As an example, Huang et al. [193] constructed an immunotherapeutic in-situ fibrin gel (HMPB/BLZ945/anti-SIRPα@ATRA@fibrin) by co-encapsulating anti-signal regulatory protein (SIRP)α antibody and CSF-1R small molecule inhibitor BLZ945-loaded hollow mesoporous PB (HMPB) and differentiation inducer all-trans retinoic acid (ATRA) into fibrin for cancer immunotherapy (Fig. 8A). Here, SIRPA is linked to cancer.