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Associations of human leukocyte antigen-G with resistance and susceptibility to HIV-1 infection in the Pumwani sex worker cohort

Turk, William J.R.a; Kimani, Joshuab,c; Bielawny, Tomasza; Wachihi, Charlesc; Ball, Terry Blakea,b,c; Plummer, Francis A.a,b; Luo, Maa,b

doi: 10.1097/QAD.0b013e32835ab1f2
BASIC SCIENCE
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Objective: To determine the association between human leukocyte antigens (HLA)-G genotypes and resistance or susceptibility to HIV-1.

Design: A group of sex workers in Pumwani, Kenya can be epidemiologically defined as resistant to HIV-1 infection despite frequent exposure and provide an example of natural protective immunity. HLA class I and II molecules have been shown to be associated with resistance/susceptibility to infection in this cohort. HLA-G is a nonclassical class I allele that is primarily involved in mucosal and inflammatory response, which is of interest in HIV-1 resistance.

Methods: In this study, we used a sequence-based typing method to genotype HLA-G for 667 women enrolled in this cohort and examined the influence of HLA-G genotypes on resistance or susceptibility to HIV-1 infection.

Results: The G*01 : 01:01 genotype was significantly enriched in the HIV-1-resistant women [P = 0.002, Odds ratio: 2.11, 95% confidence interval (CI): 0.259–0.976], whereas the G*01 : 04:04 genotype was significantly associated with susceptibility to HIV-1 infection (P = 0.039, OR:0.502, 95% CI:0.259–0.976). Kaplan-Meier survival analysis correlated with these results. G*01 : 01:01 genotype was associated with significantly lower rate of seroconversion (P = 0.001). Whereas, G*01 : 04:04 genotype was significantly associated with an increased rate of seroconversion (P = 0.013). The associations of these HLA-G alleles are independent of other HLA class I and II alleles identified in this population.

Conclusion: Our study showed that specific HLA-G alleles are associated with resistance or susceptibility to HIV-1 acquisition in this high-risk population. Further studies are needed to understand its functional significance in HIV-1 transmission.

aPublic Health Agency of Canada, National Microbiology Laboratory

bDepartment of Medical Microbiology and Infectious Disease, University of Manitoba, Winnipeg, Manitoba, Canada

cDepartment of Medical Microbiology, University of Nairobi, Nairobi, Kenya.

Correspondence to Dr Ma Luo, 1015 Arlington Street, Winnipeg, MB, R3E 3R2, Canada. Tel: +1 204 789 5072; fax: +1 204 784 4835; e-mail: Ma_Luo@phac-aspc.gc.ca

Received 7 June, 2012

Revised 20 September, 2012

Accepted 24 September, 2012

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Introduction

HIV/AIDS is currently a global pandemic with an estimated 34 million people living with HIV/AIDS and 1.8 million AIDS-related deaths annually [1]. Currently, there are 22.5 million people living with HIV/AIDS in sub-Saharan Africa where the pandemic has hit the hardest. Although effective antiretroviral therapies have been developed to control disease progression, there is still no cure. One of the best hopes to stop the spread of HIV is developing effective vaccines and microbicides. Attempts have not yet been successful due to the rapid mutations of the HIV retrovirus and insufficient understanding of protective immunity against the virus.

Variability in susceptibility to infectious disease has long been observed in human history either within a population or among different populations. When exposed to an infectious pathogen some individuals do not appear to become infected or responded with mild symptoms and recovered very quickly after being infected, whereas others succumbed to the infection. Similarly, heterogeneity in susceptibility to HIV-1 has been observed in several cohort studies [2–7]. Most individuals are susceptible to HIV-1 infection either through sexual transmission, blood transfusion, or other high-risk exposure. Some rare individuals, about 5% in the population, appear to be resistant to HIV-1 infection despite repeated exposure through high-risk sexual exposure or blood transfusion. Through two decades of research it has become clear that multiple factors are involved in the heterogeneous responses to HIV-1 infection and the genetic factors underlying the phenomenon are complex and diverse [6–23]. Polymorphisms of host genetic factors involved in host immune responses and biological process of HIV-1 infection, establishment and spread appear to play an important role in the heterogeneity in susceptibility to HIV-1 infection [18,24–53]. Several genetic factors, such as CCR5 δ-32 mutation [12,54–65], Trim5α polymorphisms [33,53,66–68], Interferon gamma regulation factor-1 polymorphisms [11,69] and specific human leukocyte antigens (HLA) class I and class II alleles [70–73] have been reported to influence a person's response to HIV-1 infection. Among the reported host genetic factors CCR5 δ-32 mutations is the only genetic defect that is shown to be resistant to HIV-1 infection [8,9]. However, this mutation is not present in African populations. Although it is well known that HLA class I and class II antigens present antigens to CD8+ and CD4+ T cells to initiate immune responses to infectious pathogens, the specific mechanisms of the associations of HLA class I and class II alleles with resistance or susceptibility to HIV-1 infection need to be carefully investigated.

The Pumwani Sex Worker Cohort was established in 1985 in Nairobi, Kenya to study risk factors in sexually transmitted infections. A sub-population of women in this cohort has remained polymerase chain reaction (PCR) and seronegative for HIV-1 despite repeated exposures through high-risk sex work [2]. These individuals have been defined as relatively resistant to HIV-1 infection. This phenomenon was not due to altered sex practices or behavioural differences or condom usage. The resistant phenotype also clustered in families, as relatives of those HIV-1-resistant women were less likely to be infected by HIV-1 (T. Blake Ball, personal communications).

Previous studies showed that this resistance to HIV-1 infection is associated with qualitatively different CD8+ and CD4+ T-cell responses [74–78]. More recently, lower baseline levels of pro-inflammatory cytokines were detected in these HIV-1-resistant individuals when compared to HIV-1-negative controls [79]. Microarray analysis has shown that HIV-resistant women have down regulation of genes involved in T-cell receptor signalling and natural killer (NK) cell cytotoxicity [80]. Host genetics factors play an important role in this natural resistance to HIV-1. Previous studies have shown that both HLA class I and class II alleles have been associated with resistance/susceptibility to HIV-1 infection in this cohort [70–73]. Thus, it is likely that both adaptive and innate immunity are contributed to this natural resistance.

HLA-G is a member of the nonclassical class I antigens [81] along with HLA-E and HLA-F. It is characterized by having low gene polymorphism, limited spatial distribution, low expression levels and seven different isoforms [25,82] due to the alternatively spliced mRNA transcripts that lack one or more exons. HLA-G has been implicated in fetal–maternal tolerance during pregnancy [83], inflammatory disease, autoimmune disease, infectious disease and tissue transplantation [84]. It is known to directly inhibit the cytolytic function of NK cells, the antigen-specific cytolytic function of CD8+ T cells, induce tolerogenic dendritic cells and affect the allo-proliferative responses of CD4+ T cells [85]. Due to its immunosuppressive properties and expression in mucosal and inflammatory tissue, HLA-G has been of great interest in relation to HIV infection. Soluble HLA-G (sHLA-G) has been detected in plasma of HIV-infected individuals [86,87]. Specific HLA-G polymorphisms have been found to be associated with mother-to-child transmission of HIV [88]. HLA-G polymorphisms have been reported to be associated with heterosexual transmission of HIV [89–91]. Because of the importance of HLA-G in modulating immune responses and its expression in mucosal tissue, we carry out this study to investigate the possible association of genetic polymorphisms of HLA-G with resistance or susceptibility to HIV-1 infection in the Pumwani cohort.

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Materials and methods

Study population

The study was conducted among 667 individuals enrolled before 2002 in the Pumwani sex worker cohort, an open prospective cohort established in 1985 in the heart of Pumwani slum in Nairobi, Kenya to study risk factors in sexually transmitted diseases. The majority of the women were from South-Central and South–West Kenya, and regions of Tanzania and Uganda around Lake Victoria. More than 95% of them are Bantus and 5% of them are Nilotes. The sexual transmitted disease status was not the requirement for the enrolment. The criteria for enrolment, sample collection and sexually transmitted infection testing have been described elsewhere [2]. The patients enrolled in the cohort have been followed biannually since the cohort establishment. In addition to research, it provides services related to sexually transmitted infections and HIV prevention and care, including consultation, provision of free condoms and treatment of other infections. Despite effective intervention programmes, the annual incidence of HIV-1 infection among initially seronegative women is currently four per 100 person years: a dramatic decrease from the initial annual incidence of 45%. The women classified as resistant in this study were all enrolled in the cohort before 1999 with an average follow-up time of 9.6±4.3 years. The control group for the genetic association studies are all HIV positive. Ethics committees at the University of Manitoba and the University of Nairobi have approved this study. Informed consent was obtained from all women enrolled in the study.

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DNA isolation

Genomic DNA was extracted from whole blood, buffy coat, B cells, peripheral blood mononuclear cells and peripheral blood lymphocytes using either the QIAamp DNA Mini Kit (Qiagen Inc., Mississauga, Ontario, Canada) or the BioRobot EZ1 (Qiagen Inc.) following manufacturer's instructions. DNA concentration and optical density (A260/A280) were determined using the Nano Drop (Nano Drop Technologies Inc., Wilmington, Delaware, USA) and NanoDrop 3.0.1 software (Coleman Technologies Inc., Glen Mills, Pennsylvania, USA).

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PCR and sequencing primers

PCR and sequencing primers were designed on the basis of HLA-G genomic DNA sequences obtained from NCBI's Genome Biology website (http://http://www.ncbi.nlm.gov/Genomes, Homo sapiens genome build 35.1) using PrimerSelect (Lasergene; DNASTAR, Madison, Wisconsin, USA) and Sequencher 4.5 (Gene Codes). The PCR primer set HLAGPCRF and HLAGPCRR designed to amplify a 994 bp fragment which covers partial intron 1, exon 2, intron 2, exon 3, and partial intron 3 of the HLA-G gene. The primer set HLAGEX4PCRF and HLAGEX4PCRR produce a 463 bp fragment, which covers partial intron 3, exon 4, and partial intron 4. Relevant information for PCR primer sequences, annealing temperatures and fragment sizes can be found in Table 1.

Table 1

Table 1

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PCR reactions

The 50 μl final PCR reaction mixture consists of 60 mmol/l Tris-HCl (pH 9.0), 1.5 mmol/l MgCl2, 15 mmol/l (NH4)2SO4, 25 μmol/l of each dNTP, 0.1% gelatin, 6.25 pmol of each primer, 1.25 Unit of Taq DNA polymerase (Gibco/ BRL, Life Technologies, Burlington, Ontario, Canada) and 50–100 ng DNA. The cycle parameters used in the PTC-200 Peltier Thermal Cycler (MJ Research, Inc., Watertown, Massachusetts, USA) was 45 cycles of 1 min at 96°C, 1 min at 63°C (exon 2 and 3) or 60°C (exon 4), and 2 min at 72°C. This was followed by a 10-min incubation at 72°C. To confirm the successful amplification of the gene, 1% agarose gel electrophoresis was used to examine the correctly sized PCR products. The PCR products were then purified using Multiwell Filter Plates (Pall Corp., Ann Arbor, Michigan, USA).

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Sequencing and human leukocyte antigens-G genotyping

The purified PCR products reaction was sequenced using BigDye v3.1 from the ABI Prism BigDye Cycle sequencing kits (Applied Biosystems, Foster City, California, USA). Sequencing primers were developed on the basis of genomic sequences to sequence each particular exon. The specific primers sequences as well as optimal annealing temperatures are listed in Table 1. The sequencing products were analyzed on an ABI 3130xl Genetic Analyzer (Applied Biosystems). The HLA-G alleles were typed using computer software CodonExpress (University of Manitoba, Winnipeg, MB, Canada) developed based on a taxonomy-based sequence analysis method [92,93]. The HLA-G database was downloaded from IMTG/HLA Database (http://www.ebi.ac.uk/imgt/hla/new.html).

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Statistical analysis

Analyses were performed with SPSS13.0 for Windows statistical analysis software package. Python for Populations (PyPop)-32-0.6.0 [94], a software program for population genetics, was used to calculate allele frequencies and to test for deviations from Hardy–Weinberg equilibrium. HLA-G allele frequencies were calculated by direct counting. Phenotypic frequencies were expressed as the percentage of individuals bearing the corresponding allele specificity. Chi-square testing and logistical regression was used to determine whether any significant associations exist between HLA-G and resistance or susceptibility to HIV. Kaplan–Meier survival analysis was conducted to examine the effect of HLA-G on seroconversion. Only the alleles with frequencies above 5% in the population were analyzed for their association with resistance or susceptibility to HIV infection. For binary logistic regression analysis, all alleles significantly associated with resistance or susceptibility to HIV-1 infection were included in the model. The previously reported HLA class I and class II alleles associated with either resistance or susceptibility to HIV-1 infection were included in the multivariate analysis to verify the independent associations of HLA-G with differential susceptibility to HIV-1 infection identified in this study.

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Results

Allele frequency distribution of human leukocyte antigens-G in the Pumwani sex worker cohort

We genotyped exon 2, 3 and 4 of HLA-G of 667 patients enrolled in the Pumwani sex worker cohort in Nairobi, Kenya. These exons encode the α 1, 2 and 3 domains of HLA-G. 17 HLA-G alleles were identified in this population (Table 2). The 17 HLA-G alleles encode six different proteins (G*01 : 01, G*01 : 03, G*01 : 04, G*01 : 06, G*01 : 10 and G*01 : 11) and one null allele (G*01 : 05N). Five HLA-G alleles were detected at the frequencies above 5% in the population with G*01 : 01:01 (38.5%) and G*01 : 01:02 (19.8%) as the most frequently observed alleles. Together with G*01 : 03 (9.28%), G*01 : 04:04 (9.87%) and G*01 : 05N (6.44%), the five HLA-G alleles are accounted for 83.9% of all HLA-G alleles in the population.

Table 2

Table 2

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Association of human leukocyte antigens-G genotypes with resistance and susceptibility to HIV infection

The frequencies of HLA-G*01 : 01:01 heterozygotes and homozygotes were significantly higher in the HIV-resistant women than in the HIV-positive women (48.42 versus 41.15%, 25.26 versus 15.9%, P = 0.005). The G*01 : 01:01 phenotype was significantly associated with resistance to HIV-1 infection (P = 0.002) (Table 3). The women with this genotype are more than two times less likely to be HIV infected [odds ratio (OR) = 2.11, 95% confidence interval (CI): 0.259–0.976).

Table 3

Table 3

The HLA-G*01 : 04:04 phenotype was significantly enriched in the HIV-positive group (P = 0.039) (Table 3). Women with this allele have a two-fold of risk of being infected by HIV-1 than those do not have this allele (OR = 0.502, 95% CI: 0.259–0.976).

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Association of human leukocyte antigen-G genotypes with reduced or increased risk of HIV seroconversion

Kaplan–Meier survival analysis was conducted among 289 women who entered the cohort seronegative to examine whether G*01 : 01:01 was associated with slower rate of seroconversion (Fig. 1a). The results showed that women with G*01 : 01:01 are significantly less likely to seroconvert than women without this allele (Log rank: 10.368, P = 0.001). Whereas, G*01 : 04:04 was significantly associated with an increased rate of seroconversion (Fig. 1b) (Log rank: 6.148, P = 0.013). These findings were consistent with the results from the cross-tab analysis, which provides further confirmation.

Fig. 1

Fig. 1

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Multivariate analysis

As HLA class I and II genes are closely located on chromosome 6, the associations may be attributed to linkage disequilibrium between different HLA alleles. We conducted binary logistic regression analysis to determine whether either of the allele associations was dependent or independent of previously reported HLA class I and class II alleles that are significantly associated with either resistance to susceptibility to HIV-1 infection. Since DPA1*01 : 03:01, DRB1*01 and A*01 have been reported to be associated with resistance to HIV-1 infection in this cohort [70–72,95], we included these alleles in the binary logistic regression analysis with G*01 : 01:01. The results showed that the association of G*01 : 01:01 was independent from DPA1*01 : 03:01, DRB1*01 and A*01(Table 4a). Because DRB1*15 : 03, DPB1*04 : 02 and A*23 : 01 have been reported to be associated with susceptibility to HIV-1 infection in this cohort [70–72,95], we included these alleles in the logistic regression analysis with G*01 : 04:04. The analysis showed that the association of G*01 : 04:04 with susceptibility to HIV-1 infection was independent of DRB1*15 : 03, DPB1*04 : 02 and A*23 : 01 (Table 4b).

Table 4

Table 4

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Discussion

The primary route of HIV infection is through mucosal heterosexual transmission, with women more at risk of infection than men [1]. HLA-G is of particular interest in HIV-1 infection due to its expression at mucosal surfaces and its influence in immunotolerance and inflammatory responses. Identification of two specific functional HLA-G alleles, G*01 : 01:01 and G*01 : 04:04 associated with resistance or susceptibility to HIV-1 acquisition in the sex workers of the Pumwani sex worker cohort is novel and could have important implications.

G*01 : 01:01 is the most common allele in the Pumwani cohort at 38.5% (Table 2). The fact that it is the most frequent allele in almost all populations [96] suggests that perhaps it has had a selective advantage over the course of human evolution that extends beyond HIV-1 infection. G*01 : 04:04 differs from G*01 : 01:01 by a mutation at codon 110 (CTC → ATC) resulting in an amino acid change of Leucine to iso-Leucine. This mutation is located in exon 3 and could potentially change the protein configuration of the antigen-binding pocket or affect interactions between HLA-G and its killer cell receptor (KIR) ligand. This is one potential explanation of the differences seen but needs to be followed up with functional studies.

Our findings are different from the previously reported associations in a West African (Benin) population [89] and an Italian Caucasian population [90]. In the West African population a significant association was found between G*01 : 05N and protection from HIV-1 infection and an association with susceptibility for two haplotypes, G*01 : 01:08/01 : 04:01 and G*01 : 01:01/01 : 01:08. In the Italian population G*01 : 05N was associated with an increased risk for HIV-1 infection. In our study the G*01 : 05N null allele was not found to be significantly associated with either resistance or susceptibility to HIV-1 infection, even though it had a frequency of 6.43% in the population.

There are several possible explanations for the differences. It is possible that the differences could be due to ethnicity. Africa is a genetically diverse place and thus the West African population could be different from the East African population. There were also significant differences in the HLA-G genotyping methods. For one, the other studies did not use a sequence-based typing method and did not include exon 4, which is necessary to determine all the functional HLA-G alleles. It is possible that the association in the West African study with susceptibility to the haplotype G*01 : 01:08/01 : 04:01 is correlated with G*01 : 04:04 in our study, as the difference between G*01 : 04:01 and G*01 : 04:04 is at codon 267 of exon 4 CCG → CCA. However without typing of exon 4, this remains speculative. Another major difference between our study and the others is the study populations. The HIV-1-resistant women in the Pumwani sex worker cohort have been very well defined and have been followed for more than 25 years [2], whereas the other cohort were HIV negative, but not necessarily resistant and with only cross-sectional analysis. Thus, it is more difficult to ascertain the patient phenotype. Lastly, our study population is larger with better power. The Italian study had 374 individuals enrolled; whereas the West African study had 431 individuals, compared with our 598 used in association analysis. Although these differences by no means discredit their results they are important factors to consider.

Viruses have evolved many mechanisms by which they can evade the host immune system. HIV-1 virus evading cytotoxic T-lymphocytes responses is a classical example. However, HLA class I expression inhibit the function of NK cells and only those cells that lack class I expression are targets for lysis by NK cells. The HIV-1 Nef protein has been shown to downregulate both HLA-A and HLA-B, a plausible means for avoiding host detection [97]. HIV-1 also induces upregulation of interleukin-10 (IL-10) which selectively upregulates HLA-G expression while downregulating HLA class I and II antigens. Importantly, HLA-G is known to interact and inhibit NK cells through specific KIR complexes. Thus, it had been postulated that the lack of expression of HLA-G protein due to the G*01 : 05N null allele might mean less inhibition of NK cells and thus the better elimination of HIV-1-infected cells [89]. Although our study did not correlate with this hypothesis for G*01 : 05N, it did add credence to the idea that HLA-G polymorphism may affect acquisition of HIV-1. A recent study of mucosal expression of sHLA-G found that high levels were associated with HIV-infected commercial sex workers (CSW) when compared with uninfected CSW and uninfected non-CSW [98]. These high mucosal levels contrast to a previous study of theirs that found sHLA-G in plasma had lower expression in HIV-positive individuals [98]. Another study has found that plasma sHLA-G levels vary considerably based on HLA-G polymorphism [99]. Therefore it seems that sHLA-G expression is different depending on which compartment one is investigating, mucosal or blood, and depending on HLA-G polymorphism. Of particular interest is that sHLA-G in the mucosal tract for those who were either heterozygous or homozygous for G*01 : 04:04 was found to be high regardless of whether they were HIV-infected CSW, uninfected CSW or uninfected non-CSW [98]. As the G*01 : 04:04 was significantly associated with susceptibility in our population, it is not unreasonable to speculate that it is possibly due to higher levels of baseline sHLA-G expression in the mucosal tract. However sHLA-G needs to be directly measured in mucosa and functional studies need to be carried out to elucidate the mechanism by which sHLA-G in HIV-1 replication in future studies.

The highly exposed seronegative (HESN) individuals who are resistant to HIV-1 infection have shown that HIV infection can be prevented in nature. Understanding of this natural resistance to HIV-1 infection can help to develop novel preventions to HIV-1. Our study contributes an important piece of the puzzle to further understanding this phenomenon. Functional studies need to be carried out for the identified associations of HLA-G*01 : 01:01 with resistance to HIV-1 infection and HLA-G*01 : 04:04 with susceptible to HIV-1 infection in the Pumwani sex worker cohort. Given the size of the population and the well defined phenotype, we will investigate the function of the identified association in future studies to assess whether HLA-G polymorphisms could be targeted to develop prevention methods to protect against HIV infection.

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Acknowledgements

This work was supported by Public Health Agency of Canada, and partially supported by the Canadian Institutes of Health Research and the Bill and Melinda Gates Foundation. We thank Tony Kariri for maintaining the databases of Pumwani cohorts at the University of Nairobi and Bing-hua Liang for managing the database at the University of Manitoba. We also thank the staff of the Majengo clinic, Jane Njoki, Jane Makene, Elazabeth Bwibo, Edith Amatiwa for their dedication, and the women of the Pumwani Sex Worker Cohort for their continued participation. Dr Francis A. Plummer is a Canadian Institutes of Health Research Senior Investigator and is currently a Tier I CIHR Canada Research Chair.

W.J.R.T. conducted the HLA-G genotyping typing, data analysis and drafting the article. J.K. and C.W. contributed to cohort management and biological data acquisition, sample collection and review the article. T.B. contributed to HLA-G genotyping typing and review the article. T.B.B. contributed to cohort maintenances and biological data acquisition, sample collection and review the article. F.A.P. contributed to cohort establishment and maintenances, biological data acquisition, sample collection and review the article. M.L. designed the study for HLA-G, contributed to HLA-G genotyping, data analysis, and drafting the article.

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Conflicts of interest

All the authors declare no conflict of interest.

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References

1. UNAIDS. AIDS epidemic update: November 2009. Geneva: UNAIDS; 2009.
2. Fowke KR, Nagelkerke NJ, Kimani J, Simonsen JN, Anzala AO, Bwayo JJ, et al. Resistance to HIV-1 infection among persistently seronegative prostitutes in Nairobi, Kenya. Lancet 1996; 348:1347–1351.
3. Plummer FA, Ball TB, Kimani J, Fowke KR. Resistance to HIV-1 infection among highly exposed sex workers in Nairobi: what mediates protection and why does it develop?. Immunol Lett 1999; 66:27–34.
4. Rowland-Jones S, Sutton J, Ariyoshi K, Dong T, Gotch F, McAdam S, et al. HIV-specific cytotoxic T-cells in HIV-exposed but uninfected Gambian women. Nat Med 1995; 1:59–64.
5. Trachtenberg EA, Erlich HA. A review of the role of the human leukocyte antigen (HLA) system as a host immunogenetic factor influencing HIV transmission and progression to AIDS. In: Korber BT, Brander C, Haynes BF, Koup R, Kuiken C, Moore JP, et al., editors. HIV molecular immunology 2001. Los Alamos, NM: Theoretical Biology and Biophysics Group, Los Alamos National Laboratory; 2001.
6. Pereyra F, Addo MM, Kaufmann DE, Liu Y, Miura T, Rathod A, et al. Genetic and immunologic heterogeneity among persons who control HIV infection in the absence of therapy. J Infect Dis 2008; 197:563–571.
7. Koning FA, Jansen CA, Dekker J, Kaslow RA, Dukers N, van Baarle D, et al. Correlates of resistance to HIV-1 infection in homosexual men with high-risk sexual behaviour. AIDS 2004; 18:1117–1126.
8. Liu R, Paxton WA, Choe S, Ceradini D, Martin SR, Horuk R, et al. Homozygous defect in HIV-1 coreceptor accounts for resistance of some multiply-exposed individuals to HIV-1 infection. Cell 1996; 86:367–377.
9. Paxton WA, Martin SR, Tse D, O’Brien TR, Skurnick J, VanDevanter NL, et al. Relative resistance to HIV-1 infection of CD4 lymphocytes from persons who remain uninfected despite multiple high-risk sexual exposure. Nat Med 1996; 2:412–417.
10. Liu H, Hwangbo Y, Holte S, Lee J, Wang C, Kaupp N, et al. Analysis of genetic polymorphisms in CCR5, CCR2, stromal cell-derived factor-1, RANTES, and dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin in seronegative individuals repeatedly exposed to HIV-1. J Infect Dis 2004; 190:1055–1058.
11. Ball TB, Ji H, Kimani J, McLaren P, Marlin C, Hill AV, et al. Polymorphisms in IRF-1 associated with resistance to HIV-1 infection in highly exposed uninfected Kenyan sex workers. AIDS 2007; 21:1091–1101.
12. Balotta C, Bagnarelli P, Violin M, Ridolfo AL, Zhou D, Berlusconi A, et al. Homozygous delta 32 deletion of the CCR-5 chemokine receptor gene in an HIV-1-infected patient. AIDS 1997; 11:F67–71.
13. Becker Y. The molecular mechanism of human resistance to HIV-1 infection in persistently infected individuals: a review, hypothesis and implications. Virus Genes 2005; 31:113–119.
14. Bhattacharya T, Stanton J, Kim EY, Kunstman KJ, Phair JP, Jacobson LP, et al. CCL3L1 and HIV/AIDS susceptibility. Nat Med 2009; 15:1112–1115.
15. Bienzle D, MacDonald KS, Smaill FM, Kovacs C, Baqi M, Courssaris B, et al. Factors contributing to the lack of human immunodeficiency virus type 1 (HIV-1) transmission in HIV-1-discordant partners. J Infect Dis 2000; 182:123–132.
16. Biti R, Ffrench R, Young J, Bennetts B, Stewart G, Liang T. HIV-1 infection in an individual homozygous for the CCR5 deletion allele. Nat Med 1997; 3:252–253.
17. Broliden K, Hinkula J, Devito C, Kiama P, Kimani J, Trabbatoni D, et al. Functional HIV-1 specific IgA antibodies in HIV-1 exposed, persistently IgG seronegative female sex workers. Immunol Lett 2001; 79:29–36.
18. Carrington M, Dean M, Martin MP, O’Brien SJ. Genetics of HIV-1 infection: chemokine receptor CCR5 polymorphism and its consequences. Hum Mol Genet 1999; 8:1939–1945.
19. Devito C, Broliden K, Kaul R, Svensson L, Johansen K, Kiama P, et al. Mucosal and plasma IgA from HIV-1-exposed uninfected individuals inhibit HIV-1 transcytosis across human epithelial cells. J Immunol 2000; 165:5170–5176.
20. Kulkarni PS, Butera ST, Duerr AC. Resistance to HIV-1 infection: lessons learned from studies of highly exposed persistently seronegative (HEPS) individuals. AIDS Rev 2003; 5:87–103.
21. Rowland-Jones SL, Pinheiro S, Kaul R, Hansasuta P, Gillespie G, Dong T, et al. How important is the ’quality’ of the cytotoxic T lymphocyte (CTL) response in protection against HIV infection?. Immunol Lett 2001; 79:15–20.
22. Tang J, Shelton B, Makhatadze NJ, Zhang Y, Schaen M, Louie LG, et al. Distribution of chemokine receptor CCR2 and CCR5 genotypes and their relative contribution to human immunodeficiency virus type 1 (HIV-1) seroconversion, early HIV-1 RNA concentration in plasma, and later disease progression. J Virol 2002; 76:662–672.
23. Yang C, Li M, Limpakarnjanarat K, Young NL, Hodge T, Butera ST, et al. Polymorphisms in the CCR5 coding and noncoding regions among HIV type 1-exposed, persistently seronegative female sex-workers from Thailand. AIDS Res Hum Retroviruses 2003; 19:661–665.
24. Castelli EC, Mendes-Junior CT, Donadi EA. HLA-G alleles and HLA-G 14 bp polymorphisms in a Brazilian population. Tissue Antigens 2007; 70:62–68.
25. Castelli EC, Mendes-Junior CT, Deghaide NH, de Albuquerque RS, Muniz YC, Simoes RT, et al. The genetic structure of 3’untranslated region of the HLA-G gene: polymorphisms and haplotypes. Genes Immun 2010; 11:134–141.
26. Chen XY, Yan WH, Lin A, Xu HH, Zhang JG, Wang XX. The 14 bp deletion polymorphisms in HLA-G gene play an important role in the expression of soluble HLA-G in plasma. Tissue Antigens 2008; 72:335–341.
27. Colobran R, Adreani P, Ashhab Y, Llano A, Este JA, Dominguez O, et al. Multiple products derived from two CCL4 loci: high incidence of a new polymorphism in HIV+ patients. J Immunol 2005; 174:5655–5664.
28. Duggal P, An P, Beaty TH, Strathdee SA, Farzadegan H, Markham RB, et al. Genetic influence of CXCR6 chemokine receptor alleles on PCP-mediated AIDS progression among African Americans. Genes Immun 2003; 4:245–250.
29. Fabris A, Catamo E, Segat L, Morgutti M, Arraes LC, de Lima-Filho JL, et al. Association between HLA-G 3’UTR 14-bp polymorphism and HIV vertical transmission in Brazilian children. AIDS 2009; 23:177–182.
30. Fellay J, Ge D, Shianna KV, Colombo S, Ledergerber B, Cirulli ET, et al. Common genetic variation and the control of HIV-1 in humans. PLoS Genet 2009; 5:e1000791.
31. Fellay J, Shianna KV, Ge D, Colombo S, Ledergerber B, Weale M, et al. A whole-genome association study of major determinants for host control of HIV-1. Science 2007; 317:944–947.
32. Geczy AF, Kuipers H, Coolen M, Ashton LJ, Kennedy C, Ng G, et al. HLA and other host factors in transfusion-acquired HIV-1 infection. Hum Immunol 2000; 61:172–176.
33. Goldschmidt V, Bleiber G, May M, Martinez R, Ortiz M, Telenti A. Role of common human TRIM5alpha variants in HIV-1 disease progression. Retrovirology 2006; 3:54.
34. Gonzalez E, Dhanda R, Bamshad M, Mummidi S, Geevarghese R, Catano G, et al. Global survey of genetic variation in CCR5, RANTES, and MIP-1alpha: impact on the epidemiology of the HIV-1 pandemic. Proc Natl Acad Sci U S A 2001; 98:5199–5204.
35. Gonzalez E, Rovin BH, Sen L, Cooke G, Dhanda R, Mummidi S, et al. HIV-1 infection and AIDS dementia are influenced by a mutant MCP-1 allele linked to increased monocyte infiltration of tissues and MCP-1 levels. Proc Natl Acad Sci U S A 2002; 99:13795–13800.
36. Gonzalez E, Kulkarni H, Bolivar H, Mangano A, Sanchez R, Catano G, et al. The influence of CCL3L1 gene-containing segmental duplications on HIV-1/AIDS susceptibility. Science 2005; 307:1434–1440.
37. Gonzalez S, Tirado G, Revuelta G, Yamamura Y, Lu Y, Nerurkar VR, et al. CCR5 chemokine receptor genotype frequencies among Puerto Rican HIV-1-seropositive individuals. Bol Asoc Med P R 1998; 90:12–15.
38. Haddad R, Ciliao Alves DC, Rocha-Junior MC, Azevedo R, do Socorro Pombo-de-Oliveira M, Takayanagui OM, et al. HLA-G 14-bp insertion/deletion polymorphism is a risk factor for HTLV-1 infection. AIDS Res Hum Retroviruses 2011; 27:283–288.
39. Harrison GA, Humphrey KE, Jakobsen IB, Cooper DW. A 14 bp deletion polymorphism in the HLA-G gene. Hum Mol Genet 1993; 2:2200.
40. Ji H, Ball TB, Kimani J, Plummer FA. Novel interferon regulatory factor-1 polymorphisms in a Kenyan population revealed by complete gene sequencing. J Hum Genet 2004; 49:528–535.
41. Ji H, Ball TB, Liang BB, Kimani J, Plummer FA. Human interferon regulatory factor-1 gene and its promoter sequences revealed by population-based complete gene sequencing. DNA Seq 2008; 19:326–331.
42. Liao HX, Montefiori DC, Patel DD, Lee DM, Scott WK, Pericak-Vance M, et al. Linkage of the CCR5 Delta 32 mutation with a functional polymorphism of CD45RA. J Immunol 2000; 165:148–157.
43. Libert F, Cochaux P, Beckman G, Samson M, Aksenova M, Cao A, et al. The deltaccr5 mutation conferring protection against HIV-1 in Caucasian populations has a single and recent origin in Northeastern Europe. Hum Mol Genet 1998; 7:399–406.
44. Lin A, Yan WH, Xu HH, Tang LJ, Chen XF, Zhu M, et al. 14 bp deletion polymorphism in the HLA-G gene is a risk factor for idiopathic dilated cardiomyopathy in a Chinese Han population. Tissue Antigens 2007; 70:427–431.
45. Martin MP, Carrington M, Dean M, O’Brien SJ, Sheppard HW, Wegner SA, et al. CXCR4 polymorphisms and HIV-1 pathogenesis. J Acquir Immune Defic Syndr Hum Retrovirol 1998; 19:430.
46. Martin MP, Lederman MM, Hutcheson HB, Goedert JJ, Nelson GW, van Kooyk Y, et al. Association of DC-SIGN promoter polymorphism with increased risk for parenteral, but not mucosal, acquisition of human immunodeficiency virus type 1 infection. J Virol 2004; 78:14053–14056.
47. Matt C, Roger M. Genetic determinants of pediatric HIV-1 infection: vertical transmission and disease progression among children. Mol Med 2001; 7:583–589.
48. McDermott DH, Colla JS, Kleeberger CA, Plankey M, Rosenberg PS, Smith ED, et al. Genetic polymorphism in CX3CR1 and risk of HIV disease. Science 2000; 290:2031.
49. McDermott DH, Zimmerman PA, Guignard F, Kleeberger CA, Leitman SF, Murphy PM. CCR5 promoter polymorphism and HIV-1 disease progression. Multicenter AIDS Cohort Study (MACS). Lancet 1998; 352:866–870.
50. McDermott DH, Beecroft MJ, Kleeberger CA, Al-Sharif FM, Ollier WE, Zimmerman PA, et al. Chemokine RANTES promoter polymorphism affects risk of both HIV infection and disease progression in the Multicenter AIDS Cohort Study. AIDS 2000; 14:2671–2678.
51. Pelak K, Goldstein DB, Walley NM, Fellay J, Ge D, Shianna KV, et al. Host determinants of HIV-1 control in African Americans. J Infect Dis 2010; 201:1141–1149.
52. Petersen DC, Glashoff RH, Shrestha S, Bergeron J, Laten A, Gold B, et al. Risk for HIV-1 infection associated with a common CXCL12 (SDF1) polymorphism and CXCR4 variation in an African population. J Acquir Immune Defic Syndr 2005; 40:521–526.
53. Price H, Lacap P, Tuff J, Wachihi C, Kimani J, Ball TB, et al. A TRIM5alpha exon 2 polymorphism is associated with protection from HIV-1 infection in the Pumwani sex worker cohort. AIDS 2010; 24:1813–1821.
54. One copy of mutation may help resistance: study.AIDS Alert 2002; 17:23–24, 14.
55. An P, Martin MP, Nelson GW, Carrington M, Smith MW, Gong K, et al. Influence of CCR5 promoter haplotypes on AIDS progression in African-Americans. AIDS 2000; 14:2117–2122.
56. Arenzana-Seisdedos F, Virelizier JL, Rousset D, Clark-Lewis I, Loetscher P, Moser B, et al. HIV blocked by chemokine antagonist. Nature 1996; 383:400.
57. Blanpain C, Libert F, Vassart G, Parmentier M. CCR5 and HIV infection. Receptors Channels 2002; 8:19–31.
58. Chalmet K, Van Wanzeele F, Demecheleer E, Dauwe K, Pelgrom J, Van Der Gucht B, et al. Impact of Delta 32-CCR5 heterozygosity on HIV-1 genetic evolution and variability--a study of 4 individuals infected with closely related HIV-1 strains. Virology 2008; 379:213–222.
59. Bratt G, Sandstrom E, Albert J, Samson M, Wahren B. The influence of MT-2 tropism on the prognostic implications of the delta32 deletion in the CCR-5 gene. AIDS 1997; 11:1415–1419.
60. Diaz FJ, Vega JA, Patino PJ, Bedoya G, Nagles J, Villegas C, et al. Frequency of CCR5 delta-32 mutation in human immunodeficiency virus (HIV)-seropositive and HIV-exposed seronegative individuals and in general population of Medellin, Colombia. Mem Inst Oswaldo Cruz 2000; 95:237–242.
61. Gonzalez E, Bamshad M, Sato N, Mummidi S, Dhanda R, Catano G, et al. Race-specific HIV-1 disease-modifying effects associated with CCR5 haplotypes. Proc Natl Acad Sci U S A 1999; 96:12004–12009.
62. Huang Y, Paxton WA, Wolinsky SM, Neumann AU, Zhang L, He T, et al. The role of a mutant CCR5 allele in HIV-1 transmission and disease progression. Nat Med 1996; 2:1240–1243.
63. Hummel S, Schmidt D, Kremeyer B, Herrmann B, Oppermann M. Detection of the CCR5-Delta32 HIV resistance gene in Bronze Age skeletons. Genes Immun 2005; 6:371–374.
64. Kokkotou E, Philippon V, Gueye-Ndiaye A, Mboup S, Wang WK, Essex M, et al. Role of the CCR5 delta 32 allele in resistance to HIV-1 infection in west Africa. J Hum Virol 1998; 1:469–474.
65. Hedrick PW, Verrelli BC. “Ground truth” for selection on CCR5-Delta32. Trends Genet 2006; 22:293–296.
66. Speelmon EC, Livingston-Rosanoff D, Li SS, Vu Q, Bui J, Geraghty DE, et al. Genetic association of the antiviral restriction factor TRIM5alpha with human immunodeficiency virus type 1 infection. J Virol 2006; 80:2463–2471.
67. Diaz-Griffero F, Perron M, McGee-Estrada K, Hanna R, Maillard PV, Trono D, et al. A human TRIM5alpha B30.2/SPRY domain mutant gains the ability to restrict and prematurely uncoat B-tropic murine leukemia virus. Virology 2008; 378:233–242.
68. Takeuchi H, Matano T. Host factors involved in resistance to retroviral infection. Microbiol Immunol 2008; 52:318–325.
69. Su RC, Sivro A, Kimani J, Jaoko W, Plummer FA, Ball TB. Epigenetic control of IRF1 responses in HIV-exposed seronegative versus HIV-susceptible individuals. Blood 2011; 117:2649–2657.
70. Hardie RA, Knight E, Bruneau B, Semeniuk C, Gill K, Nagelkerke N, et al. A common human leucocyte antigen-DP genotype is associated with resistance to HIV-1 infection in Kenyan sex workers. AIDS 2008; 22:2038–2042.
71. Hardie RA, Luo M, Bruneau B, Knight E, Nagelkerke NJ, Kimani J, et al. Human leukocyte antigen-DQ alleles and haplotypes and their associations with resistance and susceptibility to HIV-1 infection. AIDS 2008; 22:807–816.
72. Lacap PA, Huntington JD, Luo M, Nagelkerke NJ, Bielawny T, Kimani J, et al. Associations of human leukocyte antigen DRB with resistance or susceptibility to HIV-1 infection in the Pumwani Sex Worker Cohort. AIDS 2008; 22:1029–1038.
73. MacDonald KS, Fowke KR, Kimani J, Dunand VA, Nagelkerke NJ, Ball TB, et al. Influence of HLA supertypes on susceptibility and resistance to human immunodeficiency virus type 1 infection. J Infect Dis 2000; 181:1581–1589.
74. Alimonti JB, Kimani J, Matu L, Wachihi C, Kaul R, Plummer FA, et al. Characterization of CD8 T-cell responses in HIV-1-exposed seronegative commercial sex workers from Nairobi, Kenya. Immunol Cell Biol 2006; 84:482–485.
75. Alimonti JB, Koesters SA, Kimani J, Matu L, Wachihi C, Plummer FA, et al. CD4+ T cell responses in HIV-exposed seronegative women are qualitatively distinct from those in HIV-infected women. J Infect Dis 2005; 191:20–24.
76. Kaul R, Dong T, Plummer FA, Kimani J, Rostron T, Kiama P, et al. CD8(+) lymphocytes respond to different HIV epitopes in seronegative and infected subjects. J Clin Invest 2001; 107:1303–1310.
77. Kaul R, Plummer FA, Kimani J, Dong T, Kiama P, Rostron T, et al. HIV-1-specific mucosal CD8+ lymphocyte responses in the cervix of HIV-1-resistant prostitutes in Nairobi. J Immunol 2000; 164:1602–1611.
78. Kaul R, Rutherford J, Rowland-Jones SL, Kimani J, Onyango JI, Fowke K, et al. HIV-1 Env-specific cytotoxic T-lymphocyte responses in exposed, uninfected Kenyan sex workers: a prospective analysis. AIDS 2004; 18:2087–2089.
79. McLaren PJ, Ball TB, Wachihi C, Jaoko W, Kelvin DJ, Danesh A, et al. HIV-exposed seronegative commercial sex workers show a quiescent phenotype in the CD4+ T cell compartment and reduced expression of HIV-dependent host factors. J Infect Dis 2010; 202 (Suppl 3):S339–S344.
80. Songok EM, Luo M, Liang B, McLaren P, Kaefer N, Apidi W, et al. Microarray analysis of HIV resistant female sex workers reveal a gene expression signature pattern reminiscent of a lowered immune activation state. PLoS One 2012; 7:e30048.
81. Geraghty DE, Koller BH, Orr HT. A human major histocompatibility complex class I gene that encodes a protein with a shortened cytoplasmic segment. Proc Natl Acad Sci U S A 1987; 84:9145–9149.
82. Arnaiz-Villena A, Martinez-Laso J, Serrano-Vela JI, Reguera R, Moscoso J. HLA-G polymorphism and evolution. Tissue Antigens 2007; 69 (Suppl 1):156–159.
83. Ishitani A, Sageshima N, Lee N, Dorofeeva N, Hatake K, Marquardt H, et al. Protein expression and peptide binding suggest unique and interacting functional roles for HLA-E, F, and G in maternal-placental immune recognition. J Immunol 2003; 171:1376–1384.
84. Favier B, LeMaoult J, Rouas-Freiss N, Moreau P, Menier C, Carosella ED. Research on HLA-G: an update. Tissue Antigens 2007; 69:207–211.
85. Carosella ED. The tolerogenic molecule HLA-G. Immunol Lett 2011; 138:22–24.
86. Lajoie J, Massinga Loembe M, Poudrier J, Guedou F, Pepin J, Labbe AC, et al. Blood soluble human leukocyte antigen G levels are associated with human immunodeficiency virus type 1 infection in Beninese commercial sex workers. Hum Immunol 2010; 71:182–185.
87. Donaghy L, Gros F, Amiot L, Mary C, Maillard A, Guiguen C, et al. Elevated levels of soluble non-classical major histocompatibility class I molecule human leucocyte antigen (HLA)-G in the blood of HIV-infected patients with or without visceral leishmaniasis. Clin Exp Immunol 2007; 147:236–240.
88. Aikhionbare FO, Kumaresan K, Shamsa F, Bond VC. HLA-G DNA sequence variants and risk of perinatal HIV-1 transmission. AIDS Res Ther 2006; 3:28.
89. Matte C, Lajoie J, Lacaille J, Zijenah LS, Ward BJ, Roger M. Functionally active HLA-G polymorphisms are associated with the risk of heterosexual HIV-1 infection in African women. AIDS 2004; 18:427–431.
90. Segat L, Catamo E, Fabris A, Morgutti M, D’Agaro P, Campello C, et al. HLA-G*0105N allele is associated with augmented risk for HIV infection in white female patients. AIDS 2010; 24:1961–1964.
91. Lajoie J, Hargrove J, Zijenah LS, Humphrey JH, Ward BJ, Roger M. Genetic variants in nonclassical major histocompatibility complex class I human leukocyte antigen (HLA)-E and HLA-G molecules are associated with susceptibility to heterosexual acquisition of HIV-1. J Infect Dis 2006; 193:298–301.
92. Luo M, Blanchard J, Pan Y, Brunham K, Brunham RC. High-resolution sequence typing of HLA-DQA1 and -DQB1 exon 2 DNA with taxonomy-based sequence analysis (TBSA) allele assignment. Tissue Antigens 1999; 54:69–82.
93. Luo M, Blanchard J, Brunham K, Pan Y, Shen CX, Lu H, et al. Two-step high resolution sequence-based HLA-DRB typing of exon 2 DNA with taxonomy-based sequence analysis allele assignment. Hum Immunol 2001; 62:1294–1310.
94. Hens N, Aerts M, Molenberghs G. Model selection for incomplete and design-based samples. Stat Med 2006; 25:2502–2520.
95. Luo M, Daniuk CA, Diallo TO, Capina RE, Kimani J, Wachihi C, et al. For protection from HIV-1 infection, more might not be better: a systematic analysis of HIV Gag epitopes of two alleles associated with different outcomes of HIV-1 infection. J Virol 2012; 86:1166–1180.
96. Park Y, Kim YS, Kwon OJ, Kim HS. Allele frequencies of human leukocyte antigen-G in a Korean population. Int J Immunogenet 2011; 39:39–45.
97. Donadi EA, Castelli EC, Arnaiz-Villena A, Roger M, Rey D, Moreau P. Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association. Cell Mol Life Sci 2011; 68:369–395.
98. Thibodeau V, Lajoie J, Labbe AC, Zannou MD, Fowke KR, Alary M, et al. High level of soluble HLA-G in the female genital tract of Beninese commercial sex workers is associated with HIV-1 infection. PLoS One 2011; 6:e25185.
99. Rebmann V, van der Ven K, Passler M, Pfeiffer K, Krebs D, Grosse-Wilde H. Association of soluble HLA-G plasma levels with HLA-G alleles. Tissue Antigens 2001; 57:15–21.
Keywords:

disease association; highly exposed seronegative; HIV-1; human leukocyte antigens-G; sequence-based typing

© 2013 Lippincott Williams & Wilkins, Inc.