Combined Costimulation Blockade Prevents Rejection of Allogeneic Islets in Mice

Thalidomide with blockade of co-stimulatory molecules prolongs the survival of alloantigen-primed mice with cardiac allografts

Background

Miscellaneous memory cell populations that exist before organ transplantation are crucial barriers to transplantation. In the present study, we used a skin-primed heart transplantation model in mouse to evaluate the abilities of Thalidomide (TD), alone or in combination with co-stimulatory blockade, using monoclonal antibodies (mAbs) against memory T cells and alloantibodies to prolong the second cardiac survival.

Results

In the skin-primed heart transplantation model, TD combined with mAbs significantly prolonged the second cardiac survival, accompanied by inhibition of memory CD8⁺ T cells. This combined treatment enhanced the CD4⁺Foxp3⁺ regulatory T cells ratio in the spleen, restrained the infiltration of lymphocytes into the allograft, and suppressed the allo-response of spleen T cells in the recipient. The levels of allo-antibodies also decreased in the recipient serum. In addition, we detected low levels of the constitutions of the lytic machinery of cytotoxic cells, which cause allograft damage.

Conclusions

Our study indicated a potential synergistic action of TD in combination with with mAbs to suppress the function of memory T cells and increase the survival of second allografts in alloantigen-primed mice.

Immunosuppressive effect of compound K on islet transplantation in an STZ-induced diabetic mouse model

Islet transplantation is a therapeutic option for type 1 diabetes, but its long-term success is limited by islet allograft survival. Many factors imperil islet survival, especially the adverse effects and toxicity due to clinical immunosuppressants. Compound (Cpd) K is a synthesized analog of highly unsaturated fatty acids from Isatis tinctoria L. (Cruciferae). Here we investigated the therapeutic effect of Cpd K in diabetic mice and found that it significantly prolonged islet allograft survival with minimal adverse effects after 10 days. Furthermore, it reduced the proportion of CD4(+) and CD8(+) T cells in spleen and lymph nodes, inhibited inflammatory cell infiltration in allografts, suppressed serum interleukin-2 and interferon-γ secretion, and increased transforming growth factor-β and Foxp3 mRNA expression. Surprisingly, Cpd K and rapamycin had a synergistic effect. Cpd K suppressed proliferation of naïve T cells by inducing T-cell anergy and promoting the generation of regulatory T cells. In addition, nuclear factor-κB signaling was also blocked. Taken together, these findings indicate that Cpd K may have a potential immunosuppressant effect on islet transplantation.

Irinotecan combined with co-stimulatory molecule blockade prolongs survival of cardiac allografts in alloantigen-primed mice

Memory T cells play an important role in graft rejection. In this study, we investigated the potential effect of Irinotecan (CPT-11), a topoisomerase I inhibitor used in the treatment of a variety of solid tumor malignancies, on memory T cells. CPT-11 treatment alone or combined with blocking monoclonal antibodies (mAb) against co-stimulatory molecules (LFA-1 and CD154) was evaluated in the prevention of heart transplant rejection in alloantigen-primed mice. Our data suggest that CPT-11 reduced the expression of IL-2/IFN-γ and increased IL-10/TGF-β expression in both peripheral blood and within the grafts. CPT-11 could also inhibit alloresponses of memory T cells, while decreasing the proportion of CD4(+) memory T cells in the spleen of the recipients and significantly reducing serum alloantibody levels. Our study highlights obvious synergistic effects of CPT-11 when combined with co-stimulatory molecule blockade in prolonging the survival of cardiac allografts in alloantigen-primed mice.

Xenoreactive CD4+ memory T cells resist inhibition by anti-CD44 mAb and reject islet grafts via a Th2-dependent pathway

BACKGROUND

Memory T cells are a significant barrier to the induction of transplant tolerance. Our previous study demonstrated that multiple applications of anti-CD44 monoclonal antibody (mAb) could significantly inhibit CD4(+) memory T cells from mediating rejection of cardiac allografts. Now, we sought to explore the effect and mechanism of anti-CD44 mAb on the rejection of islet allografts and xenografts mediated by CD4(+) memory T cells.

METHODS

In this study, we first engrafted skin grafts of C57BL/6 (B6) mice or Dark Agouti (DA) rats onto BALB/c mice to induce donor-reactive memory T cells. We adoptively transferred purified CD4(+) memory T cells to BALB/c origin nude mice and then transplanted islet allografts and xenografts to produce the Allo-Tx and Xeno-Tx models, respectively. We subsequently administered multiple anti-CD44 mAb and observed changes in the survival times of the islet grafts.

RESULTS

In the Allo-Tx model, the mean survival time (MST) of the grafts was 7.7 days in the isotype group, and 20.3 days in the anti-CD44 group. In the Xeno-Tx model, the MST of the grafts was 7.2 days in the isotype group and 8.2 days in the anti-CD44 group. Compared with the isotype group, CD4(+) T cells on the grafts in the anti-CD44 group were significantly decreased in both the Allo-Tx and Xeno-Tx models, but the proportion of CD4(+) memory T cells in the spleens and draining lymph nodes of the recipient nude mice in the anti-CD44 group was significantly decreased in the Allo-Tx model, while it was increased in the Xeno-Tx model. The production of donor-specific IgG antibody in the anti-CD44 group did not vary in the Allo-Tx model, while it was markedly elevated in the Xeno-Tx model. Furthermore, the expression of interferon gamma in the anti-CD44 group was markedly decreased in both the Allo-Tx and Xeno-Tx models, while the expression of IL-4 in the anti-CD44 group was significantly increased only in the Xeno-Tx model.

CONCLUSION

Multiple applications of the anti-CD44 mAb could significantly inhibit donor-reactive CD4(+) memory T cells from rejecting grafts via a Th1-dependent pathway, but xenoreactive CD4(+) memory T cells can avoid the effects of anti-CD44 mAb to reject islet xenografts via a Th2-dependent pathway.

Arsenic trioxide is a novel agent for combination therapy to prolong heart allograft survival in allo-primed T cells transferred mice

Alloreactive memory T cells are major barriers to transplantation acceptance due to their capacity to accelerate rejection. Here, we investigated the effects of combined treatment with arsenic trioxide (As(2)O(3)) and blocking monoclonal antibodies (mAb) against CD154 and LFA-1 (anti-CD154/LFA-1) on graft survival as well as changes in pathology and immunological responses in mice with adoptively transferred allo-primed T cells. The mean survival time (MST) for the cardiac allografts in recipient mice receiving the combination of As(2)O(3) and anti-CD154/LFA-1 was significantly longer (>113.7days) compared to those receiving anti-CD154/LFA-1 (23.2days), As(2)O(3) (12.5days) alone or no treatment (5.5days). This combined strategy distinctly inhibited lymphocyte infiltration in grafts, proliferation of splenic T cells and the generation of memory T cells in spleens. Moreover, the combined treatment caused the significant down-regulation of IL-2 and IFN-γ accompanied by increased expression of TGF-β and regulatory T cells (Tregs) in spleens, which led to long-term cardiac allograft survival in recipient mice. These results highlight the potential application of As(2)O(3) and its contribution in combination therapy with antibody blockade to delay rejection by memory T cells.

Suppressing memory T cell activation induces islet allograft tolerance in alloantigen-primed mice

Memory T cells are known to play a key role in prevention of allograft tolerance in alloantigen-primed mice. Here, we used an adoptively transferred memory T cell model and an alloantigen-primed model to evaluate the abilities of different combinations of monoclonal antibodies (mAb) to block key signaling pathways involved in activation of effector and memory T cells. In the adoptively transferred model, the use of anti-CD134L mAb effectively prevented activation of CD4(+) memory T cells and significantly prolonged islet survival, similar to the action of anti-CD122 mAb to CD8(+) memory T cells. In the alloantigen-primed model, use of anti-CD134L and anti-CD122 mAbs in addition to co-stimulatory blockade with anti-CD154 and anti-LFA-1 prolonged secondary allograft survival and significantly reduced the proportion of memory T cells; meanwhile, this combination therapy increased the proportion of regulatory T cells (Tregs) in the spleen, inhibited lymphocyte infiltration in the graft, and suppressed alloresponse of recipient splenic T cells. However, we also detected high levels of alloantibodies in the serum which caused high levels of damage to the allogeneic spleen cells. Our results suggest that combination of four mAbs can significantly suppress the function of memory T cells and prolong allograft survival in alloantigen primed animals.

Monoclonal antibody treatment to prolong the secondary cardiac allograft survival in alloantigen-primed mice

We have previously shown that costimulation blockade using a combination of monoclonal antibodies (mAbs) - CTLA4Ig, antibodies to CD154, LFA-1, and OX40L - can induce tolerance of cardiac allografts in mice with adoptively transferred CD4(+) memory T cells [1]. However, the effect of costimulatory blockade in secondary allograft rejection has not been studied. B6 mice that rejected BALB/c skin grafts for more than 4 weeks (defined as alloantigen-primed mice) were used as recipients. The recipient mice were treated with the mAbs to CD154, LFA-1, OX40L, and CD122 on days 0, 2, 4, and 6 after the secondary transplantation of BALB/c heart. The mean survival time (MST) of secondary cardiac allografts in rats treated with antibodies to CD154 and LFA-1 (2-antibodies approach) and those treated with antibodies to CD154, LFA-1, OX40L, and CD122 (4-antibodies approach) was greater than that of the controls (MST = 6.7 days, 22.2 days, and 3.2 days, respectively). The 4-antibodies approach prevented lymphocytic infiltration in the grafts, inhibited memory T-cells proliferation in the spleen, increased IL-10 secretion in the serum, and enhanced the expression of CD4(+) Foxp3(+) regulatory T cells (Tregs) in spleen. Expression levels of alloreactive antibodies were high in the recipient mice of experimental and control groups. Inhibiting the memory T cells by costimulation blockade extended allograft survival in secondary transplant models but could not induce tolerance of graft. Alloreactive antibodies may participate in alloresponse and play an important role in secondary cardiac allograft rejection.

Operational tolerance in nonvascularized transplant models induced by AR-C117977, a monocarboxylate transporter inhibitor

AR-C117977, a monocarboxylate transporter inhibitor, reduces immune responses both in vitro and in vivo, maintains long-term graft survival, and induces operational tolerance. To evaluate the immunosuppressive limitations of AR-C117977, this study was performed in nonvascularized transplant models noted for their refractive response to standard immunosuppressive agents. Rat skin was transplanted from DA(RT1avl) into PVG(RT1c) and the reverse. Mouse islet allotransplantation was performed with BALB/c H2d donors and C57Bl/6J H2b recipients. In the skin graft model, AR-C117977 monotherapy was associated with long-term skin graft survival in one rat strain combination. AR-C117977 and cyclosporine A (CsA) in combination resulted in significant prolongation of graft survival in both rat strains. CsA monotherapy did not prevent acute rejection in either strain. Islet allograft survival was moderately prolonged with CsA or AR-C117977. AR-C117977 is an efficient immunosuppressive drug in stringent rodent transplant models and further studies are warranted.

Minimization and withdrawal of steroids in pancreas and islet transplantation

For reducing the corticosteroid (CS)-related side-effects, especially cardiovascular events, CS-sparing protocols have become increasingly common in pancreas transplantation (PT). Lympho-depleting induction antibodies, such as rabbit anti-thymocyte globulin (rATG) or alemtuzumab, have been widely used in successful trials. The results of various CS-sparing protocols combining calcineurin inhibitors (CNI) and mycophenolate or sirolimus, have been mixed for rejection and survival rates. Most of the studies were uncontrolled trials of low-risk patients, therefore the grade of evidence is limited. Large-scale prospective studies with long-term follow up are necessary to assess risks and benefits of CS-sparing regimens in PT before recommending such strategies as standard practice. Islet allo-transplantation for patients with brittle type 1 diabetes mellitus, less invasive and safer procedure than PT, has been attempted since late 1980s, but diabetogenic immunosuppressants at maintenance, mainly CS and high-dose CNI, prevented satisfactory results (10% insulin-independence at 1-year post-transplant). Since 2000, CS-free and CNI-reducing protocols, including more potent induction [daclizumab, OKT3gamma1(ala-ala) anti-CD3 antibody, rATG] and maintenance (sirolimus, mycophenolate) agents, have significantly improved short-term outcomes whereas long-term are still inadequate (from 80% to 20% insulin-independence from 1- to 5-year post-transplant). Main limitations are allo- and autoimmunity, immunosuppression-related islet and systemic toxicity and transplant site unsuitability, which tolerogenic protocols and biotechnological solutions may solve.

Transplantation tolerance: lessons from experimental rodent models

Immunological tolerance or functional unresponsiveness to a transplant is arguably the only approach that is likely to provide long-term graft survival without the problems associated with life-long global immunosuppression. Over the past 50 years, rodent models have become an invaluable tool for elucidating the mechanisms of tolerance to alloantigens. Importantly, rodent models can be adapted to ensure that they reflect more accurately the immune status of human transplant recipients. More recently, the development of genetically modified mice has enabled specific insights into the cellular and molecular mechanisms that play a key role in both the induction and maintenance of tolerance to be obtained and more complex questions to be addressed. This review highlights strategies designed to induce alloantigen specific immunological unresponsiveness leading to transplantation tolerance that have been developed through the use of experimental models.