Integrated analysis of humoral and T-cell responses to pneumococcal vaccination in allogeneic hematopoietic stem cell transplant recipients

This study provides, to our knowledge, the first integrated analysis of both humoral and T-cell immune responses to pneumococcal vaccination in allogeneic HSCT recipients, offering a translational perspective that links immunological mechanisms with clinical relevance. Our findings indicate that conjugate vaccination is essential for priming both cellular and humoral immunity, whereas polysaccharide boosting primarily broadens serotype coverage but may attenuate previously established immune responses. In the context of emerging higher-valency conjugate vaccines, including the recently introduced 21-valent formulation incorporating novel serotypes, these results support a reassessment of the need for polysaccharide boosters and inform optimisation of pneumococcal vaccination strategies in immunocompromised hosts at high risk for invasive disease.