cell clones secreted IFN-gamma in response to autologous DCs infected with viable Chlamydia, but not with DCs pulsed with inactivated chlamydial elementary bodies. MHC class Ia-restricted and non-class Ia-restricted responses were inhibited by DC treatment with a proteasomal inhibitor and an endoplasmic reticulum-Golgi transport inhibitor, suggesting that these T cells recognize a peptide Ag translocated to the host cell cytosol during infection that is processed via the classical class Ia Ag-processing pathway. Even though both restricted and nonrestricted CD8(+) T cells produced IFN-gamma in response to Chlamydia-infected fibroblasts, only the non-class Ia-restricted cells were lytic for these targets. The class Ia-restricted CTLs, however, were capable of cytolysis as measured by redirected killing. Collectively, these data demonstrate that both class Ia-restricted and non-classically restricted CD8(+) T cells are elicited in C. trachomatis-exposed individuals. Their role in host immunity remains to be elucidated.

Human CD8+ T cells recognize the 60-kDa cysteine-rich outer membrane protein from Chlamydia trachomatis.

The intracellular bacterial pathogen Chlamydia is sequestered from the host cell cytoplasm by remaining within an inclusion body during its replication cycle. Nevertheless, CD8(+) T cells recognizing Chlamydia Ags in the context of MHC class I molecules are primed during infection. We have recently described derivation of Chlamydia-specific human CD8(+) T cells by using infected dendritic cells as a surrogate system to reflect Chlamydia-specific CD8(+) T cell responses in vivo. These CD8(+) T cell clones recognize chlamydial Ags processed via the conventional class Ia processing pathway, as assessed by treatment of infected APC with lactacystin and brefeldin A, suggesting that the Ags are translocated from the chlamydial inclusion into the host cell cytosol. In this study, outer membrane protein 2 (OmcB) was identified as the Ag recognized by one of these Chlamydia-specific human CD8(+) T cells, and we defined the HLA*A0101-restricted epitope from this Ag. CD8(+) T cell responses to this epitope were present at high frequencies in the peripheral blood of both of two HLA*A0101 donors tested. In vitro chlamydial growth was completely inhibited by the OmcB-specific CD8(+) T cell clone independently of lytic mechanisms. OmcB is a 60-kDa protein that has been postulated to be associated with the Chlamydia outer membrane complex. The subcellular localization of OmcB to the cytosol of infected cells, as determined by conventional MHC class I Ag processing and presentation, suggests the possibility of an additional, cytosolic-associated function for this protein.