Introduction
Type 1 diabetes results from an autoimmune destruction of insulin-producing beta cells in the pancreatic islets of Langerhans, and is characterised by circulating islet autoantibodies to beta cell antigens [
1,
2]. Insulin is a key early autoantigen in childhood diabetes [
3,
4]. Autoimmunity against insulin often appears in genetically susceptible children aged 9 months to 3 years, with a peak incidence at 9–12 months of age [
5‐
7], and this loss of immune tolerance to insulin often leads to type 1 diabetes [
8,
9]. Immune tolerance to insulin is influenced by the
HLA DRB1*04-DQB1*0302 haplotype [
8] and allelic variations in
INS, the gene that encodes insulin [
10‐
12], via mechanisms involving thymic T cell deletion [
13,
14].
Controlled exposure to antigen leads to protection against immune-mediated diseases such as childhood allergy [
15] and in animal models of autoimmunity [
16]. In type 1 diabetes, attempts have been made to reduce disease risk in individuals with established autoimmunity by administration of autoantigen orally [
17,
18], intranasally [
19,
20], intravenously or subcutaneously [
21,
22]. Treatment-associated immune effects such as increases in antibody titres [
20‐
22] and changes in CD4
+ T cell responses to administered autoantigen were observed in some of these studies [
20], indicating that administration could lead to immune modulation. Although none of these trials achieved their primary outcomes of diabetes prevention, beneficial treatment effects were observed in exploratory analyses of subgroups within the oral insulin immunotherapy trials [
17,
18].
We reasoned that, similar to peanut allergy [
15], the efficacy of antigen-specific immune therapy to prevent autoimmune disease would improve if treatment was started early in life and as a primary prevention therapy before individuals become autoantibody positive [
23]. We previously demonstrated that daily oral administration of high doses (67.5 mg) of insulin to children with a genetic risk of type 1 diabetes did not induce unwanted hypoglycaemia and was associated with the induction of low-affinity antibodies against insulin and insulin-responsive CD4
+ T cells with features of regulation [
24]. These treatment-associated immune responses were not typical of autoimmune diabetes [
8,
25]. We, therefore, inferred that the treatment was likely to be safe and capable of inducing an immune response that might protect against the development of type 1 diabetes. While these earlier findings are an important proof of concept, they were obtained in a small number of children aged 2–7 years, which is after the period of greatest susceptibility to insulin autoimmunity and, therefore, late for primary prevention of islet autoimmunity. Here, we report the Pre-POInT-early RCT in children aged 6 months to 2 years, which represents the first intervention with autoantigen at this very early age and, therefore, uniquely analyses overall safety, immune responses and effects of exposure to exogenous autoantigen during peak susceptibility. Children in this age group undergo a transition from maternally derived immunity to acquired protection through exposure to vaccinations and infectious agents [
26], and large changes in the immune repertoire and the gut microbiome. Daily exposure of the mucosal immune system to a key autoantigen in genetically susceptible children during this period presents a rare opportunity to assess the interplay between these factors in eliciting immune responses.
The Pre-POInT-early trial had four objectives. First, to determine the safety of daily oral insulin administration in very young children with high genetic susceptibility for type 1 diabetes; second, to determine whether the previously observed antibody and CD4+ T cell responses to oral insulin could be observed in younger children; third, to explore interactions between oral insulin therapy and INS genotype and microbiome; and, fourth, to investigate immune changes and events that may influence autoimmunity during this period of high susceptibility.
Discussion
The Pre-POInT-early study is the first to expose very young genetically at-risk children to exogenous autoantigen at an age of peak susceptibility to autoimmunity. It demonstrated that daily oral administration of up to 67.5 mg of insulin to healthy, genetically at-risk, islet autoantibody-negative children at 6 months to 2 years of age was well tolerated without signs of hypoglycaemia. The study did not demonstrate an effect on its primary outcome of immune efficacy defined by the findings in older children [
24] as either antibody or T cell responses to insulin. In secondary and exploratory analyses, treatment effects were, however, found for CD4
+ T cell responses to insulin and in subgroup analyses of children with the susceptible
INS genotype. Post hoc analyses also revealed remarkably frequent treatment-independent inflammatory episodes with features of type 1 interferon responses in the participants. These inflammatory episodes influenced insulin-directed T cell responses, again in an
INS gene-associated manner, providing a potential mechanism for the high incidence of islet autoimmunity in early childhood.
Although hypoglycaemia was not previously reported during treatment with oral insulin [
17,
18,
24], children <2 years of age have not been exposed to oral insulin. Therefore, the absence of hypoglycaemia at any of the tested doses with a cumulative exposure of >21 years is an important safety outcome. We also found no differences in glucose, insulin and C-peptide over a 2 h period after administration of insulin compared with administration of a placebo. To our knowledge, this is the first study to include comprehensive metabolic measures upon administration of oral insulin in all participating children. These data indicate that oral insulin is unlikely to enter the blood stream, a conclusion that was important for initiating the Primary Oral Insulin Trial (POInT) phase 2b trial in 4–6-month-old infants [
37]. Of note, the induction of tolerance by oral antigen is thought to be via antigen uptake in the oral and/or gut mucosa and does not require entry into the blood stream.
As in the Diabetes Prevention Trial–Type 1 (DPT-1) [
17], TrialNet [
18] and Pre-POInT [
24] trials, we observed no signs of allergy or intolerance to orally administered insulin. The frequency of adverse events was not increased in the oral insulin group, except for skin and subcutaneous tissue disorders. This was not observed in larger secondary prevention DPT-1 [
17] and TrialNet [
18] trials, where children from 3 years of age were treated with a daily dose of 7.5 mg of oral insulin. It is possible that our finding was due to the exposure of younger children or the use of higher oral insulin doses that may increase the likelihood of skin exposure to study drug. The overall frequency of skin and subcutaneous tissue disorders among all reported adverse events (4.3%) is comparable to that in TrialNet (7.7%) [
18]. All skin and subcutaneous tissue adverse events in our study were classified as mild, resolved during the course of the study and were not correlated with other blood chemistry measurements or inflammatory markers.
In addition to establishing safety, our objective was to find evidence for a treatment-induced immune response. The study design and sample size were based on results from the previous Pre-POInT study, which enrolled children at 2–7 years of age with greater genetic risk [
24]. Using the same outcomes and measurement methods, we observed a higher overall reactivity to insulin in the placebo group in this study (67%) than in the previous Pre-POInT study (20%), markedly reducing the study power. The younger age of the children is a major difference of the current study and is likely to contribute to the higher observed frequency of immune responses to insulin in the placebo group. Evidence for this includes the association between the antibody responses to insulin and younger age, and the correlation between age and T cell and monocyte subset compositions, with the latter being associated with the T cell responses to insulin.
Limitations of the study include our misjudgement on the effect size in favour of oral insulin, leading to the inclusion of 44 children, and the short follow-up period on relatively few children, which prevented us from assessing the efficacy of treatment in preventing islet autoimmunity or type 1 diabetes. All participants were of European extraction and the study cannot assess effects in other racial groups. A strength of the study is that, despite the challenge of obtaining blood samples from young children, adherence to the study protocol was high with comprehensive sample and data collection. These data included deep phenotyping of the immune responses and microbiome during early childhood and provided insights into how oral insulin might perturb the immune system and into disease mechanism. As there were no previous data to justify their inclusion in primary analyses, a number of these findings were based on exploratory and post hoc analyses, and, therefore, require validation in subsequent studies such as the POInT trial [
37].
A potentially important finding was that the
INS genotype appeared to influence antibody responses to treatment. In particular, we observed an association between oral insulin and the antibody response in children with the susceptible
INS AA genotype, suggesting that the
INS gene may modify the likelihood of the immune system responding to oral insulin. The response was observed by 6 months of treatment, corresponding to a 22.5 mg dose, which is lower than in the previous study [
24] and may reflect the lower body weight of children in the present study. Genetic susceptibility criteria in the previous study were more stringent and it is likely that the majority of participants had the susceptible AA genotype. We also discovered differences in the microbiome composition between children with susceptible and non-susceptible
INS genotypes and also minor effects after oral insulin treatment in children with the susceptible
INS AA genotype. This included differences in bacterial diversity and richness, and an increased abundance of
Bacteroides dorei in children with the susceptible
INS genotype, a finding that is consistent with the increased abundance of
Bacteroides dorei in children who developed type 1 diabetes in a Finnish study [
38]. Unlike the antibody outcome, the in vitro T cell responses to insulin were not associated with treatment after stratification by the
INS genotype. The T cell responses were, however, strongly associated with monocyte CD169 expression, providing new insights into disease pathogenesis. Monocyte CD169 expression is a sensitive marker of a type 1 interferon signature, which increases before islet autoantibody seroconversion in young children and is associated with respiratory infection [
36]. CD169
+ samples were surprisingly frequent and observed in the majority of children. They were also associated with recent adverse events, younger age and several other inflammatory markers. Early infection is associated with islet autoimmunity [
39‐
41] and type 1 diabetes [
42]. Thus, our findings that in vitro T cell responses to insulin were more likely to occur in CD169
+ samples in children with the susceptible
INS AA genotype may be relevant to the mechanism of insulin autoimmunity. We believe that our results do not reflect the presence of in vivo-primed T cells, but rather a heightened ability of the CD169
+ monocytes to activate naive T cells in the in vitro assay. Children with the susceptible
INS genotype are expected to have more peripheral insulin-autoreactive T cells [
13,
14]. Extending our in vitro findings, we suggest that a type 1 interferon response to infection in antigen-presenting cells in vivo further increases the likelihood of activating these T cells and eventually leads to insulin autoimmunity. The observation that the insulin-responsive cells from the CD169
+ samples contained more Th1/Th21 cells and fewer Tregs supports this hypothesis, and may also explain our previous finding of proinflammatory, proinsulin-responsive T cells in infants who later developed islet autoimmunity [
25].
Overall, this study demonstrated safety for high-dose oral insulin administration in young children. The study did not reach its primary outcome of immune efficacy. Exploratory analyses, however, provided evidence of an interaction between an immune response to treatment and the
INS gene as previously demonstrated for autoantigen. We, therefore, advocate that ongoing trials that include insulin or peptides of proinsulin as antigen-specific immunotherapy [
43,
44] should incorporate stratification by
INS genotype into their study design and analyses.
Acknowledgements
We are grateful to the participating families and children; the members of the Data Safety Monitoring Board (C. Mathieu, M. Peakman, O. Kordonouri); all members of the Pre-POInT-early study team at the Institute of Diabetes Research, Helmholtz Zentrum München, and Forschergruppe Diabetes, Technical University Munich, Germany (S. Zillmer, C. Sebelefsky, N. Lagoda, M. Heinrich, N. Maison, A. Durmashkina, S. Hivner, F. Fischer, M. Holzmeier, A. Gavrisan, C. Peplow, R. Lickert, M. Scholz, Y. Kriesen, M. Herbst); A. Lindner (Technische Universität Dresden, Center for Regenerative Therapies Dresden, Germany) for technical assistance in measuring gene expression; and the FACS facility of the Center for Molecular Cell Biology, TU Dresden. We thank Lilly Pharmaceuticals (Indianapolis, IN, USA) for donating the insulin crystals and InPhaSol, Apotheke des Universitätsklinikums Heidelberg (Heidelberg, Germany) for the production and supply of the investigational products. The study was monitored by V. Janke (Münchner Studienzentrum, Technical University Munich, Munich, Germany). The study sponsor was the Technical University Munich, represented by the School of Medicine.
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