Transient HIV Viremia in a Brazilian Woman—A Case of Exposure but Noninfection

Abstract

Background:

Human immunodeficiency virus (HIV) prevention, care, and treatment programs have been implemented across numerous low- and middle-income countries globally. Since 1996, the Brazilian government has made a strong and sustained commitment to guaranteeing universal access to combination antiretroviral therapy, ensuring that all individuals living with HIV have equitable access to life-saving treatment, regardless of socioeconomic status or geographic location. Intriguingly, some individuals remain uninfected despite repeated exposures, and understanding this phenomenon is crucial when considering new prevention strategies or perhaps vaccine development. In the Nairobi cohort, for example, certain female sex workers remain HIV-seronegative despite frequent contact with the virus.

Methodology:

Here, we conducted a literature review and aligned it with a case of a 32-year-old woman from São Paulo, Brazil, who was exposed to HIV but did not acquire the infection.

Results:

This case exhibits an immune pattern similar to that described in highly exposed seronegative individuals, such as those documented in a cohort of sex workers from Nairobi and Gambia. They were characterized by transient viremia and a lack of seroconversion. Genetic analysis revealed protective human leukocyte antigen (HLA) alleles, a robust interferon-γ response to p24/Nef peptides, persistently high CD4⁺ T cell counts, normal immune responses to other pathogens (e.g., hepatitis A, B, C, and cytomegalovirus), and normal sera immunoglobulins.

Conclusion:

These findings suggest that the inability to establish persistent HIV infection may be linked to the interaction of multiple factors, including a potent and sustained CD4⁺ T cell and cytotoxic response.

Introduction

The human immunodeficiency virus (HIV) continues to pose a significant global health burden, affecting over 38 million individuals worldwide, with approximately one million residing in Brazil. ¹ Sexual transmission remains the predominant mode of HIV acquisition globally, with a disproportionate impact on heterosexual women, particularly in developing nations across Africa and Asia. ² While the transmission of HIV from men to women through sexual contact is a well-documented route, the precise dynamics of exposure, including frequency, viral load (VL) of the transmitting partner, and the recipient’s susceptibility, can lead to a spectrum of outcomes following exposure. ³

However, some individuals remain uninfected despite repeated exposures, and understanding this phenomenon is crucial when considering new prevention strategies or perhaps vaccine development. In the Nairobi cohort, for example, certain female sex workers remain HIV-seronegative despite frequent contact with the virus. ⁴ These women exhibit distinct immune responses, characterized by cytotoxic T lymphocytes (CTLs) that are five times smaller in magnitude and breadth than those observed in infected individuals, yet capable of sustained interferon (IFN)-γ production and specific targeting of p24 HIV antigens. In Gambia, similar observations revealed that this specific cytotoxic response was also associated with specific HLAs, such as HLA-B35. These interactions may possibly influence antigen presentation and natural killer (NK) cell activity, contributing to viral control and the prevention of persistent infection. ⁵

Here, we present a unique case of a young Brazilian woman with a history of potential prolonged HIV exposure who exhibited transient viremia without subsequent seroconversion or detectable proviral DNA integration. To elucidate the immunological and genetic mechanisms potentially responsible for this apparent control of HIV infection, we performed a comprehensive longitudinal analysis of her T cell counts, VL fluctuations, antibody responses, and performed detailed immunogenetic characterization, including HLA typing and assessment of CTL responses to key HIV antigens. This in-depth investigation aims to provide insights into the host factors that may contribute to the prevention of persistent HIV infection following exposure, but no HIV infection.

Implementation of Our Cohort Study within the Brazilian HIV Landscape

Since 1990, comprehensive HIV prevention, care, and treatment programs have been implemented across numerous low- and middle-income countries globally. ⁶ In Brazil, a pivotal moment arrived in 1996 with the government’s commitment to universal access to combination antiretroviral therapy (ART). This policy shift, driven by the advocacy of social movements and underpinned by scientific evidence, ⁷ not only challenged stigma and the perception of HIV as a death sentence but also significantly improved the lives of people living with HIV (PLHIV) and played a crucial role in reducing viral transmission on a global scale.^8,9

Our cohort study is anchored in a pioneering outpatient service established in 1983 within the Clinical Immunology Department at the Hospital das Clínicas, University of São Paulo Medical School. Initially enrolling approximately 600 PLHIV, the cohort has seen 45 deaths (8%) during follow-up, predominantly from noninfectious causes. ¹⁰ Currently, 427 participants are actively monitored, forming one of Brazil’s longest-running HIV cohorts. This well-established infrastructure offers a unique platform for longitudinal research into HIV pathogenesis, treatment outcomes, and host–virus interactions, particularly within Brazil’s evolving epidemic and treatment landscape.^11–14

Longitudinal Observation of Transient HIV Viremia Without Seroconversion in a Brazilian Woman

Among the individuals followed within this cohort, a particularly notable case emerged involving a 32-year-old Brazilian woman who, despite a likely prolonged exposure to HIV through her deceased partner, initially presented negative results in conventional serological assays. The uniqueness of this case underscored by the detection of HIV RNA through molecular testing, indicating early-stage infection. Nevertheless, this detectable viremia was not accompanied by an immediate humoral response, with antibody tests remaining nonreactive for an exceptionally prolonged period, extending for nearly 4 years since the patient’s last in-person clinical assessment.

To further characterize the woman’s initial immunological status, laboratory analyses conducted on June 12, 2003, revealed that her levels of immunoglobulins IgG, IgA, IgM, and IgE were within reference values: IgG at 1303 mg/dL, IgA at 253 mg/dL, IgM at 138 mg/dL, and IgE at 787 IU/mL. Apolipoprotein B levels were 80 mg/dL. Subsequent testing on September 23, 2004, noted slight variations in IgA and IgM. Furthermore, she exhibited antibodies for human cytomegalovirus (IgG 167,800 UA/mL) and toxoplasmosis (IgG 44.50 IU/mL), while tests for hepatitis B, hepatitis C, and IgM antibodies for hepatitis A were negative, with beta-2-microglobulin at 1.2 µg/mL. These findings indicate prior exposure to cytomegalovirus and toxoplasmosis, with no evidence of significant immune dysregulation, impaired antibody production or any antigen presentation impairment.

Following the initial follow-up, the patient was enrolled in a longitudinal observational study and monitored for approximately 10 years (2003–2013). Her inclusion in this noninterventional study was predicated on consistently high CD4⁺ T-lymphocyte counts (maintained above 1,500 cells/mm³), relatively controlled VL fluctuations, and the absence of clinical symptoms indicative of HIV disease progression. Consequently, she did not receive ART during this period. ¹ Notably, the last instance of detectable viremia was recorded in 2007. The detailed longitudinal laboratory parameters obtained during this follow-up are summarized in Table 1.

Table 1.

Long-term T cell counts and HIV plasma viral load

Date	CD3	% CD3	CD4	% CD4	CD8	% CD8	CD45	CD4/CD8 ratio	RNA HIV load (Copies/mL)	RNA HIV Load (Log)
12/06/2003	2,222	66.0	1,700	50.5	481	14.3	3,366	3.53	—	—
04/03/2004	2,039	77.1	2,141	54.3	804	20.4	—	2.66	15,600	4.193
14/10/2004	2,434	76.0	1,730	54.0	644	20.1	—	2.69	<400	—
09/05/2005	2,364	74.3	1,690	53.1	620	19.5	—	2.72	<400	—
04/07/2005	2,926	76.2	2,147	55.9	749	19.5	—	2.87	2,080	3.318
27/04/2006	2,572	72.9	1,891	53.6	607	17.2	3,528	3.12	<400	—
23/11/2006	2,525	78.2	1,837	56.9	617	19.1	3,229	2.98	<400	—
05/09/2007	2,959	73.6	2,195	54.6	700	17.4	—	3.14	98	1.991
19/03/2009	2,875	73.0	2,141	54.4	356	9.0	3,937	6.01	<50	—
07/12/2009	2,357	70.0	1,702	50.6	606	18.0	3,365	2.81	<50	—
18/06/2012	2,090	68.6	1,506	49.4	535	17.6	3,047	2.81	<50	—
26/03/2013	2,267	—-	1,613	52.0	626	21	3,117	2.58	<50	—

HIV RNA was detected using the HIV 3.0 RNA method (2003–2006) and quantified using the b-DNA method (2007–2013), both with Bayer/Siemens kits.

Longitudinal follow-up over the 10-year period revealed not only a positive correlation between the patient’s CD4⁺ T-lymphocyte counts in the presence of detectable plasma VL (Table 1) but also appeared to follow a trend higher than the logarithmic quantity of viral RNA [Figure 1]. This observation stands in stark contrast to the typical inverse relationship observed in the natural history of HIV infection, where increases in VL are usually accompanied by a decrease in CD4⁺ T-lymphocyte quantities. ¹⁵

Fig. 1.

Variation in CD4+ T cell counts and plasma viral load from 2003 to 2013. The line represents CD4⁺ T cell counts, while the dashed line represents the viral load on a logarithmic scale. The red line indicates the cutoff values for undetectable viral load (<400 copies/mL from 2003 to 2006 and <50 copies/mL from 2007 to 2013).

A similar pattern of sustained or even increasing T CD4⁺ cells count despite detectable viremia has been reported in a rare subset of individuals known as elite controllers, who maintain undetectable or very low VLs without ART—sometimes for more than 35 years. The dynamics observed in our case resemble such patterns, albeit with an apparently transient viremia. This transient viremia, confirmed by the subsequent absence of detectable viral RNA in peripheral blood, was followed by sustained spontaneous viral control without ART, as verified through records from the national public health system. Taken all together, it indicated the involvement of a distinct and potentially rare host immune mechanism capable of avoiding the CD4⁺ T-cell population infection, despite periods of active viral replication. ¹⁶

To confirm the absence of VL 10 years after the initial follow-up and prior to her release in 2013, conventional PCR was performed on cDNA and DNA extracted from the sample collected that year. The reaction targeted the reverse transcriptase (RT) and protease (PR) genes of HIV, using a three-primer strategy and the pNL4-3 plasmid as a positive control. PCR analysis revealed a weak band in the cDNA, while no amplification was observed for the DNA. Subsequently, this weak band underwent Sanger sequencing using eight primers, but the electropherogram showed a pattern consistent with the absence of a specific amplicon. PCR from the DNA was then repeated with primers flanking the HIV protease gene, without successful amplification. Furthermore, proviral DNA quantification was also performed, revealing undetectable levels, with a detection limit of 1 copy per 1 × 10⁶ CCR5 genomic equivalents [Figure 2]. ¹⁷

Fig. 2.

Agarose gel showing conventional PCR products amplified from cDNA and DNA of the 2013 sample. The K1/K2 and DP10/F2 primers (protease) were used (RT). Lanes represent PCR products from a sample of 2013 (5417), positive control (c⁺; pNL4-3), and negative control (c-; no DNA/cDNA). RT, reverse transcriptase.

Postcohort Investigations

Within the context of our long-standing cohort, this particular case caught our attention. Genotypic analysis provided a deeper understanding of the immunological profile of this woman, revealing the alleles HLA-B44, HLA-B45, HLA-A23, HLA-A24, HLA-C04, and HLA-C16, along with wild-type CCR5 (CCR5-WT). Notably, the HLA-B44 allele has been consistently associated with better clinical outcomes in PLHIV, including higher CD4⁺ T-cell counts and improved VL control,^18,19 similar to what was observed in this case. In addition, HLA-B44 is linked to robust CTL responses ²⁰ and a potential inverse correlation between VL and the amplitude of CTL responses against p24 capacity. ¹⁸

To confirm the relationship between CTL response and the immunological profile, we performed an ELISPOT assay using various viral epitopes (data not shown). The assay showed significant IFN-γ production directed at both the p24 and Nef epitopes only, indicating robust activation of CTL specific to these antigens. These results, supported by the correlation between the HLA-B44 allele and CTL,^18,19 particularly in the presentation of the p24 epitope, suggest that the ability to present Nef fragments may also contribute to the amplification of this response, playing a key role in the more effective control of viral replication [Figure 3].

Fig. 3.

Gamma interferon production quantified by ELISPOT stimulated by HIV epitopes. Legend: The graph shows the number of spots (ELISPOT) for a set of epitopes stimulated: p24 (655 spots), Nef (505 spots), RT-1 (pool 1) (100 spots), and RT2 (pool 2) (100 spots). There was no immune response to the other regions of HIV. HIV, human immunodeficiency virus.

Discussion

Although the CTL response to the p24 antigen has been consistently linked to favorable clinical outcomes in HIV infection, other immune mechanisms may play equally important roles in viral control. In the present case, the production of IFN-γ suggests a broader activation of the immune response, particularly involving T helper 1 (Th1) cells and NK cells. These cell types contribute to the recognition and elimination of infected targets by responding to conserved viral epitopes, such as those found in the p24 region, thereby enhancing the host’s capacity to limit viral persistence. ⁵ A notable example of this dynamic was observed in women from the Nairobi cohort in Kenya and Gambia, who, despite high exposure to HIV-1, remained seronegative. These women exhibited differentiated immune responses, with CTLs specifically targeting viral antigens such as p24, and a robust production of IFN-γ,⁴ similar to what was observed in our reported case.

Genetic factors also appear to contribute meaningfully to viral control in this case. The presence of HLA-C04 and HLA-C16 alleles may enhance NK cell responses through interactions with killer-cell immunoglobulin-like receptors, mechanisms known to positively regulate innate immunity and support the maintenance of CD4⁺ T cell counts as well as control of VL. ²¹ These alleles have been associated with protective outcomes in other clinical contexts. Notably, a child from the ANRS EPF-CO10 pediatric cohort, who maintained viral remission after treatment interruption, harbored a similar HLA profile, including HLA-C subtypes and HLA-A2301—a member of the A23 serogroup. ²² Although causality cannot be definitively established, the recurrence of these alleles in individuals with sustained viral control suggests a possible immunogenetic contribution to resistance or containment of HIV infection.

Despite the absence of the CCR5-Δ32 mutation—which provides intrinsic resistance to HIV by disrupting CCR5 receptor expression—the individual carried the wild-type CCR5 allele (CCR5-WT), indicating no genetic blockade of viral entry. ²³ However, other modulatory elements, such as reduced CCR5 expression levels or elevated KLF2 activity, may indirectly confer a degree of protection by limiting the availability of coreceptors for viral docking and entry. ²⁴

Virological factors may also be relevant in shaping the host–virus interaction. The presence of the GWGR motif in the V3 loop of the gp120 envelope glycoprotein—commonly referred to as the “Brazilian motif”—is characteristic of a subset of HIV-1 subtype B viruses and is associated with exclusive CCR5 usage. ²⁵ The switch from proline to tryptophan in the 313 envelope position, at the tip of the V3 loop, has been linked to slower progression to Acquired Immunodeficiency Syndrome (AIDS), possibly due to lower viral fitness or enhanced susceptibility to neutralization. ²⁶ In addition, the GWGR motif contains basic residues at critical positions that may favor recognition by broadly neutralizing antibodies directed at the V3 loop.¹³

Altogether, the convergence of cellular immune responses, favorable HLA alleles, potential CCR5 expression modulation, and unique viral characteristics underscores a multifactorial basis for the effective control of HIV observed in this case. While further studies are needed to elucidate the precise contribution of each factor, these findings support the notion that a combination of host genetics, immune activation profiles, and viral properties can synergistically determine the clinical trajectory of HIV infection, even in the absence of ART.

Ethical Considerations

The study protocol was approved by the Ethical Board of the Faculty of Medicine, University of São Paulo, Brazil (CAAE N° 05749912.6.0000.0068).