Continuing observations on the regulatory effects of donor-specific bone marrow cell infusions and chimerism in kidney transplant recipients

BACKGROUND

Continued follow-up of a series of donor bone marrow cell (DBMC)-infused first cadaver renal transplant recipients is described (n=58), now at a 36-month actuarial time point postoperatively. Serial polymerase chain reaction-flow cytometry (PCR-Flow) and cellular immune assays of iliac crest bone marrow aspirates and peripheral blood have begun to be compared with concomitantly transplanted recipients of living-related donor (LRD) kidneys and donor marrow infusions given the same immunosuppressive regimen (n=16). There have also been comparisons (36 months) with 188 controls transplanted concomitantly, i.e., recipients of first cadaver kidney transplants, who did not receive bone marrow.

METHODS

Each group was given equivalent immunosuppressive regimens of OKT3 anti-T cell induction and maintenance tacrolimus, mycophenolate mofetil, and methylprednisolone. Actuarial patient and graft survival have been 96% and 93%, respectively, in the controls and 91% and 91%, respectively, in the DBMC-infused recipients. Trough levels of tacrolimus were significantly lower in the DBMC-infused group.

RESULTS

In PCR-Flow measurements, in peripheral blood up to 6 months postoperatively, there were higher levels of chimerism, i.e., in the total number of donor cells, as well as the donor CD3+ and CD34+ subsets in the LRD recipients administered DBMC infusions, compared with cadaver DBMC recipients, supporting the notion of a positive effect of histocompatibility on chimerism levels. In PCR-Flow measurements of recipient iliac crest bone marrow aspirates as in previous studies on peripheral blood, early acute rejection episodes (<1 month) were found to be associated with a later (6-14 months) decrease in donor cell lineage chimerism. However, a trend toward recovery of chimeric levels occurred by 21-28 months in a second iliac crest marrow aspirate 1 year after the first aspirate in the DBMC-infused recipients who experienced such early rejection episodes. This was in contrast to the controls in whom there were sustained low levels of iliac crest bone marrow chimerism at both the earlier and later intervals (i.e., no chimeric recovery), with 17/183 surviving controls progressing into chronic rejection. This has not yet been seen in the DBMC-infused group (0/54). In in vitro observations on cellular immune reactivity at 1 year postoperatively, decreased peripheral blood lymphocyte proliferative reactions were seen in response to phytohemagglutinin and Staph-A mitogens, as well as to cytomegalovirus and Epstein-Barr viral protein antigens in the DBMC-infused group versus the controls. Chronic immunosuppression did not seem to effect a vigorous in vitro inhibitory (regulatory) activity of bone marrow taken from these transplant recipients 2 years postoperatively in mixed lymphocyte culture and cell-mediated lympholysis reactions, using allogeneic responding cells from "normal" laboratory volunteers. Autologous peripheral blood lymphoproliferative responses to phytohemagglutinin and Staph-A mitogens, as well as to cytomegalovirus and Epstein-Barr virus protein antigens, were also regulated by either organ donor (non-immunosuppressed) bone marrow cells or by transplant recipient (immunosuppressed) bone marrow cells. What appeared to be disparate between the DBMC-infused and control groups (both immunosuppressed) was the trend for the (autologous) bone marrow suppressive effect on antiviral lymphoproliferative responses, to be stronger in the DBMC-infused group, who also had significantly (>one order of magnitude) higher levels of chimerism (P=0.01).

CONCLUSIONS

It is concluded that the establishment of a chimeric state in DBMC-infused recipients, albeit of relatively low magnitude (approximately 1% at 2 years in recipient iliac crest bone marrow), has had a definite regulatory effect on immune responses. These results, therefore, add weight to the "causal" horn of the dilemma as to whether donor cell chimerism is a cause or an effect of

The role of liver transplantation in the subacute trauma patients

Two case reports are presented involving complex liver traumas requiring the need for liver transplantation. Both of these patients were designated unsalvageable until the transplant team was consulted. It is imperative that surgeons involved with complex hepatic trauma not give up hope and include these patients as potential liver recipients when irreversible liver failure occurs.

Small bowel transplantation in children

Small bowel transplantation has become a life-saving procedure for selected adults and children with intestinal failure who are intolerant to parental nutrition. There are few pediatric data available on the results of this procedure. In this article we review the background of intestinal transplantation, present the results from the University of Western Ontario in London, Ontario and the University of Miami in Miami, Florida, and discuss some future directions. The majority of successful transplants are fully functional, and these children are able to assume a normal diet.

Graft-versus-host disease after liver and small bowel transplantation in a child

An 8-month-old child with an immunodeficiency disorder characterized by abnormal lymphocyte function and by low IgG and IgA levels had combined liver and small bowel transplantation under tacrolimus and steroid immunosuppression for the treatment of short gut syndrome and hepatic cirrhosis. The patient developed an early postoperative episode of Pneumocystis carinii pneumonia, and a subsequent surgical complication, prompting discontinuance of tacrolimus. A skin rash eventually shown to be graft-versus-host disease (GVHD) developed in the flank on the 12th post-transplant day and gradually became generalized. Peritonitis, sepsis, multisystem organ failure including the liver allograft led to death on the 23rd post-operative day. The mechanisms leading to post-transplant GVHD under the specific circumstances in this case are discussed.

Unexpected augmentation of mycophenolic acid pharmacokinetics in renal transplant patients receiving tacrolimus and mycophenolate mofetil in combination therapy, and analogous in vitro findings

Mycophenolate mofetil (MMF) a potent immunosuppressive agent, has recently been approved for clinical use (CellCept) in renal transplant patients in combination with cyclosporine (CsA). With the expanded use of tacrolimus (Prograf) as well in renal transplant patients, there is a lack of pharmacokinetic studies clarifying drug interactions between the three agents. A pharmacokinetic study was performed on 18 stable renal transplant patients receiving MMF and tacrolimus together, and four control groups, one receiving tacrolimus alone, two receiving CsA, in combination with MMF (1.0 or 1.5 g bid), and one receiving CsA microemulsion (Neoral). Area-under-the-curve values were calculated for each drug to assess if there was a reciprocal effect on the respective bioavailability of each. In vitro, the immunosuppressive effect of trough level plasma from each patient group was studied using mixed lymphocyte culture (MLC), as well as MLC reactions spiked with various combinations of each drug. There was a minimal effect of MMF on tacrolimus pharmacokinetics. However, patients receiving tacrolimus and MMF displayed significantly higher levels (Cmin and area under the curve) of mycophenolic acid (MPA) than those receiving CsA (Sandimmune or Neoral) and the same dose of MMF (50.2 +/- 16.5 vs 32.1 +/- 16.7 micrograms h/ml AUC, p < 0.02). Equivalent MPA levels could be attained in patients receiving CsA if the MMF dose was increased by 50% (1.5 g bid). There were also significantly lower levels of the glucuronide metabolite of MPA (MPAG) (755 +/- 280 vs 1230 +/- 250 micrograms h/ml AUC, p = 0.02), suggesting a specific inhibition (either direct or indirect) of the conversion of MPA to MPAG in tacrolimus patients, as opposed to those receiving CsA. For each drug combination, there was a positive correlation between the plasma immunosuppressive effect seen in MLC assays and the MMF dose. In addition, trough plasma from patients receiving tacrolimus and MMF was significantly more MLC inhibitory than from those receiving CsA or CsA microemulsion and equivalent-dose MMF. Culture media containing MPA and tacrolimus equal to clinical therapeutic trough concentrations (10 ng/ml) were significantly more MLC inhibitory than CsA at equivalent clinical therapeutic trough concentrations (200 ng/ml) with equivalent MPA levels. These studies in renal transplant patients suggest that tacrolimus in combination with MMF may result in a greater degree of immunosuppression than may be anticipated.

Modulatory effects of human donor bone marrow cells on allogeneic cellular immune responses

BACKGROUND

In order to evaluate whether immunoregulatory mechanisms are brought about by human donor bone marrow cell infusions accompanying organ transplantation, we established in vitro culture systems analogous to the transplant model.

METHODS

Cell-mediated lympholysis (CML) and mixed lymphocyte culture (MLC) responses of peripheral blood lymphocytes or spleen cells stimulated with irradiated cadaver donor spleen cells in the presence of specific donor vertebral-body bone marrow cell (DBMC) modulators were tested.

RESULTS

When compared with spleen cells as modulator controls, DBMC inhibited both the proliferative and cytotoxic responses in a dose-dependent manner. Use of unirradiated and T cell-depleted DBMC was required for detection of the inhibitory activity. Furthermore, DBMC had to be added within the first 2 days after the initiation of the cultures for the down-regulation of CML (MLC) to occur. The down-regulation of MLC responses could not be shown to be antigen (donor) specific. Physical separation of DBMC from the responder-stimulator cells using the transwell system abrogated modulation of the CML (and MLC) reactions, suggesting the requirement of cell-cell contact for modulatory effect. The inhibitory activity by DBMC could not be overcome by addition of up to 200 U/ml of exogenous recombinant interleukin 2 to the cultures. However, it could be abrogated by restimulation with donor spleen cells, indicating that donor reactive cells were not deleted by DBMC in short-term cultures.

CONCLUSIONS

These results showed a regulatory role for DBMC in cellular immune responses against donor cell alloantigens, supporting the rationale for DBMC for facilitating clinical allograft acceptance.

The effects of chimeric cells following donor bone marrow infusions as detected by PCR-flow assays in kidney transplant recipients

40 recipients of first cadaver kidney transplants were given perioperative donor vertebral bone marrow infusions (DBMC), compared with 100 controls who did not receive donor bone marrow. The immunosuppressive regimen included OKT3, Tacrolimus, and steroid maintenance therapy, and, in some patients, newly introduced mycophenolate mofetil. This report describes the 24-mo actuarial follow-up and several immunological monitoring studies including sequential measurements of donor bone marrow lineage subset chimerism by the recently reported PCR-flow assay. This is a sensitive in situ PCR detection system for donor versus recipient histocompatibility genes as well as cell surface CD epitope markers using flow cytometry. The results indicate (a) the stabilization of the donor CD3+ and CD34+ cells in recipient peripheral blood at levels below 1% between 6 mo and 1 yr postoperatively, with a 10-fold higher level of donor cell chimerism of these lineages in recipient iliac crest marrow; (b) significantly lower levels of chimerism in peripheral blood up to 6 mo postoperatively in patients who had early acute (reversible) rejection episodes compared with those who did not; (c) a higher degree of chimerism seen in patients who were class II MHC HLA DR identical with their donors; (d) the identification of a high proportion of the donor bone marrow derived CD3 dimly staining subset of T cells (to which regulatory functions have been ascribed) in recipient peripheral blood and especially in recipient bone marrow; and (e) an unexpectedly increased susceptibility to clinically significant infections (primarily viral), and even death in the DBMC-infused group, compared with controls, but no graft losses because of rejection in the DBMC-infused group. Mixed lymphocyte culture assays showed a trend toward a greater number of nonspecifically low reactors in the DBMC group, as well as a greater number of nonspecifically high reactors in the controls (P = 0.058). The autologous mixed lymphocyte reaction also indicated a trend towards nonspecific immune activation in the DBMC group. Finally, anti-cytomegaloviral IgG antibody reactivity was significantly inhibited in the DBMC group 4-6 mo postoperatively (P = < 0.05). In the controls, there were no donor cell lineages detected by PCR-flow in the peripheral blood. These rather unexpected findings, indicating a more depressed cellular and humoral immune capacity in the DBMC cadaver kidney transplant recipients in this relatively early follow-up period, are discussed relevant to chimerism, MHC restriction, and suppressor activity brought about by specialized DBMC subsets, which still need to be defined.