Gregor Lawrence

Immunity to malaria after administration of ultra-low doses of red cells infected with Plasmodium falciparum

BACKGROUND The ability of T cells, acting independently of antibodies, to control malaria parasite growth in people has not been defined. If such was shown to be effective, an additional vaccine strategy could be pursued. Our aim was to ascertain whether or not development of cell-mediated immunity to Plasmodium falciparum blood-stage infection could be induced in human beings by exposure to malaria parasites in very low density. METHODS We enrolled five volunteers from the staff at our research institute who had never had malaria. We used a cryopreserved inoculum of red cells infected with P falciparum strain 3D7 to give them repeated subclinical infections of malaria that we then cured early with drugs, to induce cell-mediated immune responses. We tested for development of immunity by measurement of parasite concentrations in the blood of volunteers by PCR of the multicopy gene STEVOR and by following up the volunteers clinically, and by measuring antibody and cellular immune responses to the parasite. FINDINGS After challenge and a extended period without drug cure, volunteers were protected against malaria as indicated by absence of parasites or parasite DNA in the blood, and absence of clinical symptoms. Immunity was characterised by absence of detectable antibodies that bind the parasite or infected red cells, but by the presence of a proliferative T-cell response, involving CD4+ and CD8+ T cells, a cytokine response, consisting of interferon gamma but not interleukin 4 or interleukin 10, induction of high concentrations of nitric oxide synthase activity in peripheral blood mononuclear cells, and a drop in the number of peripheral natural killer T cells. INTERPRETATION People can be protected against the erythrocytic stage of malaria by a strong cell-mediated immune response, in the absence of detectable parasite-specific antibodies, suggesting an additional strategy for development of a malaria vaccine

Human phase I vaccine trials of 3 recombinant asexual stage malaria antigens with Montanide ISA720 adjuvant

Two phase I vaccine trials were conducted to test the immunogenicity and safety of a vaccine containing three recombinant malaria antigens from the asexual stage of Plasmodium falciparum. The three antigens are a fragment of MSP1 (190LCS.T3); MSP2 and a portion of RESA and were formulated in Montanide ISA720 adjuvant. These trials investigated the dose response of each antigen for eliciting both antibody and T-cell responses and the immunogenicity of a mixture of the antigens compared with the antigens injected separately. All three antigens elicited both antibody and T-cell responses. Strong T-cell responses were observed with 190LCS.T3 and RESA with stimulation indices exceeding 100 for peripheral blood leucocytes in some individuals. The antibody responses were generally weak. The human antibody responses observed with MSP2 in Montanide ISA720 were not significantly different from those obtained in an earlier trial which used MSP2 with alum as the adjuvant. No antigenic competition was observed: volunteers receiving a mixture of antigens had similar responses to those receiving the three antigens at separate sites. Tenderness and pain at the injection site were common over the first few days following immunization. In some volunteers, especially those receiving the highest doses tested, there was a delayed reaction at the injection site with pain and swelling occurring approximately 10 days after injection.

Effect of vaccination with 3 recombinant asexual-stage malaria antigens on initial growth rates of Plasmodium falciparum in non-immune volunteers.

A placebo controlled, randomised, double blind trial was conducted in human volunteers to test a mixture of three recombinant Plasmodium falciparum blood stage antigens for its ability to reduce the initial growth rates of parasites. The vaccine contained recombinant MSP2 (3D7 allele), a portion of MSP1 (190LCS.T3) and part of the RESA antigen (C terminal 771 amino acids) in the Montanide ISA 720 adjuvant (SEPPIC). Twelve volunteers received two doses of the vaccine, 6 weeks apart. The five participants in the placebo group received an equivalent volume of the adjuvant emulsion using the same schedule. Antibody responses were low, as has been reported in earlier studies with this combination, while T cell responses were stronger. All the volunteers were challenged with approximately 140 ring infected red cells of the 3D7 cloned line, 4 weeks after the second dose. Parasitaemia was determined once daily from day 4 using a sensitive and quantitative PCR assay. All the volunteers were infected and were treated on day 8, before any developed symptoms. There was no significant difference in initial parasite growth rates between the verum and placebo groups, nor was there any significant correlation between parasite growth rates and any of the measured immunological responses. These results suggest that the formulation tested in this trial did not generate immune responses that were strong enough to reduce parasite growth in naive volunteers.

PATHOGENESIS OF NEONATAL NECROTISING ENTEROCOLITIS

Neonatal necrotising enterocolitis (NEC) mostly affects the small premature infant in a neonatal intensive care unit (NICU). It is proposed that, because of physical isolation, the cleanliness of nursing procedures, and, in some cases, antibiotic treatment, the normal bacterial colonisation of infants in NICUs may be delayed. In such babies, colonised with one or a few species, the organisms multiply in the gut, unhindered by competitors. The immature gut takes up macromolecules intact, especially in the lower ileum, and toxic products from the growing bacteria may be absorbed and cause mucosal damage, initiating NEC. Thus, NEC may be a result of the NICU environment.

Phase I trial in humans of an oil-based adjuvant SEPPIC MONTANIDE ISA 720

Seppic MONTANIDE ISA 720 is a metabolizable oil adjuvant that has given good results in animals with recombinant malarial antigens. Twelve human volunteers were given increasing intramuscular doses of MONTANIDE ISA 720, ranging from 0.6 to 1.8 ml. The adjuvant was well tolerated with only minor local effects, including tenderness, local swelling and discomfort on use. MONTANIDE ISA 720 may prove to be an acceptable and effective adjuvant for use in people.

PREVENTION OF NECROTISING ENTERITIS IN PAPUA NEW GUINEA BY ACTIVE IMMUNISATION

Necrotising enteritis (pig-bel) caused by Clostridium welchii type C is a major cause of illness and death in the Highlands of Papua New Guinea. In a controlled trial of active immunisation with a clostridial toxoid prepared from type-C cultures the incidence of pig-bel in over 2500 immunised children within 24 months of immunisation was less than an eighth of that in a control group. Necrotising enteritis in Papua New Guinea is now a preventable disease.

Impact of active immunisation against enteritis necroticans in Papua New Guinea

Enteritis necroticans, known locally as pigbel, has been a major cause of illness and death among children in the highlands of Papua New Guinea. After a successful trial of active immunisation against the beta toxin of the causative organism, Clostridium perfringens type C, immunisation of children was begun in 1980. The effects of the immunisation programme on pigbel admissions in 3 of the 5 major highland hospitals were assessed. In each of the centres studied the proportion of admissions due to enteritis necroticans dropped significantly after immunisation was introduced (p less than 0.001) and hospital admissions for pigbel in 1984-86, when immunisation was well established, were less than one fifth of previous figures.

Autosomal recessive inheritance of susceptibility to tinea imbricata.

Familial distribution of chronic tinea imbricata in an untreated Melanesian population was consistent with a genetic predisposition to this disease. The pattern suggested that susceptibility to chronic Trichophyton concentricum infection is recessively inherited and controlled by genes at a single autosomal locus. In married couples there was no concordance of the disease above that expected by chance and the observed segregation of tinea imbricata accorded well with that predicted by the genetic hypothesis.

Control of group C meningococcal disease in Australian Aboriginal children by mass rifampicin chemoprophylaxis and vaccination

An outbreak of 12 cases of meningitis, 11 caused by Neisseria meningitidis serogroup C, occurred at Doomadgee from September, 1990, to April, 1991. The incidence of meningitis was 17.55/10(3) person-years. Only children aged 1-10 years were affected. In October, 1990, or shortly thereafter, 473/509 children aged between 1 and 15 years inclusive had one dose of Mencevax AC. From the time of vaccination until April, 1991, a further eight cases occurred, six in vaccinated children. Vaccine efficacy in 1-15 year olds was calculated as 77%. Despite this, in April, 1991, the prevalence of antibody to group C polysaccharide in vaccinated children (78%) was not significantly different from that in unvaccinated children and adults. 46 nonresponders were revaccinated, and, in February, 1992, 78% had antibodies to group C polysaccharide. In April, 1991, an estimated 3.0% of the population had group C organisms, carriage being directly related to household crowding. In June, 1991, 2 months after mass prophylaxis with rifampicin, none of these individuals were carriers. In October, 1991, the carriage rate of group C organisms was 0.64%. There have been no further cases caused by the epidemic strain. Although uncrowded housing is a basic need, mass chemoprophylaxis and two doses of vaccine for children should be used in similar outbreaks.

Experimental human Plasmodium falciparum infections: Longitudinal analysis of lymphocyte responses with particular reference to gamma delta T cells

The kinetics of the γδ T‐cell response was analysed in the context of the overall haematological response in subjects experimentally infected with sporozoites of Plasmodium falciparum. Numbers of γδ and αβ T cells and NK cells declined markedly during infection to reach minimum values 12–13 days post‐infection when the patients were ill. This decline commenced from the beginning of the erythrocytic cycle and well before parasites could be detected microscopically and clinical symptoms developed. Platelet numbers also declined. In vivo activation of γδ T cells was evident with sequential up‐regulation of the activation markers CD69 and HLA‐DR. γδ T cell numbers were highest after treatment with the majority being CD4−CD8−, HLA‐DR+ and showing reduced CD45RA expression. Contrary to some published observations γδ T‐cell percentages remained within the normal range. Little evidence of up‐regulation of activation or memory markers was observed in the αβ T‐cell population. In vitro proliferative responses to malaria antigen which involve γδ T cells were lost as the infection progressed and the lymphocyte count declined but these could be restored with the addition of exogenous IL‐2 to cultures. The authors findings are consistent with a protective and/or immunomodulatory role for γδ T cells in malaria.