Abstract 2626: Rac-mediated hyper-phagocytosis causes immunodeficiency and enhances cancer cell killing
Authors: Mishra Abhinava K. , Rodriguez Melanie , Morrissey Meghan , Montell Denise J. 
Published: April 2023

Background: The 21 kilodalton GTPase Rac is an evolutionarily ancient regulator of cell shape and behavior. Focal and transient Rac activity stimulates protrusion at the leading edges of migrating cells. Rac is also a component of the complex machinery cells use to engulf apoptotic bodies, pathogens, and fluid. Loss of function of the hematopoietic-expressed Rac2 gene causes immunodeficiencies due to impaired migration and survival of neutrophils, macrophages, and lymphocytes. Paradoxically, human patients with germline mutations that hyperactivate Rac2 also exhibit immunodeficiencies. In this study, we report that persistent expression of a hyperactive Rac in a subset of epithelial follicle cells in Drosophila ovary leads to tissue-scale destruction by stimulating engulfment. Further, hyperactive Rac2 enhances engulfment in macrophages and renders lymphocytes prone to engulfment, causing immunodeficiencies in a hyperactivate Rac2 mouse model. Human macrophage-like cells overexpressing a dominant activating Rac2 can engulf and kill living Raji B-cell lymphoma or Jurkat T-cell leukemia cells.

Objective: This study aims to understand the role of hyperactive Rac in causing immunodeficiency due to hyper-phagocytosis and harnessing this property to develop novel cancer therapies.

Study design: UAS-Gal4 system was used to study the tissue-specific expression of hyperactive Rac in Drosophila ovary. A loss-of-function allele of the fly engulfment receptor, draper was used to block engulfment. Primary bone marrow-derived macrophages from Rac2E62K/+ mice were co-cultured with the primary B and T cells. Doxycycline (DOX) inducible, HL60 neutrophil-like cells co-expressing RAC2E62K and GFP were generated by lentiviral infection. These cells were differentiated into macrophages and co-cultured with Raji B-cell lymphoma or Jurkat T-cell leukemia cells.

Results: Here, we report that expression of hyperactive Rac in somatic cells of the Drosophila ovary results in non-autonomous hyper-engulfment and killing of neighboring cells, complete tissue destruction, and female sterility. Blocking the fly engulfment receptor, Draper, rescues egg chamber viability suggesting that hyperactive engulfment causes tissue destruction. Primary bone marrow-derived macrophages from Rac2E62K/+ mice engulf and kill primary B and T cells. Interestingly, Rac2E62K functions in both macrophages and lymphocytes to promote phagocytosis. Expression of a hyperactivated Rac2 found in human immunodeficiency patients, Rac2E62K, is sufficient to cause HL60-derived macrophage-like cells to engulf and kill living Raji B-cell lymphoma or Jurkat T-cell leukemia cells.

Conclusion: Our studies indicate that Rac-mediated hyper-phagocytosis is a previously unrecognized cause of human immunodeficiency and that this effect can be harnessed to develop new cancer therapies.

Citation Format: Abhinava K. Mishra, Melanie Rodriguez, Meghan Morrissey, Denise J. Montell. Rac-mediated hyper-phagocytosis causes immunodeficiency and enhances cancer cell killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2626.