A Phase 2 Extension Study Evaluating the Immunogenicity, Safety, and Tolerability of 3 or 4 Doses of a Clostridioides difficile Vaccine in Healthy US Adults Aged 65 to 85 Years

BACKGROUND

This phase 2 extension explored the long-term antibody persistence of an investigational Clostridioides difficile vaccine and the safety, tolerability, and immunogenicity of dose 4 approximately 12 months post-dose 3.

METHODS

One year post-dose 3, healthy US 65- to 85-year-olds (N = 300) were randomized to dose 4 of vaccine at previously received antigen levels (100 or 200 μg) or placebo. Assessments included safety and percentages of participants achieving neutralizing antibody titers above prespecified thresholds (≥219 and ≥2586 neutralization units/mL for toxins A and B, respectively).

RESULTS

In participants previously given three 200-µg doses and placebo in the extension, toxin A and B neutralizing antibodies were above prevaccination levels 48 months post-dose 3 (36 months after placebo); 24.0% and 26.0% had toxin A and B antibodies at or above prespecified thresholds, respectively. Neutralizing antibodies increased post-dose 4 (12 months post-dose 3) and persisted to 36 months post-dose 4. Thirty days post-dose 4, all participants had toxin A and 86.5% to 100% had toxin B titers at or above prespecified thresholds. Local reactions were more frequent in vaccine recipients. Systemic and adverse event frequencies were similar across groups.

CONCLUSIONS

C difficile vaccine immune responses persisted 48 months post-dose 3. Dose 4 was immunogenic and well tolerated, supporting continued development. Clinical Trials Registration. ClinicalTrials.gov NCT02561195.

Protection against Plasmodium falciparum malaria by PfSPZ Vaccine

BACKGROUND: A radiation-attenuated Plasmodium falciparum (Pf) sporozoite (SPZ) malaria vaccine, PfSPZ Vaccine, protected 6 of 6 subjects (100%) against homologous Pf (same strain as in the vaccine) controlled human malaria infection (CHMI) 3 weeks after 5 doses administered intravenously. The next step was to assess protective efficacy against heterologous Pf (different from Pf in the vaccine), after fewer doses, and at 24 weeks. METHODS: The trial assessed tolerability, safety, immunogenicity, and protective efficacy of direct venous inoculation (DVI) of 3 or 5 doses of PfSPZ Vaccine in non-immune subjects. RESULTS: Three weeks after final immunization, 5 doses of 2.7 × 10⁵ PfSPZ protected 12 of 13 recipients (92.3% [95% CI: 48.0, 99.8]) against homologous CHMI and 4 of 5 (80.0% [10.4, 99.5]) against heterologous CHMI; 3 doses of 4.5 × 10⁵ PfSPZ protected 13 of 15 (86.7% [35.9, 98.3]) against homologous CHMI. Twenty-four weeks after final immunization, the 5-dose regimen protected 7 of 10 (70.0% [17.3, 93.3]) against homologous and 1 of 10 (10.0% [-35.8, 45.6]) against heterologous CHMI; the 3-dose regimen protected 8 of 14 (57.1% [21.5, 76.6]) against homologous CHMI. All 22 controls developed Pf parasitemia. PfSPZ Vaccine was well tolerated, safe, and easy to administer. No antibody or T cell responses correlated with protection. CONCLUSIONS: We have demonstrated for the first time to our knowledge that PfSPZ Vaccine can protect against a 3-week heterologous CHMI in a limited group of malaria-naive adult subjects. A 3-dose regimen protected against both 3-week and 24-week homologous CHMI (87% and 57%, respectively) in this population. These results provide a foundation for developing an optimized immunization regimen for preventing malaria. TRIAL REGISTRATION: ClinicalTrials.gov NCT02215707. FUNDING: Support was provided through the US Army Medical Research and Development Command, Military Infectious Diseases Research Program, and the Naval Medical Research Center's Advanced Medical Development Program.

Pharmacokinetic evaluation of intravenous artesunate in adults with uncomplicated falciparum malaria in Kenya: a phase II study

Background

Alternatives to treatment for malaria treatment of travellers are needed in the USA and in Europe for travellers who return with severe malaria infections. The objective of this study is to show the pharmacokinetic (PK) profile of intravenous artesunate (AS), which was manufactured under good manufacturing practice (GMP) conditions, in adults with uncomplicated falciparum malaria in Kenya.

Methods

The PK parameters of intravenous AS manufactured under current cGMP were evaluated after a single dose of drug at 2.4 mg/kg infused over 2 min in 28 adults with uncomplicated Plasmodium falciparum malaria. Plasma concentrations of AS and dihydroartemisinin (DHA) were measured using a validated liquid chromatography–mass spectrometry (LC-MS/MS) methodology. Pharmacokinetic data were analysed with a compartmental analysis for AS and DHA.

Results

The results suggest there were no drug-related adverse events in any of the patients. After intravenous infusion, the concentration of the parent drug rapidly declined, and the AS was converted to DHA. AS and DHA showed mean elimination half-lives of 0.17 hours and 1.30 hours, respectively. The high mean peak concentration (C_max) of AS was shown to be 28,558 ng/mL while the C_max of DHA was determined to be 2,932 ng/mL. Significant variability was noted in the PK profiles of the 28 patients tested. For example, C_max values of AS were calculated to range from 3,362 to 55,873 ng/mL, and the C_max value of DHA was noted to vary from 1,493 to 5,569 ng/mL. The mean area under the curve (AUC) of AS was shown to be approximately half that of DHA (1,878 ng·h/mL vs 3,543 ng·h/mL). The DHA/AS ratio observed was 1.94 during the one-day single treatment, and the AUC and half- life measured for DHA were significantly larger and longer than for AS.

Conclusions

Intravenous AS can provide much higher peak concentrations of AS when compared to concentrations achieved with oral therapy; this may be crucial for the rapid elimination of parasites in patients with severe malaria. Given the much longer half-life of DHA compared to the short half-life of AS, DHA also plays a significant role in treatment of severe malaria.

Pilot assessment of the sensitivity of the malaria thin film

Background

Malaria microscopy remains the reference standard for malaria diagnosis in clinical trials (drug and vaccine), new diagnostic evaluation, as well as in clinical care in much of the world today. It is known that microscopy is an imperfect gold standard, and that very low false positive rates can dramatically lower protective efficacy estimates in malaria prevention trials. Although new methods are now available, including malaria rapid diagnostic tests and PCR, neither is as yet validated in the clinical trial setting and both have limitations. Surprisingly, the sensitivity of thin smears is not well established and thin smears are not commonly used in the developing world.

Methods

Malaria thick and thin films were collected in the lowlands of Western Kenya. All had density determined by four readings with two methods, as well as species identified. Thirty-six with low density parasitaemia had the thin smear read by five independent microscopists, two were expert and three were qualified. Microscopists read the entire thin film. For the first 10 parasites seen, they reported the species, appearance, time, field number, and red blood cells in the field. Total parasites, total fields, and total time to examine the smear were also recorded.

Results

Median parasitaemia was 201 parasites/μl, mean 1,090 ± 2,195, range 6–11,124 parasites/μl for the 36 smears evaluated. The data revealed a density dependent increase in sensitivity, with 100% sensitivity achieved at >200 parasites/μl for experts and >500 parasites/μl for qualified readers. Thin film readings confirmed parasitaemia 74% of the time by experts, and 65% of the time for qualified microscopists. The 95^th percentile for time to detect parasitaemia was 15 minutes for experts, 17 minutes for qualified microscopists. This decreased to 4–10 minutes for experts at densities of > 200 parasites/μl. Additionally, substantial discordance for species identification was observed.

Conclusion

The thin film is sensitive enough to be a useful tool to confirm malaria diagnosis in study subjects in some settings. Specificity of the thin film and its utility for confirming thick film or other diagnostic test results should be assessed further.

Establishing a malaria diagnostics centre of excellence in Kisumu, Kenya

Background

Malaria microscopy, while the gold standard for malaria diagnosis, has limitations. Efficacy estimates in drug and vaccine malaria trials are very sensitive to small errors in microscopy endpoints. This fact led to the establishment of a Malaria Diagnostics Centre of Excellence in Kisumu, Kenya. The primary objective was to ensure valid clinical trial and diagnostic test evaluations. Key secondary objectives were technology transfer to host countries, establishment of partnerships, and training of clinical microscopists.

Case description

A twelve-day "long" and a four-day "short" training course consisting of supervised laboratory practicals, lectures, group discussions, demonstrations, and take home assignments were developed. Well characterized slides were developed and training materials iteratively improved. Objective pre- and post-course evaluations consisted of 30 slides (19 negative, 11 positive) with a density range of 50–660 parasites/μl, a written examination (65 questions), a photographic image examination (30 images of artifacts and species specific characteristics), and a parasite counting examination.

Discussion and Evaluation

To date, 209 microscopists have participated from 11 countries. Seventy-seven experienced microscopists participated in the "long" courses, including 47 research microscopists. Sensitivity improved by a mean of 14% (CI 9–19%) from 77% baseline (CI 73–81 %), while specificity improved by a mean of 17% (CI 11–23%) from 76% (CI 70–82%) baseline. Twenty-three microscopists who had been selected for a four-day refresher course showed continued improvement with a mean final sensitivity of 95% (CI 91–98%) and specificity of 97% (CI 95–100%). Only 9% of those taking the pre-test in the "long" course achieved a 90% sensitivity and 95% specificity, which increased to 61% of those completing the "short" course. All measures of performance improved substantially across each of the five organization types and in each course offered.

Conclusion

The data clearly illustrated that false positive and negative malaria smears are a serious problem, even with research microscopists. Training dramatically improved performance. Quality microscopy can be provided by the Centre of Excellence concept. This concept can be extended to other diagnostics of public health importance, and comprehensive disease control strategies.

Systematic comparison of two methods to measure parasite density from malaria blood smears

This study was designed to directly compare the accuracy, reproducibility, and efficiency of three methods commonly used to measure blood-stage malaria parasite density from Giemsa-stained blood films. Parasites and white blood cells (WBCs) were counted in 154 thick films by two independent microscopists. Forty-six slides were read by counting parasitized red blood cells (RBCs) in the thin film. Using these same slides, parasites were again counted by two independent microscopists using an ocular grid. Overall, parasite densities were significantly lower and discrepancy between readers was higher when using the grid method compared to the WBC method, but there was no difference when compared to the RBC method. When one reader who had difficulty with the grid method was excluded, the discrepancy between readers was equivalent for the three methods. Densities and discrepancy between readers were indistinguishable when parasites were counted until 200 or 500 WBCs. Counting beyond 200 WBCs may not significantly improve parasite density measurements. Using an ocular grid directly measures parasites per volume rather than using a WBC per microliter conversion factor and eliminates the need to switch from the thick film to the thin film for high parasitemias. However, significant differences in densities measured by the grid method and the WBC method need to be evaluated.