Apoptotic blebs from leukemic cells as a preferred source of tumor-associated antigen for dendritic cell-based vaccines

Abstract

Since few leukemia-associated antigens (LAA) are characterized for acute myeloid leukemia (AML), apoptotic tumor cells constitute an attractive LAA source for DC-based vaccines, as they contain both characterized and unknown LAA. However, loading DC with apoptotic tumor cells may interfere with DC function. Previously, it was shown in mice that apoptotic blebs induce DC maturation, whereas apoptotic cell remnants (ACR) do not. Here, we analyzed human monocyte-derived DC (MoDC) functionality in vitro, after ingesting either allogeneic AML-derived ACR or blebs. We show that MoDC ingest blebs to a higher extent and are superior in migrating toward CCL19, as compared to ACR-loaded MoDC. Although MoDC cytokine production was unaffected, co-culturing bleb-loaded MoDC with T cells led to an increased T cell proliferation and IFNγ production. Moreover, antigen-specific CD8(+) T cells frequencies increased to 0.63 % by priming with bleb-loaded MoDC, compared to 0.16 % when primed with ACR-loaded MoDC. Importantly, CD8(+) T cells primed by bleb-loaded MoDC recognized their specific epitope at one to two orders of magnitude lower concentrations compared to ACR-loaded MoDC. In conclusion, superior ingestion efficiency and migration, combined with favorable T cell cytokine release and CD8(+) T cell priming ability and avidity, point to blebs as the preferred component of apoptotic leukemic cells for LAA loading of DC for the immunotherapy of AML.

In situloading of skin dendritic cells with apoptotic bleb-derived antigens for the induction of tumor-directed immunity

“…By co-administering immunostimulatory agents (e.g., 4/GM, CpG, and TLR ligands) tumor-enforced immunosuppression may be counteracted and the T cell stimulatory capacity of skin DCs greatly enhanced. 11,12,27,46 The data presented here, combined with our previous data, 22 present a strong case for the use of blebs as potent source of TAAs for the induction of tumor-directed immunity through dermally applied vaccines.…”

“…29 Previously, we reported on apoptotic cell-derived blebs as a potent source of TAAs for ex vivo generated DC-based vaccines. 22 Here, we used a human skin explant model to explore the relative efficiency of loading skin resident DCs with either ACRs or blebs in situ as a tumor cell-based vaccine delivery method. We found i.d.…”

“…Blebs have been shown to induce DC maturation in mice, 21 and importantly, in cross-priming experiments, we have shown that monocyte-derived DC (MoDC) loaded with blebs, more efficiently cross-present TAA to CD8 C T cells as compared to MoDC loaded with larger apoptotic cell remnants (ACRs) of sizes ranging from 2-10 mm. 22 Most reported studies assessing the pre-clinical efficacy of whole apoptotic tumor cell vaccines lack detailed descriptions of isolated apoptotic cells and their vesicle by-products, and since the isolation of these microvesicles requires an additional centrifugation and isolation step, the fraction enriched for the larger ACRs, also referred to as apoptotic bodies, have been used in most, if not all, previous studies. The loading of DCs with ACRs has been shown to induce tolerance and to impair DC function, [23][24][25] thus necessitating the use of powerful immunostimulatory adjuvants.…”

Dendritic Cells as Pharmacological Tools for Cancer Immunotherapy

“…Furthermore, using tumor cells or tumor 742 cell elements as antigen source entails the risk of delivering other tumor-derived factors that have immunosuppressive effects (e.g., IL-10 and transforming growth factor-b) (Schui et al, 2002;Schottker and Schmidt-Wolf, 2011;Szczepanski et al, 2011;Ruben et al, 2013;Hong et al, 2014). Nevertheless, several studies have shown that an effective CTL immune response can be triggered by DCs charged with either necrotic leukemic cell lysates or apoptotic leukemic cells or blebs (Galea-Lauri et al, 2002;Spisek et al, 2002;Weigel et al, 2006;Ruben et al, 2014). One plausible explanation for this observation is that the potential immunosuppressive effects of tumor cells can be overcome by the various immunostimulatory factors released from tumor cells upon necrotic or apoptotic cell death induction (Chiang et al, 2010).…”

Problems of Cancer Treatment. Part 2. Treatment Based on Modification of Anticancer Immunological Responses in Therapy

“…cyclophosphamide restores homeostasis of dendritic cells [46]. Attempts are also made to activate inborn immunity using such agents as TLR agonists [62], or vaccination with dendritic cells "loaded" with antigens isolated from patient's tumour [34,63]. This, in a restricted range, is used in the treatment [39,60].…”