Structural and functional constraints limit options for cytotoxic T-lymphocyte escape in the immunodominant HLA-B27-restricted epitope in human immunodeficiency virus type 1 capsid.

Control of human immunodeficiency virus type 1 (HIV-1) by HLA-B27-positive subjects has been linked to an immunodominant CD8(+) cytotoxic T-lymphocyte (CTL) response targeting the conserved KK10 epitope (KRWIILGLNK(263-272)) in p24/Gag. Viral escape in KK10 typically occurs through development of an R(264)K substitution in conjunction with the upstream compensatory mutation S(173)A, and the difficulty of the virus to escape from the immune response against the KK10 epitope until late in infection has been associated with slower clinical progression. Rare alternative escape mutations at R(264) have been observed, but factors dictating the preferential selection of R(264)K remain unclear. Here we illustrate that while all observed R(264) mutations (K, G, Q, and T) reduced peptide binding to HLA-B27 and impaired viral replication, the replicative defects of the alternative mutants were actually less pronounced than those for R(264)K. Importantly, however, none of these mutants replicated as well as an R(264)K variant containing the compensatory mutation S(173)A. In assessing the combined effects of viral replication and CTL escape using an in vitro coculture assay, we further observed that the compensated R(264)K mutant also displayed the highest replication capacity in the presence of KK10-specific CTLs. Comparisons of codon usage for the respective variants indicated that generation of the R(264)K mutation may also be favored due to a G-to-A bias in nucleotide substitutions during HIV-1 replication. Together, these data suggest that the preference for R(264)K is due primarily to the ability of the S(173)A-compensated virus to replicate better than alternative variants in the presence of CTLs, suggesting that viral fitness is a key contributor for the selection of immune escape variants.

Use of Predictive Modeling to Plan for Special Event Medical Care During Mass Gathering Events.

OBJECTIVES: In 2010, South Africa (SA) hosted the Fédération Internationale de Football Association (FIFA) World Cup (soccer). Emergency Medical Services (EMS) used the SA mass gathering medicine (MGM) resource model to predict resource allocation. This study analyzed data from the World Cup and compared them with the resource allocation predicted by the SA mass gathering model. METHODS: Prospectively, data were collected from patient contacts at 9 venues across the Western Cape province of South Africa. Required resources were based on the number of patients seeking basic life support (BLS), intermediate life support (ILS), and advanced life support (ALS). Overall patient presentation rates (PPRs) and transport to hospital rates (TTHRs) were also calculated. RESULTS: BLS services were required for 78.4% (n = 1279) of patients and were consistently overestimated using the SA mass gathering model. ILS services were required for 14.0% (n = 228), and ALS services were required for 3.1% (n = 51) of patients. Both ILS and ALS services, and TTHR were underestimated at smaller venues. CONCLUSIONS: The MGM predictive model overestimated BLS requirements and inconsistently predicted ILS and ALS requirements. MGM resource models, which are heavily based on predicted attendance levels, have inherent limitations, which may be improved by using research-based outcomes.

Operational demands on pre-hospital emergency care for burn injuries in a middle-income setting: a study in the Western Cape, South Africa.

BACKGROUND: Burns occur disproportionately within low-socioeconomic populations. The Western Cape Province of South Africa represents a middle-income setting with a high rate of burns, few specialists and few burn centres, yet a well-developed pre-hospital system. This paper describes the burn cases from a viewpoint of operational factors important to pre-hospital emergency medical services. METHODS: A retrospective, cross-sectional study of administrative and patient records was conducted. Data were captured for all pre-hospital burn patients treated by public Emergency Medical Services over a continuous 12-month period. Data were captured separately at each site using a standardised data collection tool. Described categories included location (rural or urban), transport decision (transported or remained on scene), age (child or adult) and urgency (triage colour). RESULTS: EMS treated 1198 patients with confirmed burns representing 0.6% of the total EMS caseload; an additional 819 potential burn cases could not be confirmed. Of the confirmed cases, 625 (52.2%) were located outside the City of Cape Town and 1058 (88.3%) were transported to a medical facility. Patients from urban areas had longer mission times. Children accounted for 37.5% (n = 449) of all burns. The majority of transported patients that were triaged were yellow (n = 238, 41.6% rural and n = 182, 37.4% urban). CONCLUSIONS: Burns make up a small portion of the EMS caseload. More burns occurred in areas far from urban hospitals and burn centres. The majority of burn cases met the burn centre referral criteria.

A novel immunodominant CD8+ T cell response restricted by a common HLA-C allele targets a conserved region of Gag HIV-1 clade CRF01_AE infected Thais.

BACKGROUND: CD8+ T cell responses play an important role in the control of HIV-1. The extensive sequence diversity of HIV-1 represents a critical hurdle to developing an effective HIV-1 vaccine, and it is likely that regional-specific vaccine strains will be required to overcome the diversity of the different HIV-1 clades distributed world-wide. Unfortunately, little is known about the CD8+ T cell responses against CRF01_AE, which is responsible for the majority of infections in Southeast Asia. METHODOLOGY/PRINCIPAL FINDINGS: To identify dominant CD8+ T cell responses recognized in HIV-1 clade CRF01_AE infected subjects we drew upon data from an immunological screen of 100 HIV-1 clade CRF01_AE infected subjects using IFN-gamma ELISpot to characterize a novel immunodominant CD8+ T cell response in HIV-1 Gag restricted by HLA-Cw*0102 (p24, (277)YSPVSILDI(285), YI9). Over 75% of Cw*0102+ve subjects targeted this epitope, representing the strongest response in more than a third of these individuals. This novel CD8 epitope was located in a highly conserved region of HIV-1 Gag known to contain immunodominant CD8 epitopes, which are restricted by HLA-B*57 and -B*27 in clade B infection. Nonetheless, viral escape in this epitope was frequently observed in Cw*0102+ve subjects, suggestive of strong selection pressure being exerted by this common CD8+ T cell response. CONCLUSIONS/SIGNIFICANCE: As HLA-Cw*0102 is frequently expressed in the Thai population (allelic frequency of 16.8%), this immunodominant Cw*0102-restricted Gag epitope may represent an attractive candidate for vaccines specific to CRF01_AE and may help facilitate further studies of immunopathogenesis in this understudied HIV-1 clade.

Functional and genetic analysis of coreceptor usage by dualtropic HIV-1 subtype C isolates.

It is widely documented that a complete switch from the predominant CCR5 (R5) to CXCR4 (X4) phenotype is less common for HIV-1 subtype C (HIV-1C) compared to other major subtypes. We investigated whether dualtropic HIV-1C isolates represented dualtropic, mixed R5 and X4 clones or both. Thirty of 35 functional HIV-1 env clones generated by bulk PCR amplification from peripheral blood mononuclear cells (PBMCs) infected with seven dualtropic HIV-1C isolates utilized CXCR4 exclusively. Five of 35 clones displayed dualtropism. Endpoint dilution of one isolate did not yield a substantial proportion of R5-monotropic env clones. Sequence-based predictive algorithms showed that env sequences from PBMCs, CXCR4 or CCR5-expressing cell lines were indistinguishable and all possessed X4/dualtropic characteristics. We describe HIV-1C CXCR4-tropic env sequence features. Our results suggest a dramatic loss of CCR5 monotropism as dualtropism emerges in HIV-1C which has important implications for the use of coreceptor antagonists in therapeutic strategies for this subtype.

Selective depletion of high-avidity human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells after early HIV-1 infection.

Human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells in early infection are associated with the dramatic decline of peak viremia, whereas their antiviral activity in chronic infection is less apparent. The functional properties accounting for the antiviral activity of HIV-1-specific CD8+ T cells during early infection are unclear. Using cytokine secretion and tetramer decay assays, we demonstrated in intraindividual comparisons that the functional avidity of HIV-1-specific CD8+ T cells was consistently higher in early infection than in chronic infection in the presence of high-level viral replication. This change of HIV-1-specific CD8+ T-cell avidity between early and chronic infections was linked to a substantial switch in the clonotypic composition of epitope-specific CD8+ T cells, resulting from the preferential loss of high-avidity CD8+ T-cell clones. In contrast, the maintenance of the initially recruited clonotypic pattern of HIV-1-specific CD8+ T cells was associated with low-level set point HIV-1 viremia. These data suggest that high-avidity HIV-1-specific CD8+ T-cell clones are recruited during early infection but are subsequently lost in the presence of persistent high-level viral replication.

Escape from the dominant HLA-B27-restricted cytotoxic T-lymphocyte response in Gag is associated with a dramatic reduction in human immunodeficiency virus type 1 replication.

Human leukocyte antigen (HLA)-B27-positive subjects are uncommon in their ability to control infection with human immunodeficiency virus type 1 (HIV-1). However, late viral escape from a narrowly directed immunodominant Gag-specific CD8(+) T-lymphocyte (CTL) response has been linked to AIDS progression in these individuals. Identifying the mechanism of the immune-mediated control may provide critical insights into HIV-1 vaccine development. Here, we illustrate that the CTL escape mutation R(264)K in the HLA-B27-restricted KK10 epitope in the capsid resulted in a significant defect in viral replication in vitro. The R(264)K variant was impaired in generating late reverse transcription products, indicating that replication was blocked at a postentry step. Notably, the R(264)K mutation was associated in vivo with the development of a rare secondary mutation, S(173)A, which restored viral replication in vitro. Furthermore, infectivity of the R(264)K variant was rescued by the addition of cyclosporine A or infection of a cyclophilin A-deficient cell line. These data demonstrate a severe functional defect imposed by the R(264)K mutation during an early step in viral replication that is likely due to the inability of this variant to replicate efficiently in the presence of normal levels of cyclophilin A. We conclude that the impact of the R(264)K substitution on capsid structure constrains viral escape and enables long-term maintenance of the dominant CTL response against B27-KK10, providing an explanation for the protective effect of HLA-B27 during HIV infection.

De novo generation of escape variant-specific CD8+ T-cell responses following cytotoxic T-lymphocyte escape in chronic human immunodeficiency virus type 1 infection.

Human immunodeficiency virus type 1 (HIV-1) evades CD8(+) T-cell responses through mutations within targeted epitopes, but little is known regarding its ability to generate de novo CD8(+) T-cell responses to such mutants. Here we examined gamma interferon-positive, HIV-1-specific CD8(+) T-cell responses and autologous viral sequences in an HIV-1-infected individual for more than 6 years following acute infection. Fourteen optimal HIV-1 T-cell epitopes were targeted by CD8(+) T cells, four of which underwent mutation associated with dramatic loss of the original CD8(+) response. However, following the G(357)S escape in the HLA-A11-restricted Gag(349-359) epitope and the decline of wild-type-specific CD8(+) T-cell responses, a novel CD8(+) T-cell response equal in magnitude to the original response was generated against the variant epitope. CD8(+) T cells targeting the variant epitope did not exhibit cross-reactivity against the wild-type epitope but rather utilized a distinct T-cell receptor Vbeta repertoire. Additional studies of chronically HIV-1-infected individuals expressing HLA-A11 demonstrated that the majority of the subjects targeted the G(357)S escape variant of the Gag(349-359) epitope, while the wild-type consensus sequence was significantly less frequently recognized. These data demonstrate that de novo responses against escape variants of CD8(+) T-cell epitopes can be generated in chronic HIV-1 infection and provide the rationale for developing vaccines to induce CD8(+) T-cell responses directed against both the wild-type and variant forms of CD8 epitopes to prevent the emergence of cytotoxic T-lymphocyte escape variants.