Anti-CD3ε mAb improves thymic architecture and prevents autoimmune manifestations in a mouse model of Omenn syndrome: therapeutic implications

Abstract

Omenn syndrome (OS) is an atypical primary immunodeficiency characterized by severe autoimmunity because of activated T cells infiltrating target organs. The impaired recombinase activity in OS severely affects expression of the pre-T-cell receptor complex in immature thymocytes, which is crucial for an efficient development of the thymic epithelial component. Anti-CD3 monoclonal antibody (mAb) treatment in RAG2 ؊/؊ mice was previously shown to mimic pre-TCR signaling promoting thymic expansion. Here we show the effect of anti-CD3 mAb administration in the RAG2 R229Q mouse model, which closely recapitulates human OS. These animals, in spite of the inability to induce the autoimmune regulator, displayed a significant amelioration in thymic epithelial compartment and an important reduction of peripheral T-cell activation and tissue infiltration. IntroductionAs opposed to the classic T Ϫ B Ϫ severe combined immunodeficiencies (SCIDs), Omenn syndrome (OS) represents an atypical type of primary immunodeficiency (PID) associated with autoimmune manifestations because of activated oligoclonal T cells that infiltrate peripheral tissues and provoke generalized erythroderma, alopecia, lymphadenopathy, hepatosplenomegaly, and intractable diarrhea. 1 Patients have high levels of serum IgE despite the absence of circulating B cells. From the genetic point of view, most OS cases result from hypomorphic mutations in RAG genes 2,3 that decrease but do not completely abolish V(D)J recombination activity, allowing the generation of an oligoclonal autoreactive T-cell repertoire. [4][5][6][7] To date, allogeneic hematopoietic stem cell transplantation (HSCT) is the only beneficial therapeutic approach, although at high risk because of the myeloablative conditioning regimens necessary to eliminate autoreactive T lymphocytes and achieve successful engraftment. [8][9][10] We have recently generated and characterized a knock-in Rag2 R229Q mouse model, carrying a hypomorphic mutation in the Rag2 gene (R229Q), initially identified in patients with OS or with leaky SCID. [10][11][12] The RAG2 R229Q mouse model closely recapitulates the human disease as mice display an expansion of oligoclonal and activated T cells which infiltrate target organs including skin, gut, liver, and lung, 13 and high levels of serum IgE, despite a severe arrest of B-cell development in the bone marrow. 14 This mouse model shows an arrest at the CD4 Ϫ CD8 Ϫ CD44 Ϫ CD25 ϩ double-negative 3 (DN3) stage of thymocyte differentiation, resulting in thymic atrophy and severe depletion of CD4 ϩ CD8 ϩ double-positive (DP) and mature CD4 ϩ or CD8 ϩ single-positive (SP) cells. As previously observed in OS patients, 15,16 thymi from RAG2 R229Q mice are small, lack corticomedullary demarcation, and show a significant decrease in the expression of autoimmune regulator (AIRE), which induce the transcription of tissue-restricted antigens (TRAs) and plays a key role in the negative selection of autoreactive thymocytes. 17,18 This observation has raised the hypothesis that a defe...

Thymocyte Selection Regulates the Homeostasis of IL-7–Expressing Thymic Cortical Epithelial Cells In Vivo

“…Restoration of normal thymopoiesis following WT stem cell transplantation reduces their frequency (17), suggesting that thymic crosstalk regulates their comitant moderate improvement in mTEC development in anti-CD3ε-treated Rag2 2/2 mice. An amelioration of medullary niches upon anti-CD3ε treatment has been recently reported in a mouse model of Omenn syndrome, which is associated with a hypomorphic R229Q mutation in the RAG2 enzyme (40). In contrast to our model, TCR-expressing cells are found in the thymus of R229Q RAG2 mice (40), which may also contribute to the improvement of the medullary epithelium.…”

“…An amelioration of medullary niches upon anti-CD3ε treatment has been recently reported in a mouse model of Omenn syndrome, which is associated with a hypomorphic R229Q mutation in the RAG2 enzyme (40). In contrast to our model, TCR-expressing cells are found in the thymus of R229Q RAG2 mice (40), which may also contribute to the improvement of the medullary epithelium. In both cases, insufficient mTEC differentiation might reflect a lack of instructive signals from mature thymocytes (9).…”

Tight Interdigitating Developmental Processes within the Thymus; Lessons from Primary Immunodeficiency with Autoimmunity

“…In a Rag2 R229Q/R229Q OS mouse model, the injection of anti-CD3 antibody activated DP thymocytes and induced UEA1 + cytokeratin5 + cytokeratin8thymic medullary structure [25]. Thus, the injection of anti-CD3 antibody may be applicable to other PID diseases associated with impaired thymic development to control autoimmune manifestations via facilitating negative selection of autoreactive thymocytes and development of natural Treg cells [38].…”

“…In the instance of hypomorphic mutation of Rag genes, gene therapy in a preclinical study provided poor reconstitution of immune system due to inadequate Rag gene expression [37]. Instead, the injection of anti-CD3 antibody may be considered as a therapeutic option since anti-CD3 antibody can induce thymic organogenesis along with the induction of T cell development from DN thymocytes by crosslinking TCR complex on immature thymocytes [38].…”

RAGs and BUGS: An alliance for autoimmunity

“…Rag2 R229Q mice recapitulate the autoimmune manifestations in humans at mucosal barriers and systemic target organs 15 . Thus, we sought to determine the effect of flora depletion on autoimmune phenomena in different organs of mutant mice.…”