[Show abstract][Hide abstract] ABSTRACT: Neonatal cytotoxic T cell responses have only been elicited to date with immunogens or delivery systems inducing potent direct APC activation. To define the minimal activation requirements for the induction of neonatal CD8(+) cytotoxic responses, we used synthetic microspheres (MS) coated with a single CD8(+) T cell peptide from lymphocytic choriomeningitis virus (LCMV) or HIV-1. Unexpectedly, a single injection of peptide-conjugated MS without added adjuvant induced CD4-dependent Ag-specific neonatal murine cytotoxic responses with adult-like CTL precursor frequency, avidity for Ag, and frequency of IFN-gamma-secreting CD8(+) splenocytes. Neonatal CD8(+) T cell responses to MS-LCMV were elicited within 2 wk of a single immunization and, upon challenge, provided similar protection from viral replication as adult CTLs, demonstrating their in vivo competence. As previously reported, peptide-coated MS elicited no detectable activation of adult CD11c(+) dendritic cells (DC). In contrast, CTL responses were associated with a partial activation of neonatal CD11c(+) DC, reflected by the up-regulation of CD80 and CD86 expression but no concurrent changes in MHC class II or CD40 expression. However, this partial activation of neonatal DC was not sufficient to circumvent the requirement for CD4(+) T cell help. The effective induction of neonatal CD8(+) T cell responses by this minimal Ag delivery system demonstrates that neonatal CD11c(+) DC may mature sufficiently to stimulate naive CD8(+) neonatal T cells, even in the absence of strong maturation signals.
The Journal of Immunology 09/2004; 173(4):2669-74. · 5.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The relative immaturity of the neonatal immune system limits CD4(+) Th1 and cytotoxic T lymphocyte (CTL) responses, and represents a significant challenge for the development of vaccines against intracellular pathogens. In this report, we demonstrate the ability of a non-replicative delivery system based on parvovirus-like particles (VLP) to induce CTL responses in the neonatal period. A single immunization of 1-week-old BALB/c mice with recombinant VLP carrying a CD8(+) T cell determinant from lymphocytic choriomeningitis virus (VLP-LCMV) induced antigen-specific CD8(+) cytotoxic T cells that were similar to those elicited by adult immunization, as assessed by cytotoxic activity, interferon (IFN)-gamma secretion, cytotoxic precursor cell frequencies, in vitro avidity for antigen and protective activity against viral challenge. These CTL responses are elicited within 2 weeks of a single immunization, in the absence of adjuvant and independently of the presence and help of CD4(+) T cells, highlighting the potential of VLP as candidate vaccine vectors in early life.
[Show abstract][Hide abstract] ABSTRACT: Although initially developed in adult animals, novel viral vectors expressing recombinant measles antigens must eventually prove their success in the early life setting, where the efficacy of the currently used live-attenuated measles virus vaccine is limited. The immunological requirements for vaccine candidates include the generation of protective antibody responses as well as the induction of Th1 and cytotoxic T lymphocytes (CTL) responses, which is challenging in the neonatal setting. Here, we report that young BALB/c mice immunized with a single dose of a vaccinia-based NYVAC(K1L) vector generate adult-like antihemagglutinin (HA) antibody responses as well as adult-like Th1 and CTL responses. Despite this strong immunogenicity in early life, antibody responses (but not T-cell responses) to a single dose of NYVAC(K1L)-HA remained susceptible to inhibition by preexisting measles antibodies, calling for use of prime-boost strategies. NYVAC(K1L)-HA is the first attenuated live viral vector demonstrated as capable of inducing adult-like antibody, Th1, and CTL responses against measles in an early life murine immunization model, a capacity previously only reported for measles DNA vaccines.
[Show abstract][Hide abstract] ABSTRACT: The limited induction of Th1 and cytotoxic immune responses is regarded as the main reason for the increased susceptibility to intracellular microorganisms in early life. Recently, in vitro IL-12 supplementation was shown to enhance the limited IFN-γ release of measles-specific infant T cells. Using a series of IL-12 delivery systems, we show here that in vivo IL-12 supplementation may enhance early life murine Th1 responses to two model vaccine antigens, measles virus hemagglutinin and tetanus toxin peptide. However, this required multiple repeat injections of recombinant rIL-12, which were poorly tolerated in young mice. Local IL-12 delivery by an IL-12 expressing canarypox vector proved safe but failed to modulate vaccine responses. An IL-12 DNA plasmid or a CD40L DNA plasmid efficiently enhanced neonatal Th1 responses to measles hemagglutinin DNA vaccine. However, both plasmids only enhanced Th1 responses to DNA and not to peptide, protein, or live viral vaccines. Thus, inducing adult-like Th1 responses may be achieved in vivo by inducing (CD40L) or substituting for (IL-12 supplementation) optimal activation of neonatal APC. However, these immunomodulatory effects appear limited to certain antigen-presentation approaches and may not be broadly applicable to vaccines.
[Show abstract][Hide abstract] ABSTRACT: Early life responses to respiratory syncytial virus (RSV)-F DNA and RSV-F protein immunization were studied in murine models of neonatal immunization. RSV-F DNA induced similar antibody (Ab) responses, antigen-specific IFN- production and cytotoxic T lymphocyte (CTL) responses in 1-week-old and adult BALB / c mice. In contrast, RSV-F protein induced much higher IL-5 responses in early life. Both vaccines elicited Ab and CTL responses in spite of maternal Ab, but with distinctive kinetics. Sequential RSV-F DNA priming / protein boosting primed 1-week-old mice for RSV-F-specific CTL responses, reduced IL-5 production and enhanced Ab responses. In contrast, IL-5 exceeded IFN- responses when young mice were primed with protein and boosted with DNA. Last, when protein and DNA immunization were combined, a single vaccine dose induced early Ab responses, preferential IL-5 responses but strong CTL responses. Sequential or combined DNA / protein immunization thus represent interesting strategies for early life immunization.
European Journal of Immunology 09/1999; 29(10):3390 - 3400. · 4.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The transfer of maternal antibodies to the offspring and their inhibitory effects on active infant immunization is an important factor hampering the use of certain vaccines, such as measles or respiratory syncytial virus vaccine, in early infancy. The resulting delay in protection by conventional or novel vaccines may have significant public health consequences. To define immunization approaches which may circumvent this phenomenon, experiments were set up to further elucidate its immunological bases. The influence of maternal antibodies on antibody and T cell responses to measles hemagglutinin (MV-HA) were analyzed following MV-HA immunization of pups born to immune or control BALB/c mothers using four different antigen delivery systems: live or inactivated conventional measles vaccine, a live recombinant canarypox vector and a DNA vaccine. High levels (> 5 log10) of maternal anti-HA antibodies totally inhibited antibody responses to each of the vaccine constructs, whereas normal antibody responses were elicited in presence of lower titers of maternal antibodies. However, even high titers of maternal antibodies affected neither the induction of vaccine-specific Th1/Th2 responses, as assessed by proliferation and levels of IFN-gamma and IL-5 production, nor CTL responses in infant mice. On the basis of these unaltered T cell responses, very early priming and boosting (at 1 and 3 weeks of age, respectively) with live measles vaccine allowed to circumvent maternal antibody inhibition of antibody responses in pups of immune mothers. This was confirmed in another immunization model (tetanus toxoid). It suggests that effective vaccine responses may be obtained earlier in presence of maternal antibodies through the use of appropriate immunization strategies using conventional or novel vaccines for early priming.
European Journal of Immunology 12/1998; 28(12):4138-48. · 4.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Failure to generate CTL responses in early life has been linked to the preferential maturation of CD4 T cells into TH2 rather than TH1 cells in response to some, but not other, antigenic stimulations. Here, we provide preliminary evidence for the role of the viral replication pattern in the shaping of neonatal cellular responses to live viral vaccines. Neonatal and early life immunization with live attenuated Sendai virus vaccine led to the induction of IgG2a antibodies and cytotoxic responses as efficiently as immunization of adult animals. Similarly, although early life immunization with live attenuated measles virus led to preferential TH2 polarization of T cells compared with adult primed animals, it allowed the induction of CTL responses which had not been observed following immunization with a live recombinant canarypox vector. Thus, conversely to a non-replicating canarypox recombinant vaccine expressing the measles haemagglutonin, viral vaccines with limited but present replication capacity appear capable of activating neonatal antigen presenting cells to trigger TH1 and CTL responses, as recently observed for DNA vaccines.
[Show abstract][Hide abstract] ABSTRACT: The relative deficiency of T helper type 1 (Th1) and cytotoxic T lymphocyte (CTL) responses in early life is associated with
an increased susceptibility to infections by intracellular microorganisms. This is likely to reflect a preferential polarization
of immature CD4 T cells toward a Th2 rather than a Th1 pattern upon immunization with conventional vaccines. In this report,
it is shown that a single immunization within the first week of life with DNA plasmids encoding viral (measles virus hemagglutinin,
Sendai virus nucleoprotein) or bacterial (C fragment of tetanus toxin) vaccine antigens can induce adult-like Th1 or mixed
Th1/Th2 responses indicated by production of IgG2a vaccine-specific antibodies and preferential secretion of interferon-γ
(IFN-γ) compared with interleukin (IL)-5 by antigen-specific T cells, as well as significant CTL responses. However, in spite
of this potent Th1-driving capacity, subsequent DNA immunization was not capable of reverting the Th2-biased responses induced
after early priming with a recombinant measles canarypox vector. Thus, DNA vaccination represents a novel strategy capable
of inducing Th1 or mixed Th1/Th2 and CTL responses in neonates and early life, providing it is performed prior to exposure
to Th2-driving conventional vaccine antigens.
Proceedings of the National Academy of Sciences 08/1997; 94(16):8726-8731. · 9.81 Impact Factor