Donor specific bone marrow cells suppress lymphocyte reactivity to donor antigens and differentially modulate TH1 and TH2 cytokine gene expression in the responder cell population

Differentiation of regulatory myeloid and T-cells from adult human hematopoietic stem cells after allogeneic stimulation

Introduction

Donor hematopoietic stem cell (DHSC) infusions are increasingly being studied in transplant patients for tolerance induction.

Methods

To analyze the fate of infused DHSCs in patients, we developed an in vitro culture system utilizing CD34+DHSCs stimulated with irradiated allogeneic cells in cytokine supplemented medium long-term.

Results

Flow cytometric analyses revealed loss of the CD34 marker and an increase in CD33+ myeloid and CD3+ T-cell proportion by 10.4% and 72.7%, respectively, after 21 days in culture. T-cells primarily expressed TcR-αβ and were of both CD4+ and CD8+ subsets. Approximately 80% of CD3+ T cells lacked expression of the co-stimulatory receptor CD28. The CD4+ compartment was predominated by CD4+CD25+CD127-FOXP3+ Tregs (>50% CD4+CD127- compartment) with <1% of all leukocytes exhibiting a CD4+CD127+ phenotype. Molecular analyses for T-cell receptor excision circles showed recent and increased numbers of TcR rearrangements in generated T cells over time suggesting de novo differentiation from DHSCs. CD33+ myeloid cells mostly expressed HLA-DR, but lacked expression of co-stimulatory receptors CD80 and CD83. When studied as modulators in primary mixed lymphocyte reactions where the cells used to stimulate the DHSC were used as responders, the DHSC-lines and their purified CD8+, CD4+, CD33+ and linage negative subsets inhibited the responses in a dose-dependent and non-specific fashion. The CD8+ cell-mediated inhibition was due to direct lysis of responder cells.

Discussion

Extrapolation of these results into the clinical situation would suggest that DHSC infusions into transplant recipients may generate multiple subsets of donor "chimeric" cells and promote recipient Treg development that could regulate the anti-donor immune response in the periphery. These studies have also indicated that T cell maturation can occur in vitro in response to allogeneic stimulation without the pre-requisite of a thymic-like environment or NOTCH signaling stimulatory cell line.

Microchimerism in promoting graft acceptance in clinical transplantation

PURPOSE OF REVIEW

Infusions of bone marrow-derived cells together with 'space making' continue to be tested in clinical organ transplant tolerance protocols. These trials are based on the hypothesis that this might produce initial multilineage chimerism. There is some evidence that this in turn induces regulatory cells that control alloimmunity. Although a wealth of knowledge is available from animal models, this review deals with what we know or can speculate about donor bone marrow cells and chimerism in human organ transplantation.

RECENT FINDINGS

Calcineurin inhibitors are employed in most of these protocols to blunt the initial immune response. One protocol also has a stepwise regulatory cell generating treatment with sirolimus before total withdrawal. A number of donor chimeric lineages including stem cells, dendritic cells, myeloid precursors, and various lymphoid subpopulations have been described. Currently, it is recognized that the nature of cells that make up the chimerism could influence graft rejection versus acceptance. Tolerogenic donor chimeric cells may also generate regulatory subsets, thus controlling alloimmunity on two fronts.

SUMMARY

It might be speculated that prolonged and sustained regulation or possible anergy induced by chimerism may eventually lead to clonal deletion, thereby bringing about classical immunologic tolerance.

Favoring the risk-benefit balance for upper extremity transplantation--the Pittsburgh Protocol

Upper extremity transplantation is an innovative reconstructive strategy with potential of immediate clinical application and the most near-term pay-off for select amputees, allowing reintegration into employment and society. Routine applicability and widespread impact of such strategies for the upper extremity amputees with devastating limb loss could be enabled by implementation of cellular therapies that integrate and unify the concepts of transplant tolerance induction with those of reconstructive transplantation. Such therapies offer the promise of minimizing the risks, maximizing the benefits and optimizing outcomes of these innovative procedures.

Donor bone marrow cells play a role in the prevention of accelerated graft rejection induced by semi-allogeneic spleen cells in transplantation

Spleen or spleen plus bone marrow cells from (BALB/cxC57Bl/6)F1 donors were transferred into BALB/c recipients 21 days before skin or cardiac transplantation. Prolonged graft survival was observed on recipients treated with the mixture of donor-derived cells as compared to those treated with spleen cells alone. We evaluated the expression of CD45RB and CD44 by splenic CD4+ and CD8+ T cells 7 and 21 days after donor cell transfer. The populations of CD8+CD45RBlow and CD8+CD44high cells were significantly decreased in mice pre-treated with donor spleen and bone marrow cells as compared to animals treated with spleen cells only, although these cells expanded in both groups when compared to an earlier time-point. No differences were observed regarding CD4+ T cell population when recipients of donor-derived cells were compared. An enhanced production of IL-10 was observed seven days after transplantation in the supernatants of spleen cell cultures of mice treated with spleen and bone marrow cells. Taken together these data suggest that donor-derived bone marrow cells modulate the sensitization of the recipient by semi-allogeneic spleen cells in part by delaying the generation of activated/memory CD8+ T cells leading to enhanced graft survival.

Inhibition of NF-kappa B during human dendritic cell differentiation generates anergy and regulatory T-cell activity for one but not two human leukocyte antigen DR mismatches

We examined the in vitro inhibition of human monocyte-derived dendritic cells (DC) maturation via NF-kappaB blockade on T-cell allostimulation, cytokine production, and regulatory T-cell generation. DC were generated from CD14+ monocytes isolated from peripheral blood using GM-CSF and IL-4 for differentiation and TNF-alpha, IL-1beta, and PGE2 as maturational stimuli with or without the NF-kappaB inhibitors, BAY 11-7082 (BAY-DC) or Aspirin (ASA-DC). Stimulator and responder cells were one versus two HLA-DR mismatched in direct versus indirect presentation assays. Both BAY-DC and ASA-DC expressed high levels of HLA-DR and CD86 but always expressed less CD40 compared with controls. Some experiments showed slightly lower levels of CD80. Both BAY- and ASA-allogeneic DC and autologous alloantigen pulsed DC were weaker stimulators of T cells (by MLR) compared with controls, and there was reduced IL-2 and IFN-gamma production by T cells stimulated with BAY-DC or ASA-DC (by ELISPOT) (more marked results were always observed with ASA-treated DC). In addition, NF-kappaB blockade of DC maturation caused the generation of T cells with regulatory function (T regs) but only when T cells were stimulated by either allogeneic (direct presentation) or alloantigen pulsed autologous DC (indirect presentation) with one HLA-DR mismatch and not with two HLA-DR mismatches (either direct or indirect presentation). However, the T regs generated from these ASA-DC showed similar FoxP3 mRNA expression to those from nontreated DC. Extension of this study to human organ transplantation suggests potential therapies using one DR-matched NF-kappaB blocked DC to help generate clinical tolerance.

Immune responses and their regulation by donor bone marrow cells in clinical organ transplantation

Infusions of donor bone marrow derived cells (DBMC) continue to be tested in clinical protocols intended to induce specific immunologic tolerance of solid organ transplants based on the observations that donor-specific tolerance is induced this way in animal models. We studied the immunological effects of human DBMC infusions in renal transplantation using modifications in lymphoproliferation (MLR) and cytotoxicity (CML) assays. The salient observations and tentative conclusions are summarized in this review. Among many types of organs transplanted using DBMC at this center, it was found that the cadaver renal recipients (CAD) had significantly decreased chronic rejection and higher graft survival when compared to equivalent non-infused controls. DBMC infusion was also associated with a marginal and non-specific immune depression. It was also observed that the number of chimeric donor cells gradually increased in the iliac crest bone marrow compartment with a concomitant decrease in the peripheral blood and that the increase was more rapid in living-related donor (LRD)-kidney/DBMC recipients in spite of a lower number of DBMC infused (<25%) than in the CAD-kidney/DBMC group. In the LRD recipients with residual anti-donor responses, purified chimeric cells of either donor or recipient inhibited recipient immune responses to the donor significantly more strongly than the freshly obtained bone marrow from the specific donor or volunteer suggesting an active regulatory role for chimeric cells. A number of (non-chimeric) subpopulations of bone marrow cells including CD34(+) stem cells and the CD34(-) early progeny like CD38(+), CD2(+), CD5(+) and CD1(+) lymphoid cells as well as CD33(+) (but CD15(-)) myeloid cells down-regulated the MLR and CML responses of allogeneic PBMC stimulated with (autologous) donor spleen cells. These regulatory effects appeared to be refractory to the action of commonly used immunosuppressive drugs and occurred during the early phase of the immune response through cell-cell interactions. Most of these DBMC sub-populations had stimulatory capabilities, albeit markedly lower than donor spleen cells, but only through the indirect antigen presentation pathway. When co-cultured with allogeneic stimulators, purified CD34(+) cells were found to give rise both to CD3(-) TCRalphabeta(+), as well as CD3(+) TCRalphabeta(+) cells and, thereby, responded in MLR to allogeneic stimulation (but did not generate cytotoxic effector cells). Also, a number of DBMC subpopulations inhibited the CML and to a lesser extent the MLR, of autologous post-thymic responding T cells stimulated with allogeneic irradiated cells, mediated through soluble factors. Finally, non-chimeric DBMC also inhibited the proliferative and cytotoxic responses of autologous T cells to EBV antigens, inducing T suppressor cells, which in turn could inhibit autologous anti-EBV CTL generation and B cell anti-CMV antibody production. These studies all suggested a strong inhibitory property of a number of DBMC sub-populations in vitro and in vivo with the notion that they promote unresponsiveness.

Involvement of multiple subpopulations of human bone marrow cells in the regulation of allogeneic cellular immune responses

BACKGROUND

The identity of the cells in the human bone marrow that function as effective regulators of in vitro and possibly in vivo cellular immune responses is not well established.

METHODS

Cell subpopulations were isolated from cadaver donor vertebral-body bone marrow cells (DBMC) by using immuno-magnetic microbeads and were tested as inhibitors (modulators) in cell-mediated lympholysis (CML) and mixed lymphocyte reaction (MLR) responses of normal peripheral blood lymphocytes stimulated with irradiated cadaver donor spleen cells.

RESULTS

Compared with spleen cells as controls, un-irradiated T-cell depleted DBMC inhibited both the MLR and CML responses of allogeneic responder cells in a dose dependent manner (as in our previous reports). The inhibition was also mediated by a number of purified subpopulations including pluripotent CD34+ stem cells, and their CD34 negative early progeny of both lymphoid and myeloid lineages. These included DBMC enriched for non-T-cell lymphoid precursors (NT-LP/DBMC; i.e., DBMC depleted of CD3, CD15, and glycophorin-A positive cells) and DBMC positively selected for CD38+, CD2+, CD5+, and CD1+ lymphoid cells (all were depleted of CD3+ cells) as well as CD33+ (but CD15 negative) myeloid precursors. However, positively selected CD19+ B-cells and CD15+ myeloid cells did not inhibit the MLR and CML responses. The NT-LP/DBMC that had been repeatedly stimulated with irradiated allogeneic peripheral blood lymphocytes caused the strongest inhibition of the MLR and CML responses of the same allogeneic cells with 200 times fewer modulator cells needed than uncultured DBMC (P<0.001). Flow cytometric analysis revealed that majority of cells in these cell lines had become CD3+ TcR-alphabeta+ CD4+ and CD28+ cells.

CONCLUSION

A variety of less differentiated cells of various lineages residing in the human bone marrow are immunoregulatory in vitro. Among them, there is at least one subset that can undergo differentiation in vitro into regulatory T cells that can be maintained in long-term cultures.

In vitro immunogenicity of cadaver donor bone marrow cells used for the induction of allograft acceptance in clinical transplantation

BACKGROUND

The cascade of immunological effects brought about by donor bone marrow cell (DBMC) infusions to induce allograft acceptance in clinical transplantation is not fully understood. Aside from acting as immune responding and regulatory cells, the infused DBMC also may sensitize the recipient to the donor antigens.

METHODS

To analyze this stimulatory activity of DBMC, in vitro mixed lymphocyte cultures (MLC) and cell-mediated lymphocytotoxicity (CML) culture systems analogous to the transplant model with DBMC infusion were used.

RESULTS

When responding peripheral blood lymphocytes (PBL) from normal volunteers were placed in culture with suspensions of Ficoll-purified, T cell-depleted, un-irradiated allogeneic DBMC (NT-DBMC), a reaction was seen in both MLC and CML. However, when compared to allogeneic spleen cells as stimulating cells, the responses to NT-DBMC were of markedly lower magnitude and were not seen when the NT-DBMC was irradiated (3000 R). When responding PBL were stimulated with either NT-DBMC that had been previously cultured with irradiated cells from the responders for 1 week (activated NT-DBMC), NT-DBMC further depleted of CD15+ and glycophorin A-positive cells (NT-LP/DBMC), or purified CD34+ and CD2+ DBMC subsets, stronger lymphoproliferative and cytotoxic responses were observed. Moreover, these responses were not abrogated by irradiation of the stimulating DBMC subpopulations. Depletion of antigen-presenting cells by positive selection of CD3+ cells from the responding PBL abrogated MLC and CML reactivity, even when purified NT-LP/DBMC, the most stimulatory cells, were used. This latter observation was in contrast to the responses seen with cultures containing allogeneic stimulating spleen cell populations. This indicated the requirement for indirect alloantigen presentation, i.e., the failure of these DBMC to stimulate by direct alloantigen presentation. NT-DBMC was able to stimulate responding PBL in secondary MLC and CML responses with an equivalent magnitude, irrespective of whether the stimulators were spleen cells or NT-DBMC. Finally, the MLC and CML responses were inhibited by tacrolimus (FK506), mycophenolic acid (MPA), and cyclosporine (CsA) in a dose dependent manner, in contrast to previously observed refractoriness of DBMC preparations to these agents if DBMC was tested as responder cells or in modulatory assays.

CONCLUSIONS

These results indicate that DBMC are able to function as effective in vitro stimulators, but only by indirect antigen presentation, and that the immune responses mediated by them can be down-regulated by their own inherent suppressive nature, an effect that can be enhanced by the presence of immunosuppressive drugs.

Inhibition of cytotoxic alloreactivity by human allogeneic mononuclear cells: evidence for veto function of CD2+ cells

In animal models of organ transplantation, infusion of donor-derived leucocytes or bone marrow cells can support tolerance induction. To date, little is known about the suppressive effects of human allogeneic mononuclear cells on alloreactivity in the human system. To study this, mixed leucocyte cultures (MLC) were incubated in the presence and absence of viable allogeneic mononuclear cells (MNC) (modulator cells) of stimulator/donor origin, and the cytotoxic and proliferative potential of the resulting effector cells was determined. The experiments showed that: viable allogeneic MNC from bone marrow and from lymph nodes and peripheral blood (PBMC) were able to suppress allospecific cytotoxicity by an average of 60%; that allospecific as well as non-specific inhibitory effects could be observed with unseparated PBMC; that CD2+ PMNC showed predominantly allospecific inhibition of cytotoxicity with little effect on proliferation whereas CD2- PBMC showed non-specific inhibitory effects (both for cytotoxicity and proliferation), which could be eliminated by indomethacin; that addition of interleukin-2 (IL-2) up to 50 U/ml to the MLC could not reverse the inhibitory effect; and that selective removal of CD8+ cells from the CD2+ modulator population diminished the specific inhibitory effect only partially. These findings demonstrate that viable human MNC from different compartments can have a marked suppressive effect on alloreactivity in vitro. For peripheral blood mononuclear cells (PBMC) the data suggest that various mechanisms can contribute to allosuppression, including specific suppressive veto effects by CD2+ cells. Such inhibitory effects might be applicable in vivo for down-regulating allospecific cytotoxicity and to facilitate the acceptance of allografts.