Rescuing pathogen-specific memory B-cell from PBMC of prior Zika virus-infected individuals

Immunological memory, a fundamental immune system mechanism, is instrumental in long-term protection. Successful vaccines can elicit and sustain immunological memory against pathogens for the long term. Memory B cells (MBC) are key players in secondary responses due to their longevity and rapid differentiation into high-affinity antibody-secreting cells upon second antigen exposure. However, the availability of circulating MBCs is limited. Here we describe a protocol, which presents a straightforward and practical method for activating and expanding Zika virus (ZIKV) specific MBC. PBMCs collected from individuals who had been infected with ZIKV two years prior were cultured by supplementing with IL-2 and R848, a TLR-7/8 agonist, and then pulsed with inactivated virus. After seven days, this stimulation led to a notable rise in virus-specific functional MBC, as evidenced by a significant increase in the production of anti-ZIKV IgG. Importantly, the ZIKV pulse did not induce changes in the PBMC culture of individuals without a history of ZIKV infection. These findings demonstrate that virus-specific MBC can be expanded in vitro, even using PBMC cultures from individuals infected years before. Therefore, our protocol is a practical and effective tool for studies that require a larger number of human MBCs from previously infected individuals that are functional and specific to the pathogen under investigation.