In situ vaccine "seeds" for enhancing cancer immunotherapy by exploiting apoptosis-associated morphological changes.

Despite the development of many effective immunoadjuvants (IAs), the therapeutic efficacy of in situ vaccines for anti-tumor applications remains limited. Inspired by the morphological changes occurring during apoptosis, this study aims to leverage the release process of autologous tumor antigens (ATAs) to enhance the anti-tumor activity of in situ vaccines. We developed five distinct liposomes, each with unique characteristics and functions, incorporating FDA-approved monophosphoryl lipid A (MPLA) adjuvants into their lipid bilayers. Our findings revealed that the apoptotic bodies generated from tumor cells treated with membrane-fusion liposomes (MFLs) exhibited a greater capacity for immune activation. Mechanistic studies demonstrated that MFLs can utilize the morphological changes associated with apoptosis to accurately deliver adjuvants to apoptotic bodies. To further optimize the efficiency of antigen presentation by these apoptotic bodies as an adjuvant redistribution platform, we encapsulated a calcium chelator within the MFLs to inhibit the externalization of phosphatidylserine (PS) during apoptosis. Through a series of apoptosis-related cellular events, the vaccine can widely disseminate immunoadjuvants (IAs) within tumor tissues, similar to the dispersal of plant seeds. To the best of our knowledge, this is the first approach to utilize apoptosis-associated morphological changes to enhance the immunotherapeutic efficacy of cancer vaccines.