Benzinga | May 26, 2021 07:12AM EDT

Altimmune Announces Preclinical Results From Phase I Study Of AdCOVID; Says Similar Neutralization Titers Observed For Both Ancestral And B.1.351 South African Variant

Similar Neutralization Titers Observed for Both Ancestral

and B.1.351 South African Variant

Phase I Clinical Trial of AdCOVID Expected to Report Data in June 2021

GAITHERSBURG, Md., May 26, 2021 (GLOBE NEWSWIRE) -- Altimmune, Inc. (NASDAQ:ALT), a clinical-stage biopharmaceutical company, today announced new results from a preclinical study demonstrating the ability of its AdCOVID vaccine candidate to neutralize the rapidly emerging SARS-CoV-2 B.1.351 variant of concern that originated in South Africa. B.1.351 carries multiple mutations in the receptor binding domain (RBD) including the E484K mutation that has been shown to substantially decrease the ability of authorized vaccines to neutralize the virus.

In the current study, performed in collaboration with investigators at Saint Louis University, the neutralizing titer against the B.1.351 variant virus was only 4.4-fold lower than the neutralizing titer against an original or ancestral Wuhan-like isolate when measured seven weeks after a single intranasal dose of AdCOVID. Furthermore, in mice that received a booster dose of AdCOVID, the reduction in the neutralizing titer against the B.1.351 variant was only 1.8-fold lower at seven weeks post vaccination; statistically the same as the neutralization titer against the Wuhan isolate. The serum neutralizing antibody titers were determined using a live virus focus reduction neutralization titer (FRNT) assay with a 50% neutralization endpoint.

"These data are impressive considering the B.1.351 variant has been consistently difficult to neutralize following vaccination with the original prototype vaccines," said James Brien, Ph.D., Assistant Professor, Molecular Microbiology and Immunology at Saint Louis University. "If the simple addition of an AdCOVID booster dose is able to provide effective coverage against variants of concern it would greatly simplify our response to the challenge presented by this virus by eliminating the need to develop new variant adapted vaccines."

Importantly, AdCOVID also promoted a strong mucosal neutralizing response to the B.1.351 virus in the respiratory tract with bronchoalveolar lavages showing neutralization of the variant virus. These preclinical data suggest that vaccination with AdCOVID leads to a cross-neutralizing antibody response both systemically and locally within the respiratory tract that can effectively neutralize the B.1.351 virus.

"We believe that our selection of the RBD of the spike protein as the vaccine antigen was key in obtaining these impressive results," said Scot Roberts, Ph.D., Chief Scientific Officer at Altimmune. "From a neutralization perspective, AdCOVID is designed to focus the immune response on RBD, the most important part of the SARS-CoV-2 virus. The likely result is the development of antibodies to sub-dominant or cryptic neutralizing epitopes not readily recognized when presented in the context of the entire spike protein, which is targeted by most other vaccine candidates."