Assessment of Immune Memory - Humoral and Cellular - in mPOX-infected Patients : an Ancillary Study of the ANRS0258s MOSAIC Cohort

Primary objective The overall objective is to assess the long-term amplitude and durability of the immune responses after mpox virus (MPXV) infection. Primary endpoint The main outcomes are: the presence of neutralizing antibodies in the serum and the presence of detectable mpox virus-specific memory B cells. Neutralizing antibodies titers will be measured with a semi-automated cell-based assay using live mpox virus. Memory B cells will be measured by flow cytometry and other techniques. Secondary objectives 1. Assess the amplitude and the stability of the MPXV antigen-specific B-cell memory response after infection, against the immunodominant antigens A27, A33, B5, L1, D8, and H3. 2. Assess the breadth of the B-cell repertoire and its neutralizing capacity in a subset of patients 3. Assess the humoral immunity using different serological techniques, for the detection and quantification of anti-MPXV antibodies, and assess the seroneutralization capacities of each antibody. Secondary endpoints 1. The presence of MPXV antigen-specific B-cell memory. Memory B cells will be measured by flow cytometry and other techniques. 2. The breadth and neutralizing capacity of the B-cell repertoire in a subset of patients. 3. The humoral immunity using serological techniques.