Immune recovery and immunologic remodeling after CD19-directed chimeric antigen receptor T cell therapy in autoimmune diseases

Abstract Introduction Anti-CD19 Chimeric Antigen Receptor T cell therapy (CART19) is a promising treatment option for refractory autoimmune diseases (AD). These patients are often heavily pretreated with multiple lines of immunosuppression, increasing their susceptibility to infections. In this context, immunologic reconstitution, infectious complications, and the implementation of specific prophylactic measures are subjects of ongoing discussion. We investigated the immune recovery and immunologic remodeling in AD patients treated with CART19. Methods All patients were treated under a hospital exemption and the study was approved by the local ethics committee (771/2023BO2). Autologous T cells were collected and transduced with an anti-CD19, 2nd-generation CAR lentiviral vector containing a CD3-ζ signaling domain (Miltenyi Biotec, Germany), before infusion following lymphodepletion with fludarabine and cyclophosphamide. We analyzed immune reconstitution (cell counts, immunoglobulin levels, vaccination titers) and infectious complications within one year post-therapy, censoring patients at disease progression (PD) or follow-up completion (1 year). Febrile neutropenia, colonization, and resident flora were excluded as infections. Spectral flow phenotyping was performed to assess immunologic changes after CART19 treatment in ADs. Results Systemic sclerosis was the most common indication (n = 6), followed by antisynthetase syndrome, rheumatoid arthritis, and granulomatosis with polyangiitis (each n = 1). The median age was 50 years (range: 30–69), with 66.7% female patients. Most were heavily pretreated, with a median of 6 previous therapies. At CART therapy, 44.4% had stable disease and 55.6% had PD. Early infections (30d) occurred in 44.4%, resulting in a density of 1.85 per 100 patient-days, which later declined to 0.33 infections. Until day 30, bacterial infections were predominant; only one patient developed a non-invasive fungal infection. Later a shift from bacterial (80.0%) to predominantly viral infections (87.5%) was observed. Following CART19 infusion, blood cell lineages recovered rapidly, with neutrophil counts (500/µL) reached by a median of 11 days (with G-CSF). At day 180, AD patients had significantly higher CD4+ T- and CD19+ B-cell counts compared to our previously published DLBCL cohort (CD4+: 312 vs. 126/µl, CD19+: 135 vs. 0/µl, Mann-Whitney p=.04/.001). Humoral recovery was also rapid (Median IgG d+180: 616/µl) with only one patient receiving intravenous immunoglobulin substitution (IVIG), planned for discontinuation. To assess whether vaccination titers remain adequate following CART19, we analyzed titers for the standard vaccines—tetanus, measles, diphtheria and hepatitis B. No patients received vaccinations against the analyzed pathogens between the time of CART infusion and titer assessment. Interestingly, there was no significant difference in titers between the time points except for tetanus (approximately d180) (Wilcoxon, p=.03). One patient exhibited even higher titers after CART 19 treatment, most likely due to ongoing, potent B cell depleting therapies prior lymphodepletion. Spectral flow phenotyping revealed no significant differences in the proportions of CD8+ and CD19+ relative to CD45+ cells between previously investigated healthy individuals and patients at day 180 post CART19 treatment (Mann-Whitney U, p=.001-.006). However, significant alterations were observed in the composition of lymphocyte subsets. CART therapy resulted in significantly lower proportions of CD4+ T cells and γδ effector memory T cells, while regulatory T cells (Tregs) and activated T cells were significantly increased (Mann-Whitney U, p=.001-.02). Moreover, CD19+ B cells in CART19 patients were predominantly immature, with a significantly reduced proportions of both switched and unswitched B cells (Mann-Whitney U, p=.006-.02). Conclusion Our findings implicate effective immune reconstitution with manageable infectious risk following CART19 treatment in ADs. Vaccination titers remained stable and IgG levels were largely sufficient, suggesting preserved humoral immunity. Compared to healthy individuals, an increase in Tregs, a reduction in CD4+ T cells and γδ effector memory T cells, and a B cell compartment skewed toward immature phenotypes may reflect a beneficial immune remodeling. Additional data on immune changes relative to the preCART19 baseline will be presented at the meeting.