Suppressor cells in rhesus monkeys treated with antithymocyte globulin

Monocyte-Derived Suppressor Cells in Transplantation

Myeloid-derived suppressor cells (MDSC) are cells of myeloid origin with enhanced suppressive function. They are negative regulators of the immune responses and comprise a heterogeneous mixture of immunosuppressive cells of monocytic (M-MDSC) and granulocytic (G-MDSC) origin. A more recent nomenclature proposes the term "suppressive monocyte derived cells" (suppressive MCs) to define CSF1/CSF2-dependent mouse suppressor cells that develop from common monocyte progenitors (cMoPs) after birth. Here, we review the literature about monocytic-derived cells with demonstrated suppressor function in vitro and in vivo within the context of solid organ transplantation.

RABBIT ANTITHYMOCYTE GLOBULIN AS INDUCTION IMMUNOTHERAPY FOR PEDIATRIC DECEASED DONOR KIDNEY TRANSPLANTATION

PURPOSE

There is scant literature describing the long-term outcome of the use of antithymocyte globulin induction immunotherapy in pediatric deceased donor kidney transplants. We retrospectively studied the long-term results and safety of antithymocyte globulin as induction immunotherapy in all children undergoing transplantation at our institution since 1991.

MATERIALS AND METHODS

A total of 120 kidney transplants were performed in 95 patients 18 years or younger between January 1986 and December 1998. Patients were divided into 2 groups. The control group (63 patients) received cyclosporine, azathioprine and prednisolone, while the treatment group (59 patients) received rabbit antithymocyte globulin (RATG) induction immunotherapy for 6 to 10 days, combined with cyclosporine, azathioprine and prednisolone.

RESULTS

Actuarial patient survival rates at 1, 3, 5 and 10 years were 96%, 95%, 95% and 90%, respectively. Actuarial graft survival rates at 1, 3, 5 and 10 years were 76%, 69%, 64% and 49%, respectively. The 1, 3, 5 and 10-year graft survival rates in the control group were 62%, 57%, 51% and 36%, respectively, compared to 90%, 82%, 79% and 69%, respectively, in the RATG group (p = 0.001). There was a significant difference in the incidence of graft loss secondary to acute cellular rejection between the control and RATG groups (19.7% vs 3.3%, p = 0.008). There was no difference in infectious complications between the control and RATG groups (13% vs 20%, p = 0.33), and there was no case of post-transplant lymphoproliferative disorder encountered in either group.

CONCLUSIONS

The use of rabbit antithymocyte globulin in pediatric deceased donor kidney transplant recipients resulted in significant improvement in graft survival and was relatively safe.

Strategies for preclinical evaluation of dendritic cell subsets for promotion of transplant tolerance in the nonhuman primate

A role for dendritic cells (DC) as critical regulators of immune reactivity has become increasingly recognized. There is evidence in rodent models that donor-derived DC, particularly in the immature state, can prolong organ allograft survival and even induce donor-specific tolerance. To allow the potential tolerogenic properties of these cells to be evaluated more fully with a view to clinical testing, it is necessary to identify DC subsets in nonhuman primates. We have identified the putative rhesus monkey equivalents of circulating human DC subset precursors as lineage(-), HLA-DR(+), CD123(lo),CD11c(hi)(pDC1) and lineage(-), HLA-DR(+), CD123(hi),CD11c(lo)(pDC2). Testing of these DC populations both in vitro and in vivo, as well as in transplant models in combination with conventional or experimental immunosuppressive reagents, will aid the development of novel strategies for the promotion of allo-antigen specific tolerance in transplantation.

Successful reversal of streptozotocin-induced diabetes with stable allogeneic islet function in a preclinical model of type 1 diabetes

The recent focus on islet transplantation as primary therapy for type 1 diabetes has heightened interest in the reversal of type 1 diabetes in preclinical models using minimal immunosuppression. Here, we demonstrated in a preclinical rhesus model a consistent reversal of all measured glycemic patterns of streptozotocin-induced type 1 diabetes. The model used single-donor islet transplantation with induction of operational tolerance. The term "operational tolerance" is used to indicate durable survival of single-donor major histocompatibility complex (MHC)-mismatched islet allografts without maintenance immunosuppressive therapy and without rejection or loss of functional islet mass or insulin secretory reserve. In this operational tolerance model, all immunosuppression was discontinued after day 14 posttransplant, and recipients recovered with excellent health. The operational tolerance induction protocol combined peritransplant anti-CD3 immunotoxin to deplete T-cells and 15-deoxyspergualin to arrest proinflammatory cytokine production and maturation of dendritic cells. T-cell deficiency was specific but temporary, in that T-cell-dependent responses in long-term survivors recovered to normal, and there was no evidence of increased susceptibility to infection. Anti-donor mixed lymphocyte reaction responses were positive in the long-term survivors, but all showed clear evidence of systemic T-helper 2 deviation, suggesting that an immunoregulatory rather than a deletional process underlies this operational tolerance model. This study provides the first evidence that operational tolerance can protect MHC nonhuman primate islets from rejection as well as loss of functional islet mass. Such an approach has potential to optimize individual recipient recovery from diabetes as well as permitting more widespread islet transplantation with the limited supply of donor islets.

Production of stable rabbit-mouse heterohybridomas: characterization of a rabbit monoclonal antibody recognizing a 180 kDa human lymphocyte membrane antigen

Polyclonal rabbit antihuman thymocyte globulin (RATG) remains a key component of immunosuppressive strategies in transplantation. The human thymus immunization regimen that produces highly immunosuppressive RATG induces unique antibody specificities in the rabbit. Rabbit monoclonal antibodies (RAb MAbs) to human T cell antigens would be of value in the effort to investigate and reproduce the multiple specificities of RATG. We have fused mouse Sp2/0 cells with splenocytes from rabbits immunized with human thymus and have identified 52 rabbit-mouse heterohybridomas which secrete RAb MAbs directed against human lymphocyte surface antigens. The technical aspects of hybridoma isolation, stabilization and characterization are presented. Analysis by flow cytometry, preabsorption and immunoprecipitation suggests that RAb MAb 1A8 IgG may recognize LFA-1, one of the principal lymphocyte surface antigens recognized by RATG. The 1A8 antigen is 180 kDa and is expressed by 80-90% human PBL and thymocytes. LFA-1 and the 1A8 antigen exhibit 100% co-expression in two-color FACS analysis using four different murine anti-LFA-1 MAbs. 1A8 markedly inhibits the mitogenic response of lymphocytes to PHA, as do murine anti-LFA-1 MAbs. A combination of rabbit antilymphocyte MAbs may potentially reproduce the multiple specificities found in polyclonal RATG and lead to the production of a superior immunosuppressive clinical agent.

Natural killer cells in rhesus monkeys: properties of effector cells which lyse Raji targets

Spontaneously occurring natural killer cell activity of rhesus monkey peripheral blood mononuclear cells was assayed against five human cell lines, three of which were Epstein-Barr virus (EBV) positive, including the human B cell line Raji. The lytic activity to Raji cells was high, significantly higher than to any other cell line tested. Raji cells are normally insensitive to spontaneous lysis by human NK cells, and the contrasting vigor of the rhesus monkey cytolytic activity to Raji prompted us to investigate the properties of this effector cell. We found the effector cell-mediating lysis of Raji to be nonadherent and phagocytic with lytic activity slightly enhanced in the E-rosette-forming cell (ERFC+) fraction and decreased in the ERFC- fraction. Further isolation of FcIgG receptor-positive and FcIgG receptor-negative subsets by rosetting resulted in significant enrichment of NK activity to Raji in the positive fraction and a loss of activity in the negative fraction. Depletion studies with various monoclonal antibodies (mAb's) confirmed that nearly all lytic activity was contained in the CD16+ (Leu 11b+) population, while subsets of effector cells expressed CD2 (9.6) and CD8 (OKT8). Depletion of CD4 (OKT4)-, HLADR (OKIa)-, or LFA1 (MAC-1)-positive populations failed to reduce NK activity. We compared the phenotypic properties of alloimmune effector cells exhibiting specificity for allogeneic donor targets with those exhibiting lysis of Raji targets. Results indicated that allospecific cytotoxic T lymphocytes expressed a CD16-, CD2+ phenotype, a pattern distinct from that of the effector cell population recognizing Raji targets. The presence of CD2 mAb's in the culture had no effect on NK lytic activity. In contrast, mAbs CD8 and Leu 11b were inhibitory. This would suggest a functional role for CD8 and FcIgG molecules in the lysis of Raji cells by rhesus effectors. In summary, these studies describe a distinct population of effector cells in the blood of rhesus monkeys which exhibit spontaneous lytic activity to Raji cells and exhibit the properties of NK cells.

Cutaneous T cell lymphoma. Lymphocyte phenotype analysis after anti-thymocyte globulin therapy

In an attempt to explore new or alternative therapy for refractory cutaneous T cell lymphoma, a patient with advanced disease refractory to conventional chemotherapy was treated with anti-thymocyte globulin. The therapy was associated with tolerable and manageable toxicities. Phenotypic analysis of neoplastic cells in blood and tissue was used to follow the disease response during the trial. The therapy resulted in resolution of skin lesions and disappearance of circulating cells with neoplastic phenotype. Marked improvement in skin infiltrate and restoration of normal skin architecture seen in skin biopsy specimens after anti-thymocyte globulin were prominent correlative findings. Lymphocytes with normal T cell phenotype appeared after anti-thymocyte globulin therapy, although their mitogenic response was subnormal. The infused anti-thymocyte globulin was found to localize in the skin and bind the neoplastic cells in circulation. The anti-thymocyte globulin-bound cells, with a half-life of 4.9 days, could still be detected up to 14 days after completion of anti-thymocyte globulin therapy.

Mitogenic responses of baboon (Papio cynocephalus) peripheral blood mononuclear cells. A possible role for monocytes

Removal of carbonyl iron-adherent/phagocytic cells from baboon peripheral blood mononuclear cells generally resulted in a depressed blastogenic response to both pokeweed mitogen and concanavalin A. In the majority of cases, no alteration in dose requirement nor shift in kinetics was apparent. Staining for peroxidase activity indicated a reduced proportion of monocytes in the population of cells treated with iron. Therefore, the results of this study strongly suggest a potentiating role for monocytes in lectin stimulation of baboon lymphocytes.

Regulation of the immune response by prostaglandins

Of all the arachidonic acid metabolites, only prostaglandin E (PGE) has been shown to have a clear role in the regulation of cellular and humoral immune responses. In cellular immune responses such as T cell proliferation, lymphokine production, and cytotoxicity, PGE usually acts as a feedback inhibitor of the response. This is also true of macrophage and natural killer cytotoxicity. In some instances PGE is responsible for cellular activation rather than inhibition. This is clearest in the control of humoral immunity, where PGE production is a necessary component in the generation of some type of T suppressor cells. Disturbances in immune function found in several human conditions and diseases have been linked to changes in PGE mediated immunoregulation. Either increased production of PGE or increased sensitivity to PGE results in depressed cellular immunity. Conversely drugs which inhibit PGE production act as stimulants of cellular immune function in vitro and in vivo.