Currently, there is a significant rise in the development and clinical use of a unique class of pharmaceuticals termed as Biopharmaceuticals or Biologics, in the management of a range of disease conditions with, remarkable therapeutic benefits. However, there is an equally growing concern regarding development of adverse effects like immunogenicity in the form of anti-drug antibodies (ADA) production and hypersensitivity. Immunogenicity to biologics represents a significant hurdle in the continuing therapy of patients in a number of disease settings. Efforts focussed on the identification of factors that contribute towards the onset of immunogenic response to biologics have led to reductions in the incidence of immunogenicity. An in-depth understanding of the cellular and molecular mechanism underpinning immunogenic responses will likely improve the safety profile of biologics. This review addresses the mechanistic basis of ADA generation to biologics, with emphasis on the role of antigen processing and presentation in this process. The article also addresses the potential contribution of complement system in augmenting or modulating this response. Identifying specific factors that influences processing and presentation of biologic-derived antigens in different genotype and disease background may offer additional options for intervention in the immunogenic process and consequently, the management of immunogenicity to biologics.

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Background Abacavir is associated with hypersensitivity reactions in individuals positive for the HLA‐B*57:01 allele. The drug binds within the peptide binding groove of HLA‐B*57:01 altering peptides displayed on the cell surface. Presentation of these HLA‐abacavir‐peptide complexes to T‐cells is hypothesized to trigger a CD8+ T‐cell response underpinning the hypersensitivity. Thus, the aim of this study was to explore the relationship between the structure of abacavir with HLA‐B*57:01 binding and the CD8+ T‐cell activation. Methods Seventeen abacavir analogues were synthesized and cytokine secretion from abacavir/abacavir analogue‐responsive CD8+ T‐cell clones was measured using IFN‐γ ELIspot. In silico docking studies were undertaken to assess the predicted binding poses of the abacavir analogues within the HLA‐B*57:01 peptide binding groove. In parallel, the effect of selected abacavir analogues on the repertoire of self‐peptides presented by cellular HLA‐B*57:01 was characterized using mass spectrometry. Results Abacavir and ten analogues stimulated CD8+ T‐cell IFN‐γ release. Molecular docking of analogues that retained antiviral activity demonstrated a relationship between predicted HLA‐B*57:01 binding orientations and the ability to induce a T‐cell response. Analogues that stimulated T‐cells displayed a perturbation of the natural peptides displayed by HLA‐B*57:01. The antigen‐specific CD8+ T‐cell response was dependent on the enantiomeric form of abacavir at both cyclopropyl and cyclopentyl regions. Conclusion Alteration of the chemical constitution of abacavir generates analogues that retain a degree of pharmacological activity, but have variable ability to activate T‐cells. Modelling and immunopeptidome analysis delineate how drug HLA‐B*57:01 binding and peptide display by antigen presenting cells relate to the activation of CD8+ T‐cells.

These studies demonstrate that the unwanted T-cell activity of abacavir can be eliminated whilst maintaining the favourable antiviral profile. The in-silico model provides a tool to aid the design of safer antiviral agents that may not require a personalized medicines approach to therapy.

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