Humoral rejection of kidney transplants is responsible for a large number of kidney graft losses in a context of increasing shortage.

Although it has been established that it is largely mediated by the alloreactive B lymphocyte, anti-B therapies are only partially effective.

The mechanisms behind the loss of tolerance are also poorly understood, and the triggers of rejection remain to be elucidated.

During this study, patients admitted for kidney graft biopsy for suspicion of rejection will be included ; patients presenting non inflammatory biopsies will be studied as controls. B cells will be extracted and cultured. Their antibodies will be studied along with reactivity towards HLA, non HLA targets and the gut microbiome. The same study will be led for late rejections needing graft removal : B cells extraction, culture, antibodies reactivity testing. Controls will be graft removal for non inflammatory causes. In both cases hight throughput sequencing the immunoglobulin genes will be performed.

Inclusion Criteria:

• Adult kidney transplant recipients admitted for biopsy or graft removal in the participating nephrology departments.
• Patient participation agreement and signed consent form
• Affiliation to a health insurance system

Exclusion Criteria:

• Confounding factor of renal inflammation: acute or recurrent pyelonephritis, BK virus nephropathy
• Pregnant or breast-feeding women
• Persons under legal protection

This study covers a population of adult kidney transplant patients admitted for biopsy or graft removal in the participating nephrology departments.

The procedures carried out with the French data privacy authority (CNIL, Commission nationale de l'informatique et des libertés) do not provide for the transmission of the database, nor do the information and consent documents signed by the patients.

Consultation by the editorial board or interested researchers of individual participant data that underlie the results reported in the article after deidentification may nevertheless be considered, subject to prior determination of the terms and conditions of such consultation and in respect for compliance with the applicable regulations.

Beginning 3 months and ending 3 years following article publication. Requests out of these time frame can also be submitted to the sponsor

Researchers who provide a methodologically sound proposal.