Interfering with auto-immune plasma cell persistence during B-cell depleting therapies – PC-RITUX

Gene profiling will be used to identify a long-lived plasma cell signature in the mouse, and assess whether plasma cells change from a short-lived to a long-lived expression profile after anti-CD20-mediated B-cell depletion. Confocal microscopy and cytokine analysis will be used to identify specific survival facors and cellular components of the splenic plasma cell niche, both in mice and humans. The factors or cell types defined will be targeted by blocking antibodies in the mouse, to evaluate their capacity to interfere with plasma cell persistence.

Validation of a therapeutic strategy interfering with plasma cell persistence in immune thrombocytopenia, a bleeding disorder caused by pathogenic anti-platelets antibodies, and extension of its relevance to another disease, auto-immune hemolytic anemia.

This project aims at validating the proposition that a therapeutic option for autoimmune diseases mediated by pathogenic antibodies could rely on the simultaneous depletion of B cells together with suppression of plasma cell survival factors . If comforted by observations made in a mouse model, this option could be extended to other prevalent autoimmune diseases like lupus.

in progress

A large number of auto-immune diseases (rheumatoid arthritis, vascularitis, autoimmune cytopenia) are treated by an antibody against CD20 that depletes most of the B cells in the organism (Rituximab, RTX). The response to this treatment depends largely on the disease and on the type of lymphoid cells involved in the autoimmune process. We have recently reported that patients suffering from immune thrombocytopenia (ITP) not responding to RTX, displayed in their spleen long-lived plasma cells secreting autoimmune antibodies whereas long-lived plasma cells were not present in this organ before the treatment. Moreover the spleen of these patients contained an excess of the cytokine BAFF which, in our in vitro cultures of splenic cells, could increase the longevity of plasma cells. This result suggested that the B cell depletion, through the BAFF excess it generated, had induced the differentiation into autoimmune long-lived plasma cells (Mahévas et al., J. Clin. Invest. 2013). This observation may be of clinical relevance since patients with ITP who do not respond to RTX usually undergo a splenectomy that, for a large fraction of them, cure their disease.
We will at first confirm this observation in a mouse experimental model. We have established in the laboratory a mouse transgenic line that allows the irreversible marking at a precise time point of memory B cells and plasma cells engaged in an immune response (by EYFP labeling). This mouse model allowed us to describe the complexity of the memory B cell response (Dogan et al., Nature Immunol. 2009). This model will be used to test the validity of our hypothesis. Effectively, after immunization, mice will be treated with the anti-CD20 antibody and persisting EYFP+ plasma cells will be analyzed 2-3 months later at the transcriptomic level in order to establish the molecular signature of long-lived plasma cells in mice. We will thereafter analyze the splenic milieu generated by the B cell depletion at the cellular and cytokine level, to define therapeutic targets in order to associate with anti-CD20 another treatment preventing the differentiation of short-lived plasma cells into long-lived ones. We will in parallel analyze splenic fragments from ITP patients not responding to RTX, and thus compare the long-lived plasma cell microenvironment generated by B cell depletion in both models.
Our first hypothesis is that the association of RTX to an anti-BAFF antibody (Belimumab (GSK), a drug that has been licensed for systemic lupus) should prevent the emergence of autoimmune long-lived plasma cells and therefore obviate the need for splenectomy. Before being able to transfer this strategy to patients, one has to validate it in an experimental model. The first assay will be performed in our mouse line with a mouse anti-BAFF antibody, which is the most appealing candidate, but it is clear that the access to an animal model will allow us to test additional targets such as cytokines or accessory cells that constitute the splenic plasma cell niche.
Lastly, we will study other autoimmune diseases in order to see whether our observations can be extended beyond ITP. Our first candidate will be autoimmune hemolytic anemia, since around 30% of these patients do not respond to RTX and undergo a splenectomy. These patients are also being followed in the national referral center for adult's immune cytopenia directed by Pr Godeau and Michel, the clinical partners of this study.
In conclusion, this project will merge the skills of teams with different expertise and with strong collaborative links between them, involving clinicians, clinician-scientists and basic scientists. Its aim is to propose an innovative treatment in order to improve the ITP patient’s life by preventing them from undergoing splenectomy, a rather heavy surgical procedure with a possible infectious risk later on. Our ambition is obviously also to be able to extend these new therapeutic approaches to other autoimmune diseases.