Semi‐Allogeneic Dendritic Cells Injected via the Intratumoural Injection Route Show Efficient Antitumour Effects in Cooperation with Host‐Derived Professional Antigen‐Presenting Cells

Dendritic cells (DC)‐based immunotherapy is a potent anticancer modality. In DC‐based immunotherapy, allogeneic DC may be an alternative source, but the usefulness of allogeneic DC in DC‐based immunotherapy is still controversial. When used for immunotherapy, three factors may affect the efficiency of an allogeneic DC‐driven antitumour response: (1) survival time, which is affected by T‐cell alloresponses; (2) major histocompatibility complex incompatibility with the host cells in the context of antigen presentation; and (3) the role of host‐derived professional antigen‐presenting cells (pAPC). In addition, it is unclear which injection route is preferable when using allogeneic DC. In this study, we demonstrate that semi‐allogeneic DC, which share half of the genes of the recipient, are more effective when used via the intratumoural (i.t.) injection route, rather than the subcutaneous (s.c.) injection route, for the induction of efficient antitumour effects and the generation of a significant tumour‐specific CD8⁺ T‐cell response. The i.t. route has the advantage of not requiring ex vivo pulsation with tumour lysates or tumour antigens, because the i.t.‐injected DC can engulf tumour antigens in situ. Allogeneic bone marrow transplantation (BMT) models, which permit us to separately assess the three factors described previously, show that while all three factors are important for efficient antitumour effects, the control of the alloresponse to injected DC is the most crucial for host‐derived pAPC to function well when DC are administered intratumourally. This information may be useful for DC‐based cancer immunotherapy under circumstances that do not allow for the use of autologous DC.