Factors contributing to the lack of human immunodeficiency virus type 1 (HIV-1) transmission in HIV-1-discordant partners

Prevalence of HIV infection, access to HIV care, and response to antiretroviral therapy among partners of HIV-infected individuals in Thailand

Background

Health care providers usually focus on index HIV-infected patients and seldom obtain information from their partners. We aimed to determine HIV-preventative measures among couples, the prevalence of HIV infection, and treatment outcomes of partners.

Methods

This cross-sectional study was conducted in two hospital settings, a university hospital in Bangkok and a general hospital in northeastern Thailand, from January 2011-October 2015. Factors associated with serodiscordant relationships were determined by logistic regression.

Results

A total of 393 couples were enrolled for analysis; 156 (39.7%) were serodiscordant. The median relationship duration of serodiscordant couples was shorter than that of seroconcordant couples (6.4 years vs 11.6 years, p < 0.001). Of 237 HIV-infected partners, 17.7% had AIDS-defining illness, the median nadir CD4 count (interquartile range) was 240 (96–427) cells/mm³, 83.5% received antiretroviral therapy (ART), 98.3% had adherence > 95%, 90.3% had undetectable HIV RNA, and 22.9% had a prior history of treatment failure. There was no significant difference in condom usage in the prior 30 days between serodiscordant and seroconcordant couples. Factors of index HIV-infected patients associated with serodiscordant relationships were younger age (odds ratio [OR] 1.04 per 5 years; 95% confidence interval [CI] 1.01–1.06), receiving care at the general hospital (OR 1.73; 95% CI 1.08–2.78), a shorter duration of relationship (OR 1.04 per year; 95% CI 1.01–1.07), a higher nadir CD4 count (OR 1.06 per 50 cells/mm³; 95% CI 1.1–1.13), and not receiving a protease inhibitor-based regimen (OR 2.04; 95% CI 1.06–3.96).

Conclusions

A high number of serodiscordant couples was determined. Partners’ information should be retrieved as a holistic approach. Interventions for minimizing HIV transmission within serodiscordant couples should be evaluated and implemented.

Assessment of HIV discordance and associated risk factors among couples receiving HIV test in Dilla, Ethiopia

Background

About 60% of new HIV infections occur in HIV sero-discordant couples as 30% of married HIV positives have negative spouse. Although HIV-discordant couples are at 10% annual risk of acquiring HIV infection and large number of new HIV infections occur in stable partnerships, most HIV prevention programs focus on reducing casual sexual partners, condom use, and increasing fidelity among married partners. The purpose is assessment of sero-discordance among couples and associated factors.

Methods

The study was facility based cross sectional survey of couples who tested for HIV in 2011 and lived together at least 1 year period. The sample size was 154 couples (308 individuals) and necessary ethical issues were considered.

Results

Among 152 couples (304 individuals) who received VCT, HIV sero-prevalence in this study was found to be 11(3.6%). The prevalence in females 8(5.3%) was higher than that in males 3(2.0%). Of all participants, 9(3.0%) were found to be sero-discordant, 2(0.7%) concordant positive and 293(96.4%) concordant negative. Of all couples 9(5.9%) were found to be sero-discordant, 2(1.3%) concordant positive and 141(92.8%) concordant negative. Of the 9 sero-discordant couples, the 7(4.6%) prevalence in females was higher than 2(1.3%) in males. And, among 9 discordant couples, 5 of them were premarital sex partner and the rest 4 were married couples. Premarital couples were significantly discordant than married couples, AOR = 1.68; 95%CI (1.36- 5.40). HIV discordance was also significantly associated with having number of two or more sexual partners than one sexual partner AOR = 4.06; 95%CI (2.41-10.13).

Conclusion

The study indicated high prevalence of HIV discordance and increased risk of vulnerability. Therefore, couples should be aware of their own and their partners’ sero-status before and after engagement. Again, the following risk reduction methods were recommended: education of discordant couples on 100% correct condom use, and if condom breaks, or if they forget to use, Post-Exposure Prophylaxis must be established; for those who are not volunteer to use condom and/or have a child, early initiation of ART to positive partner.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-0500-7-893) contains supplementary material, which is available to authorized users.

Discordant HIV Couple: Analysis of the Possible Contributing Factors

Several intricacies still abound with respect to HIV infection. Discordance is one such intriguing aspect of HIV infection. Out of 35 discordant couples included in the study. husbands were positive in 29 couples and wives in 6. Pre/extramarital affairs was the probable reason for HIV infection in 23 out of 29 discordant males, and 2 out of 6 discordant females. Even though, decreased frequency of sexual acts between the couple was the reason for discordance in a few, but in majority of the couples who had regular sexual contact for many years, the exact cause for discordance could not be ascertained. inherent resistance to HIV in some individuals may be the reasons for the discordance.

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

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.

The high frequency of HIV type 1-specific cellular immune responses in seronegative individuals with parenteral and/or heterosexual HIV type 1 exposure

Some individuals remain HIV seronegative despite repeated unprotected exposure to the virus. Recent observations led to a concept that acquired immunity plays a role in protection or at least in altered susceptibility to HIV-1 infection in highly exposed seronegative (ESN) individuals. Our aim was to study HIV-specific cellular immune responses induced in parenterally and/or heterosexually ESN individuals. Nine seronegative injection drug users (IDUs), 10 seronegative individuals, and nine of their HIV-positive sexual and/or IDU partners from the cohort of IDUs were included in the study. The discordant couples had unprotected sex, and some of seronegative partners also had parenteral exposure. Cell-mediated responses were measured in peripheral blood mononuclear cells (PBMCs) by ex vivo interferon (IFN)-γ-ELISpot and ICS combining IFN-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-2 after stimulation with four consensus peptide pools (Nef, Gag, RT, Env, subtype A-EE). Thirteen out of 19 (68%) seronegative study subjects had strong Nef peptide pool-specific ELISpot responses, three (16%) subjects responded against the Gag peptide pool, and one subject had an RT peptide pool response. Nef peptide pool responses in ESN were as high as in seropositive subjects. The multiple HIV-specific cytokine production in both CD4(+) and CD8(+) T cells was shown for several ESN subjects. The functional profiles of the immune responses were different between seronegative and HIV-positive study groups. Whether the observed cellular responses have any protective role against HIV needs to be further investigated.

HIV-1-specific enzyme-linked immunosorbent spot assay responses in HIV-1-exposed uninfected partners in discordant relationships compared to those in low-risk controls

A number of studies of highly exposed HIV-1-seronegative individuals (HESN) have found HIV-1-specific cellular responses. However, there is limited evidence that responses prevent infection or are linked to HIV-1 exposure. Peripheral blood mononuclear cells (PBMC) were isolated from HESN in HIV-1-discordant relationships and low-risk controls in Nairobi, Kenya. HIV-1-specific responses were detected using gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assays stimulated by peptide pools spanning the subtype A HIV-1 genome. The HIV-1 incidence in this HESN cohort was 1.5 per 100 person years. Positive ELISpot responses were found in 34 (10%) of 331 HESN and 14 (13%) of 107 low-risk controls (odds ratio [OR] = 0.76; P = 0.476). The median immunodominant response was 18.9 spot-forming units (SFU)/10(6) peripheral blood mononuclear cells (PBMC). Among HESN, increasing age (OR = 1.24 per 5 years; P = 0.026) and longer cohabitation with the HIV-1-infected partner (OR = 5.88 per 5 years; P = 0.003) were associated with responses. These factors were not associated with responses in controls. Other exposure indicators, including the partner's HIV-1 load (OR = 0.99 per log(10) copy/ml; P = 0.974) and CD4 count (OR = 1.09 per 100 cells/μl; P = 0.238), were not associated with responses in HESN. HIV-1-specific cellular responses may be less relevant to resistance to infection among HESN who are using risk reduction strategies that decrease their direct viral exposure.

Low-level exposure to HIV induces virus-specific T cell responses and immune activation in exposed HIV-seronegative individuals

HIV-specific T cells response and T cell activation are frequently seen in exposed seronegative individuals (ESN). In this study, we report HIV-specific response and level of T cell activation in ESN partners of HIV-infected patients presenting low or undetectable levels of HIV-RNA. We evaluated 24 HIV-serodiscordant couples. ESN were classified into three categories of exposure to HIV (very low, low, and moderate-high), considering levels of HIV-RNA in their infected partner and frequency of sexual high-risk practices within the last 12 mo. HIV-specific T cell responses and activation levels in T cell subsets were evaluated by flow cytometry. We reported that 54% of ESN had detectable HIV-specific T cells response, being the highest prevalence seen in the low exposure group (64%). Several T cell subsets were significantly increased in ESN when compared with controls: CD4(+)CD38(+) (p = 0.006), CD4(+)HLA-DR(-)CD38(+) (p = 0.02), CD4(+)CD45RA(+)CD27(+)HLA-DR(-)CD38(+) (p = 0.002), CD8(+)CD45RA(+)CD27(+)CD38(-)HLA-DR(+) (p = 0.02), and CD8(+)CD45RA(+)CD27(-)CD38(+)HLA-DR(+) (p = 0.03). Activation of CD8(+) T cells was increased in ESN with detectable HIV T cell responses compared with ESN lacking these responses (p = 0.04). Taken together, these results suggest that persistent but low sexual HIV exposure is able to induce virus-specific T cells response and immune activation in a high proportion of ESN, suggesting that virus exposure may occur even in conditions of maximal viral suppression in the HIV-infected partner.

Human immunodeficiency virus serodiscordant couples on highly active antiretroviral therapies with undetectable viral load: conception by unprotected sexual intercourse or by assisted reproduction techniques?

Until recently, only assisted reproduction was proposed to serodiscordant couples wishing to conceive. Nevertheless, recent publications have proposed unprotected sexual intercourse, targeting fertile days, for couples where antiretroviral treatment has lowered blood viral load to an undetectable level. Available data and the arguments for and against conception by safe sex versus the use of a strategy of unprotected sexual intercourse targeting fertile days are reviewed and analyzed. Although the rate of transmission of human immunodeficiency virus in serodiscordant couples in precise conditions (such as an undetectable viral load on treatment by highly active antiretroviral therapies and sexual intercourse limited to the fertile days) is very low, not zero, here we stress the various factors which can increase the risk of seroconversion in this particular population. In this context, it seems less cautious to abandon the recommendations of safe sex in serodiscordant couples desiring a child. The recourse to medically assisted procreation is advised, as long as evidence from further studies does not show that unprotected sexual intercourse, targeted to fertile days, does not have unexpected harmful consequences.

Contribution of immunological and virological factors to extremely severe primary HIV type 1 infection

BACKGROUND

During acute human immunodeficiency virus (HIV) infection, high viral loads and the induction of host immune responses typically coincide with the onset of clinical symptoms. However, clinically severe presentations during acute HIV type 1 (HIV-1) infection, including AIDS-defining symptoms, are unusual.

METHODS

Virus isolates were tested for clade, drug susceptibility, coreceptor use, and growth rate in 2 case reports of sexual transmission of HIV-1 infection. Human leukocyte antigen (HLA) genotype was determined, and HIV-1-specific cytotoxic T lymphocyte responses to an overlapping peptide set spanning the entire HIV clade A and clade B proteome were assayed.

RESULTS

The viruses isolated in the 2 unrelated case reports of severe primary HIV-1 infection showed R5/X4 dual-mixed tropism, belonged to clade B and CRF02-AG, and were highly replicative in peripheral blood mononuclear cell culture. Impaired humoral responses were paralleled by a profound absence of HIV-1-specific cytotoxic T lymphocyte responses to the entire viral proteome in the 2 case reports. In 1 case report for which the virus source was available, there was a remarkable HLA similarity between the 2 patients involved in the transmission event, because 3 of 4 HLA-A and HLA-B alleles had matched HLA supertype for both patients.

CONCLUSIONS

The data suggest that concurrence of viral and host factors contributes to the clinical severity of primary HIV-1 infection and that patients infected with highly replicative, dual-tropic viruses are more prone to develop AIDS-defining symptoms during acute infection if they are unable to mount humoral and cellular HIV-1-specific immune responses. The presence of concordant HLA supertypes might facilitate the preferential transmission of HLA-adapted viral variants, further accelerating disease progression.

Not just sheer luck! Immune correlates of protection against HIV-1 infection

Susceptibility to HIV infection is widely different among individuals, and it is known that individuals can be identified who are repeatedly exposed to HIV but in whom neither infection nor disease are seen. The possibility that sheer luck is not the only determinant of this phenomenon begun to be considered in 1989 when it was reported that T cell responses to HIV proteins could be detected in antibody-negative sexual partners of known HIV-positive men. In this review, we will summarize the body of knowledge that stemmed from that first observation.

Evolutionary dynamics of HIV-1 and the control of AIDS

Human immunodeficiency viruses (HIV) have exhibited an extraordinary capacity for genetic change, exploring new evolutionary space after each transmission to a new host. This presents a great challenge to the prevention and management of HIV-1 infection. At the same time, the relentless diversification of HIV-1, developing as it does under the constraints imposed by the human immune system and other selective forces, contains within it information useful for understanding HIV epidemiology and pathogenesis. Comparing the sheer mutational potential of HIV with actual data representing viral lineages that can survive selection suggests that HIV does not have unlimited capacity for change. Rather, clinical and bioinformatic data suggest that, even in the most diverse gene of the most highly variable organism, natural selection places severe limits on the portion of amino acid sequence space that ensures viability. This suggests some optimism for those attempting to identify sets of antigens that can generate effective humoral and cellular immune responses against HIV.

Living with discordance: knowledge, challenges, and prevention strategies of HIV-discordant couples in Uganda

Prevalence of HIV-discordance among couples in sub-Saharan Africa is high. Negative partners are at high risk of HIV infection but few HIV/AIDS service providers have developed effective counseling messages for HIV-discordant couples. To identify clients' explanations for discordance, challenges, and prevention strategies, 24 in-depth interviews and 4 focus group discussions were conducted with 32 female and 35 male members of HIV-discordant couples who sought HIV voluntary counseling and testing (VCT) in Uganda. In addition, counselor explanations for discordance were gathered from 62 counselor trainers during 3 interactive workshops. Misconceptions about discordance were widespread among clients and counselors. Common explanations included: the concept of a hidden infection not detectable by HIV tests, belief in immunity, the thought that gentle sex protected HIV-negative partners, and belief in protection by God. Such explanations for discordance reinforced denial of HIV risk for the negative partner within discordant couples and potentially increased transmission risk. Couples identified negotiation of sexual relations as their most formidable challenge. Prevention strategies included condom use, abstinence and separation of beds, contractual agreements for outside sexual partners, and relationship cessation. Discordant couples represent a critical risk group and improved counseling protocols that clearly explain discordance, emphasize high risk of transmission, and support risk reduction are urgently needed.

Low-level CD4+ T cell activation is associated with low susceptibility to HIV-1 infection

Different features have been associated with low susceptibility to HIV type 1 (HIV-1) infection in exposed seronegative individuals. These include genetic make-up such as homozygosity for the CCR5-Delta32 allele and the presence of HIV-specific CTLs. We studied immune activation and immune responsiveness in relation to HIV-1 susceptibility in 42 high-risk seronegative (HRSN) participants of the Amsterdam Cohort Studies and 54 men from the same cohort who were seronegative at the moment of analysis but later became HIV seropositive. HRSN had higher naive (CD45RO CD27) CD4 and CD8 T cell numbers and lower percentages of activated (HLADR CD38, CD70) CD4 and proliferating (Ki67) CD4 and CD8 T cells, irrespective of previous episodes of sexually transmittable infections. Furthermore, whole blood cultures from HRSN showed lower lymphoproliferative responses than healthy laboratory controls. These data suggest that low levels of immune activation and low T cell responsiveness may contribute to low HIV susceptibility.

Induction of serum and mucosal FIV-specific immune responses by intranasal immunization with p24Gag

We examined the ability of FIV p24Gag to induce systemic and mucosal FIV-specific immune responses when delivered as a nasal immunogen alone, or with a mucosal adjuvant, Escherichia coli heat labile toxin LT(R192G). Nasal immunization with p24Gag alone induced FIV-specific immune responses but overall responses were weak, transient, and/or present only in a few animals. Co-administration of LT(R192G) resulted in strong FIV-specific serum IgG and enhanced salivary IgA responses. Moreover, FIV-specific IgA was detected in vaginal wash fluid from 6/6 cats co-immunized with LT(R192G) and p24Gag versus 1/6 immunized with p24Gag alone. This is the first report detailing induction of systemic or mucosal FIV-specific immune responses by nasal immunization alone. As such, this study demonstrates that nasal immunization of cats can be a relevant and effective route for the delivery of candidate vaccines. However, while nasal immunization of cats with p24Gag induces antigen-specific systemic immune responses, development of strong systemic and mucosal immune responses requires co-administration of a mucosal adjuvant, such as LT(R192G).

Modified vaccinia Ankara expressing HIVA antigen stimulates HIV-1-specific CD8 T cells in ELISpot assays of HIV-1 exposed infants

Recombinant modified vaccinia virus Ankara expressing HIV-1 antigens (MVA.HIVA) was used in ELISpot assays to monitor HIV-1-specific T cell responses in infants. Responses to MVA.HIVA and HIV-1 peptides were examined in 13 infected and 81 exposed uninfected infants in Nairobi, Kenya. Responses to MVA.HIVA (38%) and peptide stimulation (38%) were similar in frequency (p=1.0) and magnitude (mean 176 versus 385 HIVSFU/10(6), p=0.96) in HIV-1 infected infants. In exposed uninfected infants, MVA.HIVA detected more positive responses and higher magnitude responses as compared to peptide. MVA.HIVA ELISpot is a sensitive method for quantification of HIV-1-specific CD8+ T cell responses in HIV-1 exposed infants. These results demonstrate the relevance of HIV-1 clade A consensus-derived immunogen HIVA for the viruses currently circulating in Nairobi.

Influence of host genetic variation on susceptibility to HIV type 1 infection

For this review of genetic susceptibility to human immunodeficiency virus type 1 infection, far more information was available on factors involved in acquisition of the virus by an uninfected "recipient" than on propagation by the infected "donor." Genetic variation presumably alters transmission from an infected host primarily by regulating the replication of virus and the concentration of particles circulating in blood and mucosal secretions of the potential donor. Thus, the effects of host genetic variation on transmission are inextricably bound to the well-established and powerful effects on virus load at different stages of infection. Teasing apart the effects in both donors and recipients has been and will continue to be quite difficult.

Insights into the role of host genetic and T-cell factors in resistance to HIV transmission from studies of highly HIV-exposed Thais

Studies of resistance to HIV-1 transmission are likely to be valuable for the design of vaccines and other efforts to prevent HIV. Here, we review the T-cell and genetic factors associated with resistance to HIV-1 transmission in studies of highly exposed but persistently seronegative (HEPS) women from northern Thailand. Women were enrolled in two sex-worker studies and in a discordant couple study. We performed Cr51 cytotoxic T lymphocyte (CTL), interferon-gamma (IFN-gamma) ELISPOT, and proliferation assays as well as genetic studies, including HLA-class I typing. CTL and ELISPOT studies showed a skewing of T-cell responses to conserved HIV-1 proteins in HEPS, but not in HIV-1-seropositive women. T-cell responses were extremely long-lived in some HEPS women. In the two sex-worker studies, HLA-A11 was associated with resistance to HIV-1 transmission. These data provide promise for the ability of CTL to control HIV and emphasize the importance of developing HIV vaccines that stimulate strong, long-lasting Tcell responses.

Chemokine receptor expression in the human ectocervix: implications for infection by the human immunodeficiency virus-type I

Human immunodeficiency virus-type 1 (HIV-1) is a sexually transmitted pathogen that can infect cells in the female reproductive tract (FRT). The mechanism of viral transmission within the FRT and the mode of viral spread to the periphery are not well understood. To characterize the frequency of potential targets of HIV infection within the FRT, we performed a systematic study of the expression of HIV receptors (CD4, galactosyl ceramide (GalCer)) and coreceptors (CXCR4 and CCR5) on epithelial cells and leucocytes from the ectocervix. The ectocervix is a likely first site of contact with HIV-1 following heterosexual transmission, and expression of these receptors is likely to correlate with susceptibility to viral infection. We obtained ectocervical tissue specimens from women undergoing hysterectomy, and compared expression of these receptors among patients who were classified as being in the proliferative or secretory phases of their menstrual cycle at the time of hysterectomy, as well as from postmenopausal tissues. Epithelial cells from tissues at early and mid-proliferative stages of the menstrual cycle express CD4, although by late proliferative and secretory phases, CD4 expression was absent or weak. In contrast, GalCer expression was uniform in all stages of the menstrual cycle. CXCR4 expression was not detected on ectocervical epithelial cells and positive staining was only evident on individual leucocytes. In contrast, CCR5 expression was detected on ectocervical epithelial cells from tissues at all stages of the menstrual cycle. Overall, our results suggest that HIV infection of cells in the ectocervix could most likely occur through GalCer and CCR5. These findings are important to define potential targets of HIV-1 infection within the FRT, and for the future design of approaches to reduce the susceptibility of women to infection by HIV-1.

Correlates of resistance to HIV-1 infection in homosexual men with high-risk sexual behaviour

OBJECTIVE

To investigate possible correlates of HIV resistance in participants from the Amsterdam Cohort of Homosexual men who have remained HIV seronegative despite high-risk sexual behaviour.

DESIGN/METHODS

We studied in vitro HIV-1 susceptibility and adaptive and innate immunity in 29 high-risk seronegative (HRSN) and 15 HIV-negative pre-seroconversion (pre-SC) homosexual men from the same Amsterdam Cohort Study (ACS) who seroconverted to HIV-1 positive during active follow-up. Host genetics were compared between HRSN and HIV-positive ACS participants.

RESULTS

We found lower in vitro susceptibility for a CCR5-using (R5) HIV-1 variant, higher RANTES production levels, but no difference in coreceptor expression in HRSN as compared with pre-SC controls. Reduced R5 in vitro susceptibility of two HRSN tested was restored to normal levels by addition of antibodies against beta-chemokines. A higher proportion of HRSN carried the SDF-1 3'A variant and HLA-A*11, A*31 and Cw*15 alleles. ELIspot analysis with HIV-1 peptide stimulation revealed low frequencies of HIV-1-specific CD8 interferon-gamma producing cytotoxic T cells in both HRSN and pre-SC controls.

CONCLUSIONS

Low in vitro R5 susceptibility of cells from the HRSN men was due to beta-chemokine mediated inhibition of virus replication. The presence of HIV-1 specific cytotoxic T cells in both HRSN and pre-SC participants may signify exposure to the virus rather than protection from infection. Host genetic characteristics and other factors affecting innate immunity may contribute to differential resistance to HIV-1 infection among exposed seronegative individuals.

Persistent alterations in the T-cell repertoires of HIV-1-infected and at-risk uninfected men

OBJECTIVE

We examined the association between immunogenic exposure and T-cell receptor (TCR) diversity to more clearly assess the impact of HIV-1 infection on the T-cell repertoire.

METHODS

: To estimate the extent of T-cell clonality attributable to HIV-1 infection, we evaluated T-cell repertoires in low-risk and at-risk seronegative men and HIV-1 seropositive men by assessment of T-cell receptor beta-chain (TCR beta) complimentary determining region 3 (CDR3) lengths.

RESULTS

The frequency of T-cell clonality in both HIV-1 infected and at-risk uninfected men was elevated in comparison to low-risk uninfected men. Among low-risk and at-risk seronegative, and HIV-1 seropositive men, clonal expansions were present in 3, 8, and 10% of CD4+ CDR3 lengths, and 18, 22, and 28% of CD8+ CDR3 lengths respectively. In addition, the longitudinal conservation of clonal expansions was observed in at-risk seronegative men. Based on comparisons to at-risk seronegative men, we estimate that at-risk seropositive men with chronic HIV-1 infection exhibit a 27% increase in the number of expanded CD8+ CDR3 lengths.

CONCLUSION

These findings provide an approximation of the magnitude of the T-cell response in individuals undergoing chronic HIV-1 infection and demonstrate a significant association between the history of immunogenic challenge and the magnitude of clonality within the T-cell repertoire. In addition, these findings underscore the necessity of selecting controls with similar antigenic exposure histories when investigating T-cell dynamics in HIV-infected individuals.

HIV type 1 antigen-responsive CD4+ T-lymphocytes in exposed yet HIV Type 1 seronegative Ugandans

CD4(+) T cell help is important for the functionality of CD8(+) cytotoxic T-lymphocytes (CTLs) in limiting viral replication and may contribute to mediation of apparent resistance to HIV-1 infection in exposed seronegative (ESN) individuals. Using five HIV-1 antigens in an intracellular cytokine assay, the presence of specific antigen-responsive interferon- gamma-positive (IFN-gamma(+)) CD69(+) CD4(+) T-lymphocytes was evaluated in ESNs, their seropositive partners, and unexposed seronegative controls. Ten ESNs (five females, five uncircumcised males) were identified from 10 HIV-1 serodiscordant couples with a history of frequent unprotected sexual intercourse. All ESNs and controls were negative on two EIAs and for HIV-1 proviral DNA. The frequency of ESNs with antigen-responsive IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes ranged from three to five of eight for the different HIV-1 antigens. Six of eight ESNs tested had a positive response to at least one of the five antigens. Responses were on average 3.5 times higher among seropositives compared to ESNs and absent in the five unexposed controls. A negative correlation was noted between responses in ESNs and the plasma viral load of their seropositive spouse. Clade-specific and cross-clade reactivity were noted in both ESNs and seropositive partners tested. The findings confirm that ESNs are in a state of HIV-1-specific immune activation and suggest that HIV-1-specific IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes in addition to HIV-1-specific CD8(+) CTLs already described by others are potential immunological correlates of protection from persistent HIV-1 infection.

CD4 cell and CD8 cell-mediated resistance to HIV-1 infection in exposed uninfected intravascular drug users in Vietnam

OBJECTIVE

To identify mechanisms of resistance to HIV-1 infection in exposed uninfected individuals.

DESIGN

We examined in-vitro cell susceptibility to HIV-1 infection in highly exposed Vietnamese intravascular drug users (IDU) who, despite a history of more than 10 years of drug use and a high prevalence of other blood-borne viral infections, remain apparently HIV uninfected.

METHODS

Forty-five exposed uninfected IDU and 50 blood donors were included in the study. Peripheral blood mononuclear cells (PBMC) or CD4 cell susceptibilities to HIV infection were evaluated using three HIV-1 isolates with different tropisms. Polymerase chain reaction analysis of HIV-1-DNA replication intermediates was used to characterize the restriction of HIV-1 replication in CD4 cells. Homologous CD8 cells were mixed with infected CD4 cells to evaluate their role in virus suppression.

RESULTS

We observed a relative resistance to PBMC infection with HIV-1 in 21 out of 45 exposed uninfected IDU, but only in five out of 50 unexposed controls (P < 0.001). PBMC resistance was related either to an inhibition of HIV-1 replication in CD4 cells or to CD8 cell-mediated viral suppression. HIV-1 replication in CD4 cells was restricted at the early stages of the viral cycle.

CONCLUSION

Reduced PBMC susceptibility to HIV-1 infection was associated with resistance to infection in exposed uninfected IDU. Distinct mechanisms are involved in in-vitro resistance and may contribute to the apparent protection from HIV-1 transmission in this systemically exposed population.

T cell immunity to herpes simplex viruses in seronegative subjects: silent infection or acquired immunity?

During the course of investigating T cell responses to HSV among volunteers entering trials of investigational genital herpes vaccines, 6 of the 24 immunocompetent subjects with no prior history of oral/labial or genital herpes possessed HSV-specific T cell immunity but, by multiple determinants of even the most sensitive serological assays, remained seronegative to HSV-1 and -2. Of these six immune seronegative (IS; HSV-seronegative with HSV-specific T cell responses) subjects, two had transient HSV-specific T cell responses, while four had CD4(+) and CD8(+) T cell responses directed at HSV that persisted for up to 4 years. CD4(+) T cell clones were isolated that recognized and had high binding affinities to epitopes in HSV-2 tegument proteins. All six IS subjects had potential sexual exposure to an HSV-2-infected sexual partner. Oral and genital mucosal secretions were sampled and tested for the presence of infectious HSV and HSV DNA. No evidence of HSV was detected in >1500 samples obtained from these IS subjects. The identification of persistent T cell responses to HSV in seronegative subjects is a novel finding in the herpesvirus field and suggests either undetected infection or acquired immunity in the absence of infection. Understanding the basis of these acquired immune responses may be critical in developing effective vaccines for genital herpes.

The absence of HIV seropositivity contrasts with a high prevalence of markers of sexually transmitted infections among registered female sex workers in Toliary, Madagascar

In a cross-sectional study in 1998 we assessed human immunodeficiency virus (HIV) and syphilis infections and their risk factors among the 316 registered female sex workers (FSWs) of Toliary, south-west Madagascar. No case of HIV infection was detected, but 18.4% of registered FSWs had syphilis. Only half of these women regularly used condoms. In a multiple logistic regression analysis, risk factors for syphilis infection were multiple clients per week and, paradoxically, regular use of condoms. The variables associated with irregular use of condoms were younger ages of registered FSWs, multiple clients per week and Malagasy clients. The high prevalence of syphilis infection associated with irregular use of condoms might facilitate a very fast spread of HIV infection among these FSWs. Promotion of condom use and surveillance of sexually transmitted infections and HIV infection incidence are needed in the south of Madagascar.

Host genetic profiles predict virological and immunological control of HIV-1 infection in adolescents

OBJECTIVE

To evaluate the correlation between host genetic profiles and virological and immunological outcomes among HIV-1-seropositive participants from the Reaching for Excellence in Adolescent Care and Health (REACH) cohort.

METHODS

HLA class I and chemokine coreceptor (CCR) alleles and haplotypes were resolved in 227 HIV-1-seropositive adolescents (ages 13-18 years; 75% females; 71% African-Americans) and 183 HIV-seronegative individuals, with quarterly follow-up visits between 1996 and 2000. Each HLA and CCR variant with consistent risk and protective effect on HIV-1 pathogenesis was assigned a score of -1 and +1, respectively. All individual markers and genetic scores were analyzed in relation to plasma viral load (VL) and CD4 T lymphocytes during a 6-12-month interval when no antiretroviral therapy was taken.

RESULTS

HLA-B*57 alone was a strong predictor of VL (P < 0.0001), but composite genetic profiles found in over 50% of patients consistently outperformed the individual component markers in multivariable analyses with or without adjustment for gender, race, age, and membership of clinical patient groups. Adolescents (n = 37) with a favorable combination of VL (< 1000 copies/ml) and CD4 T cell counts (> 450 x 10(6) cells/l) consistently had more positive (+1 to +2) than negative (-1 to -4) HLA and CCR scores compared with those (n = 56) with an unfavorable combination (VL > 16,000 copies/ml and CD4 cells < 450 x 10(6) cells/l) or the remainder (n = 134) of the cohort (overall P < 0.0001).

CONCLUSION

A generalizable genetic scoring algorithm based on seven HLA class I and CCR markers is highly predictive of viremia and immunodeficiency in HIV-1-infected adolescents.

Immunologic profile of highly exposed yet HIV type 1-seronegative men

The host immune factors that determine susceptibility to HIV-1 infection are poorly understood. We compared multiple immunologic parameters in three groups of HIV-1-seronegative men: 14 highly exposed (HR10), 7 previously reported possibly to have sustained transient infection (PTI), and a control group of 14 low risk blood bank donors (BB). Virus-specific cellular immune assays were performed for CD4(+) T helper cell responses, CD8(+) cytotoxic T lymphocyte activity, CD8(+) cell chemokine release, and CD8(+) cell-derived antiviral soluble factor activity. General immune parameters evaluated included CCR5 genotype and phenotype, interferon alpha production by PBMCs, leukocyte subset analysis, and detailed T lymphocyte phenotyping. Comparisons revealed no detectable group-specific differences in measures of virus-specific immunity. However, the HR10 group differed from the BB group in several general immune parameters, having higher absolute monocyte counts, higher absolute CD8(+) T cell counts and percentages, lower naive and higher terminal effector CD8(+) cells, and lower levels of CD28(+)CD8(+) cells. These changes were not associated with seropositivity for other chronic viral infections. The PTI men appeared to have normal levels of monocytes and slightly elevated levels of CD8(+) T cells (also with increased effector and decreased naive cells). Although we cannot entirely exclude the contribution of other chronic viral infections, these findings suggest that long-lived systemic cellular antiviral immunity as detected by our assays is not a common mechanism for resistance to infection, and that resistance may be multifactorial. General immune parameters reflected by CD8(+) T cell levels and activation, and monocyte concentrations may affect the risk of infection with HIV-1, and/or serve as markers of exposure.

Favorable and unfavorable HLA class I alleles and haplotypes in Zambians predominantly infected with clade C human immunodeficiency virus type 1

The setpoint of viral RNA concentration (viral load [VL]) during chronic human immunodeficiency virus type 1 (HIV-1) infection reflects a virus-host equilibration closely related to CD8(+) cytotoxic T-lymphocyte (CTL) responses, which rely heavily on antigen presentation by the human major histocompatibility complex (MHC) (i.e., HLA) class I molecules. Differences in HIV-1 VL among 259 mostly clade C virus-infected individuals (137 females and 122 males) in the Zambia-UAB HIV Research Project (ZUHRP) were associated with several HLA class I alleles and haplotypes. In particular, general linear model analyses revealed lower log(10) VL among those with HLA allele B*57 (P = 0.002 [without correction]) previously implicated in favorable response and in those with HLA B*39 and A*30-Cw*03 (P = 0.002 to 0.016); the same analyses also demonstrated higher log(10) VL among individuals with A*02-Cw*16, A*23-B*14, and A*23-Cw*07 (P = 0.010 to 0.033). These HLA effects remained strong (P = 0.0002 to 0.075) after adjustment for age, gender, and duration of infection and persisted across three orders of VL categories (P = 0.001 to 0.084). In contrast, neither B*35 (n = 15) nor B*53 (n = 53) showed a clear disadvantage such as that reported elsewhere for these closely related alleles. Other HLA associations with unusually high (A*68, B*41, B*45, and Cw*16) or low (B*13, Cw*12, and Cw*18) VL were either unstable or reflected their tight linkage respecting disequilibria with other class I variants. The three consistently favorable HLA class I variants retained in multivariable models and in alternative analyses were present in 30.9% of subjects with the lowest (<10,000 copies per ml) and 3.1% of those with the highest (>100,000) VL. Clear differential distribution of HLA profiles according to level of viremia suggests important host genetic contribution to the pattern of immune control and escape during HIV-1 infection.

The quest for an AIDS vaccine: is the CD8+ T-cell approach feasible?

The rationale for developing anti-HIV vaccines that stimulate cytotoxic T-lymphocyte responses is given. We argue that such vaccines will work, provided that attention is paid to the development of memory T-cell responses that are strong and preferably activated. Furthermore, the vaccine should match the prevailing virus clade as closely as possible. Vaccines will have to stimulate a wide range of responses, but it is not clear how this can be achieved.

Correlates of nontransmission in US women at high risk of human immunodeficiency virus type 1 infection through sexual exposure

Seventeen women who were persistently uninfected by human immunodeficiency virus type 1 (HIV-1), despite repeated sexual exposure, and 12 of their HIV-positive male partners were studied for antiviral correlates of non-transmission. Thirteen women had > or = 1 immune response in the form of CD8 cell noncytotoxic HIV-1 suppressive activity, proliferative CD4 cell response to HIV antigens, CD8 cell production of macrophage inflammatory protein-1 beta, or ELISPOT assay for HIV-1-specific interferon-gamma secretion. The male HIV-positive partners without AIDS had extremely high CD8 cell counts. All 8 male partners evaluated showed CD8 cell-related cytotoxic HIV suppressive activity. Reduced CD4 cell susceptibility to infection, neutralizing antibody, single-cell cytokine production, and local antibody in the women played no apparent protective role. These observations suggest that the primary protective factor is CD8 cell activity in both the HIV-positive donor and the HIV-negative partner. These findings have substantial implications for vaccine development.

Human immunodeficiency virus (HIV)-specific cellular immune responses in newborns exposed to HIV in utero

Significant immunological changes are associated with intrauterine human immunodeficiency virus (HIV) encounter among uninfected infants of HIV-infected mothers. Peripheral blood cells of more than one-third of these exposed-uninfected infants proliferate and produce IL-2 after stimulation with HIV, and HIV-specific CD4+ T helper cell responses can be quantified in nearly all when sensitive intracellular cytokine assays are used. HIV-specific CD8+ cytotoxic T lymphocyte responses can be elicited in some, although less frequently. It is difficult to demonstrate that these responses are components of protective immunity and not simply epiphenomena of exposure. However, HIV-specific responses are associated with lack of infection, even with prolonged reexposure through breast-feeding. Elevations in nonspecific markers of immune activation provide further corroboration, as do similar findings in adults, consistent across all known routes of HIV transmission. Many questions remain, but much can be learned from this special population that may be informative for development of effective immunity in response to HIV vaccines.

New insights into HIV-1 specific cytotoxic T-lymphocyte responses in exposed, persistently seronegative Kenyan sex workers

A clearer understanding of HIV-1 specific immune responses in highly-exposed, persistently seronegative (HEPS) subjects is important in developing models of HIV-1 protective immunity. HIV-1 specific cytotoxic T-lymphocytes (CTL) have been described in a cohort of HEPS Kenyan sex workers, and recent work has further elucidated these responses. CTL specific for HIV-1 Env were found in the blood of over half the sex workers meeting criteria for HIV resistance, and in some women recognized unmapped epitopes. The proportion of women with Env-specific CTL increased with the duration of uninfected HIV exposure, suggesting that these responses were acquired over time. CD8+ lymphocyte responses directed against predefined HIV-1 CTL epitopes from various HIV-1 genes were found in the blood and genital tract of >50% resistant sex workers, at a ten-fold lower frequency than in infected subjects. The epitope specificity of CD8+ responses differs between HEPS and HIV infected women, and in HEPS the maintenance of responses appears to be dependent on persistent HIV exposure. Several HIV-1 'resistant' sex workers have become HIV infected over the past 6 years, possibly related to waning of pre-existing HIV-specific CTL, and infection has often been associated with a switch in the epitope specificity of CD8+ responses. These findings suggest that vaccine-induced protective HIV immunity is a realistic goal, but that vaccine strategies of boosting or persistent antigen may be necessary for long-lived protection.

Functional HIV-1 specific IgA antibodies in HIV-1 exposed, persistently IgG seronegative female sex workers

Although HIV-specific cellular immune responses are found in a number of HIV highly-exposed, persistently seronegative (HEPS) cohorts, late seroconversion can occur despite pre-existing cytotoxic T lymphocytes (CTL), suggesting that a protective HIV vaccine may need to induce a broader range of HIV-specific immune responses. Low levels of HIV-specific IgA have been found in the genital tract and plasma of the majority of Nairobi HEPS sex workers and appeared to be independent of HIV-specific cellular responses. IgA purified from genital tract, saliva and plasma of most HEPS sex workers were able to neutralize infection of PBMC by a primary (NSI) clade B HIV isolate, as well as viral isolates from clades A and D, which predominate in Kenya. In addition, these IgA were able to inhibit transcytosis of infective HIV virions across a transwell model of the human mucosal epithelium in an HIV-specific manner. Preliminary work in other HEPS cohorts has suggested the recognition of different gp41 epitopes in HEPS and HIV-infected subjects. Although present at low levels, these IgA demonstrated cross-clade neutralizing activity and were able to inhibit HIV mucosal transcytosis, suggesting an important functional role in protection against HIV infection.

HIV-specific cytotoxic T lymphocytes, HLA-A11, and chemokine-related factors may act synergistically to determine HIV resistance in CCR5 delta32-negative female sex workers in Chiang Rai, northern Thailand

Understanding how highly HIV-exposed individuals remain HIV uninfected may be useful for HIV vaccine design and development of new HIV prevention strategies. To elucidate mechanisms associated with resistance to HIV infection, immunologic and genetic factors were examined in 14 HIV-exposed but persistently seronegative (HEPS) female sex workers from Chiang Rai, northern Thailand and in ethnically matched, HIV-positive (n = 9) and HIV-negative women (n = 9). The HEPS women were identified in a study of commercial sex workers who had an HIV-1 incidence of 20.3 per 100 person-years. A high frequency of HLA-A11 was observed in HEPS women (86%) compared with northern Thai controls (56%). HIV-specific cytotoxic T lymphocyte (CTL) lytic responses were detected in cryopreserved peripheral blood mononuclear cells (PBMCs), using HLA-A-matched subtype E HIV-1 peptides in four of seven (57%) HEPS women, eight of eight HIV-positive women, and zero of nine HIV-negative unexposed controls (p = 0.019 HEPS women vs. HIV-negative controls). CTL lysis levels were low, but responses were detected to peptides from Nef, Pol, Gag, and Env. Nef responses predominated in HEPS women. Compared with controls, HEPS women tended to have higher frequencies of CCR5 promotor 59402GG and SDF-1 3'UTR 801A genotypes known to influence HIV transmission or course of disease. HEPS women also had higher levels of spontaneous RANTES production by PBMCs than other groups. Each of these factors could potentially contribute to HIV resistance. As most HEPS women had one or more of these factors, they may prevent HIV infection synergistically by blocking HIV cell entry, delaying its dissemination, or killing HIV-infected cells.

HIV-1 transmission and acute HIV-1 infection

An understanding of the central events in the transmission of HIV-1 infection is critical to the development of effective strategies to prevent infection. Although the main routes of transmission have been known for some time, surprisingly little is known about the factors that influence the likelihood of transmitting or acquiring HIV-1 infection. Once infection has taken place, the series of virological and immunopathological events that constitute primary HIV-1 infection are thought to be closely linked with the subsequent clinical course of the infected person. Recent studies have provided some support for the notion that intervention with aggressive anti-retroviral drug therapy at this stage has the potential to prevent some of the damage to the immune system that will otherwise develop in the vast majority of infected people.