Blocking cell microtubule assembly inhibits the alloimmune response in vitro and prolongs renal allograft survival by inhibition of Th1 and sparing of Th2 cell function in vivo

Novel colchicine derivatives enhance graft survival after transplantation via suppression of T-cell differentiation and activity

Immunosuppressants are crucial in organ transplantation but their side effects are a trade-off for long-term use. Colchicine has been shown to be effective in various diseases, albeit with many side effects. To enhance the immunosuppressive effects of colchicine, in addition to minimizing its side effects, we attempted to synthesize new colchicine derivatives (KR compounds). In rat cardiac and pancreatic islet allograft, long-term graft survival was identified in KR compound-treated groups. The use of cyclosporine A (CsA) or colchicine inhibited the CD3⁺ and CD4⁺ T-cell proliferation, whereas KR compounds inhibited the CD8⁺ T cells as well as CD4⁺ T cells. KR compounds reduced the apoptosis, interleukin-2 receptor expression, and signal transducer and activator of transcription 3 phosphorylation more than CsA. These results indicate that KR compounds have a potential therapeutic value as novel agents for prevention of graft deterioration by allograft of rejection.

Graft rejection as a Th1-type process amenable to regulation by donor Th2-type cells through an interleukin-4/STAT6 pathway

Graft rejection has been defined as the mirror image of graft-versus-host disease, which is biologically characterized primarily as a Th1-type process. As such, we reasoned that graft rejection would represent a Th1 response amenable to Th2 modulation. Indeed, adoptive transfer of host Th1-type cells mediated rejection of fully MHC-disparate murine bone marrow allografts more effectively than host Th2-type cells. Furthermore, STAT1-deficient host T cells did not differentiate into Th1-type cells in vivo and failed to mediate rejection. We next hypothesized that donor Th2 cell allograft augmentation would prevent rejection by modulation of the host Th1/Th2 balance. In the setting of donor Th2 cell therapy, host-anti-donor allospecific T cells acquired Th2 polarity, persisted posttransplantation, and did not mediate rejection. Abrogation of rejection required donor Th2 cell IL-4 secretion and host T-cell STAT6 signaling. In conclusion, T cell-mediated marrow graft rejection primarily resembles a Th1-type process that can be abrogated by donor Th2 cell therapy that promotes engraftment through a novel mechanism whereby cytokine polarization is transferred to host T cells.

Immunomodulatory effects of docetaxel on human lymphocytes

Docetaxel is an antineoplastic taxoid that interferes with microtubule polymerization dynamics and is used clinically to treat advanced cancers. Because microtubules play significant roles in T lymphocyte activation and function we characterized the in vitro immunomodulatory properties of docetaxel. Effects of docetaxel on lectin-induced peripheral blood mononuclear cell (PBMC) proliferation were measured by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and proliferating cell nuclear antigen (PCNA) staining. In addition, apoptosis was measured by annexin V staining and cell activation by determination of CD25 and CD71 cell surface expression. Intracellular calcium kinetics in lectin-activated Jurkat T lymphocytes exposed to docetaxel were investigated. Th1 cytokine production was assessed in T lymphocytes by intracellular cytokine staining. Docetaxel significantly inhibited PBMC proliferation and promoted apoptosis of lectin-activated PBMCs. Docetaxel significantly decreased expression of CD71 but not that of CD25. Docetaxel altered intracellular calcium homeostasis but did not affect Th1 cytokine production in T lymphocytes. In conclusion we demonstrate that docetaxel, although exerting significant antiproliferative effects on lymphocytes and promoting activation-induced apoptosis does affect only partially lymphocyte activation and function and does not affect Th1 cytokine production. These results suggest maintenance of lymphocyte functions important for host tumor surveillance and suggest that this compound may have a role in the treatment of cancer arising organ transplant recipients.

HLA-B2702 (77-83/83-77) peptide binds to beta-tubulin on human NK cells and blocks their cytotoxic capacity

It has been described that peptides derived from a highly conserved region of the alpha1 helix of the first domain of HLA class I Ags exhibit immunomodulatory capacity blocking both T and NK cell cytotoxicity. In vivo treatment with these peptides prolongs survival of MHC-mismatched allografts. However, the molecular bases of these effects are still unclear. In this study, we further analyze the mechanisms by which the dimeric peptide HLA-B2702 (77-83/83-77) induces suppression of NK cell cytotoxicity. This peptide inhibits natural and redirected lysis mediated by NK cells without significantly affecting effector-target cell binding. We have also isolated and sequenced a protein that binds this inhibitory peptide, which structurally corresponds to beta-tubulin. Tubulin is the major protein of microtubules and is involved in target cell killing. Furthermore, B2702 peptide promotes GTP-independent tubulin assembly, producing aggregates that cannot be depolymerized by cold. Treatment of NK cells with Taxol or demecolcine, which interfere with microtubule organization, also prevents NK cell cytotoxicity. Taken together, these results support the hypothesis that the peptide B2702 (77-83/83-77) exerts its inhibitory effect on NK cell cytotoxicity by inducing polymerization of microtubules and interfering with their normal assembly/disassembly dynamics.

Inhibition of experimental allergic encephalomyelitis in the Lewis rat by paclitaxel

Experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS), is useful for preclinical testing for agents to be considered for treatment for this human demyelinating disease. Microtubules in lymphocytes play an important role in the cascade of human T cell activation, and paclitaxel (PTX), a microtubule stabilizer, can inhibit T cell function. A new formulation of micellar PTX, free of Cremophor and ethanol, was tested for its effect on the induction of EAE in Lewis rats. Adoptive EAE was induced with an encephalitogenic T cell line activated with guinea pig myelin basic protein (GP MBP) peptide 68-88. PTX (10 mg/kg) was administered 24 and 72 h after cell transfer. The clinical signs, fulminating in controls, were completely blocked by PTX, but mild CNS inflammation remained unaltered. A similar dose of PTX, given on days 6 and 8 to animals developing active EAE after immunization with GP MBP peptide 68-88 in complete Freund's adjuvant, greatly reduced the severity of paralysis and delayed the onset of disease by 8-9 days. Marked weight loss and severe toxicity were noted with higher and more prolonged administration. In vitro micellar PTX inhibited activation of encephalitogenic T cells by both specific antigen and mitogen. Lower doses and longer treatment programs may provide effective treatment with acceptable adverse effects with this agent in the treatment of inflammatory demyelinating disease.

Role of indirect allorecognition in experimental late acute rejection

BACKGROUND

Late acute rejection affects up to 28% of renal allograft recipients and remains a major risk factor for late graft loss. As donor-origin antigen-presenting cells are depleted with time, T-cell recognition of donor-derived alloantigenic peptides presented by self antigen-presenting cells (the "indirect pathway" of allorecognition) may play a key role in the initiation of late acute rejection episodes.

METHODS

To test this hypothesis, we developed a clinically relevant experimental model in the rat (Wistar-Furth/Lewis) in which allograft recipients received cyclosporine for 1 month after transplantation and were then allowed to reject the graft upon discontinuation of immunosuppression. Lymphocyte proliferation assays to synthetic class II MHC allopeptides of donor origin and also to intact donor (Wistar-Furth) cells were performed at this time. The effector mechanisms studied included delayed-type hypersensitivity (DTH) responses, lymphocyte-mediated cytotoxicity, and alloantibody production.

RESULTS

Lymphocytes from recipients undergoing late acute rejection had marked suppression of mixed lymphocyte reaction proliferation to intact donor cells. Significant proliferation to donor-derived 25-mer polymorphic class II MHC allopeptides was elicited, however. In vivo, significant DTH responses were observed to both MHC allopeptides and intact Wistar-Furth cells. Recipient lymphocytes also exhibited significant killing of donor cells, although not third-party cells, and anti-donor alloantibodies were detected by flow cytometry.

CONCLUSION

Our results indicate that T cells primed via the indirect pathway are present during acute rejection that occurs after discontinuation of cyclosporine. Mixed lymphocyte reactivity is markedly reduced at this time. Furthermore, there is an association between such allopeptide-primed T cells and the elicitation of specific DTH responses and provision of help to B cells to produce alloantibodies and activation of CD8+ T cells to become effector cytotoxic cells.

Murine interleukin 4 transgenic heart allograft survival prolonged with down-regulation of the Th1 cytokine mRNA in grafts

BACKGROUND

Data supporting the differential activation of T helper (Th) 2 cells in transplantation acceptance/tolerance in rodents have been presented by several investigators. However, the differential activation of Th2 cells may be simply the result of allograft acceptance/tolerance induction instead of a contribution to the maintenance of grafts.

METHODS

Therefore, we established interleukin (IL)-4 transgenic mice under the control of a cardiac alpha-myosin heavy chain promotor and transplanted IL-4-expressing heart allografts into unmodified recipients to determine the actual contribution of the Th2 bias to allograft acceptance.

RESULTS

Among 16 newborn C57BL/6J (B6) mice, three were positive for the IL-4 transgene. Serum IL-4 levels of transgenic versus control B6xC3H F1 mice were not statistically different. Reverse-transcriptase polymerase chain reaction showed that the transgenic B6xC3H F1 mice expressed IL-4 mRNA in the heart and in the lung, whereas control mice did not express IL-4 in any organ. IL-4 mRNA expression in the transgenic but not in the control heart was also confirmed by RNAse protection assay and fluorescence in situ hybridization. The survival of IL-4 transgenic B6xC3H heart grafts heterotopically placed in C3H recipients was prolonged compared with that of nontransgenic grafts (19.0+/-9.1 vs. 6.8+/-2.2 days, P=0.003). Interferon-gamma mRNA expression in IL-4 transgenic heart grafts on the fifth posttransplant day as assessed by Northern blotting was suppressed compared with that in control grafts. Reverse-transcriptase polymerase chain reaction analysis showed that IL-2 mRNA was suppressed in the IL-4 transgenic grafts compared with that in control grafts, while IL-4 mRNA was observed only in IL-4 transgenic grafts. IL-10 mRNA was detected at similar levels in both transgenic and control grafts.

CONCLUSIONS

A Th2 bias may contribute to allograft acceptance in part by inducing the down-regulation of Th1-cytokine mRNAs, but it may not be sufficient to induce indefinite graft survival.