Safety and immunogenicity of a three-component blood-stage malaria vaccine in adults living in an endemic area of Papua New Guinea

A Phase I safety and immunogenicity study with a three-component blood-stage malaria vaccine was conducted in adult male subjects living in an endemic area of Papua New Guinea. The preparations were recombinant proteins which corresponded to parts of the two merozoite surface proteins of Plasmodium falciparum (MSP1 and 2), and of the ring-infected erythrocyte surface antigen (RESA). The three proteins were emulsified with the adjuvant Montanide ISA720. Ten subjects were injected twice (four weeks apart) with the vaccine formulation and two with the adjuvant alone. Mild pain at the site of injection was reported by about half of the subjects but no systemic reaction related to the formulation occurred. There was a sharp rise in geometric mean stimulation index after the second dose compared to baseline for MSP1 and RESA, while the rise was small for MSP2. Geometric mean antibody titres increased for MSP1 during the study, whereas they hardly changed for MSP2 and RESA. The vaccine formulation was safe when used in an already immune population. The vaccine induced good cellular responses, especially for MSP1 and RESA. Boosting of humoral responses was weak, probably because of high baseline antibody levels.

Isoniazid plus sulphadoxine-pyrimethamine can reduce morbidity of HIV-positive patients treated for tuberculosis in Africa: a controlled clinical trial

An annual 20% excess mortality rate is observed in HIV-seropositive patients after treatment for tuberculosis. An affordable secondary prophylaxis against main opportunistic diseases is needed, i.e. against tuberculosis, toxoplasmosis, pneumocystosis and other infections occurring in this target population. This open prospective randomized study assessed morbidity and mortality in 2 cohorts of HIV-seropositive patients having recently recovered from pulmonary tuberculosis: 134 patients assigned to prophylactic treatment with isoniazid (INH, 300 mg once daily) plus sulphadoxine-pyrimethamine (S, 500 mg/P, 25 mg once weekly), and 129 were controls, comparable for sex, age, weight and HIV-serology. Patients were followed-up for up to 2 years: 192 person-years (PY) in the prophylaxis group and 142 PY in the control group. Four patients developed tuberculosis and 20 patients died in the prophylaxis group, compared to 10 and 23 controls, respectively. Sick days were reported by 22 patients in the prophylaxis group and by 77 patients in the control group. This prophylaxis was associated with a moderate decrease of mortality (log rank test: p = 0.1736), a significant decrease of tuberculosis incidence (log rank test: p = 0. 0234), a highly significant reduction of adverse events and sick days, and a prevention of wasting (p = 0.008) and anaemia (p = 0. 045). No death from toxoplasmosis occurred in the prophylaxis group as compared to 2 possible cases among controls; toxoplasmosis IgG levels declined in treated patients, but increased in controls (p = 0.01). There was no adverse drug reaction due to SP (10,006 doses) or to INH. Compliance with SP intake was good, but moderate as with INH intake. We conclude that a secondary prophylaxis with INH+SP represents a cost-effective measure to improve health conditions of HIV-infected adults in Côte d'Ivoire, following a full treatment course against tuberculosis.

Mefloquine-sulphadoxine-pyrimethamine (Fansimef, Roche) in the prophylaxis of Plasmodium falciparum malaria: a double-blind, comparative, placebo-controlled study

From July 1987 to June 1988 a randomized, double-blind, comparative placebo-controlled field trial was conducted in a group of villages near Ibadan, Nigeria. The aim of the study was to assess the suppressive tolerability and efficacy of four antimalarials (Fansimef, Lariam, Fansidar, chloroquine) given for 24 weeks. Fansimef and Lariam were given with loading and maintenance doses, Fansidar and chloroquine as one tablet per week for 24 weeks. Of 567 enrolled subjects, 114 (20%) had parasitaemia on entry. Eight episodes of symptomatic falciparum malaria occurred during the trial, seven in the placebo group, and one in the Fansimef group. Compared with placebo, parasitaemia was effectively suppressed by all four drug regimens. Adverse event data were not significantly different between groups: six adverse events per 114 participants in the Fansimef group, six/113 in the mefloquine group, five/111 in the Fansidar group, 17/115 in the chloroquine group and eight/114 in the placebo group. Safety of Fansimef for 24 weeks in endemic areas was comparable for standard antimalarials in this trial and provides support for the use of this drug for the treatment of resistant malaria in indigenous African populations.

Evaluation of 5.1-[NANP]19, a recombinant Plasmodium falciparum vaccine candidate, in adults

In a randomized single-blind study, 13 healthy adult volunteers were subcutaneously immunized with 2 or 3 single 50 or 400 micrograms doses of a Plasmodium falciparum recombinant vaccine candidate designated 5.1-[NANP]19. The vaccine caused transitory reactions at the injection site. Eight (62%) volunteers had a greater than or equal to 4-fold increase of antibody titer against sporozoites in immunofluorescence assay, all 13 seroconverted in IgG enzyme-linked immunosorbent assay against [NANP]50 antigen, and in 6 (46%) a lymphocyte proliferation index greater than or equal to 3 against 5.1 antigen was observed. Seven volunteers were challenged with mosquitoes infected with P. falciparum. All developed detectable parasitemia after 7 to 12 days and all received drug therapy within 24 hours. One volunteer with a cellular response to 5.1 had two negative in vitro parasite cultures before treatment, despite overt parasitemia. He was the only challenged volunteer who remained free of malaria symptoms.

Blockade of physiologically secreted IFN-gamma inhibits human T lymphocyte and natural killer cell activation

The role of physiologically secreted human IFN-gamma in T lymphocyte and NK cell activation has been probed with a panel of mouse mAb directed against various epitopes of the human IFN-gamma molecule, or human IFN-gamma R. Addition to the culture medium of those mAb that neutralize the antiviral activity of IFN-gamma or interact with its receptor inhibited proliferative and cytotoxic responses elicited in PBL by HLA alloantigens, anti-CD3 mAb, and IL-2, but not the proliferative response to PHA. The IFN-gamma blockade also inhibited IFN-gamma, IL-2, and TNF-alpha release during MLC. Kinetic experiments showed that reduction of proliferative and cytotoxic responses to HLA alloantigens is maximal when IFN-gamma is blocked within the first 48 h. Exogenous rIFN-gamma restored the proliferative response only when added at the beginning. Moreover, when IFN-gamma was blocked, T lymphocytes recovered from 6-day MLC displayed a profound decrease in their expression of p55 and p75 chains of the IL-2R, as well as in the number of high-affinity IL-2 binding sites. These findings strongly suggest that IFN-gamma is required in the early phases of induction of the oligo- and polyclonal proliferative and cytotoxic responses of lymphocytes.

Blockade of physiologically secreted IFN-gamma inhibits human T lymphocyte and natural killer cell activation

The role of physiologically secreted human IFN-gamma in T lymphocyte and NK cell activation has been probed with a panel of mouse mAb directed against various epitopes of the human IFN-gamma molecule, or human IFN-gamma R. Addition to the culture medium of those mAb that neutralize the antiviral activity of IFN-gamma or interact with its receptor inhibited proliferative and cytotoxic responses elicited in PBL by HLA alloantigens, anti-CD3 mAb, and IL-2, but not the proliferative response to PHA. The IFN-gamma blockade also inhibited IFN-gamma, IL-2, and TNF-alpha release during MLC. Kinetic experiments showed that reduction of proliferative and cytotoxic responses to HLA alloantigens is maximal when IFN-gamma is blocked within the first 48 h. Exogenous rIFN-gamma restored the proliferative response only when added at the beginning. Moreover, when IFN-gamma was blocked, T lymphocytes recovered from 6-day MLC displayed a profound decrease in their expression of p55 and p75 chains of the IL-2R, as well as in the number of high-affinity IL-2 binding sites. These findings strongly suggest that IFN-gamma is required in the early phases of induction of the oligo- and polyclonal proliferative and cytotoxic responses of lymphocytes.

A naturally occurring gene encoding the major surface antigen precursor p190 of Plasmodium falciparum lacks tripeptide repeats

Plasmodium falciparum merozoites have variable surface proteins that are processed from a 190-kd precursor protein (p190). The gene encoding p190 exists in two allelic forms and cross-over events occurring mainly near the 5' end, combined with isolate-specific tripeptide repeats, contribute to its antigen diversity. We have sequenced a large portion of the p190 gene from the parasite isolate RO-33 (Ghana). Remarkably, the typical N-terminal tripeptide repeat structure is lacking. Apart from mutations in the variable parts, the gene appears identical to the MAD-20 allele (Papua, New Guinea). Southern blot analysis detects p190 genes similar to RO-33 in other parasite isolates independent of their geographical origin. The lack of p190 repeats in RO-33 eliminates the possibility that they are involved in host cell recognition or integration and restricts their function to immune escape.

Plasmodium falciparum-specific human T cell clones: recognition of different parasite antigens

T lymphocyte clones specific for malarial (Plasmodium falciparum) blood stage antigens were obtained from acutely infected patients or from donors living in a malaria-endemic area of West Africa. Thirty-four clones carrying the CD4 antigen, and one CD8+ clone, were tested in a proliferation assay for their capacity to recognize P. falciparum isolates of different geographical origins. Only one clone distinguished between different parasite isolates (it failed to react with a parasite isolate originating from East Africa, but did recognize West African and Asian isolates). All of the clones responded well to intact erythrocytes containing viable parasites, but some responded poorly to extracts of parasitized cells. Eight of 19 clones studied (all CD4+) recognized parasite antigens which had characteristic mobilities in sodium dodecyl sulfate-containing polyacrylamide gels. The antigens had apparent molecular weights of about 20,000, 35,000, 40,000, 120,000, 150,000-200,000 and 200,000. These results (together with a previous report of two clones recognizing an antigen of molecular weight about 50,000, Sinigaglia and Pink, EMBO J. 1985. 4:3819) show that T cells in infected individuals react with at least 6 different parasite proteins.

A labour-saving method for the in vitro culture of Plasmodium falciparum

The in vitro cultivation of Plasmodium falciparum requires at least daily changes of medium (Trager and Jensen, 1976). Addition of 50 mg per litre of hypoxanthine to medium RPMI 1640 permits to postpone the change of medium for up to 72 hours. A single subculture step is required to remove unlabelled hypoxanthine prior to the use of the cultured material in 3H-hypoxanthine incorporation assays. The method constitutes a considerable saving of time and medium.

[A case of chloroquine-resistant tropical malaria from eastern Africa (Kenya)]

A case of chloroquine-resistant falciparum malaria in a non-immune Swiss tourist is described. The infection was acquired in Kenya in spite of regular chloroquine prophylaxis with therapeutic serum levels. The isolated plasmodia showed marked in vitro resistance to chloroquine and sensitivity to mefloquine and pyrimethamine.

Note on the stability of mefloquine hydrochloride in aqueous solution

Using Desjardins' technique for the testing of antimalarials against Plasmodium falciparum in vitro, a 4-year-old solution of mefloquine in water (10(-3) mol/litre) was compared with a freshly prepared solution.The results showed that the two solutions had almost identical activity. There was no evidence for any instability of mefloquine in aqueous solution.