Intracellular cytokine analysis shows the presence of antigen-specific cytokine production by CD4+ cells.

<p>Peripheral blood mononuclear cells from vaccinated subjects were stimulated with VMP001 and production of IL-2, IFN-γ and TNF-α was assessed. Pie chart depicts the percentage of CD4⁺ cytokine-producing cells for each cohort 2 weeks post 3^rd vaccination (Day of challenge). G, 2 and T indicate IFN-γIL-2 and TNF-α, respectively. Cytokine producers are represented by a “+” and non-producers by a “-”.</p

Vaccinated subjects who showed a delayed time to parasitemia had higher anti-Type 1 repeat antibodies.

<p>A. Vaccinated individuals from all three cohorts could be grouped into those that showed a delay (green, n = 16) compared to the controls, and those that did not show a delay (red, n = 11). B. Individuals with a delay in patency had higher anti-type 1 repeat antibodies compared to those with no delay (p = 0.02). Each symbol represents an individual. Cohorts 1, 2 and 3 are represented by red, blue, and green, respectively.</p

All volunteers immunized with VMP001/AS01_B generated antibodies to VMP001.

<p>Anti-VMP001 antibodies were detected in 80% of vaccinated individuals starting at two weeks post-1^st immunization. Titers were boosted to peak levels post-2^nd immunization, with 100% of subjects developing antibodies. A decrease in antibody titers was observed on the day of third immunization (8, 6 and 4 weeks post 2^nd immunization for cohorts 1, 2 and 3, respectively) followed by a slight increase post 3^rd immunization. Antibody titers, defined as a serum dilution that gives an OD₄₁₄ of 1.0, showed a continual decline post challenge (Po Ch). Box plot represents the 25–75 percentiles and Whiskers indicate the minimum and maximum values. GMTs of anti-VMP001 antibody were significantly higher in group 1 compared to group 2 at 2 time points (2weeks post 2nd, p = 0.01, and on the day of 3rd, vaccination, p = 0.002). GMTs of anti-VMP001 antibody were significantly higher in group 2 compared to group 3 at 2 time points (4weeks post DOC, p = 0.03, and 6 months post-DOC, P = 0.04). GMTs of anti-VMP001 antibody were significantly higher in group 1 compared to group 3 at 5 time points (2 weeks post 1st vaccination, p = 0.02, on the day of 2nd vaccination, p = 0.01, 2 weeks post 2nd vaccination, p = 0.04, on the day of 3rd vaccination p = 0.002, and 6 months post DOC, p = 0.034).</p

Adverse events.

<p>Solicited Adverse Events (AEs) were recorded following each vaccination and are reported as the percentage of subjects in each cohort reporting the event. Pain was the most frequently reported AE, being reported by 80–100% of the subjects. A majority of the AEs presented as Grade 1 (G1, mild). Grade 2 (G2, moderate) erythema, fever, headache and Grade 3 (G3, severe) erythema were seen in a small percentage of individuals. AEs are shown post 1^st (V1), 2^nd (V2) and 3^rd (V3) vaccine dose.</p

Fine-specificity analysis demonstrates that all domains of CSP are recognized following immunization with VMP001.

<p>Day of Challenge (DOC, or 2 weeks post-3^rd vaccination) sera from all subjects were reactive to the N-term, type-1 Repeat peptide, as well as C-term region of the protein with the highest reactivity to the C-term. C- term GMTs were significantly higher in all three cohorts compared to the N- term and Type 1 repeat GMTs. Cohort 2 had significantly higher anti-Repeat antibodies compared to Cohorts 1 and 3 (p = 0.003, p = 0.01, respectively).</p

Study design.

<p>Immunization dose and schedule for the three cohorts of ten volunteers who were immunized three times with either a low (15 μg), medium (30 μg) or high (60 μg) dose of the vaccine, VMP001 formulated in AS01_B adjuvant (VMP001/AS01_B). The first 2 immunizations for each cohort were staggered by two weeks in order to monitor vaccine safety. The 2^nd dose was delivered 4 weeks after the 1^st and the 3^rd immunization was performed 8, 6 and 4 weeks post 2^nd dose for cohorts 1 (red), 2 (blue) and 3 (green), respectively. Control and vaccinated subjects were challenged at WRAIR with mosquitoes infected with P. vivax parasites that originated in Thailand.</p

Phase 1/2a Trial of <i>Plasmodium vivax</i> Malaria Vaccine Candidate VMP001/AS01_B in Malaria-Naive Adults: Safety, Immunogenicity, and Efficacy

<div><p>Background</p><p>A vaccine to prevent infection and disease caused by <i>Plasmodium vivax</i> is needed both to reduce the morbidity caused by this parasite and as a key component in efforts to eradicate malaria worldwide. Vivax malaria protein 1 (VMP001), a novel chimeric protein that incorporates the amino- and carboxy- terminal regions of the circumsporozoite protein (CSP) and a truncated repeat region that contains repeat sequences from both the VK210 (type 1) and the VK247 (type 2) parasites, was developed as a vaccine candidate for global use.</p><p>Methods</p><p>We conducted a first-in-human Phase 1 dose escalation vaccine study with controlled human malaria infection (CHMI) of VMP001 formulated in the GSK Adjuvant System AS01_B. A total of 30 volunteers divided into 3 groups (10 per group) were given 3 intramuscular injections of 15μg, 30μg, or 60μg respectively of VMP001, all formulated in 500μL of AS01_B at each immunization. All vaccinated volunteers participated in a <i>P</i>. <i>vivax</i> CHMI 14 days following the third immunization. Six non-vaccinated subjects served as infectivity controls.</p><p>Results</p><p>The vaccine was shown to be well tolerated and immunogenic. All volunteers generated robust humoral and cellular immune responses to the vaccine antigen. Vaccination did not induce sterile protection; however, a small but significant delay in time to parasitemia was seen in 59% of vaccinated subjects compared to the control group. An association was identified between levels of anti-type 1 repeat antibodies and prepatent period.</p><p>Significance</p><p>This trial was the first to assess the efficacy of a <i>P</i>. <i>vivax</i> CSP vaccine candidate by CHMI. The association of type 1 repeat-specific antibody responses with delay in the prepatency period suggests that augmenting the immune responses to this domain may improve strain-specific vaccine efficacy. The availability of a <i>P</i>. <i>vivax</i> CHMI model will accelerate the process of <i>P</i>. <i>vivax</i> vaccine development, allowing better selection of candidate vaccines for advancement to field trials.</p></div

Kaplan-Meier survival curves were used to plot time to parasitemia.

<p>Nine volunteers from cohort 1 (red), 8 volunteers from cohort 2 (blue) and 10 volunteers from cohort 3 (green) were challenged along with 6 non-vaccinated controls via the bites of 5 of Anopheles dirus mosquitoes infected with P. vivax parasites originating in Thailand. The median time to parasitemia for all three vaccinated cohorts was significantly longer compared to the infectivity controls with cohort 2 having the longest delay in median time to patency (12.6 days).</p

Cellular immune responses by vaccine group and days post immunization.

<p>A. Geometric mean CS-specific CD4⁺ T cells producing IFN-γ by ELISpot. Comparisons between ARR and RRR on days 42, 77, 105,140, and 236 were significant (P < .05) by Student’s <i>t</i>-test on log-transformed data. Error bars represent standard deviation of the mean. B. Geometric mean CS-specific CD4⁺ T cell responses expressing ≥2 cytokine/activation markers among IL2, IFN-γ, TNF-α, and CD40L, per million PBMC. Comparisons between ARR and RRR on days 42, 77, 105, 140 were significant (P < .05) by Student’s <i>t</i>-test on log-transformed data. Error bars represent standard deviation of the mean. C. Pie charts showing the pattern of CS-specific polyfunctional CD4⁺ CD40L⁺ T cells expressing ≥2 cytokine markers at Day 77 (day of challenge). Each slice within the pie chart represents a specific combination of two or three cytokines. The size of the pie chart is proportional to the magnitude of the response.</p

Flow diagram.

<p>The number of subjects completing each immunization and controlled human malaria infection. ARR = first dose with Ad35.CS, second and third doses with RTS,S/AS01_B. RRR = three doses of RTS,S/AS01_B</p