Vaccine response, antimicrobial immunity and immune reconstitution after hematopoietic stem cell transplantation ; Réponse vaccinale, immunité anti-infectieuse et reconstitution immunitaire après greffe de cellules souches hématopoïétiques

During immune reconstitution following allogeneic hematopoietic stem cell transplantation (allo-HSCT), complete revaccination of allo-HSCT recipients is recommended. Few data exist regarding the immunogenicity and safety of the recommended vaccine regimen. Between 2014 and 2021, we successively conducted two single-center prospective cohort studies (VaccHemInf) among adult allo-HSCT recipients (n=106 and n=109), vaccinated according to current guidelines and followed for 2 years. We herein present data regarding humoral response to the (3+1)-dose regimen of hexavalent pediatric combination vaccine and its determinants. The seroprotection rates obtained at the end of the vaccination schedule were high for tetanus (>95%), diphtheria (>90%) and Haemophilus influenzae type b (>85%), lower for hepatitis B (around 80%). Stem cell source, donor type, history of chronic graft-versus-host disease, treatment with extracorporeal photochemotherapy and naive CD4+ T-cell count differentially influenced the level of antibodies measured after primary vaccination depending on the valency examined. After the 4th dose, the effect of these characteristics on the antibody level was no longer observed, underlining the importance of this booster dose for effective and long-lasting vaccine protection in allo-HSCT recipients. The vaccination was well tolerated. These data suggest that the (3+1)-dose regimen of pediatric combination vaccine is suitable for the immunization of adult allo-HSCT recipients, except for the hepatitis B valence, whose immunogenicity should be optimized by using vaccine regimens adapted to the age and immunosuppression of patients. In the second part of this work, we investigated the reconstitution of varicella zoster virus (VZV) specific cell-mediated immunity by three immune functional assays. Our results suggest that approximately one quarter of allo-HSCT recipients at 6 months post-transplant are able to respond to ex vivo antigenic stimulation by VZV, and that VZV-specific CMI can be estimated from ...