Monoclonal antibodies have been significant in the effort to treat coronavirus disease 2019 (COVID-19), conferring immediate immunity against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, being designer proteins, they must be given intravenously, which reduces the amount of antibodies available to the body in the lungs.
A new study, released as a preprint on the bioRxiv* server, presents a new monoclonal antibody (MAb) called DZIF-10c that powerfully neutralizes SARS-CoV-2, including the current variants of concern (VOCs). With high bioavailability in the lungs and wide distribution in the body, the antibody was able to prevent SARS-CoV-2 infection in mice after intranasal administration.
Monoclonal neutralizing antibodies bind to viral surface proteins, in this case, the spike protein that mediates viral entry into the host cell via the cell surface receptor, the angiotensin-converting enzyme 2 (ACE2).
DZIF-10c is an Mab previously identified from a panel of highly neutralizing antibodies because of its commercial production possibilities for clinical use. In the current study, it is shown to bind with high affinity to the receptor-binding domain (RBD) of the SARS-CoV-2.
In comparison with the already tested Regeneron antibodies, DZIF-10c showed a 50% effective concentration (EC50) of 0.046 μg/ml, vs. 0.057 μg/ml for REGN10933) and 0.061 μg/ml (REGN10987).
Interestingly, DZIF-10c binds preferentially to the “up” conformation of the spike RBD, which indicates the spike is primed but still in the prefusion state. It also appears to inhibit spike-receptor binding without directly interfering with the receptor-binding motif on the RBD.
High neutralizing capacity against wildtype and two VOCs
Moreover, it efficiently inhibited cell infection by SARS-CoV-2 pseudoviruses expressing six variants of the spike protein. The antibody concentration needed to neutralize 50% of the viral particles (half-maximal inhibitory concentration, IC50) was 0.007 μg/ml.
This included the D614G mutation, as well as the 69-70 155 deletion mutant and other single mutations superimposed on the wildtype Wuhan virus and also actual VOCs. In 16/19 cases, the presence of the mutation did not affect neutralization by DZIF-10c.
Those mutations that reduced its neutralizing activity included E484K and F490S, while the B.1.351 VOC was also resistant, all three showing a 2.5-log-fold increase in the IC50.
When tested against the authentic virus and the authentic VOC B.1.1.7, it completely inhibited infection with an IC100 of 0.01 μg/ml. Its activity was 17-fold lower against VOC B.1.351, though it continued to inhibit infection.
This antibody also has a half-life in vivo of about two weeks, similar to that of human antiviral antibodies, showing a prolonged period of activity at exceptionally high levels, favorable to its clinical use.
Pre-treatment with DZIF-10c averts SARS-CoV-2 infection
In the second stage, mice were treated with the preparation in advance, either by systemic administration, following intraperitoneal injection, or by the topical route, spraying it inside the nose. The mice were then exposed to the virus, DZIF-10c efficiently prevented infection.
In both cases, DZIF-10c efficiently prevented infection, as shown by the absence of infectious virus and 2-log reduction in viral genomic ribonucleic acid (RNA). The decrease in viral RNA was three times higher in the intranasal group compared to the intraperitoneal group.
Subgenomic RNA, indicating viral replication, was also reduced by 3 logs and 2 logs in the intranasal and intraperitoneal group, compared to the control mice. Thus, viral replication was six times less after intranasal administration.
In the DZIF-10c-treated mice, lung injury was significantly reduced, with viral RNA limited to single cells, sparing the adjacent tissue in the intraperitoneal group, and no trace of viral RNA in the intranasal group.
“These findings indicate that prophylactic treatment with DZIF-10c efficiently protected hACE2-transduced mice from infection with SARS-CoV-2 as well as SARS-CoV-2-248 related lung pathology.” The effects were more marked with intranasal administration.
Therapeutic efficacy of DZIF-10c
The scientists also showed that following intranasal inoculation with SARS-CoV-2, the intranasal or intraperitoneal administration of DZIF-10c neutralized the virus efficiently. No viral particles were recovered from lung tissue in the treatment group.
Both genomic and subgenomic viral RNA levels were somewhat less, by 2-3-fold in the treated groups compared to controls. There were no signs of antibody-dependent enhancement of infection either in vitro.
What are the implications?
Not only does DZIF-10c prevent and treat SARS-CoV-2 infection in a mouse model, but its remarkably increased efficacy following intranasal efficacy makes it especially relevant for respiratory viruses such as SARS-CoV-2. When given systemically, these antibodies fail to achieve high concentrations in the lung compared to the serum, perhaps even below the therapeutic levels.
DZIF-10c also neutralized two circulating VOCs (B.1.1.7 at full efficiency, with reduced but still potent inhibition of B.1.351). The latter finding is especially important since B.1.351 completely resists the two Regeneron MAbs in clinical use at present.
DZIF-10c also proved its ability to inhibit 16/19 spike mutations, several of which abolished the neutralizing efficacy of several MAbs. Thus, not only is it remarkably potent, fully comparable with currently available neutralizing antibodies in clinical use at present, but it has a wider breadth of coverage of SARS-CoV-2 variants.
“These results not only identify DZIF-10c as a novel highly potent neutralizing antibody, but further pave the way for a topical application of anti-SARS-CoV-2 antibodies.” Phase I/II trials are now underway to test this pioneering inhaled neutralizing antibody against SARS-CoV-2.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.