Nancy Andon, MSc
A COVID Vaccine Strategy that Attacks Multiple Parts of SARS-CoV-2
Researchers involved in the clinical investigation of a new COVID-19 vaccine cited using HemaCare healthy donor starting materials for their study
There has been ongoing concern regarding whether current vaccines may show diminished protection against new strains of the virus. In the midst of intense debate over the timing and efficacy of vaccine booster shots, it’s important to remember that scientists are working to develop new COVID-19 vaccines that will potentially offer even greater protection from the disease than first-generation success stories.
Scientists, most of whom work at ImmunityBio in Culver City, CA, are conducting a Phase 1 clinical trial for their new dual-antigen COVID-19 vaccine. 
Immune research done in the wake of the COVID-19 pandemic demonstrated that a robust T cell immune response is critical to fighting off the disease.  With this knowledge in hand, the Culver City research team set out to develop a vaccine against SARS-CoV-2, the virus that causes COVID-19. The new vaccine would include both the SARS-CoV-2 viral spike protein, or “S” protein, and the viral nucleocapsid protein, or “N protein”. SARS-CoV-2 N protein is a highly conserved viral protein that has been shown to elicit a strong memory T cell immune response in convalescent COVID-19 patients. The team hopes that including the N protein in the vaccine will enable significantly expanded protection from new strains of the virus.
The researchers incorporated genetically modified versions of both viral peptides into their therapeutic design. They prepared an altered version of the S protein which was designed to increase its cell surface expression. This is referred to as “S-fusion” protein. They also designed a customized version of the viral N peptide with an enhanced T cell stimulation domain. This is referred to as N-ETSD. The newly modified antigens are delivered by way of a harmless human adenoviral vector, hAd5.
HemaCare Apheresis Materials Aid COVID-19 Vaccine Trial
For their research, the scientific team needed whole blood from healthy volunteer donors. They therefore obtained HemaCare healthy donor apheresis samples, which were used as starting material for the isolation of dendritic cells and T cells needed for antigen presentation studies.
Adenoviral vector constructs either without modification or containing the S-fusion protein, unmodified N protein, N-ETSD protein, or both S-fusion and N-ETSD were prepared for testing. The research team then isolated PBMCs from healthy donor whole blood. Monocyte-derived dendritic cells were differentiated from the PBMCs and transduced with the previously prepared human adenoviral test vectors to create “vaccinated” dendritic cells. Immune responses to the vaccinated dendritic cells were analyzed in culture using T cell preparations derived from either people who had no exposure to the SARS-CoV-2 virus, or who had been infected and were no longer symptomatic.
The scientists then carried out a number of in vitro experiments to look for S and N protein specific T cell immune response. As they expected, convalescent COVID-19 patient T cells had a significantly increased immune response compared to T cells from naïve COVID-19 individuals, as measured by ELISpot and interferon assays. This supported the case that convalescent individuals had S and N protein specific memory T cells capable of rapid immune response.
Over the next few months, the research team carried out a Phase 1 clinical trial to assess responses to vaccination with each of their test constructs, including the dual antigen construct. The team collected plasma from volunteer study subjects either immediately pre-vaccination, 14-16 days post-vaccination, and 21-23 days post-vaccination. Analysis of a vaccination time series gives scientists critical information about the strength and specific cellular make-up of immune responses over time.
Strong immune response to different strains of the COVID-19 virus
The results of the Phase 1 trial have been overwhelmingly positive. After a single injection of the dual antigen vaccine, SARS-CoV-2 naïve study participants showed an S and N protein specific immune response comparable to that of previously SARS-CoV-2 infected patients. Additionally, vaccinated participants demonstrated a comparable immune response to several different currently prevalent strains of the virus. SARS-CoV-2 convalescent participants vaccinated with the new constructs showed significantly greater T cell stimulation responses than naïve participants, and CD4+ and CD8+ T cells from both groups showed greater recognition of N-ETSD compared to N.
T cells collected at 14-16 days post-vaccination showed a ten-fold increase in T cell specific interferon-gamma secretion in response to N peptides compared to pre-vaccination samples. This response was maintained in Day 21-23 samples. T-cell secretion of IFN-g in response to S peptides also increased post-vaccination, by more than 3-fold by Day 14-16, and more than 10-fold by Day 21-23.
Adenoviral vector delivery has long been used as an effective means of introducing genetic material into a cell. One of the first COVID-19 vaccines (Johnson and Johnson) used an adenoviral delivery strategy, and several new adenovirus-based vaccines are currently in clinical trial. Current COVID-19 vaccine strategies are designed to provoke an immune response to the SARS-CoV-2 spike protein, and these vaccines have demonstrated significant protection from COVID-19. The ImmunityBio scientists believe that when this strategy is combined with strong stimulation of memory T cell immunity to the SARS-CoV-2 N protein, vaccination will likely result in a strong, long-lasting immune response to a wide array of SARS-CoV-2 strains. This new strategy could protect vaccinated populations not only from SARS-CoV-2 variants, but potentially from closely related respiratory diseases such as SARS and MERS. The team hope in the near future to continue to Phase 2 clinical trials of their dual-antigen vaccine.
- Sieling P. et al. Prime hAd5 Spike + Nucleocapsid Vaccination Induces Ten-Fold Increases in Mean T-Cell Responses in Phase 1 Subjects that are Sustained Against Spike Variants. MedRxiv preprint. Jun 2021.
- Painter MM., et al. Rapid induction of antigen-specific CD4+T cells is associated with coordinated humoral and cellular immunity to SARS-CoV-2 mRNA vaccination. Immunity. 54(9). Aug 2021.
This article was written by free-lance science writer Nancy Andon, MSc. It originally appeared on a blog managed by HemaCare, which Charles River acquired in 2020. HemaCare sells biological products such as T cells, stem cells, bone marrow, plasma, and other medical products.