IgG‑degrading enzyme have made breakthroughs in the field of kidney transplantation. In vitro, IgG‑degrading enzyme inhibits HLA antibody-mediated NK cell activation and antibody-dependent cell-mediated cytotoxicity [15]. IgG‑degrading enzyme degrades also the IgG of the B cell Receptor (BCR), inhibiting BCR-mediated cell signal, transiently preventing memory B cell response to antigenic stimulation and their transition into antibody-producing cells [16]. DSA positive patients who have received IdeS can successfully undergo allogeneic kidney transplantation surgery, achieving higher kidney and patient survival rates [17]. The French consensus guidelines indicate that Imlifidase (IgG degrading enzyme) has been authorized for early use in highly sensitized adult kidney transplant candidates who are cross matched positive for ABO compatible deceased donors [18].
IgG‑degrading enzyme also demonstrate enormous therapeutic potential in the field of gene therapy. The most commonly used viral vectors for in vivo gene therapy are based on AAV, a non-enveloped single-stranded DNA virus. However neutralizing antibodies (NAbs) to AAV vectors are highly prevalent in humans, block liver transduction and vector readministration, thus representing a major limitation to in AAV-based in vivo gene therapy[19]. Evidence from ongoing clinical trials (ClinicalTrials.gov NCT03368742, NCT04281485, and NCT03882437) suggests that high doses of AAV significantly increase complement activation. Some participants in these studies presented with severe and life-threatening inflammatory responses that were likely secondary to the activation of the complement system [20–24]. In addition to nausea, fever, and vomiting likely due to cytokine release, participants presented with complement-mediated thrombotic microangiopathy (CM-TMA) [25], acute kidney injury due to atypical hemolytic uremic syndrome–like (aHUS-like) complement activation, thrombocytopenia, and immune-mediated myocardial injury[22, 25–27]. Activation of complement is a major safety consideration for gene therapy, as growing evidence suggests that high-dose intravenous (i.v.) AAV infusion or high exposure to AAV empty capsids leads to antibody-dependent activation of the complement system in human plasma[28]. It was confirmed that IgG‑degrading enzyme reduced anti-AAV antibody levels from human plasma samples in vitro, including plasma from prospective gene therapy trial participants [29]. These results provide a potential solution to overcome NAbs to AAV-mediated gene therapy and inhibit antibody-dependent activation of the complement system. Based on the above mechanisms, KJ103 has the potential to alleviate the problem of inability to accept first and second treatment due to high anti-AAV antibody titers, improve gene transduction efficiency, and prevent treatment failure caused by complement mediated immune reactions after administration in the field of AAV-mediated gene therapy.
Although degrading enzymes have shown excellent therapeutic potential in many therapeutic fields, the immunogenicity of biologicals in therapy cannot be ignored. Pre-existing anti-drug antibodies may increase the risk of infusion reactions and hypersensitivity reactions during intravenous delivery of biologicals[30, 31]. The widespread presence of pre-existing anti-IdeS antibodies limits clinical applications of IdeS, and can potentially compromise drug efficacy[10]. During clinical studies, individuals with anti-IdeS IgG titers exceeding 15mg/L were excluded from the research, and therefore not all populations can receive IdeS treatment[10]. These shortcoming are illustrated by its use in intravenous administration for AAV gene therapy.
Here, we report an IdeE(IgG‑degrading enzyme of S. equi) variant of KJ103 with lgG-cleaving activity like that of ldeS. Our studies confirm that KJ103, a novel IgG-degrading enzyme derived from S. equi, exhibits a low positivity rate and low titers of pre-existing anti-KJ103 antibodies in the population. In clinical trials of IdeS, anti-IdeS antibodies were present in all participants at baseline, and participants experienced an increase in ADAs starting on day 7 of dosing. ADA levels then peaked at approximately 19.6 times baseline at about two weeks, and then declined progressively, reaching approximately 16.6 times baseline ADA concentrations after two months of dosing[10]. In comparison to ADA formation following IdeS administration, the pre-existing anti-KJ103 antibodies positivity rate for all enrolled participants was 33.82% (23/68), and the median value of pre-existing antibodies titers was 0 (range: 0 to 1:429.61). ADAs appeared and peaked at approximately two weeks after KJ103 administration, with a median ADA titre in positive participants that was 15.95 times that of the baseline positive participants, and then declined progressively, reaching a titre of approximately 5.35 times that of the baseline in positive participants after two months of dosing. The maximum dose of IdeS applied in humans was 0.25 mg/kg, whereas the maximum dose of KJ103 first applied in humans was 0.40 mg/kg dose, with an excellent safety and tolerability profile across all dose groups of KJ103. ADA emergence post-KJ103 administration occurred later than for IdeS, with lower titers and a shorter duration to return to baseline levels, highlighting the advantage of KJ103.
Due to the low prevalence and low titers of pre-existing KJ103 antibodies in the population, it is possible to administer KJ103 twice in humans at 7-day intervals without significant safety concerns. Theoretically, this would enable the salvage of intravenously administered AAV-mediated gene therapy in individuals positive for pre-existing anti-AAV antibodies. This approach could potentially ensure the sustained maintenance of low IgG levels in the body, allow sufficient time for the clearance of degraded F(ab')2 fragments and maintain low IgG levels by second administration of KJ103 at 3 ~ 7 days interval. Validation of this hypothesis was observed in an AAV gene therapy mouse model infused with human anti-AAV antibodies (IgG), where KJ103 protected AAV9-mediated luciferase delivery from the impact of human anti-AAV antibodies. KJ103 is therefore promising as means of overcoming limitations posed by pre-existing anti-AAV antibodies in the clinical application of AAV gene therapy.
We observed no events meeting the dose-escalation termination criteria during the DLT observation period in all participants. Most TEAEs and TRAEs were graded as grade 1 or 2, with a few at grade 3. Safety profiles of TRAEs for KJ103 were overall comparable to IdeS [32]. No severe infection events occurred during either studies. KJ103 demonstrated excellent tolerability and safety.
Post-administration, KJ103 exhibited a dose-dependent reduction in IgG levels in healthy participants. We observed a greater reduction in IgG after administration of KJ103 at a dose of 0.12 mg/kg to Asian participants in both studies. The average IgG levels for participants in China and New Zealand were 11.67g/L and 14.63g/L, respectively, while the average levels of pre-existing anti-KJ103 antibodies were not significantly different. Our PK/PD models indicated that gender influences efficacy. Men constituted 85.3% and 20.6% of participants in China and New Zealand, respectively; while Caucasians accounted for 0% and 58.8% in China and New Zealand, respectively. A meta-analysis involving 28 studies indicated that factors such as being Caucasian, smoking, or using corticosteroids tend to decrease IgG levels, whereas the use of probiotics, hypertension, or acute psychological stress tends to elevate IgG levels[33]. Overall, differences in pharmacodynamics between the 0.12 mg/kg group in the two trials were caused by differences in baseline IgG levels. We infer that these differences may be due to gender disparities, but we do not rule out racial differences.Additionally, utilizing the PopPK model, we simulated various gender and baseline IgG levels and found their impact on efficacy to be negligible at a 0.25 mg/kg dose.
Both trials demonstrate exceptional safety, tolerability and IgG cleavage efficiency of KJ103. The 0.25 mg/kg dose of KJ103 efficiently, rapidly, and specifically enzymatically cleaved human IgG and maintained a low serum IgG level for 1 week. The promising safety and tolerability of KJ103 was indicated by several lines of evidence including low positive rates and low titers of pre-existing anti-KJ103 antibody in the population and a quick return of ADA to a basal level within 6 months in nearly half of the participants after KJ103 administration. The trials show that KJ103 avoids IdeS shortcomings, with a higher safe dose, wide safety window, low pre-existing antibody ratio and titre, and a broader application population. It is likely that patients would not need to screen for pre-existing antibody titres prior to KJ103 administration. The advantages mentioned above can be leveraged in multiple patient populations including those requiring kidney transplantation and the emerging applications of AAV gene therapy in patients with anti-AAV antibodies[34].