Engineered Marrow Macrophages Engorge and Accumulate in Tumors before Differentiating into Tumor Associated Macrophages

Engineered marrow macrophages engorge and accumulate in
tumors before differentiating into TAMs

Cory Alvey,^{1, 2} Kyle Spinler¹, Jerome
Irianto¹, Charlotte Pfeifer¹, Yuntao Xia¹,
Sangkyun Cho¹,

P.C.P Dave Dingal¹,
Jake Hsu¹, Manu Tewari¹, and Dennis Discher,^{1, 2*}

¹Molecular and Cell Biophysics Laboratory, University
of Pennsylvania, Philadelphia, PA, USA.

²Department of Pharmacology, Perelman School of
Medicine, University of Pennsylvania, Philadelphia, PA, USA.

�

Abstract:

Monocytes and macrophages in cardiovascular
and neuroinflammatory diseases are found to engorge and accumulate in solid
tissues but mechanisms remain unclear. Within highly collagenous solid tumors,
tumor associated macrophages (TAMs) are visibly motile, but limited studies
also suggest TAMs are less phagocytic than macrophages in other tissues. Marrow-derived
macrophages can be highly phagocytic, but whether they can also be made to
accumulate in solid tumors and engulf cancer cells is questionable. By blocking
marrow-derived macrophages from recognizing other cells as �self�, tail-vein
injected donor cells accumulate in solid tumors in proportion to their
engorgement on antibody-opsonized cancer cells. Blockade of SIRPA on both mouse
and human donor macrophages inhibits binding of �self-marker� CD47 on targeted
cells to drive tumor shrinkage for 1-2 wks, whereas TAMs can only slowly shrink
opsonized tumors after tumor-CD47 knockdown. Nearly all donor macrophages in
tumors � unlike TAMs � can be made to engulf tdTomato tumors, with phagocytosis
impeding migration and causing accumulation, quantitatively predicting tumor
shrinkage. However, expression profiles of donor macrophages change upon
tumor-localization, with SIRPA increasing towards levels on non-phagocytic
TAMs. RNA isolated from macrophages from tissues of varying stiffness shows
that SIRPA expression correlates with microenvironment stiffness confirmed by in
vitro studies using different stiffness gels. Nonetheless, multiple
injections of engineered macrophages can re-initiate shrinkage of solid tumors
in vivo during which blood parameters remain normal suggesting safety as
well as efficacy.

�