Most infants exposed to HIV-1 in utero and at delivery do not acquire infection. We show that mothers and infants who have CD3-negative cells that respond to HIV-1 peptides are substantially less likely to transmit and acquire infection, respectively. The CD3-negative cells, shown to be NK cells, respond with remarkable specificity and high magnitude to HIV-1 peptides from Env (envelope) and Reg (regulatory) protein regions, as measured by a whole blood intracellular cytokine assay only in the context of HIV-1 infection or exposure. These findings identify an important new measure of protective immunity to HIV-1 that highlights the importance of innate immunity in preventing the establishment of HIV-1 infection.

Understanding HIV remission in rare individuals who initiated antiretroviral therapy (ART) soon after infection and then discontinued, may inform HIV cure interventions. Here we describe features of virus and host of a perinatally HIV-1 infected child with long-term sustained virological control. The child received early limited ART in the Children with HIV Early antiRetroviral therapy (CHER) trial. At age 9.5 years, diagnostic tests for HIV are negative and the child has characteristics similar to uninfected children that include a high CD4:CD8 ratio, low T cell activation and low CCR5 expression. Virus persistence (HIV-1 DNA and plasma RNA) is confirmed with sensitive methods, but replication-competent virus is not detected. The child has weak HIV-specific antibody and T cell responses. Furthermore, we determine his HLA and KIR genotypes. This case aids in understanding post-treatment control and may help design of future intervention strategies.

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BackgroundUnderstanding the role of different classes of T cells during HIV infection is critical to determining which responses correlate with protective immunity. To date, it is unclear whether alterations in regulatory T cell (Treg) function are contributory to progression of HIV infection.MethodologyFOXP3 expression was measured by both qRT-PCR and by flow cytometry in HIV-infected individuals and uninfected controls together with expression of CD25, GITR and CTLA-4. Cultured peripheral blood mononuclear cells were stimulated with anti-CD3 and cell proliferation was assessed by CFSE dilution.Principal FindingsHIV infected individuals had significantly higher frequencies of CD4+FOXP3+ T cells (median of 8.11%; range 1.33%–26.27%) than healthy controls (median 3.72%; range 1.3–7.5%; P = 0.002), despite having lower absolute counts of CD4+FOXP3+ T cells. There was a significant positive correlation between the frequency of CD4+FOXP3+ T cells and viral load (rho = 0.593 P = 0.003) and a significant negative correlation with CD4 count (rho = −0.423 P = 0.044). 48% of our patients had CD4 counts below 200 cells/µl and these patients showed a marked elevation of FOXP3 percentage (median 10% range 4.07%–26.27%). Assessing the mechanism of increased FOXP3 frequency, we found that the high FOXP3 levels noted in HIV infected individuals dropped rapidly in unstimulated culture conditions but could be restimulated by T cell receptor stimulation. This suggests that the high FOXP3 expression in HIV infected patients is likely due to FOXP3 upregulation by individual CD4+ T cells following antigenic or other stimulation.Conclusions/SignificanceFOXP3 expression in the CD4+ T cell population is a marker of severity of HIV infection and a potential prognostic marker of disease progression.

BackgroundRift Valley fever (RVF) is a mosquito-borne viral zoonosis affecting domestic and wild ruminants, camels and humans. Outbreaks of RVF are characterized by a sudden onset of abortions and high mortality amongst domestic ruminants. Humans develop disease ranging from a mild flu-like illness to more severe complications including hemorrhagic syndrome, ocular and neurological lesions and death. During the RVF outbreak in South Africa in 2010/11, a total of 278 human cases were laboratory confirmed, including 25 deaths. The role of the host inflammatory response to RVF pathogenesis is not completely understood.MethodsVirus load in serum from human fatal and non-fatal cases was determined by standard tissue culture infective dose 50 (TCID50) titration on Vero cells. Patient serum concentration of chemokines and cytokines involved in inflammatory responses (IL-8, RANTES, CXCL9, MCP-1, IP-10, IL-1β, IL-6, IL-10, TNF and IL-12p70) was determined using cytometric bead assays and flow cytometry.ResultsFatal cases had a 1-log10 higher TCID50/ml serum concentration of RVF virus (RVFV) than survivors (p < 0.05). There were no significant sequence differences between isolates recovered from fatal and non-fatal cases. Chemokines and pro- and anti-inflammatory cytokines were detected at significantly increased (IL-8, CXCL9, MCP-1, IP-10, IL-10) or decreased (RANTES) levels when comparing fatal cases to infected survivors and uninfected controls, or when comparing combined infected patients to uninfected controls.ConclusionsThe results suggest that regulation of the host inflammatory responses plays an important role in the outcome of RVFV infection in humans. Dysregulation of the inflammatory response contributes to a fatal outcome. The cytokines and chemokines identified in this study that correlate with fatal outcomes warrant further investigation as markers for disease severity.

Background What characterizes individuals whose natural killer (NK) cells are able to respond to HIV-1 peptides is not known. Methods The association between NK cell responses and KIR gene profiles and HLA-B and HLA-C alleles was investigated among 76 HIV-1-infected women in South Africa previously categorized as responders (n = 39) or nonresponders (n = 37) to HIV-1 peptide pools in a whole blood intracellular cytokine assay. Viral load was significantly lower and CD4 T-cell counts higher among responders compared with nonresponders (P = 0.023 and P = 0.030, respectively). Results Possession of one HLA-C1 allele associated with increased magnitude of NK cell responses to Env (P = 0.031) and significantly decreased viral load (P = 0.027) compared with its absence. There was a trend to increased possession of KIR2DL3+HLA-C1 in responders (71.8% vs 51.4%, P = 0.098) and decreased possession of KIR2DL3/2DL3+C2C2 (2.6% vs 16.2%, P = 0.053). A total of 64.1% of responders versus 32.4% of nonresponders had 13 or more KIR genes (P = 0.0067). Notably, the 13-KIR gene containing the Bx21 genotype (has eight inhibitory and three activating genes KIR2DS2, 2DS4, 2DS5) showed substantially higher representation among the responders (28.2% vs 2.6%, P = 0.001). A significantly higher proportion of responders had both KIR2DS2 and KIR2DS5 compared with either gene alone (72.4% vs 37%; P = 0.015). At least one HLA-C1 allele together with 13 or more KIR genes was associated with NK cell responsiveness (48.7% vs 13.5%; P = 0.001). Conclusion NK cell responses to HIV-1 peptides are more likely to occur among individuals with a genotype supporting a more activating NK cell phenotype and who possess at least one HLA-C1 allele.

Summary HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4+ and CD8+ T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-γ and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r = −0.239, P = 0.045), as did magnitudes of Gag CD4+ (r = −0.362, P =0.002) and CD8+ (r = −0.261, P = 0.028) T-cell responses. Patients with a Gag CD4+ response (P = 0.002) or dominant Gag CD8+ (P = 0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8+ T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4+ Gag responses (P = 0.017), and women who had CD4+ and CD8+ Gag-specific responses had significantly lower viral loads (P = 0.004) and higher CCL3L1 copy number (P = 0.015) than those women with only CD8+ Gag-specific responses.

HIV-specific NK (CD3-negative 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, Env) with use of a whole blood intracellular cytokine staining (ICS) assay that measures IFN-γ and/or IL-2. HIV-specific CD3-negative responses to any region (Env and Reg predominantly targeted) were associated with lower viral load (P=0.031) and higher CD4 T-cell count (P=0.015). Env-specific CD3-negative responses were stronger where women had both Gag CD4 and CD8 T-cell responses, in turn associated with lower viral loads (P=0.005). CD3-negative cell responders had significantly higher representation of CD4 T-cell responses to Env and Reg (P=0.012 and P=0.015, respectively) and higher magnitudes of CD4 T-cell responses (P=0.017 and P=0.037, respectively) than non-responders. Peptide-specific NK cells are associated with markers of less severe disease progression among HIV-1 infected women (lower viral load, higher CD4 count) and associate with stronger HIV-specific T-cell responses.