A multimerized form of recombinant human CD40 ligand supports long-term activation and proliferation of B cells

The Evolving Landscape of B Cells in Cancer Metastasis

Metastasis is the leading cause of cancer mortality. Functional and clinical studies have documented diverse B-cell and antibody responses in cancer metastasis. The presence of B cells in tumor microenvironments and metastatic sites has been associated with diverse effects that can promote or inhibit metastasis. Specifically, B cells can contribute to the spread of cancer cells by enhancing tumor cell motility, invasion, angiogenesis, lymphangiogenesis, and extracellular matrix remodeling. Moreover, they can promote metastatic colonization by triggering pathogenic immunoglobulin responses and recruiting immune suppressive cells. Contrastingly, B cells can also exhibit antimetastatic effects. For example, they aid in enhanced antigen presentation, which helps activate immune responses against cancer cells. In addition, B cells play a crucial role in preventing the dissemination of metastatic cells from the primary tumor and secrete antibodies that can aid in tumor recognition. Here, we review the complex roles of B cells in metastasis, delineating the heterogeneity of B-cell activity and subtypes by metastatic site, antibody class, antigen (if known), and molecular phenotype. These important attributes of B cells emphasize the need for a deeper understanding and characterization of B-cell phenotypes to define their effects in metastasis.

Presentation and integration of multiple signals that modulate oligodendrocyte lineage progression and myelination

Myelination is critical for fast saltatory conduction of action potentials. Recent studies have revealed that myelin is not a static structure as previously considered but continues to be made and remodeled throughout adulthood in tune with the network requirement. Synthesis of new myelin requires turning on the switch in oligodendrocytes (OL) to initiate the myelination program that includes synthesis and transport of macromolecules needed for myelin production as well as the metabolic and other cellular functions needed to support this process. A significant amount of information is available regarding the individual intrinsic and extrinsic signals that promote OL commitment, expansion, terminal differentiation, and myelination. However, it is less clear how these signals are made available to OL lineage cells when needed, and how multiple signals are integrated to generate the correct amount of myelin that is needed in a given neural network state. Here we review the pleiotropic effects of some of the extracellular signals that affect myelination and discuss the cellular processes used by the source cells that contribute to the variation in the temporal and spatial availability of the signals, and how the recipient OL lineage cells might integrate the multiple signals presented to them in a manner dialed to the strength of the input.

Development of a Nanocarrier-Based Splenic B Cell-Targeting System for Loading Antigens in Vitro

B cells are types of lymphocytes that are involved in the production of antibodies against pathogens. They also deliver and present antigens for the priming of T cells. Recently, we developed an in vivo splenic marginal zone (MZ) B cell-targeting liposomes decorated with polyethylene glycol (PEG) containing a hydroxyl-terminus group (HO-PEG-Lip). In an expansion of a previous study, we used HO-PEG-Lip as an in vitro antigen delivery tool to splenic B cells to test the ability of this formulation to overcome the limitations of the poor antigen uptake ability of B cells for implantation. To achieve our purpose, various factors were optimized. These factors include cell number, liposome concentration, pre-opsonization of liposomes, fresh serum concentration, and incubation time, all of which affect the extent of interaction between liposomes and B cells. As a result, we confirmed that the HO-PEG-Lip required incubation at 37 °C for at least 20 min with 50% mouse fresh serum followed by a subsequent incubation at 37 °C for at least another 30 min with splenic B cells. By using such a loading system, fluorescein isothiocyanate (FITC)-labeled ovalbumin (OVA), a model antigen, encapsulated in HO-PEG-Lip could be efficiently loaded into splenic B cells. In addition, HO-PEG-Lip and FITC-labeled OVA encapsulated in HO-PEG-Lip were efficiently associated with MZ-B cells with high levels of complement receptors (CRs) rather than follicular B cells with low levels of CRs. These results propose a novel and useful system to efficiently load antigens into B cells in vitro by taking advantage of complement systems.

CD40L-Stimulated B Lymphocytes Are Polarized toward APC Functions after Exposure to IL-4 and IL-21

B lymphocytes have multiple functions central to humoral immunity, including Ag presentation to T cells, cytokine secretion, and differentiation into Ab-secreting plasma cells. In vitro expansion of human B cells by continuous IL-4 stimulation and engagement of their CD40 receptor by CD40L has allowed the use of these IL-4-CD40-B cells in research for the induction of Ag-specific T cell immune responses. However, in vivo, follicular helper T cells also influence B cell activity through the secretion of IL-21. The impact of both cytokines on multiple B cell functions is not clearly defined. To further understand these cytokines in CD40-B cell biology, we stimulated CD40-B cells with IL-4 or IL-21 or both (Combo) and characterized the proliferation, subsets, and functions of these cells. We demonstrate that IL-21- and Combo-CD40-B cells are highly proliferative cells that can be rapidly expanded to high numbers. We show that IL-21-CD40-B cells polarize to Ab-secreting plasma cells, whereas IL-4- and Combo-CD40-B cells are mostly activated mature B cells that express molecules associated with favorable APC functions. We further demonstrate that both IL-4- and Combo-CD40-B cells are efficient in promoting T cell activation and proliferation compared with IL-21-CD40-B cells. Thus, our study provides a better appreciation of CD40-B cell plasticity and biology. In addition, the stimulation of B cells with CD40L, IL-4, and IL-21 allows for the fast generation of high numbers of efficient APC, therefore providing a prospective tool for research and clinical applications such as cancer immunotherapy.

B Cell-Based Cancer Immunotherapy

B cells are not only producers of antibodies, but also contribute to immune regulation or act as potent antigen-presenting cells. The potential of B cells for cellular therapy is still largely underestimated, despite their multiple diverse effector functions. The CD40L/CD40 signaling pathway is the most potent activator of antigen presentation capacity in B lymphocytes. CD40-activated B cells are potent antigen-presenting cells that induce specific T-cell responses in vitro and in vivo. In preclinical cancer models in mice and dogs, CD40-activated B cell-based cancer immunotherapy was able to induce effective antitumor immunity. So far, there have been only few early-stage clinical studies involving B cell-based cancer vaccines. These trials indicate that B cell-based immunotherapy is generally safe and associated with little toxicity. Furthermore, these studies suggest that B-cell immunotherapy can elicit antitumor T-cell responses. Alongside the recent advances in cellular therapies in general, major obstacles for generation of good manufacturing practice-manufactured B-cell immunotherapies have been overcome. Thus, a first clinical trial involving CD40-activated B cells might be in reach.

A tetrameric form of CD40 ligand with potent biological activities in both mouse and human primary B cells

CD40 ligand (CD40 L) expressed by activated T cells interacts with CD40 on B cells and triggers B cell survival, proliferation and differentiation. Deficiency in CD40 L or CD40 in humans causes hyper IgM syndrome due to a defect in T-B interaction that is essential for Ig gene class switch recombination (CSR). CD40 L belongs to the tumor necrosis factor family and normally forms a homotrimer on the cell surface, which is important for its biological activity. To generate a multimeric CD40 L that can be used to stimulate both mouse and human B cells, we fused the extracellular domain of mouse CD40 L, which is known to also bind human CD40, with streptavidin (SA) that forms a stable tetramer under physiological conditions. As expected, 293 T cells transiently transfected with an SA-CD40 L expression vector secreted tetrameric SA-CD40 L in the culture supernatant. The secreted SA-CD40 L exhibited > 25-fold stronger activities in inducing the survival, activation and proliferation of both mouse and human primary B cells than did an agonistic anti-mouse or anti-human CD40 antibody. In the presence of IL-4, SA-CD40 L also induced efficient CSR and plasma cell differentiation in both mouse and human B cells. Moreover, administration of SA-CD40 L in mice induced activation and proliferation of spleen B cells in vivo. These results demonstrate that the SA-CD40 L fusion protein generated in the present study recapitulates the function of membrane-bound trimeric CD40 L and has potent biological activities in both mouse and human primary B cells.

Using Antigen-Specific B Cells to Combine Antibody and T Cell-Based Cancer Immunotherapy

Cancer immunotherapy by therapeutic activation of T cells has demonstrated clinical potential. Approaches include checkpoint inhibitors and chimeric antigen receptor T cells. Here, we report the development of an alternative strategy for cellular immunotherapy that combines induction of a tumor-directed T-cell response and antibody secretion without the need for genetic engineering. CD40 ligand stimulation of murine tumor antigen-specific B cells, isolated by antigen-biotin tetramers, resulted in the development of an antigen-presenting phenotype and the induction of a tumor antigen-specific T-cell response. Differentiation of antigen-specific B cells into antibody-secreting plasma cells was achieved by stimulation with IL21, IL4, anti-CD40, and the specific antigen. Combined treatment of tumor-bearing mice with antigen-specific CD40-activated B cells and antigen-specific plasma cells induced a therapeutic antitumor immune response resulting in remission of established tumors. Human CEA or NY-ESO-1-specific B cells were detected in tumor-draining lymph nodes and were able to induce antigen-specific T-cell responses in vitro, indicating that this approach could be translated into clinical applications. Our results describe a technique for the exploitation of B-cell effector functions and provide the rationale for their use in combinatorial cancer immunotherapy. Cancer Immunol Res; 5(9); 730-43. ©2017 AACR.

CD40-activated B cells induce anti-tumor immunity in vivo

The introduction of checkpoint inhibitors represents a major advance in cancer immunotherapy. Some studies on checkpoint inhibition demonstrate that combinatorial immunotherapies with secondary drivers of anti-tumor immunity provide beneficial effects for patients that do not show a strong endogenous immune response. CD40-activated B cells (CD40B cells) are potent antigen presenting cells by activating and expanding naïve and memory CD4+ and CD8+ and homing to the secondary lymphoid organs. In contrast to dendritic cells, the generation of highly pure CD40B cells is simple and time efficient and they can be expanded almost limitlessly from small blood samples of cancer patients. Here, we show that the vaccination with antigen-loaded CD40B cells induces a specific T-cell response in vivo comparable to that of dendritic cells. Moreover, we identify vaccination parameters, including injection route, cell dose and vaccination repetitions to optimize immunization and demonstrate that application of CD40B cells is safe in terms of toxicity in the recipient. We furthermore show that preventive immunization of tumor-bearing mice with tumor antigen-pulsed CD40B cells induces a protective anti-tumor immunity against B16.F10 melanomas and E.G7 lymphomas leading to reduced tumor growth. These results and our straightforward method of CD40B-cell generation underline the potential of CD40B cells for cancer immunotherapy.

Papular mycosis fungoides: Six new cases and association with chronic lymphocytic leukemia

Papular mycosis fungoides (MF) is a rare presentation of MF. Six illustrative cases of papular MF were retrospectively reviewed. Five of the cases studied by immunohistochemistry had variable numbers (range: 1%-20%) of CD30+ cells in the dermal infiltrate, a finding that is characteristic of lymphomatoid papulosis but may occasionally occur in typical early MF. Although none of our papular MF patients had progressive disease, lesions with relatively high numbers of CD30+ cells in 3 patients did not respond well to skin-directed treatments used for MF. Interestingly, these patients had evidence of co-existing clonal B cell populations in the blood (one with clonal B cell lymphocytosis and two with B-cell chronic lymphocytic leukemia). We conclude that: (1) papular MF may contain CD30+ cells, thereby causing confusion with lymphomatoid papulosis; and (2) papular MF, like more typical MF, may be associated with clonal B-cell proliferations including chronic lymphocytic leukemia.

Efficient Culture of Human Naive and Memory B Cells for Use as APCs

The ability to culture and expand B cells in vitro has become a useful tool for studying human immunity. A limitation of current methods for human B cell culture is the capacity to support mature B cell proliferation. We developed a culture method to support the efficient activation and proliferation of naive and memory human B cells. This culture supports extensive B cell proliferation, with ∼10³-fold increases following 8 d in culture and 10⁶-fold increases when cultures are split and cultured for 8 more days. In culture, a significant fraction of naive B cells undergo isotype switching and differentiate into plasmacytes. Culture-derived (CD) B cells are readily cryopreserved and, when recovered, retain their ability to proliferate and differentiate. Significantly, proliferating CD B cells express high levels of MHC class II, CD80, and CD86. CD B cells act as APCs and present alloantigens and microbial Ags to T cells. We are able to activate and expand Ag-specific memory B cells; these cultured cells are highly effective in presenting Ag to T cells. We characterized the TCR repertoire of rare Ag-specific CD4⁺ T cells that proliferated in response to tetanus toxoid (TT) presented by autologous CD B cells. TCR Vβ usage by TT-activated CD4⁺ T cells differs from resting and unspecifically activated CD4⁺ T cells. Moreover, we found that TT-specific TCR Vβ usage by CD4⁺ T cells was substantially different between donors. This culture method provides a platform for studying the BCR and TCR repertoires within a single individual.