Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into “passive” and “active” based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches

Improving efficacy and reducing toxicity of anti-PD-L1 treatment: T-cells as delivery vehicles for anti-PD-L1 blocking nanobodies

Background Cancer therapy has experienced a paradigm shift due to the clinical success of immune checkpoint inhibitors (ICI) such as anti-PD-L1 antibodies, yet ICI benefits remain limited to a minority of patients. On top of the resistance mechanisms limiting their efficacy, ICI are causing auto-immune side effects related to the activation of self-directed CD8 T cells. We propose a new approach using antitumoral T cells as vehicles to deliver anti-PD-L1 nanobodies specifically at the tumor site. Compared to antibodies, nanobodies offer the advantage of a good penetration ability in tissues while displaying a very short half-life in the blood stream. We evaluated whether this approach could improve efficacy and reduce toxicity compared to classical anti-PD-L1 antibody treatment. Methods Ovalbumin-specific OT-I T cells were engineered to secrete an anti-PD-L1 blocking nanobody. In MC38 Ova murine colon carcinoma model, adoptive transfer of nanobody-secreting T cells was compared with wildtype T cells alone or wildtype T cells in combination with an anti-PD-L1 antibody given by intraperitoneal injection. Treatment efficacy was assessed by measuring tumor growth over time. Flow cytometry and immuno-histochemistry (IHC) analysis on tumor, lymph nodes and spleen samples were performed to compare the distribution of the anti-PD-L1 treatment across different tissues. Results Intratumoral delivery of anti-PD-L1 nanobody improved tumor rejection compared to systemically given anti-PD-L1 antibody. According to flow cytometry and IHC analysis, anti-PD-L1 nanobody was enriched in the tumor compared to spleen and lymph nodes, while anti-PD-L1 antibody was rather enriched in spleen and lymph nodes and weakly detected in the tumor. This low systemic exposure to the nanobody could minimize the risk of developing auto-immune side effects. Conclusions Our study points out the poor penetration of anti-PD-L1 antibody in established tumors as a limitation factor for its efficacy in treating MC38 Ova tumors. Local delivery of an anti-PD-L1 nanobody could both overcome this limitation and reduce the risk of side effects as the nanobody is enriched in the tumor compared to the periphery

Navigating Critical Challenges Associated with Immunopeptidomics-Based Detection of Proteasomal Spliced Peptide Candidates.

Within the tumor immunology community, the topic of proteasomal spliced peptides (PSP) has generated a great deal of controversy. In the earliest reports, careful biological validation led to the conclusion that proteasome-catalyzed peptide splicing was a rare event. To date, six PSPs have been validated biologically. However, the advent of algorithms to identify candidate PSPs in mass spectrometry data challenged this notion, with several studies concluding that the frequency of spliced peptides binding to MHC class I was quite high. Since this time, much debate has centered around the methodologies used in these studies. Several reanalyses of data from these studies have led to questions about the validity of the conclusions. Furthermore, the biological and technical validation that should be necessary for verifying PSP assignments was often lacking. It has been suggested therefore that the research community should unite around a common set of standards for validating candidate PSPs. In this review, we propose and highlight the necessary steps for validation of proteasomal splicing at both the mass spectrometry and biological levels. We hope that these guidelines will serve as a foundation for critical assessment of results from proteasomal splicing studies

Differential suppression of tumor-specific CD8+ T cells by regulatory T cells

In the CT26 BALB/c murine model of colorectal carcinoma, depletion of regulatory T cells (Tregs) prior to tumor inoculation results in protective immunity to both CT26 and other BALB/c-derived tumors of diverse histological origin. In this paper, we show that cross-protection can be conferred by adoptively transferred CD8(+) CTLs. Other schedules for inducing immunity to CT26 have been described, but they do not lead to cross-protection. We show that Treg ablation facilitates the development of new CTL specificities that are normally cryptic, and have mapped the root epitope of one of these responses. This work has allowed us to demonstrate how the specificity of CTL responses to tumor Ags can be controlled via differential suppression of CTL specificities by Tregs, and how this can result in very different physiological outcomes

Processing of tumor-associated antigen by the proteasomes of dendritic cells controls in vivo T-cell responses.

Dendritic cells are unique in their capacity to process antigens and prime naive CD8(+) T cells. Contrary to most cells, which express the standard proteasomes, dendritic cells express immunoproteasomes constitutively. The melanoma-associated protein Melan-A(MART1) contains an HLA-A2-restricted peptide that is poorly processed by melanoma cells expressing immunoproteasomes in vitro. Here, we show that the expression of Melan-A in dendritic cells fails to elicit T-cell responses in vitro and in vivo because it is not processed by the proteasomes of dendritic cells. In contrast, dendritic cells lacking immunoproteasomes induce strong anti-Melan-A T-cell responses in vitro and in vivo. These results suggest that the inefficient processing of self-antigens, such as Melan-A, by the immunoproteasomes of professional antigen-presenting cells prevents the induction of antitumor T-cell responses in vivo

The final N-terminal trimming of a subaminoterminal proline-containing HLA class I-restricted antigenic peptide in the cytosol is mediated by two peptidases.

The proteasome produces MHC class I-restricted antigenic peptides carrying N-terminal extensions, which are trimmed by other peptidases in the cytosol or within the endoplasmic reticulum. In this study, we show that the N-terminal editing of an antigenic peptide with a predicted low TAP affinity can occur in the cytosol. Using proteomics, we identified two cytosolic peptidases, tripeptidyl peptidase II and puromycin-sensitive aminopeptidase, that trimmed the N-terminal extensions of the precursors produced by the proteasome, and led to a transient enrichment of the final antigenic peptide. These peptidases acted either sequentially or redundantly, depending on the extension remaining at the N terminus of the peptides released from the proteasome. Inhibition of these peptidases abolished the CTL-mediated recognition of Ag-expressing cells. Although we observed some proteolytic activity in fractions enriched in endoplasmic reticulum, it could not compensate for the loss of tripeptidyl peptidase II/puromycin-sensitive aminopeptidase activities