Antibody responses in HUU compared to HIV-infected infants
Compared to HUU, ART-Immed and ART-Def infants had lower antibody GMCs to tetanus-toxoid (P < 0.001 for both), HBsAg (P = 0.01 for ART-Immed; P = 0.002 for ART-Def) and pertussis toxoid (P < 0.001 for both); Table 2. The proportion of infants with antibodies above the sero-protective threshold were generally similar between HUU and the HIV-infected groups, except for HBV which was lower in ART-Def (39.5% vs. 49.6% in HUU, P = 0.03); Table 2.
Compared to HUU, lower postvaccination GMCs were observed in the ART-Immed and ART-Def groups for tetanus-toxoid (P < 0.001 for both) and HBsAg (P < 0.001 for both); Table 3. Also, lower GMCs were observed in ART-Immed infants to diphtheria-toxoid (P = 0.001) and FHA (P < 0.001), as well as for pertussis toxoid in ART-Def children (P < 0.001) compared to HUU infants, Table 3.
In HUU, despite higher postvaccination antibody GMCs to some epitopes, the proportion with sero-protective levels of antibody were similar for tetanus-toxoid (82.7% to 100%), diphtheria-toxoid at ≥0.01IU/ml (100%), PRP (>96%) and HBsAg (>84%) compared to ART-Immed and ART-Def infants; Table 3. Also, a similar proportion in each group had antibody above ≥1.0 μg/ml for PRP (>88%), HBsAg ≥100mIU/ml (>84%) and diphtheria-toxoid ≥0.1IU/ml (76.9 to 100%); Table 3. Sero-conversion rates associated with pertussis vaccination, however, were higher in HUU (38.2%) for FHA compared to ART-Immed infants (20.6%, P = 0.008), and lower for pertussis toxoid in HUU (39.1%) compared with ART-Def (51.4%, P = 0.02) infants, Table 3.
Despite no differences in PRP antibody concentrations, the SBA geometric mean titers (GMTs) were higher for HUU than ART-Def infants (P < 0.001) and more HUU infants had SBA titers ≥8 (90.3 vs. 71.1%; P < 0.001). There was no difference in SBA GMTs or proportion with titers ≥8 in HUU compared with ART-Immed infants; Table 3.
Antibody responses in HUU compared with HEU infants
Prior to vaccination, HEU only had lower antibody GMCs to tetanus-toxoid (P = 0.001) than HUU infants; but higher GMCs for diphtheria-toxoid, HBsAg and FHA (P < 0.001 for all); Table 2. HEU were also more likely than HUU infants to have sero-protective diphtheria-toxoid (61.0 vs. 29.2%, P < 0.001) and HBsAg (80.5 vs. 49.6%, P < 0.001) antibody concentrations at prevaccination; Table 2.
Antibody GMCs were similar postvaccination between HUU and HEU for tetanus-toxoid, diphtheria-toxoid, PRP and FHA. Antibody GMCs in HUU were, however, slightly higher for HBsAg (2521.0 vs. 2019.3 mIU/ml; P = 0.041) and lower for pertussis-toxoid (134.3 vs. 261.3 IU/ml, P < 0.001) than in HEU; Table 3.
A high proportion (>99%) of HEU and HUU children developed sero-protective levels to tetanus-toxoid, diphtheria-toxoid, HBV and PRP postvaccination, which did not differ by group. Similarly, more than 99% of HUU and HEU infants had antibody levels ≥100 mIU/ml to HBsAg and more than 88% had ≥1.0 μg/ml to PRP postvaccination. The proportion of HUU compared with HEU children with sero-conversion (i.e. at least four-fold increase between prevaccination and postvaccination) to pertussis antigens was similar for FHA (38.2 vs. 21.6%; P = 0.53), however, against pertussis toxoid this proportion was lower in HUU infants (39.1 vs. 76.7%; P > 0.001). There was no difference in SBA GMTs or proportion with SBA titers ≥8 between HUU (90.3%) and HEU (94.1%) infants; Table 3.
Antibody responses in HEU compared to HIV-infected infants
Prevaccination antibody GMCs were lower in ART-Immed and ART-Def children than HEU infants for all epitopes (P < 0.001 for all comparisons), except for PRP; Table 2. HEU infants were also more likely to have sero-protective antibody concentrations against diphtheria-toxoid (61.0%) and HBV (80.5%) compared with ART-Immed (39.9, and 45.8%, respectively) and ART-Def (34.2, and 39.5%, respectively); P < 0.001 for all comparisons, Table 2.
Postvaccination antibody GMCs were higher in HEU than ART-Immed or ART-Def infants to tetanus-toxoid, diphtheria-toxoid, PRP, HBsAg and PT; Table 3. The proportion of children with sero-protective antibody levels were similar in HEU and ART-Immed infants, although the latter were less likely to have anti-diphtheria-toxoid antibody ≥0.1 IU/ml for diphtheria-toxoid (99.2 vs. 76.9%; P < 0.001). In contrast, lower proportions of ART-Immed infants had sero-protective antibody levels postvaccination compared to HEU infants to tetanus-toxoid (82.7 vs. 98.3%; P = 0.02), diphtheria-toxoid at the ≥0.1 IU/ml threshold (80.0 vs. 99.2%; P = 0.001), HBV at ≥100 mIU/ml threshold (84.0 vs. 99.2%; P = 0.02) and were also less likely to demonstrate sero-conversion to pertussis toxin (51.4 vs. 76.7%; P < 0.001); Table 3. HEU also had higher SBA GMTs compared with either ART-Immed (P = 0.03) or ART-Def (P < 0.001) groups and were also more likely (94.1%) to have SBA titers ≥8 compared with ART-Immed (87.8%, P = 0.06) and ART-Def infants (71.1%, P = 0.02).
Antibody responses in antiretroviral treatment-Immed compared to antiretroviral treatment-Def infants
There were no differences between ART-Immed and ART-Def groups prior to vaccination in either GMCs or the proportion of children with sero-protective antibody levels for any vaccine; Table 2
Postimmunization immune GMCs against most epitopes were similar, but higher in ART-Immed for HBV (P = 0.017) and lower for FHA (P = 0.02) than ART-Def infants; Table 3. A similar proportion of ART-Immed and ART-Def infants developed antibody concentrations above the sero-protective threshold for most vaccines, except for more ART-Immed infants with tetanus-toxoid antibody ≥0.1 IU/ml (92.3 vs. 82.7%; P = 0.03) and HBsAg antibody ≥100 mIU/ml (97.0 vs. 84.0%; P = 0.02). Serum bactericidal assay GMTs trended to be higher in ART-Immed children, among whom it was more likely to be ≥8 (87.8%) compared with ART-Def group (71.1%; P = 0.02; Table 3).
The proportion of ART-CD4 < 25% group with sero-protective levels of antibody and/or with sero-conversion to pertussis-toxoid and FHA was similar to ART-Immed infants.
Because of the imbalance of race in the population among the different groups, a sensitivity analysis was performed restricting the analysis to black African participants. P-values were similar to those when including mixed race participants suggesting that any differences can be attributed to HIV exposure and not race (data not shown).
This is the first and most-comprehensive study evaluating immune responses to routine vaccines in HIV-infected infants receiving early ART, irrespective of CD4+ count/percentage according to current WHO recommendations . Our findings show that early ART in HIV-infected infants, is associated with similar quantitative and qualitative immune responses to vaccines as in HUU infants. Although the immune responses in infants among whom ART was deferred was generally similar to the ART-Immed group, the ART-Def infants had lower proportion with anti-HBsAg antibody ≥100 mIU/ml and was also associated with lower levels of functional antibody to HibCV. A similar observation was observed on opsonophagocytic activity assay following PCV vaccination in ART-Def compared to ART-Immed groups . Therefore, only measuring quantitative antibody responses could over-estimate protection induced by some vaccines among HIV-infected infants not yet on ART.
Differences observed between ART-Immed and ART-Def infants may have been masked by survivor bias in the ART-Def group especially in the postvaccination comparison. It is plausible that vaccine immune responses were even poorer among ART-Def infants who died compared to surviving children. A recent review on the association of ART on vaccine immune responses in HIV-infected children, included studies in older children re-vaccinated between 28 weeks and 5.3 years after ART initiation . We report a higher proportion of children with sero-protective antibody concentrations than in previous studies, undertaken prior to early ART initiation in infants becoming policy, where the proportion of HIV-infected children without severe immunosuppression developing sero-protective antibody levels varied between 37 and 86% with GMCs generally much lower than in HIV-uninfected infants [39–41].
Our data on the relative immune responses to DTwP-HibCV/HBV in HEU compared with HUU infants differed from other reports. In-utero HIV-exposure was not consistently associated with lower GMCs prior to immunization in HEU compared with HUU infants as proposed by others [31,32,42–44]. Although we also identified lower GMCs to tetanus-toxoid in HEU infants prevaccination, the converse was true for antibody GMCs to diphtheria-toxoid, HBsAg and FHA. This could be due to regional differences in maternal antibody concentrations to different vaccine-epitopes and variations in factors which may influence transplacental antibody transfer, including differences in maternal HIV-viral load, total IgG antibody concentrations and placental function sufficiency in different populations [31,32,42–44]. These factors may influence HEU infants’ susceptibility to vaccine-preventable diseases during early infancy and prior to vaccination.
Comparing HEU and HUU infants, HEU had a trend toward lower prevaccination anti-pertussis toxoid GMCs but higher postvaccination levels, and conversely had higher prevaccination HBsAg antibody GMCs, but lower postvaccination levels to HBsAg. This corroborates that higher epitope-specific antibody levels prevaccination may interfere with the immunogenicity to homotypic epitopes. The higher preimmunization HBsAg antibody GMCs in HEU in our study has been attributed to higher hepatitis B virus infection prevalence in HIV-infected than HIV-uninfected women . However, we also observed higher antibody levels to HBsAg and other vaccine-epitope GMCs (except PRP) in HEU compared with both ART-Immed and ART-Def infants. Our study did not determine HIV-infection status at birth and since only 10% of HIV-exposed infants were breast-fed, it is likely that the majority of HIV-infection in infants of our cohort occurred either in utero or the immediate peri-partum period. Therefore, differences in prevaccination GMCs to most epitopes between HEU and either ART-Immed or ART-Def infants, suggests an association between factors related to acquiring maternal-derived vaccine-related antibodies and the risk of the infant being HIV-infected. Placental abnormalities can affect transplacental antibody transfer. For example, placentas from HIV-infected women from the Tygerberg site showed a higher percentage of villitis and infarcts than from HIV-uninfected controls, especially in women with CD4+ cell counts below 200 cells/μl .
Our study has some limitations, including that we were unable to distinguish in utero from intra-partum infection and placentas were not collected in our study. Also, we recruited only a small number of HIV-infected infants in whom with baseline CD4+ lymphocyte <25%. Data from CHER showed that by 7 weeks of age, 20% of HIV-infected infants already have severe CD4+-lymphocyte depletion. The trends in immune responses in the ART-CD4<25% group included in our study was, however, similar to that of ART-Immed infants. Also, despite having used whole cell pertussis vaccine, we elected to measure antibody to pertussis toxoid and FHA rather than using the whole-cell pertussis ELISA assay, as this was more practical for inclusion in the multiplex Luminex assay. The pertussis toxoid and FHA antibody responses, although providing a relative measure of immunogenicity of the whole cell pertussis vaccine between groups in our study, is not recommended as a measure of immunogenicity of whole cell pertussis vaccine.
In conclusion, HEU infants were not at increased susceptibility to most of the studied vaccine-preventable diseases by 6-weeks of age, suggesting similar acquisition of antibody from their mothers in our study. Furthermore, the immune responses in HEU were similar to HUU infants postvaccination. Although HIV-infected children had lower GMCs postvaccination, including to tetanus-toxoid and HBsAg irrespective of timing of ART initiation, the proportion with sero-protective antibody concentrations postvaccination were similar and timing of ART initiation generally did not affect immune responses between the HIV-infected groups. Our study indicates that vaccination of HEU and HIV-infected infants initiated on early-ART confers with DTwP-HibCV/HBV would provide similar immunity to the targeted vaccine-preventable disease compared with HUU infants. The persistence of sero-protective antibody concentrations and anamnestic responses to the studied vaccines among HEU and HIV-infected children initiated on early ART needs to be investigated.
Collaborators and Centers for study: South Africa: Avy Violari, James McIntyre, Wilma Pelser, Ravindre Panchia, Kennedy Otwombe, Afaaf Liberty, Nastassja Choolinal (Perinatal HIV Research Unit); Mark F Cotton, Helena Rabie, Anita Janse van Rensburg, Els Dobbels, George Fourie, Marietjie Bester, Wilma Orange, Ronelle Arendze, Catherine Andrea, Marlize Smuts, Kurt Smith, Theresa Louw, Alec Abrahams, Kenny Kelly, Amelia Bohle, Irene Mong, Jodie Howard, Tanya Cyster, Genevieve Solomon, Galroy Benjamin, Jennifer Mkhalipi, Edward Barnes (Children's Infectious Diseases Clinical Research Unit); Peter Adrian; Shabir A Madhi; Nadia van Niekerk (Respiratory and Meningeal Pathogens Research Unit). United States of America: Karen Reese, Patrick Jean-Philippe (HJF-DAIDS). United Kingdom: Diana M Gibb, Abdel Babiker (Medical Research Council Clinical Trials Unit, London). We acknowledge the assistance of Dr Marta Nunes in the editing of this article.
Author contributions: O.E.S., P.V.A. and S.A.M. were involved in study design. O.E.S. and P.V.A. were involved in setting up the assays and testing of samples. NvN assisted in processing of the samples. O.E.S. and A.I. undertook the data analysis. O.E.S. and S.A.M. were the primary authors of the article. A.V. and M.F.C. were involved in patient enrolment. All authors critically reviewed the article and approved the final submission.
This study was funded through the Department of Science and Technology/National Research Foundation: South African Research Chair Initiative in Vaccine Preventable Diseases. The parent study was funded by National Institute of Allergy and Infectious Diseases (NIAID) of the US National Institutes for Health (NIH), through the Comprehensive International Program of Research on AIDS (CIPRA) network, grant number U19 AI53217. Additional support for this work was provided with Federal funds from the National Institute of Allergies & Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under Contract No. HHSN272200800014C.
Conflicts of interest
There are no conflicts of interest.
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Keywords:Copyright © 2014 Wolters Kluwer Health, Inc.
diphtheria vaccine; Haemophilus influenzae type b conjugate vaccine; hepatitis B vaccine; HIV-exposed uninfected; HIV-infected; pertussis vaccine; tetanus vaccine