Viral Immunity in TrAnsplanted Patients Depending on iMmunosupressIon

Solid Organ Transplantation (SOT) is the reference treatment for end stage kidney disease (Kidney Transplantation, KT) and liver failure (Liver Transplantation, LT). As of 2023, an immunosuppressive treatment remains mandatory for long-term graft survival. This treatment translates into a weaker response to vaccines. The recent example of Severe Acute Respiratory Syndrom (SARS) - Coronavirus (CoV), SARS-CoV-2, showed different vaccinal responses depending on the immunosuppressive drug, comparing belatacept- to tacrolimus-based immunosuppression.

Hepatitis B virus (HBV)-vaccination is recommended in chronic kidney failure and liver failure. However, post-transplantation, a loss of HBV seroprotection is seen in ~ 30 % of the patients. A booster HBV vaccine dose is recommended in such case, but the evaluation of the response to this booster dose is limited.

In the Viral Immunity in TrAnsplanted patients depending on iMmunosupressIoN (VITAMIN) study, investigators will investigate the effect of a HBV-vaccine booster on the immune system, comparing KT recipients treated with Belatacept with KT and LT recipients treated with Tacrolimus. The VITAMIN study is a prospective observational study recruiting KT and LT recipients from the time of a booster HBV vaccine injection and over the following 6 months. The idea is to take advantage of this very particular sensitizing event, at a defined timepoint, to investigate the immune response to HBV through vaccination. Investigators will focus on comparing the immunological state before and after vaccination, in kidney and liver transplant recipients receiving immunosuppression.

The immunological state will be described through 1/ the antibody response, 2/ its phenotype (both exploring the T cell compartment and the B cell compartment, including memory B cells, using flow cytometry) and 3/ its functional response (through the ELISpot assessment of the T response against HBV HBs antigen). Sequential blood samples will be taken, using Peripheral Blood Monocytic Cells (PBMC). Also, investigators will focus on HBV-specific memory B cells, to detect potential antibody secreting cells. This project will provide a longitudinal picture of all immune compartments stimulated by HBV vaccination. This longitudinal picture will be compared between tacrolimus-treated KT and LT recipients and belatacept-treated KT recipients.

The main objective is to compare the serological response (anti-HBs antibodies) between tacrolimus- and belatacept-treated patients. The secondary objective is to describe and compare the phenotype and functional T and B responses between tacrolimus- and belatacept-treated patients.