ATG--a polyclonal sledgehammer?

A partial conditioning approach to achieve mixed chimerism in the rat: depletion of host natural killer cells significantly reduces the amount of total body irradiation required for engraftment

BACKGROUND

Mixed allogeneic bone marrow chimerism induces tolerance to solid organ grafts. Although we previously reported that partially ablative conditioning with 700 cGy of total body irradiation (TBI) is sufficient to allow for bone marrow engraftment in mice, we determined that a minimum of 1000 cGy was required in the rat. Because T cells and NK cells are critical in bone marrow graft rejection, our purpose was to examine whether targeting of radioresistant NK cells and/or T cells in the recipient hematopoietic microenvironment would reduce the TBI dose required for engraftment of allogeneic rat bone marrow.

METHODS

Wistar Furth rats received either anti-NK3.2.3 monoclonal antibodies on days -3 and -2, anti-lymphocyte serum on day -5, a combination of both or no pretreatment. TBI was performed on day 0 and rats were reconstituted with 100x10(6) T cell-depleted bone marrow cells from ACI donors.

RESULTS

Engraftment of T cell-depleted rat bone marrow was readily achieved in animals conditioned with 1000 cGy TBI alone (12/12) and the level of donor chimerism averaged 89%. At 900 cGy TBI alone only one of eight recipients engrafted. In striking contrast, 11 of 12 animals pretreated with anti-NK monoclonal antibodies and irradiated with 900 cGy showed donor chimerism at a mean level of 41%. No further enhancement of bone marrow engraftment could be achieved when recipients were pretreated with antilymphocyte serum alone or antilymphocyte serum plus anti-NK monoclonal antibodies. Mixed allogeneic chimeras exhibited stable multilineage chimerism and donor-specific tolerance to subsequent cardiac allografts.

CONCLUSION

Specific targeting of radioresistant host NK cells allows for a significant reduction of the TBI dose required for allogeneic bone marrow engraftment.

Cytolytic induction therapy in heart and lung transplantation: the protagonist opinion

From the studies analysed as well as based on our own experience, induction therapy mainly with polyclonal cytolytic agents represents a helpful tool in the individualised immunosuppressive approach, whereas monoclonal induction therapies have to be discussed carefully. Although transplantation is also feasible without cytolytic agents, certain patients at risk will further encourage the need for this valuable therapy also in the future, where new immunosuppressants are available. However, it is anticipated that the application should be conducted on an individual patient basis to achieve optimal individual benefit.

In vivo depletion of host CD4+ and CD8+ cells permits engraftment of bone marrow stem cells and tolerance induction with minimal conditioning

BACKGROUND

Solid organ transplantation has become the preferred approach for the treatment of end-stage organ failure. However, the toxicity associated with the nonspecific immunosuppression essential to graft survival is substantial. Bone marrow transplantation (BMT) can overcome these limitations by the induction of donor-specific tolerance. The morbidity and mortality associated with fully ablative conditioning used to achieve engraftment has prevented the clinical application of BMT for induction of tolerance for solid organ transplantation. Although it was previously believed that fully ablative conditioning was essential to achieve engraftment, it has recently become apparent that partial conditioning may be sufficient to achieve chimerism and tolerance. The focus of this study was to characterize which cells in the host microenvironment must be eliminated for engraftment of MHC-disparate bone marrow to be achieved.

METHODS

C57BL/10SnJ mice were depleted of CD4+, CD8+, or both cell types with monoclonal antibodies before irradiation with 300 centigray (cGy) and transplantation of 15 x 10(6) allogeneic (B10.BR) bone marrow cells. Two days after transplantation the animals were treated with 200 mg/kg cyclophosphamide. Animals were typed for chimerism at 28 days and monthly thereafter.

RESULTS

The combination of CD4+ and CD8+ depletion resulted in multilineage engraftment in 76.5% of the animals at a level of 57.1 +/- 17.7%. The depletion of CD4+ cells alone was not sufficient to allow engraftment, whereas depletion of CD8+ cells alone was.

CONCLUSIONS

T cells in the recipient's marrow space play an important role in hindering allogeneic engraftment in the mouse. The T-cell subset responsible appears to be CD8+ cells rather than CD4+ cells.

Pharmacology of immunosuppressive medications used in renal diseases and transplantation

As understanding of the molecular basis for the immune response has expanded rapidly, so have the possibilities for designing therapeutic interventions that are more effective, more specific, and safer than current treatment options. The promise of therapeutic advances in the future is based on the rapidly expanding insights into the pathogenesis of abnormal immunologic reactions. Nowhere is the understanding of molecular mechanisms, pathophysiology, and targeted therapy more relevant than in the field of renal transplantation, which makes up much of the clinical database for the use of immunosuppressive therapy for renal disease. Despite the recent advances in basic immunology, clinical validation of new agents and approaches is lacking for most drugs at present. This review will focus in the pharmacology of agents used in the therapy of immunologic renal disease and in renal transplantation. It should be recognized that clinical pharmacology and experience with newer agents is limited, and potential utility is based largely on experimental data.