Humoral theory of transplantation: some hot topics

Sex-Specific Differences in HLA Antibodies after Pneumococcal Vaccination in Kidney Transplant Recipients

In transplant recipients vaccination against Streptococcus pneumoniae is recommended to reduce mortality from invasive pneumococcal disease. It is still debated if vaccination in transplant recipients triggers alloresponses. Therefore, it was our aim to define if vaccination with Prevenar 13^®, a 13-valent, conjugated pneumococcal vaccine (Pfizer, New York, NY, USA) that acts T cell dependently, induces human leukocyte antigen (HLA) antibodies in clinically stable kidney transplant recipients. Forty-seven patients were vaccinated once with Prevenar 13^® and HLA antibodies were determined prior to vaccination and at month 1 and 12 thereafter. In parallel, pneumococcal IgG antibodies were measured. Using Luminex™ Mixed Beads technology (One Lambda/Thermo Fisher, Canoga Park, CA, USA) we observed overall no change in HLA antibodies after vaccination. Pneumococcal antibodies increased significantly at month 1 (p < 0.0001) and remained elevated at month 12 (p < 0.005). A more detailed analysis of HLA antibodies showed that in 18 females HLA class I and II antibodies increased significantly at month 1 and 12 (p < 0.05); whereas in 29 males HLA class I and II antibodies tended to decrease. Using Luminex™ Single Antigen Beads assay, no de novo donor-specific HLA antibodies were detected after vaccination. In conclusion, the current data indicate that females may be more susceptible to the induction of (non-specific) HLA antibodies after vaccination.

Tofacitinib Halts Progression of Graft Dysfunction in a Rat Model of Mixed Cellular and Humoral Rejection

BACKGROUND

The progression from acute to chronic antibody-mediated rejection in kidney transplant recipients is usually not prevented by current therapeutic options. Here, we investigated whether the use of tofacitinib (TOFA), a Janus kinase 3 inhibitor, was capable of preventing the progression of allograft dysfunction in a Fisher-to-Lewis rat model of kidney transplantation.

METHODS

Rats were treated from the third week after transplantation to allow the development of rejection. Treatment was based on cyclosporin A, rapamycin or TOFA. Renal function was assessed at 1, 4, 8, and 12 weeks after transplantation, whereas rat survival, histological lesions, and infiltrating lymphocytes were analyzed at 12 weeks.

RESULTS

Tofacitinib prolonged graft survival, preserved tubular and glomerular structures and reduced humoral damage characterized by C4d deposition. Tofacitinib was able to reduce donor-specific antibodies. In addition, T and natural killer cell graft infiltration was reduced in TOFA-treated rats. Although rapamycin-treated rats also showed prolonged graft survival, glomerular structures were more affected. Moreover, only TOFA treatment reduced the presence of T, B and natural killer cells in splenic parenchyma.

CONCLUSIONS

Tofacitinib is able to reduce the immune response generated in a rat model of kidney graft rejection, providing prolonged graft and recipient survival, better graft function, and less histological lesions.

Quantification of Alloantibody-Mediated Cytotoxicity In Vivo

BACKGROUND

Preexisting, donor-specific antibodies (DSAs) are culprits of hyperacute rejection. Donor-specific antibodies are also formed de novo, and their role in acute and chronic rejection is increasingly appreciated. However, it is difficult to assess damage inflicted exclusively by DSAs when alloreactive T cell and B cell responses coincide. We reasoned that allosensitization with "costimulation-deficient" cells should induce DSA synthesis but not naive cytotoxic T lymphocyte (CTL) precursors' priming via direct allorecognition. Accordingly, we have developed a novel model to quantify DSA-mediated cytotoxicity in vivo.

METHODS

C57BL/6 (H-2b) mice were sensitized with H-2 kidney epithelial cells, and a cytofluorimetric killing assay was tailored to the measurement of allocytotoxicity. We took cell/complement depletion, costimulation blockade, and serum transfer approaches to reveal the mediators of cytotoxicity. "Third-party" controls and a skin allotransplantation model were used to confirm DSAs' specificity for allo-major histocompatibility complex. We validated our experimental approach in other mouse strains primed with different allogeneic cell types, including endothelial cells. To demonstrate the usefulness of our model/method for drug efficacy testing, we examined the effect of CTLA4-Ig and rapamycin on DSA-mediated cytolysis.

RESULTS

Allosensitization of MHC-disparate mouse strains with costimulation-deficient cells led to robust cytotoxicity mediated by complement-fixing DSAs and phagocytic cells. This response was independent of CTLs, natural killer or natural killer T cells. It required CD4 T cell help, CD40 signaling and CD28-based costimulation during allosensitization and could be reversed by sustained rapamycin treatment.

CONCLUSIONS

The unique model described herein should enable mechanistic studies on sensitization and effector phases of humoral alloreactivity as well as efficacy testing of future immunotherapies to prevent DSA-induced pathology.

Inhibition of JAK3 and PKC via Immunosuppressive Drugs Tofacitinib and Sotrastaurin Inhibits Proliferation of Human B Lymphocytes In Vitro

BACKGROUND

Antibody-mediated response in solid organ transplantation is critical for graft dysfunction and loss. The use of immunosuppressive agents partially inhibits the B-lymphocyte response leading to a risk of acute and chronic antibody-mediated rejection. This study evaluated the impact of JAK3 and PKC inhibitors tofacitinib (Tofa) and sotrastaurin (STN), respectively, on B-cell proliferation, apoptosis, and activation in vitro.

METHODS

Human B cells isolated from peripheral blood of healthy volunteers were cocultured with CD40 ligand-transfected fibroblasts as feeder cells in the presence of interleukin (IL) 2, IL-10, and IL-21. The cocultures were treated with immunosuppressants Tofa, STN, and rapamycin (as a control), to analyze the proliferation and apoptosis of B cells by means of Cyquant and flow cytometry, respectively. CD27 and IgG staining were applied to evaluate whether treatments modified the activation of B cells.

RESULTS

Tofa and STN were able to inhibit B-cell proliferation to the same extent as rapamycin, without inducing cell apoptosis. After 6 days in coculture with feeder cells, all B cells showed CD27 memory B-cell phenotype. None of the immunosuppressive treatments modified the proportion between class-switched and non-class-switched memory B cells observed in nontreated cultures. The high predominance of CD27⁺CD24⁺ phenotype was not modified by any immunosuppressive treatment.

CONCLUSIONS

Our results show that Tofa and STN can suppress B-cell antibody responses to an extent similar to rapamycin, in vitro; therefore these compounds may be a useful therapy against antibody-mediated rejection in transplantation.

Off-label use of the expensive orphan drug eculizumab in France 2009-2013 and the impact of literature: focus on the transplantation field

PURPOSE

The orphan drug eculizumab (Soliris ®) is one of the most expensive in the world and based on expenditures is classed among the highest in France, a scenario suggestive of off-label use. Given its pharmacological properties, it is likely to be used in organ transplantation. Our purposes were to describe the consumption trends of eculizumab for off-label indications overall and in the organ transplantation field and to assess the impact of publications on the latter use.

METHODS

We carried out a temporal ecological study within the French national hospitalization database (PMSI). First, the trend of eculizumab consumption (2009-2013) was compared to our estimate of the maximum on-label consumption (overall and for transplantation). Second, we evaluated the impact of the publications supporting the effectiveness of eculizumab in the transplantation field on temporal trends of eculizumab consumption.

RESULTS

Eculizumab total consumption exceeded our estimate of the maximum on-label consumption since the end of 2011 and increased until the end of the study. The off-label consumption represented at least 50 % of the total consumption. The off-label consumption in organ transplantation also increased since 2011. The amount of publications grew through the study period, but overall, the evidence level remained low. Statistically, publications were neither associated with the drug consumption for transplantation in the long term nor in the short term.

CONCLUSION

Eculizumab started being notably used for off-label indications in France since the end of 2011, and this use increased until the end of the study. We found only low-level evidence concerning the off-label use of eculizumab in the transplantation field through the studied period.

Probable C4d-negative accelerated acute antibody-mediated rejection due to non-HLA antibodies

We report a case of probable C4d-negative accelerated acute antibody-mediated rejection due to non-HLA antibodies. A 44 year-old male was admitted to our hospital for a kidney transplant. The donor, his wife, was an ABO minor mismatch (blood type O to A) and had Gitelman syndrome. Graft function was delayed; his serum creatinine level was 10.1 mg/dL at 3 days after transplantation. Open biopsy was performed immediately; no venous thrombosis was observed during surgery. Histology revealed moderate peritubular capillaritis and mild glomerulitis without C4d immunoreactivity. Flow cytometric crossmatching was positive, but no panel-reactive antibodies against HLA or donor-specific antibodies (DSAbs) to major histocompatibility complex class I-related chain A (MICA) were detected. Taken together, we diagnosed him with probable C4d-negative accelerated antibody-mediated rejection due to non-HLA, non-MICA antibodies, the patient was treated with steroid pulse therapy (methylprednisolone 500 mg/day for 3 days), plasma exchange, intravenous immunoglobulin (40 g/body), and rituximab (200 mg/body) were performed. Biopsy at 58 days after transplantation, at which time S-Cr levels were 1.56 mg/dL, found no evidence of rejection. This case, presented with a review of relevant literature, demonstrates that probable C4d-negative accelerated acute AMR can result from non-HLA antibodies.

Preformed class II donor-specific antibodies are associated with an increased risk of early rejection after liver transplantation

Preformed donor-specific human leukocyte antigen antibodies (DSAs) are considered a contraindication to the transplantation of most solid organs other than the liver. Conflicting data currently exist on the importance of preformed DSAs in rejection and patient survival after liver transplantation (LT). To evaluate preformed DSAs in LT, we retrospectively analyzed prospectively collected samples from all adult recipients of primary LT without another organ from January 1, 2000 to May 31, 2009 with a pre-LT sample available (95.8% of the patients). Fourteen percent of the patients had preformed class I and/or II DSAs with a mean fluorescence intensity (MFI) ≥ 5000. Preformed class I DSAs with an MFI ≥ 5000 remained persistent in only 5% of patients and were not associated with rejection. Preformed class II DSAs with an MFI of 5000 to 10,000 remained persistent in 23% of patients, and this rate increased to 33% for patients whose MFI was ≥10,000 (P < 0.001). Preformed class II DSAs in multivariable Cox proportional hazards modeling were associated with an increased risk of early rejection [hazard ratio (HR) = 1.58; p = 0.004]. In addition, multivariate modeling showed that in comparison with no DSAs (MFI < 1000), preformed class I and/or II DSAs with an MFI ≥ 5000 were independently correlated with the risk of death (HR = 1.51; p = 0.02).