Lymphocyte response to tetanus toxin T-cell epitopes: effects of tetanus vaccination and concurrent malaria prophylaxis

Synthesized T-cell epitopes of tetanus toxin are universally immunogenic and serve to enhance immune response when they are used as vaccine carriers of B-cell epitopes. The immunogenicity of the P2, P30, and P2P30 T-cell epitopes of tetanus toxin and whole tetanus toxoid (TT) was evaluated by in vitro proliferation assay of lymphocytes from men with no history of tetanus vaccination who were enrolled in a malaria prophylaxis trial. The enhancement of immune response by tetanus vaccination (Td) and possible antagonism by the antimalarial drugs, was measured by pre- and post-Td comparisons within and between immunized prophylaxis groups (primaquine, chloroquine, placebo) and a nonimmunized control group. Constructs demonstrated low immunogenicity relative to TT in all groups. Relative to both control and its own baseline, the immunized primaquine prophylaxis group was distinct in demonstrating significantly increased proliferation against all three subunits and at both high (30 microg ml(-1)) and low (3 microg ml(-1)) concentrations. Immunization elicited significantly increased proliferation responses by placebo and chloroquine prophylaxis groups against only the P2P30 construct. Despite these significant post-Td changes, a low concentration of TT 0.1 microg ml(-1)) stimulated proliferation 7-10 times over that induced by the greatest concentration of the constructs.

Phase I/IIa safety, immunogenicity, and efficacy trial of NYVAC-Pf7, a pox-vectored, multiantigen, multistage vaccine candidate for Plasmodium falciparum malaria

Candidate malaria vaccines have failed to elicit consistently protective immune responses against challenge with Plasmodium falciparum. NYVAC-Pf7, a highly attenuated vaccinia virus with 7 P. falciparum genes inserted into its genome, was tested in a phase I/IIa safety, immunogenicity, and efficacy vaccine trial in human volunteers. Malaria genes inserted into the NYVAC genome encoded proteins from all stages of the parasite's life cycle. Volunteers received three immunizations of two different dosages of NYVAC-Pf7. The vaccine was safe and well tolerated but variably immunogenic. While antibody responses were generally poor, cellular immune responses were detected in >90% of the volunteers. Of the 35 volunteers challenged with the bite of 5 P. falciparum-infected Anopheles mosquitoes, 1 was completely protected, and there was a significant delay in time to parasite patency in the groups of volunteers who received either the low or high dose of vaccine compared with control volunteers.

Humoral immune response to tetanus-diphtheria vaccine given during extended use of chloroquine or primaquine malaria chemoprophylaxis

Immune suppression resulting from prolonged chemoprophylaxis and potential drug-vaccine interaction were investigated within the context of a randomized placebo-controlled trial that compared daily primaquine or weekly chloroquine administration for malaria prevention. After 11 months of prophylaxis, adult male subjects received a tetanus-diphtheria (Td) vaccination. Prophylaxis continued 4 weeks longer. Anti-tetanus and anti-diphtheria antibody levels were measured by ELISA at baseline and at 1, 3, 7, and 14 months after Td vaccination. All groups were comparable at baseline. Immunization triggered significant increases in anti-tetanus and anti-diphtheria IgG levels over each group's pre-Td baseline levels and those of an unvaccinated control group. Geometric mean anti-tetanus titers (GMTs) in the primaquine group were significantly higher than those of the placebo group at 1, 3, and 14 months. Anti-tetanus GMTs in placebo and chloroquine groups declined over 14 months to levels comparable to those of unvaccinated controls, but levels in the primaquine group remained significantly higher than in controls.

Immunogenicity of Plasmodium falciparum circumsporozoite protein multiple antigen peptide vaccine formulated with different adjuvants

Only low antibody levels were obtained from vaccinating human volunteers with single-chain peptide from the Plasmodium falciparum circumsporozoite protein (PfCSP). This resulted in modest protection against sporozoite challenge. In addition, HLA restriction limits the probability of synthesis of a vaccine effective for a diverse population. We report immunization studies with a multiple antigen peptide (MAP) system consisting of multiple copies of a B-cell epitope from the central repeat region of the PfCSP in combination with a universal T-cell epitope, the P2P30 portion of tetanus toxin. This MAP4(NANP)6P2P30 vaccine was highly immunogenic in four different strains of mice when used with various safe and nontoxic adjuvants. When this MAP vaccine was encapsulated in liposomes with lipid A and adsorbed to aluminium hydroxide and given three times at 4-week intervals, the resultant antibody prevented 100% of sporozoites from invading and developing into liver stage infection. This high degree of immunogenicity of MAP4(NANP)6P2P30 vaccine formulated in liposomes, lipid A and aluminum hydroxide provides the foundation for consideration of human trials with this formulation.

Lymphocyte response to tetanus toxoid among Indonesian men immunized with tetanus-diphtheria during extended chloroquine or primaquine prophylaxis

Immune suppression, a potential side effect of long-term chemoprophylaxis, was evaluated as part of a randomized, placebo-controlled trial that compared daily primaquine against weekly chloroquine for malaria prevention. In the last month of the year-long trial, baseline in vitro lymphoproliferative responses to tetanus toxoid were measured, and a tetanus-diphtheria (Td) immunization was administered. Proliferative responses to tetanus toxoid in each Td-immunized group increased significantly over pre-Td baselines and those of the unvaccinated control. Highest initial responses were measured in the primaquine group. The proportion of responders and the magnitude of proliferation was consistently low in the chloroquine group, and end point responses in this group were significantly below those of the placebo. These results suggest that the development and duration of the cellular response to tetanus immunization was impaired by long-term weekly chloroquine prophylaxis, while daily primaquine prophylaxis over the same time period had no inhibitory effect.

Clinical manifestations of Plasmodium falciparum malaria experimentally induced by mosquito challenge

To determine the characteristics of clinical illness accompanying Plasmodium falciparum infection induced by controlled exposure to infected mosquitoes, records of 118 volunteers participating in studies conducted between 1985 and 1992 were reviewed. One hundred fourteen volunteers (97%) reported at least one symptom attributable to malaria, with fatigue, myalgias or arthralgias, headache, and chills most commonly reported. The median duration of symptoms was 3 days. Fever was recorded in 61% of volunteers; 4 volunteers had temperatures >40 degrees C. Neutropenia and thrombocytopenia were present in 9% and 12% of volunteers, respectively. Despite counts as low as 658/microL (neutrophils) or 73,000/microL (platelets), no secondary infectious or hemorrhagic complications occurred. In all cases, volunteers recovered completely and laboratory values returned to baseline after specific antimalarial therapy. Recrudescence did not occur in any volunteer. In this model, mosquito inoculation of P. falciparum is a reliable, safe, and well-tolerated method of experimental challenge.

Quantitative bacteriology of tonsils removed from children with tonsillitis hypertrophy and recurrent tonsillitis with and without hypertrophy

The aerobic and anaerobic bacterial species and their numbers were studied in tonsillar specimens from children who had undergone elective tonsillectomy: 6 patients with recurrent tonsillitis (RT), 9 with recurrent tonsillitis with hypertrophy (RTH), and 8 with obstructive tonsillar hypertrophy (OTH). Mixed flora were present in all tonsils, yielding an average of 6.7 isolates (5.6 aerobic or facultative and 1.1 anaerobic bacteria). The highest recovery rate of organisms per tonsil was in patients with OTH (7.7 per tonsil), compared to 6.3 per tonsil in RT and 5.9 per tonsil in RTH. The predominant aerobic and facultative organisms were Haemophilus influenzae (22 isolates), Neisseria sp (16), Staphylococcus aureus (14), and Eikenella corrodens (14), and the predominant anaerobic bacteria were Fusobacterium sp (8), Bacteroides sp (7), and Prevotella melaninogenica (5). The number of bacteria per gram of tonsillar tissue varied between 10(4) and 10(8). A higher concentration of S aureus and H influenzae was found in hypertrophic tonsils (RTH and OTH) as compared to RT. These findings suggest the presence of an increased bacterial load and supports an etiologic role for H influenzae and S aureus in hypertrophic tonsils with and without inflammation (RTH and OTH). Further studies to elucidate the effect of selective antimicrobial therapy directed at these organisms may offer an alternative management of hypertrophic tonsils.