Circulating Biomarkers, Fraction of Exhaled Nitric Oxide, and Lung Function in Patients With Human Immunodeficiency Virus and Tuberculosis.

BACKGROUND: Identification of proinflammatory factors responding to Mycobacterium tuberculosis is important to reduce long-term sequelae of pulmonary tuberculosis (TB). METHODS: We examined the association between plasma biomarkers, the fraction of exhaled nitric oxide (FeNO), and lung function among a prospective cohort of 105 adults newly diagnosed with TB/human immunodeficiency virus (HIV) in South Africa. Participants were followed for 48 weeks from antiretroviral therapy (ART) initiation with serial assessments of plasma biomarkers, FeNO, lung function, and respiratory symptoms. Linear regression and generalized estimating equations were used to examine the associations at baseline and over the course of TB treatment, respectively. RESULTS: At baseline, higher FeNO levels were associated with preserved lung function, whereas greater respiratory symptoms and higher interleukin (IL)-6 plasma levels were associated with worse lung function. After ART and TB treatment initiation, improvements in lung function were associated with increases in FeNO (rate ratio [RR] = 86 mL, 95% confidence interval [CI] = 34-139) and decreases in IL-6 (RR = -118 mL, 95% CI = -193 to -43) and vascular endothelial growth factor ([VEGF] RR = -178 mL, 95% CI = -314 to -43). CONCLUSIONS: Circulating IL-6, VEGF, and FeNO are associated with lung function in adults being treated for TB/HIV. These biomarkers may help identify individuals at higher risk for post-TB lung disease and elucidate targetable pathways to modify the risk of chronic lung impairment among TB survivors.

Lung function and collagen 1a levels are associated with changes in 6 min walk test distance during treatment of TB among HIV-infected adults: a prospective cohort study.

BACKGROUND: Patients with tuberculosis (TB) and HIV often present with impairments in lung function and exercise capacity after treatment. We evaluated clinical and immunologic variables associated with a minimum clinically important difference (MCID) in the change in the 6 min walk test distance during the first 24 weeks of antiretroviral (ART) and anti-tubercular therapy. METHODS: Adults initiating ART and anti-TB treatment in the setting of newly-diagnosed HIV and pulmonary TB were enrolled in a prospective cohort study in South Africa. Patients underwent 6 min walk tests and spirometry at weeks 0, 4, 12, and 24 and biomarker level measurements early during treatment, at weeks 0, 4, and 12, when inflammation levels are typically elevated. Biomarkers included matrix metalloproteinases-1 (MMP-1), tissue inhibitor of MMP (TIMP)-1, collagen 1a, IL-6, IL-8, vascular cell adhesion molecule 1 (VCAM-1), C-X-C motif chemokine 10 (CXCL-10), CXCL-11, macrophage colony-stimulating factor (M-CSF), plasminogen activator, vascular endothelial growth factor, and chemokine (C-C) motif-2 (CCL-2). An MCID was derived statistically, and achievement of an MCID was modeled as the outcome using logistic regression model. RESULTS: Eighty-nine patients walked an average of 393 (± standard deviation = 69) meters at baseline, which increased by an average of 9% (430 ± 70 m) at week 24. The MCID for change in walk distance was estimated as 41 m. Patients experiencing an MCID on treatment had worse lung function, lower 6 min walk test distance, higher levels of proinflammatory biomarkers including TIMP-1 and M-CSF, and lower levels of collagen 1a at baseline. Experiencing an MCID during treatment was associated with increases in forced expiratory volume in 1-s [odds ratio (OR) = 1.17, 95% confidence interval (CI) = 1.05-1.33] and increases in blood collagen 1a levels (OR = 1.31, 95%CI 1.06-1.62). CONCLUSIONS: ART and TB treatment are associated with substantial improvements in 6 min walk test distance over time. Achievement of an MCID in the 6 min walk test in this study was associated with more severe disease at baseline and increases in collagen 1a levels and lung function during therapy.

Cytokine response in cerebrospinal fluid of meningitis patients and outcome associated with pneumococcal serotype.

Streptococcus pneumoniae causes life-threatening meningitis. Its capsular polysaccharide determines the serotype and influences disease severity but the mechanism is largely unknown. Due to evidence of elevated cytokines levels in the meningeal inflammatory response, we measured 41 cytokines/chemokines and growth factors in cerebrospinal fluid (CSF) samples from 57 South African meningitis patients (collected in the period 2018-2019), with confirmed S. pneumoniae serotypes, using a multiplexed bead-based immunoassay. Based on multivariable Bayesian regression, using serotype 10A as a reference and after adjusting for HIV and age, we found IL-6 concentrations significantly lower in patients infected with serotypes 6D (undetectable) and 23A (1601 pg/ml), IL-8 concentrations significantly higher in those infected with 22A (40,459 pg/ml), 7F (32,400 pg/ml) and 15B/C (6845 pg/ml), and TNFα concentration significantly higher in those infected with serotype 18A (33,097 pg/ml). Although a relatively small number of clinical samples were available for this study and 28% of samples could not be assigned to a definitive serotype, our data suggests 15B/C worthy of monitoring during surveillance as it is associated with in-hospital case fatality and not included in the 13-valent polysaccharide conjugate vaccine, PCV13. Our data provides average CSF concentrations of a range of cytokines and growth factors for 18 different serotypes (14, 19F, 3, 6A, 7F, 19A, 8, 9N, 10A, 12F, 15B/C, 22F, 16F, 23A, 31, 18A, 6D, 22A) to serve as a basis for future studies investigating host-pathogen interaction during pneumococcal meningitis. We note that differences in induction of IL-8 between serotypes may be particularly worthy of future study.

Low Pretreatment Viral Loads in Infants With HIV in an Era of High-maternal Antiretroviral Therapy Coverage.

BACKGROUND: With expansion of antiretroviral therapy (ART) programs, transmission rates are low but new infant infections still occur. We investigated predictors of pre-ART viral load (VL) and CD4+ T-cell counts and percentages in infants diagnosed with HIV at birth in a setting with high coverage of maternal ART and infant prophylaxis. METHODS: As part of an early treatment study, 97 infants with confirmed HIV-infection were identified at a hospital in Johannesburg, South Africa. Infant VL and CD4+ T-cell parameters were measured before ART initiation. Data were collected on maternal characteristics, including VL, CD4+ T-cell counts and ART, and infant characteristics, including sex, birth weight, and mode of delivery. RESULTS: Pre-ART, median infant VL was 28,405 copies/mL [interquartile range (IQR): 2515-218,150], CD4+ T-cell count 1914 cells/mm (IQR: 1474-2639) and percentage 40.8% (IQR: 32.2-51.2). Most (80.4%) infants were born to mothers who received ART during pregnancy and 97.9% of infants received daily nevirapine prophylaxis until ART initiation at median of 2 days of age (IQR: 1-7). Infant pre-ART VL was more likely to be ≥1000 copies/mL when their mothers had VL ≥1000 copies/mL [Odds Ratio (OR): 6.88, 95% confidence interval (CI): 2.32-20.41] and was higher in boys than girls (OR: 3.29, 95% CI: 1.07-9.95). Lower maternal CD4+ T-cell count (<350 cells/mm) was associated with lower infant CD4+ T-cell count (<1500 cells/mm) (OR: 3.59, 95% CI: 1.24-10.43). CONCLUSIONS: Pre-ART VL and CD4+ T-cell parameters of intrauterine-infected infants were associated with VL and CD4+ T-cell counts of their mothers. Maternal ART during pregnancy may begin treatment of intrauterine infection and may mask the severity of disease in infected infants identified in the current era with high-maternal ART coverage.

A child with perinatal HIV infection and long-term sustained virological control following antiretroviral treatment cessation.

Understanding HIV remission in rare individuals who initiated antiretroviral therapy (ART) soon after infection and then discontinued, may inform HIV cure interventions. Here we describe features of virus and host of a perinatally HIV-1 infected child with long-term sustained virological control. The child received early limited ART in the Children with HIV Early antiRetroviral therapy (CHER) trial. At age 9.5 years, diagnostic tests for HIV are negative and the child has characteristics similar to uninfected children that include a high CD4:CD8 ratio, low T cell activation and low CCR5 expression. Virus persistence (HIV-1 DNA and plasma RNA) is confirmed with sensitive methods, but replication-competent virus is not detected. The child has weak HIV-specific antibody and T cell responses. Furthermore, we determine his HLA and KIR genotypes. This case aids in understanding post-treatment control and may help design of future intervention strategies.

Young age at start of antiretroviral therapy and negative HIV antibody results in HIV-infected children when suppressed.

BACKGROUND: Negative results on standard HIV antibody tests have been described among HIV-infected children suppressed on antiretroviral therapy (ART) started early in life. Here, we describe the frequency and predictors of this phenomenon in a well characterized cohort of treated children. METHODS: We selected samples from 103 HIV-infected children who started ART 14 months of age or less and from 122 children who started 6 months of age or less followed as part of two sequential clinical trials in Johannesburg, South Africa. Children had attained viral suppression on ART and had received ART for between 3 and 6.4 years (mean 4.3 years) when tested for HIV antibody using a standard ELISA (Genescreen HIV1/2 version 2; Bio-rad). RESULTS: Only children 6 months of age or less when ART was started had negative antibody results when tested after suppression on ART several years later. Negative or low-positive antibody results were observed in 40.0, 37.0 and 27.8% of children starting ART less than 2 months of age, or starting during month 2 or 3, respectively. This dropped to 5.9, 3.5 and 5.3% if ART was started during month 4, 5 and 6, respectively. Higher CD4 percentage prior to ART initiation and no recorded intermittent viremia also predicted negative antibody results. CONCLUSION: Testing negative on standard HIV antibody tests occurs fairly commonly among HIV-infected children who started ART 3 months of age or less and are virally suppressed. It would be prudent in clinical practice to avoid HIV antibody tests among virally suppressed, early-treated children to prevent unnecessary confusion.

Differences are evident within the CXCR4-CXCL12 axis between ethnically divergent South African populations.

The G-protein-coupled receptor, CXCR4, is highly expressed on a number of cell types, and together with its ligand, CXCL12, plays an important role in immune development and trafficking of cells. CXCR4 promotes tumor growth, angiogenesis and metastasis, and is a prognostic marker in a number of different types of tumors. Additionally, CXCR4 is utilized, together with CD4, for entry of T-tropic HIV viruses. Ethnic differences in incidence and mortality of various cancers, and in the response to highly active antiretroviral treatment (HAART) of HIV-1 infected individuals have been reported. The aim of this study was to establish if differences in the CXCR4-CXCL12 axis exist between ethnically divergent uninfected South Africans. CXCR4 density was significantly higher on CD4(+) and CD8(+) T cells, B cells and CD56(dim) NK cells, and CXCL12 levels lower in Black compared with Caucasian individuals. Furthermore, an inverse correlation was observed between CXCR4 density on CD56(+) and CD3(+) cells and age, only in Black individuals. CXCL12-3'A heterozygosity (AG) found in 28% of Caucasians did not explain the higher plasma levels of CXCL12 compared to Black individuals who were all GG genotypes, suggesting that other factors influence homeostatic levels of CXCL12. In conclusion, this study demonstrates that ethnically divergent populations show clear differences in both CXCR4 density and CXCL12 plasma levels which may influence the course of cancer and HIV-1 infection.

KIR-HLA and maternal-infant HIV-1 transmission in sub-Saharan Africa.

Numerous studies have suggested a role for natural killer (NK) cells in attenuation of HIV-1 disease progression via recognition by killer-cell immunoglobulin-like receptors (KIRs) of specific HLA class I molecules. The role of KIR and HLA class I has not been addressed in the context of maternal-infant HIV-1 transmission. KIR and HLA class I B and C genes from 224 HIV-1-infected mothers and 222 infants (72 infected and 150 uninfected) from South Africa were characterized. Although a number of significant associations were determined in both the total group and in the nevirapine (NVP) exposed group, the most significant findings involved KIR2DL2 and KIR2DL3 and HLA-C. KIR2DL2/KIR2DL3 was underrepresented in intrapartum (IP)-transmitting mothers compared to non-transmitting (NT) mothers (P = 0.008) and remained significant (P = 0.036) after correction for maternal viral load (MVL). Homozygosity for KIR2DL3 alone and in combination with HLA-C allotype heterozygosity (C1C2) was elevated in IP-transmitting mothers compared to NT mothers (P = 0.034 and P = 0.01 respectively), and after MVL correction (P = 0.033 and P = 0.027, respectively). In infants, KIR2DL3 in combination with its HLA-C1 ligand (C1) as well as homozygosity for KIR2DL3 with C1C2, were both found to be underrepresented in infected infants compared to exposed uninfected infants in the total group (P = 0.06 and P = 0.038, respectively) and in the sub-group of infants whose mothers received NVP (P = 0.007 and P = 0.03, respectively). These associations were stronger post MVL adjustment (total group: P = 0.02 and P = 0.009, respectively; NVP group: P = 0.004 and P = 0.02, respectively). Upon stratification according to low and high MVL, all significant associations fell within the low MVL group, suggesting that with low viral load, the effects of genotype can be more easily detected. In conclusion this study has identified a number of significant associations that suggest an important role for NK cells in maternal-to-infant HIV-1 transmission.

Natural killer cells that respond to human immunodeficiency virus type 1 (HIV­1) peptides are associated with control of HIV­1 infection.

Human immunodeficiency virus (HIV)-specific natural killer (CD3- cells), CD4, and CD8 T cellular responses were determined in 79 HIV­1-infected women in response to HIV­1 peptide pools (Gag, Pol, Nef, Reg, and Env) with use of a whole­blood intracellular cytokine staining assay that measures interferon-γ and/or interleukin-2. HIV­specific CD3- cell responses to any region (Env and Reg predominantly targeted) were associated with lower viral load (P = .031) and higher CD4 T cell count (P = .015). Env­specific CD3- cell responses were stronger in women who had both Gag CD4 and CD8 T cell responses and, in turn, was associated with lower viral load (P = .005). CD3- cell responders had significantly higher representation of CD4 T cell responses to Env and Reg (P = .012 and P = .015, respectively) and higher magnitudes of CD4 T cell responses (P = .017 and P = .037, respectively) than did nonresponders. Peptide­specific natural killer cells are associated with markers of less severe disease progression among HIV­1-infected women (lower viral load and higher CD4 T cell count) and with stronger HIV­specific T cell responses.

Effect of Maternal HIV-1 Status and Antiretroviral Drugs on Haematological Profiles of South African Infants in Early Life.

Maternal HIV-1 status and antiretroviral drug exposure may influence the haematological profiles of infants. We recruited infants from 118 uninfected control women and from 483 HIV-1 infected women who received no antiretroviral drugs (n=28), or received single-dose Nevirapine (sdNVP) (n=424) or triple-drug combination therapy (n=31) to reduce HIV-1 transmission. Blood was drawn from infants within 24 hours of delivery or 6-12 weeks post-delivery and full blood counts performed using a fully automated AcT-5-diff haematology analyser and reference controls. Exposed uninfected (EU; no NVP) differed from control infants only in having lower basophil counts and percentages. In all infant groups, leukocyte profiles showed characteristic quantitative changes with age in the first 6 weeks of life. HIV-1 infected infants displayed by 6 weeks elevations in white blood cells, lymphocyte, monocyte and basophil counts, and monocyte and basophil percentages, when compared to EU infants. At birth EU NVP-treated infants exhibited elevated monocyte percentages and counts and basophil counts that did not persist at 6 weeks. Interestingly, EU newborns of mothers with high CD4 counts (> 500 cells/µl) that had taken sdNVP had significantly elevated white blood cell, monocyte and basophil counts when compared to newborn infants of mothers with similar CD4 counts that had not taken sdNVP; this was not evident in infants of mothers with CD4 counts <200 cells/µl. These previously undescribed features may affect immune response capability in early life and clinical consequences of such changes need to be further investigated.

Cutting Edge: Unusual NK cell responses to HIV-1 peptides are associated with protection against maternal-infant transmission of HIV-1.

Most infants exposed to HIV-1 in utero and at delivery do not acquire infection. We show that mothers and infants who have CD3-negative cells that respond to HIV-1 peptides are substantially less likely to transmit and acquire infection, respectively. The CD3-negative cells, shown to be NK cells, respond with remarkable specificity and high magnitude to HIV-1 peptides from Env (envelope) and Reg (regulatory) protein regions, as measured by a whole blood intracellular cytokine assay only in the context of HIV-1 infection or exposure. These findings identify an important new measure of protective immunity to HIV-1 that highlights the importance of innate immunity in preventing the establishment of HIV-1 infection.

Host CCL3L1 gene copy number in relation to HIV-1-specific CD4+ and CD8+ T-cell responses and viral load in South African women.

HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4 and CD8 T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-gamma and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r=-0.239, P=0.045), as did magnitudes of Gag CD4 (r=-0.362, P=0.002) and CD8 (r=-0.261, P=0.028) T-cell responses. Patients with a Gag CD4 response (P=0.002) or dominant Gag CD8 (P=0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8 T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4 Gag responses (P=0.017), and women who had CD4 and CD8 Gag-specific responses had significantly lower viral loads (P=0.004) and higher CCL3L1 copy number (P=0.015) than those women with only CD8 Gag-specific responses.

African infants' CCL3 gene copies influence perinatal HIV transmission in the absence of maternal nevirapine.

BACKGROUND: Individuals with more copies of CCL3L1 (CCR5 ligand) than their population median have been found to be less susceptible to HIV infection. We investigated whether maternal or infant CCL3L1 gene copy numbers are associated with perinatal HIV transmission when single-dose nevirapine is given for prevention. METHOD: A nested case-control study was undertaken combining data from four cohorts including 849 HIV-infected mothers and their infants followed prospectively in Johannesburg, South Africa. Access to antiretroviral drugs for the prevention of perinatal transmission differed across the cohorts. Maternal and infant CCL3L1 gene copy numbers per diploid genome (pdg) were determined by real-time polymerase chain reaction for 79 out of 83 transmitting pairs ( approximately 10% transmission rate) and 235 randomly selected non-transmitting pairs. RESULTS: Higher numbers of infant, but not maternal, CCL3L1 gene copies were associated with reduced HIV transmission (P = 0.004) overall, but the association was attenuated if mothers took single-dose nevirapine or if the maternal viral load was low. Maternal nevirapine was also associated with reduced spontaneously released CCL3 (P = 0.007) and phytohemagglutinin-stimulated CCL3 (P = 0.005) production in cord blood mononuclear cells from uninfected infants. CONCLUSION: We observed a strong association between higher infant CCL3L1 gene copies and reduced susceptibility to HIV in the absence of maternal nevirapine. We also observed a reduction in newborn CCL3 production with nevirapine exposure. Taken together, we hypothesize that nevirapine may have direct or indirect effects that partly modify the role of the CCR5 ligand CCL3 in HIV transmission, obscuring the relationship between this genetic marker and perinatal HIV transmission.

Low maternal viral loads and reduced granulocyte-macrophage colony-stimulating factor levels characterize exposed, uninfected infants who develop protective human immunodeficiency virus type 1-specific responses.

Human immunodeficiency virus type 1 (HIV-1)-specific cellular immune responses are elicited in a proportion of infants born to HIV-1-infected mothers and are associated with protection against vertical transmission. To investigate correlates of these HIV-1-specific responses, we examined levels of the immune activation markers neopterin, beta(2)-microglobulin (beta(2)-m), and soluble l-selectin (sl-selectin); the immunomodulatory and hematopoietic factors interleukin-7 (IL-7), stromal-cell-derived factor 1 alpha (CXCL12), and granulocyte-macrophage colony-stimulating factor (GM-CSF); and the immunoregulatory cytokine IL-10 among a group of newborns born to HIV-1-positive mothers who did not receive any antiretroviral drugs for prevention of perinatal HIV-1 transmission. Cellular immune responses to HIV-1 envelope (Env) peptides were also measured. We aimed to determine whether newborns who elicit HIV-1-specific cellular immune responses (Env(+)) and those who lack these responses (Env(-)) exhibit unique immune features. Our data confirmed that no Env(+) infants acquired HIV-1 infection. Among exposed, uninfected infants, Env(+) infants had reduced immune activation (as measured by beta(2)-m and sl-selectin levels in cord blood plasma) compared to Env(-) infants as well as reduced GM-CSF levels in cord blood plasma. There was also a reduced ability of cord blood mononuclear cells to be induced to produce GM-CSF among Env(+) infants. Maternal viral load was lower in Env(+) infants, suggesting that exposure to low levels of antigen may be responsible for priming the protective responses. These findings suggest that infants who are able to develop apparently protective HIV-1-specific cellular immune responses have immunological features and viral exposure histories that distinguish them from their nonresponder counterparts, providing new insights into the development of HIV-1 protective immunity.

Homer Wheelon, M.D., physiologist, artist, and poet: origins of the tailpieces in journals of the American Physiological Society.

Since 1953, illustrations have been inserted as "tailpieces" at the ends of articles in The American Journal of Physiology and The Journal of Applied Physiology. The drawings were made by Homer Wheelon, a member of the American Physiological Society from 1919 until his death in 1960. Forty-five years after his death, Wheelon is unknown, but he contributed 32 publications to the medical literature and trained J. Earl Thomas, an important 20th century gastrointestinal physiologist. Wheelon was born into poverty in 1883 to itinerant Methodist preachers, circumstances that guided his education and career choices. Throughout his life, Wheelon exhibited a fondness and talent for art and photography and an unusual breadth of intellectual interests and knowledge. Wheelon received a bachelor's degree from the University of Washington, then studied at the University of Oregon, Northwestern University, and St. Louis University. Earning his M.D. from St. Louis University and assuming a faculty position there, Wheelon and his graduate student, Thomas, conducted widely recognized gastrointestinal research. Returning to Seattle in 1921, Wheelon became a highly respected physician and hospital administrator, but he also found time to indulge his interest in visual art and poetry. In 1933, inspired by observing a rabbit being used in a pregnancy test, Wheelon began to write and illustrate an epic, 322-page poem, Rabbit No. 202, illustrations from which became the journals' tailpieces. The present study traces Wheelon's personal life and scientific career in an attempt to understand this complex man and the origins of his unusual poem and its drawings.

In vivo effects of HIV-1 exposure in the presence and absence of single-dose nevirapine on cellular plasma activation markers of infants born to HIV-1-seropositive mothers.

Short-course antiretroviral drug regimens reduce the risk of mother-to-child transmission of HIV-1, but mechanisms affording protection of such interventions remain poorly defined. Because T-cell activation is an important factor in productive HIV-1 infection, we tested the hypothesis that single-dose nevirapine (NVP) reduces immune activation, which in turn reduces the likelihood of transmission. We compared concentrations of cord and maternal blood plasma immune activation markers, neopterin, beta2-microglobulin, and soluble l-selectin, in 2 groups of HIV-1-exposed newborns whose mothers either received NVP at the onset of labor or who only received NVP as postexposure prophylaxis within 72 hours of birth and among HIV-unexposed controls. In utero exposure of the infant to HIV-1, regardless of NVP exposure, led to demonstrable increases in immune activation markers, this being most notable in the presence of preexisting infection. Contrary to what was hypothesized, immune activation was increased by prebirth exposure to single-dose NVP, with this effect being enhanced in infants already infected at birth. Our data suggest that reductions in immune activation do not explain transmission prevention effects of single-dose NVP. Our data also suggest a biological explanation for why HIV-1-infected infants exposed perinatally to antiretroviral drugs might experience hastened disease progression, namely, in some HIV-1-infected individuals, NVP may synergize with HIV-1 to enhance an environment that favors increased HIV-1 replication.

Reduced ability of newborns to produce CCL3 is associated with increased susceptibility to perinatal human immunodeficiency virus 1 transmission.

The role of CC chemokines in protection against mother-to-child human immunodeficiency virus type 1 (HIV-1) transmission is not well understood. It was observed that mitogen-induced production of CCL3 and CCL4 by cord-blood mononuclear cells was increased among infants born to HIV-positive compared with HIV-negative mothers, and that a deficiency in production of CCL3 was associated with increased susceptibility to intrapartum HIV-1 infection. CCL3-L1 gene copy number was associated with CCL3 production and with vertical transmission. However, at equivalent CCL3-L1 gene copy numbers, infants who acquired HIV-1 infection relative to their exposed but uninfected counterparts had lower production of CCL3, suggesting that they may harbour some non-functional copies of this gene. Nucleotide changes that may influence CCL3 production were evident in the CCL3 and CCL3-L1 genes upstream of exon 2. Our findings suggest that infants who display a deficient-production phenotype of CCL3 are at increased risk of acquiring HIV-1, indicating that this chemokine in particular plays an essential role in protective immunity.