JAIDS Journal of Acquired Immune Deficiency Syndromes:
Humoral and Cellular Response to Influenza Vaccine in HIV-Infected Children With Full Viroimmunologic Response to Antiretroviral Therapy
Viganò, Alessandra MD*; Zuccotti, Gian Vincenzo MD*; Pacei, Michela BS†; Erba, Paola MD*; Castelletti, Eleonora BS†; Giacomet, Vania MD*; Amendola, Antonella MD‡; Pariani, Elena BS‡; Tanzi, Elisabetta BS‡; Clerici, Mario MD†
From the *Clinic of Pediatrics, Luigi Sacco Hospital, University of Milan, Milan, Italy; †Chair of Immunology, University of Milan, Milan, Italy; and the ‡Department of Public Health-Microbiology-Virology, University of Milan, Milan, Italy.
Received for publication June 5, 2007; accepted November 26, 2007.
Supported by grants from the Istituto Superiore di Sanita' “Programma Nazionale di Ricerca sull' AIDS,” the Centro di Eccellenza CISI, the EMPRO and AVIP EC WP6 Projects, and the Japan Health Science Foundation.
Correspondence to: Mario Clerici, MD, Chair of Immunology, University of Milano, DISTeB LITA Segrate, Via Flli Grassi 93, 20090 Segrate (Milano), Italy (e-mail: email@example.com).
Objective: It is unclear whether the ability to respond to vaccines is restored by antiretroviral therapy. We evaluated the influenza-specific immune responses elicited by a virosomal vaccine in HIV-infected children on long-term successful highly active antiretroviral therapy (HAART).
Methods: This was an observational, prospective, open-label study enrolling 24 HIV-infected, HAART-treated (85 months' mean exposure), vaccine-naive children (median age = 11.9 years) and 14 age- and gender-matched healthy controls. Mean CD4 T-cell counts (>900 cells/μL) and percentages (>37%) were comparable. The HIV RNA level was <50 copies/mL in all patients. Children received a single dose of trivalent virosome-adjuvanted influenza vaccine. A/H3N2-, A/H1N1-, and B-antigen-specific antibody (Ab) titers and subclasses and vaccine-specific interferon-γ (IFNγ)- and interleukin (IL)-2-producing T lymphocytes were analyzed at baseline and 1 and 6 months after immunization.
Results: Seroconversion (≥4-fold Ab titer raise in >40% of patients) and seroprotection (Ab titer ≥1:40 in >70% of patients) was achieved at 1 month in both groups; however, fewer HIV-infected children fulfilled these criteria. The A/H3N2- and A/H1N1-specific Ab geometric mean titers were lower in HIV-infected children compared with healthy controls at 1 and 6 months; interestingly, a boost in vaccine-specific IgG3 T helper 1 type Ab was seen in healthy controls alone. Finally, vaccine specific-IFNγ- and IL-2-producing T lymphocytes were reduced at both time points in HIV-infected children compared with healthy controls.
Conclusions: One injection of virosomal-adjuvanted influenza vaccine stimulates good immune responses, although the humoral and cellular immune responses are reduced in HIV-infected children compared to healthy children. This indicates that immunologic function impairments may persist upon HIV infection even if HIV-positive viremia is suppressed and immune recovery seems to be achieved.
HIV infection results in a complex pattern of impairments that involves all components of the immune system.1-3 Antiretroviral therapy (highly active antiretroviral treatment [HAART]) is associated with a certain degree of immune reconstitution; nevertheless, functional defects persist even in patients who have successfully undergone HAART for long periods.4-9 Thus, residual functional defects can be seen in T helper (Th) cells, cytotoxic T lymphocytes (CTLs), and B lymphocytes, even in patients in whom HAART results in near-complete suppression of circulating HIV viremia and in restoration of CD4 T-cell counts to physiologic numbers.4-9 It is important to underline that because the thymus is still present in children, the likelihood for success of HAART-associated immune restoration should be higher in children than in adults. As a matter of fact, a number of studies have shown that successful therapy in prepubertal patients results in dramatic increases of the thymic mass and, consequently, in satisfying restoration of CD4 T-cell counts and function.10-19
A question that has not yet found an unequivocal answer is whether immune responses elicited by vaccination are fully restored in HIV-infected and HAART-treated individuals. In particular, it is still not clear whether the persistence of vaccine-induced immune responses is comparable in HIV-infected and -uninfected subjects. Contrasting data are reported. Therefore, whereas immunization with pneumococcal, measles, and rubella vaccines were shown to elicit optimal responses,20-23 tetanus immunization resulted in antigen-specific responses of limited duration.24 The results obtained with influenza vaccination are even more controversial, because contrasting results have shown that influenza vaccination elicits immune functions comparable to those observed in healthy controls and that a compromised response to vaccination is seen in HIV-infected patients.25-33
Annual routine vaccination against influenza is recommended in children, in whom the health burden caused by this infectious disease is even greater than in the elderly in terms of incidence and hospitalization.34,35 Because influenza can cause severe complications in HIV-infected patients, influenza vaccination is particularly useful in such patients. Recently, a virosomal-adjuvanted subunit influenza vaccine was shown to be well tolerated and endowed with improved immunogenicity.36-40 To evaluate the amplitude and duration of the cell-mediated and humoral immune responses elicited by such vaccine preparation in pediatric HIV infection, we designed a study protocol enrolling HIV-infected children in whom long-term HAART resulted in an optimal immunovirologic response to therapy.
The success of a vaccination protocol is determined by the ability of the vaccine to elicit increases in antibody (Ab) titers that ensure protection against influenza disease. These criteria have a strong epidemiologic/public health value but are not designed to verify finer immunologic parameters. We thus performed in-depth immunologic analyses to verify the effect of vaccination on a single-patient level. The primary outcome of this study was to evaluate vaccine-induced cell-mediated and humoral immune responses at 1 month after vaccination and the incidence of local and systemic vaccine-related adverse events (AEs); the secondary outcome was to investigate the persistence of such responses 6 months after the vaccination.
MATERIALS AND METHODS
Study Design and Population
This was an observational, prospective, open-label study enrolling HIV-infected children (N = 24) and age- and gender-matched healthy controls (N = 14) undergoing influenza vaccination in the Department of Pediatrics University of Milan, Luigi Sacco Hospital (Milan, Italy) during the period spanning October 15 to November 15, 2005. Inclusion criteria for the HIV-infected children were undetectable viral load, >6 months of HAART, and having never received influenza vaccination before. Exclusion criteria were a contraindication for the influenza vaccine, sensitivity to any component of the vaccine, acute respiratory and/or allergic illness, history of egg allergy, severe atopia, fever >38°C (axillary), treatment with immunosuppressive drugs (including systemic corticosteroids), and having received blood transfusions or immunoglobulins during the previous 3 months. HIV infection was diagnosed and classified in accordance with the Centers for Disease Control and Prevention (CDC) criteria for immunologic (classes 1, 2, and 3) and clinical (classes N, A, B, and C) disease stages.41 The parents of eligible children or their legal guardians received a careful explanation about the aim of the study; if they agreed, they signed a written consent form. The Ethics Committee of the Luigi Sacco Hospital approved the study protocol.
HIV-infected children (8 in CDC class A and 16 in CDC class B+C, 11 in CDC class 1 and 13 in CDC class 2+3) were clinically stable and had long-lasting control of viral replication and immune recovery (Table 1). All showed an undetectable plasma viral load and had a long duration of HAART exposure (mean = 85 months; range: 21 to 116 months). The median nadir CD4 T-cell count was 244 cells/μL (see Table 1). CD4 T- lymphocyte and B-lymphocyte counts and percentages and CD8 T-lymphocyte counts were comparable in HIV-infected children and in healthy controls, whereas CD8 T-cell percentages were increased in HIV-infected children (see Table 1).
All children received 1 dose (0.5 mL) of a trivalent virosome-adjuvanted influenza vaccine (Inflexal V; Berna Biotech AG, Berne, Switzerland), licensed in Italy for the 2005 to 2006 season. This vaccine contains 15 μg each of A/New Caledonia/20/99 (H1N1)-like, A/California/7/2004 (H3N2)-like, and B/Shanghai/361/2002-like purified influenza surface antigens hemagglutinin, and neuraminidase, integrated into the lipid membrane of the virosome with solvent added to 0.5 mL.42,43 The vaccine was injected intramuscularly in the deltoid muscle or in the lateral upper thigh. Immunogenicity assessments were made before vaccination (baseline) and 1 month and 6 months after vaccination.
Safety assessments of local and systemic reactions were made by the investigators at baseline and at the 1-month follow-up visit and by the parents/legal guardians for 4 days after vaccination. Children were examined for the presence of local AEs (pain/tenderness, redness and swelling/induration) and questioned for systemic AEs (body temperature >38°C, shivering, and malaise/irritability).
Detection of Hemagglutination-Inhibiting Antibodies
Serum samples were collected immediately before and 1 and 6 months after the immunization. The samples were simultaneously examined for hemagglutination-inhibiting (HI) Abs using standard microtiter assays for each of the influenza strains contained in the vaccine.44 The HI Ab titer was expressed as the reciprocal of the highest dilution inhibiting agglutination. Minimum response was defined as seroconversion or as a 4-fold or greater increase in Ab titer in the postimmunization samples. Ab titers ≥1:40 were considered protective against influenza infection. To allow the calculation of the HI geometric mean titers (GMTs), a titer of 1:5 was assigned arbitrarily to nonresponder vaccinees. The HI Abs were evaluated according to criteria described in the guideline of the European Agency for the Evaluation of Medical Products (EMEA).45 Because there are no EMEA-defined criteria for the pediatric population, immunogenicity was assessed on the basis of the criteria for adults aged 18 to 60 years, which require at least 1 of the following criteria to be met for each strain to confirm immunogenicity: (1) seroconversion (≥4-fold increase in HI Ab titer, with a titer of ≥1:40 being reached in >40% of the subjects), (2) seroprotection (HI Ab titer of ≥1:40 in >70% of the subjects), and (3) GMT (>2.5-fold increase in the HI Ab GMT).
Blood Sample Collection and Separation of Peripheral Blood Mononuclear Cells
Whole blood was collected by venipuncture in Vacutainer tubes containing ethylenediaminetetraacetic acid (EDTA; Becton Dickinson, Rutherford, NJ). Peripheral blood mononuclear cells (PBMCs) were separated on lymphocyte separation medium (Organon Teknica, Durham, NC) and washed twice in phosphate-buffered saline (Organon Teknica). The number of viable leukocytes was determined by trypan blue exclusion. All analyses were performed on freshly collected cells.
Measurement of Influenza-Specific IgG1 and IgG3
A final concentration of 3 μg/mL of Inflexal V vaccine (Berna Biotech AG, Berne, Switzerland) (New Caledonia 20/99, 591 μg hemagglutinin (HA)/mL; New York 55/2004, 553 μg HA/mL; and Jiangsu 10/2003, 544 μg HA/mL) was used to coat the wells overnight at 4°C. A blocking solution (3% bovine serum albumin [BSA] in Tris-buffered saline [TBS]) was added for 2 hours at 37°C before incubation with plasma. Six serial dilutions (1:1, 1:10, 1:100, 1:400, 1:1600, and 1:6400) of patient plasma were evaluated to define the best condition. After washing, secondary Abs to IgG1 (100 ng/mL; mouse antihuman IgG1 fucose [Fc] fragment horseradish peroxidase [HRP] conjugate; Chemicon Int., Temecula, CA) or IgG3 (300 ng/mL; mouse antihuman IgG3 HRP conjugate; Serotec Ltd, Oxford, UK) were added for 1 hour at 37°C. The reaction was developed with O-phenylenediamine (0.4 mg/mL; Sigma, St. Louis, MO) in 0.05 M of phosphate-citrate buffer containing 0.03% sodium perborate (pH 5.0, Sigma) and stopped after 30 minutes by adding 0.4 N of H2SO4. Optical density was measured at 450 nm (620-nm reference filter).
Enzyme-Linked Immunospot Assays
Ninety-six-well nitrocellulose plates were precoated with a first layer of monoclonal Abs to interferon-γ (IFNγ) or interleukin (IL)-2 (MABTECH, Nacka, Sweden). PBMCs were added in duplicate wells at a rate of 2 × 205 cells/well and were unstimulated or stimulated with the Inflexal V vaccine (1:2000 final concentration) in the presence or the absence of neutralizing anti-CD4 monoclonal Ab. IFNγ production by CD4 T lymphocytes was blocked by preincubating PBMCs with 100 ng/mL of neutralizing recombinant human monoclonal Ab to CD4. IL-2 production by CD8 T cells was prevented by preincubating PBMCs with 100 ng/mL of neutralizing recombinant human monoclonal Ab to CD8 (R&D Systems, Minneapolis, MN). Plates were incubated overnight at 37°C in 7% CO2; the cells were then discarded and the plates incubated at room temperature for 3 hours. A second biotinylated anti-IFNγ or anti-IL-2 monoclonal Ab (7-B6 to 1 biotin; MABTECH), followed by streptavidin-conjugated alkaline phosphatase (MABTECH) for 2 hours, was subsequently used. Cytokine-producing cells were detected using an alkaline phosphatase conjugate substrate kit (Bio-Rad Laboratories, Hercules, CA). Finally, plates were dried and spots were counted using an automated enzyme-linked immunospot (ELISPOT) reader (EliScan Aelvis; Aelvis GmbH, Hannover, Germany). Influenza-specific responses were reported as the number of spot-forming units (SFUs) per 106 mononuclear cells after subtraction of background cytokine secretion.
Seroconversion and seroprotection rates in the 2 groups were compared using the Fisher exact test or the χ2 test (χ2). The Student t test was used to compare GMTs of HI Abs, lymphocyte subset counts, and age. A P value <0.05 was considered significant for all the statistical tests.
Response to Vaccination: Adverse Effects
No serious systemic or local vaccine-related AEs were observed after vaccination at clinical examination. A total of 9 solicited AEs were reported by 4 HIV-infected children (16.6%) and by 2 healthy controls (14.3%). Local reactions (pain/tenderness) occurred in 3 HIV-infected patients and in 2 healthy controls. Systemic events (body temperature >38°C axillary) were observed in 2 children per group.
Response to Vaccination: Seroconversion and Seroprotection Rates
Pre- and postvaccination seroconversion and seroprotection rates for each of the 3 vaccine antigens were tested in paired serum samples. Tables 2 and 3 show the HI Ab responses to the vaccine. The EMEA criteria for seroconversion and seroprotection 1 month after immunization were fulfilled for all 3 influenza strains in HIV-infected children and healthy controls. Nevertheless, HIV-infected children showed lower seroconversion and seroprotection rates as compared with those observed in healthy controls (SC: A/H3N2: 54% vs. 71%, A/H1N1: 71% vs. 93%, B: 71% vs. 86%). These differences, however, did not reach statistical significance. Finally, stratification of children according to age revealed no difference in seroconversion rates in children younger or older than 9 years in HIV-infected children or healthy controls.
Before immunization, a significantly lower percentage of HIV-infected children showed the presence of protective A/H1N1-specific Ab titers compared to healthy controls (≥1:40; P = 0.014), whereas the percentage of individuals with protective A/H3N2- and B-specific Ab titers was similar in both groups. One month after immunization, an increase in the percentage of subjects with a protective Ab titer against all 3 influenza strains was seen in both groups, although, again, the increase was lower in HIV-infected children (A/H3N2 and A/H1N1: 79% vs. 93%, B: 75% vs. 93%). This difference was retained 6 months after immunization (A/H3N2: 54% vs. 71%, A/H1N1: 75% vs. 93%, B: 62% vs. 93%) and became statistically significant (P = 0.04) for B-specific Ab titers. Similar to what was observed for seroconversion, seroprotection rates were similar at both time points after vaccination when younger (<9 years) and older (>9 years) HIV-infected and -uninfected children were analyzed separately.
Response to Vaccination: Geometric Mean Antibody Titers
GMTs against all 3 influenza strains were significantly increased at 1 month and 6 months after immunization in HIV-infected children and in healthy controls. At both time points, however, A/H3N2- and A/H1N1-specific GMTs were significantly lower (P > 0.01) in HIV-infected children compared with healthy controls. These data are shown in Table 3.
The time course of GMTs against all 3 influenza strains according to the preexistence of Ab for any specific strains at baseline are shown in Table 4. The numbers of HIV-infected and -uninfected children without preexisting Abs (ie, HI Ab <10) were as follows: A/H3N2, 14 of 24 HIV-infected children versus 7 of 14 healthy controls; A/H1N1, 10 of 24 HIV-infected children versus 2 of 14 healthy controls; and B, 7 of 24 HIV-infected children versus 5 of 14 healthy controls. GMTs for any specific strain were comparable in HIV-infected children and healthy controls without preexisting Abs at 1 month and 6 months after immunization. Conversely, lower GMTs for A/H3N2 and A/H1N1 strains were observed at both time points in HIV-infected children with preexisting Abs (A/H3N2: P < 0.02 at 1 and 6 months, A/H1N1: P < 0.0006 at 1 month, and P < 0.004 at 6 months).
Response to Vaccination: Influenza-Specific IgG3 Antibodies
Influenza -specific IgG1 and IgG3 titers were measured in plasma of all patients. Whereas a comparable augmentation of influenza-specific IgG1 Ab was seen in both groups of children (data not shown), results presented in Figure 1 indicate that a more than 2-fold increase in influenza-specific IgG3 was seen 1 month after vaccination in healthy controls alone. This difference was statistically significant (P = 0.01).
Response to Vaccination: Influenza-Specific CD4 and CD8 T Lymphocytes
Influenza-specific CD8 IFNγ-secreting T lymphocytes and CD4 IL-2-secreting T lymphocytes were analyzed in all individuals using an ELISPOT assay. Results showed that on vaccination, IFNγ-producing influenza-specific CD8 T lymphocytes were significantly increased 1 month after immunization in HIV-infected patients (P > 0.001) and healthy controls (P = 0.02). This difference was still significant 6 months after vaccination in healthy controls (P > 0. 01) but not in HIV-infected children. At both time points considered, the number of IFNγ-producing influenza-specific CD8 T lymphocytes was statistically higher in healthy controls compared with HIV-infected children (P > 0.01 in both cases).
Vaccination also increased the number of IL-2-producing influenza-specific CD4 T lymphocytes. The increase was statistically significant compared with baseline in healthy controls alone (P > 0.001 at months 1 and 6). Finally, a significantly larger number of IL-2-producing influenza-specific CD4 T lymphocytes were induced by immunization in healthy controls compared with HIV-infected children (P = 0.01 at both time points). These results are shown in Figure 2.
The question of whether immune responses to vaccines are impaired in HIV-infected individuals, and whether the functionality of the immune system can be drastically improved by antiviral therapy, is still not fully elucidated. This question is even more relevant in the pediatric setting, where the presence of an active thymus suggests the possibility that an effective therapy could elicit nearly complete immune restoration.10-19 The immunogenicity of vaccines in HIV-infected children has been analyzed by a number of investigators, showing that an immune response against Pneumococcus, rubella, measles, and tetanus, among others, can be elicited in these children.20-33 Conversely, in the few studies that have performed in-depth analyses to dissect the immune response stimulated by such vaccines, it was shown that the magnitude and duration of Ab response was lower in HIV-infected individuals as compared with controls.46-49
To our knowledge, no study has been performed in children with a full immunovirologic response to HAART, and no study has evaluated immunogenic persistence at 6 months after influenza vaccination. To shed light on this question, we studied the response to influenza vaccine in a group of HIV-infected children with an optimal response to HAART. The vaccine used was a virosomal influenza vaccine. Although, the US Advisory Committee on Immunization Practices recommends 2 doses of influenza vaccine for children younger than 9 years of age,50 protocols based on a single dose were shown to be as effective. In particular, Salleras et al40 administered a single dose of virosomal influenza vaccine in 966 children (94% unprimed; L. Salleras, personal communication, 2006) ranging in age from 3 to 14 years, observing an effectiveness of 88.4% in preventing laboratory-confirmed cases of influenza. Virosomes represent a novel vaccine formulation; they closely mimic the native virus and have the capacity to elicit broad immune responses, activating the humoral and cellular arms of the adaptive immune system.42,43 In particular, the vaccine used, Inflexal V, is an adjuvanted influenza vaccine characterized by exceptional purity, because it is completely viral RNA- and thimerosal-free. This vaccine has been shown to be highly immunogenic, effective, and safe in healthy children and in children with cystic fibrosis.36-40 Our results indicate that a single dose of virosomal influenza vaccine elicits effective immune responses in HIV-infected children and in healthy controls. The results also show that even if EMEA criteria for registration of influenza vaccines are fulfilled up to 6 months post vaccination, in the presence of undetectable HIV plasma viremia and CD4 T-cell counts comparable to those of healthy uninfected controls, the response to vaccination is lower in HIV-infected children. Immune impairment may thus persists even in the context of an apparent perfect response to therapy. Finally, the results of the present study indicate that virosomal-adjuvanted vaccine is safe and well tolerated in HIV-infected children.
From a public health point of view, it is interesting to observe that the EMEA criteria for seroconversion and seroprotection45 were satisfied by the vaccine protocol in both groups of children. Despite this favorable overall result, more in-depth analyses in HIV-infected children as compared with healthy children indicate that (1) the percentage reaching the criteria for seroconversion and seroprotection is lower, (2) the duration of response is shorter, and (3) GMT Ab titers are reduced. These observations suggest that, although useful at analyzing the efficacy of a vaccine at the population level, the EMEA criteria might be inadequate in particular settings, such as HIV infection.
CD4 T-lymphocyte counts and percentages reached by HAART-treated children were optimal for their age and fully comparable to those seen in healthy controls of the same age. This observation notwithstanding, data showed that T lymphocytes were functionally impaired in HIV-infected children. The discrepancy between CD4 T-cell numbers and functions has been described early in HIV research.51,52 Therefore, it may be concluded that the presence of a conspicuous number of CD4 T lymphocytes does not warrant their functionality. As a matter of fact, it is known that a complex pattern of functional impairment is observed during the progression of infection in HIV-infected patients.53 Conversely, whereas it was convincingly shown that HAART can restore CD4 T-cell counts to an almost optimal degree, functional immune defects are much less susceptible to being fully reverted by therapy.4-9,54,55 The response to a protein antigen, such as that used in this vaccine, needs full collaboration between T and B lymphocytes56; we observed the presence of defects in both of these cell types. Thus, influenza-stimulated IL-2 production by CD4 T lymphocytes, IFNγ production by CD8 T lymphocytes, and influenza-specific Ab production by B lymphocytes were fully defective in HIV-infected children compared with healthy controls. These data raise the possibility that an immune defect in antigen processing and/or presentation could be involved in the impairment of the immune response observed in HIV-infected children. Antigen presentation was shown to be defective only in the final stages of disease;55 preliminary data obtained in the children enrolled in the study showed that the expression of major histocompatibility complex (MHC) class I and class II molecules was not reduced on the immune cells of HIV-infected patients, suggesting that antigen presentation is not impaired in this setting.
An isotype switch occurs after B cells have been stimulated by antigens and is finely regulated by cytokines produced by the T lymphocytes present in the cellular milieu.57 In particular, IFNγ and IL-12 stimulate IgG3 production, whereas IL-4 favors the generation of IgG1.58-60 Antigen-specific Ab subclasses can thus be used as a biologic indicator to characterize antigen-specific immune responses functionally. IFNγ production by CD8 T cells was reduced in HIV-infected children; as a result, influenza vaccination was associated with a significant increase of antigen-specific IgG3 in healthy controls alone. These findings indicate that defects in Th1-like cytokine production that cannot be reversed by antiviral therapy persist even in the face of a complete immune restoration.
In conclusion, whereas a single injection of virosomal vaccine elicits strong immune responses in healthy children, the effect of a single dose administration is reduced in HIV-infected children, even in the context of an apparently totally satisfactory immunovirologic response to HAART. The persistence of immune defects in HIV-infected children prevents the possibility of mounting fully efficient immune responses to vaccination. The efficacy of different, more frequent, and/or more intense vaccine schedules should be considered in these children.
1. Cohen OJ, Kinter A, Fauci AS. Host factors in the pathogenesis of HIV disease. Immunol Rev
2. Shearer GM. HIV-induced immunopathogenesis. Immunity
3. Simon V, Ho DD, Karim QA. HIV/AIDS epidemiology, pathogenesis, prevention, and treatment. Lancet
4. Saag MS. The impact of highly active antiretroviral therapy on HIV-specific immune function. AIDS
. 2001;15(Suppl 2):S4-S10.
5. Lederman MM. Immune restoration and CD4+ T-cell function with antiretroviral therapies. AIDS
. 2001;15(Suppl 2):S11-S15.
6. Lederman MM, Valdez H. Immune restoration with antiretroviral therapies-implications for clinical management. JAMA
7. Cooper DA. Immunological effects of antiretroviral therapy. Antivir Ther
8. Autran B, Carcelain G, Li TS, et al. Positive effects of combined antiretroviral therapy on CD4+ T cell homeostasis and function in advanced HIV disease. Science
9. Trabattoni D, Piconi S, Biasin M, et al. Granule-dependent mechanisms of lysis are defective in CD8+ T cells of HIV-infected, antiviral therapy-treated individuals. AIDS
10. Clerici M, Saresella M, Trabattoni D, et al. Thymic volume predicts long term immune reconstitution in HIV-infected, HAART-treated children. AIDS
11. Viganò A, Vella S, Principi N, et al. Thymus volume correlates with the progression of vertical HIV infection. AIDS
12. Resino S, Abad ML, Navarro J, et al. Stimulated proliferative responses in vertically HIV-infected children on HAART correlate with clinical and immunological markers. Clin Exp Immunol
13. Kalayjian RC, Landay A, Pollard RB, et al. Age-related immune dysfunction in health and in HIV disease: association of age and HIV infection with naïve CD8+ cell depletion, reduced expression of CD28 on CD8+ cells, and reduced thymic volumes. J Infect Dis
14. Kalayjian RC, Spritzler J, Pu M, et al. Distinct mechanisms of T cell reconstitution can be identified by estimating thymic volume in adult HIV-1 disease. J Infect Dis
15. Hakim FT, Memon SA, Cepeda R, et al. Age-dependent incidence, time course, and consequence on thymic renewal in adults. J Clin Invest
16. Gibb DM, Newberry A, Klein N, et al. Immune repopulation after HAART in previously untreated HIV-1-infected children. Lancet
17. Texeira L, Valdez H, McCune JM, et al. Poor CD4 T cell restoration after suppression of HIV-1 replication may reflect lower thymic function. AIDS
18. Smith KY, Valdez H, Landay A, et al. Thymic size and lymphocyte restoration in patients with HIV infection after 48 weeks of zidovudine, lamivudine, and ritonavir therapy. J Infect Dis
19. Douek DC, Koup RA, McFarland RD, et al. Effect of HIV on thymic function before and after antiretroviral therapy in children. J Infect Dis
20. Falcó V, Jordano Q, Cruz MJ, et al. Serological response to pneumococcal vaccination in HAART-treated HIV-infected patients: one year follow-up study. Vaccine
21. Amendola A, Tanzi E, Zappa A, et al. Safety and immunogenicity of 23-valent pneumococcal polysaccharide vaccine in HIV-1 infected former drug users. Vaccine
22. Berkelhamer S, Borocj E, Elsen C, et al. Effect of highly active antiretroviral therapy on the serologic response to additional measles vaccination in HIV-infected children. Clin Infect Dis
23. Lima M, Succi de Menezes RC, Nunes Dos Santos AM, et al. Rubella immunization in HIV-1-infected children, cause for concerns in vaccination strategies. Pediatr Infect Dis J
24. Rosenblatt HM, Song LY, Nachman SA, et al. Tetanus immunity after diphtheria, tetanus toxoid, and acellular pertussis vaccination in children with clinically stable HIV infection. J Allergy Clin Immunol
25. Amendola A, Boschini A, Colzani D, et al. Influenza vaccination of HIV-1-positive and HIV-1-negative former intravenous drug users. J Med Virol
26. Zanetti AR, Amendola A, Besana S, et al. Safety and immunogenicity of influenza vaccination in individuals infected with HIV. Vaccine
27. Tanzi E, Esposito S, Bojanin J, et al. Immunogenicity and effect of a virosomal influenza vaccine on viral replication and T-cell activation in HIV-infected children receiving highly active antiretroviral therapy. J Med Virol
28. Kroon FP, van Dissel JT, de Jong JC, et al. Antibody response after influenza vaccination in HIV-infected individuals: a consecutive 3-year study. Vaccine
29. Jackson CR, Vavro CL, Valentine M, et al. Effect of influenza immunization on immunologic and virologic characteristics of pediatric patients infected with HIV. Pediatr Infect Dis J
30. Kroon FP, Rimmelzwaan GF, Roos MTL, et al. Restored humoral immune response to influenza vaccination in HIV-infected adults treated with highly active antiretroviral therapy. AIDS
31. Fuller JD, Craven DE, Steger KA, et al. Influenza vaccination of HIV-infected adults: impact of plasma levels of HIV type 1 RNA and determinants of antibody responses. Clin Infect Dis
32. Fowke KR, D'Amico R, Chernoff DN, et al. Immunologic and virologic evaluation after influenza vaccination of HIV-1-infected patients. AIDS
33. Malaspina A, Moir S, Orsega SM, et al. Compromised B cell responses to influenza vaccination in HIV-infected individuals. J Infect Dis
34. World Health Organization. Recommendations for the use of inactivated influenza vaccines and other preventive measures. Wkly Epidemiol Rec
35. Harper SA, Fukuda K, Uyeki TM, et al. Prevention and control of influenza. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep
36. Schaad UB, Buhlmann U, Burger R, et al. Comparison of immunogenicity and safety of a virosome influenza vaccine with those of a subunit influenza vaccine in pediatric patients with cystic fibrosis. Antimicrob Agents Chemother
37. Zuccotti GV, Cucchi C, Sala D, et al. Immunogenicity and safety of a virosomal influenza vaccine in HIV-infected children. Acta Paediatr
38. Herzog C, Metcalfe IC, Schaad UB. Virosome influenza vaccine in children. Vaccine
39. Kanra G, Marchisio P, Feiterna-Sperling C, et al. Comparison of immunogenicity and tolerability of a virosome-adjuvanted and a split influenza vaccine in children. Pediatr Infect Dis J
40. Salleras L, Dominguez A, Pumarola T, et al. Effectiveness of virosomal subunit influenza vaccine in preventing influenza-related illnesses and its social and economic consequences in children aged 3-14 years: a prospective cohort study. Vaccine
41. Centers for Disease Control and Prevention. 1993 Revised classification system for HIV infection and expanded surveillance case definition for AIDS among adolescents and adults. MMWR Morb Mortal Wkly Rep
42. Huckriede A, Bungener L, Stegmann T, et al. The virosome concept for influenza vaccines. Vaccine
43. Moser C, Metcalfe IC, Viret JF. Virosomal adjuvanted antigen delivery systems. Expert Rev Vaccines
44. Dowdle WA, Kendal AP, Noble GR. Influenza viruses. In: Lennette EM, Schmidt NJ, eds. Diagnostic Procedures for Viral, Rickettsial and Chlamydial Infections
. Washington, DC: American Public Health Association; 1979:585-609.
45. The European Agency for the Evaluation of Medical Products (EMEA), Committee for Proprietary Medical Products (CPMP). Note for Guidance on Harmonization of Requirements for Influenza Vaccine
(CPMP/BWP/214/96). London; 1997.
46. Kroon FP, van Dissel JT, Ravensbergen E, et al. Antibodies against pneumococcal polysaccharides after vaccination in HIV-infected individuals: 5-year follow-up of antibody concentrations. Vaccine
47. Talesnik E, Vial PA, Labarca J, et al. Time course of antibody response to tetanus toxoid and pneumococcal capsular polysaccharides in patients infected with HIV. J Acquir Immune Defic Syndr Hum Retrovirol
48. Kroon FP, van Dissel JT, de Jong JC, et al. Antibody response to influenza, tetanus and pneumococcal vaccines in HIV-seropositive individuals in relation to the number of CD4+ lymphocytes. AIDS
49. King JC, Vink PE, Chang I, et al. Antibody titers eight months after three doses of a five-valent pneumococcal conjugate vaccine in HIV and non-HIV-infected children less than two years of age. Vaccine
50. Fiore AE, Shay DK, Haber P, et al. Advisory Committee on Immunization Practices (ACIP), Centers for Disease Control and Prevention (CDC). Prevention and control of influenza. Recommendations of the Advisory Committe on Immunization Practices (ACIP), 2007. MMWR Recomm Rep
51. Miedema F, Petit AJ, Terpstra FG. Immunological abnormalities in human immunodeficiency virus (HIV)-infected asymptomatic homosexual men. HIV affects the immune system before CD4+ T helper cell depletion occurs. J Clin Invest
52. Clerici M, Stocks NI, Zajac RC, et al. Detection of three distinct patterns of T helper cell dysfunction in asymptomatic human immunodeficiency virus-seropositive patients. Independence of CD4+ cell numbers and clinical staging. J Clin Invest
53. Viganò A, Dally L, Bricalli D, et al. An 18 months clinical and immunovirologic characterization of the efficacy of stavudine, lamivudine and indinavir in pediatric HIV infection. J Pediatr
54. Resino S, Galan I, Perez A, et al. HIV-infected children with moderate/severe immune suppression: changes in the immune system after highly active antiretroviral therapy. Clin Exp Immunol
55. Cambier JC. Signal transduction by T and B cell antigen receptors: converging structures and concepts. Curr Opin Immunol
56. Clerici M, Landay AL, Kessler HA, et al. Multiple patterns of alloantigen presenting/stimulating cell dysfunction in HIV infected individuals. J Immunol
57. Wabe MR, Forni L, Loor F. Switch in immunoglobulin class production observed in single clones of committed lymphocytes. Science
58. Finkelman FD, Holmes J, Katona IM, et al. Lymphokine control of in vivo immunoglobulin isotype selection. Annu Rev Immunol
59. Coffman RL, Lebman DA, Rothman P. Mechanism and regulation of immunoglobulin isotype switching. Adv Immunol
60. Germann T, Bongartz M, Dlugonska H, et al. Interleukin-12 profoundly up-regulates the synthesis of antigen-specific complement-fixing IgG2a, IgG2b and IgG3 antibody subclasses in vivo. Eur J Immunol
HIV infection; immunology; influenza; pediatrics; vaccine
© 2008 Lippincott Williams & Wilkins, Inc.
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