Mother-to-infant transmission (MTIT) of HIV is a serious global health concern, with over 300,000 children newly infected in 2011. SIV infection of rhesus macaques (RMs) results in similar rates of MTIT to that of HIV in humans. In contrast, SIV infection of sooty mangabeys (SMs) rarely results in MTIT. The mechanisms underlying protection from MTIT in SMs are unknown. In this study we tested the hypotheses that breast milk factors and/or target cell availability dictate the rate of MTIT in RMs (transmitters) and SMs (non-transmitters). We measured viral loads (cell-free and cell-associated), levels of immune mediators, and the ability to inhibit SIV infection in vitro in milk obtained from lactating RMs and SMs. In addition, we assessed the levels of target cells (CD4+CCR5+ T cells) in gastrointestinal and lymphoid tissues, including those relevant to breastfeeding transmission, as well as peripheral blood from uninfected RM and SM infants. We found that frequently-transmitting RMs did not have higher levels of cell-free or cell-associated viral loads in milk compared to rarely-transmitting SMs. Milk from both RMs and SMs moderately inhibited in vitro SIV infection, and presence of the examined immune mediators in these two species did not readily explain the differential rates of transmission. Importantly, we found that the percentage of CD4+CCR5+ T cells was significantly lower in all tissues in infant SMs as compared to infant RMs despite robust levels of CD4+ T cell proliferation in both species. The difference between the frequently-transmitting RMs and rarely-transmitting SMs was most pronounced in CD4+ memory T cells in the spleen, jejunum, and colon as well as in central and effector memory CD4+ T cells in the peripheral blood. We propose that limited availability of SIV target cells in infant SMs represents a key evolutionary adaptation to reduce the risk of MTIT in SIV-infected SMs.
Chronic immune activation is a key determinant of AIDS progression in HIV-infected humans and simian immunodeficiency virus (SIV)-infected macaques but is singularly absent in SIV-infected natural hosts. To investigate whether natural killer T (NKT) lymphocytes contribute to the differential modulation of immune activation in AIDS-susceptible and AIDS-resistant hosts, we compared NKT function in macaques and sooty mangabeys in the absence and presence of SIV infection. Cynomolgus macaques had significantly higher frequencies of circulating invariant NKT lymphocytes compared to both rhesus macaques and AIDS-resistant sooty mangabeys. Despite this difference, mangabey NKT lymphocytes were functionally distinct from both macaque species in their ability to secrete significantly more IFN-γ, IL-13, and IL-17 in response to CD1d/α-galactosylceramide stimulation. While NKT number and function remained intact in SIV-infected mangabeys, there was a profound reduction in NKT activation-induced, but not mitogen-induced, secretion of IFN-γ, IL-2, IL -10, and TGF-β in SIV-infected macaques. SIV-infected macaques also showed a selective decline in CD4 + NKT lymphocytes which correlated significantly with an increase in circulating activated memory CD4 + T lymphocytes. Macaques with lower pre-infection NKT frequencies showed a significantly greater CD4 + T lymphocyte decline post SIV infection. The disparate effect of SIV infection on NKT function in mangabeys and macaques could be a manifestation of their differential susceptibility to AIDS. Alternately, these data also raise the possibility that loss of anti-inflammatory NKT function promotes chronic immune activation in pathogenic SIV infection, while intact NKT function helps to protect natural hosts from developing immunodeficiency and aberrant immune activation.
Background
CCR5 is a main co-receptor for HIV, but also homes lymphocytes to sites of inflammation. We hypothesized that inhibition of CCR5 signaling would reduce HIV-associated chronic immune activation.
Methods
To test this hypothesis, we administered an antagonistic anti-CCR5 monoclonal antibody (HGS101) to five uninfected rhesus macaques (RMs) and monitored lymphocyte dynamics in blood and tissue.
Results
CCR5 blockade resulted in decreased levels of CCR5+ T-cells in blood and, at later timepoints, in lymph nodes. Additionally, the levels of CD25+ T-cells increased in lymph nodes, but decreased in blood, bone marrow, and rectal mucosa. Finally, a profile of gene expression from HGS101-treated RMs revealed a subtle, but consistent, in vivo signature of CCR5 blockade that suggests a mild immune modulatory effect.
Conclusions
Treatment with anti-CCR5 antibody induces changes in the tissue distribution of CCR5+ and CD25+ T-cells that may impact on the overall levels of immune activation during HIV and SIV infection.
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Alexandra M. Ortiz;
Nichole R. Klatt;
Bing Li;
Yanjie Yi;
Brian Tabb;
Xing Pei Hao;
Lawrence Sternberg;
Benton Lawson;
Paul M. Carnathan;
Elizabeth M. Cramer;
Jessica C. Engram;
Dawn Little;
Elena Ryzhova;
Francisco Gonzalez-Scarano;
Mirko Paiardini;
Aftab A Ansari;
Sarah Ratcliffe;
Jim Else;
Jason M. Brenchley;
Ronald G. Collman;
Jacob D. Estes;
Cynthia Derdeyn;
Guido Silvestri
CD4+ T cells play a central role in the immunopathogenesis of HIV/AIDS, and their depletion during chronic HIV infection is a hallmark of disease progression. However, the relative contribution of CD4+ T cells as mediators of antiviral immune responses and targets for virus replication is still unclear. Here, we have generated data in SIV-infected rhesus macaques (RMs) that suggest that CD4+ T cells are essential in establishing control of virus replication during acute infection. To directly assess the role of CD4+ T cells during primary SIV infection, we in vivo depleted these cells from RMs prior to infecting the primates with a pathogenic strain of SIV. Compared with undepleted animals, CD4+ lymphocyte–depleted RMs showed a similar peak of viremia, but did not manifest any post-peak decline of virus replication despite CD8+ T cell– and B cell–mediated SIV-specific immune responses comparable to those observed in control animals. Interestingly, depleted animals displayed rapid disease progression, which was associated with increased virus replication in non-T cells as well as the emergence of CD4-independent SIV-envelopes. Our results suggest that the antiviral CD4+ T cell response may play an important role in limiting SIV replication, which has implications for the design of HIV vaccines.
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Nichole R. Klatt;
Francois Villinger;
Pavel Bostik;
Shari N. Gordon;
Lara Pereira;
Jessica C. Engram;
Ann Mayne;
Richard M. Dunham;
Benton Lawson;
Sarah J. Ratcliffe;
Donald L. Sodora;
Jim Else;
Keith Reimann;
Silvija I. Staprans;
Ashley T. Haase;
Jacob D. Estes;
Guido Silvestri;
Aftab A Ansari
Naturally SIV-infected sooty mangabeys (SMs) remain asymptomatic despite high virus replication. Elucidating the mechanisms underlying AIDS resistance of SIV-infected SMs may provide crucial information to better understand AIDS pathogenesis. In this study, we assessed the determinants of set-point viremia in naturally SIV-infected SMs, i.e., immune control of SIV replication versus target cell limitation. We depleted CD4+ T cells in 6 naturally SIV-infected SMs by treating with humanized anti-CD4 mAb (Cdr-OKT4A-huIgG1). CD4+ T cells were depleted almost completely in blood and BM and at variable levels in mucosal tissues and LNs. No marked depletion of CD14+ monocytes was observed. Importantly, CD4+ T cell depletion was associated with a rapid, significant decline in viral load, which returned to baseline level at day 30–45, coincident with an increased fraction of proliferating and activated CD4+ T cells. Throughout the study, virus replication correlated with the level of proliferating CD4+ T cells. CD4+ T cell depletion did not induce any changes in the fraction of Tregs or the level of SIV-specific CD8+ T cells. Our results suggest that the availability of activated CD4+ T cells, rather than immune control of SIV replication, is the main determinant of set-point viral load during natural SIV infection of SMs.
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Barbara Cervasi;
Diane G. Carnathan;
Katherine M. Sheehan;
Luca Micci;
Mirko Paiardini;
Raj Kurupati;
Steven Tuyishime;
Xiang Yang Zhou;
Jim Else;
Sarah J. Ratcliffe;
Hildegund C. J. Ertl;
Guido Silvestri
Human adenovirus (AdHu)-based candidate AIDS vaccine can provide protection from simian immunodeficiency virus (SIV) transmission and disease progression. However, their potential use may be limited by widespread preexisting immunity to the vector. In contrast, preexisting immunity to chimpanzee adenoviruses (AdC) is relatively rare. In this study, we utilized two regimens of prime-boost immunizations with AdC serotype SAd-V23 (also called AdC6) and SAd-V24 (also called AdC7) expressing SIV Gag/Tat to test their immunogenicity and ability to protect rhesus macaques (RMs) from a repeated low-dose SIVmac239 challenge. Both AdC6 followed by AdC7 (AdC6/7) and AdC7 followed by AdC6 (AdC7/6) induced robust SIV Gag/Tat-specific T cell responses as measured by tetramer staining and functional assays. However, no significant protection from SIV transmission was observed in either AdC7/6- or AdC7/6-vaccinated RMs. Interestingly, in the RMs showing breakthrough infections, AdC7/6-SIV immunization was associated with a transient but significant (P = 0.035 at day 90 and P = 0.033 at day 120 postinfection) reduction in the setpoint viral load compared to unvaccinated controls. None of the measured immunological markers (i.e., number or functionality of SIV-specific CD8+ and CD4+ T cell responses and level of activated and/or CCR5+ CD4+ target cells) at the time of challenge correlated with protection from SIV transmission in the AdC-SIV-vaccinated RMs. The robust immunogenicity observed in all AdC-immunized RMs and the transient signal of protection from SIV replication exhibited by AdC7/6-vaccinated RMs even in the absence of any envelope immunogen suggest that AdC-based vectors may represent a promising platform for candidate AIDS vaccines.
Simian immunodeficiency virus (SIV) infection of natural-host species, such as sooty mangabeys (SMs), is characterized by a high level of viral replication and a low level of generalized immune activation, despite evidence of an adaptive immune response. Here the ability of SIV-infected SMs to mount neutralizing antibodies (Nab) against autologous virus was compared to that of human immunodeficiency virus type 1 (HIV-1) subtype C-infected subjects. While high levels of Nab were observed in HIV-1 infection, samples obtained at comparable time points from SM exhibited relatively low titers of autologous Nab. Nevertheless, SM plasma with higher Nab titers also contained elevated peripheral CD4+ T-cell levels, suggesting a potential immunologic benefit for SMs. These data indicate that AIDS resistance in these primates is not due to high Nab titers and raise the possibility that low levels of Nab might be an inherent feature of natural-host SIV infections.
Mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1) occurs in utero, intrapartum, and through breastfeeding, with a cumulative rate of transmission of 35 to 40%. As a result, ∼400,000 children become infected each year. Little is known about mother-to-infant transmission (MTIT) during natural simian immunodeficiency virus (SIV) infection of sooty mangabeys (SMs) that typically is nonpathogenic despite high viral loads. In this study, we retrospectively investigated the rates of MTIT in a large colony of naturally SIV-infected SMs using serological (anti-SIV antibody by enzyme-linked immunosorbent assay [ELISA] and Western blot analysis) and virological (SIVsmm real-time reverse transcription-PCR) methods. We examined 161 SM infants born to SIV-infected mothers and found that 150 (93.2%) were infected by non-MTIT (n = 120) or remained uninfected (n = 30). The remaining 11 SM infants (6.8%) were defined as acquiring SIV by presumptive MTIT based on (i) the presence of anti-SIV antibodies without seroreversion and (ii) a viral load of >500 copies/ml of serum in the first year of life. SM infants infected with SIV by presumptive MTIT did not show any increased morbidity or mortality, indicating that the infection is nonpathogenic even when acquired early in life. Interestingly, viral loads of SIV-infected SM infants with presumptive MTIT were 2-log lower than those of SIV-infected adult SMs living in the same colony (i.e., ∼1,000 and 100,000 copies/ml, respectively). These results indicate that MTIT is substantially less frequent in naturally SIV-infected SMs than in HIV-1-infected humans and results in nonpathogenic infection associated with low SIV viremia. Evolutionary pressure to reduce MTIT may have contributed to the restriction of SIV pathogenesis in natural hosts.
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Z. P. Johnson;
R. D. Eady;
S. F. Ahmad;
S. Agravat;
T Morris;
S. M. Lank;
R. W. Wiseman;
D. H. O’Connor;
M. C. T. Penedo;
James Else;
Christian P Larsen;
Leslie S. Kean
Here we describe the Immunogenetic Management Software (IMS) system, a novel web-based application that permitsmultiplexed analysis of complex immunogenetic traits that are necessary for the accurate planning and execution of experiments involving large animal models, including nonhuman primates. IMS is capable of housing complex pedigree relationships, microsatellite-based MHC typing data, as well as MHC pyrosequencing expression analysis of class I alleles. It includes a novel, automated MHC haplotype naming algorithm and has accomplished an innovative visualization protocol that allows users to view multiple familial and MHC haplotype relationships through a single, interactive graphical interface. Detailed DNA and RNA-based data can also be queried and analyzed in a highly accessible fashion, and flexible search capabilities allow experimental choices to be made based on multiple, individualized and expandable immunogenetic factors. This web application is implemented in Java, MySQL, Tomcat, and Apache, with supported browsers including Internet Explorer and Firefox onWindows and Safari on Mac OS. The software is freely available for distribution to noncommercial users by contacting Leslie. kean@emory.edu. A demonstration site for the software is available at http://typing.emory.edu/typing_demo, user name: imsdemo7@gmail.com and password: imsdemo.