Objective
The overarching objective of this proposal is to develop next-generation ASIs that more effectively reduce inflammatory autoimmune responses and enhance regulatory T cell responses. The long-term goal is to provide clinicians with new immunotherapeutics that will aid in treating individuals with T1D, LADA, or who received islet transplants.
Background Rationale
The results from clinical trials with individuals newly diagnosed with T1D who were given different ß-cell autoantigens as monotherapies have supported the safety of ASIs and their capacity to induce shifts in immune responses to ß-cell autoantigens that are expected to be beneficial. Yet, clinically relevant long-term improvements remain elusive.
Further enhancements of ASI's ability to help inhibit the loss of insulin production in newly diabetic individuals, or to prolong the survival of transplanted islets, are sorely needed. However, ASI development is hampered by a lack of guiding principles as to which target tissue antigens should be selected for ASI clinical trials. There is little information on which antigens are optimal for disease reversal in NOD mice because ASI monotherapies are ineffective in NOD mice after T1D onset, probably because by the time ASI-induced regulatory immune responses arise, there are few remaining ß-cells. Moreover, this issue is difficult to address in clinical trials since it would require multiple treatment arms (greatly increasing the expense of the trial) and there are limited numbers of new-onset T1D patients willing to enroll in clinical trials.
Basic immunological studies of the factors that contribute to the magnitude of immune responses to antigens, as well as advances in cancer immunotherapy and our preclinical studies of ASIs using targeted and ignored ß-cell autoantigen determinants in NOD mice, suggest that ignored determinants of autoantigens may induce robust regulatory responses with less likelihood of boosting pre-existing inflammatory responses. These findings provide a new framework for the selection of antigens that are anticipated to have enhanced efficacy and safety for use as prophylactic monotherapies and in combined therapies for disease intervention.
The goal of this proposal is to lay the groundwork for translating these preclinical advances in T1D immunotherapy toward human clinical trials.
Description of Project
Ever since their inception, antigen-specific immunotherapies (ASIs) for T1D have focused on treating with whole autoantigens or peptides containing the major T cell epitopes (“determinants”) that are targeted by autoreactive T cells with the goal of inducing suppressive (“regulatory”) T cell responses. Our studies have revealed, however, that two inherent factors hamper the efficacy of this approach: 1) it leads to the increased presentation of autoantigen determinants that are already targets of activated autoimmune responses and can boost these pathogenic responses and 2) there are few remaining naïve (unactivated) T cells that can be activated by ASI toward regulatory responses because most of the ASI-reactive (“cognate”) T cells have already been recruited into the pathogenic autoimmune response.
Basic immunological studies have shown that the magnitude of an immune response to a new antigen is greatly influenced by the size of the pool of naïve T cells that recognize the antigen. Accordingly, we have hypothesized that the antigens used for ASIs should not be the antigens that are the major targets of pre-existing autoimmune responses, but rather immunogenic target cell autoantigen determinants which are ignored by the autoimmune response and have large pools of naive reactive T cells available for priming toward regulatory responses by ASI. This approach is the converse of traditional ASI approaches but has parallels with recent advances in cancer treatment that are based on vaccination with tumor neoantigens which are highly immunogenic and can induce more robust anti-tumor T cell responses in cancer patients.
As described herein, we have shown in NOD mice that this approach could prime larger magnitude regulatory responses, avoid the boosting of established inflammatory responses, and provide more effective immunotherapies. Our findings provide a new framework for the selection of antigens to be used in personalized ASIs that are anticipated to have enhanced efficacy and safety for use as prophylactic monotherapies and in combined therapies for disease intervention.
To extend this therapeutic strategy to human clinical trials it will be necessary to identify ignored ß-cell autoantigen determinants in the context of human HLAs. To accomplish that, we will utilize transgenic mice that express human HLAs (HLA-DQ8 or HLA-DR4). These mice will be immunized with peptides of preproinsulin, GAD65, or IA2 that do not contain known targets of autoreactive T cells. The peptides with high immunogenicity will be candidate ASIs for future clinical testing in HLA-DQ8 or HLA-DR4 individuals at risk, or newly diagnosed with T1D. This approach may also be useful to extend the survival of transplanted islets.
Anticipated Outcome
We propose a conservative research plan in which we will first provide a proof-of-concept that immunogenic but ignored autoantigen determinants can be identified within ß-cell autoantigens in the context of human T1D-susceptibility HLAs. In future studies, the ignored peptides with high immunogenicity will be candidate ASIs for further clinical testing in HLA-DR4 or HLA-DQ8 individuals at risk, or newly diagnosed with T1D or LADA.
Relevance to T1D
To our knowledge, no ASI clinical trial with T1D patients has examined the frequency of naïve T cell precursors in a patient’s PBMC that could recognize the ASI’s antigen before initiating the treatment. We have shown that the size of the naive precursor pool recognizing a ß-cell autoantigen determines the magnitude of the induced regulatory responses, the extent to which inflammatory autoantigen-specific responses are reduced, and the efficacy of the treatment.
This proposal will take the first steps towards translating these findings to the clinic. Specifically, we will use “humanized” mice to find peptides of autoantigens that are ignored by the autoimmune response but are highly immunogenic and can induce strong regulatory responses after immunization. This is anticipated to lead to next-generation ASIs that will have enhanced efficacy and safety for use as prophylactic monotherapies and in combined therapies for disease intervention, as well as to prolong islet graft survival.