Study Probes How Immune Reactions to Replacement Therapy Can Happen

Changes in cellular microenvironment could influence immune responses

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Changes in the cellular microenvironment could influence immune responses against factor VIII (FVIII) replacement therapy in people with hemophilia A, a new study suggests.

Data from the cell culture study showed that FVIII proteins that cause an immune reaction differ depending on which other molecules are present in the environment.

Findings overall offer new insight into the potential mechanisms by which some patients develop immune reactions against replacement therapy, the researchers noted.

The study, “Modulating the microenvironment during FVIII uptake influences the nature of FVIII-peptides presented by antigen-presenting cells,” was published in the journal Frontiers in Immunology

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Nearly a third of patients develop immune response against FVIII replacement

Replacement therapy is a mainstay treatment for hemophilia A. It works by supplying a working version of FVIII, the blood clotting protein that is missing in people diagnosed with the bleeding disorder.

However, nearly a third of patients develop an immune response against the treatment, generating neutralizing antibodies (inhibitors) that may render replacement therapy ineffective.

It isn’t well-understood, however, why some patients develop these immune reactions and others don’t.

Normally, for the immune system to target a certain protein, or antigen, the protein is taken up by antigen presenting cells (APCs), where they are broken down into different components, called peptides.

These peptides are then presented on the surface of APCs, where they will be recognized by CD4-positive immune T-cells that will mediate an immune response against them.

Which peptides will be presented by APCs depends on a number of different factors that can occur when the protein is being taken in and processed. This in turn can influence the immune system’s overall response.

In the study, researchers set out to better understand how the cellular microenvironment of APCs during this process might influence the development of FVIII inhibitors.

“The experimental design of our cell culture study was aimed at taking a closer look at the response of different immune cells in the context of FVIII administration and thereby gaining better insight into the underlying processes,” Christian Lubich, PhD, deputy head of the Institute Krems Bioanalytics of IMC University of Applied Sciences Krems, in Austria, and the study’s first author, said in a university press release.

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Researchers used spleens from mouse model of hemophilia A

Spleens — an organ rich in immune cells — were obtained from a mouse model of hemophilia A that had been treated with FVIII. Populations of CD4-positive T-cells that could specifically recognize various FVIII peptides were then isolated.

Overall, the researchers identified that different T-cell subsets could recognize nine distinct FVIII peptides.

A variety of APC cell types, including B-cells, monocytes, and dendritic cells, demonstrated an ability to activate CD4-positive T-cells, regardless of which particular FVIII peptide the T-cell could recognize.

But when the cellular microenvironment was altered by introducing other molecules into cell cultures, the composition of the peptides presented to T-cells — and which T-cell subsets were activated — was changed.

This was evaluated by the addition of three different molecules: von Willebrand Factor and thrombin, two proteins that interact with FVIII in the blood clotting cascade, as well as a compound that blocks certain receptors on APCs that have been implicated in FVIII uptake.

The addition of each led to the activation of distinct repertoires of FVIII-recognizing T-cell subsets, suggesting that particular peptides were presented by the APCs in response to each change in the environment.

The experimental design of our cell culture study was aimed at taking a closer look at the response of different immune cells in the context of FVIII administration and thereby gaining better insight into the underlying processes

Results altogether “indicate that modifications of the microenvironment during FVIII uptake by APCs alter the peptide specificity of subsequently activated FVIII-specific [CD4-positive T-cells],” the researchers wrote.

“Whether alterations in the FVIII peptide repertoire presented on APCs results in subsequent alterations in the induction of neutralizing or non-neutralizing antibodies against FVIII requires further studies,” the team wrote.

Lubich noted that a strategy called immunopeptidomics could be useful to better understand the relevance of their findings in humans.

“This method can be used, for example, to determine peptides of a pathogen [disease-causing microbe], a tumor cell or, as in this case, a biotherapeutic agent that elicit an immune response,” Lubich said.

“This platform will therefore not only help to better understand adverse reactions of the immune system to biotherapeutics, but will also enable the identification of important antigens for the development of immunotherapies,” he added.

The research was conducted as a collaboration between Institute Krems Bioanalytics and the pharmaceutical company Takeda.