Estimation of the number of CD154 molecules in membrane extracts used as a source of CD40 stimulation of human B lymphocytes

Characterization of the growth modulatory activities of osteoblast conditioned media on cord blood progenitor cells

Engraftment outcomes are strongly correlated with the numbers of hematopoietic stem and progenitor cells (HSPC) infused. Expansion of umbilical cord blood (CB) HSPC has gained much interest lately since infusion of expanded HSPC can accelerate engraftment and improve clinical outcomes. Many novel protocols based on different expansion strategies of HSPC and their downstream derivatives are under development. Herein, we describe the production and properties of serum-free medium (SFM) conditioned with mesenchymal stromal cells derived-osteoblasts (OCM) for the expansion of umbilical CB cells and progenitors. After optimization of the conditioning length, we show that OCM increased the production of human CB total nucleated cells and CD34⁺ cells by 1.8-fold and 1.5-fold over standard SFM, respectively. Production of immature CD34⁺ subpopulations enriched in hematopoietic stem cells was also improved with a shorter conditioning period. Moreover, we show that the growth modulatory activities of OCM on progenitor expansion are regulated by both soluble factors and non-soluble cellular elements. Finally, the growth and differentiation modulatory activities of OCM were fully retained after high dose-ionizing irradiation and highly stable when OCM is stored frozen. In summary, our results suggest that OCM efficiently mimics some of the natural regulatory activities of osteoblasts on HSPC and highlight the marked expansion potentials of SFM conditioned with osteoblasts.

Comparison of the glycosylation of in vitro generated polyclonal human IgG and therapeutic immunoglobulins

We have recently developed an in vitro culture model enabling the large-scale expansion of switched-memory B lymphocytes, producing a polyclonal human IgG repertoire. Given the importance of glycosylation for the functions of immunoglobulins, we analyzed the N-glycosylation profiles of the immunoglobulin G (IgG) in this model. Switched-memory B cells were cultured for 38 days and, using liquid chromatography-mass spectrometry, we analyzed IgGs' glycosylation profiles which were then compared to the glycosylation patterns of commercial intravenous immunoglobulin (IVIG). We observed a reproducible proliferation rate, high viability through the cultures as well as a good maintenance of the switched-memory B cells repertoire. The glycosylation pattern analyses revealed a variety of the typical biantennary N-glycan structures with diverse terminal monosaccharides. While many similarities were detected in comparison to the glycosylation profile of IVIG, in vitro-produced polyclonal IgGs were bearing higher levels of bisecting GlcNAc known to affect the effector functions of therapeutic antibodies. This data highlights the need for monitoring of the glycoform distribution in antibodies produced in vitro.

Large-scale in vitro expansion of polyclonal human switched-memory B lymphocytes

Polyclonal preparations of therapeutic immunoglobulins, namely intravenous immunoglobulins (IVIg), are essential in the treatment of immunodeficiency and are increasingly used for the treatment of autoimmune and inflammatory diseases. Currently, patients’ accessibility to IVIg depends exclusively upon volunteer blood donations followed by the fractionation of pooled human plasma obtained from thousands of individuals. Presently, there are no in vitro cell culture procedures allowing the preparation of polyclonal human antibodies. All in vitro human therapeutic antibodies that are currently generated are based on monoclonal antibodies, which are mostly issued from genetic engineering or single cell antibody technologies. Here, we describe an in vitro cell culture system, using CD40-CD154 interactions, that leads to a 1×10⁶-fold expansion of switched memory B lymphocytes in approximately 50 days. These expanded cells secrete polyclonal IgG, which distribution into IgG₁, IgG₂, IgG₃ and IgG₄ is similar to that of normal human serum. Such in vitro generated IgG showed relatively low self-reactivity since they interacted moderately with only 24 human antigens among a total of 9484 targets. Furthermore, up to one liter of IgG secreting cells can be produced in about 40 days. This experimental model, providing large-scale expansion of human B lymphocytes, represents a critical step toward the in vitro production of polyclonal human IgG and a new method for the ex vivo expansion of B cells for therapeutic purposes.