Quantitation of CD8+ T cell expansion,memory, and protective immunity after immunization with peptide-coated dendritic cells

Dendritic cells (DCs) are potent APCs for naive CD8(+) T cells and are being investigated as vaccine delivery vehicles. In this study, we examine the CD8(+) T cell response to defined peptides from Listeria monocytogenes (LM), lymphocytic choriomeningitis virus, and murine CMV coated singly and in combination onto mature bone marrow-derived DCs (BMDCs). We show that immunization of mice with 2 x 10(5) mature BMDCs coated with multiple MHC class I peptides generates a significant Ag-specific CD8(+) T cell response in both the spleen and nonlymphoid organs. This immunization resulted in a peptide-specific hierarchy in the magnitude of CD8(+) T cell priming and noncoordinate kinetics in response to different peptide epitopes. Kinetics were not exclusively due to specific characteristics of the MHC class I molecule, and were not altered in an Ag-independent manner by concurrent LM infection. Mice immunized with listeriolysin O 91-99-coated BMDCs are protected against high dose challenge with virulent LM. This protection was enhanced by diversifying the memory CD8(+) T cell compartment, even in the absence of a large increase in Ag-specific CD8(+) memory T cells.     

PDL-1 blockade impedes T cell expansion and protective immunity primed by attenuated Listeria monocytogenes

Infection with attenuated Listeria monocytogenes (Lm) is a robust in vivo model for examining how Ag-specific T cells are primed, and subsequent challenge with virulent Lm allows for the protective effects of T cell priming to be quantified. Herein, we investigated the role of programmed death ligand 1 (PDL-1) in T cell priming and immunity conferred after primary infection with Lm DeltaactA followed by virulent Lm challenge. In striking contrast to the inhibitory role of PDL-1 on T cell immunity in other infection models, marked reductions in the magnitude of T cell expansion and the kinetics of T cell proliferation were observed with PDL-1 blockade after primary Lm DeltaactA infection. More importantly, PDL-1 blockade beginning before primary infection and maintained throughout the experiment resulted in delayed bacterial clearance and T cell expansion after secondary challenge with virulent Lm. These results indicate that for immunity to intracellular bacterial infection, PDL-1 plays an important stimulatory role for priming and expansion of protective T cells.     

Antigen presentation by nonhemopoietic cells amplifies clonal expansion of effector CD8 T cells in a pathogen-specific manner

Professional APCs of hemopoietic-origin prime pathogen-specific naive CD8 T cells. The primed CD8 T cells can encounter Ag on infected nonhemopoietic cell types. Whether these nonhemopoietic interactions perpetuate effector T cell expansion remains unknown. We addressed this question in vivo, using four viral and bacterial pathogens, by comparing expansion of effector CD8 T cells in bone marrow chimeric mice expressing restricting MHC on all cell types vs mice that specifically lack restricting MHC on nonhemopoietic cell types or radiation-sensitive hemopoietic cell types. Absence of Ag presentation by nonhemopoietic cell types allowed priming of naive CD8 T cells in all four infection models tested, but diminished their sustained expansion by approximately 10-fold during lymphocytic choriomeningitis virus and by < or =2-fold during vaccinia virus, vesicular stomatitis virus, or Listeria monocytogenes infections. Absence of Ag presentation by a majority (>99%) of hemopoietic cells surprisingly also allowed initial priming of naive CD8 T cells in all the four infection models, albeit with delayed kinetics, but the sustained expansion of these primed CD8 T cells was markedly evident only during lymphocytic choriomeningitis virus, but not during vaccinia virus, vesicular stomatitis virus, or L. monocytogenes. Thus, infected nonhemopoietic cells can amplify effector CD8 T cell expansion during infection, but the extent to which they can amplify is determined by the pathogen. Further understanding of mechanisms by which pathogens differentially affect the ability of nonhemopoietic cell types to contribute to T cell expansion, how these processes alter during acute vs chronic phase of infections, and how these processes influence the quality and quantity of memory cells will have implications for rational vaccine design.     

Efficacy of DNA and fowlpox virus priming/boosting vaccines for simian/human immunodeficiency virus

Further advances are required in understanding protection from AIDS by T-cell immunity. We analyzed a set of multigenic simian/human immunodeficiency virus (SHIV) DNA and fowlpox virus priming and boosting vaccines for immunogenicity and protective efficacy in outbred pigtail macaques. The number of vaccinations required, the effect of DNA vaccination alone, and the effect of cytokine (gamma interferon) coexpression by the fowlpox virus boost was also studied. A coordinated induction of high levels of broadly reactive CD4 and CD8 T-cell immune responses was induced by sequential DNA and fowlpox virus vaccination. The immunogenicity of regimens utilizing fowlpox virus coexpressing gamma interferon, a single DNA priming vaccination, or DNA vaccines alone was inferior. Significant control of a virulent SHIV challenge was observed despite a loss of SHIV-specific proliferating T cells. The outcome of challenge with virulent SHIV(mn229) correlated with vaccine immunogenicity except that DNA vaccination alone primed for protection almost as effectively as the DNA/fowlpox virus regimen despite negligible immunogenicity by standard assays. These studies suggest that priming of immunity with DNA and fowlpox virus vaccines could delay AIDS in humans.     

Serine protease inhibitor 6 is required to protect dendritic cells from the kiss of death

How dendritic cells (DC) present Ag to cytotoxic T cells (CTL) without themselves being killed through contact-mediated cytotoxicity (so-called kiss of death) has proved to be controversial. Using mice deficient in serine protease inhibitor 6 (Spi6), we show that Spi6 protects DC from the kiss of death by inhibiting granzyme B (GrB) delivered by CTL. Infection of Spi6 knockout mice with lymphocytic choriomeningitis virus revealed impaired survival of CD8α DC. The impaired survival of Spi6 knockout CD8α DC resulted in impaired priming and expansion of both primary and memory lymphocytic choriomeningitis virus-specific CTL, which could be corrected by GrB deficiency. The rescue in the clonal burst obtained by GrB elimination demonstrated that GrB was the physiological target through which Spi6 protected DC from CTL. We conclude that the negative regulation of DC priming of CD8 T lymphocyte immunity by CTL killing is mitigated by the physiological inhibition of GrB by Spi6.     

Adaptive immunity and enhanced CD8+ T cell response to Listeria monocytogenes in the absence of perforin and IFN-gamma

Single Ag-specific CD8+ T cells from IFN-gamma-deficient (GKO) or perforin-deficient (PKO) mice provide substantial immunity against murine infection with Listeria monocytogenes. To address the potential for redundancy between perforin and IFN-gamma as CD8+ T cell effector mechanisms, we generated perforin/IFN-gamma (PKO/GKO) double-deficient mice. PKO/GKO-derived CD8+ T cells specific for the immunodominant listeriolysin O (LLO91-99) epitope provide immunity to LM infection similar to that provided by Ag-matched wild-type (WT) CD8+ T cells in the liver but reduced in the spleen. Strikingly, polyclonal CD8+ T cells from immunized PKO/GKO mice were approximately 100-fold more potent in reducing bacterial numbers than the same number of polyclonal CD8+ T cells from immunized WT mice. This result is probably quantitative, because the frequency of the CD8+ T cell response against the immunodominant LLO91-99 epitope is >4.5-fold higher in PKO/GKO mice than WT mice at 7 days after identical immunizations. Moreover, PKO/GKO mice can be immunized by a single infection with attenuated Listeria to resist >80,000-fold higher challenges with virulent organisms than naive PKO/GKO mice. These data demonstrate that neither perforin nor IFN-gamma is required for the development or expression of adaptive immunity to LM. In addition, the results suggest the potential for perforin and IFN-gamma to regulate the magnitude of the CD8+ T cell response to infection.     

CD8alpha+ dendritic cells selectively present MHC class I-restricted noncytolytic viral and intracellular bacterial antigens in vivo

CD8alpha(+) dendritic cells (DCs) have been shown to be the principal DC subset involved in priming MHC class I-restricted CTL immunity to a variety of cytolytic viruses, including HSV type 1, influenza, and vaccinia virus. Whether priming of CTLs by CD8alpha(+) DCs is limited to cytolytic viruses, which may provide dead cellular material for this DC subset, or whether these DCs selectively present intracellular Ags, is unknown. To address this question, we examined Ag presentation to a noncytolytic virus, lymphocytic choriomeningitis virus, and to an intracellular bacterium, Listeria monocytogenes. We show that regardless of the type of intracellular infection, CD8alpha(+) DCs are the principal DC subset that initiate CD8(+) T cell immunity.     

Deficient CD4+ T cell priming and regression of CD8+ T cell functionality in virus-infected mice lacking a normal B cell compartment

In this study, we investigate the state of T cell-mediated immunity in B cell-deficient (B(-/-)) mice infected with two strains of lymphocytic choriomeningitis virus known to differ markedly in their capacity to persist. In B(-/-) C57BL mice infected with the more persisting virus, virus-specific CD8(+) T cells are initially generated that are qualitatively similar to those in wild-type mice. However, although cell numbers are well sustained over time, the capacity to produce cytokines is rapidly impaired. In similarly infected B(-/-) BALB/c mice, virus-specific CD8(+) T cells are completely deleted, indicating that host genotype influences the severity of the T cell defect. In B(-/-) C57BL mice infected with the less persisting virus, CD8(+) T cell dysfunction was not as pronounced, although it was clearly present. Most importantly, the appearance of dysfunctional CD8(+) T cells clearly precedes recrudescence of detectable virus, indicating that the T cell defect is not simply a secondary event due to virus buildup resulting from the failure of B(-/-) mice to produce neutralizing Abs. In contrast with CD8(+) T cells, which initially respond almost as in wild-type mice, the priming of virus-specific CD4(+) T cells was markedly impaired in B(-/-) mice infected with either virus strain. Thus, our results indicate that B cells play an important role in antiviral immunity not only as Ab producers, but also in promoting an optimal and sustained T cell response. The T cell defects are likely to contribute to the chronic course of viral infection in B(-/-) mice.     

MHC class II-associated invariant chain linkage of antigen dramatically improves cell-mediated immunity induced by adenovirus vaccines

The ideal vaccine induces a potent protective immune response, which should be rapidly induced, long-standing, and of broad specificity. Recombinant adenoviral vectors induce potent Ab and CD8+ T cell responses against transgenic Ags within weeks of administration, and they are among the most potent and versatile Ag delivery vehicles available. However, the impact of chronic infections like HIV and hepatitis C virus underscore the need for further improvements. In this study, we show that the protective immune response to an adenovirus-encoded vaccine Ag can be accelerated, enhanced, broadened, and prolonged by tethering of the rAg to the MHC class II-associated invariant chain (Ii). Thus, adenovirus-vectored vaccines expressing lymphocytic choriomeningitis virus (LCMV)-derived glycoprotein linked to Ii increased the CD4+ and CD8+ T cell stimulatory capacity in vitro and in vivo. Furthermore, mice vaccinated with a single dose of adenovirus-expressing LCMV-derived glycoprotein linked to Ii were protected against lethal virus-induced choriomeningitis, lethal challenge with strains mutated in immunodominant T cell epitopes, and systemic infection with a highly invasive strain. In therapeutic tumor vaccination, the vaccine was as efficient as live LCMV. In comparison, animals vaccinated with a conventional adenovirus vaccine expressing unmodified glycoprotein were protected against systemic infection, but only temporarily against lethal choriomeningitis, and this vaccine was less efficient in tumor therapy.     

Priming with cold-adapted influenza A does not prevent infection but elicits long-lived protection against supralethal challenge with heterosubtypic virus

We show in this study several novel features of T cell-based heterosubtypic immunity against the influenza A virus in mice. First, T cell-mediated heterosubtypic protection against lethal challenge can be generated by a very low priming dose. Second, it becomes effective within 5-6 days. Third, it provides protection against a very high dose challenge for >70 days. Also novel is the finding that strong, long-lasting, heterosubtypic protection can be elicited by priming with attenuated cold-adapted strains. We demonstrate that priming does not prevent infection of the lungs following challenge, but leads to earlier clearance of the virus and 100% survival after otherwise lethal challenge. Protection is dependent on CD8 T cells, and we show that CD4 and CD8 T cells reactive to conserved epitopes of the core proteins of the challenge virus are present after priming. Our results suggest that intranasal vaccination with cold-adapted, attenuated live virus has the potential to provide effective emergency protection against emerging influenza strains for several months.     

Vaccination against lymphocytic choriomeningitis virus infection in MHC class II-deficient mice

The impact of prophylactic vaccination against acute and chronic infection in a Th-deficient host has not been adequately addressed because of difficulties in generating protective immunity in the absence of CD4(+) T cell help. In this study, we demonstrated that a broad CD8(+) T cell immune response could be elicited in MHC class II-deficient mice by vaccination with adenovirus encoding lymphocytic choriomeningitis virus (LCMV) glycoprotein tethered to MHC class II-associated invariant chain. Moreover, the response induced conferred significant cytolytic CD8(+) T cell-mediated protection against challenge with a high dose of the invasive clone 13 strain of LCMV. In contrast, vaccination with adenovirus encoding unlinked LCMV glycoprotein induced weak virus control in the absence of CD4(+) T cells, and mice may die of increased immunopathology associated with incomplete protection. Acute mortality was not observed in any vaccinated mice following infection with the less-invasive Traub strain. However, LCMV Traub infection caused accelerated late mortality in unvaccinated MHC class II-deficient mice; in this case, we observed a strong trend toward delayed mortality in vaccinated mice, irrespective of the nature of the vaccine. These results indicated that optimized vaccination may lead to efficient protection against acute viral infection, even in Th-deficient individuals, but that the duration of such immunity is limited. Nevertheless, for select immunodeficiencies in which CD4(+) T cell deficiency is incomplete or transient, these results are very encouraging.     

Deficient anti-listerial immunity in the absence of perforin can be restored by increasing memory CD8+ T cell numbers

Compared with wild-type (WT) mice, Listeria monocytogenes (LM)-vaccinated perforin-deficient (PKO) mice have elevated levels of CD8(+) T cell memory, but exhibit reduced levels of protection against virulent LM. In this study, Ag-specific CD8(+) T cells from LM-vaccinated WT and PKO mice were used in adoptive transfer assays to determine the contribution of perforin-dependent cytolysis in protective immunity to LM. Perforin deficiency resulted in an approximately 5-fold reduction in the per-cell protective capacity of Ag-specific memory CD8(+) T cells that was not caused by differences in memory cell quality as measured by CD62L/CD27 expression, TCR repertoire use, functional avidity, differences in expansion of Ag-specific cells upon infection, or maintenance of memory levels over time. However, perforin-deficient CD8(+) T cells exhibited reduced in vivo cytotoxic function compared to WT CD8(+) T cells. Consistent with the existence of perforin-independent effector pathways, double-vaccinated PKO mice were as resistant to challenge with LM as single-vaccinated WT mice. Thus, increasing the number of memory CD8(+) T cells can overcome diminished per-cell protective immunity in the absence of perforin.     

Reducing the stimulation of CD8+ T cells during infection with intracellular bacteria promotes differentiation primarily into a central (CD62LhighCD44high) subset

During infection with lymphocytic choriomeningitis virus, CD8(+) T cells differentiate rapidly into effectors (CD62L(low)CD44(high)) that differentiate further into the central memory phenotype (CD62L(high)CD44(high)) gradually. To evaluate whether this CD8(+) T cell differentiation program operates in all infection models, we evaluated CD8(+) T cell differentiation during infection of mice with recombinant intracellular bacteria, Listeria monocytogenes (LM) and Mycobacterium bovis (BCG), expressing OVA. We report that CD8(+) T cells primed during infection with the attenuated pathogen BCG-OVA differentiated primarily into the central subset that correlated to reduced attrition of the primed cells subsequently. CD8(+) T cells induced by LM-OVA also differentiated into central phenotype cells first, but the cells rapidly converted into effectors in contrast to BCG-OVA. Memory CD8(+) T cells induced by both LM-OVA as well as BCG-OVA were functional in that they produced cytokines and proliferated extensively in response to antigenic stimulation after adoptive transfer. During LM-OVA infection, if CD8(+) T cells were guided to compete for access to APCs, then they received reduced stimulation that was associated with increased differentiation into the central subset and reduced attrition subsequently. Similar effect was observed when CD8(+) T cells encountered APCs selectively during the waning phase of LM-OVA infection. Taken together, our results indicate that the potency of the pathogen can influence the differentiation and fate of CD8(+) T cells enormously, and the extent of attrition of primed CD8(+) T cells correlates inversely to the early differentiation of CD8(+) T cells primarily into the central CD8(+) T cell subset.     

CD4 T cell-dependent CD8 T cell maturation

We have investigated the contribution of CD4 T cells to the optimal priming of functionally robust memory CD8 T cell subsets. Intranasal infection of CD4 T cell-deficient (CD4(-/-)) mice with lymphocytic choriomeningitis virus resulted in the elaboration of virus-specific CD8 T cell responses that cleared the infection. However, by comparison with normal mice, the virus-specific CD8 T cells in CD4(-/-) mice were quantitatively and qualitatively different. In normal mice, lymphocytic choriomeningitis virus-specific memory CD8 T cells are CD44(high), many are CD122(high), and a majority of these cells regain expression of CD62L overtime. These cells produce IFN-gamma and TNF-alpha, and a subset also produces IL-2. In the absence of CD4 T cell help, a distinct subset of memory CD8 T cells develops that remains CD62L(low) up to 1 year after infection and exhibits a CD44(int)CD122(low) phenotype. These cells are qualitatively different from their counterparts in normal hosts, as their capacity to produce TNF-alpha and IL-2 is diminished. In addition, although CD4-independent CD8 T cells can contain the infection following secondary viral challenge, their ability to expand is impaired. These findings suggest that CD4 T cell responses not only contribute to the optimal priming of CD8 T cells in chronically infected hosts, but are also critical for the phenotypic and functional maturation of CD8 T cell responses to Ags that are more rapidly cleared. Moreover, these data imply that the development of CD62L(high) central memory CD8 T cells is arrested in the absence of CD4 T cell help.     

Kinetic and mechanistic requirements for helping CD8 T cells

The requirements for the generation of fully competent long-lived memory CD8 T cells and in particular the role and the mechanisms of help from CD4 T cells remain ill-defined. Memory CD8 T cells generated in the absence of CD4 T cell help often have an impaired recall proliferation and are thus unable to confer protection against certain pathogens. However, the timing and the mechanisms involved in the delivery of help are still unclear and differ between various experimental systems. In this study, we investigated the role of CD4 T help in generating memory CD8 T cells in a defined heterologous prime-boost system, consisting of priming with replication incompetent virus-like particles and challenge with recombinant vaccinia virus, both sharing only a common lymphocytic choriomeningitis virus-derived CD8 T cell epitope. We show in this system that delivery of help is only essential during the challenge phase for recall proliferation of memory CD8 T cells. Furthermore, we show that generation of proliferation-competent memory CD8 T cells is independent of CD40 and CCR5 and that in vivo IL-2 supplementation neither during priming nor during challenge was able to rescue recall proliferation of "unhelped" memory CD8 T cells.     

Loss of Anti-Viral Immunity by Infection with a Virus Encoding a Cross-Reactive Pathogenic Epitope

T cell cross-reactivity between different strains of the same virus, between different members of the same virus group, and even between unrelated viruses is a common occurrence. We questioned here how an intervening infection with a virus containing a sub-dominant cross-reactive T cell epitope would affect protective immunity to a previously encountered virus. Pichinde virus (PV) and lymphocytic choriomeningitis virus (LCMV) encode subdominant cross-reactive NP_205–212 CD8 T cell epitopes sharing 6 of 8 amino acids, differing only in the MHC anchoring regions. These pMHC epitopes induce cross-reactive but non-identical T cell receptor (TCR) repertoires, and structural studies showed that the differing anchoring amino acids altered the conformation of the MHC landscape presented to the TCR. PV-immune mice receiving an intervening infection with wild type but not NP205-mutant LCMV developed severe immunopathology in the form of acute fatty necrosis on re-challenge with PV, and this pathology could be predicted by the ratio of NP205-specific to the normally immunodominant PV NP_38–45 -specific T cells. Thus, cross-reactive epitopes can exert pathogenic properties that compromise protective immunity by impairing more protective T cell responses.     

CD4(+) T cells induced by a DNA vaccine: immunological consequences of epitope-specific lysosomal targeting

Our previous studies have shown that targeting DNA vaccine-encoded major histocompatibility complex class I epitopes to the proteasome enhanced CD8(+) T-cell induction and protection against lymphocytic choriomeningitis virus (LCMV) challenge. Here, we expand these studies to evaluate CD4(+) T-cell responses induced by DNA immunization and describe a system for targeting proteins and minigenes to lysosomes. Full-length proteins can be targeted to the lysosomal compartment by covalent attachment to the 20-amino-acid C-terminal tail of lysosomal integral membrane protein-II (LIMP-II). Using minigenes encoding defined T-helper epitopes from lymphocytic choriomeningitis virus, we show that the CD4(+) T-cell response induced by the NP(309-328) epitope of LCMV was greatly enhanced by addition of the LIMP-II tail. However, the immunological consequence of lysosomal targeting is not invariably positive; the CD4(+) T-cell response induced by the GP(61-80) epitope was almost abolished when attached to the LIMP-II tail. We identify the mechanism which underlies this marked difference in outcome. The GP(61-80) epitope is highly susceptible to cleavage by cathepsin D, an aspartic endopeptidase found almost exclusively in lysosomes. We show, using mass spectrometry, that the GP(61-80) peptide is cleaved between residues F(74) and K(75) and that this destroys its ability to stimulate virus-specific CD4(+) T cells. Thus, the immunological result of lysosomal targeting varies, depending upon the primary sequence of the encoded antigen. We analyze the effects of CD4(+) T-cell priming on the virus-specific antibody and CD8(+) T-cell responses which are mounted after virus infection and show that neither response appears to be accelerated or enhanced. Finally, we evaluate the protective benefits of CD4(+) T-cell vaccination in the LCMV model system; in contrast to DNA vaccine-induced CD8(+) T cells, which can confer solid protection against LCMV challenge, DNA vaccine-mediated priming of CD4(+) T cells does not appear to enhance the vaccinee's ability to combat viral challenge.     

Enhanced type 1 immunity after secondary viral challenge in mice primed as neonates

The goal of infant immunization against viral infection is to develop protective long term memory responses. Priming neonatal mice with a low dose of Cas-Br-E murine leukemia virus (Cas) results in adult-like, type 1 protective responses. However, other studies suggest that Ag priming of neonates leads to an increase in type 2 secondary responses even when primary responses were type 1. We assessed whether type 1 CD8+ T cell-mediated responses developed in murine neonates are maintained after secondary challenge with Cas in adulthood. Despite the induction of significant anti-viral CD8+-mediated cytotoxic T lymphocyte and IFN-gamma responses, initial neonatal priming led to a lower frequency of virus-specific T cells compared with adult priming. Adult frequencies were reached in mice primed as neonates only after secondary challenge in adulthood. A nonspecific and transient CD4+-mediated IL-4 response was present in all groups after secondary challenge with Cas or medium, indicating that this rise in type 2 cytokine production was not unique to mice that had been primed as neonates. Rather, type 1 anti-viral memory CD8+ T cell responses developed in neonatal mice are stable, protective, and enhanced after secondary challenge.     

Direct ex vivo kinetic and phenotypic analyses of CD8(+) T-cell responses induced by DNA immunization

CD8(+) T-cell responses can be induced by DNA immunization, but little is known about the kinetics of these responses in vivo in the absence of restimulation or how soon protective immunity is conferred by a DNA vaccine. It is also unclear if CD8(+) T cells primed by DNA vaccines express the vigorous effector functions characteristic of cells primed by natural infection or by immunization with a recombinant live virus vaccine. To address these issues, we have used the sensitive technique of intracellular cytokine staining to carry out direct ex vivo kinetic and phenotypic analyses of antigen-specific CD8(+) T cells present in the spleens of mice at various times after (i) a single intramuscular administration of a plasmid expressing the nucleoprotein (NP) gene from lymphocytic choriomeningitis virus (LCMV), (ii) infection by a recombinant vaccinia virus carrying the same protein (vvNP), or (iii) LCMV infection. In addition, we have evaluated the rapidity with which protective immunity against both lethal and sublethal LCMV infections is achieved following DNA vaccination. The CD8(+) T-cell response in DNA-vaccinated mice was slightly delayed compared to LCMV or vvNP vaccinees, peaking at 15 days postimmunization. Interestingly, the percentage of antigen-specific CD8(+) T cells present in the spleen at day 15 and later time points was similar to that observed following vvNP infection. T cells primed by DNA vaccination or by infection exhibited similar cytokine expression profiles and had similar avidities for an immunodominant cytotoxic T lymphocyte epitope peptide, implying that the responses induced by DNA vaccination differ quantitatively but not qualitatively from those induced by live virus infection. Surprisingly, protection from both lethal and sublethal LCMV infections was conferred within 1 week of DNA vaccination, well before the peak of the CD8(+) T-cell response.     

Normal establishment of virus-specific memory CD8 T cell pool following primary infection during pregnancy

Suppression of cell-mediated immunity has been proposed as a mechanism that promotes maternal tolerance of the fetus but also contributes to increased occurrence and severity of certain infections during pregnancy. Despite decades of research examining the effect of pregnancy on Ag-specific T cell responses, many questions remain. In particular, quantitative examination of memory CD8 T cell generation following infection during pregnancy remains largely unknown. To examine this issue, we evaluated the generation of protective immunity following infection during pregnancy with a nonpersistent strain of lymphocytic choriomeningitis virus (LCMV) in mice. The CD8 T cell response to LCMV occurred normally in pregnant mice compared with the nonpregnant cohort with rapid viral clearance in all tissues tested except for the placenta. Despite significant infiltration of CD8 T cells to the maternal-fetal interface, virus persisted in the placenta until delivery. Live pups were not infected and generated normal primary immune responses when challenged as adults. Memory CD8 T cell development in mice that were pregnant during primary infection was normal with regards to the proliferative capacity, number of Ag-specific cells, cytokine production upon re-stimulation, and the ability to protect from re-infection. These data suggest that virus-specific adaptive memory is normally generated in mice during pregnancy.