Immune checkpoint blockade has proven its efficacy in hypermutated subtypes of metastatic colorectal cancers (mCRC). Immunogenic potential can also be observed with conventional chemotherapies, but this property has never been explored thoroughly in CRC patients. The CRC therapeutic arsenal includes oxaliplatin, a well‐characterized platinum drug already described as immunogenic. Here, we investigated the impact of the oxaliplatin‐based treatment on mCRC immunopeptidome. We demonstrated that oxaliplatin‐resistant CRC cell lines overexpressed telomerase reverse transcriptase (TERT), colorectal‐associated‐tumor antigen‐1 (COA‐1) and mesothelin tumor‐associated antigens. We identified new HLA class‐II‐restricted and promiscuous peptides derived from COA‐1 and mesothelin. The two naturally processed peptides COA‐1_331‐345 and Meso_366‐380 appear to be the most immunogenic in mCRC patients. A prospective cohort of 162 mCRC patients enabled us to explore the impact of oxaliplatin exposure on the antitumor‐specific immune response. Interestingly, chemotherapy‐naive mCRC patients present high immune CD4 T‐cell responses directed against TERT, COA‐1 and mesothelin‐derived peptides. These antitumor T‐cell responses were maintained after 3 months of oxaliplatin‐based treatment. Altogether, these findings highlight the interest of immunostimulatory agents to improve the management of chemoresistant mCRC patients. Finally, the high frequency of immune responses targeting the new immunogenic peptides derived from COA‐1 and mesothelin support their use in immunomonitoring strategies.

Chimeric Antigen Receptor (CAR) therapy has led to great successes in patients with leukemia and lymphoma. Umbilical Cord Blood (UCB), stored in UCB banks, is an attractive source of T cells for CAR-T production. We used a third generation CD123 CAR-T (CD28/4-1BB), which was previously developed using an adult’s Peripheral Blood (PB), to test the ability of obtaining CD123 CAR-T from fresh or cryopreserved UCB. We obtained a cell product with a high and stable transduction efficacy, and a poorly differentiated phenotype of CAR-T cells, while retaining high cytotoxic functions in vitro and in vivo. Moreover, CAR-T produced from cryopreserved UCB are as functional as CAR-T produced from fresh UCB. Overall, these data pave the way for the clinical development of UCB-derived CAR-T. UCB CAR-T could be transferred in an autologous manner (after an UCB transplant) to reduce post-transplant relapses, or in an allogeneic setting, thanks to fewer HLA restrictions which ease the requirements for a match between the donor and recipient.

Purpose: To investigate the immunoprevalence of SALL4-derived peptides in healthy volunteers and cancer patients. Experimental Design: A multistep approach including prediction algorithms was used to design in silico SALL4-derived peptides theoretically able to bind on common HLA-DR and HLA-A/B molecules. The presence of T-cell responses after a long term T-cell assay (28 days) against SALL4 was monitored in 14 healthy donors and the presence of T-cell responses after a short term T-cell assay (10 days) was monitored in 67 cancer patients using IFN-γ ELISPOT assay. A T-cell clone specific for the immunoprevalent A18 K-derived peptide was isolated, characterized and used as a tool to characterize the natural processing of A18 K. Results: A SALL4 specific T-cell repertoire was present in healthy donors (8/14) and cancer patients (29/67) after short term T-cell assay. We further identified two immunoprevalant SALL4-derived peptides, R18 A and A18 K, which bind MHC-class II. In parallel, an A18 K specific Th1 clone recognized monocyte derived Dendritic Cell (moDC) loaded with SALL4 containing cell lysate. The level of IFN-γ secreted by specific T-cell clone was greater in presence of moDC loaded with SALL4 containing cell lysate (49.23 ± 14.02%) than with moDC alone (18.03 ± 3.072%) (p = 0.0477) Conclusion: These results show for the first time immunogenicity of SALL4 oncogenic protein-derived peptides, especially A18 K and R18 A peptides and make them potential targets for personalized medicine. Thus, SALL4 possess major characteristics of a tumor antigen.

Treatment with T cells expressing chimeric antigen receptors (CAR) is a promising anticancer therapy. However, this approach has several limitations and has not yet been effectively applied to treat solid tumors. The study by Panowski and colleagues represents the first comparative analysis of multiple single chain fragment variable (scFv)-based anti-CD70 CAR T-cell clones for the development of a clinical product to treat renal cell carcinoma (RCC). Despite the risk of T-cell fratricide due to CD70 expression on T cells, CD70 CAR T cells were produced successfully thanks to the protective CD70 masking phenomenon. Two distinct classes of CAR T cells were identified with different memory phenotypes, activation statuses, and cytotoxic activity. CD70 CAR T cells presented high cytotoxic activity against RCC both in vitro in RCC cell lines and in vivo in patient-derived xenograft mouse models. The off-target effects expected on the lymphoid compartment were confirmed by tissue cross-reactivity staining and in a cynomolgus monkey preclinical model with CD3-CD70 bispecific antibody treatment. The efficacy and the toxicity profile of the lead CD70 CAR T-cell candidate instigated the researchers to proceed with upscaled clinical production. This article emphasizes the influence of the scFv of the CARs on their efficacy:toxicity balance. Ultimately, they successfully managed to develop a highly effective CAR T-cell candidate to treat a solid tumor by an allogeneic approach, thereby overcoming two major hurdles to broaden application of CAR T-cell therapy. See related article by Panowski et al., p. 2610

Chimeric antigen receptor (CAR) T cells express an extracellular domain consisting of a single-chain fragment variable (scFv) targeting a surface tumor-associated antigen. scFv selection should involve safety profiling with evaluation of the efficacy/toxicity balance, especially when the target antigen also is expressed on healthy cells. Here, to assess differences in terms of efficacy and on-target/off-tumor effects, we generated five different CARs targeting CD123 by substituting only the scFv. In in vitro models, T cells engineered to express three of these five CD123 CARs were effectively cytotoxic on leukemic cells without increasing lysis of monocytes or endothelial cells. Using the IncuCyte system, we confirmed the low cytotoxicity of CD123 CAR T cells on endothelial cells. Hematotoxicity evaluation using progenitor culture and CD34 cell lysis showed that two of the five CD123 CAR T cells were less cytotoxic on hematopoietic stem cells. Using a humanized mouse model, we confirmed that CD123− cells were not eliminated by the CD123 CAR T cells. Two CD123 CAR T cells reduced tumor infiltration and increased the overall survival of mice in three in vivo models of blastic plasmacytoid dendritic cell neoplasm. In an aggressive version of this model, bulk RNA sequencing analysis showed that these CD123 CAR T cells upregulated genes associated with cytotoxicity and activation/exhaustion a few days after the injection. Together, these results emphasize the importance of screening different scFvs for the development of CAR constructs to support selection of cells with the optimal risk–benefit ratio for clinical development.