Potential therapeutic anti-tumor effect of a Salmonella-based vaccine

Figures & data

Table 1. Cancer immunotherapy based on killing of bacteria-infected tumor cells

Microorgamisms	Injection route	Model	Target cancer	Mechanism	Reference
Salmonella Typhimurium A1 (Leu and Arg auxotroph)	Intravenous or Intratumoral	Nu/nu mice	Human PC-3 prostate cancer cells	Apoptosis induction	2
			Primary orthotopic pancreatic tumor		3
			Orthotopic human breast tumor		4
Salmonella Typhimurium 14028 strain	Intraperitoneal	C57BL/6 mice	B16F1 melanoma cells	Downregulation of CD44^high and CD4^+CD25^+Tregs	5
Salmonella Typhimurium SL3261AT InvA	Intratumoral	C57BL/6J mice	B16F10 and EG-7 cells	Cytotoxic T cells and intratumoral recruitment of Gr1^hi granulocytes	6
Salmonella Typhi CVD915	Intratumoral and peritumoral	BALB/c mice	LM3 mammary adenocarcinoma	IFN-γ-secreting CD4^+ and CD8^+ T cells Reduction of Tregs TNF-α-secreting neutrophils	7
		C57BL/6 mice	EL4 T cell lymphoma		8
Salmonella choleraesuis	Intraperitoneal	C3H/HeN and C3H/HeJ mice	Murine K1735 melanoma cells	TLR4-dependent TH1 response	9
Propionibacterium acnes	Intratumoral	C57BL/6 mice	B16 melanoma cells	TH1 immune responses and secretion of IL-12, IFN-γ, and TNF-α	10
Toxoplasma gondii (cps, uracil auxotroph)	Intratumoral	C57BL/6 mice	B16F10 melanoma cells	CD8^+ T cells and NK cells	11
Bacillus Calmette–Guérin	Intravesical	Human patients	Bladder cancer	TNF-α, TRAIL and neutrophils	12,13
Listeria monocytogenes-LLO	Intraperitoneal	BALB/c mice	4T1 mammary carcinoma	CD8^+ T cells	14
Clostridium novyi non-toxic (NT) spore	Intravenous	C57BL/6N mice	Pancreatic tumor Panc02 cells	NK cells and innate immunity	46

Figure 1. RASV increased Ly6-G^high MDSCs in the tumor. Two subsets of MDSCs were evident, Ly6-G^highLy6-C^inter cells (upper panel) and Ly6-G ^interLy6-C^high cells (lower panel). (A) FACS plot percentages and (B) absolute number of each MDSC subset in the tumor. *p < 0.05. Adapted from Hong et al.¹⁵

Table 2. Approaches to overcome the immune suppression mediated by MDSCs

Major goal	Approach	Result	Reference
Regulation of MDSC generation	Anti-c-kit mAb	Blockade of stem cell factor (SCF)-c-kit signaling and reduction of MDSC number	24
	Tyrosine kinase inhibitor (sunitinib)	Blockade of vascular endothelial growth factor receptors (VEGFR), c-Kit, STAT3, etc., and reduction of MDSC number	25,26
Further differentiation of MDSC	All-trans-retinoic acid	MDSC differentiation into mature myeloid cells	27
	Vitamin D3	CD34^+ cell maturation	28,29
Depletion of MDSC	Gemcitabine	Elimination of MDSCs	30,31
	5-fluorouracil		32
	Anti-IL-6 receptor mAb		33
Prevention of MDSC recruitment to tumor	COX-2 inhibitor (celecoxib)	Downregulation of CCL2 production and decrease in MDSC recruitment	34
	Inhibitor of CSF1R signaling (GW2580)	Decrease in monocytic MDSC recruitment	35
Inhibition of MDSC immunosuppressive function	PDE-5 inhibitor (sildenafil)	Inhibition of iNOS and/or ARG-1 activities	36
	COX-2 inhibitor (celecoxib)		37
	Nitroaspirin		38
	CpG ODNs	Reduction of suppressive function of Ly6G^high MDSC	39
	Triterpenoid	Inhibition of MDSC immune suppressive effect	40
	Rapamycin	Downregulation of ARG1, iNOS and Nox2 in MDSC	41
	α-galactosylceramide	Conversion of MDSC into nonsuppressor cells and increase in immunogenecity of MDSC	47,48

Figure 2. Intratumoral injection of RASV induced Ly6-G^high granulocytic MDSCs highly secreting TNF-α in the tumor. Tumor-infiltrating cells were stimulated with 200 ng/ml LPS for 2 h, and then, TNF-α secretion by Ly6-G^highLy6-C^inter and Ly6-G^interLy6-C^high MDSCs was analyzed by intracellular staining. (A) Percentages of TNF-α⁺ MDSCs in the tumor. (B) The absolute number of TNF-α⁺ MDSC subsets in the tumor. *p < 0.05. Adapted from Hong et al.¹⁵

Figure 3. CD4⁺CD25⁺FoxP3⁺ regulatory T-cell levels decreased in tumor-bearing mice after i.t. injection of RASV. (A) The percentages of CD4⁺CD25⁺FoxP3⁺ Tregs among the CD4⁺ T cell population in splenocytes (n = 6 mice per group). **p < 0.01, ***p < 0.001 compared with naïve control mice. ^†p < 0.01, Her2/CT26-PBS vs. Her2/CT26-RASV i.t. and Her2/CT26-RASV i.t. vs. Her2/CT26-RASV oral. (B) The percentages of FoxP3⁺ Tregs among the CD25⁺ cells are shown after gating the tumor-infiltrating CD4⁺ T cells. (C) The absolute number of tumor-infiltrating CD4⁺ T cells and CD4⁺ CD25⁺ FoxP3⁺ Tregs in the tumors. NS, not significant. Adapted from Hong et al.¹⁵

Figure 4. Tumor antigen-specific CTL activity and tumor-infiltrating CD8⁺ T cells. (A) Spleens from RASV-treated mice were obtained, and specific lysis of hP63 (TYLPTNASL) peptide-loaded target cells was estimated by in vivo CTL levels. (B) Results are expressed as the mean cytotoxicity ± SEM from in vivo CTL assays. (C) The absolute number of tumor-infiltrating CD8⁺ T cells per tumor (left) and per tumor weight (right). *p < 0.05. Adapted from Hong et al.¹⁵

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