Human leukocyte antigen antibody incompatible renal transplantation

Anti-human leukocyte antigen (HLA) antibodies are recognized as an important problem in organ transplant recipients. This is because antibodies formed against a graft months or years after implantations are the major cause of late allograft failure, and also because protocols allow the transplantation of some grafts across pre-formed HLA antibodies. Advances in our understanding of anti-HLA antibody- mediated rejection (AMR) have occurred because of a better understanding of the histological findings during AMR; more sensitive and specific methods to measure anti-HLA antibodies; and through clinical investigation of patients transplanted across an HLA barrier. Despite advances in therapy and investigation, AMR remains a major problem and treatment protocols often fail to treat it successfully. This review aims to describe the issues in each of these areas and to suggest how clinicians may be able to improve the management of patients with anti-HLA antibodies.

HA-1 Mismatch Has Significant Effect in Chronic Allograft Nephropathy in Clinical Renal Transplantation

BACKGROUND

The minor histocompatibility antigen HA-1 occurs in two allelic forms: H and R. The HA-1(H) form presented in the context of HLA A2 can elicit specific cytotoxic lymphocyte (CTL) responses and can cause graft-versus-host disease in marrow transplants. However, its significance in solid organ transplants is unknown. We determined whether incompatibility of the HA-1 resulted in enhanced rejection and whether HA-1 specific CTLs were generated.

MATERIALS AND METHODS

HLA A2-matched donor/recipient pairs were selected and typed for HA-1 antigens by polymerase chain reaction. Nineteen of 81 pairs were mismatched for HA-1. Peripheral blood mononuclear leucocytes from five recipients, HLA A2 DR-matched with donors, were stimulated for 3 days with third-party donor, matched for HLA A2 DR but mismatched for HA-1. Cells were stained for surface markers, HA-1(H)-specific tetramer reagent, and analyzed by flow cytometry. Controls were unstimulated cells; PBML from two patients never exposed to HA-1(H); immunoglobulin G isotype-matched controls. For all patients, acute rejection rates posttransplant was ascertained. Long-term data was available for 36 patients.

RESULTS AND CONCLUSIONS

There was no difference in acute rejection rates between the HA-1-matched and -mismatched groups, but there was a significant difference in chronic rejection rates, evidenced by increased graft failures during the follow-up period (P = .0024). Lymphocytes from five HA-1-mismatched recipients were stimulated in vitro with cells from HLA-A2 and DR-matched but HA-1-mismatched surrogate donor. Though there seemed to be an excess of tetramer-positive cells, anti-HA-1-specific CTL responses were not conclusively elicited in vitro.

Acute rejection after renal transplantation is reduced by approximately 50% by prior therapeutic blood transfusions, even in tacrolimus-treated patients

BACKGROUND

The authors investigated the relationship between therapeutic blood transfusion before renal transplantation and rejection rates in cyclosporine- and tacrolimus-treated patients.

METHODS

In one center, 265 consecutive recipients were studied. Protocol induction was with azathioprine, prednisolone, and cyclosporine or tacrolimus; 37% had biopsy-proven acute rejection in the first 6 months and 46% had received zero to two units of blood before transplantation.

RESULTS

Lower risk of rejection was associated with tacrolimus induction (odds ratio [OR], 0.53; 95% confidence interval [CI], 0.29-0.95; P=0.049), prior transfusion of three or more units of blood (OR, 0.54; 95% CI, 0.33-0.90; P=0.024), and older age at transplantation (mean, 44.23 +/- 12.56 [+/- SD] years vs. 38.96 +/- 12.37 years; P=0.001). Multiple logistic regression modeling showed the effect of three or more prior transfusions on acute rejection was as follows: OR, 0.49; 95% CI, 0.29 to 0.83; P=0.008.

CONCLUSIONS

Induction immunosuppression should take account of the higher risk of rejection in patients coming to transplantation who have previously received zero to two units of blood.

Agonist binding and affinity state transitions in reconstituted nicotinic acetylcholine receptors revealed by single and sequential mixing stopped-flow fluorescence spectroscopies

The affinity state of nicotinic acetylcholine receptors (nAcChoRs) reconstituted into either dioleoylphosphatidylcholine (DOPC) or a mixture of dioleoylphosphatidylcholine, dioleoylphosphatidic acid, and cholesterol (DOPC/DOPA/cholesterol) has been determined using single and sequential mixing stopped-flow fluorescence spectroscopies. These techniques have millisecond temporal resolution, permitting low- and high-affinity conformational states of the nAcChoR to be resolved following mixing with the fluorescent partial agonist Dns-C6-Cho from their characteristic Dns-C6-Cho dissociation rates. Our studies reveal that prior to agonist-induced affinity state conversion, nAcChoRs reconstituted into either DOPC or DOPC/DOPA/cholesterol are predominantly in a conformational state that has a low affinity for agonist. Prolonged exposure to Dns-C6-Cho converts nearly all DOPC/DOPA/cholesterol-reconstituted nAcChoRs to the high-affinity state. In contrast, Dns-C6-Cho converts only half of all DOPC-reconstituted nAcChoRs to the high-affinity state. The other half persists in a low-affinity state characterized by a Kd for Dns-C6-Cho of 0.61+/-0.07 microM. This Kd is similar to that previously reported for Dns-C6-Cho binding to low-affinity, resting-state nAcChoRs in native membranes. However, affinity state conversion of DOPC-reconstituted nAcChoRs may be facilitated by re-reconstituting them into bilayers composed of DOPC/DOPA/cholesterol. These results indicate that the lipid bilayer composition modulates nAcChoR agonist-induced affinity state transitions.

Transient low-affinity agonist binding to Torpedo postsynaptic membranes resolved by using sequential mixing stopped-flow fluorescence spectroscopy

We have detected the binding of the fluorescent agonist Dns-C6-Cho to both low- and high-affinity states of the nicotinic acetylcholine receptor (nAcChoR) using sequential mixing stopped-flow fluorescence spectroscopy. Our approach to resolving low- and high-affinity binding was to first preincubate receptor membranes with the fluorescent partial agonist Dns-C6-Cho for 15 ms to 1000 s and then to follow the fluorescence decay upon chemical dilution into excess acetylcholine. The fast and slow decays, reflecting Dns-C6-Cho dissociation from low- and high-affinity receptors, had rates of 140 +/- 27 s-1 and 0.1 +/- 0.02 s-1, respectively. With increasing preincubation times, the number of low-affinity receptors decreased while the number of high-affinity receptors increased in a Dns-C6-Cho concentration-dependent manner consistent with current models for agonist-induced affinity state conversion. At receptor-activating concentrations of Dns-C6-Cho, the apparent rates with which high-affinity receptors formed approximated those of ion flux desensitization, implying that the fast desensitized state has an agonist dissociation rate that is indistinguishable from the equilibrium slow desensitized state. The KD for the low-affinity binding site was determined to be 1.1 microM from the increase in the amplitude of the fast decay with Dns-C6-Cho concentration with preincubation times that were sufficiently brief to minimize affinity state conversion. Assuming a bimolecular association rate of 10(8) M-1 s-1, a second estimate of 1.4 microM was made for low-affinity binding. We also detected a fluorescence enhancement consistent with a conformational isomerization of Dns-C6-Cho-inhibited nAcChoRs.