Elucidating the consequences of HIV-1 immune escape from host CTL selection pressure

This thesis focuses on HIV-1 adaptation to CTL immune response and presents original data on the consequences of 10 published HLA-B*13-associated CTL escape mutations in Gag, Pol and Nef on HIV-1 replication capacity (RC) and Nef-mediated CD4 and HLA class I downregulation. B*13-driven immune escape at Gag-I147L and -I437L incurred replicative costs of 5% and 17% on in vitro viral RC, which was rescued to wild-type (HIV-1NL4.3) levels by Gag-A146S/K436R and Gag-K436R, respectively. One major observation was that B*13-driven double mutation, NefE24Q/Q107R impaired this protein’s HLA class I downregulation ability by 40%, with no evidence of replicative or expression defects. Moreover, cells infected with double mutant virus were “visible” to HIV-specific T cells. Our results thus suggest that B*13-mediated protective effects on HIV-1 disease progression may be attributable, in part to a novel mechanism – namely, the selection of escape mutations in Nef that dampen one of HIV-1’s key immune evasion strategies

Patterns of HIV infection among native and refugee Afghans

The current study was conducted to explore the origins of the HIV epidemics among the Afghan refugees in Pakistan and the native Afghans in Afghanistan. Phylogenetic analysis of HIV gag gene from 40 samples showed diverse HIV variants, originating from a number of countries. Intermixing of diverse HIV variants among Afghans may give rise to seeding of infections with rare HIV strains which may pose serious challenges for the treatment and control of infection

HIV-1 progression links with viral genetic variability and subtype, and patient’s HLA type: analysis of a Nairobi-Kenyan cohort

In a Nairobi-Kenyan cohort of 50 HIV-1 positive patients, we analysed the prevalence of HIV-1 subtypes and human leucocyte antigen (HLA) alleles. From this cohort, 33 patients were selected for the analysis of HIV-1 infection progression markers (i.e. CD4 cell counts and viral loads) and their association with HIV-1 genetic variability and subtype, and patient’s HLA type. HIV-1 gag genetic variability, analysed using bioinformatics tools, showed an inverse relationship with CD4 cell count whereas with viral load that relationship was direct. Certain HLA types and viral subtypes were also found to associate with patients’ viral load. Associations between disease parameters and the genetic makeup of the host and virus may be crucial in determining the outcome of HIV-1 infection

Population-specific evolution of HIV gag epitopes in genetically diverged patients

Background: Under the host selection pressure HIV evolves rapidly to override crucial steps in the antigen presentation pathway. This allows the virus to escape binding and recognition by cytotoxic T lymphocytes. Selection pressures on HIV can be unique depending on the immunogenetics of host populations. It is therefore logical to hypothesize that the virus evolving in a given population will carry signature mutations that will allow it to survive in that particular host milieu.Objectives: The aim of this study was to perform a comparative analysis of HIV-1 Gag subtype A sequences from two genetically diverged populations, namely, Kenyan and Pakistani. We analyzed unique mutations that could intercept the antigen processing pathway and potentially change the repertoire of Gag epitopes in each study group.Methods: Twenty-nine Kenyan and 56 Pakistani samples from HIV-1 subtype A-infected patients were used in this study. The HIV-1 gag region p24 and p2p7p1p6 was sequenced and mutations affecting proteasomal degradation, TAP binding, HLA binding and CTL epitope generation, were analyzed using the in silicosoftwares NetChop and MAPPP, TAPPred, nHLAPred and CTLPred, respectively.Results: Certain mutations unique to either Pakistani or Kenyan patients were observed to affect sites for proteasomal degradation, TAP binding, and HLA binding. As a consequence of these mutations, epitope pattern in these populations was altered.Conclusion: Unique selection pressures can steer the direction of viral epitope evolution in the host populations. Population-specific HIV epitopes have to be taken into account while designing treatment as well as vaccine for HIV

HIV proviral genetic diversity, compartmentalization and inferred dynamics in lung and blood during long-term suppressive antiretroviral therapy.

The lung is an understudied site of HIV persistence. We isolated 898 subgenomic proviral sequences (nef) by single-genome approaches from blood and lung from nine individuals on long-term suppressive antiretroviral therapy (ART), and characterized genetic diversity and compartmentalization using formal tests. Consistent with clonal expansion as a driver of HIV persistence, identical sequences comprised between 8% to 86% of within-host datasets, though their location (blood vs. lung) followed no consistent pattern. The majority (77%) of participants harboured at least one sequence shared across blood and lung, supporting the migration of clonally-expanded cells between sites. The extent of blood proviral diversity on ART was also a strong indicator of diversity in lung (Spearman's ρ = 0.98, p<0.0001). For three participants, insufficient lung sequences were recovered to reliably investigate genetic compartmentalization. Of the remainder, only two participants showed statistically significant support for compartmentalization when analysis was restricted to distinct proviruses per site, and the extent of compartmentalization was modest in both cases. When all within-host sequences (including duplicates) were considered, the number of compartmentalized datasets increased to four. Thus, while a subset of individuals harbour somewhat distinctive proviral populations in blood and lung, this can simply be due to unequal distributions of clonally-expanded sequences. For two participants, on-ART proviruses were also phylogenetically analyzed in context of plasma HIV RNA populations sampled up to 18 years prior, including pre-ART and during previous treatment interruptions. In both participants, on-ART proviruses represented the most ancestral sequences sampled within-host, confirming that HIV sequences can persist in the body for decades. This analysis also revealed evidence of re-seeding of the reservoir during treatment interruptions. Results highlight the genetic complexity of proviruses persisting in lung and blood during ART, and the uniqueness of each individual's proviral composition. Personalized HIV remission and cure strategies may be needed to overcome these challenges

Prevalence and Correlates of Pre-Treatment HIV Drug Resistance among HIV-Infected Children in Ethiopia

Pediatric human immunodeficiency virus (HIV) care in resource-limited settings remains a major challenge to achieving global HIV treatment and virologic suppression targets, in part because the administration of combination antiretroviral therapies (cART) is inherently complex in this population and because viral load and drug resistance genotyping are not routinely available in these settings. Children may also be at elevated risk of transmission of drug-resistant HIV as a result of suboptimal antiretroviral administration for prevention of mother-to-child transmission. We investigated the prevalence and the correlates of pretreatment HIV drug resistance (PDR) among HIV-infected, cART-naive children in Ethiopia. We observed an overall PDR rate of 14%, where all cases featured resistance to non-nucleoside reverse transcriptase inhibitors (NNRTIs): ~9% of participants harbored resistance solely to NNRTIs while ~5% harbored resistance to both NNRTIs and nucleoside reverse transcriptase inhibitors (NRTIs). No resistance to protease inhibitors was observed. No sociodemographic or clinical parameters were significantly associated with PDR, though limited statistical power is noted. The relatively high (14%) rate of NNRTI resistance in cART-naive children supports the use of non-NNRTI-based regimens in first-line pediatric treatment in Ethiopia and underscores the urgent need for access to additional antiretroviral classes in resource-limited settings.Medicine, Faculty ofOther UBCNon UBCInfectious Diseases, Division ofMedicine, Department ofReviewedFacult

Molecular Epidemiology of HIV-1 in Ghana: Subtype Distribution, Drug Resistance and Coreceptor Usage

The greatest HIV-1 genetic diversity is found in West/Central Africa due to the pandemic’s origins in this region, but this diversity remains understudied. We characterized HIV-1 subtype diversity (from both sub-genomic and full-genome viral sequences), drug resistance and coreceptor usage in 103 predominantly (90%) antiretroviral-naive individuals living with HIV-1 in Ghana. Full-genome HIV-1 subtyping confirmed the circulating recombinant form CRF02_AG as the dominant (53.9%) subtype in the region, with the complex recombinant 06_cpx (4%) present as well. Unique recombinants, most of which were mosaics containing CRF02_AG and/or 06_cpx, made up 37% of sequences, while “pure” subtypes were rare (<6%). Pretreatment resistance to at least one drug class was observed in 17% of the cohort, with NNRTI resistance being the most common (12%) and INSTI resistance being relatively rare (2%). CXCR4-using HIV-1 sequences were identified in 23% of participants. Overall, our findings advance our understanding of HIV-1 molecular epidemiology in Ghana. Extensive HIV-1 genetic diversity in the region appears to be fueling the ongoing creation of novel recombinants, the majority CRF02_AG-containing, in the region. The relatively high prevalence of pretreatment NNRTI resistance but low prevalence of INSTI resistance supports the use of INSTI-based first-line regimens in Ghana