Tumor eradication by immunotherapy with biodegradable PLGA microspheres—an alternative to incomplete Freund's adjuvant

Abstract

In experimental tumor immunotherapy, incomplete Freund's adjuvant (IFA) has been considered as the “gold standard” for T‐cell vaccination in mice and humans in spite of its considerable adverse effects. Recently, we succeeded in eliciting strong CTL responses in mice after vaccination with biodegradable poly(D,L‐lactide‐co‐glycolide) (PLGA) microspheres (MS). In our study, we compared the immune response to IFA and PLGA‐MS containing ovalbumin (OVA) and CpG‐oligodeoxynucleotide (MS‐OVA/CpG) or we used a mixture of MS‐OVA/CpG and MS‐polyI:C. A single vaccination with MS‐OVA/CpG elicited long‐lasting titers of IgG1 and IgG2a, but only low IgE titers, and also the T‐cell response was biased toward Th1 differentiation. Antigen presentation to CD4+ and CD8+ cells and activation of a cytotoxic T‐cell response in mice vaccinated with PLGA‐MS and IFA lasted for over 3 weeks. Preconditioning of the injection site with TNF‐α and heterologous prime‐boost regimen further enhanced the cytotoxic response. PLGA‐MS were as efficient or superior to IFA in eradication of preexisting tumors and suppression of lung metastases. Taken together, PLGA‐MS are well‐defined, biodegradable and clinically compatible antigen carrier systems that compare favorably with IFA in their efficacy of tumor immunotherapy in mouse models and hence deserve to be tested for their effectiveness against human malignant diseases.

The STEAP1262–270 peptide encapsulated into PLGA microspheres elicits strong cytotoxic T cell immunity in HLA‐A*0201 transgenic mice—A new approach to immunotherapy against prostate carcinoma

“…The synthetic peptides PSA 154-163 , PSCA [14][15][16][17][18][19][20][21][22] , PAP 112-120 , TRPM8 [187][188][189][190][191][192][193][194][195] , PSMA [27][28][29][30][31][32][33][34][35] , Survivin 96-104 , STEAP1 86-94 , and STEAP1 262-270 from human prostate and TLR ligands were microencapsulated by spray drying as described elsewhere [32]. Briefly, 10 mg peptide and 5 mg CpG oligodeoxynucleotides with a phosphothioate backbone (CpG ODN 1826, Microsynth) or 0.5 mg polyI: C (Sigma-Aldrich) were dissolved in 0.5 ml 0.1 M NaHCO 3 and mixed with 1 g of PLGA dissolved in 20 ml dichloromethane.…”

“…Stabilization of the HLA-A Ã 0201 peptide complex on the cell surface was compared to the immunodominant, high affinity HLA-A Ã 0201 ligand influenza virus matrix peptide M1 [58][59][60][61][62][63][64][65][66] . Like the M1 reference peptide, PSCA [14][15][16][17][18][19][20][21][22] and PSMA [27][28][29][30][31][32][33][34][35] stabilized HLA-A Ã 0201 even at concentrations below 0.5 mM (Fig. 2).…”

“…Restimulation of the splenocytes from these control mice with STEAP1 262-270 peptide induced no IFN-g response. Surprisingly, vaccination with PSA 154-163 , PSCA [14][15][16][17][18][19][20][21][22] , PAP 112-120 , TRPM8 [187][188][189][190][191][192][193][194][195] , PSMA [27][28][29][30][31][32][33][34][35] , Survivin 96-104 , and STEAP1 86-94 peptides co-encapsulated with CpG-ODN in PLGA MS and coadministered with polyI:C PLGA MS induced no peptide specific CTLs. This lack of a detectable CTL response was not only observed after PLGA MS-based vaccination but also when mice were vaccinated with the same peptides emulsified in IFA (Fig.…”

“…2). As some of the antigens like PAP 112-120 display complete and others like PSMA [27][28][29][30][31][32][33][34][35] only minor conservation between human and mouse sequences neither the induction of xeno-CTLs nor self-tolerance seems to play a crucial role for the immunogenicity of the peptides (Fig. 6).…”

“…The main objective of cancer immunotherapy thus is to strongly stimulate the immune system to boost the natural anti-tumor immunity [23]. We and other groups have investigated poly(D,L-lactide-co-glycolide) microspheres (PLGA MS) as antigen delivery system targeting dendritic cells (DCs) and macrophages in vitro and in vivo as an alternative to incomplete Freund's adjuvant (IFA) which has failed to be approved for routine clinical use [24][25][26][27]. Uptake of the antigens and TLR ligands encapsulated in PLGA MS by APCs does not negatively affect their cardinal properties like migratory capacity, cytokine secretion, and antigen presentation [28].…”