Brufsky et al. J Transl Med (2020) 18:261 https://doi.org/10.1186/s12967-020-02433-6 Journal of Translational Medicine REVIEW Open Access Boning up: amino-bisphophonates as immunostimulants and endosomal disruptors of dendritic cell in SARS-CoV-2 infection Adam Brufsky1* , Juan Luis Gomez Marti2, Azadeh Nasrazadani3 and Michael T. Lotze4 Abstract Amino-bisphosphonates such as zoledronic acid (ZA) can possibly ameliorate or prevent severe COVID-19 disease by at least three distinct mechanisms: (1) as immunostimulants which could boost γδ T cell expansion, important in the acute response in the lung; (2) as DC modulators, limiting their ability to only partially activate T cells; and (3) as prenylation inhibitors of small GTPases in the endosomal pathway of the DC to prevent expulsion of lysosomes containing SARS-CoV-2 virions. Use of ZA or other amino-bisphosphonates as modulators of COVID-19 disease should be considered. Keywords: SARS Coronavirus, Immune response, Glycoproteins, Bisphosphonates Zoledronic acid as an immunostimulant of γδ T cancer cells in vitro [6]. In early stage breast cancer, cells treatment with a single dose of ZA results in long last- Zoledronic acid (ZA) is a nitrogen containing aminobi- ing activation of efector subsets of γ9δ2 T lymphocytes sphosphonate with wide use in breast cancer in patients [7]. ZA can also increase natural killer (NK) cells through taking aromatase inhibitors to prevent osteoporosis [1]. a DC mediated mechanism modulated by γ9δ2 T cells ZA was frst noted in 2009 to reduce the incidence of [8]. Approximately 50% of patients taking ZA and other bone metastases in post-menopausal women [2]. Large aminobisphosphonates experience an acute phase reac- clinical trials [3] and a meta-analysis [4] confrmed the tion [9], which is correlated with γδ T cell subset expan- beneft of ZA in early stage post-menopausal breast can- sion [10]. cer, with highly signifcant reductions in distant recur- T cells that express gamma/delta (γδ) T cell receptors rence, bone recurrence, and breast cancer mortality. are important in the immune response to viruses [11] ZA inhibits the mevalonate pathway (Fig. 1) through as well as cancer [12]. In the setting of HIV infection, inhibition of farnesyl diphosphate synthetase, leading the circulating γ9δ2 T cells, most responsive to buty- to upstream accumulation of phosphoantigen isopentyl rophilin presented mevalonate pathway molecules, are diphosphate (IPP), stimulating γ9δ2 T cell expansion [5]. eradicated for years even with successful control of viral Some γδ T cells have direct cytotoxicity against breast infection [13]. Tree months after recovery from SARS, patients exhibited selective expansion of γδ T cell popu- lations, but not alpha/beta (αβ) T cell populations [14]. *Correspondence: [email protected] 1 UPMC Hillman Cancer Center, Magee Women’s Hospital, University γδ T cell expansion is associated with higher anti-SARS- of Pittsburgh, School of Medicine, Suite 4628, 300 Halket Street, CoV IgG titers [14]. When non-MHC restricted γδ T cell Pittsburgh, PA 15213, USA are stimulated with SARS-CoV in vitro, they kill SARS- Full list of author information is available at the end of the article Co-V infected THP-1 myeloid cells in culture with high © The Author(s) 2020. 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The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdo- main/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Brufsky et al. J Transl Med (2020) 18:261 Page 2 of 6 Fig. 1 Zoledronic acid (ZA) acts as immunostimulant and endosomal disruptor of dendritic cell in SARS-CoV-2 infection. Inhaled SARS-CoV-2 particles are internalized by the DC (top). In COVID-19 disease, there is depletion of γδ T cells (bottom-left). In addition, virion release depends on prenylation signaling derived from the mevalonate pathway. On the other hand, ZA (bottom-right) inhibits the conversion of geranyl pyrophosphate (GPP) to farnesyl pyrophosphate (FPP), increasing the concentrations of isopentenyl pyrophosphate (IPP). Release of IPP induces γ9δ2 T-cell expansion by phosphoantigen recognition, mediated by butyrophilin-presentation. Downstream inhibition of prenylation reduces the activity of GTPases, decreasing the release of SARS-CoV-2. ZA also afects diferentiation of the DC with downregulation of the expression of CD1a, CD11c, CD83, CD86, DC-SIGN, and HLA-DR and enhancement of the expression of CD80. Figure was created using BioRender https ://biore nder. com/ efciency. Tis suggests a protective efect of γδ T cells populations within the lung [14] could protect individu- in SARS-CoV infection. Agents which expand γδ T cell als from COVID-19 and/or ameliorate symptoms. Brufsky et al. J Transl Med (2020) 18:261 Page 3 of 6 Pamidronate reduces disease severity and mortal- onset of severe SARS-CoV-2 infection but recover during ity from human H1N1 infuenza virus and avian H5N1 the convalescent stage [26]. Such reduction of T cells sug- infuenza virus in an immunodefcient mouse–human gest acute wholesale apoptotic death with engagement of immune chimera [15] through expansion of γδ T cell sub- the TCR in the absence of costimulatory molecules, nor- sets. Inhaled intranasal liposomal clodronate can reduce mally provided by DC [27]. inhibitory alveolar macrophages and increase respiratory DC migration and activation in a mouse model of SARS- Zoledronic acid as a dendritic cell modulator CoV [16]. Tis can reduce viral titers and protect the ani- ZA treatment can afect DC diferentiation and matu- mals from lethal infection. ration, decreasing expression of CD1a, CD11c, CD83, Concerns regarding the clinical consequences and CD86, DC-SIGN, HLA-DR and enhancing expression of safety of γδ T cell expansion are valid. In preclinical CD80 [28]. ZA can augment the allostimulatory activity models, Oberg et al. [17] demonstrate the successful of DCs [28]. ZA can also activate human NK cells in a recruitment of γδ T cells to sites of tumor in a model of DC dependent but γδ T cell independent manner [8]. ZA pancreatic adenocarcinoma by which tumor growth is could therefore act on the DC to further stimulate the ini- retarded in immunocompromised mice. Tese mice may tial immune response to pathogens such as SARS-CoV-2. not be able to manifest the full consequences of immune Te interplay between γδ T cells and dendritic cells is activation. In human studies, no major toxicities were indeed complex [29]. Depending on the clinical setting appreciated in a phase I trial of metastatic hormone- and the pathogen involved, such interaction can generate refractory prostate cancer patients in which ZA was uti- and inhibitory or stimulatory immune response. lized to activate Vγ9 Vδ2 T cells with or without IL-2 In regard to the connection between DC and γ9δ2 [18]. ZA expanded γδ T cells were additionally noted to cells, it is important to point out that Calmette-Guerin be safe in patients with NSCLC [19] following adoptive recognition by dendritic cells promotes the expansion of transfer. γ9δ2 cells, which occurs via isopentyl diphosphate (IPP) Te anti-viral efects of γδ T cells, mediated by release release [30]. In this regard, ZA also prompts IPP release of infected-cell specifc IFN-γ [20] promotes an anti- from dendritic cells. Tis potent inhibitor of farnesyl SARS-CoV (2003 outbreak) efect with expansion of diphosphate synthase is known to induce the release of γδ-cells [14]. T cells, including γδ subpopulations, are IPP from dendritic cells when these are treated with ZA depleted in patients with severe COVID-19 illness [21]. [31]. In fact, 1-Hydroxy-2-methyl-2-buten-4-yl 4-diphos- Indeed stimulation of γ9δ2 T cells early in the disease phate (HDMAPP) is the most potent phosphoantigen would be safe but would require careful analysis of the that stimulates γ9δ2 cells. Tis appears to a critical mech- cytokine profles after γδ T cell-expansion. Recent fnd- anism of chemical synapse between DCs and γδ cells. ings in malaria models suggest that M-CSF production from γδ T cells is important for long-lasting control of Zoledronic acid as a disruptor of the endosome the disease [22]. Such an M-CSF producing cell may be in SARS‑CoV‑2 infection important in regulating and controlling the SARS-CoV2 While virus replication of SARS-Co-V within infected virus. human monocytes is limited, the virions are observed by electron microscopy to accumulate in phagolysosomes The respiratory DC as central to SARS‑CoV‑2 of the endosomal system [32]. Some of the potential pathogenesis immune dysfunction of DCs in SARS-CoV-2 infection In the SARS-CoV-2 infection, there is initial lymphope- can therefore be traced to the endosome. Te endoso- nia. Te lymphocyte count is predictive of disease sever- mal pathway is critically important in DC antigen func- ity and mortality [23]. Lymphocyte counts recover with tion, processing, and cross presentation of antigens [33]. viral clearance and disease resolution, with adaptive Proper ion and pH homeostasis in the endosomal com- immune cells (CD3+ T cells) being especially important partment appears to be required for glycosylation of pro- [24].