Developing Multivalent Nanoparticle Vaccines Against Current and Future Viruses

Citation

Cohen, Alexander Armand (2021) Developing Multivalent Nanoparticle Vaccines Against Current and Future Viruses. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/r33z-kj46. https://resolver.caltech.edu/CaltechTHESIS:06082021-015935441

Abstract

The 1918-1919 flu pandemic resulted in an estimated 50 to 100 million deaths worldwide, making it the deadliest pandemic in modern history. It was caused by a new influenza virus that likely spilled over from birds and reassorted with a human influenza virus. Since the human population was immunologically naïve to this virus, transmission and lethality was much higher than for seasonal influenza outbreaks. Numerous pandemic influenza viruses emerged within the next century, with none causing the same amount of carnage. There is likely to be future influenza pandemics, with wild migratory birds being carriers of a wide swath of different influenza A viruses. Zoonotic transmission of Avian influenza has taken place with limited human to human transmission. There is evidence showing that the barrier of human transmissibility by some of these avian viruses is not very high, and therefore emergence into humans is possible, with most if not all of the population immunologically naïve. The humoral immune response to influenza is defined by the imprinting of the antibody response to immunodominant epitopes. Such responses can impair immunity, providing less adequate protection against seasonal and pandemic infections, as well as poorer immunity induced by seasonal vaccines. There are instances where imprinting can be advantageous and even offer protection against pandemic or avian viruses, particularly when conserved epitopes to the HA stalk are exploited. Manipulating the antibody response to recognizing conserved stalk epitopes on influenza HA is therefore a strategy being used for universal influenza vaccines. In the second Chapter of this thesis, a mosaic nanoparticle immunization strategy for inducing breadth of antibody responses against HA will be described. This strategy involves the co-display of HAs from up to eight different strains on a particle platform. Although the breadth of antibody responses elicited by immunization of these particles was limited, this work provides insight into the antigenicity of such particles, and a possible alternative to current influenza vaccines.

Approximately 100 years after the 1918-1919 flu pandemic, a deadly SARS-like coronavirus, known as SARS-CoV-2, emerged in the human population resulting in a currently ongoing pandemic. This came less than two decades after the small but deadly SARS outbreak, essentially a warning call for this class of coronaviruses. Other SARS-like coronavirus strains in bats have been identified and shown to be human tropic, though resulting in an attenuated infection. Some of these viruses can infect via hACE2 but there are others that may use an unknown receptor for entry into VERO cells as well as human cell lines. There is evidence that the major barrier to zoonosis is protease compatibility, which could be gained through recombination events or errors during replication. Therefore, future SARS-like coronaviruses (sarbecovirus) may emerge in humans, seeding future outbreaks. The antibody response to SARS-CoV-2 is robust and protective. Furthermore, there is the presence of conserved epitopes particularly on the RBD that can be targeted by antibodies that are cross-neutralizing against many SARS-like coronaviruses. Exploiting these cross-reactive epitopes is one strategy that can be used for developing a universal coronavirus vaccine. In Chapter 3 of this thesis, a similar mosaic nanoparticle immunization strategy will be described, that attempts to elicit cross-reactive antibodies against the SARS-like coronavirus family. The mosaic nanoparticles co-display the RBDs of eight different sarbecovirus strains including SARS-CoV-2. Immunization with these mosaic-RBD nanoparticles elicited polyclonal antibody responses that were cross-reactive as well as cross-neutralizing against sarbecoviruses strains both present and not present on the particles.

Thesis Files