Possible mechanism of action of transfusion effect in renal transplantation

Pretransplant blood transfusion without additional immunotherapy generates CD25+CD4+ regulatory T cells: a potential explanation for the blood-transfusion effect

BACKGROUND

Preoperative blood transfusion has had a significant historic impact on graft outcome in clinical kidney transplantation, and the effect has been widely replicated in many experimental transplant models. Although the mechanisms underlying the blood-transfusion effect are poorly understood, one possibility is that preexposure to alloantigen results in the induction of regulatory cells with the capacity to control the effector arm of the immune response.

METHODS

Recent studies in autoimmune models have shown that T cells with regulatory function can be isolated from unmanipulated animals on the basis of CD25 expression, and we have recently shown that pretreatment of recipient mice with donor alloantigen combined with anti-CD4 antibody therapy generates CD25+CD4+ T cells that can prevent graft rejection. We therefore used this sensitive adoptive transfer mouse model to ask whether blood transfusion in the absence of any other treatment can also lead to the generation of alloreactive CD25+CD4+ regulatory T cells.

RESULTS

Although a single donor-specific transfusion (DST) fails to induce dominant regulation, we demonstrate that pretreatment with multiple DSTs generates CD25+CD4+ T cells that are as effective as those that result from blood transfusion under anti-CD4 antibody cover. More importantly, our results show that these cells also develop following multiple transfusions of unrelated (random) blood.

CONCLUSION

These results provide a basis for understanding the blood-transfusion effect in transplantation and, by providing a link between naturally occurring regulatory cells and those induced by alloantigen, may shed new light on the fundamental basis of the effect itself.

Detection of lymphocyte Fc gamma receptor-blocking factors by the EA rosette inhibition assay. Refinement of the conventional method and development of a novel flow-cytometric assay

Serum factors which interact with human peripheral blood lymphocyte Fc gamma receptors (Fc gamma Rs) may be detected in vitro by the EA rosette inhibition assay (EARIA). This assay has been used to detect circulating immune complexes and certain alloantibodies directed against cell surface antigens situated in close proximity to Fc gamma Rs. Three main types of FcR-blocking factor have been demonstrated by the EARIA in human serum following exposure to alloantigens. A strong correlation was observed between the presence of one of these FcR-blocking factors (FcBF1) and human renal allograft survival. This factor was previously shown to bind preferentially to CD32+ B cells and to inhibit antibody synthesis. In this study we have shown that detection of FcBF1 by the EARIA depends on the type of erythrocyte and on the amount of antibody used to sensitise the erythrocytes. Furthermore, we have developed a flow-cytometric version of the EARIA which is rapid, reproducible and, most importantly, objective. Inter-laboratory comparisons using this standardised EARIA should now be possible.

Preformed lymphocytotoxic antibodies: the effects of class, titer and specificity on liver vs. heart allografts

The effect on liver and heart allograft survival (ACI rats to Lewis rats) was studied after three methods of recipient presensitization and after different intervals between sensitization and transplantation. With comparable lymphocytotoxic antibody titers, liver allografts always survived longer than heart grafts. The titer, class and specificity of the antibodies varied with the method of sensitization. Four skin grafts produced IgG and IgM lymphocytotoxic antibody titers of 1:2,000 to 4,000. The IgG fraction was shown to have hepatic vascular endothelial specificity by indirect immunofluorescence. These primed recipients hyperacutely rejected both heart and liver allografts, which showed vascular deposition of IgG antibodies. Survival of either kind of graft was inversely proportional to the lymphocytotoxic antibody titer and length of time after placement of the last skin graft. Presensitization with a single heterotopic heart graft produced an even higher mixed IgG and IgM lymphocytotoxic antibody titer of 1:8,000 but with less IgG vascular endothelial specificity. These animals also hyperacutely rejected heart or liver grafts with tissue deposition of IgG but less consistently and with a weaker correlation with lymphocytotoxic antibody titers and time after sensitization. Sensitization with two pretransplant blood transfusions produced the lowest titer (1:500 to 1,000) and the least IgG vascular endothelial specificity. Liver allograft survival was routinely enhanced in these animals, and little effect was seen on heart grafts. Collectively, the experiments showed that the liver is not only resistant to antibody-mediated rejection relative to the heart but is more easily enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunomodulatory activity of different blood products on the mitogen-induced human lymphocyte transformation

Blood transfusions have an immunosuppressive effect on the recipient and induce changes in several immunological parameters. We studied the effect of homologous and autologous fresh plasma (FP), fresh frozen plasma (FFP), heparinized plasma, as well as the influence of red blood cells (RBC), CPDA-1, CPD, heparin, PAGGS-mannitol, SAG-mannitol and ADSOL on mitogen-induced lymphocyte transformation. Both homologous and autologous FP and FFP decreased the PHA and ConA response of human lymphocytes (P < 0.05). The PWM response was reduced by FP (P < 0.05). The mean t1/2 of plasma-induced suppression was approximately 38 h. Dose-dependent suppression rates were observed with pure CPDA-1 and CPD solutions. In contrast, heparinized plasma showed an elevated PHA- and ConA-induced transformation rate (P < 0.025), whereas PWM induction was unaffected. In addition, washed RBC, pure PAGGS-M, SAG-M and ADSOL solutions revealed no effect on the PHA response. Freezing, heating or recalcification of plasma resulted in an increase in the PHA response. Adenine was not immunosuppressive in vitro. We conclude that, in addition to unspecific mechanisms by CPDA-1 or CPD, an unknown plasma factor, which is susceptible to changes in temperature or storage conditions, suppresses the PHA-, PWM- or ConA-induced T-cell immune response. Further clinical studies are needed to correlate these observations with clinical phenomena.

Influence of antiidiotypic antibody activity on renal transplant outcome

The presence of cytotoxic HLA antibodies (Ab1) against donor lymphocytes in pretransplant sera is almost always associated with rapid rejection of the renal transplant. We have investigated the possibility that antiidiotypic antibodies (Ab2) to cytotoxic HLA antibodies might modulate the immune response and favorably influence renal allograft outcome. The role of antibodies (Ab3) which potentiate the cytotoxic effect of Ab1 was also studied. Pretransplant sera from 63 patients were tested for inhibitory or potentiating activity in the short antiidiotypic assay. Inhibitory activity was detected in 30 patients and in 28 the transplant survived more than a year. Of patients without antibody activity 11 of 17 had grafts surviving more than one year, and of those showing potentiating activity 11 of 16 were functioning at a year. The difference in transplant survival between the first group and the other two groups was statistically significant (P less than 0.05). There was no significant difference in survival rates between the latter two groups. Potentiating activity is therefore not an independent predictor of transplant failure, whereas the presence of antiidiotypic antibody activity did correlate with improved allograft survival.

The blood transfusion effect: clinical aspects

In 1973, Opelz et al. demonstrated a one-year renal transplant survival of 29% in patients who had never been transfused and 66% in those receiving over ten units of blood before transplantation. Subsequent reports were contradictory, but by the early 1980s it was generally accepted that pretransplant blood transfusions were beneficial. By 1983 only 4% of patients awaiting transplantation were untransfused. Since 1985 the data have again become much less clear. In 1987, Opelz showed no improvement in transplant survival, irrespective of whether immunosuppression was with cyclosporin or with conventional therapy. Recently, however, several American studies have again shown beneficial effects of transfusions particularly in patients less well matched for HLA antigens with their donor. There is evidence also that blood transfusion from the specific donor improves survival of a transplant from a living related donor. The risk of sensitisation can be minimised by giving cyclosporin along with the transfusion. Mechanism of the transfusion effect is unclear, but the following have been suggested: (a) clonal deletion or inactivation; (b) the induction of suppressor lymphocytes; (c) the presence of blocking alloantibodies or anti-idiotypic antibodies. There is clearly a need to determine from large studies whether the beneficial transfusion effect still exists, and also to determine whether, for example, numbers of rejection episodes which require expensive therapy are different in transfused and non-transfused patients.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro studies on lymphocyte Fc gamma receptor blocking factors in human renal transplantation

In this study we have confirmed our earlier observation that the presence in pre-transplant serum of a high-molecular-weight lymphocyte Fc gamma receptor blocking factor correlates with improved human renal allograft survival. This factor was found to bind preferentially to B cells and to impair B cell function in vitro.

Isolation and characterization of a high molecular weight lymphocyte Fc gamma receptor-blocking factor associated with renal allograft survival

We have confirmed our previous observation that improved human renal allograft survival is associated with the presence in pre-transplant serum of a high molecular weight lymphocyte Fc gamma receptor-blocking factor. Serum fractionation studies suggest that this factor is a complex protein consisting of IgG together with an IgG-binding protein which has an apparent molecular weight of approximately 60 kD.

What is known about blocking factors in renal allograft recipients

A variety of substances present in serum or plasma, either at the time of renal transplant or during stable graft function in long-term recipients, may interfere with cell-mediated immune functions. In several cases the presence of serum blocking factors has been correlated with decreased graft vulnerability to acute rejection. The question is: are serum blocking factors important for the induction or maintenance of allograft tolerance or, alternatively, are they merely by-products of the tolerant state? Perhaps the most compelling case for an essential role of serum blocking factors can be made in instances where vigorous cell-mediated immune responses can be demonstrated in vitro, but anergy (for example, absence of DTH response) is seen in vivo. However, in renal transplant recipients the majority of studies that show the presence of receptor blocking antibodies or other immunoregulatory serum factors also found a decreased cell-mediated immune response in vitro. Thus, allograft tolerance would appear to involve multiple mechanisms as suggested elsewhere. Due to the recent discovery of the molecular structure of the T cell receptor 33,34, it is now possible to identify determinants associated with the binding of T cell receptor blocking antibodies in renal transplant recipients; for example, one should be able to determine if families of V beta genes are involved. Alternatively, it may be possible to identify polymorphic structures on T cells other than the alpha, beta receptor complex as ligands for blocking antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-cytotoxic antibodies in chronic lymphocytic leukaemia

Non-cytotoxic Fc receptor blocking antibodies against autologous B lymphocytes were sought in sera from patients with chronic lymphocytic leukaemia (CLL), using a rosette inhibition assay. They were found in 11 of 52 (21%) of patients with CLL, but were not associated with previous blood transfusion or pregnancy, suggesting that they were unlikely to have resulted from allogeneic stimulation. Fc receptor blockade was more commonly detected in sera from patients with stage B rather than stage A CLL (Binet classification), though this did not achieve significance beyond the 90% level, and it was noted in 62.5% of those with lymphocyte doubling times of less than one year, compared with 36.3% of those whose lymphocyte doubling time was more than one year. The results indicate that autologous Fc receptor blocking antibody activity occurs in sera from patients with CLL, is more likely to be generated by the tumour itself than by allogeneic stimulation, and is associated with increased tumour load. Such antibodies may permit tolerance of tumour by the host.

Effect of cyclosporin, previous third-party transfusion, and pregnancy on antibody development after donor-specific transfusion before renal transplantation

Non-cytotoxic and cytotoxic antibodies were sought after donor-specific transfusion (DST) in 12 potential renal transplant recipients given concomitant cyclosporin therapy and 13 given DST alone. Non-cytotoxic antibodies, which have been shown to develop after third-party transfusion and to be associated with successful transplantation, developed after DST whether or not cyclosporin was given. Donor and panel reactive lymphocytotoxic antibodies developed relatively infrequently after DST with or without cyclosporin. Donor-specific sensitisation occurred only in patients who were multiparous or had over 10 third-party transfusions. Non-cytotoxic Fc-receptor-blocking antibodies may play a part in the improved survival of one-haplotype-mismatched transplants pretreated with DST.

Maternal cell-mediated immunity to the fetus in human pregnancy

Cell-mediated sensitisation of the mother to her fetus is not a regular event in human pregnancy, and the role of suppressor cells and blocking antibodies in preventing this sensitisation is unresolved. There is as yet little evidence to support the hypothesis that maternal immune recognition of the fetus is essential for the success of the pregnancy. Further progress in this area will depend on systematic investigations of the development of specific maternal humoral and cell-mediated responses to the fetus throughout gestation, and whether a deficiency of these responses results in the failure of the pregnancy.