International clinical trials of HIV vaccines: II. phase I trial of an HIV-1 synthetic peptide vaccine evaluating an accelerated immunization schedule in Yunnan, China.

A Phase 1, double-blind, placebo controlled trial was conducted in Longchuan County, China, to evaluate the safety and immunogenicity of a prototype HIV-1 synthetic peptide vaccine in a target population at risk for HIV infection, and to establish the infrastructure for future large-scale HIV vaccine efficacy trials. Subjects were randomly assigned to receive 100 microg or 500 microg of vaccine or alum placebo, and were given three injections at an accelerated 0, 1, and 2 month schedule. The vaccine was well tolerated with no significant local or systemic reactions observed in any subjects. Fifty-five percent (100 microg dose) and 64% (500 microg dose) of subjects who received the vaccine produced binding antibody to the immunogen as determined by ELISA. However, HIV-1 (MN) neutralizing antibody was detected in only 23% (3/13) of subjects with detectable HIV-1 specific binding antibody. It was concluded that this prototype HIV-1 synthetic peptide vaccine was well tolerated, safe and immunogenic, and that a 0, 1, 2 month schedule was not as effective in stimulating HIV-1 specific neutralizing antibodies compared with previous trials utilizing a 0, 1, 6 month schedule. Finally, this trial demonstrated that well-designed HIV vaccine trials can be performed at this clinical trials site in Yunnan, China, and that this site should be considered for conducting larger safety, immunogenicity and efficacy trials of candidate HIV vaccines.

International clinical trials of HIV vaccines: I. Phase I trial of an HIV-1 synthetic peptide vaccine in Bangkok, Thailand.

A randomized, double blind, placebo controlled Phase I trial of a prototype human immunodeficiency virus type 1 (HIV-1) synthetic peptide vaccine was conducted in Bangkok, Thailand, to evaluate the safety and immunogenicity of the vaccine in a population of healthy adults at low risk for HIV infection, and to establish essential infrastructure for future HIV vaccine trials in Thailand. Thirty volunteers (25 males; 5 females) were recruited and randomized into 3 groups, receiving 3 intramuscular injections of either 100 micrograms vaccine (N = 12) or 500 micrograms vaccine (N = 12) or alum placebo (N = 6) on weeks 0, 4 and 25. The vaccine was well tolerated without any serious adverse effects. HIV-1 specific ELISA responses were detected in 20/24 subjects who received the vaccine, with V3 binding antibody titers ranging from 1:69 to 1:5,041. HIV-1 (MN) specific neutralizing antibody was detected in 19/20 of subjects with detectable HIV-1 specific binding antibody. Neutralization titers ranged from 1:14 to 1:1,294, which were less than titers observed in HIV-infected subjects. The results of this study indicate that the vaccine was well tolerated, and that the vaccine stimulated anti-HIV humoral immune responses in Thai subjects. The successful undertaking of this first HIV vaccine trial conducted in Thailand provided important preparatory information surrounding volunteer recruitment and motivations, and paves the way for future trials of HIV vaccines in Thailand.

Induction of immunologic memory in Gambian children by vaccination in infancy with a group A plus group C meningococcal polysaccharide-protein conjugate vaccine.

Two hundred twenty-one Gambian children vaccinated previously with one, two, or three doses of a meningococcal conjugate vaccine or two doses of polysaccharide vaccine before the age of 6 months were revaccinated at the age of 18-24 months with either meningococcal polysaccharide, conjugate, or inactivated polio vaccines. Children who had previously received one, two, or three doses of conjugate vaccine had significantly (P < .001) higher anti-group C meningococcal antibody levels following revaccination than did children vaccinated with a polysaccharide vaccine for the first time. Children vaccinated previously with two doses of polysaccharide vaccine had a lower group C antibody response than did control children. Group A antibody responses following revaccination of children who had previously received polysaccharide or conjugate vaccine were not significantly higher than those in control children. Thus, immunologic memory was probably induced by the group C but not by the group A component of the conjugate vaccine.

Safety and immunogenicity of UBI HIV-1MN octameric V3 peptide vaccine administered by subcutaneous injection.

Twenty-four HIV-seronegative men, at high risk of HIV infection, were recruited into a phase I/II safety and immunogenicity trial of a prototype HIV vaccine. The immunogen was a synthetic, monovalent, octameric HIV-1MN V3 peptide in an aluminum hydroxide (alum) adjuvant. The vaccine had been evaluated previously using a standard 0-, 1-, 6-month intramuscular schedule and was found to stimulate neutralizing antibody in 60-90% of volunteers. Participants were randomized to receive either 500 micrograms (n = 10; high dose) or 100 micrograms (n = 10; low dose) of immunogen or placebo (alum alone; n = 4) at 0, 1, and 6 months by subcutaneous injection. Responses to the immunogen were evaluated by enzyme-linked immunosorbent assay (ELISA)-detectable antibody and by proliferative responses. Safety was monitored by both clinical assessment and regular review with a clinical psychologist. No serious adverse experiences were observed following administration of the assigned medication. One individual (placebo) seroconverted while on study, following exposure to HIV. After the vaccination course only four individuals (three high dose and one low dose) had ELISA-detectable antibody against the immunogen. In the evaluable samples, from 19 volunteers, only 7 vaccine recipients (3 high dose and 4 low dose) had demonstrable lymphoproliferative responses to preparations of the immunogen. Subcutaneous administration of its candidate vaccine was safe but did not result in uniform or robust immunological responses.

A dose-ranging study of a prototype synthetic HIV-1MN V3 branched peptide vaccine. The National Institute of Allergy and Infectious Diseases AIDS Vaccine Evaluation Group.

A phase I double-blind trial was done to examine the safety and immunogenicity of a prototype synthetic human immunodeficiency virus type 1 MN strain (HIV-1MN) third variable region domain (V3) branched peptide vaccine in HIV-1-uninfected healthy adult volunteers. Subjects were randomly assigned to receive 20, 100, or 500 micrograms of vaccine or alum adjuvant control on days 0, 28, and 168. The vaccine was well-tolerated and appeared safe. Induction of binding antibody to V3 MN branched peptide was vaccine dose-related and was detectable in 9 of 10 subjects in the highest-vaccine-dose group. HIV-1MN-neutralizing antibody was detected after the third 500-micrograms dose in 8 of 10 subjects at the 90% neutralization end point. V3 MN peptide stimulated lymphocyte proliferation in 15 (75%) of 20 subjects after vaccination. In conclusion, this prototype vaccine was safe and it induced humoral and cell-mediated immune responses.

Diarrhoeal disease: current concepts and future challenges. Diarrhoeal disease and vaccine development.

Vaccination against diarrhoeal disease offers many opportunities to reduce significantly disease burden and childhood mortality from preventable disease world-wide. Regrettably, vaccine development has become an issue more of the development of the ultimate vaccine rather than the provision of a useful public health tool. The delay in implementing the delivery of vaccines with only 50% protective efficacy while awaiting the development of single dose vaccines that will provide lifelong immunity in more than 90% of recipients has resulted in no vaccine becoming available to those people who need it. Any alleviation of the disease burden would be of considerable benefit in an endemic region, to both the people and the governments, while researchers continue pursuing the ideal vaccine. The issues are discussed in this paper.

Effect of parenteral immunization on the intestinal immune response to Salmonella typhi Ty21a as measured using peripheral blood lymphocytes.

The effects of parenteral administration of a killed typhoid vaccine on the intestinal immune response to live orally administered Salmonella typhi Ty21a in human subjects was assessed using an assay of in vitro specific antibody production by circulating peripheral blood lymphocytes (PBL). Previous priming with the parenterally administered vaccine had no effect on secondary immune responses to a live oral vaccine in humans with this response not differing in magnitude or duration from that following the primary oral vaccination course (p = 0.38). Following the primary PBL anti-LPS IgA response to an oral course of live vaccine in all subjects (6/6), boosting with a single oral dose of live vaccine resulted in 0/6 responders, while 2/11 subjects responded after a single dose of parenteral vaccine. No additional responses were evident after the second parenterally administered booster dose. PBL IgG and IgM responses were also demonstrated following oral vaccination, with 1/6 and 2/6 subjects parenterally vaccinated demonstrating IgM PBL responses after the first and second vaccination respectively. This study confirmed that parenteral vaccination did not impair the PBL IgA immune response to a secondary course of live orally administered organisms, and that multiple parenteral booster doses did not induce primary or secondary recirculation of antigen-specific PBL.

Indirect measurement of intestinal immune responses to an orally administered attenuated bacterial vaccine.

Intestinal fluid, saliva, circulating peripheral blood lymphocytes (PBL), and serum samples obtained from 81 human adult subjects who had been orally vaccinated with either Salmonella typhi Ty21a or one of its recombinant derivatives were examined to determine the value of indirect measurements of an antigen-specific intestinal-immunoglobulin A (IgA) response. Salivary IgA failed to provide consistent or correlative responses, and no evidence of a significant relationship was apparent with the intestinal-IgA responses. No significant correlation between the specific increase in responses in serum IgA and intestinal IgA was evident. While the magnitude of the serum IgG response significantly correlated with the intestinal-IgA response (P = 0.00064), it failed to detect 14.8% of the intestinal-IgA responses. The observation that 16.6% of the subjects had delayed serum IgA responses, with a peak occurring after day 23 compared with days 12 to 14, may have contributed to the inadequacy of the serum IgA response as a correlative indicator. The serum IgG responses in these subjects were also of a diminished magnitude. Specific IgA production by circulating PBL was found to be the most sensitive (92.6% response rate) and correlative (P = 0.00071) indicator of a specific intestinal-IgA immune response. However, its value in predicting protective efficacy is untried. These studies confirm that for the assessment of an enteric bacterial vaccine, determination of in vitro specific IgA production by circulating PBL may offer a single measurement of specific immunity which is as useful as serum and intestinal measurements combined.

Effect of parenteral immunization on the intestinal immune response to Salmonella typhi Ty21a.

The effects of parenteral administration of a killed typhoid vaccine on the intestinal immune response to live orally administered Salmonella typhi Ty21a in human subjects was evaluated. Priming with parenteral vaccination neither enhanced nor suppressed the subsequent specific serum and intestinal immunoglobulin A (IgA) immune responses to a booster course of live oral vaccine. Neither a single oral dose of live vaccine nor a single dose of parenteral vaccine had any measurable booster effect on the observed primary intestinal IgA response to the live oral vaccine. Two booster doses of subcutaneously administered killed typhoid vaccine did result in a significant increase in the specific intestinal IgA antibody in those subjects primed with the oral live vaccine. This response was comparable in magnitude to the primary intestinal response. No evidence of this response could be found in serum IgA, although nonsignificant rises in serum IgG were evident. Previous parenteral priming had no effect on secondary immune responses to a live oral vaccine in humans. Serum immune responses were generally found to be of little value as indicators of local intestinal immunity. This study confirmed that parenteral vaccination was only able to induce an intestinal immune response following priming with live, orally administered organisms and that multiple parenteral booster doses were necessary to induce a measurable effect on intestinal immune responses.

Effects of sample processing on the measurement of specific intestinal IgA immune responses.

The effects of techniques commonly used in the collection and processing of human intestinal fluid on the specific secretory immunoglobulin A (sIgA) response following oral immunization with the live typhoid vaccine Salmonella typhi Ty21a were examined. It was observed that the failure to adjust specific intestinal anti-typhoid lipopolysaccharide IgA antibody titres for total secretory IgA resulted in a false-negative detection rate of 19.8% and a false-positive detection rate of 7.4%. Furthermore, these specific responses were significantly diminished if the intestinal fluid was subjected to heat inactivation to reduce intestinal protease activity (p = 0.0083), but were not affected if stored at -70 degrees C for up to 1 year, without heat inactivation. It was concluded that in the processing of the intestinal fluid samples for specific sIgA determination heat inactivation significantly reduced specific sIgA titres, and that the failure to adjust absolute titres for total sIgA content resulted in a significant false-negative detection rate.

In vivo evidence of immunological masking of the Vibrio cholerae O antigen of a hybrid Salmonella typhi Ty21a-Vibrio cholerae oral vaccine in humans.

The immunogenicity of the live oral hybrid vaccine organism Salmonella typhi Ty21a/V. cholerae Inaba (EX210) following its growth in media containing variable concentrations of supplemental galactose was examined in human volunteer subjects. The local intestinal IgA-specific antibody responses to both typhoid and cholera lipopolysaccharide (LPS) preparations were determined. It was observed that the immunogenicity of the galactose-independent Vibrio cholerae O antigen in vivo was dependent upon the variation in galactose-dependent long chain S. typhi O antigen production which was directly proportional to the media galactose concentration. It is likely that this observation was a result of steric hindrance of the presentation of the V. cholerae O antigen by S. typhi Ty21a in the presence of the longer, immunodominant S. typhi Ty21a O antigen. This observation may have relevance to the use of S. typhi vectors in vaccine development involving the presentation of LPS-associated heterologous antigens.

Specific immune response in the human respiratory tract following oral immunization with live typhoid vaccine.

Specific antibody responses in the lower respiratory tract of human subjects to orally administered Salmonella typhi Ty21a are reported. These responses, predominantly of the immunoglobulin G class, were determined to be a transudate from serum. These results were supported by the similarity in responses to parenteral administration of heat-killed typhoid vaccine. Specific immunoglobulin A antibody was a poor contributor to the respiratory antibody response to either vaccine.

The human humoral immune response to Salmonella typhi Ty21a.

The short-term kinetics and the effects of different dose regimens and formulations on the humoral immune response induced in human subjects by the live attenuated typhoid vaccine Salmonella typhi Ty21a were examined. Antibody responses in jejunal fluid and serum and by specific antibody production in vitro by peripheral blood lymphocytes to S. typhi lipopolysaccharide were determined. A short vaccination schedule of three doses of 10(11) live organisms over 5 days induced significantly greater intestinal IgA antityphoid antibody responses than did two comparable doses 21 days apart. The humoral immune response was dose dependent with 10(10) and 10(11) live organisms stimulating greater intestinal immune responses than did 10(11) killed organisms. No responses were evident with either 10(9) viable organisms or with an enteric-coated preparation. In the continued development and assessment of oral typhoid vaccines, the effects of different doses and formulations and the timing of sampling on the humoral immune response should be considered.

Lymphocyte activation as measured by interleukin-2 receptor expression to gluten fraction 111 in coeliac disease.

Lymphocyte activation was examined by interleukin-2 (IL-2) receptor expression on peripheral blood mononuclear cells from coeliac and control subjects. Purified T cells were incubated with gluten fraction 111 (a known toxic peptide for coeliac subjects), soyabean hydrolysate (an unrelated hydrolysed food antigen), and Concanavalin-A (Con-A, a non-specific mitogen). After 1-5 days incubation, expression of IL-2 receptors was assessed using a cellular enzyme-linked immunosorbent assay (ELISA). Gluten fraction 111 induced expression of IL-2 receptors on T lymphocytes from coeliac but not from normal subjects (P = 0.0005), whereas soyabean hydrolysate did not induce IL-2 receptor expression. Lymphocytes from both coeliac and normal subjects had similar increased IL-2 receptor expression after incubation with Con-A. Flow cytometry was also used to confirm specific expression of IL-2 receptor expression of lymphocytes from coeliac subjects. Interleukin-2 receptor expression increased from 0 to 5.4% of cultured mononuclear cells after 7 days incubation with gluten fraction III. These cells were CD3-positive and CD4-positive. We conclude that peripheral blood lymphocytes from coeliac subjects are sensitized specifically to gluten fraction III.