Relevance of cytotoxic alloreactivity under different immunosuppressive regimens in clinical islet cell transplantation.

Islet or beta cell transplantation provides a promising cure for type 1 diabetes patients, but insulin-independency decreases frequently over time. Immunosuppressive regimens are implemented attempting to cope with both auto- and alloimmunity after transplantation. We analysed the influence of different immunotherapies on autoreactive and alloreactive T cell patterns and transplant outcome. Patients receiving three different immunosuppressive regimens were analysed. All patients received anti-thymocyte globulin induction therapy. Twenty-one patients received tacrolimus-mycophenolate mofetil maintenance immunosuppression, whereas the other patients received tacrolimus-sirolimus (SIR, n = 5) or SIR only (n = 5). Cellular autoreactivity and alloreactivity (CTL precursor frequency) were measured ex vivo. Clinical outcome in the first 6 months after transplantation was correlated with immunological parameters. C-peptide levels were significantly different between the three groups studied (P = 0.01). We confirm that C-peptide production was correlated negatively with pretransplant cellular autoreactivity and low graft size (P = 0.001, P = 0.007 respectively). Combining all three therapies, cellular autoimmunity after transplantation was not associated with delayed insulin-independence or C-peptide production. In combined tacrolimus-SIR and SIR-treated patients, CTL alloreactivity was associated with less insulin independence and C-peptide production (P = 0.03). The percentage of donors to whom high CTLp frequencies were measured was lower in insulin-independent recipients (P = 0.03). In this cohort of islet cell graft recipients, clinical outcome in the first 6 months after transplantation correlates with the applied immunosuppressive regimen. An association exists between insulin-independence and lower incidence of CTL alloreactivity towards donor human leucocyte antigen. This observational study demonstrates the usefulness of monitoring T cell reactivity against islet allografts to correlate immune function with graft survival.

Immunomodulation by intrathymic injection of donor leukocytes in rhesus monkeys.

BACKGROUND: Several studies have demonstrated that intrathymic injection of donor cells into adult rodents can result in long-term allograft survival. The rationale for using the intrathymic route of donor cell administration is that in the thymic environment immature T cells are educated to discriminate between self and non-self antigens. The validity of this approach was tested in non-human primates. METHODS: The effect of the intrathymic injection of allogeneic donor cells was investigated in rhesus monkeys and compared with IV and intracutaneous administration of donor cells. Intrathymic injections were carried out without and with antithymocyte globulin. All animals received subsequently an allogeneic skin graft of the same donor and no immunosuppression post transplantation. RESULTS: Skin graft survival was slightly shorter in animals treated with IC donor cell injections (mean survival time [MST]=8.9+/-0.52) than untreated control animals (MST=10.0+/-0.44), indicating that this route caused sensitisation. Intravenous donor cell injection showed prolongation of graft survival times (MST=11.6+/-1.69). Intrathymic donor cell injection resulted in a graft survival of 9.2+/-1.44 days although addition of antithymocyte globulin slightly prolonged graft survival to 10.3+/-2.84 (not significant). Whereas the cellular responses after intrathymic and intravenous donor cell injections increased, antithymocyte globulin treated animals did not show an increased cellular response. Recipients of intrathymic donor cells showed a significantly decreased humoral anti-donor response as compared to other groups. CONCLUSIONS: Donor cell pretreatment alters the subsequent response to an allogeneic skin graft in monkeys and is dependent on the route of donor cell administration. This is also reflected in the alloantibody response and the in vitro cellular reactivity. Intrathymic administration of donor cells does not lead to prolonged skin graft acceptance.

Rejection of a kidney transplant does not always lead to priming of cytotoxic T cells against mismatched donor HLA class I antigens.

BACKGROUND: Previous studies showed that graft rejection is often associated with the presence of primed cytotoxic T cells (CTLs) with a high avidity for donor cells. Similar high avidity CTLs have been found in individuals who have formed IgG anti-HLA antibodies. The presence of such CTLs to a specific HLA mismatch is therefore considered to be a reflection of an activated immune system, and a contraindication for retransplantation with a donor sharing this particular HLA class I mismatch. METHODS: In our study we investigated whether patients have always primed CTLs against all individual HLA class I mismatches present on a rejected graft. Therefore, 14 patients who had undergone transplantectomy after irreversible kidney graft rejection were analyzed with respect to donor-specific CTLp frequencies and the presence or absence of high avidity CTLs directed against HLA class I mismatches present on the rejected graft. RESULTS: Patients, who have not formed anti-HLA antibodies against the donor have mainly naive CTLs. Most of the patients, that have developed IgG anti-HLA antibodies against a donor mismatch, have primed CTLs directed against that particular mismatch. However, patients with IgM anti-HLA antibodies only, and patients with IgG anti-HLA antibodies in historical sera but no IgG anti-HLA antibodies in current sera, have mainly naive CTLs against the donor HLA mismatch. CONCLUSION: Our results suggest that it is not always necessary to exclude repeated HLA class I mismatches for a subsequent transplantation. In addition to good anti-HLA antibody screening, the CTLp-assay may be a useful tool for donor-selection in retransplant candidates.

Pregnancy can induce long-persisting primed CTLs specific for inherited paternal HLA antigens.

Previous studies showed that pregnancy can prime the maternal cellular immune response directed against paternal HLA antigens. Primed CTLs specific for inherited paternal HLA antigens (IPA) were found in women who had formed HLA allo antibodies, whereas naive CTLs were present in women who did not form antibodies against the paternal HLA antigens. As HLA allo antibodies may disappear in time, it is not clear which women on the waiting list for transplantation have been sensitized to paternal HLA antigens and are at risk for graft rejection if paternal HLA antigens are shared by the donor organ. The presence of primed CTLs specific for a particular antigen is considered to be a reflection of sensitization.In the present study we investigated whether these primed CTLs persist in women who had been pregnant and had formed antibodies against the inherited paternal HLA class I antigens. For this purpose 14 women who had their last pregnancy 10 years ago were analyzed with respect to IPA-specific CTLp frequencies and the presence of high avidity CTLs directed against inherited paternal HLA class I antigens. Although primed CTLs specific for IPA's were found more frequently in women with persisting alloantibodies, they still can be detected when the antibodies have disappeared. The current data show that primed CTLs directed against inherited paternal HLA antigens towards which antibodies have been formed in the past can persist for more than 10 years after pregnancy. The cellular test used in our study can be useful to detect presensitization in women with a history of pregnancy, who enter the waiting list for transplantation.