The Regulation of Nucleic Acid Vaccine Responses by the Microbiome.

Nucleic acid vaccines, including both RNA and DNA platforms, are key technologies that have considerable promise in combating both infectious disease and cancer. However, little is known about the extrinsic factors that regulate nucleic acid vaccine responses and which may determine their effectiveness. The microbiome is recognized as a significant regulator of immune development and response, whose role in regulating some traditional vaccine platforms has recently been discovered. Using germ-free and specific pathogen-free mouse models in combination with different protein, DNA, and mRNA vaccine regimens, we demonstrate that the microbiome is a significant regulator of nucleic acid vaccine immunogenicity. Although the presence of the microbiome enhances CD8+ T cell responses to mRNA lipid nanoparticle immunization, the microbiome suppresses Ig and CD4+ T cell responses to DNA-prime, DNA-protein-boost immunization, indicating contrasting roles for the microbiome in the regulation of these different nucleic acid vaccine platforms. In the case of mRNA lipid nanoparticle vaccination, germ-free mice display reduced dendritic cell/macrophage activation that may underlie the deficient vaccine response. Our study identifies the microbiome as a relevant determinant of nucleic acid vaccine response with implications for continued therapeutic development and deployment of these vaccines.

Review of Current Tuberculosis Human Infection Studies for Use in Accelerating Tuberculosis Vaccine Development: A Meeting Report.

Tools to evaluate and accelerate tuberculosis (TB) vaccine development are needed to advance global TB control strategies. Validated human infection studies for TB have the potential to facilitate breakthroughs in understanding disease pathogenesis, identify correlates of protection, develop diagnostic tools, and accelerate and de-risk vaccine and drug development. However, key challenges remain for realizing the clinical utility of these models, which require further discussion and alignment among key stakeholders. In March 2023, the Wellcome Trust and the International AIDS Vaccine Initiative convened international experts involved in developing both TB and bacillus Calmette-Guérin (BCG) human infection studies (including mucosal and intradermal challenge routes) to discuss the status of each of the models and the key enablers to move the field forward. This report provides a summary of the presentations and discussion from the meeting. Discussions identified key issues, including demonstrating model validity, to provide confidence for vaccine developers, which may be addressed through demonstration of known vaccine effects (eg, BCG vaccination in specific populations), and by comparing results from field efficacy and human infection studies. The workshop underscored the importance of establishing safe and acceptable studies in high-burden settings, and the need to validate >1 model to allow for different scientific questions to be addressed as well as to provide confidence to vaccine developers and regulators around use of human infection study data in vaccine development and licensure pathways.

Association Between SARS-CoV-2 Viral Load and COVID-19 Vaccination in 4 Phase 3 Trials.

Coronavirus disease 2019 (COVID-19) vaccines reduce severe disease and mortality and may lessen transmission, measured by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load (VL). Evaluating vaccine associations in VL at COVID-19 diagnosis in 4 phase 3 randomized, placebo-controlled vaccine trials, July 2020 to July 2021, VL reductions were 2.78 log10 copies/mL (95% confidence interval [CI], 1.38-4.18; n = 60 placebo, 11 vaccine) and 2.12 log10 copies/mL (95% CI, 1.44-2.80; n = 594 placebo, 36 vaccine) for NVX-CoV2373 and mRNA-1273, respectively. Associations were not significant for AZD1222 (0.59 log10 copies/mL; 95% CI, -.19 to 1.36; n = 90 placebo, 78 vaccine) or Ad26.COV2.S (0.23 log10 copies/mL; 95% CI, -.01 to .47; n = 916 placebo, 424 vaccine). Thus, vaccines potentially decreased transmission when ancestral SARS-CoV-2 predominated. Clinical Trials Registration. NCT04470427, NCT04505722, NCT04516746, NCT04611802.

COVID-19 Vaccine Efficacy in Participants With Weakened Immune Systems From 4 Randomized Controlled Trials.

BACKGROUND: Although the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are highly efficacious at preventing severe disease in the general population, current data are lacking regarding vaccine efficacy (VE) for individuals with mild immunocompromising conditions. METHODS: A post hoc, cross-protocol analysis of participant-level data from the blinded phase of four randomized, placebo-controlled, coronavirus disease 2019 (COVID-19) vaccine phase 3 trials (Moderna, AstraZeneca, Janssen, and Novavax) was performed. We defined a "tempered immune system" (TIS) variable via a consensus panel based on medical history and medications to determine VE against symptomatic and severe COVID-19 cases in TIS participants versus non-TIS individuals starting at 14 days after completion of the primary series through the blinded phase for each of the 4 trials. An analysis of participants living with well-controlled human immunodeficiency virus was conducted using the same methods. RESULTS: A total of 3852/30 351 (12.7%) Moderna participants, 3088/29 868 (10.3%) Novavax participants, 3549/32 380 (11.0%) AstraZeneca participants, and 5047/43 788 (11.5%) Janssen participants were identified as having a TIS. Most TIS conditions (73.9%) were due to metabolism and nutritional disorders. Vaccination (vs placebo) significantly reduced the likelihood of symptomatic and severe COVID-19 for all participants for each trial. VE was not significantly different for TIS participants versus non-TIS for either symptomatic or severe COVID-19 for each trial, nor was VE significantly different in the symptomatic endpoint for participants with human immunodeficiency virus. CONCLUSIONS: For individuals with mildly immunocompromising conditions, there is no evidence of differences in VE against symptomatic or severe COVID-19 compared with those with non-TIS in the 4 COVID-19 vaccine randomized controlled efficacy trials.

Safety and immunogenicity of a subtype C ALVAC-HIV (vCP2438) vaccine prime plus bivalent subtype C gp120 vaccine boost adjuvanted with MF59 or alum in healthy adults without HIV (HVTN 107): A phase 1/2a randomized trial.

BACKGROUND: Adjuvants are widely used to enhance and/or direct vaccine-induced immune responses yet rarely evaluated head-to-head. Our trial directly compared immune responses elicited by MF59 versus alum adjuvants in the RV144-like HIV vaccine regimen modified for the Southern African region. The RV144 trial of a recombinant canarypox vaccine vector expressing HIV env subtype B (ALVAC-HIV) prime followed by ALVAC-HIV plus a bivalent gp120 protein vaccine boost adjuvanted with alum is the only trial to have shown modest HIV vaccine efficacy. Data generated after RV144 suggested that use of MF59 adjuvant might allow lower protein doses to be used while maintaining robust immune responses. We evaluated safety and immunogenicity of an HIV recombinant canarypox vaccine vector expressing HIV env subtype C (ALVAC-HIV) prime followed by ALVAC-HIV plus a bivalent gp120 protein vaccine boost (gp120) adjuvanted with alum (ALVAC-HIV+gp120/alum) or MF59 (ALVAC-HIV+gp120/MF59) or unadjuvanted (ALVAC-HIV+gp120/no-adjuvant) and a regimen where ALVAC-HIV+gp120 adjuvanted with MF59 was used for the prime and boost (ALVAC-HIV+gp120/MF59 coadministration). METHODS AND FINDINGS: Between June 19, 2017 and June 14, 2018, 132 healthy adults without HIV in South Africa, Zimbabwe, and Mozambique were randomized to receive intramuscularly: (1) 2 priming doses of ALVAC-HIV (months 0 and 1) followed by 3 booster doses of ALVAC-HIV+gp120/MF59 (months 3, 6, and 12), n = 36; (2) 2 priming doses of ALVAC-HIV (months 0 and 1) followed by 3 booster doses of ALVAC-HIV+gp120/alum (months 3, 6, and 12), n = 36; (3) 4 doses of ALVAC-HIV+gp120/MF59 coadministered (months 0, 1, 6, and 12), n = 36; or (4) 2 priming doses of ALVAC-HIV (months 0 and 1) followed by 3 booster doses of ALVAC-HIV+gp120/no adjuvant (months 3, 6, and 12), n = 24. Primary outcomes were safety and occurrence and mean fluorescence intensity (MFI) of vaccine-induced gp120-specific IgG and IgA binding antibodies at month 6.5. All vaccinations were safe and well-tolerated; increased alanine aminotransferase was the most frequent related adverse event, occurring in 2 (1.5%) participants (1 severe, 1 mild). At month 6.5, vaccine-specific gp120 IgG binding antibodies were detected in 100% of vaccinees for all 4 vaccine groups. No significant differences were seen in the occurrence and net MFI of vaccine-specific IgA responses between the ALVAC-HIV+gp120/MF59-prime-boost and ALVAC-HIV+gp120/alum-prime-boost groups or between the ALVAC-HIV+gp120/MF59-prime-boost and ALVAC-HIV+gp120/MF59 coadministration groups. Limitations were the relatively small sample size per group and lack of evaluation of higher gp120 doses. CONCLUSIONS: Although MF59 was expected to enhance immune responses, alum induced similar responses to MF59, suggesting that the choice between these adjuvants may not be critical for the ALVAC+gp120 regimen. TRIAL REGISTRATION: HVTN 107 was registered with the South African National Clinical Trials Registry (DOH-27-0715-4894) and ClinicalTrials.gov (NCT03284710).

Two Randomized Trials of Neutralizing Antibodies to Prevent HIV-1 Acquisition.

BACKGROUND: Whether a broadly neutralizing antibody (bnAb) can be used to prevent human immunodeficiency virus type 1 (HIV-1) acquisition is unclear. METHODS: We enrolled at-risk cisgender men and transgender persons in the Americas and Europe in the HVTN 704/HPTN 085 trial and at-risk women in sub-Saharan Africa in the HVTN 703/HPTN 081 trial. Participants were randomly assigned to receive, every 8 weeks, infusions of a bnAb (VRC01) at a dose of either 10 or 30 mg per kilogram (low-dose group and high-dose group, respectively) or placebo, for 10 infusions in total. HIV-1 testing was performed every 4 weeks. The VRC01 80% inhibitory concentration (IC80) of acquired isolates was measured with the TZM-bl assay. RESULTS: Adverse events were similar in number and severity among the treatment groups within each trial. Among the 2699 participants in HVTN 704/HPTN 085, HIV-1 infection occurred in 32 in the low-dose group, 28 in the high-dose group, and 38 in the placebo group. Among the 1924 participants in HVTN 703/HPTN 081, infection occurred in 28 in the low-dose group, 19 in the high-dose group, and 29 in the placebo group. The incidence of HIV-1 infection per 100 person-years in HVTN 704/HPTN 085 was 2.35 in the pooled VRC01 groups and 2.98 in the placebo group (estimated prevention efficacy, 26.6%; 95% confidence interval [CI], -11.7 to 51.8; P = 0.15), and the incidence per 100 person-years in HVTN 703/HPTN 081 was 2.49 in the pooled VRC01 groups and 3.10 in the placebo group (estimated prevention efficacy, 8.8%; 95% CI, -45.1 to 42.6; P = 0.70). In prespecified analyses pooling data across the trials, the incidence of infection with VRC01-sensitive isolates (IC80 <1 µg per milliliter) per 100 person-years was 0.20 among VRC01 recipients and 0.86 among placebo recipients (estimated prevention efficacy, 75.4%; 95% CI, 45.5 to 88.9). The prevention efficacy against sensitive isolates was similar for each VRC01 dose and trial; VRC01 did not prevent acquisition of other HIV-1 isolates. CONCLUSIONS: VRC01 did not prevent overall HIV-1 acquisition more effectively than placebo, but analyses of VRC01-sensitive HIV-1 isolates provided proof-of-concept that bnAb prophylaxis can be effective. (Supported by the National Institute of Allergy and Infectious Diseases; HVTN 704/HPTN 085 and HVTN 703/HPTN 081 ClinicalTrials.gov numbers, NCT02716675 and NCT02568215.).

Statistical design and analysis of controlled human malaria infection trials.

BACKGROUND: Malaria is a potentially life-threatening disease caused by Plasmodium protozoa transmitted by infected Anopheles mosquitoes. Controlled human malaria infection (CHMI) trials are used to assess the efficacy of interventions for malaria elimination. The operating characteristics of statistical methods for assessing the ability of interventions to protect individuals from malaria is uncertain in small CHMI studies. This paper presents simulation studies comparing the performance of a variety of statistical methods for assessing efficacy of intervention in CHMI trials. METHODS: Two types of CHMI designs were investigated: the commonly used single high-dose design (SHD) and the repeated low-dose design (RLD), motivated by simian immunodeficiency virus (SIV) challenge studies. In the context of SHD, the primary efficacy endpoint is typically time to infection. Using a continuous time survival model, five statistical tests for assessing the extent to which an intervention confers partial or full protection under single dose CHMI designs were evaluated. For RLD, the primary efficacy endpoint is typically the binary infection status after a specific number of challenges. A discrete time survival model was used to study the characteristics of RLD versus SHD challenge studies. RESULTS: In a SHD study with the continuous time survival model, log-rank test and t-test are the most powerful and provide more interpretable results than Wilcoxon rank-sum tests and Lachenbruch tests, while the likelihood ratio test is uniformly most powerful but requires knowledge of the underlying probability model. In the discrete time survival model setting, SHDs are more powerful for assessing the efficacy of an intervention to prevent infection than RLDs. However, additional information can be inferred from RLD challenge designs, particularly using a likelihood ratio test. CONCLUSIONS: Different statistical methods can be used to analyze controlled human malaria infection (CHMI) experiments, and the choice of method depends on the specific characteristics of the experiment, such as the sample size allocation between the control and intervention groups, and the nature of the intervention. The simulation results provide guidance for the trade off in statistical power when choosing between different statistical methods and study designs.

Safety and Immunogenicity of Ad26-Vectored HIV Vaccine With Mosaic Immunogens and a Novel Mosaic Envelope Protein in HIV-Uninfected Adults: A Phase 1/2a Study.

BACKGROUND: Developing a cross-clade, globally effective HIV vaccine remains crucial for eliminating HIV. METHODS: This placebo-controlled, double-blind, phase 1/2a study enrolled healthy HIV-uninfected adults at low risk for HIV infection. They were randomized (1:4:1) to receive 4 doses of an adenovirus 26-based HIV-1 vaccine encoding 2 mosaic Gag and Pol, and 2 mosaic Env proteins plus adjuvanted clade C gp140 (referred to here as clade C regimen), bivalent protein regimen (clade C regimen plus mosaic gp140), or placebo. Primary end points were safety and antibody responses. RESULTS: In total 152/155 participants (clade C, n = 26; bivalent protein, n = 103; placebo, n = 26) received ≥1 injection. The highest adverse event (AE) severity was grade 3 (local pain/tenderness, 12%, 2%, and 0% of the respective groups; solicited systemic AEs, 19%, 15%, 0%). HIV-1 mosaic gp140-binding antibody titers were 79 595 ELISA units (EU)/mL and 137 520 EU/mL in the clade C and bivalent protein groups (P < .001) after dose 4 and 16 862 EU/mL and 25 162 EU/mL 6 months later. Antibody response breadth against clade C gp140 and clade C/non-clade C gp120 was highest in the bivalent protein group. CONCLUSIONS: Adding mosaic gp140 to the clade C regimen increased and broadened the elicited immune response without compromising safety or clade C responses. Clinical Trials Registration. NCT02935686.

Innate immune signatures to a partially-efficacious HIV vaccine predict correlates of HIV-1 infection risk.

The pox-protein regimen tested in the RV144 trial is the only vaccine strategy demonstrated to prevent HIV-1 infection. Subsequent analyses identified antibody and cellular immune responses as correlates of risk (CoRs) for HIV infection. Early predictors of these CoRs could provide insight into vaccine-induced protection and guide efforts to enhance vaccine efficacy. Using specimens from a phase 1b trial of the RV144 regimen in HIV-1-uninfected South Africans (HVTN 097), we profiled innate responses to the first ALVAC-HIV immunization. PBMC transcriptional responses peaked 1 day post-vaccination. Type I and II interferon signaling pathways were activated, as were innate pathways critical for adaptive immune priming. We then identified two innate immune transcriptional signatures strongly associated with adaptive immune CoR after completion of the 4-dose regimen. Day 1 signatures were positively associated with antibody-dependent cellular cytotoxicity and phagocytosis activity at Month 6.5. Conversely, a signature present on Days 3 and 7 was inversely associated with Env-specific CD4+ T cell responses at Months 6.5 and 12; rapid resolution of this signature was associated with higher Env-specific CD4+ T-cell responses. These are the first-reported early immune biomarkers of vaccine-induced responses associated with HIV-1 acquisition risk in humans and suggest hypotheses to improve HIV-1 vaccine regimens.

PfSPZ-CVac efficacy against malaria increases from 0% to 75% when administered in the absence of erythrocyte stage parasitemia: A randomized, placebo-controlled trial with controlled human malaria infection.

PfSPZ-CVac combines 'PfSPZ Challenge', which consists of infectious Plasmodium falciparum sporozoites (PfSPZ), with concurrent antimalarial chemoprophylaxis. In a previously-published PfSPZ-CVac study, three doses of 5.12x104 PfSPZ-CVac given 28 days apart had 100% vaccine efficacy (VE) against controlled human malaria infection (CHMI) 10 weeks after the last immunization, while the same dose given as three injections five days apart had 63% VE. Here, we conducted a dose escalation trial of similarly condensed schedules. Of the groups proceeding to CHMI, the first study group received three direct venous inoculations (DVIs) of a dose of 5.12x104 PfSPZ-CVac seven days apart and the next full dose group received three DVIs of a higher dose of 1.024x105 PfSPZ-CVac five days apart. CHMI (3.2x103 PfSPZ Challenge) was performed by DVI 10 weeks after the last vaccination. In both CHMI groups, transient parasitemia occurred starting seven days after each vaccination. For the seven-day interval group, the second and third vaccinations were therefore administered coincident with parasitemia from the prior vaccination. Parasitemia was associated with systemic symptoms which were severe in 25% of subjects. VE in the seven-day group was 0% (7/7 infected) and in the higher-dose, five-day group was 75% (2/8 infected). Thus, the same dose of PfSPZ-CVac previously associated with 63% VE when given on a five-day schedule in the prior study had zero VE here when given on a seven-day schedule, while a double dose given on a five-day schedule here achieved 75% VE. The relative contributions of the five-day schedule and/or the higher dose to improved VE warrant further investigation. It is notable that administration of PfSPZ-CVac on a schedule where vaccine administration coincided with blood-stage parasitemia was associated with an absence of sterile protective immunity. Clinical trials registration: NCT02773979.

Analysis of the HIV Vaccine Trials Network 702 Phase 2b-3 HIV-1 Vaccine Trial in South Africa Assessing RV144 Antibody and T-Cell Correlates of HIV-1 Acquisition Risk.

BACKGROUND: The ALVAC/gp120 + MF59 vaccines in the HIV Vaccine Trials Network (HVTN) 702 efficacy trial did not prevent human immunodeficiency virus-1 (HIV-1) acquisition. Vaccine-matched immunological endpoints that were correlates of HIV-1 acquisition risk in RV144 were measured in HVTN 702 and evaluated as correlates of HIV-1 acquisition. METHODS: Among 1893 HVTN 702 female vaccinees, 60 HIV-1-seropositive cases and 60 matched seronegative noncases were sampled. HIV-specific CD4+ T-cell and binding antibody responses were measured 2 weeks after fourth and fifth immunizations. Cox proportional hazards models assessed prespecified responses as predictors of HIV-1 acquisition. RESULTS: The HVTN 702 Env-specific CD4+ T-cell response rate was significantly higher than in RV144 (63% vs 40%, P = .03) with significantly lower IgG binding antibody response rate and magnitude to 1086.C V1V2 (67% vs 100%, P < .001; Pmag < .001). Although no significant univariate associations were observed between any T-cell or binding antibody response and HIV-1 acquisition, significant interactions were observed (multiplicity-adjusted P ≤.03). Among vaccinees with high IgG A244 V1V2 binding antibody responses, vaccine-matched CD4+ T-cell endpoints associated with decreased HIV-1 acquisition (estimated hazard ratios = 0.40-0.49 per 1-SD increase in CD4+ T-cell endpoint). CONCLUSIONS: HVTN 702 and RV144 had distinct immunogenicity profiles. However, both identified significant correlations (univariate or interaction) for IgG V1V2 and polyfunctional CD4+ T cells with HIV-1 acquisition. Clinical Trials Registration . NCT02968849.

A Deferred-Vaccination Design to Assess Durability of COVID-19 Vaccine Effect After the Placebo Group Is Vaccinated.

Multiple candidate vaccines to prevent COVID-19 have entered large-scale phase 3 placebo-controlled randomized clinical trials, and several have demonstrated substantial short-term efficacy. At some point after demonstration of substantial efficacy, placebo recipients should be offered the efficacious vaccine from their trial, which will occur before longer-term efficacy and safety are known. The absence of a placebo group could compromise assessment of longer-term vaccine effects. However, by continuing follow-up after vaccination of the placebo group, this study shows that placebo-controlled vaccine efficacy can be mathematically derived by assuming that the benefit of vaccination over time has the same profile for the original vaccine recipients and the original placebo recipients after their vaccination. Although this derivation provides less precise estimates than would be obtained by a standard trial where the placebo group remains unvaccinated, this proposed approach allows estimation of longer-term effect, including durability of vaccine efficacy and whether the vaccine eventually becomes harmful for some. Deferred vaccination, if done open-label, may lead to riskier behavior in the unblinded original vaccine group, confounding estimates of long-term vaccine efficacy. Hence, deferred vaccination via blinded crossover, where the vaccine group receives placebo and vice versa, would be the preferred way to assess vaccine durability and potential delayed harm. Deferred vaccination allows placebo recipients timely access to the vaccine when it would no longer be proper to maintain them on placebo, yet still allows important insights about immunologic and clinical effectiveness over time.

Safety, Pharmacokinetics, and Causal Prophylactic Efficacy of KAF156 in a Plasmodium falciparum Human Infection Study.

BACKGROUND: KAF156 is a novel antimalarial drug that is active against both liver- and blood-stage Plasmodium parasites, including drug-resistant strains. Here, we investigated the causal prophylactic efficacy of KAF156 in a controlled human malaria infection (CHMI) model. METHODS: In part 1, healthy, malaria-naive participants received 800 mg KAF156 or placebo 3 hours before CHMI with P. falciparum-infected mosquitoes. In part 2, KAF156 was administered as single doses of 800, 300, 100, 50, or 20 mg 21 hours post-CHMI. All participants received atovaquone/proguanil treatment if blood-stage infection was detected or on day 29. For each cohort, 7-14 subjects were enrolled to KAF156 treatment and up to 4 subjects to placebo. RESULTS: KAF156 at all dose levels was safe and well tolerated. Two serious adverse events were reported-both resolved without sequelae and neither was considered related to KAF156. In part 1, all participants treated with KAF156 and none of those randomized to placebo were protected against malaria infection. In part 2, all participants treated with placebo or 20 mg KAF156 developed malaria infection. In contrast, 50 mg KAF156 protected 3 of 14 participants from infection, and doses of 800, 300, and 100 mg KAF156 protected all subjects against infection. An exposure-response analysis suggested that a 24-hour postdose concentration of KAF156 of 21.5 ng/mL (90% confidence interval, 17.66-25.32 ng/mL) would ensure a 95% chance of protection from malaria parasite infection. CONCLUSIONS: KAF156 was safe and well tolerated and demonstrated high levels of pre- and post-CHMI protective efficacy. CLINICAL TRIALS REGISTRATION: NCT04072302.

Phase 1 Human Immunodeficiency Virus (HIV) Vaccine Trial to Evaluate the Safety and Immunogenicity of HIV Subtype C DNA and MF59-Adjuvanted Subtype C Envelope Protein.

BACKGROUND: The Pox-Protein Public-Private Partnership is performing a suite of trials to evaluate the bivalent subtype C envelope protein (TV1.C and 1086.C glycoprotein 120) vaccine in the context of different adjuvants and priming agents for human immunodeficiency virus (HIV) type 1 (HIV-1) prevention. METHODS: In the HIV Vaccine Trials Network 111 trial, we compared the safety and immunogenicity of DNA prime followed by DNA/protein boost with DNA/protein coadministration injected intramuscularly via either needle/syringe or a needle-free injection device (Biojector). One hundred thirty-two healthy, HIV-1-uninfected adults were enrolled from Zambia, South Africa, and Tanzania and were randomized to 1 of 6 arms: DNA prime, protein boost by needle/syringe; DNA and protein coadministration by needle/syringe; placebo by needle/syringe; DNA prime, protein boost with DNA given by Biojector; DNA and protein coadministration with DNA given by Biojector; and placebo by Biojector. RESULTS: All vaccinations were safe and well tolerated. DNA and protein coadministration was associated with increased HIV-1 V1/V2 antibody response rate, a known correlate of decreased HIV-1 infection risk. DNA administration by Biojector elicited significantly higher CD4+ T-cell response rates to HIV envelope protein than administration by needle/syringe in the prime/boost regimen (85.7% vs 55.6%; P = .02), but not in the coadministration regimen (43.3% vs 48.3%; P = .61). CONCLUSIONS: Both the prime/boost and coadministration regimens are safe and may be promising for advancement into efficacy trials depending on whether cellular or humoral responses are desired. CLINICAL TRIALS REGISTRATION: South African National Clinical Trials Registry (application 3947; Department of Health [DoH] no. DOH-27-0715-4917) and ClinicalTrials.gov (NCT02997969).

Neutralizing antibody responses over time in demographically and clinically diverse individuals recovered from SARS-CoV-2 infection in the United States and Peru: A cohort study.

BACKGROUND: People infected with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) experience a wide range of clinical manifestations, from asymptomatic and mild illness to severe illness and death, influenced by age and a variety of comorbidities. Neutralizing antibodies (nAbs) are thought to be a primary immune defense against the virus. Large, diverse, well-characterized cohorts of convalescent individuals provide standardized values to benchmark nAb responses to past SARS-CoV-2 infection and define potentially protective levels of immunity. METHODS AND FINDINGS: This analysis comprises an observational cohort of 329 HIV-seronegative adults in the United States (n = 167) and Peru (n = 162) convalescing from SARS-CoV-2 infection from May through October 2020. The mean age was 48 years (range 18 to 86), 54% of the cohort overall was Hispanic, and 34% identified as White. nAb titers were measured in serum by SARS-CoV-2.D614G Spike-pseudotyped virus infection of 293T/ACE2 cells. Multiple linear regression was applied to define associations between nAb titers and demographic variables, disease severity and time from infection or disease onset, and comorbidities within and across US and Peruvian cohorts over time. nAb titers peaked 28 to 42 days post-diagnosis and were higher in participants with a history of severe Coronavirus Disease 2019 (COVID-19) (p < 0.001). Diabetes, age >55 years, male sex assigned at birth, and, in some cases, body mass index were also independently associated with higher nAb titers, whereas hypertension was independently associated with lower nAb titers. nAb titers did not differ by race, underlying pulmonary disease or smoking. Two months post-enrollment, nAb ID50 (ID80) titers declined 3.5 (2.8)-fold overall. Study limitations in this observational, convalescent cohort include survivorship bias and missing early viral loads and acute immune responses to correlate with the convalescent responses we observed. CONCLUSIONS: In summary, in our cohort, nAb titers after SARS-CoV-2 infection peaked approximately 1 month post-diagnosis and varied by age, sex assigned at birth, disease severity, and underlying comorbidities. Our data show great heterogeneity in nAb responses among people with recent COVID-19, highlighting the challenges of interpreting natural history studies and gauging responses to vaccines and therapeutics among people with recent infection. Our observations illuminate potential correlations of demographic and clinical characteristics with nAb responses, a key element for protection from COVID-19, thus informing development and implementation of preventative and therapeutic strategies globally. TRIAL REGISTRATION: ClinicalTrials.gov NCT04403880.

Growth Rate of Plasmodium falciparum: Analysis of Parasite Growth Data From Malaria Volunteer Infection Studies.

BACKGROUND: Growth rate of malaria parasites in the blood of infected subjects is an important measure of efficacy of drugs and vaccines. METHODS: We used log-linear and sine-wave models to estimate the parasite growth rate of the 3D7 strain of Plasmodium falciparum using data from 177 subjects from 14 induced blood stage malaria (IBSM) studies conducted at QIMR Berghofer. We estimated parasite multiplication rate per 48 hours (PMR48), PMR per life-cycle (PMRLC), and parasite life-cycle duration. We compared these parameters to those from studies conducted elsewhere with infections induced by IBSM (n = 66), sporozoites via mosquito bite (n = 336), or injection (n = 51). RESULTS: The parasite growth rate of 3D7 in QIMR Berghofer studies was 0.75/day (95% confidence interval [CI], .73-.77/day), PMR48 was 31.9 (95% CI, 28.7-35.4), PMRLC was 16.4 (95% CI, 15.1-17.8), and parasite life-cycle was 38.8 hours (95% CI, 38.3-39.2 hours). These parameters were similar to estimates from IBSM studies elsewhere (0.71/day, 95% CI, .67-.75/day; PMR48 26.6, 95% CI, 22.2-31.8) but significantly higher (P < .001) than in sporozoite studies (0.47/day, 95% CI, .43-.50/day; PMR48 8.6, 95% CI, 7.3-10.1). CONCLUSIONS: Parasite growth rates were similar across different IBSM studies and higher than infections induced by sporozoite.

Chemoprophylaxis Vaccination: Phase I Study to Explore Stage-specific Immunity to Plasmodium falciparum in US Adults.

BACKGROUND: Chemoprophylaxis vaccination with sporozoites (CVac) with chloroquine induces protection against a homologous Plasmodium falciparum sporozoite (PfSPZ) challenge, but whether blood-stage parasite exposure is required for protection remains unclear. Chloroquine suppresses and clears blood-stage parasitemia, while other antimalarial drugs, such as primaquine, act against liver-stage parasites. Here, we evaluated CVac regimens using primaquine and/or chloroquine as the partner drug to discern whether blood-stage parasite exposure impacts protection against homologous controlled human malaria infection. METHODS: In a Phase I, randomized, partial double-blind, placebo-controlled study of 36 malaria-naive adults, all CVac subjects received chloroquine prophylaxis and bites from 12-15 P. falciparum-infected mosquitoes (CVac-chloroquine arm) at 3 monthly iterations, and some received postexposure primaquine (CVac-primaquine/chloroquine arm). Drug control subjects received primaquine, chloroquine, and uninfected mosquito bites. After a chloroquine washout, subjects, including treatment-naive infectivity controls, underwent homologous, PfSPZ controlled human malaria infection and were monitored for parasitemia for 21 days. RESULTS: No serious adverse events occurred. During CVac, all but 1 subject in the study remained blood-smear negative, while only 1 subject (primaquine/chloroquine arm) remained polymerase chain reaction-negative. Upon challenge, compared to infectivity controls, 3/3 chloroquine arm subjects displayed delayed patent parasitemia (P = .01) but not sterile protection, while 3/11 primaquine/chloroquine subjects remained blood-smear negative. CONCLUSIONS: CVac-primaquine/chloroquine is safe and induces sterile immunity to P. falciparum in some recipients, but a single 45 mg dose of primaquine postexposure does not completely prevent blood-stage parasitemia. Unlike previous studies, CVac-chloroquine did not produce sterile immunity. CLINICAL TRIALS REGISTRATION: NCT01500980.

Antibody and cellular responses to HIV vaccine regimens with DNA plasmid as compared with ALVAC priming: An analysis of two randomized controlled trials.

BACKGROUND: DNA plasmids promise a pragmatic alternative to viral vectors for prime-boost HIV-1 vaccines. We evaluated DNA plasmid versus canarypox virus (ALVAC) primes in 2 randomized, double-blind, placebo-controlled trials in southern Africa with harmonized trial designs. HIV Vaccine Trials Network (HVTN) 111 tested DNA plasmid prime by needle or needleless injection device (Biojector) and DNA plasmid plus gp120 protein plus MF59 adjuvant boost. HVTN 100 tested ALVAC prime and ALVAC plus gp120 protein plus MF59 adjuvant boost (same protein/adjuvant as HVTN 111) by needle. METHODS AND FINDINGS: The primary endpoints for this analysis were binding antibody (bAb) responses to HIV antigens (gp120 from strains ZM96, 1086, and TV1; variable 1 and 2 [V1V2] regions of gp120 from strains TV1, 1086, and B.CaseA, as 1086 V1V2 and B.CaseA were correlates of risk in the RV144 efficacy trial), neutralizing antibody (nAb) responses to pseudoviruses TV1c8.2 and MW925.26, and cellular responses to vaccine-matched antigens (envelope [Env] from strains ZM96, 1086, and TV1; and Gag from strains LAI and ZM96) at month 6.5, two weeks after the fourth vaccination. Per-protocol cohorts included vaccine recipients from HVTN 100 (n = 186, 60% male, median age 23 years) enrolled between February 9, 2015, and May 26, 2015 and from HVTN 111 (n = 56, 48% male, median age 24 years) enrolled between June 21, 2016, and July 13, 2017. IgG bAb response rates were 100% to 3 Env gp120 antigens in both trials. Response rates to V1V2 were lower and similar in both trials except to vaccine-matched 1086 V1V2, with rates significantly higher for the DNA-primed regimen than the ALVAC-primed regimen: 96.6% versus 72.7% (difference = 23.9%, 95% CI 15.6%-32.2%, p < 0.001). Among positive responders, bAb net mean fluorescence intensity (MFI) was significantly higher with the DNA-primed regimen than ALVAC-primed for 1086 V1V2 (geometric mean [GM] 2,833.3 versus 1,200.9; ratio = 2.36, 95% CI 1.42-3.92, p < 0.001) and B.CaseA V1V2 (GM 2314.0 versus 744.6, ratio = 3.11, 95% CI 1.51-6.38, p = 0.002). nAb response rates were >98% in both trials, with significantly higher 50% inhibitory dilution (ID50) among DNA-primed positive responders (n = 53) versus ALVAC-primed (n = 182) to tier 1A MW965.26 (GM 577.7 versus 265.7, ratio = 2.17, 95% CI 1.67-2.83, p < 0.001) and to TV1c8.2 (GM 187.3 versus 100.4, ratio = 1.87, 95% CI 1.48-2.35, p < 0.001). CD4+ T-cell response rates were significantly higher with DNA plasmid prime via Biojector than ALVAC prime (91.4% versus 52.8%, difference = 38.6%, 95% CI 20.5%-56.6%, p < 0.001 for ZM96.C; 88.0% versus 43.1%, difference = 44.9%, 95% CI 26.7%-63.1%, p < 0.001 for 1086.C; 55.5% versus 2.2%, difference = 53.3%, 95% CI 23.9%-82.7%, p < 0.001 for Gag LAI/ZM96). The study's main limitations include the nonrandomized comparison of vaccines from 2 different trials, the lack of data on immune responses to other non-vaccine-matched antigens, and the uncertain clinical significance of the observed immunological effects. CONCLUSIONS: In this study, we found that further investigation of DNA/protein regimens is warranted given enhanced immunogenicity to the V1V2 correlates of decreased HIV-1 acquisition risk identified in RV144, the only HIV vaccine trial to date to show any efficacy.

Safety and immune responses after a 12-month booster in healthy HIV-uninfected adults in HVTN 100 in South Africa: A randomized double-blind placebo-controlled trial of ALVAC-HIV (vCP2438) and bivalent subtype C gp120/MF59 vaccines.

BACKGROUND: HVTN 100 evaluated the safety and immunogenicity of an HIV subtype C pox-protein vaccine regimen, investigating a 12-month booster to extend vaccine-induced immune responses. METHODS AND FINDINGS: A phase 1-2 randomized double-blind placebo-controlled trial enrolled 252 participants (210 vaccine/42 placebo; median age 23 years; 43% female) between 9 February 2015 and 26 May 2015. Vaccine recipients received ALVAC-HIV (vCP2438) alone at months 0 and 1 and with bivalent subtype C gp120/MF59 at months 3, 6, and 12. Antibody (IgG, IgG3 binding, and neutralizing) and CD4+ T-cell (expressing interferon-gamma, interleukin-2, and CD40 ligand) responses were evaluated at month 6.5 for all participants and at months 12, 12.5, and 18 for a randomly selected subset. The primary analysis compared IgG binding antibody (bAb) responses and CD4+ T-cell responses to 3 vaccine-matched antigens at peak (month 6.5 versus 12.5) and durability (month 12 versus 18) timepoints; IgG responses to CaseA2_gp70_V1V2.B, a primary correlate of risk in RV144, were also compared at these same timepoints. Secondary and exploratory analyses compared IgG3 bAb responses, IgG bAb breadth scores, neutralizing antibody (nAb) responses, antibody-dependent cellular phagocytosis, CD4+ polyfunctionality responses, and CD4+ memory sub-population responses at the same timepoints. Vaccines were generally safe and well tolerated. During the study, there were 2 deaths (both in the vaccine group and both unrelated to study products). Ten participants became HIV-infected during the trial, 7% (3/42) of placebo recipients and 3% (7/210) of vaccine recipients. All 8 serious adverse events were unrelated to study products. Less waning of immune responses was seen after the fifth vaccination than after the fourth, with higher antibody and cellular response rates at month 18 than at month 12: IgG bAb response rates to 1086.C V1V2, 21.0% versus 9.7% (difference = 11.3%, 95% CI = 0.6%-22.0%, P = 0.039), and ZM96.C V1V2, 21.0% versus 6.5% (difference = 14.5%, 95% CI = 4.1%-24.9%, P = 0.004). IgG bAb response rates to all 4 primary V1V2 antigens were higher 2 weeks after the fifth vaccination than 2 weeks after the fourth vaccination: 87.7% versus 75.4% (difference = 12.3%, 95% CI = 1.7%-22.9%, P = 0.022) for 1086.C V1V2, 86.0% versus 63.2% (difference = 22.8%, 95% CI = 9.1%-36.5%, P = 0.001) for TV1c8.2.C V1V2, 67.7% versus 44.6% (difference = 23.1%, 95% CI = 10.4%-35.7%, P < 0.001) for ZM96.C V1V2, and 81.5% versus 60.0% (difference = 21.5%, 95% CI = 7.6%-35.5%, P = 0.002) for CaseA2_gp70_V1V2.B. IgG bAb response rates to the 3 primary vaccine-matched gp120 antigens were all above 90% at both peak timepoints, with no significant differences seen, except a higher response rate to ZM96.C gp120 at month 18 versus month 12: 64.5% versus 1.6% (difference = 62.9%, 95% CI = 49.3%-76.5%, P < 0.001). CD4+ T-cell response rates were higher at month 18 than month 12 for all 3 primary vaccine-matched antigens: 47.3% versus 29.1% (difference = 18.2%, 95% CI = 2.9%-33.4%, P = 0.021) for 1086.C, 61.8% versus 38.2% (difference = 23.6%, 95% CI = 9.5%-37.8%, P = 0.001) for TV1.C, and 63.6% versus 41.8% (difference = 21.8%, 95% CI = 5.1%-38.5%, P = 0.007) for ZM96.C, with no significant differences seen at the peak timepoints. Limitations were that higher doses of gp120 were not evaluated, this study was not designed to investigate HIV prevention efficacy, and the clinical significance of the observed immunological effects is uncertain. CONCLUSIONS: In this study, a 12-month booster of subtype C pox-protein vaccines restored immune responses, and slowed response decay compared to the 6-month vaccination. TRIAL REGISTRATION: ClinicalTrials.gov NCT02404311. South African National Clinical Trials Registry (SANCTR number: DOH--27-0215-4796).

A Randomized Trial Evaluating the Prophylactic Activity of DSM265 Against Preerythrocytic Plasmodium falciparum Infection During Controlled Human Malarial Infection by Mosquito Bites and Direct Venous Inoculation.

Background: DSM265 is a selective inhibitor of Plasmodium dihydroorotate dehydrogenase that fully protected against controlled human malarial infection (CHMI) by direct venous inoculation of Plasmodium falciparum sporozoites when administered 1 day before challenge and provided partial protection when administered 7 days before challenge. Methods: A double-blinded, randomized, placebo-controlled trial was performed to assess safety, tolerability, pharmacokinetics, and efficacy of 1 oral dose of 400 mg of DSM265 before CHMI. Three cohorts were studied, with DSM265 administered 3 or 7 days before direct venous inoculation of sporozoites or 7 days before 5 bites from infected mosquitoes. Results: DSM265-related adverse events consisted of mild-to-moderate headache and gastrointestinal symptoms. DSM265 concentrations were consistent with pharmacokinetic models (mean area under the curve extrapolated to infinity, 1707 µg*h/mL). Placebo-treated participants became positive by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and were treated 7-10 days after CHMI. Among DSM265-treated subjects, 2 of 6 in each cohort were sterilely protected. DSM265-treated recipients had longer times to development of parasitemia than placebo-treated participants (P < .004). Conclusions: This was the first CHMI study of a novel antimalarial compound to compare direct venous inoculation of sporozoites and mosquito bites. Times to qRT-PCR positivity and treatment were comparable for both routes. DSM265 given 3 or 7 days before CHMI was safe and well tolerated but sterilely protected only one third of participants.