Anti-drug antibodies in patients with multiple sclerosis

Abstract: Multiple sclerosis (MS) is an inflammatory disease affecting the brain and spinal cord and it is the main cause of neurological disability among young adults. Recombinant interferon beta (IFNβ) and natalizumab are commonly used disease-modifying drugs that reduce disease severity. Even though these treatments show beneficial clinical effects they are associated with the development of anti-drug antibodies (ADAs), which at high titer levels reduce drug efficacy. Although ADAs are known to adversely affect the clinical effect of the treatment on a group level, the treatment response in individual patients is less characterized. In addition, it is unknown why only a subgroup of treated MS patients develops ADAs. The objective of this thesis was to identify biologically relevant ADA titer cut-points that can be used to predict treatment response and persistence of ADAs in individual patients, and to investigate if genetic and immunological factors influence the development of ADAs in MS patients. MS patients analyzed for the presence of ADAs against IFNβ or natalizumab in the routine NAb laboratory at Karolinska Institutet were included in this project. In Sweden, NAb monitoring became clinical practice in 2003 and during 2003-2004 the overall seroprevalence of neutralizing antibodies (NAbs) against IFNβ was 32%. When the NAb seroprevalence was analyzed five years later, in 2009-2010, the overall frequency of NAb-positive patients had decreased significantly to 19%. Importantly, the greatest reduction was observed in patients with high NAb titers (study I). By correlating the in vivo IFNβ bioactivity with patients’ NAb titers we identified that a NAb titer of 150 TRU/ml is a biologically functional cut-point for treatment response, since titers above 150 TRU/ml completely block IFNβ bioactivity (study II). Furthermore, characterization of ADA responses in natalizumab-treated patients revealed that the level of total anti-natalizumab antibodies in a first positive sample can be used to predict patients at risk of becoming persistently antibody positive (study V). It is known that factors such as protein modifications and/or impurities impact the immunogenicity of IFNβ, which can explain the variation in NAb positivity between IFNβ preparations. In addition, since only a subgroup of IFNβ-treated patients develops NAbs, patient-related factors are likely to influence the immunogenicity of IFNβ. In study III, we hypothesized that MS patients with and without intrathecal production of oligoclonal IgG bands (OCB) have different propensities to induce humoral immune responses. The presence of OCB was found to be associated with NAb development, and this risk was confined to NAbs against IFNβ-1a. From these results we proposed that MS patients with and without OCB differ immunologically, potentially influenced by distinct human leukocyte antigen (HLA) alleles. The role of HLA in the immunogenicity of IFNβ was further investigated in study IV, in which we found that HLA-DRB1'15 carriage was associated with increased risk of developing NAbs. Stratification on type of IFNβ preparation showed that HLA-DRB1'15 increased the risk of NAbs against IFNβ-1a, while HLA-DRB1'04 increased the risk of NAbs against IFNβ-1b, indicating that there is an IFNβ preparation-specific genetically determined risk to develop NAbs. Overall, these results can be used to assist when making decisions about whether treatment should be discontinued or not. In addition, the identification of factors contributing to the immunogenicity of protein therapeutics can increase our understanding of the immunological mechanisms leading to ADA responses, possibly resulting in less immunogenic drugs in the future.