Induction of transgene-specific cytotoxic T lymphocyte responses after transplantation of gene-modified CD34+ cells despite nonablative immunosuppressive conditioning.

In previous studies we showed that low-dose irradiation and immunosuppression with cyclosporine and mycophenolate mofetil prolonged in vivo persistence of gene-modified T cells but was unable to induce tolerance. We hypothesized that the lack of sustained antigen presentation because of the limited life span of the infused T cells might be responsible for the lack of tolerance induction. Thus, we examined whether tolerance could be induced by infusion of long-lived stem cells. Two baboons were transplanted with YFP/neo-transduced CD34+ cells. The transgene-marked cells disappeared completely within 5 weeks and CD8+ transgene-specific cytotoxic T lymphocytes were detected in both animals. Thus, this nonablative conditioning regimen did not provide sufficient immunosuppression for the induction of tolerance after infusion of gene-modified CD34+ cells.

Comparison of mesenchymal stem cells from different tissues to suppress T-cell activation.

Graft-versus-host disease (GvHD) and graft rejection have remained significant complications of allogeneic stem cell transplantation. Mesenchymal stem cells (MSCs) from the bone marrow have been shown to suppress T-cell activation in vitro and in vivo, and may be used to reduce GvHD in the recipient or to facilitate engraftment across MHC barriers. MSCs can be derived from a variety of tissues. Thus, we asked whether MSCs from different tissues might have differential effects on T-cell responses. We were particularly interested in MSCs derived from adipose tissue because of its abundance and accessibility. We investigated and compared the immunosuppressive potential of murine MSCs derived from muscle tissue, adipose tissue, omentum, and bone. Cells from the different tissues were enriched for MSCs and cultured for 2-3 weeks to deplete hematopoietic cells. Mixed lymphocyte reactions (MLRs) including MSCs were performed using concanavalin A or allogeneic T cells as inducers of T-cell activation. MSCs from all tissues differentiated into multiple lineages. Mitogen-induced T-cell activation, as well as allogeneic T-cell responses, was reduced in MLRs mediated by the addition of MSCs. Reduction of T-cell activation was most pronounced for muscle tissue in the mitogen-induced MLR and fat tissue during the allogeneic MLR. These data demonstrate that MSCs from multiple tissues efficiently reduce T-cell activation. The results suggest that MSCs from adipose tissue can serve as an alternative source for MSCs to bone or bone marrow for the modulation of GvHD after allogeneic stem cell transplantation or to enhance engraftment across MHC barriers.

Systemic morphine administration suppresses genes involved in antigen presentation.

Administration of opioids in both humans and animal models results in significant alterations in immune system responsiveness. Although the majority of studies have focused on phenotypic changes in immune cells after short- and long-term morphine administration, few studies have determined whether alterations in gene expression profiles accompany these effects. To address this question, rats were treated with either morphine (20 mg/kg) or saline, and changes in gene expression and function in blood leukocytes were examined. Within 2 h, morphine administration resulted in a decrease in blood leukocyte expression of the major histocompatibility complex class II (MHC II RT1.B beta) (-3.27-fold) and related molecules, including the MHC II invariant chain (-2.73-fold). Furthermore, these changes in gene expression were accompanied by a significant decrease in surface MHC II RT1.B beta protein expression, specifically on B lymphocytes. Morphine administration was also found to inhibit IL-4 induced up-regulation of MHC II RT1.B beta cell surface expression on B lymphocytes. This is the first demonstration that receptors involved in antigen presentation are modified after systemic morphine administration. We propose that the inability of B lymphocytes to up-regulate key immune proteins, such as the MHC II molecule, after exposure to antigen-induced cytokine production may account for the increase in the susceptibility to bacterial and viral infections such as HIV in both drug abusers and patients receiving morphine.