Abatacept Induces Long-Term Reconstitution of the B-Cell Niche in a Patient With CTLA-4 Haploinsufficiency: A Case Report.

Objectives: Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) haploinsufficiency is a rare genetic condition characterized by development of immune cytopenia, hypogammaglobulinemia, and/or lymphoproliferative disorder, as well as multiple autoimmunity. Treatment with abatacept was shown to alleviate autoimmune conditions, yet its long-lasting impact on bone marrow function remains undetermined.

Methods: We here present the case of a now 39-year-old woman with CTLA-4 haploinsufficiency with predominant CNS affection, yet multiorgan autoimmunity and lymphopenia. We conducted single-cell RNA sequencing (scRNA-seq) of peripheral mononuclear blood cells before and after abatacept induction.

Results: After several high-efficacy immunosuppressive treatments with little-to-no response, she started abatacept in 2017 and experienced ongoing remission including resolution of pre-existing immune cytopenia and hypogammaglobulinemia. Using scRNA-seq, we were able to demonstrate reconstitution of peripheral B cells accompanied by reduction of CD8⁺ T cells. CD4⁺ and CD8⁺ T cells were characterized by downregulation of pathways involved in activation of innate immune cells.

Discussion: Our findings demonstrate long-lasting resolution of lymphopenia after abatacept treatment in CTLA-4 haploinsufficiency despite severity and duration of symptoms. Thus, abatacept should be considered throughout before stem cell transplantation also in CTLA-4 haploinsufficiency with severe symptoms.

Classification of evidence: As a single report without controls, this report provides class IV evidence that abatacept might revert lymphopenia in patients with CTLA-4 haploinsufficiency.