Natural killer (NK) cells constitute about 10-15% of the normal lymphocytes in human peripheral blood. They are important sentinels of the innate immune system that can detect and kill tumor cells and virus-infected cells, and produce cytokines, including interferon-g and tumor necrosis factor-α. NK cells are regulated by a dynamic balance between positive and negative intracellular signals that are transduced from cell surface activating and inhibitory receptors. This makes them an ideal cellular model system to study signal transduction crosstalk. Our goal is to understand the molecular mechanisms by which NK cells recognize and attack abnormal cells in the body, but are tolerant toward normal cells. This knowledge should lead to therapeutic strategies that can enhance NK cell responsiveness toward tumors and viruses in patients.

Killer cell immunoglobulin-like receptors (KIRs) are key regulators of human NK cell function. KIRs bind major histocompatibility complex class I (MHC-I) molecules on the surfaces of all healthy normal cells in the body. Upon detecting MHC-I, KIRs transduce a negative intracellular signal that suppresses NK cell killing responses. In this way, the inhibitory signal derived when KIR detect MHC-I is important for establishing tolerance toward normal cells. Many abnormal tumor cells and virally infected cells eliminate MHC-I expression, however, which abolishes the KIR negative signals and releases the NK cells to specifically attack only these abnormal cells and eliminate them from the body. We are studying the molecular mechanisms controlling the function and surface expression of KIRs. Recent work in collaboration with Dr. Heinrich Roder at FCCC used NMR analysis to detect structural changes in the cytoplasmic domain of an inhibitory KIR upon its interaction with the SHP-2 protein tyrosine phosphatase (Cheng et al., Structure 2019). Improved understanding of the regulation and molecular function of KIR should lead to therapeutic treatments to lower the NK cell activation threshold to more efficiently attack tumor cells and virus-infected cells.

In addition, we are also studying the contributions of NK cells in immune responses toward cancer.  Multiparametric flow cytometry is being employed to study the phenotype and function of NK cells in the peripheral blood of cancer patients.  Over the past decade, we have been studying cohorts of patients with renal cell carcinoma (MacFarlane et al., Cancer Immunol. Res. 2014), chronic lymphocytic leukemia (MacFarlane et al., Oncoimmunol. 2017), inflammatory breast cancer (Fernandez et al., Breast Cancer Res. 2020), multiple myeloma (Pazina et al., submitted), and acute myeloid leukemia (Zhigarev et al., in preparation). These immune phenotyping studies have identified biomarkers with prognostic value and potential targets for immunotherapy.   The work also provided the foundation for a collaborative co-PI project with a psychologist at FCCC, Dr. Carolyn Fang, to establish relationships between psychosocial functioning and immune phenotype in indolent non-Hodgkins Lymphoma (NHL) patients. NHL patients were chosen for study, because they can become particularly stressed during their untreated indolent stage of disease. Exciting preliminary data indicate a strong association between increased stress and reduced expression of some common NK cell activating receptors.

Immunotherapies that enhance NK cell function to treat cancer are also under study, including therapeutic antibodies targeting PD-1, KIR, and SLAMF7.  We are characterizing mechanisms by which these and other antibodies enhance NK cell antitumor responses through blocking inhibitory pathways, co-stimulating, or initiating antibody dependent cellular cytotoxicity (ADCC) responses. For example, our mechanistic studies have revealed that the therapeutic anti-SLAMF7 antibody, elotuzumab, triggers both ADCC and co-stimulatory signaling in NK cells toward multiple myeloma (Pazina et al., Oncoimmunol. 2017 and Cancer Immunol. Res. 2019). Furthermore, previous collaborative studies with Dr. Yuri Sykulev (Kimmel Cancer Center, Thomas Jefferson University, Philadelphia) studying the roles of integrins in ADCC responses (Steblyanko et al., 2015) spawned a co-PI project to perform basic mechanistic analysis of how nano- and micro-clustering of FcgRIIIa (CD16), integrins, and inhibitory receptors influences ADCC responses.  Results from these studies are expected to substantially advance our understanding of basic mechanisms of NK cell receptor function and lead to improved designs of anti-tumor antibodies.

Upon gaining significant experience in immune phenotyping studies of cancer patients, Dr. Campbell became Co-Director of the new FCCC Immune Monitoring Facility (IMF) in 2016, where he designs, guides, and interprets flow cytometry-based correlative studies for ongoing immunotherapy clinical trials at Fox Chase and collaborating outside institutions. These studies have benefited from the rich clinical resources at FCCC and involve collaborations with a vast array of clinicians.  The IMF is processing fresh blood samples from multiple clinical trials with the goals of identifying biomarkers that predict responses to immunotherapies in patients and discovering potential targets for additional immune therapy intervention.  Accordingly, T-cell lymphoma patients treated with the PD-1 blocking antibody, pembrolizumab, had better progression free survival (PFS) if they started therapy with a higher relative percentage of CD4⁺ T lymphocytes in peripheral blood (Barta et al., Clin. Lymphoma Myeloma Leuk. 2019).  Another study with Vijayvergia (Dept. of Hematology/Oncology) found that patients with grade 3 neuroendocrine neoplasms treated with pembrolizumab had improved PFS if their peripheral blood pretreatment had higher peripheral T cell counts, lower TIM-3 expression on T cells, and lower activation state of NK cells and naïve T cells (MacFarlane et al., Cancer Immunol. Immunother. 2020).