The BH3-mimetic ABT-737 inhibits allogeneic immune responses

BCL-2 levels do not predict azathioprine treatment response in inflammatory bowel disease, but inhibition induces lymphocyte apoptosis and ameliorates colitis in mice

In inflammatory bowel disease (IBD), inflammation is sustained by an exaggerated response of lymphocytes. This results from enhanced expression of anti-apoptotic B cell lymphoma (BCL-2) and BCL-XL associated with a diminished turnover. Azathioprine (AZA) directly targets BCL-2 family-mediated apoptosis. We investigated whether the BCL-2 family expression pattern could be used to predict treatment response to AZA and determined whether BCL-2 inhibitor A-1211212 effectively diminishes lymphocytes and ameliorates inflammation in a model of colitis. BCL-2 family expression pattern was determined by next-generation sequencing (NGS). BCL-2 inhibitor was administered orally to Il10-/- mice. Haematological analyses were performed with an ADVIA 2120 and changes in immune cells were investigated using quantitative polymerase chain reaction (qPCR) and fluorescence activated cell sorter (FACS). We determined similar expression levels of BCL-2 family members in patients with remission and patients refractory to treatment, showing that BCL-2 family expression can not predict AZA treatment response. Expression was not correlated with the modified Truelove and Witts activity index (MTWAI). BCL-2 inhibitor initiated cell death in T cells from patients refractory to AZA and reduced lymphocyte count in Il10-/- mice. FACS revealed diminished CD8⁺ T cells upon BCL-2 inhibitor in Il10-/- mice without influencing platelets. Tnf, Il1β, IfnƔ and Mcp-1 were decreased upon BCL-2 inhibitor. A-1211212 positively altered the colonic mucosa and ameliorated inflammation in mice. Pro-apoptotic BCL-2 inhibitor A-1211212 diminishes lymphocytes and ameliorates colitis in Il10-/- mice without inducing thrombocytopenia. BCL-2 inhibition could be a new therapy option for patients refractory to AZA.

BCL2 Regulates Differentiation of Intestinal Fibroblasts

BACKGROUND

Fibrosis in patients with Crohn's disease (CD) results from an imbalance toward excessive fibrous tissue formation driven by fibroblasts. Activation of fibroblasts is linked to the B-cell lymphoma 2 (BCL2) family, which is involved in the induction of apoptosis. We investigated the impact of BCL2 repression on fibrogenesis.

METHODS

The model of dextran sodium sulfate (DSS)-induced chronic colitis and the heterotopic transplantation model of fibrosis were used. Following the administration of the BCL2 antagonist (ABT-737, 50 mg/kg/d), collagen layer thickness and hydroxyproline (HYP) content were determined. Fibroblasts were stimulated with the BCL2 antagonist (0.01-100 µM). BCL2, alpha smooth muscle actin (αSMA), and collagen I (COL1A1) were determined by quantitative polymerase chain reaction (qPCR), immunofluorescence microscopy (IF), and western blot (WB). mRNA expression pattern was determined by next-generation sequencing (NGS).

RESULTS

Collagen layer thickness was significantly decreased in both DSS-induced chronic colitis and the transplantation model of fibrosis upon BCL2 antagonist administration compared with vehicle. Decreased HYP content confirmed the preventive effects of the BCL2 antagonist on fibrosis. In vitro, a significant increase in PI+/annexin V+ human colonic fibroblasts was determined by fluorescence-activated cell sorting upon treatment with high-dose BCL2 antagonist; at a lower dose, αSMA, COL1A1, and TGF were decreased. NGS, IF, and qPCR revealed decreased expression and nuclear translocation of GATA6 and SOX9, known for reprogramming fibroblasts.

CONCLUSION

BCL2 antagonist administration partially prevented fibrogenesis in both fibrosis models. The BCL2 antagonist reduced the expression of TGFβ-induced factors involved in differentiation of myofibroblasts, and therefore might represent a potential treatment option against CD-associated fibrosis.

Pharmacological modulation of cell death in organ transplantation

New options to pharmacologically modulate fundamental mechanisms of regulated cell death are rapidly evolving and found first clinical applications in cancer therapy. Here, we present an overview on how the recent advances in the understanding of the biology and pharmacology of cell death might influence research and clinical practice in solid organ transplantation. Of particular interest are the novel opportunities related to organ preservation and immunomodulation, which might contribute to promote organ repair and to develop more selective ways to modulate allogeneic immune responses to prevent rejection and induce immunological tolerance.

Dying to protect: cell death and the control of T-cell homeostasis

T cells play a critical role in immune responses as they specifically recognize peptide/MHC complexes with their T-cell receptors and initiate adaptive immune responses. While T cells are critical for performing appropriate effector functions and maintaining immune memory, they also can cause autoimmunity or neoplasia if misdirected or dysregulated. Thus, T cells must be tightly regulated from their development onward. Maintenance of appropriate T-cell homeostasis is essential to promote protective immunity and limit autoimmunity and neoplasia. This review will focus on the role of cell death in maintenance of T-cell homeostasis and outline novel therapeutic strategies tailored to manipulate cell death to limit T-cell survival (eg, autoimmunity and transplantation) or enhance T-cell survival (eg, vaccination and immune deficiency).

The Role of T Cell Costimulation via DNAM-1 in Kidney Transplantation

DNAX accessory protein-1 (DNAM-1, CD226) is a co-stimulatory and adhesion molecule expressed mainly by natural killer cells and T cells. DNAM-1 and its two ligands CD112 and CD155 are important in graft-versus-host disease, but their role in solid organ transplantation is largely unknown. We investigated the relevance of this pathway in a mouse kidney transplantation model. CD112 and CD155 are constitutively expressed on renal tubular cells and strongly upregulated in acutely rejected renal allografts. In vitro DNAM-1 blockade during allogeneic priming reduced the allospecific T cell response but not the allospecific cytotoxicity against renal tubular epithelial cells. Accordingly, absence of DNAM-1 in recipient mice or absence of CD112 or CD155 in the kidney allograft did not significantly influence renal function and severity of rejection after transplantation, but led to a higher incidence of infarcts in CD112 and CD155 deficient kidney allografts. Thus, DNAM-1 blockade is not effective in preventing transplant rejection. Despite of being highly expressed, CD112 and CD155 do not appear to play a major immunogenic role in kidney transplantation. Considering the high incidence of renal infarcts in CD112 and CD155 deficient grafts, blocking these molecules might be detrimental.

Killing Two Cells with One Stone: Pharmacologic BCL-2 Family Targeting for Cancer Cell Death and Immune Modulation

A crucial component of regulating organismal homeostasis is maintaining proper cell number and eliminating damaged or potentially malignant cells. Apoptosis, or programed cell death, is the mechanism responsible for this equilibrium. The intrinsic apoptotic pathway is also especially important in the development and maintenance of the immune system. Apoptosis is essential for proper positive and negative selection during B- and T-cell development and for efficient contraction of expanded lymphocytes following an immune response. Tight regulation of the apoptotic pathway is critical, as excessive cell death can lead to immunodeficiency while apoptotic resistance can lead to aberrant lymphoproliferation and autoimmune disease. Dysregulation of cell death is implicated in a wide range of hematological malignancies, and targeting various components of the apoptotic machinery in these cases is an attractive chemotherapeutic strategy. A wide array of compounds has been developed with the purpose of reactivating the intrinsic apoptotic pathway. These compounds, termed BH3 mimetics are garnering considerable attention as they gain greater clinical oncologic significance. As their use expands, it will be imperative to understand the effects these compounds have on immune homeostasis. Uncovering their potential immunomodulatory activity may allow for administration of BH3 mimetics for direct tumor cell killing as well as novel therapies for a wide range of immune-based directives. This review will summarize the major proteins involved in the intrinsic apoptotic pathway and define their roles in normal immune development and disease. Clinical and preclinical BH3 mimetics are described within the context of what is currently known about their ability to affect immune function. Prospects for future antitumor immune amplification and immune modulation are then proposed.

Increased lymphocyte apoptosis in mouse models of colitis upon ABT-737 treatment is dependent upon BIM expression

Exaggerated activation of lymphocytes contributes to the pathogenesis of inflammatory bowel disease (IBD). Medical therapies are linked to the BCL-2 family-mediated apoptosis. Imbalance in BCL-2 family proteins may cause failure in therapeutic responses. We investigated the role of BCL-2 inhibitor ABT-737 for lymphocyte apoptosis in mice under inflammatory conditions. B.6129P2-interleukin (IL)-10(tm1Cgn) /J (IL-10(-/-) ) weighing 25-30 g with ongoing colitis were used. Fifty mg/kg/day ABT-737 was injected intraperitoneally (i.p.). Haematological analyses were performed with an ADVIA 2120 flow cytometer and mass cytometry with a CyTOF 2. Following i.p. administration, ABT-737 was detected in both spontaneous and acute colitis in peripheral blood (PBL) and colon tissue. Treatment led to lymphopenia. CD4(+) CD44(+) CD62L(+) central memory and CD8(+) , CD44(+) CD62L(-) central memory T cells were decreased in PBL upon ABT-737 compared to vehicle-receiving controls. Increased apoptosis upon ABT-737 was determined in blood lymphocytes, splenocytes and Peyer's patches and was accompanied by a decrease in TNF and IL-1B. ABT-737 positively altered the colonic mucosa and ameliorated inflammation, as shown by colonoscopy, histology and colon length. A decreased BIM/BCL-2 ratio or absence of BIM in both Bim(-) (/) (-) and Il10(-) (/) (-) × Bim(-) (/) (-) impeded the protective effect of ABT-737. The BIM/BCL-2 ratio decreased with age and during the course of treatment. Thus, long-term treatment resulted in adapted TNF levels and macroscopic mucosal damage. ABT-737 was efficacious in diminishing lymphocytes and ameliorating colitis in a BIM-dependent manner. Regulation of inappropriate survival of lymphocytes by ABT-737 may provide a therapeutic strategy in IBD.

Bcl-2 inhibition to overcome memory cell barriers in transplantation

Memory T cells (Tm) represent a major barrier for immunosuppression and tolerance induction after solid organ transplantation. Taking into consideration the critical role of the intrinsic apoptosis pathway in the generation and maintenance of Tm, we developed a new concept to deplete alloreactive Tm by targeting Bcl-2 proteins. The small-molecule Bcl-2/Bcl-XL inhibitor ABT-737 efficiently induced apoptosis in alloreactive Tm in vitro and in vivo and prolonged skin graft survival in sensitized recipients. A short course of ABT-737 induction therapy prevented Tm-mediated resistance in a donor-specific transfusion model and allowed mixed chimerism induction across Tm barriers. Since Bcl-2 inhibitors yielded encouraging safety results in cancer trials, this novel approach might represent a substantial advance to prevent allograft rejection and induce tolerance in sensitized recipients.

Synergistic Bcl-2 inhibition by ABT-737 and cyclosporine A

Survival of lymphocytes and melanocyte stem cells critically depends on B cell lymphoma 2 (Bcl-2). In T lymphocytes, a basal calcineurin activity maintains Bcl-2 expression in naïve cells, and the activation of the calcineurin pathway orchestrates the regulation of the intrinsic apoptosis pathway after antigen recognition. Therefore, calcineurin inhibitors might potentiate the pro-apoptotic effect of pharmacological Bcl-2 inhibitors on lymphatic cells. In vitro, a reduced Bcl-2 expression in lymphocytes exposed to calcineurin inhibitors increased their sensitivity to the small molecule Bcl-2 inhibitor ABT-737. This correlated with an augmented pro-apoptotic activity of ABT-737 on lymphocytes in combination with cyclosporine A in naïve mice in vivo. Interestingly, similar processes were observed in melanocytes. ABT-737 induced a fur depigmentation at the site of injection, and this effect was expanded to a generalized depigmentation in combination with cyclosporine A. Thus, inhibiting calcineurin increases the pro-apoptotic potency of ABT-737 in cells depending on Bcl-2 for survival. The increased efficacy of Bcl-2 inhibitors in combination with cyclosporine A might be relevant to exploit their anti-neoplastic and immuno-modulatory properties.

Targeting apoptosis to induce stable mixed hematopoietic chimerism and long-term allograft survival without myelosuppressive conditioning in mice

Induction of mixed hematopoietic chimerism results in donor-specific immunological tolerance by apoptosis-mediated deletion of donor-reactive lymphocytes. A broad clinical application of this approach is currently hampered by limited predictability and toxicity of the available conditioning protocols. We developed a new therapeutic approach to induce mixed chimerism and tolerance by a direct pharmacological modulation of the intrinsic apoptosis pathway in peripheral T cells. The proapoptotic small-molecule Bcl-2 inhibitor ABT-737 promoted mixed chimerism induction and reversed the antitolerogenic effect of calcineurin inhibitors by boosting the critical role of the proapoptotic Bcl-2 factor Bim. A short conditioning protocol with ABT-737 in combination with costimulation blockade and low-dose cyclosporine A resulted in a complete deletion of peripheral donor-reactive lymphocytes and was sufficient to induce mixed chimerism and robust systemic tolerance across full major histocompatibility complex barriers, without myelosuppression and by using moderate doses of bone marrow cells. Thus, immunological tolerance can be achieved by direct modulation of the intrinsic apoptosis pathway in peripheral lymphocytes-a new approach to translate immunological tolerance into clinically applicable protocols.

Resistance to ABT-737 in activated T lymphocytes: molecular mechanisms and reversibility by inhibition of the calcineurin-NFAT pathway

Dynamic regulation of the intrinsic apoptosis pathway controls central and peripheral lymphocyte deletion, and may interfere with the pro-apoptotic potency of B-cell lymphoma 2 inhibitors such as ABT-737. By following a T-cell receptor (TCR) transgenic population of alloantigen-specific T cells, we found that sensitivity to ABT-737 radically changed during the course of allo-specific immune responses. Particularly, activated T cells were fully resistant to ABT-737 during the first days after antigen recognition. This phenomenon was caused by a TCR–calcineurin–nuclear factor of activated T cells-dependent upregulation of A1, and was therefore prevented by cyclosporine A (CsA). As a result, exposure to ABT-737 after alloantigen recognition induced selection of alloreactive T cells in vivo, whereas in combination with low-dose CsA, ABT-737 efficiently depleted alloreactive T cells in murine host-versus-graft and graft-versus-host models. Thus, ABT-737 resistance is not a prerogative of neoplastic cells, but it physiologically occurs in T cells after antigen recognition. Reversibility of this process by calcineurin inhibitors opens new pharmacological opportunities to modulate this process in the context of cancer, autoimmunity and transplantation.