Blockade of the CD40/CD154 pathway enhances T-cell-depleted allogeneic bone marrow engraftment under nonmyeloablative and irradiation-free conditioning therapy

siRNA against CD40 delivered via a fungal recognition receptor ameliorates murine acute graft‐versus‐host disease

Acute graft‐versus‐host disease (aGvHD) remains a major threat to a successful outcome after allogeneic hematopoietic stem cell transplantation (HSCT). Although antibody‐based targeting of the CD40/CD40 ligand costimulatory pathway can prevent aGvHD, side effects hampered their clinical application, prompting a need for other ways to interfere with this important dendritic T‐cell costimulatory pathway. Here, we used small interfering RNA (siRNA) complexed with β‐glucan allowing the binding and uptake of the siRNA/β‐glucan complex (siCD40/schizophyllan [SPG]; chemical modifications called NJA‐312, NJA‐302, and NJA‐515) into Dectin1+ cells, which recognize this pathogen‐associated molecular pattern receptor. aGvHD was induced by the transplantation of splenocytes and bone marrow cells from C57BL/6J into CBF1 mice. Splenic dendritic cells retained Dectin1 expression after HSCT but showed lower expression after irradiation. The administration of siCD40/SPG, NJA‐312, and NJA‐302 ameliorated aGvHD‐mediated lethality and tissue damage of spleen and liver, but not skin. Multiple NJA‐312high injections prevented aGvHD but resulted in early weight loss in allogeneic HSCT mice. In addition, NJA‐312 treatment caused delayed initial donor T and B‐cell recovery but resulted in stable chimerism in surviving mice. Mechanistically, NJA‐312 reduced organ damage by suppressing CCR2+, F4/80+, and IL17A‐expressing cell accumulation in spleen, liver, and thymus but not the skin of mice with aGvHD. Our work demonstrates that siRNA targeting of CD40 delivered via the PAMP‐recognizing lectin Dectin1 changes the immunological niche, suppresses organ‐specific murine aGvHD, and induces immune tolerance after organ transplantation. Our work charts future directions for therapeutic interventions to modulate tissue‐specific immune reactions using Pathogen‐associated molecular pattern (PAMP) molecules like 1,3‐β‐glucan for cell delivery of siRNA.

Transplantation of photoreceptors into the degenerative retina: Current state and future perspectives

The mammalian retina displays no intrinsic regenerative capacities, therefore retinal degenerative diseases such as age-related macular degeneration (AMD) or retinitis pigmentosa (RP) result in a permanent loss of the light-sensing photoreceptor cells. The degeneration of photoreceptors leads to vision impairment and, in later stages, complete blindness. Several therapeutic strategies have been developed to slow down or prevent further retinal degeneration, however a definitive cure i.e. replacement of the lost photoreceptors, has not yet been established. Cell-based treatment approaches, by means of photoreceptor transplantation, have been studied in pre-clinical animal models over the last three decades. The introduction of pluripotent stem cell-derived retinal organoids represents, in principle, an unlimited source for the generation of transplantable human photoreceptors. However, safety, immunological and reproducibility-related issues regarding the use of such cells still need to be solved. Moreover, the recent finding of cytoplasmic material transfer between donor and host photoreceptors demands reinterpretation of several former transplantation studies. At the same time, material transfer between healthy donor and dysfunctional patient photoreceptors also offers a potential alternative strategy for therapeutic intervention. In this review we discuss the history and current state of photoreceptor transplantation, the techniques used to assess rescue of visual function, the prerequisites for effective transplantation as well as the main roadblocks, including safety and immune response to the graft, that need to be overcome for successful clinical translation of photoreceptor transplantation approaches.

Short-term immunosuppression promotes engraftment of embryonic and induced pluripotent stem cells

Embryonic stem cells (ESCs) are an attractive source for tissue regeneration and repair therapies because they can be differentiated into virtually any cell type in the adult body. However, for this approach to succeed, the transplanted ESCs must survive long enough to generate a therapeutic benefit. A major obstacle facing the engraftment of ESCs is transplant rejection by the immune system. Here we show that blocking leukocyte costimulatory molecules permits ESC engraftment. We demonstrate the success of this immunosuppressive therapy for mouse ESCs, human ESCs, mouse induced pluripotent stem cells (iPSCs), human induced pluripotent stem cells, and more differentiated ESC/(iPSCs) derivatives. Additionally, we provide evidence describing the mechanism by which inhibition of costimulatory molecules suppresses T cell activation. This report describes a short-term immunosuppressive approach capable of inducing engraftment of transplanted ESCs and iPSCs, providing a significant improvement in our mechanistic understanding of the critical role costimulatory molecules play in leukocyte activation.

Differential outcomes in prediabetic vs. overtly diabetic NOD mice nonmyeloablatively conditioned with costimulatory blockade

OBJECTIVE

Autoimmune diabetes can be reversed with mixed chimerism. However, the myelotoxic agents currently required to establish chimerism have prevented the translation of this approach to the clinic. Here, we investigated whether multimodal costimulatory blockade would enhance chimerism and promote islet allograft tolerance in spontaneously diabetic nonobese diabetic (NOD) mice.

MATERIALS AND METHODS

Prediabetic and spontaneously diabetic NOD mice were preconditioned with anti-CD8 monoclonal antibody before conditioning with 500 cGy total body irradiation and transplantation with 30 × 10(6) B10.BR bone marrow cells. Overtly diabetic animals were conditioned similarly and transplanted with 300 to 400 B10.BR islets. After irradiation, both groups of recipients were treated with anti-CD154, anti-OX40L, and anti-inducible T-cell costimulatory monoclonal antibodies. Urine, blood glucose levels, and chimerism were monitored.

RESULTS

Conditioning of NOD mice with costimulatory blockade significantly enhanced engraftment, with 61% of mice engrafting at 1 month. Eleven of 12 chimeric animals with engraftment at 1 month remained diabetes-free over a 12-month follow-up, whereas nonchimeric animals progressed to diabetes. In contrast, similar conditioning prolonged islet allograft survival in only 2 of 11 overtly diabetic NOD recipients. Chimerism levels in the 9 islet rejector animals were 0%.

CONCLUSIONS

Although nonmyeloablative conditioning reversed the autoimmune process in prediabetic NOD mice, the same regimen was significantly less effective in establishing chimerism and reversing autoimmune diabetes in spontaneously diabetic NOD mice.

Contribution of regulatory T cells and effector T cell deletion in tolerance induction by costimulation blockade

Blocking of costimulatory signals for T cell activation leads to tolerance in several transplantation models, but the underlying mechanisms are incompletely understood. We analyzed the involvement of regulatory T cells (Treg) and deletion of alloreactive cells in the induction and maintenance of tolerance after costimulation blockade in a mouse model of graft-vs-host reaction. Injection of splenocytes from the C57BL/6 parent strain into a sublethally irradiated F(1) offspring (C57BL/6 x C3H) induced a GVHR characterized by severe pancytopenia. Treatment with anti-CD40L mAb and CTLA4-Ig every 3 days during 3 wk after splenocyte injection prevented disease development and induced a long-lasting state of stable mixed chimerism (>120 days). In parallel, host-specific tolerance was achieved as demonstrated by lack of host-directed alloreactivity of donor-type T cells in vitro and in vivo. Chimerism and tolerance were also obtained after CD25(+) cell-depleted splenocyte transfer, showing that CD25(+) natural Treg are not essential for tolerance induction. We further show that costimulation blockade results in enhanced Treg cell activity at early time points (days 6-30) after splenocyte transfer. This was demonstrated by the presence of a high percentage of Foxp3(+) cells among donor CD4(+) cells in the spleen of treated animals, and our finding that isolated donor-type T cells at an early time point (day 30) after splenocyte transfer displayed suppressive capacity in vitro. At later time points (>30 days after splenocyte transfer), clonal deletion of host-reactive T cells was found to be a major mechanism responsible for tolerance.

Non-myeloablative mixed chimerism approaches and tolerance, a split decision

Stable mixed chimerism has been considered the most robust tolerance strategy. However, rejection of solid donor tissues by chimeras has been observed, a state termed split tolerance. Since new non-myeloablative mixed chimerism approaches are being actively pursued, we sought to determine whether they lead to full tolerance or split tolerance and to define the mechanisms involved. Fully mismatched mixed chimeras generated by induction with various lymphocyte-depleting antibodies along with either low-dose irradiation or busulfan and temporary sirolimus, maintained stable mixed chimerism but nevertheless rejected donor skin grafts. Generation of stable mixed chimerism using antibody targeting CD40L, but not depleting antibodies to CD4 and CD8, could prevent split tolerance when skin grafts were given together with donor bone marrow. Minor antigen matching abrogated the ability of effector T cells to reject donor skin grafts. A CFSE killing assay indicated that chimeras were both directly and indirectly tolerant of donor hematopoietic cell antigens, suggesting that minor mismatches triggered a tissue-specific response. Thus, split tolerance due to tissue-restricted polymorphic antigens prevents full tolerance in a number of non-myeloablative mixed chimerism protocols and a 'tolerizing' agent is required to overcome split tolerance. A model of the requirements for split tolerance is presented.

Resistance to the induction of mixed chimerism in spontaneously diabetic NOD mice depends on the CD40/CD154 pathway and donor MHC disparity

Blockade of CD40/CD154 pathway has proven effective in promoting the induction of allogeneic mixed chimerism. Using NOD mouse model of human type 1 diabetes, we investigated whether allogeneic mixed chimerism can be induced in prediabetic NOD mice and in spontaneously diabetic NOD mice under nonmyeloablative and irradiation-free conditioning therapy and anti-CD154 mAb as a short-term posttransplant treatment. We found that spontaneously diabetic NOD mice are more resistant to the induction of allogeneic mixed chimerism than prediabetic NOD mice under our nonmyeloablative and irradiation-free conditioning therapy. This alloresistance in spontaneously diabetic NOD mice is dependent on the CD40/CD154 pathway and donor MHC disparity.

CD154 blockade and donor-specific transfusions in DLA-identical marrow transplantation in dogs conditioned with 1-Gy total body irradiation

Stable mixed donor/host chimerism has been reliably established in dogs given a sublethal dose (2 Gy) of total body irradiation (TBI) before and immunosuppression with mycophenolate mofetil (MMF) or rapamycin combined with cyclosporine (CSP) after marrow transplantation from dog leukocyte antigen (DLA)-identical littermates (hematopoietic cell transplantation [HCT]). When TBI was reduced to 1 Gy, only transient engraftment was observed. Here we investigated whether stable engraftment after 1-Gy TBI could be accomplished by reducing host-versus-donor immune responsiveness through preceding CD154 blockade and infusion of donor peripheral blood mononuclear cells (PBMCs). We found that the anti-human CD154 antibody, 5c8, cross-reacted with canine lymphocytes and blocked alloimmune responses in vitro. Based on pharmacokinetic studies, 6 dogs received a single intravenous injection of 5 mg/kg anti-CD154 antibody (on day −5), followed 1 day later by donor PBMCs. On day 0, the dogs were given 1 Gy of TBI and underwent DLA-identical marrow grafts. Postgraft immunosuppression consisted of MMF and CSP. All 6 dogs demonstrated initial engraftment; 3 dogs sustained the engraftment for >26 weeks, whereas 3 dogs rejected their grafts, after 9, 22, and 24 weeks, and survived with autologous recovery. Graft survival was significantly improved over that in 11 historical controls conditioned with 1-Gy TBI and given either MMF or rapamycin with CSP after HCT, all of which rejected their grafts between 3 and 12 weeks (P = .03). Preceding donor PBMC infusion and CD154 blockade improved survival of DLA-identical marrow grafts after 1-Gy TBI.

Modulation of acute graft-versus-host disease and chimerism after adoptive transfer of in vitro-expanded invariant Valpha14 natural killer T cells

Mouse natural killer T cells with an invariant Valpha14-Jalpha18 TCR rearrangement (Valpha14i NKT cells) are able to regulate immune responses through rapid and large amounts of Th1 and Th2 cytokine production. It has been reported that in vivo administration of the Valpha14i NKT cell ligand, alpha-galactosylceramide (alpha-GalCer) significantly reduced morbidity and mortality of acute graft-versus-host disease (GVHD) in mice. In this study, we examined whether adoptive transfer of in vitro-expanded Valpha14i NKT cells using alpha-GalCer and IL-2 could modulate acute GVHD in the transplantation of spleen cells of C57BL/6 mice into (B6xDBA/2) F(1) mice. We found that the adoptive transfer of cultured spleen cells with a combination of alpha-GalCer and IL-2, which contained many Valpha14i NKT cells, modulated acute GVHD by exhibiting long-term mixed chimerism and reducing liver damage. Subsequently, the transfer of Valpha14i NKT cells purified from spleen cells cultured with alpha-GalCer and IL-2 also inhibited acute GVHD. This inhibition of acute GVHD by Valpha14i NKT cells was blocked by anti-IL-4 but not by anti-IFN-gamma monoclonal antibody. Therefore, the inhibition was dependent on IL-4 production by Valpha14i NKT cells. Our findings highlight the therapeutic potential of in vitro-expanded Valpha14i NKT cells for the prevention of acute GVHD after allogeneic hematopoietic stem cell transplantation.

An Irradiation-Free Nonmyeloablative Bone Marrow Transplantation Model: Importance of the Balance between Donor T-cell Number and the Intensity of Conditioning

BACKGROUND

Animal allogeneic bone marrow transplantation (BMT) models with nonmyeloablative conditioning regimens have so far required irradiation or antibodies in addition to immunosuppressive drugs for engraftment. Moreover, although it is known that the balance between donor T-cell number and the dose of immunosuppressive drugs would be critical for engraftment, it has not been experimentally clarified in a nonmyeloablative regimen.

METHODS

We used C57BL/6 mice as donors and DBA/2 mice as recipients with a nonmyeloablative regimen including fludarabine (Flu) and cyclophosphamide (CPA) without irradiation or antibodies. To determine the adequate doses, we injected recipients with various doses of Flu and CPA, and 2x10 bone marrow cells (BMC) and 5x10 splenocytes (SC). Furthermore, using T-cell-depleted BMC and enriched T cells, we investigated the balance between donor T-cell number and the dose of Flu.

RESULTS

Doses of Flu at 150 mg/kg/dayx6 and CPA at 150 mg/kg/dayx2 were most appropriate for engraftment with low mortality. All mice appropriately pretreated and transplanted with both BMC and SC exhibited complete donor chimeras. Donor cell engraftment was not enhanced by any increase of BMC transplanted, and dose escalation of donor T cells but not BMC led to the reduction of Flu dose required for engraftment of donor cells.

CONCLUSIONS

We have established a murine nonmyeloablative BMT model in a fully MHC-mismatched combination for donor cell engraftment with complete donor chimerism. Simultaneously, we have quantitatively demonstrated that the balance between donor T-cell number and the dose of immunosuppressive drugs is critical for stable engraftment.

The influence of the conditions of hematopoietic cell transplantation on infectious complications

PURPOSE OF REVIEW

The multitude of factors that influence the risk of infection after hematopoietic cell transplantation has been further complicated by the rapid evolution of this therapy in the past 5 years. The degree to which functional immune reconstitution has been achieved reflects the equilibrium reached by the immune systems of the recipient and donor in the context of host non-hematopoietic tissue. Thus immunomodulatory influences on the recipient and the transplanted graft, both before and after hematopoietic cell transplantation, have a profound influence on the incidence and severity of infection. This review of the recent literature contributes to our understanding of how the conditions of hematopoietic cell transplantation influence the timing and nature of infectious complications.

RECENT FINDINGS

The main themes of published primary research from 2004 to the present focus on non-myeloablative conditioning regimens and their effects on immune reconstitution after hematopoietic cell transplantation.

SUMMARY

A plethora of clinical trials are ongoing, focused on the outcome after conditioning regimens designed to result in less regimen-related toxicity while preserving or enhancing the graft-versus-tumor effect. Given the infancy of these new approaches, it is not possible to make definitive statements regarding the relative risk of serious infection with each therapy. It is clear that a reduction in regimen-related non-infectious complications or mortality does not necessarily ensure a reduction in clinically significant infections. Improvements in early diagnostic and therapeutic options for these infections now bring us to an era of understanding pathogens as probes of the functional reconstitution of immunity.