Objective
This proposal aims to develop and validate non-invasive immune cell imaging technology capable of detecting islet transplant (IT) rejection. We expect multiple immune cells of importance are involved in IT rejection. We will conduct preclinical experiments in research mouse models reflecting alloimmune and T1D autoimmune state to address the following specific objectives: 1) We will identify key immune cell types driving IT rejection using single cell immunoPET imaging; 2) Develop multiplex immunoPET imaging allowing serial scans in same or consecutive days; 3) Determine sensitivity of multiplex imaging to detect differences in immune response to anti-rejection treatments. Mice will be given standard IT immunosuppression, gastrin (shown by our team to have islet anti-inflammatory effects), and Treg cell treatment.; and, 4) We will confirm the clinical relevance of the immune cell types and multiplex immunoPET imaging strategy in a humanized mouse model. These studies will constitute a major step towards clinical translation of the imaging technologies.
Background Rationale
Our team has established reliable methods for studying islet transplant in rodents, imaging islet cells transplanted in the liver that is going into clinical trial, and engineering antibody fragments for imaging immune cells in animals with cancer and autoimmune disease. Development of radiolabeled antibody fragments provides a platform for same-day or next-day non-invasive imaging of multiple immune cell types. Recently, we used this approach to image CD8 T-cells infiltrating the pancreas during T1D development. These immunoPET methods are already being studied clinically in cancer. In this project, we will develop this immunoimaging approach, in combination with our existing islet imaging method, to provide direct monitoring of immune cell responses to transplanted islets.
Description of Project
Islet transplantation (IT) is effective at treating severe Type 1 Diabetes (T1D), but challenges with immune rejection, reactivation of autoimmunity, and islet exhaustion limit success over time. Islets are usually transplanted into the liver, where it is difficult to directly monitor their health and survival. Some islet stem cell trials transplant under the skin (subcutaneously). There is a need for non-invasive imaging that can distinguish immune/inflammatory rejection from non-immune-mediated loss of islet function and guide development of new targeted interventions.
Our team has established reliable methods for: studying islet transplant in rodents, imaging islet cells transplanted in the liver that is going into clinical trial, and engineering antibody fragments for imaging immune cells in animals with cancer and autoimmune disease. Development and radiolabeling such antibody fragments provide a platform for same-day or next-day non-invasive immunoPET imaging of multiple immune cell types. Recently, we used radiolabeled antibody to image CD8 T cells infiltrating the pancreas during T1D development.
In this project, we will develop and use this immunoimaging approach, in combination with our existing islet imaging method, to provide direct monitoring of immune cell responses to transplanted islets. Preclinical studies conducted in research mouse models reflecting alloimmune rejection and autoimmune reactivation over 3 years. We will study IT rejection at two transplant sites: to the liver (reflecting standard clinical site of IT) and subcutaneoulsy (to model some islet stem cell approaches) will be studied. First, we will collect single immunoPET images of multiple T, NK and B immune cell types (one cell type per scan and per animal) at 3 different timepoints to determine the most important and imageable immune cell types and time points involved in IT rejection. Assessment will be based on immune cell image intensity, islet image intensity, blood glucose and confirmation of liver immune cells upon microscopic examination. Secondly, using the important cell types identified in the first experiment, we will develop and test the feasibility of imaging multiple immune cell types in the same animal. A different radiolabel that has a short radioactivity time will be used to allow repeat imaging on same or next day. In Aim 3, we will evaluate the sensitivity of the multiple immunoPET imaging to detect differences in immune cell infiltration in animals receiving 3 different treatments to curb IT rejection (immunosuppression, gastrin, or Treg cell treatment). Finally, experiments will be repeated in a humanized mouse model involving human islet transplant into mice who have been reconstituted with human immune cells to confirm significance of immune cell targets and feasibility of multiplex imaging approach to inform future clinical translation.
If successful, immunoimaging will allow direct monitoring of immune cell responses to transplanted islets and inform new, targeted interventions to prevent/reverse rejection.
Anticipated Outcome
Our combined imaging approach using both immune cell- and islet-specific probes is expected to allow direct monitoring of immune cell responses to transplanted islets. We anticipate learning important new information about: 1) the key imageable immune cells involved in alloimmune and autoimmune islet transplant rejection and the time course of their presentation; 2) the feasibility of our immunoPET approach to visualize multiple immune cell types; 3) the sensitivity of the approach to distinguish different strengths of immune response to anti-rejection treatments; 4) possible differences in immune response to islets transplant to the liver vs. under the skin; 5) similarities and differences in mouse vs human immune response to islet transplant. These studies will constitute a major step towards advancing imaging technologies for clinical use. If successful, immunoimaging will allow direct monitoring of immune cell responses to transplanted islets and help inform new, targeted interventions to prevent/reverse rejection.
Relevance to T1D
Replacement of the lost insulin-producing beta cells, such as donor islet transplant or transplantation of islet stem cell products, is a promising strategy for reversal of type-1 diabetes and insulin independence. However, immune rejection of the transplanted islets and the inability to predict it currently hinder long-term success. This proposal directly aligns with the JDRF RFA to develop and validate non-invasive immune imaging technology to advance beta cell replacement strategies for treatment of type-1 diabetes. Our proposed non-invasive imaging approach is expected to allow direct monitoring of immune cell responses to transplanted islets and insulin-producing stem cells and help inform development of new, targeted interventions to prevent and reverse immune rejection.