Lyophilized, antigen-bound liposomes with reduced MPLA and enhanced thermostability.

Thermostability and decreased component costs are desirable features for adjuvanted, recombinant vaccines. We previously showed that a model malaria transmission-blocking vaccine candidate antigen, Pfs25, can be rendered more immunogenic when mixed with liposomes containing cobalt porphyrin-phospholipid (CoPoP) and a synthetic monophosphoryl lipid A (MPLA) variant. CoPoP can induce stable particle formation of recombinant antigens based on interaction with their polyhistidine tag. In the present work, different synthetic MPLA variants and concentrations were assessed in CoPoP liposomes. Long-term biophysical stability and immunogenicity were not adversely impacted by a 60% reduction in MPLA content. When admixed with Pfs25, the adjuvant formulations effectively induced functional antibodies in immunized mice and rabbits. Lyophilized, antigen-bound liposomes were formed using sucrose and trehalose cryoprotectants, which improved vaccine reconstitution for a variety of model antigens. Compared to liquid storage, the lyophilized Pfs25 and CoPoP liposomes exhibited thermostability with respect to size, biochemical integrity, binding capacity, protein folding and immunogenicity. Following 6 weeks of storage at 60 °C, the most extended storage period assessed, the lyophilized formulation induced functional antibodies in mice with immunization.