Suppression of the host's immune system plays a major role in cancer progression. Tumor signaling of programmed death 1 (PD1) on T cells and expansion of myeloid-derived suppressor cells (MDSCs) are major mechanisms of tumor immune escape. We sought to target these pathways in rhabdomyosarcoma (RMS), the most common soft tissue sarcoma of childhood. Murine RMS showed high surface expression of PD-L1, and anti-PD1 prevented tumor growth if initiated early after tumor inoculation; however, delayed anti-PD1 had limited benefit. RMS induced robust expansion of CXCR2(+)CD11b(+)Ly6G(hi) MDSCs, and CXCR2 deficiency prevented CD11b(+)Ly6G(hi) MDSC trafficking to the tumor. When tumor trafficking of MDSCs was inhibited by CXCR2 deficiency, or after anti-CXCR2 monoclonal antibody therapy, delayed anti-PD1 treatment induced significant antitumor effects. Thus, CXCR2(+)CD11b(+)Ly6G(hi) MDSCs mediate local immunosuppression, which limits the efficacy of checkpoint blockade in murine RMS. Human pediatric sarcomas also produce CXCR2 ligands, including CXCL8. Patients with metastatic pediatric sarcomas display elevated serum CXCR2 ligands, and elevated CXCL8 is associated with diminished survival in this population. We conclude that accumulation of MDSCs in the tumor bed limits the efficacy of checkpoint blockade in cancer. We also identify CXCR2 as a novel target for modulating tumor immune escape and present evidence that CXCR2(+)CD11b(+)Ly6G(hi) MDSCs are an important suppressive myeloid subset in pediatric sarcomas. These findings present a translatable strategy to improve the efficacy of checkpoint blockade by preventing trafficking of MDSCs to the tumor site.

Myeloid-derived suppressor cells (MDSCs

PURPOSE Patients with B-cell acute lymphoblastic leukemia who experience relapse after or are resistant to CD19-targeted immunotherapies have limited treatment options. Targeting CD22, an alternative B-cell antigen, represents an alternate strategy. We report outcomes on the largest patient cohort treated with CD22 chimeric antigen receptor (CAR) T cells. PATIENTS AND METHODS We conducted a single-center, phase I, 3 + 3 dose-escalation trial with a large expansion cohort that tested CD22-targeted CAR T cells for children and young adults with relapsed/refractory CD22+ malignancies. Primary objectives were to assess the safety, toxicity, and feasibility. Secondary objectives included efficacy, CD22 CAR T-cell persistence, and cytokine profiling. RESULTS Fifty-eight participants were infused; 51 (87.9%) after prior CD19-targeted therapy. Cytokine release syndrome occurred in 50 participants (86.2%) and was grade 1-2 in 45 (90%). Symptoms of neurotoxicity were minimal and transient. Hemophagocytic lymphohistiocytosis–like manifestations were seen in 19/58 (32.8%) of subjects, prompting utilization of anakinra. CD4/CD8 T-cell selection of the apheresis product improved CAR T-cell manufacturing feasibility as well as heightened inflammatory toxicities, leading to dose de-escalation. The complete remission rate was 70%. The median overall survival was 13.4 months (95% CI, 7.7 to 20.3 months). Among those who achieved a complete response, the median relapse-free survival was 6.0 months (95% CI, 4.1 to 6.5 months). Thirteen participants proceeded to stem-cell transplantation. CONCLUSION In the largest experience of CD22 CAR T-cells to our knowledge, we provide novel information on the impact of manufacturing changes on clinical outcomes and report on unique CD22 CAR T-cell toxicities and toxicity mitigation strategies. The remission induction rate supports further development of CD22 CAR T cells as a therapeutic option in patients resistant to CD19-targeted immunotherapy.

Genetically engineered T cells expressing CD19-specific chimeric antigen receptors (CARs) have shown impressive activity against B cell malignancies, and preliminary results suggest that T cells expressing a first generation disialoganglioside (GD2)-specific CAR can also provide clinical benefit in patients with neuroblastoma. We sought to assess the potential of GD2-CAR therapies to treat pediatric sarcomas. We observed that 18/18 (100%) of osteosarcomas, 2/15 (13%) of rhabdomyosarcomas, and 7/35 (20%) of Ewing sarcomas expressed GD2. T cells engineered to express a third generation GD2-CAR incorporating the 14g2a-scFv with the CD28, OX40, and CD3ζ signaling domains (14g2a.CD28.OX40.ζ) mediated efficient and comparable lysis of both GD2+ sarcoma and neuroblastoma cell lines in vitro. However in xenograft models, GD2-CAR T cells had no antitumor effect against GD2+ sarcoma, despite effectively controlling GD2+ neuroblastoma. We observed that pediatric sarcoma xenografts, but not neuroblastoma xenografts, induced large populations of monocytic and granulocytic murine myeloid-derived suppressor cells (MDSCs) that inhibited human CAR T-cell responses in vitro. Treatment of sarcoma-bearing mice with all-trans retinoic acid (ATRA) largely eradicated monocytic MDSCs and diminished the suppressive capacity of granulocytic MDSCs. Combined therapy using GD2-CAR T cells plus ATRA significantly improved antitumor efficacy against sarcoma xenografts. We conclude that retinoids provide a clinically accessible class of agents capable of diminishing the suppressive effects of MDSCs, and that co-administration of retinoids may enhance the efficacy of CAR therapies targeting solid tumors.