Monoclonal antibodies in renal transplantation: a review

Monoclonal antibody therapy and renal transplantation: focus on adverse effects

A series of monoclonal antibodies (mAbs) are commonly utilized in renal transplantation as induction therapy (a period of intense immunosuppression immediately before and following the implant of the allograft), to treat steroid-resistant acute rejections, to decrease the incidence and mitigate effects of delayed graft function, and to allow immunosuppressive minimization. Additionally, in the last few years, their use has been proposed for the treatment of chronic antibody-mediated rejection, a major cause of late renal allograft loss. Although the exact mechanism of immunosuppression and allograft tolerance with any of the currently used induction agents is not completely defined, the majority of these medications are targeted against specific CD proteins on the T or B cells surface (e.g., CD3, CD25, CD52). Moreover, some of them have different mechanisms of action. In particular, eculizumab, interrupting the complement pathway, is a new promising treatment tool for acute graft complications and for post-transplant hemolytic uremic syndrome. While it is clear their utility in renal transplantation, it is also unquestionable that by using these highly potent immunosuppressive agents, the body loses much of its innate ability to mount an adequate immune response, thereby increasing the risk of severe adverse effects (e.g., infections, malignancies, haematological complications). Therefore, it is extremely important for clinicians involved in renal transplantation to know the potential side effects of monoclonal antibodies in order to plan a correct therapeutic strategy minimizing/avoiding the onset and development of severe clinical complications.

Pharmacologic approaches to composite tissue allograft

This article discusses the pharmacologic approaches and the most promising new compounds for composite tissue allograft tolerance. Although some approaches rely on a combination of immunosuppressive agents that act synergistically against rejection, other strategies use immunologic manipulation, including major histocompatibility complex matching, induction of chimerism, and use of monoclonal antibodies to abrogate the immune response. There is still a need, however, to reproduce these findings in species phylogenetically closer to humans. This may be the target of future research efforts, which may overcome the challenge of limb and face transplant rejection.

Down-modulation of host reactivity by anti-CD44 in skin transplantation

BACKGROUND

A major goal in transplantation medicine is to achieve donor-specific tolerance while sustaining unaltered immunoreactivity toward donor-independent stimuli. Pretransplant immunization and concomitant blockade of costimulatory molecules may be one way to achieve this goal. We investigated whether transplant acceptance could be achieved by sensitization with semiallogeneic blood and blockade of CD44s (standard isoform) or CD44v6 (variant exon 6), since the adhesion molecule CD44 is known to function as a costimulatory molecule in T-cell activation.

METHODS

Immunoregulatory regimens were examined in BDX rats that had received full-thickness (DA x BDX)F1 skin grafts by controlling graft acceptance and immunoreactivity.

RESULTS

When BDX rats received full-thickness (DA x BDX)F1 skin grafts together with either anti-CD44s or anti-CD44v6, graft rejection was delayed, but none of the animals accepted the graft. An analysis of immunoreactivity revealed reduced numbers of infiltrating lymphocytes in anti-CD44s- as well as anti-CD44v6-treated rats. Expansion of donor-specific helper and cytotoxic T cells was particularly impaired in anti-CD44v6-treated rats. The effect of anti-CD44s could not be intensified by presensitization with donor-derived blood. However, when rats received anti-CD44v6 concomitantly with presensitization, 75% permanently accepted the graft and 50% accepted a second graft provided they were continuously treated with anti-CD44v6 and received a low dose of cyclosporine (CsA) during the first weeks after grafting. The frequency of graft-reactive helper T cells was reduced to less than 10% of the level in controls, and cytotoxic T cells could hardly be detected.

CONCLUSION

According to the in vivo and the vitro analyses of the graft and the draining lymph nodes, anti-CD44s blocked homing of activated lymphocytes into the graft, while anti-CD44v6 inhibited clonal expansion of donor-specific T cells. Suppression by anti-CD44v6 apparently functioned distinctly to cyclosporine and was most effective in combination with presensitization. Since expression of CD44v6 on lymphocytes is restricted to a short period during lymphocyte activation, anti-CD44v6 treatment could lead to a quite specific immunosuppression during a limited time period.

Short course single agent therapy with an LFA-3-IgG1 fusion protein prolongs primate cardiac allograft survival

The interaction of T cell costimulatory molecules with their ligands is required for optimal T cell activation. Interference with such interactions can induce antigen unresponsiveness and delay xeno- and allograft rejection. We have previously shown that LFA3TIP, a soluble human lymphocyte function-associated antigen (LFA)-3 construct, binds CD2 and inhibits responses of human T cells in vitro. This study reports the first use of a human fusion protein, LFA3TIP, to significantly prolong primate cardiac allograft survival. Based on our observations that LFA3TIP inhibits baboon allogeneic mixed lymphocyte reactions, we gave baboon recipients of heterotopic cardiac allografts injections of LFA3TIP, 3 mg/kg i.v., for 12 consecutive days, starting 2 days before transplantation. This regimen delayed graft rejection from an average of 10.6 +/- 2.3 days for human IgG-treated controls (n = 5) to an average of 18.0 +/- 5.3 days for LFA3TIP-injected animals (n = 7; P < or = 0.01). Grafts from LFA3TIP-treated animals showed markedly diminished coronary endothelialitis as compared with control animals. LFA3TIP reached peak serum levels of approximately 100 micrograms/ml after 7-9 injections and persisted in the 10-micrograms/ml range for 1 to 2 weeks after the final injection. Despite these blood levels, circulating antibodies to LFA3TIP were not detected in the serum. No renal or hepatic toxicity was noted. The possible mechanism by which LFA3TIP acts to inhibit graft rejection is discussed; success in prolonging graft survival when LFA3TIP is used as a single-agent therapy suggests great potential for this novel therapeutic agent.

Toxicity of OKT3 increases with dosage: a controlled study in renal transplant recipients

In the present study we prospectively compared side effects occurring in 12 patients after the first administration of low-dose OKT3 (0.5 mg twice daily) induction therapy with those in 10 patients who were treated with a conventional dose of OKT3 (5 mg daily) for acute rejection. We also investigated cytokine release and activation of complement and neutrophils as all of these are held responsible for OKT3-induced side effects. Low-dose OKT3 resulted in a significantly decreased side effects score compared to that after a conventional dose of OKT3 (1.8 vs 5.1, p = 0.0006). Following the first administration of low-dose OKT3, TNF peak levels were significantly lower than after a conventional dose of OKT3. In contrast to our data on conventional dose OKT3 treatment, the first administration of low-dose OKT3 did not induce complement activation as reflected by C3a and C4b/c levels in plasma. Finally, the increase in neutrophil degranulation products lactoferrin and elastase-varies; is directly proportional to 1-antitrypsin was much less following 0.5 mg OKT3 than following 5 mg. We conclude that OKT3-induced toxicity is dose-dependent and is mediated not only by cytokine release but also by activation of complement and neutrophils.

High-dose glucocorticosteroids increase the procoagulant effects of OKT3

The use of OKT3 as prophylaxis in renal transplantation carries an increased risk of intragraft thrombosis, which is related to the systemic activation of the coagulation system that consistently occurs after the first dose of OKT3. As only a few patients develop thrombosis after OKT3 therapy, we searched for possible additional risk factor by comparing the demographic and clinical parameters of the 13 patients who developed thrombosis in our institution to those of 218 patients who did not. Multivariate analysis showed a relationship between the dose of methylprednisolone (mPDS) given before the first OKT3 injection and the risk of thrombosis: 6 out of 42 patients (14%) who received high (30 mg/kg) mPDS experienced a thrombotic event, as compared to 7 out of the 189 patients (3.7%) who received < or = 8 mg/kg of mPDS (P < 0.01). This led us to study the effects of mPDS on the procoagulant activity induced by OKT3 on peripheral blood mononuclear cells (PBMC) in vitro. The procoagulant activity of unstimulated PBMC (mean +/- SEM: 0.6 +/- 0.1 mU/ml) reached 3.0 +/- 0.7 mU/ml after OKT3 stimulation (P = 0.0062) and further increased to 7.4 +/- 2.0 mU/ml when PBMC were first preincubated overnight with mPDS before OKT3 stimulation (P = 0.018 as compared to OKT3 alone). This process involved the tissue factor/factor VII pathway, as shown by increased membrane expression of tissue factor on monocytes as well as by a marked reduction of the induced procoagulant activity when the clotting assay was performed with factor VII-deficient plasma.(ABSTRACT TRUNCATED AT 250 WORDS)