Safety, tolerability, and immunogenicity of a SARS-CoV-2 recombinant spike protein vaccine: a randomised, double-blind, placebo-controlled, phase 1-2 clinical trial (ABDALA Study). (preprint)

AimTo evaluate the safety and immunogenicity of a SARS-CoV-2 recombinant spike protein vaccine (Abdala), administered intramuscularly in different strengths and vaccination schedules. MethodA phase 1-2, randomized, double-blind, placebo-controlled trial was done. Subjects were randomly distributed in 3 groups: placebo, 25 and 50{micro}g RBD. The product was applied intramuscularly, 0.5 mL in the deltoid region. During the first phase, two immunization schedules were studied: short (0-14-28 days) and long (0-28-56 days). In phase 2, only the short scheme was evaluated. The main endpoints were: safety and proportion of subjects with seroconversion of anti-RBD IgG antibodies to SARS-CoV-2. Blood samples were collected in several points according to the corresponding vaccination schedule to determine the level of RBD-specific IgG antibodies (seroconversion rates and geometric mean of the titers), the percentage of inhibition of RBD-ACE-2 binding and levels of neutralizing antibodies. ResultsThe product was well tolerated. Severe adverse events were not reported. Adverse reactions were minimal, mostly mild and local (from the injection site), resolved in the first 24-48 hours without medication. In phase 1, at day 56 (28 days after the third dose of the short vaccination schedule, 0-14-28 days) seroconversion of anti-RBD IgG was seen in 95.2 % of the participants (20/21) for the 50g group and 81 % of the participants (17/21) for the 25g group, and none in the placebo group (0/22); whereas neutralizing antibodies to SARS-CoV-2 were seen in 80 % of the participants (8/10) for the 50g group and 94.7% of the participants (18/19) for the 25g group. For the long schedule, at day 70 (14 days after the third dose) seroconversion of anti-RBD IgG was seen in 100% of the participants (21/21) for the 50g group and 94.7% of the participants (18/19) for the 25g group, and none in the placebo group (0/22); whereas neutralizing antibodies to SARS-CoV-2 were seen in 95 % of the participants (19/20) for the 50g group and 93.8% of the participants (15/16) for the 25g group In phase 2, at day 56 seroconversion of anti-RBD IgG was seen in 89.2% of the participants (214/240) for the 50g group, 77.7% of the participants (185/238) for the 25g group, and 4.6% in the placebo group (11/239); whereas neutralizing antibodies to SARS-CoV-2 were seen in 97.3% of the participants (146/150) for the 50g group and 95.1% of the participants (58/61) for the 25g group. ConclusionAbdala vaccine against SARS-CoV-2 was safe, well tolerated and induced humoral immune responses against SARS-CoV-2 among adults from 19 to 80 years of age. Trial registration / Review protocolRPCEC00000346. Cuban Public Clinical Trial Registry (WHO accepted Primary Registry). Available from: https://rpcec.sld.cu/en/trials/RPCEC00000346-En Information about the ethical aspects and IRB approvalThe protocol was approved by the Ethic Committee of the participating hospital and by the Cuban Regulatory Authority (Center for State Control of Drugs, Medical Devices and Equipment). Summary boxCOVID-19 is a serious global health problem. Vaccines are urgently needed to protect humanity. Multiple vaccine candidates are currently being evaluated. The article shows promising safety and immunogenicity results for a vaccine candidate, based on the recombinant RBD subunit of the spike protein.

Elevated antibody titers in Abdala vaccinees evaluated by Elecsys(R) anti-SARS-CoV-2 S highly correlate with UMELISA SARS-CoV-2 ANTI RBD, ACE-2 binding inhibition and viral neutralization assays. (preprint)

SARS-CoV-2, a recently emerged coronavirus, is causing high morbidity and mortality worldwide since December 2019, posing an enormous health, social and economic problem. Obtaining effective treatments that can diminish deaths and sequelae and vaccines to slow or prevent viral transmission, and reduce disease severity and/or death are of utmost importance. Abdala is a Cuban vaccine based on the recombinant RBD subunit of the spike protein expressed in Pichia pastoris yeast. It demonstrated high efficacy (92.28 %) in phase III clinical trials for reducing transmission, and more than 90% effectiveness in reducing disease severity and mortality. Antibody titers were evaluated in 42 Abdala vaccinees using the Elecsys(R) Anti-SARS-CoV-2 S test. Fifteen days after immunization, sera from vaccinees showed high antibody titers (median of 1595 U/mL). The results obtained in this study also demonstrate correlation between the Cuban test UMELISA SARS-CoV-2 ANTI RBD used during the clinical trials and Elecsys(R) test results.

The SARS-CoV-2 receptor-binding domain expressed in Pichia pastoris as a candidate vaccine antigen (preprint)

1. The effort to develop vaccines based on economically accessible technological platforms available by developing countries vaccine manufacturers is essential to extend the immunization to the whole world population and to achieve the desired herd immunity, necessary to end the COVID-19 pandemic. Here we report on the development of a SARS-CoV-2 receptor-binding domain (RBD) protein, expressed in yeast Pichia pastoris. The RBD was modified with addition of flexible N- and C-terminal amino acid extensions aimed to modulate the protein/protein interactions and facilitate protein purification. Fermentation with yeast extract culture medium yielded 30–40 mg/L. After purification by immobilized metal ion affinity chromatography and hydrophobic interaction chromatography, the RBD protein was characterized by mass-spectrometry, circular dichroism, and binding affinity to angiotensin-converting enzyme 2 (ACE2) receptor. The recombinant protein shows high antigenicity with convalescent human sera and also with sera from individuals vaccinated with the Pfizer-BioNTech mRNA or Sputnik V adenoviral-based vaccines. The RBD protein stimulates IFNγ, IL-2, IL-6, IL-4, and TNFα in mice secreting splenocytes from PBMC and lung CD3+ enriched cells. Immunogenicity studies with 50 µg of the recombinant RBD formulated with alum, induce high levels of binding antibodies in mice and non-human primates, assessed by ELISA plates covered with RBD protein expressed in HEK293T cells. The mouse sera inhibited the RBD binding to ACE2 receptor in an in-vitro test and show neutralization of SARS-CoV-2 infection of Vero E6 cells. These data suggest that the RBD recombinant protein expressed in yeast P. pastoris is suitable as a vaccine candidate against COVID-19. Highlights The RBD protein (C-RBD-H6 PP) is expressed with high purity in P. pastoris . Physico-chemical characterization confirms the right folding of the protein. The recombinant protein shows high antigenicity with sera from convalescents. The sera from animals inhibit the RBD-ACE2 binding and neutralize the virus. The C-RBD-H6 protein stimulates IFNγ, IL-2, IL-6, IL-4, and TNFα in mice.