Rapid Reconstitution of Human Antibody Secreting Cells After Haploidentical Allogeneic Stem Cell Transplantation.

Abstract 3682

Poster Board III-618

Innate immunity including granulocytes, monocytes, and NK cells is reported to recover rapidly after allogeneic stem cell transplantation within weeks. In contrast, adaptive immunity, including T- and B-cells, has delayed recovery over months. In murine models innate type marginal zone and B1 B cells, established at fetal age and providing natural antibodies, are distinguished from adaptive B2 or follicular B cells. A crucial maturation and survival factor for adaptive murine B cells was shown to be TNF-family member BAFF (B cell-activating factor), while development of innate B1 B cells is BAFF independent. Kinetics in reconstitution of innate and adaptive immunity after ablation in adults may give insight into hierarchy and attribution to innate and adaptive immunity of defined lymphocyte populations. Reconstitution of lymphopoiesis after CD3 and CD19 depleted haploidentical stem cell transplantation was analyzed in 10 patients, which received monoclonal anti-CD3 antibody OKT3 as immunosuppressant only. This model may enable detailed in vivo evaluation of de novo B cell formation. Weekly samples before and after reduced-intensity conditioning were analyzed by flow cytometry for absolute numbers of T-cell, NK-, and B-cell subsets. Their origin of host or donor hematopoiesis was differentiated by HLA-FACS. Antibody secreting cells (ASC) were enumerated by ELISPOT. Plasma cytokine concentrations were determined by bead based arrays and ELISA. Complete reconstitution of allogeneic NK cells was found at day +21 after transplantation. CD4+ and CD8+ T-cells and their subsets had delayed reconstitution with less then 100 cells/μl at 3 months after transplantation. CD19+ B-lymphocytes of naïve and memory phenotype (>0,5% of all lymphocytes) were detected not before day +60. In contrast, complete reconstitution of antibody-secreting cells after a nadir (<0,05/μl) was observed at day +14. Absolute numbers of ASC were comparable to those of healthy controls (d+14: 72 ASC/μl vs. control: 12 ASC/μl). ASC secreting the isotypes IgM and IgA were more prevalent than IgG compared to controls (time increase: IgM 20; IgA 10; IgG 2,9). These ASC appear CD19low/neg, CD38+, and intracellular Ig+ in flow cytometry and carried donor HLA-haplotype. Reconstitution of ASC occurred without detectable circulating T-cells and before increase of BAFF concentrations were observed. In summary, the rapid and complete reconstitution of peripheral blood ASC after allogeneic transplantation, far proceeding detection of naïve and memory type B-cells, is a novel observation. Incidence before T-cell reconstitution and increase in BAFF concentrations indicates a T-cell and BAFF independent mechanism allocating these early ASC to innate immunity, potentially maintaining natural antibody levels.