MRC1 and neoplasm: Thanks to oxygen delivery to the tumor sites by Hb@Hf‐Ce6 NPs, Hb@Hf‐Ce6 NPs plus PD‐1 (+) significantly induced higher frequency of total macrophages (CD11b+, F4/80+) and lower frequency of M2 macrophages (CD11b+, F4/80+, CD206+) infiltration in both primary and distant tumors when comparing to PBS control group (Figure 6a; Figures S17,S18, Supporting Information).