Review Article ISSN: 2056-4546 Integrative Cancer Science and Terapeutics Integr Cancer Sci Terap, 2018 doi: 10.15761/ICST.1000263 Volume 5(1): 1-7 Natural cancer-killing activity of human granulocytes Wenjun Le 1 and Zheng Cui 2 * 1 The Institute for Translational Nanomedicine, Shanghai East Hospital, Tongji University School of Medicine, China 2 Department of Pathology, Wake Forest University School of Medicine, USA Abstract Natural existence of cancer killing activity (CKA) predominantly in granulocytes was frst discovered in the cancer-resistant mice (SR/CR mice) and later in humans. Te in vitro assay conditions for CKA are diferent from the conventional cytotoxicity assays. An experimental therapy based on the transfusion of the collected human granulocytes from the healthy donors as the direct therapeutic agent was conceptualized previously. In this perspective, the fndings of our ongoing studies are summarized in hope to help clinicians who may be interested in testing the efcacy of donor granulocytes for treating cancer. Granulocyte CKA is expected to play a protective role against cancers in humans and is afected by factors, such as age, stress, seasonality, nutrients, BCG and irradiation etc. Based on our recent fndings that all the target cells tested so far have negative charges on the surface whereas normal cells are charge-neutral on the surface, we propose that the negative surface charge is the cellular property targeted by granulocytes which are the only cells with positively-charged surfaces. Correspondence to: Zheng Cui, Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA, E-mail: zheng.cui@gmail.com Received: January 12, 2018; Accepted: February 04, 2018; Published: February 06, 2018 Introduction Granulocytes are the most abundant leukocyte type well known for its major role in defense against bacterial infection. Although they are ofen observed in cancer lesions, their roles in the immunity against cancer had always been controversial. Nevertheless, most studies on this topic were done in cancer patients where no protective function of any immunity against cancer is expected. Te involvement of granulocytes in anti-cancer immunity at a decisive level was serendipitously discovered in our lab in 1999 [1]. One of normal BALB/c mice unexpectedly survived the otherwise lethal injection of sarcoma 180 (S180). Te opportunity of studying this resistance came when such a profound survivability against injection of lethal cancer cells turned out to be a germline transmissible dominant phenotype. Te colony lasted for 15 years in our lab and is still being kept at another European lab [2]. Further studies demonstrated that granulocytes are solely responsible for the entire cancer-resistance by directly killing cancer cells and can be transferred to other mice to cure established malignancies [3]. Te resistance was not limited to just sarcoma cells, but also other lethal cancer cell lines [4]. Based on these in vivo observations, we confrmed the cancer cell killing activity in vitro by showing that it is only present in the cancer- resistant mice but not normal mice. Tis simple in vitro assay is unique in comparison to conventional cell killing assay in which release of radioactive materials from pre-labeled target cells was measured to determine the level of cells killed. But conventional assays were done in 4 hours. For our assay, any adherent cancer cells can be used as the target. Afer incubation of at least 24 hours with non-adherent efector cells, the live cells still attached to the culture surface are determined as a percentage of the control in which no efector cell is added and all target cells are alive [3,5]. Based on the in vivo diference between the cancer- resistant mice and normal mice, the conditions of the assay in terms of co-incubation time, co-incubation temperature, the co-culture media and the choice of target cells were fne-tuned to refect the phenotype of cancer-resistance in mice. In other words, the assay condition is set to be able to determine which mouse is cancer-resistant or not. So far, while being able to detect signifcant CKA in the cancer-resistant SR/ CR mice, no CKA has been detected in wild-type mice. It is apparent that this assay is able to refect the cancer-resistant phenotype via the leukocytes collected from the peritoneum afer mobilization. CKA was also detected in other cell populations of the resistant mice, primarily in the macrophage fraction, but at much lower level of specifc activity. Once the assay is established to screen the cancer-resistant mice by using mouse cancer cells as targets, it was then the time to address the question whether there were humans having a similar CKA in their leukocytes. Defnition of CKA It is not possible now to challenge humans with live cancer cells to fnd out who is cancer-resistant and who is not. It was done several decades ago but drew severe ethical concerns [6-8]. It is possible, however, that a blood test can be used to screen humans for an activity similar to that of the cancer-resistant mice. Our in vitro assay could be easily adapted into a simple blood test to determine the level of CKA in human leukocytes. First, leukocytes could be easily purifed from human peripheral blood and be further separated into the fractions of granulocytes, monocytes, and lymphocytes. Second, there are numerous cell lines of human cancers from nearly all tissue/organ origins available as target cells. Te relative levels of CKA are defned by the percentage of target cells killed by efector cells at designed efector:target cell ratios (for each assay in our lab, E:T are routinely at 3:1, 10:1 and 20:1) afer 24 hours of co-culture at 39°C. For example, 20% killing at 3:1, 50% killing at 10:1 and 70% killing at 20:1 can be used to make sure that CKA levels are proportional to E:T ratios. Additionally, the killing percentage at each E:T ratio can be compared to that of another individual to determine the relative level of CKA between individuals. Te co-culture temperature is set at 39°C instead