Objective
New, validated tests are needed to accurately diagnose patients who have the clinical features of T1D but lack the classic, known antibodies, and to understand the mechanisms that cause their failure to make insulin. Such a diagnostic test would also open the doors to clinical trials of immunotherapy that are currently closed to patients who do not have the current antibodies that define T1D.
The objective of this proposal is to test and validate a newly developed, clinically feasible assay (the AIM test) in blood samples from a wide range of patients who have the clinical features of T1D but lack the currently known antibodies, as well as as from misdiagnosed “T2D” patients with likely autoimmunity. We will also use the PhIP-Seq technique to optimize the AIM test as a diagnostic tool as well as to discover new antibodies that could serve as additional diagnostic biomarkers in such patients.
Background Rationale
About 15% of patients with type 1 diabetes (T1D) lack the classic antibodies that are currently used to diagnose T1D. Diagnostic confusion regarding the “type” of diabetes in these patients with atypical T1D can lead to delayed management and exclusion from clinical trials of immunotherapy for T1D. Limited research studies show that most of these “antibody-negative T1D” patients actually have autoimmunity associated with cellular (T cell) attack on their insulin-producing cells – diagnosis of their condition is hampered by the lack of a clinically viable assay for T cell autoimmunity. They may also have undiscovered antibodies that could serve as additional biomarkers for the condition.
Recent evidence from clinical trials of patients with apparent type 2 diabetes (T2D) show that a substantial proportion of these patients also have evidence of T cell autoimmunity although they lack the classic T1D antibodies. The T2D patients with evidence for T cell autoimmunity make less insulin and have worse glucose control than those without T cell autoimmunity. The test used to identify the T cell-positive T2D patients in these previous studies is too hard to replicate to be useful in clinical practice. Just as with “antibody-negative T1D” patients, a clinically viable assay for T cell autoimmunity and discovery of new antibodies would improve the diagnosis of such patients with atypical T2D diabetes and advance our understanding of their failure to make enough insulin.
Description of Project
About 15% of patients with type 1 diabetes (T1D) lack the classic antibodies that are used to diagnose T1D. These patients are often misdiagnosed as having “type 2 diabetes” (T2D) or some other form of diabetes, leading to delayed management or mismanagement. Importantly, such patients, despite being insulin-dependent and prone to developing diabetic ketoacidosis, are excluded from clinical trials of new immunotherapies for T1D - due to uncertainty of the diagnosis and the presumption that they would not benefit from immunotherapy. It is very likely that many of these “antibody-negative T1D” patients do have islet autoimmunity – it is just not manifested by the traditional T1D-associated antibodies. Their form of autoimmunity that may be manifested by different biomarkers, such as T cell activity or the presence of currently unknown antibodies. Tests for T cell-mediated autoimmunity or novel antibodies are not available for clinical use.
Furthermore, we found in the GRADE study that a substantial proportion of patients diagnosed with T2D have evidence of T cell autoimmunity while lacking the classic T1D antibodies. T cells are cells that are involved in the autoimmune process that causes T1D. These “T cell-positive” T2D patients have worse insulin secretion and poorer glucose control than T2D patients who are “T cell-negative”. Essentially, these “T cell-positive” T2D patients have a form of autoimmune diabetes similar to T1D but are misdiagnosed as T2D because they initially do not need insulin and often lack the traditional T1D antibodies. The test used to identify the T cell-positive T2D patients in the GRADE study is too hard to replicate for it to be useful in clinical practice.
The goal of this project is to test and validate a newly developed, clinically feasible assay for T cell-mediated islet autoimmunity (the AIM test) in blood samples from a wide range of patients with antibody-negative T1D as well as from misdiagnosed “T2D” patients with likely T cell-mediated islet autoimmunity. A further goal is to use “phage immunoprecipitation sequencing” (PhIP-Seq), a cutting-edge method to identify self-antigens in autoimmune diseases, to discover novel islet autoantibodies in the same blood samples.
In Specific Aim 1, we will first use the PhIP-Seq assay to identify novel islet antigen targets in stored blood samples from T1D and T2D patients who lack the classic T1D antibodies. Then we will implement the AIM T cell test with both the novel and known antigen targets, calibrating the AIM test against the previously utilized T cell test on the GRADE samples. Finally, we will measure the utility of the calibrated AIM test to diagnose T cell-mediated autoimmunity in blood samples of pediatric and adult patients with antibody-negative T1D from different well-characterized diabetes cohorts. We will also have a group of patients with classic T1D for comparison.
In Specific Aim 2, we will apply the AIM T cell test on longitudinally-collected samples from the above cohorts, including the classic T1D patients for comparison, to assess the trajectory of T cell-mediated autoimmunity over time, as well as the association of T cell autoimmune status with insulin secretion function and glucose control over time.
This study will establish the ability of the AIM T cell test to identify an autoimmune cause for beta cell failure in patients with “antibody-negative T1D”. Together with any novel antibodies identified by the PhIP-Seq analysis, it will provide to the clinical community new diagnostic tests to define autoimmune forms of both T1D and T2D, paving the way for targeted therapies and opportunities for these patients to participate in important clinical trials of immunotherapy to delay or prevent the complications of diabetes.
Anticipated Outcome
We expect that the AIM assay will show that patients who have negative antibodies but otherwise look like they have T1D will have T-cell responses that are like the responses seen in patients with positive diabetes antibodies (T1D). We expect that the PhiP-Seq assay will identify new antibodies that can not only lead to a more robust AIM assay, but also be useful in identifying patients with T1D. These new antibodies will be present in patients that we know have T1D (because they have one or more of the usual positive antibodies) and will be present in those whose clinical picture is similar to patients with type 1 diabetes but none of the traditional antibodies are positive. As in the GRADE study, we expect that some patients with a clinical diagnosis of T1D will have positive novel antibodies and their T cells will respond like people with T1D. Finally, we expect to find that patients with positive novel antibodies, positive T cell response, or both, will lose the ability to make insulin more quickly than those with neither positive novel antibodies nor T cells.
Relevance to T1D
The new antibody and T cell tests will make it easier to identify patients with T1D. This will help us predict their clinical course more readily. It will also allow these patients to enroll in research studies of new immunotherapies for diabetes prevention or treatment.