Cynthia S. Hendel

Protection Against Malaria by Intravenous Immunization with a Nonreplicating Sporozoite Vaccine

Malaria Sporozoite Vaccine Each year, hundreds of millions of people are infected with Plasmodium falciparum, the mosquito-borne parasite that causes malaria. A preventative vaccine is greatly needed. Seder et al. (p. 1359, published online 8 August; see the Perspective by Good) now report the results from a phase I clinical trial where subjects were immunized intravenously with a whole, attenuated sporozoite vaccine. Three of 9 subjects who received four doses and zero of 6 subjects who received five doses of the vaccine went on to develop malaria after controlled malaria infection. Both antibody titers and cellular immune responses correlated positively with the dose of vaccine received, suggesting that both arms of the adaptive immune response may have participated in the observed protection. Intravenous immunization with an attenuated whole malaria sporozoite vaccine protected volunteers in a phase I clinical trial. [Also see Perspective by Good] Consistent, high-level, vaccine-induced protection against human malaria has only been achieved by inoculation of Plasmodium falciparum (Pf) sporozoites (SPZ) by mosquito bites. We report that the PfSPZ Vaccine—composed of attenuated, aseptic, purified, cryopreserved PfSPZ—was safe and wel-tolerated when administered four to six times intravenously (IV) to 40 adults. Zero of six subjects receiving five doses and three of nine subjects receiving four doses of 1.35 × 105 PfSPZ Vaccine and five of six nonvaccinated controls developed malaria after controlled human malaria infection (P = 0.015 in the five-dose group and P = 0.028 for overall, both versus controls). PfSPZ-specific antibody and T cell responses were dose-dependent. These data indicate that there is a dose-dependent immunological threshold for establishing high-level protection against malaria that can be achieved with IV administration of a vaccine that is safe and meets regulatory standards.

Chimpanzee Adenovirus Vector Ebola Vaccine - Preliminary Report.

Background The unprecedented 2014 epidemic of Ebola virus disease (EVD) prompted an international response to accelerate the availability of a preventive vaccine. A replication‐defective recombinant chimpanzee adenovirus type 3–vectored ebolavirus vaccine (cAd3‐EBO), encoding the glycoprotein from Zaire and Sudan species, that offers protection in the nonhuman primate model, was rapidly advanced into phase 1 clinical evaluation. Methods We conducted a phase 1, dose‐escalation, open‐label trial of cAd3‐EBO. Twenty healthy adults, in sequentially enrolled groups of 10 each, received vaccination intramuscularly in doses of 2×1010 particle units or 2×1011 particle units. Primary and secondary end points related to safety and immunogenicity were assessed throughout the first 8 weeks after vaccination; in addition, longer‐term vaccine durability was assessed at 48 weeks after vaccination. Results In this small study, no safety concerns were identified; however, transient fever developed within 1 day after vaccination in two participants who had received the 2×1011 particle‐unit dose. Glycoprotein‐specific antibodies were induced in all 20 participants; the titers were of greater magnitude in the group that received the 2×1011 particle‐unit dose than in the group that received the 2×1010 particle‐unit dose (geometric mean titer against the Zaire antigen at week 4, 2037 vs. 331; P=0.001). Glycoprotein‐specific T‐cell responses were more frequent among those who received the 2×1011 particle‐unit dose than among those who received the 2×1010 particle‐unit dose, with a CD4 response in 10 of 10 participants versus 3 of 10 participants (P=0.004) and a CD8 response in 7 of 10 participants versus 2 of 10 participants (P=0.07) at week 4. Assessment of the durability of the antibody response showed that titers remained high at week 48, with the highest titers in those who received the 2×1011 particle‐unit dose. Conclusions Reactogenicity and immune responses to cAd3‐EBO vaccine were dose‐dependent. At the 2×1011 particle‐unit dose, glycoprotein Zaire–specific antibody responses were in the range reported to be associated with vaccine‐induced protective immunity in challenge studies involving nonhuman primates, and responses were sustained to week 48. Phase 2 studies and efficacy trials assessing cAd3‐EBO are in progress. (Funded by the Intramural Research Program of the National Institutes of Health; VRC 207 ClinicalTrials.gov number, NCT02231866.)

Virologic effects of broadly neutralizing antibody VRC01 administration during chronic HIV-1 infection

A single infusion with broadly neutralizing antibody VRC01 resulted in lowered plasma virus load in HIV-1–infected subjects. Passive aggression for HIV Antibodies that neutralize HIV could add to the therapeutic arsenal to prevent and treat disease. Lynch et al. have now tested one such antibody—VRC01—in HIV-infected individuals. Although little difference was observed in viral reservoir in individuals on antiretroviral therapy, plasma viremia was reduced in untreated subjects with a single infusion of VRC01, preferentially suppressing neutralization-sensitive strains. Passive immunization with neutralizing antibodies could therefore aid in viral suppression in HIV-infected individuals. Passive immunization with HIV-1–neutralizing monoclonal antibodies (mAbs) is being considered for prevention and treatment of HIV-1 infection. As therapeutic agents, mAbs could be used to suppress active virus replication, maintain suppression induced by antiretroviral therapy (ART), and/or decrease the size of the persistent virus reservoir. We assessed the impact of VRC01, a potent human mAb targeting the HIV-1 CD4 binding site, on ART-treated and untreated HIV-1–infected subjects. Among six ART-treated individuals with undetectable plasma viremia, two infusions of VRC01 did not reduce the peripheral blood cell–associated virus reservoir measured 4 weeks after the second infusion. In contrast, six of eight ART-untreated, viremic subjects infused with a single dose of VRC01 experienced a 1.1 to 1.8 log10 reduction in plasma viremia. The two subjects with minimal responses to VRC01 were found to have predominantly VRC01-resistant virus before treatment. Notably, two subjects with plasma virus load <1000 copies/ml demonstrated virus suppression to undetectable levels for over 20 days until VRC01 levels declined. Among the remaining four subjects with baseline virus loads between 3000 and 30,000 copies, viremia was only partially suppressed by mAb infusion, and we observed strong selection pressure for the outgrowth of less neutralization-sensitive viruses. In summary, a single infusion of mAb VRC01 significantly decreased plasma viremia and preferentially suppressed neutralization-sensitive virus strains. These data demonstrate the virological effect of this neutralizing antibody and highlight the need for combination strategies to maintain virus suppression.

DNA priming and influenza vaccine immunogenicity: two phase 1 open label randomised clinical trials

Summary Background Because the general population is largely naive to H5N1 influenza, antibodies generated to H5 allow analysis of novel influenza vaccines independent of background immunity from previous infection. We assessed the safety and immunogenicity of DNA encoding H5 as a priming vaccine to improve antibody responses to inactivated influenza vaccination. Methods In VRC 306 and VRC 310, two sequentially enrolled phase 1, open-label, randomised clinical trials, healthy adults (age 18–60 years) were randomly assigned to receive intramuscular H5 DNA (4 mg) at day 0 or twice, at day 0 and week 4, followed by H5N1 monovalent inactivated vaccine (MIV; 90 μg) at 4 or 24 weeks, and compared with a two-dose regimen of H5N1 MIV with either a 4 or 24 week interval. Antibody responses were assessed by haemagglutination inhibition (HAI), ELISA, neutralisation (ID80), and immunoassays for stem-directed antibodies. T cell responses were assessed by intracellular cytokine staining. After enrolment, investigators and individuals were not masked to group assignment. VRC 306 and VRC 310 are registered with ClinicalTrials.gov, numbers NCT00776711 and NCT01086657, respectively. Findings In VRC 306, 60 individuals were randomly assigned to the four groups (15 in each) and 59 received the vaccinations. In VRC 310, of the 21 individuals enrolled, 20 received the vaccinations (nine received a two-dose regimen of H5N1 MIV and 11 received H5 DNA at day 0 followed by H5N1 MIV at week 24). H5 DNA priming was safe and enhanced H5-specific antibody titres following an H5N1 MIV boost, especially when the interval between DNA prime and MIV boost was extended to 24 weeks. In the two studies, DNA priming with a 24-week MIV boost interval induced protective HAI titres in 21 (81%) of 26 of individuals, with an increase in geometric mean titre (GMT) of more than four times that of individuals given the MIV-MIV regimen at 4 or 24 weeks (GMT 103–206 vs GMT 27–33). Additionally, neutralising antibodies directed to the conserved stem region of H5 were induced by this prime-boost regimen in several individuals. No vaccine-related serious adverse events were recorded. Interpretation DNA priming 24 weeks in advance of influenza vaccine boosting increased the magnitude of protective antibody responses (HAI) and in some cases induced haemagglutinin-stem-specific neutralising antibodies. A DNA-MIV vaccine regimen could enhance the efficacy of H5 or other influenza vaccines and shows that anti-stem antibodies can be elicited by vaccination in man. Funding National Institutes of Health.

Safety, pharmacokinetics and neutralization of the broadly neutralizing HIV-1 human monoclonal antibody VRC01 in healthy adults

VRC‐HIVMAB060‐00‐AB (VRC01) is a broadly neutralizing HIV‐1 monoclonal antibody (mAb) isolated from the B cells of an HIV‐infected patient. It is directed against the HIV‐1 CD4 binding site and is capable of potently neutralizing the majority of diverse HIV‐1 strains. This Phase I dose‐escalation study in healthy adults was conducted at the National Institutes of Health (NIH) Clinical Center (Bethesda, MD, USA). Primary objectives were the safety, tolerability and pharmacokinetics (PK) of VRC01 intravenous (i.v.) infusion at 5, 20 or 40 mg/kg, given either once (20 mg/kg) or twice 28 days apart (all doses), and of subcutaneous (s.c.) delivery at 5 mg/kg compared to s.c. placebo given twice, 28 days apart. Cumulatively, 28 subjects received 43 VRC01 and nine received placebo administrations. There were no serious adverse events or dose‐limiting toxicities. Mean 28‐day serum trough concentrations after the first infusion were 35 and 57 μg/ml for groups infused with 20 mg/kg (n = 8) and 40 mg/kg (n = 5) doses, respectively. Mean 28‐day trough concentrations after the second infusion were 56 and 89 μg/ml for the same two doses. Over the 5–40 mg/kg i.v. dose range (n = 18), the clearance was 0·016 l/h and terminal half‐life was 15 days. After infusion VRC01 retained expected neutralizing activity in serum, and anti‐VRC01 antibody responses were not detected. The human monoclonal antibody (mAb) VRC01 was well tolerated when delivered i.v. or s.c. The mAb demonstrated expected half‐life and pharmacokinetics for a human immunoglobulin G. The safety and PK results support and inform VRC01 dosing schedules for planning HIV‐1 prevention efficacy studies.

Protection against malaria at 1 year and immune correlates following PfSPZ vaccination

An attenuated Plasmodium falciparum (Pf) sporozoite (SPZ) vaccine, PfSPZ Vaccine, is highly protective against controlled human malaria infection (CHMI) 3 weeks after immunization, but the durability of protection is unknown. We assessed how vaccine dosage, regimen, and route of administration affected durable protection in malaria-naive adults. After four intravenous immunizations with 2.7 × 105 PfSPZ, 6/11 (55%) vaccinated subjects remained without parasitemia following CHMI 21 weeks after immunization. Five non-parasitemic subjects from this dosage group underwent repeat CHMI at 59 weeks, and none developed parasitemia. Although Pf-specific serum antibody levels correlated with protection up to 21–25 weeks after immunization, antibody levels waned substantially by 59 weeks. Pf-specific T cell responses also declined in blood by 59 weeks. To determine whether T cell responses in blood reflected responses in liver, we vaccinated nonhuman primates with PfSPZ Vaccine. Pf-specific interferon-γ-producing CD8 T cells were present at ∼100-fold higher frequencies in liver than in blood. Our findings suggest that PfSPZ Vaccine conferred durable protection to malaria through long-lived tissue-resident T cells and that administration of higher doses may further enhance protection.

Safety and Immunogenicity of DNA Vaccines Encoding Ebolavirus and Marburgvirus Wild-Type Glycoproteins in a Phase I Clinical Trial

Background Ebolavirus and Marburgvirus cause severe hemorrhagic fever with high mortality and are potential bioterrorism agents. There are no available vaccines or therapeutic agents. Previous clinical trials evaluated transmembrane-deleted and point-mutation Ebolavirus glycoproteins (GPs) in candidate vaccines. Constructs evaluated in this trial encode wild-type (WT) GP from Ebolavirus Zaire and Sudan species and the Marburgvirus Angola strain expressed in a DNA vaccine. Methods The VRC 206 study evaluated the safety and immunogenicity of these DNA vaccines (4 mg administered intramuscularly by Biojector) at weeks 0, 4, and 8, with a homologous boost at or after week 32. Safety evaluations included solicited reactogenicity and coagulation parameters. Primary immune assessment was done by means of GP-specific enzyme-linked immunosorbent assay. Results The vaccines were well tolerated, with no serious adverse events; 80% of subjects had positive enzyme-linked immunosorbent assay results (≥30) at week 12. The fourth DNA vaccination boosted the immune responses. Conclusions The investigational Ebolavirus and Marburgvirus WT GP DNA vaccines were safe, well tolerated, and immunogenic in this phase I study. These results will further inform filovirus vaccine research toward a goal of inducing protective immunity by using WT GP antigens in candidate vaccine regimens. Clinical Trials Registration NCT00605514.

DNA Vaccines Encoding Ebolavirus and Marburgvirus Wild Type Glycoproteins are Safe and Immunogenic in a Phase I Clinical Trial

Background Ebolavirus and Marburgvirus cause severe hemorrhagic fever with high mortality and are potential bioterrorism agents. There are no available vaccines or therapeutic agents. Previous clinical trials evaluated transmembrane-deleted and point-mutation Ebolavirus glycoproteins (GPs) in candidate vaccines. Constructs evaluated in this trial encode wild-type (WT) GP from Ebolavirus Zaire and Sudan species and the Marburgvirus Angola strain expressed in a DNA vaccine. Methods The VRC 206 study evaluated the safety and immunogenicity of these DNA vaccines (4 mg administered intramuscularly by Biojector) at weeks 0, 4, and 8, with a homologous boost at or after week 32. Safety evaluations included solicited reactogenicity and coagulation parameters. Primary immune assessment was done by means of GP-specific enzyme-linked immunosorbent assay. Results The vaccines were well tolerated, with no serious adverse events; 80% of subjects had positive enzyme-linked immunosorbent assay results (≥30) at week 12. The fourth DNA vaccination boosted the immune responses. Conclusions The investigational Ebolavirus and Marburgvirus WT GP DNA vaccines were safe, well tolerated, and immunogenic in this phase I study. These results will further inform filovirus vaccine research toward a goal of inducing protective immunity by using WT GP antigens in candidate vaccine regimens. Clinical Trials Registration NCT00605514.

Attenuated PfSPZ Vaccine induces strain-transcending T cells and durable protection against heterologous controlled human malaria infection

Significance A highly effective malaria vaccine capable of long-term protection against genetically diverse strains is urgently needed. Here, we demonstrate that a three-dose regimen of a live attenuated whole-parasite malaria vaccine conferred durable sterile protection through 33 weeks in ∼50% of subjects against a controlled human malaria infection strain that is heterologous to the vaccine strain. Prior studies by others and us have shown that T cells are critical to mediating sterile protection after live-attenuated malaria vaccination. Here, we provide evidence that this Plasmodium falciparum sporozoite vaccine (PfSPZ Vaccine) induces antigen-specific IFN-γ-producing CD8 and CD4 T cells that recognize both the homologous and the heterologous Pf strain. A live-attenuated malaria vaccine, Plasmodium falciparum sporozoite vaccine (PfSPZ Vaccine), confers sterile protection against controlled human malaria infection (CHMI) with Plasmodium falciparum (Pf) parasites homologous to the vaccine strain up to 14 mo after final vaccination. No injectable malaria vaccine has demonstrated long-term protection against CHMI using Pf parasites heterologous to the vaccine strain. Here, we conducted an open-label trial with PfSPZ Vaccine at a dose of 9.0 × 105 PfSPZ administered i.v. three times at 8-wk intervals to 15 malaria-naive adults. After CHMI with homologous Pf parasites 19 wk after final immunization, nine (64%) of 14 (95% CI, 35–87%) vaccinated volunteers remained without parasitemia compared with none of six nonvaccinated controls (P = 0.012). Of the nine nonparasitemic subjects, six underwent repeat CHMI with heterologous Pf7G8 parasites 33 wk after final immunization. Five (83%) of six (95% CI, 36–99%) remained without parasitemia compared with none of six nonvaccinated controls. PfSPZ-specific T-cell and antibody responses were detected in all vaccine recipients. Cytokine production by T cells from vaccinated subjects after in vitro stimulation with homologous (NF54) or heterologous (7G8) PfSPZ were highly correlated. Interestingly, PfSPZ-specific T-cell responses in the blood peaked after the first immunization and were not enhanced by subsequent immunizations. Collectively, these data suggest durable protection against homologous and heterologous Pf parasites can be achieved with PfSPZ Vaccine. Ongoing studies will determine whether protective efficacy can be enhanced by additional alterations in the vaccine dose and number of immunizations.

Safety, tolerability, and immunogenicity of two Zika virus DNA vaccine candidates in healthy adults: randomised, open-label, phase 1 clinical trials

Summary Background The Zika virus epidemic and associated congenital infections have prompted rapid vaccine development. We assessed two new DNA vaccines expressing premembrane and envelope Zika virus structural proteins. Methods We did two phase 1, randomised, open-label trials involving healthy adult volunteers. The VRC 319 trial, done in three centres, assessed plasmid VRC5288 (Zika virus and Japanese encephalitis virus chimera), and the VRC 320, done in one centre, assessed plasmid VRC5283 (wild-type Zika virus). Eligible participants were aged 18–35 years in VRC19 and 18–50 years in VRC 320. Participants were randomly assigned 1:1 by a computer-generated randomisation schedule prepared by the study statistician. All participants received intramuscular injection of 4 mg vaccine. In VRC 319 participants were assigned to receive vaccinations via needle and syringe at 0 and 8 weeks, 0 and 12 weeks, 0, 4, and 8 weeks, or 0, 4, and 20 weeks. In VRC 320 participants were assigned to receive vaccinations at 0, 4, and 8 weeks via single-dose needle and syringe injection in one deltoid or split-dose needle and syringe or needle-free injection with the Stratis device (Pharmajet, Golden, CO, USA) in each deltoid. Both trials followed up volunteers for 24 months for the primary endpoint of safety, assessed as local and systemic reactogenicity in the 7 days after each vaccination and all adverse events in the 28 days after each vaccination. The secondary endpoint in both trials was immunogenicity 4 weeks after last vaccination. These trials are registered with ClinicalTrials.gov, numbers NCT02840487 and NCT02996461. Findings VRC 319 enrolled 80 participants (20 in each group), and VRC 320 enrolled 45 participants (15 in each group). One participant in VRC 319 and two in VRC 320 withdrew after one dose of vaccine, but were included in the safety analyses. Both vaccines were safe and well tolerated. All local and systemic symptoms were mild to moderate. In both studies, pain and tenderness at the injection site was the most frequent local symptoms (37 [46%] of 80 participants in VRC 319 and 36 [80%] of 45 in VRC 320) and malaise and headache were the most frequent systemic symptoms (22 [27%] and 18 [22%], respectively, in VRC 319 and 17 [38%] and 15 [33%], respectively, in VRC 320). For VRC5283, 14 of 14 (100%) participants who received split-dose vaccinations by needle-free injection had detectable positive antibody responses, and the geometric mean titre of 304 was the highest across all groups in both trials. Interpretation VRC5283 was well tolerated and has advanced to phase 2 efficacy testing. Funding Intramural Research Program of the Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health.