A murine model for the study of immune memory in response to pneumococcal conjugate vaccination

We developed a murine model for assessment of immunological memory and antibody-induced protection to nasopharyngeal (NP) challenges. BALB/c female mice (n = 10 mice per study parameter) were immunized with two priming doses of the licensed 7-valent pneumococcal (Pnc) conjugate vaccine and immune responses [antibody immunoglobulin G (IgG) levels, avidity and opsonophagocytic activity] were monitored for 26 weeks until IgG levels decreased to nearly baseline. A booster dose of either 2 microg conjugate or 5 microg polysaccharide vaccine was given at week 26. The ability of these two treatments to recall immune memory established by the conjugate vaccine was determined for types 4 and 14 for up to 63 days post-booster. The ability of challenge with pneumococcal type 14 to recall the immune response was also evaluated, as well as, the number of antibody secreting cells (ASC) specific to polysaccharide (Ps) 4, 6B, and 14. A higher dose of conjugate vaccine (2 microg) was necessary to elicit a significant increase in IgG levels after priming with one dose. Priming with lower doses (0.5 and 1.0 microg) only elicited modest increases in IgG levels. Recall of the immune response was found with either conjugate or Ps vaccines. NP challenge with type 14 at week 26 did not recall the immune response, although reduction in NP Pnc load was seen post-primary immunization at 5, 10 and 26 weeks. ASCs were detected in response to either conjugate or Ps booster doses. This model allows for the screening and determination of potential alternative vaccination regimens and the study of immunological markers of memory following Pnc vaccination.

Evaluation of synthetic, M type-specific peptides as antigens in a multivalent group A streptococcal vaccine

The recent development of emm gene sequence-based typing methodology has allowed group A streptococci (GAS) M serotype prevalence data to be determined. This information has been used to identify the components of a multivalent M protein peptide vaccine that could theoretically prevent most of the GAS-mediated diseases in the USA. In this study, we have evaluated in mice the immunogenicity and protective ability of multiple synthetic, M type-specific peptides, derived from the N-termini of three prevalent GAS serotypes (three peptides per serotype, total of nine peptides). At least one peptide, representing each of the three M types tested, was immunogenic. Five of the nine synthetic peptides tested, elicited an immune response in mice, and sera raised against four of the peptides, all possessed functional activity as demonstrated in a bactericidal assay. In vivo nasopharyngeal challenge experiments were carried out with peptides from the M1 (peptide M1-3) and M3 (peptide M3-2) proteins induced in vivo immune protection by reducing intranasal carriage. Reduction in colonization for M1-3 and M3-2 was 90% (P=0.02) and 66% (P<0.17), respectively. A reduction in colonization of 67% (P=0.03) was observed for M3-2 immunized mice when M43, a heterologous serotype, was used as the challenge strain. These results show the utility of synthetic, M type-specific peptides as antigens in a multivalent GAS vaccine.

Intranasal immunization of mice with a mixture of the pneumococcal proteins PsaA and PspA is highly protective against nasopharyngeal carriage of Streptococcus pneumoniae

Acquisition of pneumococci is generally from carriers rather than from infected individuals. Therefore, to induce herd immunity against Streptococcus pneumoniae it will be necessary to elicit protection against carriage. Capsular polysaccharide-protein conjugates, PspA, and PsaA are known to elicit some protection against nasopharyngeal carriage of pneumococci but do not always completely eliminate carriage. In this study, we observed that PsaA elicited better protection than did PspA against carriage. Pneumolysin elicited no protection against carriage. Immunization with a mixture of PsaA and PspA elicited the best protection against carriage. These results indicate that PspA and PsaA may be useful for the elicitation of herd immunity in humans. As PspA and pneumolysin are known to elicit immunity to bacteremia and pneumonia, their inclusion in a mucosal vaccine may enable such a vaccine to prevent invasive disease as well as carriage.

Confirmation of psaA in all 90 serotypes of Streptococcus pneumoniae by PCR and potential of this assay for identification and diagnosis

The gene encoding the pneumococcal surface adhesin A (PsaA) protein, psaA, was confirmed in all Streptococcus pneumoniae serotypes by a newly developed PCR (psaA PCR) assay. Eighty-nine of the 90 serotypes amplified produced an 838-bp fragment; the exception was a serotype 16F strain acquired from the American Type Culture Collection (ATCC). Analysis of 20 additional 16F strains from the United States and Brazil showed that the gene was amplified in all 16F strains, implying that the serotype 16F ATCC strain must be a variant. The specificity of the assay was verified by the lack of signal from analysis of heterologous bacterial species (n = 30) and genera (n = 14), including viridans group streptococci. The potential of the assay for clinical application was shown by its ability to detect pneumococci in culture-positive nasopharyngeal specimens. Demonstration of psaA in all 90 serotypes and lack of amplification of heterologous organisms suggest that this assay could be a useful tool for detection of pneumococci and diagnosis of disease.

Correlation of opsonophagocytosis and passive protection assays using human anticapsular antibodies in an infant mouse model of bacteremia for Streptococcus pneumoniae

An infant mouse assay system for assessment of protective concentrations of human serum pneumococcal anticapsular antibodies is described. Passive immunization of anticapsular antibodies was evaluated for protection of infant mice challenged with Streptococcus pneumoniae serotypes 1, 4, 5, 6B, 18C, and 23A, with bacteremia as an end point. Protection was defined as no detectable bacteremia in 70% of mice 48 h after challenge. Type-specific anticapsular concentrations required for protection varied with serotype (</=0.05 to >0.4 microg/mL). Across serotypes, there was no significant correlation between human IgG concentration in mouse serum and protection from bacteremia or between IgG concentration and opsonophagocytic titer. Significant correlation (r=.84, P<.001) was observed between opsonophagocytic titer of human IgG antibody in mouse sera and protection from bacteremia. Thus, protective concentrations of anticapsular antibodies against bacteremia are serotype dependent. Opsonophagocytosis is a better predictor of in vivo protective capacity of pneumococcal anticapsular antibodies than are ELISA IgG antibody concentrations.

Adhesion of tumour-infiltrating lymphocytes to endothelium: a phenotypic and functional analysis

Efficacy of cancer immunotherapy with cultured tumour-infiltrating lymphocytes (TILs) depends upon infused TILs migrating into tumour-bearing tissue, in which they mediate an anti-tumour response. For TILs to enter a tumour, they must first bind to tumour endothelium, and this process depends on TILs expressing and regulating the function of relevant cell-surface receptors. We analysed the cell-surface phenotype and endothelial binding of TILs cultured from human melanoma and compared them with peripheral blood T cells and with allostimulated T cells cultured under similar conditions. Compared with peripheral blood T cells, TILs expressed high levels of five integrins, two other adhesion molecules, including the skin homing molecule CLA, and several activation markers and showed markedly enhanced integrin-mediated adhesion to a dermal microvascular endothelial cell line in vitro. Compared with the allostimulated T cells, TILs expressed higher levels of the cutaneous lymphocyte antigen (CLA), the adhesion molecule CD31 and the activation markers CD30 and CD69, but lower levels of several other adhesion and activation molecules. These phenotypic and functional properties of TILs should have complex effects on their migration in vivo. Expression of CLA, the skin homing receptor, may increase migration to melanoma (a skin cancer), whereas integrin activation may cause non-specific binding of TILs to other endothelium. Manipulation of the culture conditions in which TILs are expanded might result in a phenotype that is more conducive to selective tumour homing in vivo.

Down-regulation of interleukin-2 receptor expression on natural killer cells/large granular lymphocytes by interleukin-4

It has recently been demonstrated that IL-4 inhibits IL-2 receptor expression on T cells. Studies have also shown that IL-4 can inhibit IL-2-induced natural killer cell (NK) cytotoxicity, and that IL-4 in combination with IL-2 and large granular lymphocyte (NK/LGL) cells suppresses Ig synthesis. Therefore, we examine whether IL-2 receptor expression on NK/LGL cells is affected with or without IL-4, using fluorescent receptor analysis. Our results demonstrate that IL-4 inhibits/down-regulates the expression of IL-2 receptors on either phytohemagglutinin or IL-2-stimulated NK/LGL cells.

Suppression of human immunoglobulin synthesis by interleukin-4 in tandem with interleukin-2 through large granular lymphocytes

Recent studies have shown that interleukin (IL)-4 can affect secretion of immunoglobulins (Igs) or activation of cytotoxic cells by IL-2, while other studies have shown that natural killer (NK) cells/large granular lymphocytes (LGLs) can also affect Ig synthesis. Therefore, we examined the effect of IL-4 with and without IL-2 or human NK/LGLs on pokeweed mitogen (PWM)-stimulated production of IgM and IgG. We found that when IL-4 and/or IL-2 were incubated with peripheral blood lymphocytes and PWM for 7 days and an enzyme-linked immunosorbent assay was run to measure Ig synthesis, IL-4 with IL-2 caused a greater suppression of Ig synthesis than either cytokine alone. A further experiment was done to determine the effect IL-4 and IL-2 would have on LGL suppression of Ig synthesis. IL-4 and IL-2 alone and in combination, when added to LGL, caused the LGL to suppress Ig synthesis to a greater extent than alone. We conclude that IL-4 acts on NK/LGLs separately and jointly with IL-2, to suppress Ig synthesis (IgM and IgG).

Studies of adenovirus subtypes and down-regulation of HLA class I expression: correlations to natural-killer-mediated cytolysis

Natural killer cell (NK) cytotoxicity historically has been accepted to be unrelated to major histocompatibility complex (MHC) expression. However, recent studies have indicated that a decrease in MHC antigen expression leads to a concomitant increase in NK cytotoxicity. We have, therefore, studied the alteration of HLA class I expression by 6 types of adenovirus in the human cell line HEp-2. We conclude that for the 6 types of adenovirus tested, HLA class I expression and NK cytotoxicity are not interrelated.

Acute megakaryocytic leukemia. Flow cytometric analysis of DNA content at diagnosis and during the course of therapy

Flow cytometry (FCM) for the determination of DNA content and cell cycle analysis was performed on multiple bone marrows from a case of acute megakaryocytic leukemia in a 71-year-old woman. Two aneuploid (multiploid) peaks were present at diagnosis. This multiploidy was a stable characteristic when studied temporally. The disappearance of the peaks in the bone marrow specimens directly correlated with complete remission morphologically. These findings further support the concept of FCM as an adjunct to morphologic study in identifying residual tumor burden.

Heterogeneity of human peripheral blood mononuclear cells detected by monoclonal antibodies to monomorphic determinants of human Ia antigens

The reactivity patterns of several monoclonal antibodies specific for monomorphic determinants of human Ia antigens were studied using flow cytometric techniques. We observed differential reactivity of these antibodies with human lymphoid cell lines, normal fresh human mononuclear cells, and lymphoblasts from PHA-activated cultures. The molecular heterogeneity of Ia antigens previously identified with immunochemical techniques was accompanied by heterogeneity of cell surface expression as identified by an immunofluorescent probe. The determinants identified by these anti-Ia monoclonal antibodies may provide useful markers in the isolation of cellular subpopulations responsive in the immune system.