Noncognate function of B cells in transplantation

Epigenetic-based therapy in allogenic hematopoietic stem cell transplantation: Novel opportunities for personalized treatment

Current management of patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) lacks immunosuppressant drugs able to block the host immune response toward the graft antigens. Novel treatments may include epigenetic compounds (epidrugs) some of which have been yet approved by the Food and Drugs Administration for the treatment of specific blood malignancies. The most investigated in clinical trials for allo-HSCT are DNA demethylating agents (DNMTi), such as azacitidine (Vidaza) and decitabine (Dacogen) as well as histone deacetylases inhibitors (HDACi), such as vorinostat (Zolinza) and panobinostat (Farydak). Indeed, azacitidine monotherapy before allo-HSCT may reduce the conventional chemotherapy-related complications, whereas it may reduce relapse risk and death after allo-HSCT. Besides, a decitabine-containing conditioning regimen could protect against graft versus host disease (GVHD) and respiratory infections after allo-HSCT. Regarding HDACi, the addition of vorinostat and panobinostat to the conditioning regimen after allo-HSCT seems to reduce the incidence of acute GVHD. Furthermore, panobinostat alone or in combination with low-dose decitabine may reduce the relapse rate in high-risk patients with acute myeloid leukemia patients after allo-HSCT. We discuss the phase 1 and 2 clinical trials evaluating the possible beneficial effects of repurposing specific epidrugs which may guide personalized therapy in the setting of allo-HSCT.

Immunosuppression in the sensitized heart transplant recipient

PURPOSE OF REVIEW

The proportion of heart transplant candidates who are allosensitized has increased over time. Advances in tissue typing and immunosuppression have improved the rate of successful transplant in this challenging population. Recently published data regarding contemporary approaches to desensitization prior to and immunosuppression following transplant are summarized.

RECENT FINDINGS

Continued progress in measurement and characterization of antibodies and strategies to abrogate antibody production both prior to and following heart transplant have been encouraging. Updates on the role of non-human leukocyte antigen antibodies and the impact of mechanical circulatory support on allosensitization are provided. Data on current desensitization strategies, including the increasing use of monoclonal antibodies, are provided and the potential role of complement inhibitors will be reviewed. Increasing experience with potent novel agents is likely to provide the opportunity to improve transplant outcomes for highly sensitized patients.

SUMMARY

Although allosensitized heart transplant candidates remain a management challenge, excellent outcomes can be achieved with contemporary approaches. Advances in the understanding of B-cell biology are anticipated to further broaden options and improve outcomes.

Antibodies in transplantation

Transplantation of cells, tissues, and organs from one individual to another can incite the production of antibodies specific for foreign antigens, especially major histocompatibility antigens, in the graft. Antibodies specific for a graft provide an index of immunity and a potential trigger for injury and rejection. However, the index of immunity can sometimes miss antibody-mediated rejection and besides causing injury the antibodies against a graft can also protect a graft from injury by blocking immune recognition, called enhancement, regulating activation of complement, and inducing changes in the graft that resist damage. Reviewed here are potential limitations in the use of antibodies as an index of immunity and the ways antibodies cause and/or prevent injury.

Transplantation immunology: solid organ and bone marrow

Development of the field of organ and tissue transplantation has accelerated remarkably since the human MHC was discovered in 1967. Matching of donor and recipient for MHC antigens has been shown to have a significant positive effect on graft acceptance. The roles of the different components of the immune system involved in the tolerance or rejection of grafts and in graft-versus-host disease have been clarified. These components include antibodies, antigen-presenting cells, helper and cytotoxic T-cell subsets, immune cell-surface molecules, signaling mechanisms, and cytokines. The development of pharmacologic and biological agents that interfere with the alloimmune response has had a crucial role in the success of organ transplantation. Combinations of these agents work synergistically, leading to lower doses of immunosuppressive drugs and reduced toxicity. Reports of significant numbers of successful solid-organ transplantations include those of the kidneys, liver, heart, and lung. The use of bone marrow transplantation for hematologic diseases, particularly hematologic malignancies and primary immunodeficiencies, has become the treatment of choice in many of these conditions. Other sources of hematopoietic stem cells are also being used, and diverse immunosuppressive drug regimens of reduced intensity are being proposed to circumvent the mortality associated with the toxicity of these drugs. Gene therapy to correct inherited diseases by means of infusion of gene-modified autologous hematopoietic stem cells has shown efficacy in 2 forms of severe combined immunodeficiency, providing an alternative to allogeneic tissue transplantation.

Effect of end-stage renal disease on B-lymphocyte subpopulations, IL-7, BAFF and BAFF receptor expression

BACKGROUND

End-stage renal disease (ESRD) results in increased susceptibility to infections, impaired response to vaccination and diffuse B-cell lymphopenia. However, the precise nature and mechanism of ESRD-induced B-cell lymphopenia remains unclear. Therefore, we studied the distribution of major B-cell subsets, B-cell growth, differentiation and survival factors, IL-7 and BAFF, and their receptors in 21 haemodialysis patients and 21 controls.

METHODS

Innate B1 cells (CD19+, CD5+), conventional B2 cells (CD19+, CD5-), newly formed transitional B cells (CD19+, CD10+, CD27-), naïve B cells (CD19+, CD27-) and memory B cells (CD19+, CD27+) and BAFF receptor were quantified by flow cytometry. Plasma IL-7, BAFF, IL-6, TNF-alpha and IL-10 were measured by ELISA.

RESULTS

The ESRD group exhibited significant reductions of all B-cell subpopulations except for transitional B cells that were less severely affected. No significant difference was found in B-cell apoptosis between the ESRD and control groups. Moreover, plasma IL-7 and BAFF levels were elevated in ESRD patients, therefore excluding their deficiencies as a possible culprit. However, BAFF receptor expression was significantly reduced in transitional but not mature B cells in the ESRD group. Interestingly, B-cell activation with the TLR9 agonist resulted in significantly greater production of IL-6 and TNF alpha but not IL-10 in the ESRD group.

CONCLUSIONS

Thus, despite elevation of B-cell growth, differentiation and survival factors, ESRD patients exhibited diffuse reduction of B-cell subpopulations. This was associated with the down-regulation of BAFF receptor in transitional B cells. The latter can, in part, contribute to B-cell lymphopenia by promoting resistance to the biological actions of BAFF that is a potent B-cell differentiation and survival factor.