Vaccine-Elicited Mucosal and Systemic Antibody Responses Are Associated with Reduced Simian Immunodeficiency Viremia in Infant Rhesus Macaques.

UNLABELLED: Despite significant progress in reducing peripartum mother-to-child transmission (MTCT) of human immunodeficiency virus (HIV) with antiretroviral therapy (ART), continued access to ART throughout the breastfeeding period is still a limiting factor, and breast milk exposure to HIV accounts for up to 44% of MTCT. As abstinence from breastfeeding is not recommended, alternative means are needed to prevent MTCT of HIV. We have previously shown that oral vaccination at birth with live attenuated Mycobacterium tuberculosis strains expressing simian immunodeficiency virus (SIV) genes safely induces persistent SIV-specific cellular and humoral immune responses both systemically and at the oral and intestinal mucosa. Here, we tested the ability of oral M. tuberculosis vaccine strains expressing SIV Env and Gag proteins, followed by systemic heterologous (MVA-SIV Env/Gag/Pol) boosting, to protect neonatal macaques against oral SIV challenge. While vaccination did not protect infant macaques against oral SIV acquisition, a subset of immunized animals had significantly lower peak viremia which inversely correlated with prechallenge SIV Env-specific salivary and intestinal IgA responses and higher-avidity SIV Env-specific IgG in plasma. These controller animals also maintained CD4(+) T cell populations better and showed reduced tissue pathology compared to noncontroller animals. We show that infants vaccinated at birth can develop vaccine-induced SIV-specific IgA and IgG antibodies and cellular immune responses within weeks of life. Our data further suggest that affinity maturation of vaccine-induced plasma antibodies and induction of mucosal IgA responses at potential SIV entry sites are associated with better control of viral replication, thereby likely reducing SIV morbidity. IMPORTANCE: Despite significant progress in reducing peripartum MTCT of HIV with ART, continued access to ART throughout the breastfeeding period is still a limiting factor. Breast milk exposure to HIV accounts for up to 44% of MTCT. Alternative measures, in addition to ART, are needed to achieve the goal of an AIDS-free generation. Pediatric HIV vaccines constitute a core component of such efforts. The results of our pediatric vaccine study highlight the potential importance of vaccine-elicited mucosal Env-specific IgA responses in combination with high-avidity systemic Env-specific IgG in protection against oral SIV transmission and control of viral replication in infant macaques. The induction of potent mucosal IgA antibodies by our vaccine is remarkable considering the age-dependent development of mucosal IgA responses postbirth. A deeper understanding of postnatal immune development may inform the design of improved vaccine strategies to enhance systemic and mucosal SIV/HIV antibody responses.

Protective T cell immunity against respiratory syncytial virus is efficiently induced by recombinant BCG.

Respiratory syncytial virus (RSV) is one of the leading causes of childhood hospitalization and a major health burden worldwide. Unfortunately, because of an inefficient immunological memory, RSV infection provides limited immune protection against reinfection. Furthermore, RSV can induce an inadequate Th2-type immune response that causes severe respiratory tract inflammation and obstruction. It is thought that effective RSV clearance requires the induction of balanced Th1-type immunity, involving the activation of IFN-gamma-secreting cytotoxic T cells. A recognized inducer of Th1 immunity is Mycobacterium bovis bacillus Calmette-Guérin (BCG), which has been used in newborns for decades in several countries as a tuberculosis vaccine. Here, we show that immunization with recombinant BCG strains expressing RSV antigens promotes protective Th1-type immunity against RSV in mice. Activation of RSV-specific T cells producing IFN-gamma and IL-2 was efficiently obtained after immunization with recombinant BCG. This type of T cell immunity was protective against RSV challenge and caused a significant reduction of inflammatory cell infiltration in the airways. Furthermore, mice immunized with recombinant BCG showed no weight loss and reduced lung viral loads. These data strongly support recombinant BCG as an efficient vaccine against RSV because of its capacity to promote protective Th1 immunity.

Child care-associated outbreak of Escherichia coli O157:H7 and hemolytic uremic syndrome.

We present an outbreak of E. coli O157:H7 diarrhea in an urban child care center. Eleven of 45 attendees with diarrhea had positive tests (stool culture or shiga-like toxin assay) for E. coli O157:H7. Two of these 11 (18%) progressed to hemolytic uremic syndrome. Diarrheal illness in child care centers should be considered a public health risk. Staff education, hand washing, and cohorting or exclusion of attendees with diarrhea must be performed to help control infectious outbreaks.

Balancing Trained Immunity with Persistent Immune Activation and the Risk of Simian Immunodeficiency Virus Infection in Infant Macaques Vaccinated with Attenuated Mycobacterium tuberculosis or Mycobacterium bovis BCG Vaccine.

Our goal is to develop a pediatric combination vaccine to protect the vulnerable infant population against human immunodeficiency virus type 1 (HIV-1) and tuberculosis (TB) infections. The vaccine consists of an auxotroph Mycobacterium tuberculosis strain that coexpresses HIV antigens. Utilizing an infant rhesus macaque model, we have previously shown that this attenuated M. tuberculosis (AMtb)-simian immunodeficiency virus (SIV) vaccine is immunogenic, and although the vaccine did not prevent oral SIV infection, a subset of vaccinated animals was able to partially control virus replication. However, unexpectedly, vaccinated infants required fewer SIV exposures to become infected compared to naive controls. Considering that the current TB vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), can induce potent innate immune responses and confer pathogen-unspecific trained immunity, we hypothesized that an imbalance between enhanced myeloid cell function and immune activation might have influenced the outcome of oral SIV challenge in AMtb-SIV-vaccinated infants. To address this question, we used archived samples from unchallenged animals from our previous AMtb-SIV vaccine studies and vaccinated additional infant macaques with BCG or AMtb only. Our results show that vaccinated infants, regardless of vaccine strain or regimen, had enhanced myeloid cell responses. However, CD4+ T cells were concurrently activated, and the persistence of these activated target cells in oral and/or gastrointestinal tissues may have facilitated oral SIV infection. Immune activation was more pronounced in BCG-vaccinated infant macaques than in AMtb-vaccinated infant macaques, indicating a role for vaccine attenuation. These findings underline the importance of understanding the interplay of vaccine-induced immunity and immune activation and its effect on HIV acquisition risk and outcome in infants.

Partial treatment interruption of protease inhibitors augments HIV-specific immune responses in vertically infected pediatric patients.

BACKGROUND: Although highly active antiretroviral therapy has significantly reduced morbidity and mortality in HIV-infected children, it often fails to completely suppress viral replication, thereby allowing the emergence of drug-resistant variants. Protease inhibitor (PI) based therapy has been hypothesized to depress cell-mediated immune responses by reducing antigen presentation. OBJECTIVES: To determine the effects of partial treatment interruption (PTI) of PI on HIV-specific cellular immune responses in children. METHODS: We conducted a retrospective longitudinal study of HIV-specific cellular immune responses in 13 children who were vertically infected with HIV. All had detectable plasma viremia and had undergone PTI for a median of 1.0 year (range, 0.41-3.35 years) while continuing nucleoside reverse transcriptase inhibitor and non-nucleoside reverse transcriptase inhibitor therapy. RESULTS: No significant changes in viral load were observed in the immediate time-point before and during PTI (P = 0.84) as well as in the overall period before and during PTI (P = 0.17). CD4 T-cell levels declined slowly immediately before and during PTI (P = 0.07) as well as during the overall PTI period (P = 0.0002), but the rate of CD4 T-cell decline was not significantly increased during PTI. Immediate to PTI, HIV-specific CD4 and CD8 T-cell responses increased by 70% (P < 0.0001) and 92% (P < 0.0001), respectively, and CD4 and CD8 T-cell activation levels (P = 0.6834 and P = 0.6081, respectively) remained unchanged. CONCLUSION: HIV-specific cellular immune responses are boosted in children who have interrupted PI-based therapy.

Baylisascaris procyonis and Herpes Simplex Virus 2 Coinfection Presenting as Ocular Larva Migrans with Granuloma Formation in a Child.

Ocular Baylisascaris procyonis infection results from ingestion of infective eggs of B. procyonis, the raccoon ascarid. Herpes simplex virus type 2 (HSV-2) infection of the retina is the result of either primary infection or reactivated disease. Herein, we report a case of a 12-year-old female resident of the Bronx in New York City, who presented with pan-uveitis and vision loss. Initial evaluation for etiologic causes was nondiagnostic. Serology for anti-Baylisascaris procyonis antibodies in serum and vitreous fluid were both positive. Polymerase chain reaction (PCR) of vitreous fluid was positive for HSV-2. Treatment with vitrectomy, albendazole, and acyclovir resulted in mild improvement of visual acuity. The atypical presentation of B. procyonis in this case, as ocular larva migrans with a peripheral granuloma and retinal detachment, underscores the importance of maintaining a high degree of suspicion for this pathogen even in non-diffuse unilateral subacute neuroretinitis (DUSN) patients in urban areas. This case further illustrates that it is possible to have coexisting infections in cases of posterior uveitis.

Mucosal DNA vaccination with highly attenuated Shigella is superior to attenuated Salmonella and comparable to intramuscular DNA vaccination for T cells against HIV.

An immunization strategy using attenuated bacteria to deliver DNA vaccine plasmids to mucosal sites may induce protective T cell responses against sexual HIV transmission. In a murine intranasal (i.n.) immunization model, we demonstrate that transiently persistent Deltaasd Shigella flexneri strain 15D harboring DNA vaccines induces HIV- and SIV-specific gamma interferon (IFN-gamma) producing CD8+ T cells among splenocytes more efficiently than either a longer persisting DeltaaroD Salmonella typhimurium strain SL7207 or transiently persistent S. typhi strain Ty21a harboring DNA vaccines. Also, the frequency of antigen-specific gamma interferon (IFN-gamma) producing cells induced by Shigella 15D harboring a DNA vaccine were comparable to that induced by intramuscular (i.m.) immunization with purified DNA vaccine. Moreover, the magnitude of mucosal and systemic antigen-specific IgA and IgG responses after immunization were dependent upon the route (i.m. vs. i.n.) of inoculation, with i.n. Shigella 15D DNA vaccines generating higher levels of HIV-specific IgA in vaginal washings than i.m. purified DNA vaccine. Deltaasd S. flexneri is a promising vector for mucosal DNA vaccine immunization against HIV.

Mycobacterium bovis versus Mycobacterium tuberculosis as a cause of acute cervical lymphadenitis without pulmonary disease.

Bovine tuberculosis remains a common disease of cattle in countries such as Mexico. Children eating unpasteurized dairy products from Mexican cattle can develop Mycobacterium bovis cervical lymphadenitis. However, the bovine mycobacterium can be misdiagnosed as Mycobacterium tuberculosis based on standard laboratory testing. Accurate speciation is important for selection of the preferred antibiotic regimen for treatment of Mycobacterium bovis infection.

Nontyphoidal salmonella bacteremia and pneumonia as the initial manifestation of human immunodeficiency virus infection in a four-year-old child.

This report describes the case of a 4-year-old human immunodeficiency virus (HIV)-infected girl with Salmonella typhimurium bacteremia and pneumonia. The girl presented with a history of fever for 1 month and mild pulmonary symptoms. Subsequent studies revealed previously undiagnosed HIV disease.

A neonatal oral Mycobacterium tuberculosis-SIV prime / intramuscular MVA-SIV boost combination vaccine induces both SIV and Mtb-specific immune responses in infant macaques.

Mother-to-child-transmission of HIV by breast-feeding remains a major obstacle in the eradication of HIV infection. Compared to adults, HIV-infected infants have more rapid disease and show higher susceptibility to co-infections like tuberculosis (TB). Although the Bacille Calmette-Guérin vaccine can be administered at birth to protect against TB, BCG can disseminate in HIV-infected infants and increase mortality. Thus, a pediatric combination vaccine to stop both HIV and TB infection in infants is urgently needed. Towards the goal of developing a pediatric combination HIV-TB vaccine to prevent both oral HIV acquisition by breast-feeding and TB infection, we tested and optimized an immunization regimen using a novel live attenuated Mycobacterium tuberculosis vaccine engineered to express simian immunodeficiency (SIV) antigens followed by heterologous MVA-SIV boosting in the infant macaque model. A single oral dose of the attenuated Mtb-SIV vaccine strain mc26435 during the first week of life was sufficient to induce persistent TB-specific immune responses. SIV-specific immunity was induced at low but comparable magnitudes after oral or intradermal priming, and was enhanced following MVA-SIV boosts. T cell responses were most pronounced in intestinal tissues and oral lymph nodes. Importantly, in addition to plasma SIV-specific IgG and IgA antibodies, infant macaques developed mucosal SIV-specific IgA in saliva and intestinal IgA and IgG. While future SIV and Mtb challenge studies will be needed to determine the protective efficacy of the Mtb-SIV / MVA-SIV vaccine, infants at high risk for oral HIV acquisition by breast-feeding and TB infection could profoundly benefit from an effective combination vaccine.

Association of differentiation state of CD4+ T cells and disease progression in HIV-1 perinatally infected children.

BACKGROUND: In the USA, most HIV-1 infected children are on antiretroviral drug regimens, with many individuals surviving through adolescence and into adulthood. The course of HIV-1 infection in these children is variable, and understudied. METHODOLOGY/PRINCIPAL FINDINGS: We determined whether qualitative differences in immune cell subsets could explain a slower disease course in long term survivors with no evidence of immune suppression (LTS-NS; CD4%≥25%) compared to those with severe immune suppression (LTS-SS; CD4%≤15%). Subjects in the LTS-NS group had significantly higher frequencies of naïve (CCR7+CD45RA+) and central memory (CCR7+CD45RA-) CD4+ T cells compared to LTS-SS subjects (p = 0.0005 and <0.0001, respectively). Subjects in the rapid progressing group had significantly higher levels of CD4+ T(EMRA) (CCR7-CD45RA+) cells compared to slow progressing subjects (p<0.0001). CONCLUSIONS/SIGNIFICANCE: Rapid disease progression in vertical infection is associated with significantly higher levels of CD4+ T(EMRA) (CCR7-CD45RA+) cells.

A recombinant attenuated Mycobacterium tuberculosis vaccine strain is safe in immunosuppressed simian immunodeficiency virus-infected infant macaques.

Many resource-poor countries are faced with concurrent epidemics of AIDS and tuberculosis (TB) caused by human immunodeficiency virus (HIV) and Mycobacterium tuberculosis, respectively. Dual infections with HIV and M. tuberculosis are especially severe in infants. There is, however, no effective HIV vaccine, and the only licensed TB vaccine, the Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine, can cause disseminated mycobacterial disease in HIV-infected children. Thus, a pediatric vaccine to prevent HIV and M. tuberculosis infections is urgently needed. We hypothesized that a highly attenuated M. tuberculosis strain containing HIV antigens could be safely administered at birth and induce mucosal and systemic immune responses to protect against HIV and TB infections, and we rationalized that vaccine safety could be most rigorously assessed in immunocompromised hosts. Of three vaccine candidates tested, the recombinant attenuated M. tuberculosis strain mc(2)6435 carrying a simian immunodeficiency virus (SIV) Gag expression plasmid and harboring attenuations of genes critical for replication (panCD and leuCD) and immune evasion (secA2), was found to be safe for oral or intradermal administration to non-SIV-infected and SIV-infected infant macaques. Safety was defined as the absence of clinical symptoms, a lack of histopathological changes indicative of M. tuberculosis infection, and a lack of mycobacterial dissemination. These data represent an important step in the development of novel TB vaccines and suggest that a combination recombinant attenuated M. tuberculosis-HIV vaccine could be a safe alternative to BCG for the pediatric population as a whole and, more importantly, for the extreme at-risk group of HIV-infected infants.

Immunodominance of HIV-1 specific CD8+ T-cell responses is related to disease progression rate in vertically infected adolescents.

BACKGROUND: HIV-1 vertically infected children in the USA are living into adolescence and beyond with the widespread use of antiretroviral drugs. These patients exhibit striking differences in the rate of HIV-1 disease progression which could provide insights into mechanisms of control. We hypothesized that differences in the pattern of immunodomination including breadth, magnitude and polyfunctionality of HIV-1 specific CD8+ T cell response could partially explain differences in progression rate. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we mapped, quantified, and assessed the functionality of these responses against individual HIV-1 Gag peptides in 58 HIV-1 vertically infected adolescents. Subjects were divided into two groups depending upon the rate of disease progression: adolescents with a sustained CD4%≥25 were categorized as having no immune suppression (NS), and those with CD4%≤15 categorized as having severe immune suppression (SS). We observed differences in the area of HIV-1-Gag to which the two groups made responses. In addition, subjects who expressed the HLA- B*57 or B*42 alleles were highly likely to restrict their immunodominant response through these alleles. There was a significantly higher frequency of naïve CD8+ T cells in the NS subjects (p = 0.0066) compared to the SS subjects. In contrast, there were no statistically significant differences in any other CD8+ T cell subsets. The differentiation profiles and multifunctionality of Gag-specific CD8+ T cells, regardless of immunodominance, also failed to demonstrate meaningful differences between the two groups. CONCLUSIONS/SIGNIFICANCE: Together, these data suggest that, at least in vertically infected adolescents, the region of HIV-1-Gag targeted by CD8+ T cells and the magnitude of that response relative to other responses may have more importance on the rate of disease progression than their qualitative effector functions.

Recombinant pro-apoptotic Mycobacterium tuberculosis generates CD8+ T cell responses against human immunodeficiency virus type 1 Env and M. tuberculosis in neonatal mice.

Mycobacterium bovis BCG is an attractive vaccine vector against breast milk HIV transmission because it elicits Th1-type responses in newborns. However, BCG causes disease in HIV-infected infants. Genetically attenuated Mycobacterium tuberculosis (Mtb) mutants represent a safer alternative for immunocompromised populations. In the current study, we compared the immunogenicity in mice of three different recombinant attenuated Mtb strains expressing an HIV envelope (Env) antigen construct. Two of these strains (DeltalysA DeltapanCD Mtb and DeltaRD1 DeltapanCD Mtb) failed to induce significant levels of HIV Env-specific CD8(+) T cell responses. In striking contrast, an HIV-1 Env-expressing attenuated DeltalysA Mtb containing a deletion in secA2, which encodes a virulence-related secretion system involved in evading adaptive immunity, generated consistently measurable Env-specific CD8(+) T cell responses that were significantly greater than those observed after immunization with BCG expressing HIV Env. Similarly, another strain of DeltalysA DeltasecA2 Mtb expressing SIV Gag induced Gag- and Mtb-specific CD8(+) T cells producing perforin or IFNgamma, and Gag-specific CD4(+) T cells producing IFNgamma within 3 weeks after immunization in adult mice; in addition, IFNgamma-producing Gag-specific CD8(+) T cells and Mtb-specific CD4(+) T cells were observed in neonatal mice within 1 week of immunization. We conclude that DeltalysA DeltasecA2 Mtb is a promising vaccine platform to construct a safe combination HIV-TB vaccine for use in neonates.

Genetic alteration of Mycobacterium smegmatis to improve mycobacterium-mediated transfer of plasmid DNA into mammalian cells and DNA immunization.

Mycobacteria target and persist within phagocytic monocytes and are strong adjuvants, making them attractive candidate vectors for DNA vaccines. We characterized the ability of mycobacteria to deliver transgenes to mammalian cells and the effects of various bacterial chromosomal mutations on the efficiency of transfer in vivo and in vitro. First, we observed green fluorescent protein expression via microscopy and fluorescence-activated cell sorting analysis after infection of phagocytic and nonphagocytic cell lines by Mycobacterium smegmatis or M. bovis BCG harboring a plasmid encoding the fluorescence gene under the control of a eukaryotic promoter. Next, we compared the efficiencies of gene transfer using M. smegmatis or BCG containing chromosomal insertions or deletions that cause early lysis, hyperconjugation, or an increased plasmid copy number. We observed a significant-albeit only 1.7-fold-increase in the level of plasmid transfer to eukaryotic cells infected with M. smegmatis hyperconjugation mutants. M. smegmatis strains that overexpressed replication proteins (Rep) of pAL5000, a plasmid whose replicon is incorporated in many mycobacterial constructs, generated a 10-fold increase in plasmid copy number and 3.5-fold and 3-fold increases in gene transfer efficiency to HeLa cells and J774 cells, respectively. Although BCG strains overexpressing Rep could not be recovered, BCG harboring a plasmid with a copy-up mutation in oriM resulted in a threefold increase in gene transfer to J774 cells. Moreover, M. smegmatis strains overexpressing Rep enhanced gene transfer in vivo compared with a wild-type control. Immunization of mice with mycobacteria harboring a plasmid (pgp120(h)(E)) encoding human immunodeficiency virus gp120 elicited gp120-specific CD8 T-cell responses among splenocytes and peripheral blood mononuclear cells that were up to twofold (P < 0.05) and threefold (P < 0.001) higher, respectively, in strains supporting higher copy numbers. The magnitude of these responses was approximately one-half of that observed after intramuscular immunization with pgp120(h)(E). M. smegmatis and other nonpathogenic mycobacteria are promising candidate vectors for DNA vaccine delivery.

Natural killer cells in perinatally HIV-1-infected children exhibit less degranulation compared to HIV-1-exposed uninfected children and their expression of KIR2DL3, NKG2C, and NKp46 correlates with disease severity.

NK cells play an integral role in the innate immune response by targeting virally infected and transformed cells with direct killing and providing help to adaptive responses through cytokine secretion. Whereas recent studies have focused on NK cells in HIV-1-infected adults, the role of NK cells in perinatally HIV-1-infected children is less studied. Using multiparametric flow cytometric analysis, we assessed the number, phenotype, and function of NK cell subsets in the peripheral blood of perinatally HIV-1-infected children on highly active antiretroviral therapy and compared them to perinatally exposed but uninfected children. We observed an increased frequency of NK cells expressing inhibitory killer Ig-like receptors in infected children. This difference existed despite comparable levels of total NK cells and NK cell subpopulations between the two groups. Additionally, NK cell subsets from infected children expressed, with and without stimulation, significantly lower levels of the degranulation marker CD107, which correlates with NK cell cytotoxicity. Lastly, increased expression of KIR2DL3, NKG2C, and NKp46 on NK cells correlated with decreased CD4+ T-lymphocyte percentage, an indicator of disease severity in HIV-1- infected children. Taken together, these results show that HIV-1-infected children retain a large population of cytotoxically dysfunctional NK cells relative to perinatally exposed uninfected children. This reduced function appears concurrently with distinct NK cell surface receptor expression and is associated with a loss of CD4+ T cells. This finding suggests that NK cells may have an important role in HIV-1 disease pathogenesis in HIV-1-infected children.

Partial treatment interruption of protease inhibitor-based highly active antiretroviral therapy regimens in HIV-infected children.

Treatment guidelines for HIV-infected children recommend using combinations of reverse transcriptase inhibitors (RTIs) and protease inhibitors (PIs). Successful suppression of HIV replication and adherence to these regimens are often suboptimal because of multiple factors. For patients with detectable viremia and limited treatment options, therapy simplification consisting of RTIs, referred to as partial treatment interruption (PTI), may represent a temporizing option. We describe a cohort of 26 HIV-infected children who underwent treatment simplification by discontinuing the PI and continuing therapy with 2 or more RTIs. The subjects, who were identified retrospectively, were followed for a period of 24 to 96 weeks. Data collected included clinical information, viral load, and CD4T lymphocyte percentage (CD4%) at baseline and 24, 48, and 96 weeks after PTI. Twenty-six, 21, and 11 patients were evaluated at 24, 48, and 96 weeks, respectively. No child had Centers for Disease Control and Prevention-defined disease progression, and there were no significant changes in viral loads (P > 0.5) across all study intervals after interruption of the PIs. Although most children maintained a CD4% > 15%, comparisons of CD4% at 24 and 48 weeks demonstrated a statistically significant decrease compared with baseline. Therapy simplification by PTI may provide a practical option in patients intolerant of or failing PI-based highly active antiretroviral therapy.

Generation of CD8+ T-cell responses by a recombinant nonpathogenic Mycobacterium smegmatis vaccine vector expressing human immunodeficiency virus type 1 Env.

Because the vaccine vectors currently being evaluated in human populations all have significant limitations in their immunogenicity, novel vaccine strategies are needed for the elicitation of cell-mediated immunity. The nonpathogenic, rapidly growing mycobacterium Mycobacterium smegmatis was engineered as a vector expressing full-length human immunodeficiency virus type 1 (HIV-1) HXBc2 envelope protein. Immunization of mice with recombinant M. smegmatis led to the expansion of major histocompatibility complex class I-restricted HIV-1 epitope-specific CD8(+) T cells that were cytolytic and secreted gamma interferon. Effector and memory T lymphocytes were elicited, and repeated immunization generated a stable central memory pool of virus-specific cells. Importantly, preexisting immunity to Mycobacterium bovis BCG had only a marginal effect on the immunogenicity of recombinant M. smegmatis. This mycobacterium may therefore be a useful vaccine vector.

Mucosal immunization with attenuated Shigella flexneri harboring an influenza hemagglutinin DNA vaccine protects mice against a lethal influenza challenge.

Mucosal surfaces are important for the induction of immunity against influenza virus. In a murine intranasal immunization model, we demonstrated that the attenuated Shigella flexneri Deltaasd strain 15D, carrying a DNA construct encoding the influenza virus hemagglutinin (HA), induces protective immunity against a lethal respiratory challenge with influenza A/WSN/33. Influenza virus-specific IFN-gamma T cells were detected among splenocytes, and anti-HA IgG was detected in serum post-immunization, albeit at low levels. Following influenza virus challenge, an accelerated anti-HA IgA antibody response was detected in bronchoalveolar lavage (BAL) washings from mice vaccinated with attenuated shigella containing the HA construct. These results suggest that S. flexneri Deltaasd strain 15D is a promising vector for mucosal DNA vaccine immunization against influenza virus and other mucosal pathogens.