Superior protection in a relapsing Plasmodium cynomolgi rhesus macaque model by a chemoprophylaxis with sporozoite immunization regimen with atovaquone-proguanil followed by primaquine

BACKGROUND

To gain a deeper understanding of protective immunity against relapsing malaria, this study examined sporozoite-specific T cell responses induced by a chemoprophylaxis with sporozoite (CPS) immunization in a relapsing Plasmodium cynomolgi rhesus macaque model.

METHODS

The animals received three CPS immunizations with P. cynomolgi sporozoites, administered by mosquito bite, while under two anti-malarial drug regimens. Group 1 (n = 6) received artesunate/chloroquine (AS/CQ) followed by a radical cure with CQ plus primaquine (PQ). Group 2 (n = 6) received atovaquone-proguanil (AP) followed by PQ. After the final immunization, the animals were challenged with intravenous injection of 104 P. cynomolgi sporozoites, the dose that induced reliable infection and relapse rate. These animals, along with control animals (n = 6), were monitored for primary infection and subsequent relapses. Immunogenicity blood draws were done after each of the three CPS session, before and after the challenge, with liver, spleen and bone marrow sampling and analysis done after the challenge.

RESULTS

Group 2 animals demonstrated superior protection, with two achieving protection and two experiencing partial protection, while only one animal in group 1 had partial protection. These animals displayed high sporozoite-specific IFN-γ T cell responses in the liver, spleen, and bone marrow after the challenge with one protected animal having the highest frequency of IFN-γ+ CD8+, IFN-γ+ CD4+, and IFN-γ+ γδ T cells in the liver. Partially protected animals also demonstrated a relatively high frequency of IFN-γ+ CD8+, IFN-γ+ CD4+, and IFN-γ+ γδ T cells in the liver. It is important to highlight that the second animal in group 2, which experienced protection, exhibited deficient sporozoite-specific T cell responses in the liver while displaying average to high T cell responses in the spleen and bone marrow.

CONCLUSIONS

This research supports the notion that local liver T cell immunity plays a crucial role in defending against liver-stage infection. Nevertheless, there is an instance where protection occurs independently of T cell responses in the liver, suggesting the involvement of the liver's innate immunity. The relapsing P. cynomolgi rhesus macaque model holds promise for informing the development of vaccines against relapsing P. vivax.

Integrative Genetic Manipulation of Plasmodium cynomolgi Reveals Multidrug Resistance-1 Y976F Associated With Increased In Vitro Susceptibility to Mefloquine

The lack of a long-term in vitro culture method has severely restricted the study of Plasmodium vivax, in part because it limits genetic manipulation and reverse genetics. We used the recently optimized Plasmodium cynomolgi Berok in vitro culture model to investigate the putative P. vivax drug resistance marker MDR1 Y976F. Introduction of this mutation using clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9) increased sensitivity to mefloquine, but had no significant effect on sensitivity to chloroquine, amodiaquine, piperaquine, and artesunate. To our knowledge, this is the first reported use of CRISPR-Cas9 in P. cynomolgi, and the first reported integrative genetic manipulation of this species.

Systems biology of malaria explored with nonhuman primates

"The Primate Malarias" book has been a uniquely important resource for multiple generations of scientists, since its debut in 1971, and remains pertinent to the present day. Indeed, nonhuman primates (NHPs) have been instrumental for major breakthroughs in basic and pre-clinical research on malaria for over 50 years. Research involving NHPs have provided critical insights and data that have been essential for malaria research on many parasite species, drugs, vaccines, pathogenesis, and transmission, leading to improved clinical care and advancing research goals for malaria control, elimination, and eradication. Whilst most malaria scientists over the decades have been studying Plasmodium falciparum, with NHP infections, in clinical studies with humans, or using in vitro culture or rodent model systems, others have been dedicated to advancing research on Plasmodium vivax, as well as on phylogenetically related simian species, including Plasmodium cynomolgi, Plasmodium coatneyi, and Plasmodium knowlesi. In-depth study of these four phylogenetically related species over the years has spawned the design of NHP longitudinal infection strategies for gathering information about ongoing infections, which can be related to human infections. These Plasmodium-NHP infection model systems are reviewed here, with emphasis on modern systems biological approaches to studying longitudinal infections, pathogenesis, immunity, and vaccines. Recent discoveries capitalizing on NHP longitudinal infections include an advanced understanding of chronic infections, relapses, anaemia, and immune memory. With quickly emerging new technological advances, more in-depth research and mechanistic discoveries can be anticipated on these and additional critical topics, including hypnozoite biology, antigenic variation, gametocyte transmission, bone marrow dysfunction, and loss of uninfected RBCs. New strategies and insights published by the Malaria Host-Pathogen Interaction Center (MaHPIC) are recapped here along with a vision that stresses the importance of educating future experts well trained in utilizing NHP infection model systems for the pursuit of innovative, effective interventions against malaria.

Plasmodium cynomolgi Co-infections among Symptomatic Malaria Patients, Thailand

Among 1,180 symptomatic malaria patients, 9 (0.76%) infected with Plasmodium cynomolgi were co-infected with P. vivax (n = 7), P. falciparum (n = 1), or P. vivax and P. knowlesi (n = 1). Patients were from Tak, Chanthaburi, Ubon Ratchathani, Yala, and Narathiwat Provinces, suggesting P. cynomolgi is widespread in this country.

knowlesi Infections, Malaysian Borneo

To monitor the incidence of Plasmodium knowlesi infections and determine whether other simian malaria parasites are being transmitted to humans, we examined 1,047 blood samples from patients with malaria at Kapit Hospital in Kapit, Malaysia, during June 24, 2013–December 31, 2017. Using nested PCR assays, we found 845 (80.6%) patients had either P. knowlesi monoinfection (n = 815) or co-infection with other Plasmodium species (n = 30). We noted the annual number of these zoonotic infections increased greatly in 2017 (n = 284). We identified 6 patients, 17–65 years of age, with P. cynomolgi and P. knowlesi co-infections, confirmed by phylogenetic analyses of the Plasmodium cytochrome c oxidase subunit 1 gene sequences. P. knowlesi continues to be a public health concern in the Kapit Division of Sarawak, Malaysian Borneo. In addition, another simian malaria parasite, P. cynomolgi, also is an emerging cause of malaria in humans.

Neither the HIV protease inhibitor lopinavir-ritonavir nor the antimicrobial trimethoprim-sulfamethoxazole prevent malaria relapse in plasmodium cynomolgi-infected non-human primates

Plasmodium vivax malaria causes significant morbidity and mortality worldwide, and only one drug is in clinical use that can kill the hypnozoites that cause P. vivax relapses. HIV and P. vivax malaria geographically overlap in many areas of the world, including South America and Asia. Despite the increasing body of knowledge regarding HIV protease inhibitors (HIV PIs) on P. falciparum malaria, there are no data regarding the effects of these treatments on P. vivax's hypnozoite form and clinical relapses of malaria. We have previously shown that the HIV protease inhibitor lopinavir-ritonavir (LPV-RTV) and the antibiotic trimethoprim sulfamethoxazole (TMP-SMX) inhibit Plasmodium actively dividing liver stages in rodent malarias and in vitro in P. falciparum, but effect against Plasmodium dormant hypnozoite forms remains untested. Separately, although other antifolates have been tested against hypnozoites, the antibiotic trimethoprim sulfamethoxazole, commonly used in HIV infection and exposure management, has not been evaluated for hypnozoite-killing activity. Since Plasmodium cynomolgi is an established animal model for the study of liver stages of malaria as a surrogate for P. vivax infection, we investigated the antimalarial activity of these drugs on Plasmodium cynomolgi relapsing malaria in rhesus macaques. Herein, we demonstrate that neither TMP-SMX nor LPV-RTV kills hypnozoite parasite liver stage forms at the doses tested. Because HIV and malaria geographically overlap, and more patients are being managed for HIV infection and exposure, understanding HIV drug impact on malaria infection is important.

Detection of new Babesia microti-like parasites in a rhesus monkey (Macaca mulatta) with a suppressed Plasmodium cynomolgi infection

A new type of piroplasm, phylogenetically closest to Babesia microti-like parasites previously detected in Eurasian red squirrels (Sciurus vulgaris orientis), was identified in a rhesus monkey (Macaca mulatta) imported from China. After challenge with Plasmodium cynomolgi M strain blood-stage parasites, the rhesus monkey repeatedly showed markedly reduced levels of Plasmodium parasitemia when compared with animals not infected with this organism.

Hydrolytic enzyme activity in rhesus monkey placenta during early gestational malaria: histochemical studies

BACKGROUND & OBJECTIVES

Early gestational malaria is found to be more fatal than late gestational infection but the pathophysiology of early gestational placenta, the maternofoetal organ responsible for maintenance of pregnancy, remains unexplored. Present study dealing with hydrolytic enzymes in early gestational placenta of rhesus monkeys during Plasmodium cynomolgi infection was anticipated to provide a better insight into the functional impairment of this organ during early gestational maternal malaria.

METHODS

Experimental monkeys (Macaca multtta) at 2-2 1/2 months of pregnancy were inoculated with P. cynomolgi bastianelli. After attaining first peak of parasitaemia the animals were anesthetised and placentae were collected for histochemical studies. The snap-frozen, cryostat sections were subjected to histochemical reactions for acid phosphatase and alkaline phosphatase.

RESULTS

The placental syncytiotrophoblast showed a loss in alkaline phosphatase activity, while the trophoblast layers and phagocytic cells of the maternal blood showed increased acid phosphatase activity during early gestational malarial infection. Morphological damage to the placental tissue whenever occurred was associated with altered Alk pase activity.

INTERPRETATION & CONCLUSION

The altered distribution of Ac pase and Alk pase in malaria infected early gestational placenta has been discussed in the light of placental function. It could be concluded by present studies that these malaria induced changes in hydrolytic enzyme activities in monkey placenta have a direct bearing on functional and morphological integrity of the placental tissue. These changes are apparently responsible for early gestational foetal death and abortions as reported in literature.

[Induction of protective immunity in rhesus monkey by inoculation with recombinant fusion protein of cholera toxin B subunit-multivalent epitopes of Plasmodium falciparum]

Rhesus monkeys (5 in each group) were inoculated with recombinant fusion protein of cholera toxin B subunit and multi-valent epitopes of Plasmodium falciparum intranasal or intramuscular (i.m.). Immune-responses and protective effect were evaluated. The antibody titer (Geometry mean) against CTB reached 1:512 (intranasal) and 1:10000 (i.m.) 14 day after 3rd immunization, and antibodies against P. falciparum were also elucidated, the titers in i.m. group were also significantly higher than that in intranasal group. The monkeys were challenged with 1.25 x 10(8) sporozoites of P. cynomolgi, Patent infection was observed in all 5 monkeys in control group inoculated with PBS in 10 - 14 days after challenge. Patent infection was also observed in 5 animals inoculated via intranasal and 2 animals in intramuscular group 19th days after challenge, But the infection last only 4 days in 3 animals in intranasal group and 2 animals in intramuscular group. The results demonstrated that the vaccine candidate could induce protective immune-responses in rhesus monkey against the challenge of P. cynomolgi.

Blood schizontocidal activity of WR 238605 (Tafenoquine) against Plasmodium cynomolgi and Plasmodium fragile infections in rhesus monkeys

A new 8-aminoquinoline antimalarial WR 238605 (Tafenoquine), developed initially as a primaquine alternative for prevention of Plasmodium vivax relapses was evaluated for blood schizontocidal activity against two simian malaria infections namely Plasmodium cynomolgi B and Plasmodium fragile in rhesus monkeys. Treatment with WR 238605 at a dose of 3.16 mg(base)/kg/day x 7 days cured established trophozoite induced infections in monkeys with both these parasites. The lower dose of 1.00 mg/kg/day cured 9 out of 12 monkeys infected with P. cynomolgi B and 10 out of 11 monkeys infected with P. fragile. Primaquine was only partially curative at 10.0 mg(base)/kg/day x 7 dose regimen against both these infections. The potent blood schizontocidal activity of tafenoquine adds to the armoury of antimalarial drugs.

Sterile protection of monkeys against malaria after administration of interleukin-12

An estimated 300-500 million new infections and 1.5-2.7 million deaths attributed to malaria occur annually in the developing world, and every year tens of millions of travelers from countries where malaria is not transmitted visit countries with malaria. Because the parasites that cause malaria have developed resistance to many antimalarial drugs, new methods for prevention are required. Intraperitoneal injection into mice of one dose of 150 ng (approximately 7.5 micrograms per kg body weight) recombinant mouse interleukin-12 (rmIL-12) 2 days before challenge with Plasmodium yoelii sporozoites protects 100% of mice against malaria. We report that one subcutaneous injection of 10 micrograms/kg recombinant human IL-12 (rhIL-12) 2 days before challenge with P. cynomolgi sporozoites protected seven of seven rhesus monkeys. Protection was associated with marked increases in plasma levels of interferon-gamma (IFN-gamma), and relative increases of lymphoid cell messenger RNA coding for IFN-gamma and several other cytokines. We speculate that rIL-12 protects monkeys through IFN-gamma-dependent elimination of P. cynomolgi-infected hepatocytes. This first report of rIL-12-induced protection of primates against an infectious agent supports assessment of rhIL-12 for immunoprophylaxis of human malaria.

Histochemical changes in host tissues from Plasmodium cynomolgi B infected rhesus monkey (Macaca mulatta)

Plasmodium cynomolgi B has been used to infect the rhesus monkey to study the histochemical changes (lipid infiltration, glycogen, protein, DNA and RNA) in liver, kidney and spleen during early (exoerythrocytic) and late (chronic) stages of malarial infection. Infected liver showed significant lipid infiltration during exoerythrocytic and erythrocytic (acute phase) stage of infection. Kidney showed lipid deposition during acute phase of infection while spleen sections were negative for lipid depositions. As a result of malarial infection there was significant depletion of glycogen in liver during exoerythrocytic stage of infection. Glycogen content increased in liver and kidney during erythrocytic stage of infection. The spleen which is the main target of immunopathology in malaria showed no change in glycogen content. During exoerythrocytic phase host tissue organs showed no change in protein and nucleic acids while erythrocytic phase showed slightly increased proteins in liver and kidney. Nucleic acids became decreased in liver and spleen during erythrocytic phase of infection. The parasite used in this study has a defined prepatent period, can be cyclically passaged with ease and non fatal in nature.

Poly ICLC inhibits Plasmodium cynomolgi B malaria infection in rhesus monkeys

Prophylatic treatment with a single dose of 1.0 or 2.0 mg/kg (body weight) of polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (Poly ICLC), a potent interferon (IFN) inducer and immune enhancer, 18 h before intravenous inoculation of sporozoites (1.04 x 10(5)-0.70 x 10(6) sporozoites) of Plasmodium cynomolgi B in the rhesus monkey, completely abolished the infectivity of sporozoites. The inhibitory effect of Poly ICLC is dose dependent in monkeys infected with P. cynomolgi B sporozoites. Treatment with lower doses of Poly ICLC (0.5 mg/kg) provided significant protection, but the lowest dose of Poly ICLC used (0.1 mg/kg) failed to provide any protection. Prophylactic treatment with Poly ICLC, however, had no protective effect against trophozoite-induced infection.

Proguanil plus sulfamethoxazole is not causally prophylactic in the Macaca mulatta--Plasmodium cynomolgi model

New drugs for causal prophylaxis of malaria are needed. A proguanil/sulfamethoxazole combination was investigated using a rhesus monkey model (Macaca mulatta infected with Plasmodium cynomolgi) to determine whether causal prophylaxis could be achieved. When a five-day regimen of proguanil (40 mg/kg/day) combined with sulfamethoxazole (100 mg/kg/day) was used, infection of all animals (6 of 6) was observed, with an extended prepatent period (median 40 days). Two control animals became infected on days 9 and 23 following sporozoite inoculation. Plasma concentrations indicated that proguanil and sulfamethoxazole were adequately absorbed and metabolized to cycloguanil and N4-acetylsulfamethoxazole, respectively. Analysis of liver biopsy specimens demonstrated that the drugs were present two days following sporozoite inoculation but were not detectable one week later. Proguanil plus sulfamethoxazole does not eliminate exoerythrocytic-stage parasites in the rhesus monkey--P. cynomolgi model.

Evaluation of WR250417 (a proguanil analog) for causal prophylactic activity in the Plasmodium cynomolgi-Macaca mulatta model

The Plasmodium cynomolgi-Macaca mulatta model has been used to test the antimalarial activity of new drugs for both radical cure and casual prophylaxis. The proguanil analog WR250417 (also known as PS-15) was evaluated for causal prophylactic activity in rhesus monkeys infected with P. cynomolgi bastianelli. Four monkeys were orally dosed with 40 mg/kg/day of WR250417 over three days (-1, 0, and +1). Sporozoite-induced infection of P. cynomolgi was initiated on day 0 with 1 x 10(6) sporozoites to each monkey. Compound WR250417 extended the prepatent period from an average of 8.5 days for controls (n = 2) to a mean of 18.3 days (range 18-19 days, n = 4) for drug-treated monkeys. Analysis of plasma drug concentrations by high-performance liquid chromatography showed that the monkeys converted the WR250417 to its putative principal active metabolite WR99210 (a dihydrotriazine). These findings demonstrate that WR250417 and its principal metabolite do not prevent primary infection by P. cynomolgi.

Role of fatty infiltration during malaria in rhesus monkey

P. cynomolgi B-rhesus monkey model of malarial infection has been used to study lipid infiltration in host tissues in early (exoerythrocytic) and late (chronic) stages of malaria infection. Histochemically we could demonstrate significant infiltration of neutral & total lipids in liver during the exoerythrocytic stage and in liver and kidney in the erythrocytic stage. The parasite used in the study closely resembles the human parasite P. vivax. It has a defined prepatent period, can be cyclically passaged with ease and non fatal in nature.

[Studies on residual antimalarial activity of tripynadine in mice and monkeys]

This paper reports the experiments in which tripynadine free base at a dose 4.5 times that of ED50 was given to mice by intragastric administration. On the 20th day following the administration the mice were inoculated with 1 x 10(7) RBC infected with Plasmodium berghei ANKA strain. The infection rate was zero, implying that all mice had acquired protection. Although the residual activity time of tripynadine phosphate was longer than that of tripynadine free base or piperaquine phosphate, but tripynadine phosphate caused vomiting in monkeys during the medication. The residual antimalarial activity of tripynadine hydroxynaphthoate was less than that of tripynadine phosphate or tripynadine free base. A total dose of 200 mg/kg of tripynadine free base ensured residual antimalarial activity against P. cynomolgi bastianellii for 20 days. However, the residual activity decreased evidently when the total dose was reduced to 100 mg/kg. In short, it seems that the residual antimalarial activity of tripynadine free base is slightly less than that of piperaquine in monkeys.

Hydrolytic enzymes of rhesus placenta during Plasmodium cynomolgi infection: ultrastructural and biochemical studies

Placenta in monkey demonstrated altered pathophysiology after P cynomolgi infection. The electronmicroscopic observations showed slight complete focal necrosis of the placental tissue, besides alterations in total protein, phosphatases and proteinases. These changes in cellular constituents of placenta during malaria infection may be responsible for malfunctioning of the organ and in turn, abnormal development of foetus.

POTENTIATION OF ACTIVITY OF DIAPHENYLSULFONE AND PYRIMETHAMINE AGAINST PLASMODIUM GALLINACEUM AND PLASMODIUM CYNOMOLGI BASTIANELLII

In view of the fact that diaphenylsulfone has been shown to have low schizontocidal activity against Plasmodium gallinaceum and to lead to resistance in strains of P. cynomolgi, investigations were undertaken into the joint action of diaphenylsulfone and pyrimethamine against P. gallinaceum in chicks and P. cynomolgi bastianellii in monkeys. These drugs were assayed separately and in various combinations. It was found that at certain dose levels combination of the two drugs led to potentiation of their plasmocidal activity. On the other hand, this synergistic effect was not noted with combinations containing lower dosages of either drug; with these, a simple additive effect occurred. The authors suggest that the two drugs probably act on the same metabolic pathway but that their points of attack may be different. They note also that there was a difference in the response of P. gallinaceum in chicks and of P. cynomolgi bastianellii in monkeys to the combined use of the two drugs.