Zachary Kazaz—McMaster Integrated Science Program, Specialization in Biology 2025
Recent advancements in genome editing have facilitated major developments in both existing and new gene therapies (Hirakawa et al., 2020). The culmination of these findings became most evident on July 5th 2018, when Dr. Carl June and Professor Michel Sadelain published a seminal review article in the New England Journal of Medicine, reporting the clinical success of chimeric antigen receptor (CAR) T cell therapy against certain haematological cancers; the therapy subsequently received FDA approval for lymphoma and leukaemia treatment (June & Sadelain, 2018). T cells were modified with artificial receptors that associated the recognition of target antigens with the signalling and immunological responses of the T cell (Ellis et al., 2021). Furthermore, genome editing was successfully used to remove immune checkpoints limiting T cell functionality and improving receptor efficacy (Ellis et al., 2021). The successes of CAR T cell therapies have extended the applications of immune cell reprogramming to a population less investigated thus far — the B cell.
Adaptive immune responses are facilitated by white blood cells, or lymphocytes. There are two classes of adaptive immune response: humoral (antibody responses) and cell-mediated responses, primarily enabled by two types of lymphocytes: B-cells and T-cells, respectively (Alberts et al., 2002). Humoral adaptive immunity produces antigen-specific antibodies via B-cells that identify pathogens by binding to their expressed antigens, stimulating cell-mediated immunity by signalling T-cells, cytokines, macrophages and chemical mediators which attack and neutralize the pathogen (Johnson et al., 2018). Thus, B-cells regulate the entire adaptive immune system via general and specific mechanisms, facilitated by cytokine secretion and antigen presentation respectively (Rogers & Cannon, 2021). As a result, B-cells provide a means of modifying holistic immune responses which is a more effective immunotherapy than the sole modification of cell-mediated immunity found in current immunotherapies (e.g., T-cells).
Following the first, primary, response to a specific antigen, the responding, naive, B-cells will proliferate into a colony, differentiate into effector B-cells which produce antibodies, and following infection, will form memory B-cells which encode for and maintain the antigen-specific antibody of the pathogen encountered (Akkaya et al., 2019). This enables more rapid secondary active immune response mobilization if the same antigen exposure occurs subsequently, and can provide lifelong immune surveillance (Akkaya et al., 2019). As a result, humoral immunity facilitated by B-cells is the most capable mechanism of providing prolonged immune surveillance (Rogers & Cannon, 2021).
B-cells possess many unique characteristics that make them a promising focal point for genetic engineering in immunotherapy settings. B-cells can be easily isolated in abundance from peripheral blood, then subsequently activated, grown, and matured in culture ex-vivo (Liebig et al., 2009). It is possible to engineer these isolated B-cells to express a particular gene, mature them into effector B-cells, which produce large amounts of antibodies, and add them back to the host as a remarkably effective form of gene therapy enabling long-term immunity to disease, as seen in Figure 1 (Johnson et al., 2018). In particular, gene editing can be used to alter antigen specificity with a predetermined antibody by means that permit access to all functions of the B-cell during every stage of its life cycle (Rogers & Cannon, 2021).
Figure 1. Diagram displaying the procedure of B-cell immunotherapy in patients using host donor cells (Traxinger, 2019).
By altering the variations of modified antigen-specificity, the response of B-cells to target antigens, their subsequent production of antibodies, expansion, and formation of long-term immunity, we can introduce and evolve long-term antibody specificity to reprogram B-cells that will continue to adapt to their associated pathogens (Rogers & Cannon, 2021). This is particularly relevant, as a majority of current literature on B-cell engineering focuses on producing HIV-specific B-cells (Rogers & Cannon, 2021). The prolonged antibody expression of B-cell therapy can be used to suppress chronic viral infections such as HIV. More importantly, highly mutagenic viruses, such as HIV, are capable of evading antigen-specific antibody responses, and edited B-cells can adapt to these changes, enabling B-cells to keep pace with viral mutations (Ouyang et al., 2017). This is not possible with current therapies that use fixed antigen-specificities.
The broad array of B-cell functions open many potential immune cell gene therapies. For example, the ability of antibody production in effector B-cells allows them to be used as a long-term source for the production of therapeutic proteins in-vivo, such as bnAbs and factor IX to combat hepatitis C virus and HIV (Kuhlmann et al., 2018). Also, it is possible to create these “cellular factories” using stem cells or editing B-cells ex-vivo which can be altered with a variety of methods such as CRISPR/CAS9 and viral vectors which transport the modified gene to loci of interest (Luo et al., 2020). Moreover, naive B-cells can be modified to present antigens and suppress or prevent immune responses to particular antigens, which can be used to combat autoimmune diseases (Scott, 2011).
Interestingly, B-cell engineering offers potential as an improved means of vaccination. In May of 2019, Howell et al. published findings in Scientific Immunology showing that B-cells edited to express antibodies countering respiratory syncytial virus (RSV) produced highly effective and long-lasting protection from RSV infection in mice (Moffett et al., 2019). Such findings convey that sterilizing immunity to pathogens can be accomplished in a more effective manner than current vaccination methods are able to induce or sustain.
Though great strides have been made, moving forwards, many further steps are needed for B-cell therapies to become viable in the future. Up to now, studies have used mice, however, larger animal models more related to human immunology are required to gain more practical insights. Further, studies must be conducted long-term to assess the durability of antibody production and memory in edited B-cells (Rogers & Cannon, 2021). Additionally, novel methods of delivering B-cell therapies to patients must be developed to make B-cells commercially viable and accessible on a broad scale. Engineered B-cells should be manufactured en masse from universally matching batches of unrelated donor cells (i.e. allogeneic) instead of an exclusive therapy manfactured from a single sample of patient-related donor cells (i.e. autologous). Current studies propose using B-cells from induced pluripotent stem cells, which is currently being investigated for use in CAR T cells (French et al., 2015).
Today, genetically engineered B-cells present a great capacity as a highly effective immunotherapy for particular autoimmune disorders, cancers, chronic infectious diseases, and pathogens. Further experimentation is required to progress B-cell gene therapy to human trials, however, in the near future, we are likely to see B-cells accompany CAR T-cells as a novel immune cell therapy. In the far future, the broad and holistic applications of engineered B-cells may become the basis of future immunotherapies, vaccines, and disease treatments.
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