The myeloid SRC family kinase HCK regulates breast cancer growth by activating tumor-associated macrophage-led invasion and inhibiting cytotoxic T cell activity

The normal developmental and homeostatic roles of tissue resident macrophages are subverted in tumor-associated macrophages to promote tumor progression. Pro-tumoral macrophage activities include immune evasion and promotion of invasion and metastasis. We show that both activities are regulated by the myeloid Src family kinase HCK, which drives macrophage motility and invasive capacity. Loss of HCK reduced the growth of the aggressively invasive Py8119 mammary tumor by 70–80% while excessive HCK activity increased tumor growth. Consistent with a role for HCK in regulating macrophage invasiveness, plasma membrane-associated Src family kinase activity at the tumor margins was lost in the absence of HCK. Additionally, tumors from HCK-deficient hosts contained increased CD8 ⁺ T cell numbers and CD8 ⁺ T cell depletion reduced survival of tumor-bearing mice. However, CD8 ⁺ T cell-depleted HCK-deficient mice continued to show a significant survival advantage over CD8 ⁺ T cell-replete control mice, confirming a T cell-independent role for HCK in the promotion of tumor invasion and metastasis. Single cell RNA sequencing confirmed that macrophages comprised more than 40% of tumor mass associated with CSF-1 and IL-34 secretion by Py8119 cells and that loss of HCK activity did not affect macrophage recruitment. Tumor-associated macrophages were clustered into 5 subtypes, immunoregulatory (Folr2 ^high ), inflammatory (H2-Aa ^high ), interferon-primed, angiogenic and tissue resident, and their relative proportions were not affected by HCK activity. Thus, HCK regulates macrophage invasive capacity and cytotoxic T cell numbers but not macrophage numbers or their subtype distribution to drive Py8119 tumor growth.