Objective
This proposal will test whether targeting the transferrin receptor, also called CD71, is a therapeutic target common to multiple autoimmune diseases. We previously showed that targeting CD71 with an antibody to lower iron inside cells has different effects on different types of T cells, where pro-inflammatory T cells are limited and anti-inflammatory T cells are enhanced. The evidence for this type of immunotherapy in SLE is strong, but less is known about iron metabolism in T cells in other autoimmune diseases such as T1D and MS. Therefore, the first goal of this proposal is to test whether T cells from patients with these diseases also have increased iron and CD71 expression, providing justification for targeting this pathway in T1D and MS.
Next, we have generated small antibodies in alpaca called nanobodies that bind to the human version of the CD71 receptor. Here, we will test these anti-CD71 nanobodies in humanized mouse models of autoimmunity, which is the second goal of this proposal. In these mouse models, human T cells from patients with autoimmune disease are engrafted into a mouse and develop a similar disease to the human donor. This strategy will allow us to test our anti-CD71 nanobodies, which recognize the human form of CD71, in a relevant disease model.
Background Rationale
A key issue in autoimmune diseases is the disruption of T helper cell subsets like Th1, Th17, and Tregs. These subsets rely on specific metabolic pathways for their function. In autoimmunity, there is an increase in Th1 and Th17 cells and a decrease in Tregs which are anti-inflammatory. Recognizing these metabolic weaknesses can help restore balance in T cell populations affected by these diseases. My research indicates that targeting iron metabolism is effective for systemic lupus erythematosus (SLE). Specifically, targeting the transferrin receptor that takes iron into cells, called CD71, affected T cell populations differently; Th1 cells died, Th17 cells became less pathogenic, and Tregs thrived. I found that blocking CD71 with an antibody reduced autoimmunity and increased Treg numbers in lupus mice. Additionally, patients with SLE had T cells with higher CD71 than healthy control T cells, giving the rationale for targeting this pathway in SLE. Furthermore, deleting the gene for CD71 in T cells prevented autoimmunity in a graft-versus-host disease model. Despite the evidence that antibody therapy targeting CD71 can help treat SLE, it is not clear whether this could also be applied to other autoimmune diseases such as type 1 diabetes (T1D) or multiple sclerosis (MS). Indeed, all of these diseases have similar imbalances in their T cell populations, suggesting that this strategy may be widely applicable.
Description of Project
The transferrin receptor, CD71, is a receptor that brings iron into cells. The immune cells known as T lymphocytes (T cells) also rely on CD71 for iron, which they use for different metabolic processes. My previous work has shown that different types of T cells rely on this receptor for different reasons. By targeting or "blocking" the receptor with an antibody, we can limit the pro-inflammatory types of T cells and give a boost to the anti-inflammatory T cells. This method of immunotherapy was successful in mouse models of system lupus erythematosus (SLE), and may have similar benefits in other autoimmune diseases including type 1 diabetes (T1D) and multiple sclerosis (MS). Although there is evidence that CD71 and iron metabolism is dysregulated in T cells in patients with SLE, validation of patient samples with these other diseases needs to be done. Thus, this pathway could be a common target to multiple diseases that would benefit from anti-CD71 immunotherapy.
We vaccinated an alpaca with human CD71 receptors to discover human-specific versions of antibodies that could accomplish this in people. Alpacas also make a smaller type of antibody known as nanobodies that are highly stable and can cross the blood-brain barrier. In this proposal, we will test the anti-CD71 nanobodies we discovered from this alpaca in mouse models of autoimmune disease.
Anticipated Outcome
We expect that T cells from patients with T1D or MS will have high levels of CD71 expression on their T cells compared to healthy controls. Higher CD71 would also predict high levels of intracellular iron. Patient serum samples may also have increased levels of HFE, similar to what was previously observed in SLE samples. If our anti-CD71 nanobodies (Nbs) are successful, we would expect them to significantly decrease autoimmunity in both humanized mouse models (graft-versus-host disease and EAE). Nbs would bind to CD71 and lower iron in T cells, favoring Tregs over the pro-inflammatory T cell types and reducing disease.
Relevance to T1D
Any immunotherapy that limits Th1 and Th17 cells while simultaneously boosting Tregs should be beneficial to autoimmune diseases, including T1D. Although islet transplantation and other modes of treatment are advancing, the long-term success of those treatments will also depend on maintaining immune homeostasis of these T cell subsets.