Overview of major research thrusts

1. Infectious diseases

HIV/AIDS, severe pneumococcal disease, and tuberculosis remain the major focus areas of the infectious diseases research programme.

HIV/AIDS Research (Prof S. Cassol and Prof. S.W. Van der Merwe)

The primary objectives of the HIV/AIDS sub-programme are to establish the effects of HIV-1 infection on regional T-lymphocyte colonization and macrophage activation in the gastrointestinal tract, as well as the effects of antiretroviral therapy on reconstitution of various sub-populations of T-lymphocytes, macrophage activation status and privileged viral reservoirs, especially in relation to anatomical site and drug resistance. The role of chronic activation of monocytes/macrophages, especially in the GIT, in driving treatment failure is a priority research initiative.

Exessive immune activation is a major force driving HIV-1 replication and progression to AIDS. In most patients, antiretroviral therapy (ART) results in a sustained reduction in plasma HIV-RNA and a decrease in AIDS-related morbidity and mortality. However, ART does not always lead to a normalization of systemic inflammation. In approximately 20% of patients, the persistence of inflammation during ART is associated with poor CD4+ T cell recovery, suboptimal therapeutic gains and an increased risk of cancer and other non-AIDS-related diseases, especially in patients who begin therapy after their CD4 T cells drop below 200cell/ml. It is our hypothesis that such patients will also have higher levels of residual viral replication and thus, will be more likely to develop drug resistance.

Cell of the monocyte-macrophage lineage play a key role in the initiation and resolution of inflammation. They respond to a wider range of antigenic and microbial stimuli and the outcome of these interactions depends on the differentiation status of the cell. If properly regulated, these responses result in the activation of effector mechanisms and the killing of invading pathogens. However, if excessive, or inappropriate, they can lead to severe immune dysregulation, secondary infection, uncontrolled sepsis and death. Activation of moncyte-macrophages occurs through both Toll-Like Receptor (TLR)-dependent mechanisms.

Recent studies have suggested that HIV-1-induced damage to the intestinal mucosa and sustained microbial translocation during ART may be responsible, at least in part, for the inability of ART to completely suppress immune activation. Interactions between LPS (a marker of microbial translocation) and the CD14/TLR4 complex on mononuclear phagocytes are associated with an increase in the cytokines that drive T-cell activation and activation-induced cell death (AICD) and high levels of LPS correlate with poor CD4 T cell recovery.

For these reasons, we are conducting an extensive investigation of the role of monocyte/macrophage activation in fuelling treatment failure, with special emphasis on the GIT. The over-riding hypothesis of this work is that it will be impossible to maximally suppress/eliminate viral replication and prevent drug resistance, until we have a thorough understanding of the mechanisms controlling HIV-1 transmission and immune pathogenesis in the GIT.

Pneumococcal disease research (Prof. R. Anderson)

Severe pneumococcal disease, in spite of the advent of pneumococcal polysaccharide conjugate vaccines, continues to be a major cause of morbidity and mortality, especially in the very young, the elderly and those infected with HIV-1. Our efforts in this sub-programme continue to focus on optimization of antimicrobial chemotherapy and the identification of adjunctive therapies which target the major virulence factors, particularly pneumolysin, of the pneumococcus. In collaboration with UK researchers, we are also contributing to the development of a novel conjugate vaccine which utilizes broadly immunogenic pneumococcal proteins, as opposed to tetanus or other non-pneumococcal-derived toxoids, as the protein carrier for pneumococcal polysaccharides. 

Tuberculosis research (Dr. C. Cholo)

Our tuberculosis research continues to focus on the potassium (K⁺) transporters of mycobacterium tuberculosis (MTB), specifically their preferential utilization at various stages of bacterial growth, their role in intracellular survival and virulence, as well as their potential to serve as novel targets for drug/vaccine design.

Inflammatory diseases of non-infective origin (Prof. R. Anderson)

In the case of acute/chronic inflammatory diseases of non-infective origin, our efforts are targeted primarily at identifying the mechanisms which initiate mobilization of calcium during receptor-mediated activation of inflammatory cells, particularly the neutrophil, as well as those which restore Ca²⁺ homeostasis to the cells. This research has identified several novel Ca²⁺-handling-based targets for anti-inflammatory therapy. The second component in this research programme involves identification of the mechanisms by which heavy metals of environmental/industrial significance (cobalt, manganese, palladium, platinum, and palladium) trigger and/or potentiate harmful inflammatory responses.

2. Stem cells

Stem cell therapy for HIV/AIDS (Prof. M. Pepper)

The long term objective of this project is to generate HIV-resistant haematopoietic stem cells (HSCs) and to transplant these cells into patients with HIV/AIDS to replace their endogenous HSCs. This procedure may avoid many problems seen with anti-retroviral drugs (side effects, compliance) and theoretically could provide life-long protection against HIV.

HIV entry into CD4 T-lymphocytes is mediated by CD4 and two co-receptors, namely CCR5 and CXCR4. Absence of CCR5 has been shown to confer resistance to HIV infection.

The initial objectives of this project are:

1. to understand normal hematopoietic stem cell (HSC) growth and differentiation and the effects that HIV has on these processes in patients that are HIV-positive;
2. to develop lentiviral vectors that allow knock-down of CCR5 expression;
3. to demonstrate proof of principle with regard to haematopoietic stem cell transduction and the consequences of CCR5 knockdown (i.e. inhibition of HIV infectivity);
4. to develop pre-clinical models to demonstrate the efficacy of CCR5 knockdown.
5. to determine the prevalence of individuals with a CCR5-null phenotype with a view to establishing a CCR5-null cord blood bank.

The ultimate objective is to build capacity for genetic engineering of HIV-resistant autologous cells for bone marrow transplantation in a country (South Africa) that is severely affected by the HIV/AIDS epidemic.

Mesenchymal stem cell group (Dr. M. Potgieter and Prof. M.S. Pepper)

Mesenchymal stem cells (MSCs) have the capacity to develop into various derivatives of the mesodermal germ layer including bone, cartilage, muscle and adipose tissue. We have established a facility for the isolation and characterization of MSCs which will be used for the treatment of orthopaedic, maxillofacial and muscular disorders (including muscular dystrophy).

Public cord blood stem cell bank (Prof. M.S. Pepper)

We are undertaking a feasibility study on the creation of a public cord blood stem cell bank, which is a much needed resource on the sub-continent for the provision of genetically-compatible stem cells for bone marrow transplantation (BMT). BMT is used to treat a wide spectrum of blood cancers and other disorders, and this form of treatment is currently denied to the majority of our population due to the lack of genetically-compatible stem cells. This study is being conducted for the National Department of Health in collaboration with the South African National Blood Service (SANBS).

3. Pharmacogenetics

CYP450 drug metabolism (Prof. M.S. Pepper)

The objective of these studies is to predict patients’ responses to the medications they take through the assessment of activity of the cytochrome P450 drug metabolizing system. Our particular interest is to relate this ability, as determined by measuring the metabolism of a test drug (phenotype), to the genetic make-up (genotype) of the patient, a so-called genotype-phenotype correlation. We have discovered several variations in our African population, which may assist in understanding why different groups of individuals respond differently to the medications they receive. This will lead to the emergence of personalized medicine, which will assist clinicians to optimize the choice and dosage of medications prescribed to patients in order to avoid non-response or adverse side effects.