Lymphocyte Activation

Lanzavecchio (Switzerland) talked about the life cycle of dendritic cells and T cell activation and the steps that control the generation of effector and memory T cells. He made the distinction between central and memory T cells. Central memory cells are able to re-enter lymph nodes and re-stimulate dendritic cells. He demonstrated that in the primary immune response different T cell response (TH 1, TH 2) are generated by modulating the state of activation of dendritic cells and the duration of the DC-TC interaction.

Nicole Succu-Foca Cortesini (USA) presented data on the age-old issue of suppressor cells. She demonstrated a population of CD8+ CD28- cells which are class I restricted. Antigen presenting cells exposed to these suppressor cells become tolerogenic. She studied mRNA from cells exposed and not exposed to suppressor cells, and demonstrated that many genes are suppressed including cell survival, co-stimulation, transcription, activation and adhesion genes. She also stressed the problem of translating mouse experimental results to the human since in mice tolerance is transferred by CD4+ cells.

An interesting clinical study was reported by Trivedi et al (India). They used GM-CSF to mobilise bone marrow cells of the donor and then infused these cells into the recipient of living related renal transplant recipients in an attempt to create chimerism and tolerance. There were 120 patients in the treated group and 100 in the control group. The graft survival and patient survival was the same in both groups but the incidence of rejection episodes was much lower in the treated group (3% versus 30%). As part of a weaning protocol, 88 of the patients had their immunosuppression reduced. One patient became immunosuppression free, 8 were maintained on Prednisolone alone, 58 on Azathopine and Prednisolone and 21 of the patients required the re-instatement of Cyclosporin.

Wekerle et al (Austria) reported on a mouse model of donor bone marrow infusion concomitant with co-stimulatory blockage using an anti-CD 154 monoclonal reagent. Donor specific tolerance was achieved apparently by deletion of donor reactive T cells.

Huang et al (USA) showed in a rat bone marrow transplant model that depleting both host CD8+ T cells and NK cells allowed durable mixed chimerism to be achieved at a lower dose of total body irradiation and demonstrated the important role these cells play in engraftment.

Administration of cyclosporine after autologous bone marrow transplantation is associated with an auto-immune graft versus host type response. Hess et al (USA) demonstrated that the T cells responsible for this syndrome have a restricted repertoire and recognise a peptide from the CLIP invariant chain presented by MHC class II molecules. Clonal analysis revealed two subsets of T cells defined by their requirement for either the N terminal or the C terminal flanking region of CLIP and by their cytokine profile.

The T cells recognising the N terminal region produce type I cytokines IFNg , IL-R and TNFa , T cells recognising the C terminal region produce the type 2 cytokines IL-4, IL-10 and TGF b . The cells recognising the N terminal region mediate the GVHD type responses. These responses can be ameliorated by the T cells recognizing the C region. This regulatory affect appears to be due to the down regulation of mRNA for type I cytokines. The C terminally restricted auto clones can manifest disease with dermal changes similar to chronic GVHD. The results suggest that acute and chronic auto GVHD are mediated by distinct auto-reactive T cells.

There was quite a deal of discussion in this session on the use of non heart beating donors. Metcalfe (UK) reported on the Leicester Hospital experience involving 72 non heart beating donors (NHBD) and 192 beating donors (HBD). After matching for all other variables there was no significant difference in the overall graft survival between the two groups. The 5 year survival was 73% for NHBD and 65% for HBD. This group strongly recommends the use of NHBD as a means of combating organ shortage. These findings were supported by the Japanese experience (Hoshinaga et al).

Arrieta (Spain) presented data on the ‘Spanish model’ of organ retrieval. The organ donation rate has increased from 15.5 to 50.7 donors per 10⁶ population/year in the last 12 years. Data suggests three are two main reasons for the increase; firstly an increase in detection of potential donors and secondly an increase in family consent. Efficiency defined as the conversion from potential donor to actual donor has remained unchanged over this period.

The UK Renal Transplant Allocation Scheme was presented as a poster by Johnson et al on behalf of the UKTSSA Users Kidney Advisory Group. Factors which are considered important and used in the allocation algorithm include: HLA mismatching, high degrees of sensitisation, recipient age, donor recipient age difference, waiting time, matchability (no. of donors in a pool of 10,000) who are favorable matches, overall sensitisation (%PRA), centre balance of exchange. Factors which were considered but not included in the algorithm include recipient disease, clinical urgency, CMV status, weight and size of donor and recipient, and cold ischaemia time.

Fully HLA matched paediatric recipients receive priority and are ranked using sensitisation levels and waiting time. Well matched adults are sorted by sensitisation levels, recipient age, recipient matchability, waiting time, donor recipient age difference and centre balance. The first year of operation of this scheme has seen an increase in HLA matching levels achieved, and transplantation of more highly sensitised patients.

West et al (Canada) presented an interesting report on the use of ABO incompatible hearts in paediatric transplantation. The age of the 14 recipients was 4 hours to 14 months. Only two of the older patients had detectable ABO antibodies at the time of transplantation. With immunosuppression the onset of ABO antibodies is delayed and when they do occur they are not associated with rejection. Representatives from a couple of other units reported similar results. These findings have implications for the more effective use of paediatric hearts when they become available.

Marrack (USA) presented some interesting data on memory cells. She uses a dye CFSE which binds to protein in cells and is active for weeks. When a cell divides the daughter cells receive half the amount of dye. She used this technique to show that memory cells divide. This technique was used in a mouse model to label memory cells, inject them into recipient animals and then block this action with a range of antibodies. IL-15 maintains while IL-2 reduces the size of the CD8+ memory T cell population. IL-2 actually results in the death of memory cells while IL-15 stimulates proliferation. However IL-2 does not prevent proliferation of memory cells in vitro and therefore would appear to act though another regulatory T cell population in vivo. Anti IL-2 treatment of recipient mice increases the level of memory cells.

There were two interesting papers on the use of Campath IH which is a humanised anti-CD52 monoclonal antibody. Waldman (UK) reported on the successful use of Campath IH as GVHD prophylaxis in stem cell transplantation in the absence of the concomitant use of cyclosporin or methotrexate. There is a Campath user group involving 9 transplant centres. In 64 patients Campath was given from day –8 to 04 and acute GVHD was observed in only 5 patients. A high incidence of durable engraftment was observed. This reagent has also been used in autoimmune diseases such as Wegener’s granulomatosis and multiple sclerosis (Annals of Neurology, 36, 296, 1998). In MS the antibody does not reduce lesions but prevents new lesions being formed.

Calne (UK) presented data on kidney transplantation and Campath IH. Campath IH given in two doses of 20 mg at the time of transplantation allows immunosuppression to be drastically reduced. Instead of triple therapy, one non-steroid immunusuppressive drug is given at half dose as maintenance. Presumably this approach will result in a dramatic decrease in immunosuppressive related complications eg. cancers, cyclosporin related nephrotoxicity etc.

Shapiro (USA) presented data on the outcome of 118 patients undergoing cadaveric kidney / bone marrow transplantation. Each patient was given unmodified bone marrow 3-5 x 10⁸ cells / kg as a single or as multiple infusions in an attempt to create tolerance. The control group were patients receiving cadaveric kidneys without bone marrow transplanted during the same time period. Chimerism was demonstrated in 94% of patients receiving bone marrow compared with 60% in the control group. While there was no difference in graft survival in the two groups there was less allograft nephropathy in patients receiving bone marrow.

Worthington (UK) showed data which supported Terasaki’s results concerning post transplant HLA antibodies and graft survival. In this group 6% of transplants failed that were antibody negative pre and post transplant compared with 76% in the groups who converted. This supports Terasaki’s contention that HLA antibody production post transplant is a powerful predictor of future graft failure.

A strong effect of the B8/DR3 haplotype on high grade acute rejection in a group of 478 adult cardiac transplant recipients was shown by Lietz et al (USA). Interestingly, despite this strong association there was no association there was no association of this haplotype with transplant related coronary artery disease. The authors suggest the observed effect might be due to polymorphism of other non class I or class II genes on this haplotype, such as tumour necrosis factor.

Gerhard Opelz (Germany) presented the latest HLA matching and graft survival results in kidney transplantation. The focus of his talk was the impact of HLA matching on patients receiving the newer immunosuppressive drugs such as Neoral, Tacrolimus (FK506) or mycophenolate mofetil (MMF). In summary an HLA matching effect could be seen in patients receiving these drugs. The big difference however is that the early losses are decreased with the new immunosuppressive regimes compared with cyclosporine but at three years the effects are the same.

Duquesnoy (USA) described a new computer algorithm which identifies acceptable HLA mismatches for highly immunised patients without extensive antibody analysis. It is based on the concept that immunogenic epitopes are represented by amino acid triplets on class I protein molecules, which are accessible to antibodies. The programme compares the triplets both interlocus and intralocus between the antibody producer and other individuals (ie potential donors). By matching these triplets cells can be identified which do not react with the antibody producer. This concept has been tested with more than 10 high antibody producers and has been shown to predict which cells will be negative in a crossmatch. This could be a useful programme with highly sensitised transplant recipients or for sensitised patients requiring platelet support. The programme can be obtained by accessing http:/tpis.upmc.edu.

The highlight of this plenary session for me was the presentation by Anne Durandy on EBV and post transplant lymphoproliferative disease (BLPD). EBV induced BLPD continues to be a major complication in both solid organ and bone marrow transplantation. Forty to sixty percent of solid organ recipients and 90% of bone marrow transplant recipients who develop BLPD die despite reduction of immunosuppressive treatment. She discussed the treatment options which are available and their benefits. Anti-viral therapy such as Acyclovir have proven not to be efficient when used in isolation. More promising treatments include the use of monoclonal antibody treatment such as CD24, CD21, CD20 and more recently IL-6. Also the use of interferon a , high doses of immunoglobulin and the infusion of EBV specific donor cytotoxic T lymphocytes have all demonstrated degrees of efficacy. She did stress the importance of early treatment and therefore the regular monitoring of patients by EBV RT-PCR is recommended.

There has been a surge of interest in the role of both donor and recipient cytokine polymorphisms and their role in allograft survival. There was an entire session devoted to this topic. Cytokines which have been investigated include IL-2, IL-6, IL-10, TNFa , IFNg , TGFb . While individual reports describe single polymorphisms with transplant outcome in renal, heart, lung and bone marrow transplants, it is difficult to see a common thread. The effect that these polymorphisms have on expression and in turn transplant outcome are likely to be exerted via interaction with a host of other factors such as level of HLA matching and degree of immunosuppression. Further research needs to be done in this area not only in terms of genetic polymorphism, but how the pattern of cytokine production itself is indicative of transplant success.

In the final session of the meeting Tony Monaco addressed future directions in immunological manipulation of solid organ transplant recipients.

He felt that there are two approaches ready for extensive clinical trials – they are co-stimulatory blockade and cytoreduction followed by haemopoetic reconstitution. Non radiation based methods of cytoreduction include polyclonal anti lymphocyte serum and immunotoxin. He discussed possible methods of achieving tolerance such as clonal deletion, suppression or anergy, but stressed that the marker of tolerance is chimerism. He demonstrated a direct relationship between the dose of marrow given and the degree of tolerance achieved.

The foregoing is merely a snapshot of what was an incredible week and reflects unashamedly my personal interests. I have not touched on the in excess of 500 posters which were on display over the week. I have concentrated solely on the oral presentations. I have returned with a CD-ROM containing all the abstracts including posters. I am having several copies made and I intend to circulate one to each state. The next International Transplant Meeting will be held in two years in Buenos Aires. The task of maintaining the standards set in Rome is not to be envied! I wish them success.