Table III.

Active Targeting of Different Immune Cell Types

	Receptor	Ligand	Delivery System	Type of nucleic acid	Key results	Reference
Macrophages
	Mannose receptor	Mannose	PLL polyplexes	DNA	Transfection to monocyte-derived macrophages using Man-PLL polyplexes	[151]
		Mannose	PLL polyplexes and pAsp(DET) polyplexes	DNA	8× increased transfection efficacy for Man-PLL polyplexes, 500× increased transfection efficacy for Man-pAsp(DET) polyplexes in murine bone marrow derived macrophages	[152]
		CM Mannose	Direct conjugate	siRNA	Ligand-dependent gene silencing in monocyte-derived macrophages (in vitro) and in splenic and liver macrophages (in vivo)	[61]
		Mannose	Cationic nano-hydrogel	siRNA	Receptor-dependent delivery of siRNA to M2 macrophages and efficient gene knockdown in primary cells and in mice	[153, 154]
Dendritic cells
	Mannose receptor	Mannose	PEI polyplexes	pDNA	Increase of transfection efficacy by mannosylation of PEI polyplexes, uptake was reduced in presence of the inhibitor Mannose-BSA	[82]
		Mannose	PEGylated LNPs	mRNA	Variation of PEG-spacer length (PEG100, PEG1000 and PEG2000) was evaluated; LNPs with Man-PEG1000 showed highest transfection efficacy	[156]
		CMM	Direct conjugate	siRNA	Ligand-dependent gene silencing activity in monocyte derived DCs	[61]
		Mannan	LNP	Self-amplifying RNA	Enhanced immunization was observed for LNPs decorated with multivalent mannose residues	[157]
	DEC205	Anti-DEC205 scFv	LNP	siRNA	DEC205-dependency on uptake was demonstrated; targeted LNPs showed twofold increase in uptake compared to untargeted LNPs and LNPs with an isotype of scFv	[160]
T-lymphocytes
	CD3 T-cell receptor	Anti-CD3 antibodies	PLL polyplexes	pDNA	1000-fold enhanced gene expression compared to unmodified PLL and Tf-PLL in T-cells; successful transfection to primary human lymphocytes	[58]
	CD4	Anti-CD4 mAb	LNP	siRNA	Specific delivery to CD4+ cells ex vivo; gene silencing activity was observed in blood, bone marrow, spleen and lymph nodes	[59]
	Ly6c	Anti-Ly6-mAb	LNP	mmRNA	Targeted delivery to Ly6c positive cells in vitro; in vivo evaluation in IBD mouse model showed increased protein expression [20-fold in intestine, tenfold in spleen]; expression of anti-inflammatory IL-10 after delivery of IL-10 encoding mmRNA	[164, 165]
	n.a	None (chemical targeting)	LNP	Barcode siRNA, sgRNA	Screening of 168 different LNP formulations in vivo with variations of head group, lipid alkyl chains, phospholipid and molar composition; adamantyl-DSPC delivered siRNA and sgRNA to T cells (and Kupffer cells)	[166]
	n.a	None (chemical targeting)	LNP	siRNA	Variation of head group and alkyl chain; piperazine headgroup led to accumulation and gene silencing in the spleen	[167]
	Integrin β7	Anti-β7-mAb	LNP	siRNA	CD45 mRNA silencing in CD4+ and CD8+ T cells in spleen and lymph nodes	[167]

Abbreviations: PLL, Poly-L-lysine; Man, Mannose; pAsp(DET) poly(N-[N-[2-aminoethyl]-2-aminoethyl] aspartamide); CM Mannose, chemically modified mannose; PEI, polyethylene imine; BSA, bovine serum albumin; DCs, dendritic cells; scFv, single chain antibody; CD, cluster of differentiation; Tf, Transferrin; mAb, monoclonal antibody; Ly6c, lymphocyte antigen 6 complex; mmRNA, modified messenger RNA; IBD, inflammatory bowel disease; mAb, monoclonal antibody