The Journal of urology. using the (CIS); Ta stage S55746 (low-grade non-invasive); and T1 stage (invasiveness into lamina propria). For non-muscle invasive BCa, patients are usually treated with a transurethral resection of bladder tumor (TURBT) to remove the existing tumors. Then, patients undergo a series of intravesical therapies, such as Bacillus Calmette-Gurin (BCG) or mitomycin C, to eliminate the residual cancer cells and prevent recurrence. BCG was initially developed as a vaccine for tuberculosis (TB) in 1921 and was used as an adjuvant immunotherapy for BCa in 1976 [4]. Since then, BCG has been the most effective adjuvant treatment for non-muscle invasive BCa. It was proven that BCG can prevent tumor recurrence and slow the progression to muscle invasive stage [5], thereby yielding a higher survival rate than TURBT surgery alone [6]. The mechanism of BCG in BCa therapy is known to involve both innate and adaptive immune cells. In brief, BCG is given intravesically, and the BCG adheres to urothelial cells through fibronectin [7] and alpha 5 beta 1 integrin receptors [8] followed by internalization. Urothelial cells are then induced to secrete cytokines, including IL-6, IL-8, and TNF-alpha, that recruit neutrophils and monocytes/macrophages [9]. Neutrophils play multiple roles in BCG therapy, through directly eliminating tumor cells by secreting TNF-related apoptosis-inducing ligand (TRAIL) [10] and indirectly contributing to tumor elimination by secreting cytokines to recruit effector cells, such as T cells and NK cells [5]. In addition to neutrophils, several lines of evidence suggest that macrophage actively mediates BCG-induced anti-BCa activity. Following BCG installation, increased numbers of macrophage, along with T cells, and natural killer (NK) cells are observed in BCa infiltrates. In addition to antigen presenting cells, macrophage also acts as a cytotoxic effector against BCa cells by releasing INF-alpha, INF-gamma, and NO S55746 after BCG stimulation [11]. Those effector molecules are known to induce cell apoptosis [11]. IL-8 is a potent chemoattractant for pro-inflammatory mediator, and it is expressed by immune cells and epithelial cells in response to BCG [12]. Urinary IL-8 can predict BCG responsiveness [13, 14]. Also, IL-2 secreted from BCG-stimulated macrophages contributes to the maturation of S55746 natural killer (NK) cells and S55746 cytotoxic T cells that serve as effector cells to kill bladder tumor cells [15]. BCG stimulates innate immune cells to secrete a panel of cytokine to further recruit adaptive immune cells, such as CD4+ and CD8+ T cells, as well as NK cells [16]. Then, Th1 cytokines are produced by both innate and adaptive immune cells, including IL-2, TNF-alpha, and INF-gamma, and these cytokines are required for eradicating tumor cells [5]. One recent study confirmed that the BCG-induced immune response in both innate and adaptive immune cells is critical for BCG efficacy where pre-existing BCG immunity improves BCG immune response to tumors in mice. The results were further proven in BCa patients showing that patients with pre-existing BCG response, determined by positive purified protein derivative (PPD) skin test, had a significantly better recurrence-free survival after standard BCG therapy than patients with a negative PPD skin test [17, 18]. The clinical BCG response rate in BC patients is 50-70%, and a significant amount of patients fail BCG therapy. Currently, there is no biomarker to predict the patient’s BCG responsiveness. Also, the majority of BCG patients developed mild cystitis, including urgency, malaise, and fever [19]. Interestingly, many reports suggest BCG-induced symptoms are associated with therapeutic efficacy [5], including cytokine release in the urine [20] and cystitis symptoms. Occasionally, patients may suffer from severe side effects such as a life-threatening sepsis. Once severe symptoms occur, BCG therapy may be postponed VEGFA or withheld, and patients need to take long-term anti-tuberculosis treatment to reduce the potential side effects [21]. Better understanding of BCG functional mechanism is indeed greatly needed for improving BCG therapy efficacy as well as development of biomarkers for a better selection of BCa patients before and during the therapy. Accumulating evidence suggests that vitamin D is beneficial to BCG vaccination against TB. Low serum vitamin D level is associated S55746 with susceptibility to TB infection [22]. Recent studies found that activation of toll-like receptor 1/2 (TLR1/2) by mycobacteria, like BCG,.