A primate model of severe malarial anaemia: a comparative pathogenesis study.

Severe malarial anaemia (SMA) is the most common life-threatening complication of Plasmodium falciparum infection in African children. SMA is characterised by haemolysis and inadequate erythropoiesis, and is associated with dysregulated inflammatory responses and reduced complement regulatory protein levels (including CD35). However, a deeper mechanistic understanding of the pathogenesis requires improved animal models. In this comparative study of two closely related macaque species, we interrogated potential causal factors for their differential and temporal relationships to onset of SMA. We found that rhesus macaques inoculated with blood-stage Plasmodium coatneyi developed SMA within 2 weeks, with no other severe outcomes, whereas infected cynomolgus macaques experienced only mild/ moderate anaemia. The abrupt drop in haematocrit in rhesus was accompanied by consumption of haptoglobin (haemolysis) and poor reticulocyte production. Rhesus developed a greater inflammatory response than cynomolgus macaques, and had lower baseline levels of CD35 on red blood cells (RBCs) leading to a significant reduction in the proportion of CD35+ RBCs during infection. Overall, severe anaemia in rhesus macaques infected with P. coatneyi has similar features to SMA in children. Our comparisons are consistent with an association of low baseline CD35 levels on RBCs and of early inflammatory responses with the pathogenesis of SMA

A Novel CCR5 Mutation Common in Sooty Mangabeys Reveals SIVsmm Infection of CCR5-Null Natural Hosts and Efficient Alternative Coreceptor Use In Vivo

In contrast to HIV infection in humans and SIV in macaques, SIV infection of natural hosts including sooty mangabeys (SM) is non-pathogenic despite robust virus replication. We identified a novel SM CCR5 allele containing a two base pair deletion (Δ2) encoding a truncated molecule that is not expressed on the cell surface and does not support SIV entry in vitro. The allele was present at a 26% frequency in a large SM colony, along with 3% for a CCR5Δ24 deletion allele that also abrogates surface expression. Overall, 8% of animals were homozygous for defective CCR5 alleles and 41% were heterozygous. The mutant allele was also present in wild SM in West Africa. CD8+ and CD4+ T cells displayed a gradient of CCR5 expression across genotype groups, which was highly significant for CD8+ cells. Remarkably, the prevalence of natural SIVsmm infection was not significantly different in animals lacking functional CCR5 compared to heterozygous and homozygous wild-type animals. Furthermore, animals lacking functional CCR5 had robust plasma viral loads, which were only modestly lower than wild-type animals. SIVsmm primary isolates infected both homozygous mutant and wild-type PBMC in a CCR5-independent manner in vitro, and Envs from both CCR5-null and wild-type infected animals used CXCR6, GPR15 and GPR1 in addition to CCR5 in transfected cells. These data clearly indicate that SIVsmm relies on CCR5-independent entry pathways in SM that are homozygous for defective CCR5 alleles and, while the extent of alternative coreceptor use in SM with CCR5 wild type alleles is uncertain, strongly suggest that SIVsmm tropism and host cell targeting in vivo is defined by the distribution and use of alternative entry pathways in addition to CCR5. SIVsmm entry through alternative pathways in vivo raises the possibility of novel CCR5-negative target cells that may be more expendable than CCR5+ cells and enable the virus to replicate efficiently without causing disease in the face of extremely restricted CCR5 expression seen in SM and several other natural host species

Comparative studies of progressive and non-progressive AIDS virus infections in human and non-human primates

Since its discovery in the 1980\u27s, HIV infection has expanded into pandemic proportions and is responsible for a staggering amount of death and disease worldwide. Although antiretroviral therapy has drastically reduced the morbidity and mortality associated with HIV infection, it is not a cure and requires life-long adherence to avoid disease progression. As such, sustained efforts into studying HIV pathogenesis are necessary to develop better therapies. An integrated approach to studying HIV pathogenesis involves using various progressive and non-progressive models of HIV and SIV infection comparatively, and this approach has guided the work in this thesis. Sooty mangabeys (SMs) are examples of SIV natural hosts for whom SIV infection is characteristically non-progressive, and have been studied extensively to elucidate features associated with protection from disease. However, these studies have been cross-sectional or experimental in nature. Therefore, we conducted a five-year longitudinal analysis to characterize the clinical and immunologic dynamics of naturally SIV-infected SMs. We found that natural SIV infection in SMs is associated with slowly declining CD4+ T cell counts, stable levels of viremia, and consistently low T cell activation. Low CCRS expression on CD4+ T cells is another feature associated with SIV natural hosts. This is intriguing, since the reduction in CD4+CCR5+ viral target cells does not prevent persistently high viral loads in SIV-infected natural hosts. As such, we hypothesized that low CCR5 expression in SIV natural hosts contributes to reduced activated T cell trafficking and low immune activation, and we tested this hypothesis in a non-natural host, the rhesus macaque. We found that blocking CCR5 in vivo resulted in an altered distribution of CCR5+ and CD25+ T cells in blood and tissues that may reduce inflammation during progressive SIV infection. Finally, human Viremic Non-Progressors (VNPs) represent a largely uncharacterized HIV infection phenotype that clinically resembles SIV infection in natural hosts with high viral loads and maintenance of healthy CD4+ T cell counts. We conducted a preliminary immunophenotyping study that revealed trends in lower T cell activation in VNPs as compared to HIV normal progressors. In conclusion, the work presented here should assist future investigations in comparative AIDS research

Comparative studies of progressive and non-progressive AIDS virus infections in human and non-human primates

Since its discovery in the 1980\u27s, HIV infection has expanded into pandemic proportions and is responsible for a staggering amount of death and disease worldwide. Although antiretroviral therapy has drastically reduced the morbidity and mortality associated with HIV infection, it is not a cure and requires life-long adherence to avoid disease progression. As such, sustained efforts into studying HIV pathogenesis are necessary to develop better therapies. An integrated approach to studying HIV pathogenesis involves using various progressive and non-progressive models of HIV and SIV infection comparatively, and this approach has guided the work in this thesis. Sooty mangabeys (SMs) are examples of SIV natural hosts for whom SIV infection is characteristically non-progressive, and have been studied extensively to elucidate features associated with protection from disease. However, these studies have been cross-sectional or experimental in nature. Therefore, we conducted a five-year longitudinal analysis to characterize the clinical and immunologic dynamics of naturally SIV-infected SMs. We found that natural SIV infection in SMs is associated with slowly declining CD4+ T cell counts, stable levels of viremia, and consistently low T cell activation. Low CCRS expression on CD4+ T cells is another feature associated with SIV natural hosts. This is intriguing, since the reduction in CD4+CCR5+ viral target cells does not prevent persistently high viral loads in SIV-infected natural hosts. As such, we hypothesized that low CCR5 expression in SIV natural hosts contributes to reduced activated T cell trafficking and low immune activation, and we tested this hypothesis in a non-natural host, the rhesus macaque. We found that blocking CCR5 in vivo resulted in an altered distribution of CCR5+ and CD25+ T cells in blood and tissues that may reduce inflammation during progressive SIV infection. Finally, human Viremic Non-Progressors (VNPs) represent a largely uncharacterized HIV infection phenotype that clinically resembles SIV infection in natural hosts with high viral loads and maintenance of healthy CD4+ T cell counts. We conducted a preliminary immunophenotyping study that revealed trends in lower T cell activation in VNPs as compared to HIV normal progressors. In conclusion, the work presented here should assist future investigations in comparative AIDS research

Mobilising a global response to hepatitis: Lessons learned from the HIV movement

Hepatitis caused by hepatitis B and C virus is increasingly becoming a significant global health threat, with widespread prevalence that may have severe disease and economic impacts in the future. Yet, preventative measures are not implemented universally and high costs of medicines limits treatment efforts. The global response to HIV/AIDS faced similar issues, but overcame them through a global movement that brought attention to the crisis and ultimately resulted in the creation and implementation of and access to better tools for HIV prevention and treatment. This also included effective policies and programmes behind and supporting the movement. Such could be done for hepatitis, specifically using lessons from the HIV response. Here, we will discuss the current and potentially severe future burden of hepatitis globally, the challenges in addressing this epidemic, and how principles applied from the global HIV response can facilitate a successful and similar hepatitis movement

Hemagglutinin (HA) proteins from H1 and H3 serotypes of influenza A viruses require different antigen designs for the induction of optimal protective antibody responses as studied by codon-optimized HA DNA vaccines

Effective antibody responses provide crucial immunity against influenza virus infection. The hemagglutinin (HA) protein is the major target of protective antibody responses induced by viral infection and by vaccination with both inactivated and live-attenuated flu vaccines, but knowledge about the optimal designs of protective HA antigens from different flu serotypes is still limited. In this study, we have significantly improved the immunogenicity of HA-expressing DNA vaccines by using codon-optimized HA sequences for either an H1 serotype (A/NewCal/20/99) or an H3 serotype (A/Panama/2007/99) human influenza A virus and then used these constructs as model antigens to identify the optimal HA antigen designs to elicit high-level protective antibody responses. Two forms of HA antigen, a wild-type, full-length HA and a secreted form with transmembrane (TM) domain-truncated HA, were produced. Both forms of HA DNA vaccines, from either H1 or H3 serotypes, were able to elicit high levels of HA-specific immunoglobulin G responses in immunized rabbits as measured by enzyme-linked immunosorbent assay. Interestingly, the abilities of H1 HA and H3 HA antigens to elicit hemagglutination inhibition (HI) and neutralizing antibody (NAb) responses differ. For the H1 HA antigens, the full-length HA induced significantly higher HI and NAb responses than did the TM-truncated HA. For the H3 HA antigen, both the full-length HA and TM-truncated HA induced high levels of HI and NAb responses. These data indicate that H1 and H3 antigens have different expression requirements for the induction of an optimal protective antibody response and that the structure integrity of HA antigens is critical for eliciting type-specific protective antibody responses. Our findings will have an important impact on future subunit-based flu vaccine development

Limited HIV infection of central memory and stem cell memory CD4+ T cells is associated with lack of progression in viremic individuals

A rare subset of HIV-infected individuals, designated viremic non-progressors (VNP), remain asymptomatic and maintain normal levels of CD4+ T-cells despite persistently high viremia. To identify mechanisms potentially responsible for the VNP phenotype, we compared VNPs (average >9 years of HIV infection) to HIV-infected individuals who have similar CD4+ T-cell counts and viral load, but who are likely to progress if left untreated ("putative progressors", PP), thus avoiding the confounding effect of differences related to substantial CD4+ T cell depletion. We found that VNPs, compared to PPs, had preserved levels of CD4+ stem cell memory cells (TSCM (p<0.0001), which was associated with decreased HIV infection of these cells in VNPs (r = -0.649, p = 0.019). In addition, VNPs had decreased HIV infection in CD4+ central memory (TCM) cells (p = 0.035), and the total number of TCM cells was associated with increased proliferation of memory CD4+ T cells (r = 0.733, p = 0.01). Our results suggest that, in HIV-infected VNPs, decreased infection of CD4+ TCM and TSCM, cells are involved in preservation of CD4+ T cell homeostasis and lack of disease progression despite high viremia